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  • Electronic Resource  (4,121)
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  • 1
    Electronic Resource
    Electronic Resource
    Effects of orally administered interferon-α on the pathogenesis of feline leukaemia virus-induced erythroid aplasia (1995)
    Springer
    Comparative clinical pathology 5 (1995), S. 79-83 
    Details
    ISSN: 1433-2981
    Keywords: Cat ; Feline leukaemia virus ; Interferon-α
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The use of orally administered interferon-α as a treatment for retroviral disease was evaluated in the experimental model of feline leukaemia virus (FeLV)-induced erythroid aplasia. Progressive anaemia, FeLV viraemia, and leukopenia developed in cats inoculated with the Kawakami-Theilen isolate of feline leukaemia virus (FeLV-KT). A treatment regimen with orally administered recombinant interferon-α or natural interferon-α as employed in this study had no significant effects on viraemia, course of disease, or differential leucocyte counts. The results of this study did not reveal any beneficial effects of human interferon-α administered by the oral route for treatment of cats with experimentally induced FeLV infection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00638923
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of decalcification on bone mineral content and bending strength of feline femur (1995)
    Springer
    Calcified tissue international 56 (1995), S. 78-82 
    Details
    ISSN: 1432-0827
    Keywords: Bone mineral content (BMC) ; Cat ; Decalcification ; Ethylene diaminetetra acetic acid (EDTA) ; Femur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract The relationships between bone mineral content (BMC), bone calcium, and bone strength were studied in fractionally demineralized feline femurs. In 44 pairs of cat femurs, the right bones were decalcified in ethylene diaminetetra acetic acid (EDTA) to 20%, 40%, 60%, 80%, and 100% of the mineral content of the intact left bone (=control). The bones were then loaded to failure, and maximum strength values were recorded. The data were then used to calculate the percentage strength of the right relative to the left femurs. A correlation coefficient (r) of 0.970 was found between the percentage decalcification and percentage bending strength. A direct relationship (r=0.876) was also observed between the total calcium extracted and total loss in BMC. The EDTA solutions were spot checked for protein content to determine if the organic matrices had been altered by demineralization. Protein was never detected. Nor did the demineralized tissues display histologic evidence of gross microscopic damage. This study has shown that in cat femurs, 20% decalcification led to about 35% loss in bending strength, and 60% decalcification caused 75% loss in strength. These values are significant as they highlight the importance of calcium to the strength of osteopenic bone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298748
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  • 3
    Electronic Resource
    Electronic Resource
    Different patterns of fore-hindlimb coordination during overground locomotion in cats with ventral and lateral spinal lesions (1995)
    Springer
    Experimental brain research 104 (1995), S. 70-80 
    Details
    ISSN: 1432-1106
    Keywords: Locomotion ; Spinal lesions ; Interlimb coordination ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of large, low thoracic (T10–T11), partial spinal lesions involving the ventral quadrants of the spinal cord and, to a different extent, the dorsolateral funiculi, on fore-hindlimb coordination was examined in cats walking overground at moderate speeds (40–100 cm/s). Three different forms of impairment of fore-hindlimb coordination depending on the extent of the lesions, were observed. Lesions sparing the dorsolateral or the ventral funiculus on one side preserved the equality of the fore- and hindlimb locomotor rhythms but changed the coupling between the movements of both girdles as compared to intact animals. Larger lesions in which, in addition to the ventral quadrants of the spinal cord, also major parts of the dorsolateral funiculi were destroyed elicited episodes of rhythm oscillations in both girdles, which appeared at the background of a small difference in these rhythms. Lesions destroying almost the whole spinal cord induced a permanent difference (about 200 ms) in the step cycle duration of the fore- and the hindlimbs. However, even in these animals some remnant form of fore-hindlimb coordination was found. The results suggest that dorsolateral funiculi play a major role in preserving the equality of rhythms in the foreand the hindlimbs, while lesions of the ventral quadrants change the coupling between limbs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229856
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of neonatal splitting of the optic chiasm on the development of feline visual callosal connections (1995)
    Springer
    Experimental brain research 104 (1995), S. 275-286 
    Details
    ISSN: 1432-1106
    Keywords: Corpus callosum ; Vision ; Cortex ; Plasticity ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract During normal postnatal development, there is an overproduction and subsequent partial elimination of the callosal projections of cortical areas 17 and 18 in the cat. In the present study, we investigated how neonatal splitting of the optic chiasm affects this process. Our results indicate that neonatal splitting of the optic chiasm exaggerates the normally occurring partial elimination of immature callosal projections: it causes a significant reduction in the total number of neurons in the supragranular layers that send an axon through the corpus callosum. It does not, however, cause a significant change in the number of callosally projecting neurons in the infragranular layers. These data suggest that in addition to other factors previously described, the level or spatial distribution of correlated binocular input to visual cortical neurons may influence the stabilization/elimination of immature callosal connections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242013
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  • 5
    Electronic Resource
    Electronic Resource
    Dopaminergic control of transmission from group II muscle afferents to spinal neurones in the cat and guinea-pig (1995)
    Springer
    Experimental brain research 105 (1995), S. 39-47 
    Details
    ISSN: 1432-1106
    Keywords: Dopamine ; Group II muscle afferents ; Spinal cord ; Cat ; Guinea-pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of dopamine and its agonists on transmission from muscle afferents to spinal neurones were investigated in the cat and guinea-pig spinal cord, by measuring the drug effects on the amplitude of monosynaptic field potentials evoked by electrical stimulation of group I and group II muscle afferents. Local iontophoretic application of dopamine, the dopamine D1/D5 agonist SKF-38393 and the D2/D3/D4 agonist quinpirole all depressed the group II field potentials evoked at the base of the dorsal horn. Group II field potentials in the intermediate zone were depressed by dopamine to a similar degree as the dorsal horn field potentials, whereas the dopamine agonists were without effect upon them. The intermediate zone field potentials evoked by group I muscle afferents were not depressed by any of the drugs. The dopamine-evoked depression of the group II-evoked field potentials in the dorsal horn in the guinea-pig spinal cord was reduced by the simultaneous application of haloperidol. The results demonstrate that dopamine receptors mediate the depression of transmission from group II muscle afferents to interneurones in the dorsal horn, but not to neurones in the intermediate zone of the spinal cord.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242180
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  • 6
    Electronic Resource
    Electronic Resource
    Transmission characteristics for the 1:1 linkage between slowly adapting type II fibers and their cuneate target neurons in cat (1995)
    Springer
    Experimental brain research 105 (1995), S. 67-75 
    Details
    ISSN: 1432-1106
    Keywords: Slowly adapting type II ; Cuneate neuron ; Synaptic transmission ; Tactile afferent fiber ; Somatosensory system ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Transmission from single, identified, slowly adapting type II (SAII) tactile fibers to their target neurons in the cuneate nucleus was examined in anesthetized cats. Simultaneous recordings were made from cuneate neurons and from fine, intact fascicles of the superficial radial nerve in which it was possible to identify and monitor the activity of each group II fiber. Selective activation of individual SAII fibers was achieved by means of skin stimulation with fine probes, in conjunction with extensive forelimb denervation. Responses were studied for seven SAII-driven cuneate neurons. For three there was unequivocal monitoring of the identified SAII input fiber. However, in six of the seven there was evidence that just one SAII fiber provided suprathreshold input to the cuneate neuron, and neither temporal nor spatial summation was required for reliable transmission. Cuneate impulse rates, in response to SAII inputs lasting 1 s, were less than 250 impulses per second, even though the SAII impulse rates could be 500 s-1. Responses to individual SAII impulses consisted of a burst of 2–3 impulses at low SAII input rates, but burst responses disappeared at high SAII rates. In all three SAII-cuneate pairs studied, the transmission security (the percentage of SAII impulses that evoked cuneate spike output) exceeded 80% in response to static skin displacement and in response to certain frequencies of skin vibration, in particular, at 100–200 Hz, exceeded 98% when the SAII fiber responded near the 1∶1 level (one impulse per vibration cycle). Transmission characteristics for the SAII-cuneate linkage resulted in the cuneate neuron showing tight phaselocking of responses to high-frequency (〉100 Hz) vibrotactile stimuli and higher impulse rates than its SAII input (up to input rates of ∼50 impulses s-1). Security of transmission across the SAII-cuneate synapse is similar to that demonstrated previously for tactile fibers of the SAI and Pacinian corpuscle (PC)-related classes, which suggests that there is no marked differential specialization in transmission characteristics for dorsal column nuclei neurons that receive input from different tactile fiber classes. Furthermore, it means that the reported failure of individual SAII fiber inputs to generate conscious sensation in man following intraneural microstimulation is not related to transmission failure at the first central relay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242183
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  • 7
    Electronic Resource
    Electronic Resource
    Relationship of simultaneously recorded cerebellar nuclear neuron discharge to the acquisition of a complex, operantly conditioned forelimb movement in cats (1995)
    Springer
    Experimental brain research 105 (1995), S. 325-330 
    Details
    ISSN: 1432-1106
    Keywords: Cerebellum ; Motor learning ; Reaching ; Cerebellar nuclei ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study was designed to examine the changes in the modulation of small populations of cerebellar neurons during the acquisition of a complex, operantly conditioned forelimb task in cats. The experiments are based on the general postulate that, during the learning of a complex motor behavior, the cerebellum is important for generating a coordinated movement that meets the task's objectives, and that, as the cerebellum participates in this process, it acts to reinforce the effective motor pattern once it has been established. This specific study examines whether the changes in the modulation of cerebellar nuclear neurons during the learning of this task are consistent with this view. Cats were required to learn to move the manipulandum through a novel pattern of 2–3 consecutive straight grooves connected end to end in different spatial configurations, e.g., the letter L, an inverted L, and the letter C. Throughout the acquisition process, 6–12 single units were recorded simultaneously in the cerebellar nuclei, and the kinematics of the movement were evaluated using an Optotrak system. Cells were recorded from the two interposed nuclei and the dentate nucleus in these initial studies. Trials were sorted off-line based on the level of skill at which the required movement was performed. This was assessed using several objective criteria such as movement times, kinematic characteristics, and smoothness (number of peaks in the velocity profile). Event-related histograms then were constructed from each group of sorted trials. Changes in modulation related to a specific event were measured in successive histograms for each neuron. One of the most consistent findings across the cells in all nuclei was that the magnitude of the task-related modulation reached a peak at the time the task was first performed reasonably well and then progressively decreased (but did not disappear) as the task became well practiced. Both the initial increase and the subsequent decrease in response amplitude were significant statistically. The implications of these observations are discussed in the context of the role the cerebellum may play in the acquisition of complex motor tasks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00240970
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  • 8
    Electronic Resource
    Electronic Resource
    Express saccades in cat: effects of task and target modality (1995)
    Springer
    Experimental brain research 103 (1995), S. 209-217 
    Details
    ISSN: 1432-1106
    Keywords: Express saccade ; Reaction time ; Attention ; Fixation ; Orienting response ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Saccadic eye movements to visual, auditory, and bimodal targets were measured in four adult cats. Bimodal targets were visual and auditory stimuli presented simultaneously at the same location. Three behavioral tasks were used: a fixation task and two saccadic tracking tasks (gap and overlap task). In the fixation task, a sensory stimulus was presented at a randomly selected location, and the saccade to fixate that stimulus was measured. In the gap and overlap tasks, a second target (hereafter called the saccade target) was presented after the cat had fixated the first target. In the gap task, the fixation target was switched off before the saccade target was turned on; in the overlap task, the saccade target was presented before the fixation target was switched off. All tasks required the cats to redirect their gaze toward the target (within a specified degree of accuracy) within 500 ms of target onset, and in all tasks target positions were varied randomly over five possible locations along the horizontal meridian within the cat's oculomotor range. In the gap task, a significantly greater proportion of saccadic reaction times (SRTs) were less than 125 ms, and mean SRTs were significantly shorter than in the fixation task. With visual targets, saccade latencies were significantly shorter in the gap task than in the overlap task, while, with bimodal targets, saccade latencies were similar in the gap and overlap tasks. On the fixation task, SRTs to auditory targets were longer than those to either visual or bimodal targets, but on the gap task, SRTs to auditory targets were shorter than those to visual or bimodal targets. Thus, SRTs reflected an interaction between target modality and task. Because target locations were unpredictable, these results demonstrate that cats, as well as primates, can produce very short latency goal-directed saccades.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231707
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  • 9
    Electronic Resource
    Electronic Resource
    Cross-correlation of augmenting expiratory neurons of the Bötzinger complex in the cat (1995)
    Springer
    Experimental brain research 103 (1995), S. 251-255 
    Details
    ISSN: 1432-1106
    Keywords: Respiratory neurophysiology ; Cross-correlation ; Bötzinger complex ; Expiratory neurons ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Ipsilateral and contralateral pairs of augmenting expiratory neurons were recorded simultaneously from the Bötzinger complex using glass-coated tungsten microelectrodes in pentobarbitone-anaesthetized cats. The neurons were identified both by firing pattern and by antidromic activation from the contralateral site of the dorsal respiratory group. Cross-correlation histograms of the extracellularly recorded action potentials were calculated in order to detect short time-scale synchronizations of firing indicative of synaptic connections between the neurons. The cross-correlation histograms for 40 ipsilateral pairs of neurons less than 1 mm apart showed eight (20%) narrow troughs (mean half-amplitude width ±SD, 1.1±0.37 ms) at short latencies (mean latency±SD, 1.0±0.35 ms) suggestive of monosynaptic inhibition. These included two cross-correlation histograms which showed troughs on both sides of time zero, indicating a mutual inhibition. For another four pairs of neurons (10%), a central broad peak suggestive of common activation due to either excitation or release from inhibition was evident. Contralateral pairs of expiratory neurons of the Bötzinger complex were examined in a similar manner. The cross-correlation histograms for 43 pairs of neurons showed five (12%) narrow troughs (mean half-amplitude width±SD, 1.2±0.67 ms) at short latencies (mean latency±SD, 2.7±1.47 ms) suggestive of monosynaptic inhibition. These included one cross-correlation histogram which showed troughs (one not statistically significant) on both sides of time zero, indicating a mutual inhibition. For another two pairs of neurons (4.6%) a central, broad peak suggestive of common activation due to either excitation or release from inhibition was evident. We conclude that inhibitory interconnections exist between augmenting expiratory neurons of the Bötzinger complex ipsilaterally and contralaterally. These connections may synchronize the expiratory burst of activity within this population and assist in the patterning of the burst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231711
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  • 10
    Electronic Resource
    Electronic Resource
    Binaural noise stimulation of auditory callosal fibers of the cat: responses to interaural time delays (1995)
    Springer
    Experimental brain research 104 (1995), S. 30-40 
    Details
    ISSN: 1432-1106
    Keywords: Corpus callosum ; Sound localization ; Interaural time delays ; Midline fusion ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The corpus callosum, the principal neocortical commissure, allows for the interhemispheric transfer of lateralized information between the hemispheres. The aim of the present experiment was to study callosal transfer of auditory information in the cat, with particular reference to its contribution to sound localization. The corpus callosum was approached under direct visual control, and axonic responses were recorded under light anesthesia using glass micro-pipettes. Results showed that auditory information is transmitted in the posterior portion of the callosum. Diotic presentations, in which interaural time delay was manipulated, indicated that, for a large number of fibers, the largest excitatory or inhibitory interactions were obtained at null interaural time delay, a condition which supports the notion of a callosal contribution to auditory midline fusion. However, an important number of callosal fibers was also found to be excited maximally at specific, non-zero interaural time delays, suggesting that they preferred sounds situated at spatial locations other than the midline. The results are discussed in relation to those obtained electrophysiologically for the visual and somesthesic modalities and in terms of results obtained in human and animal behavioral experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229853
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  • 11
    Electronic Resource
    Electronic Resource
    Brainstem modulation of signal transmission through the cat dorsal lateral geniculate nucleus (1995)
    Springer
    Experimental brain research 103 (1995), S. 372-384 
    Details
    ISSN: 1432-1106
    Keywords: Contrast gain ; Lateral geniculate nucleus ; Neuromodulation ; Retinogeniculate transmission Lagged and nonlagged cells ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We studied changes in retinogeniculate transmission that occur during variation of modulatory brainstem input and during variation of stimulus contrast. Responses of single cells in the dorsal lateral geniculate nucleus (dLGN) to a stationary flashing light spot of varying contrast were measured with and without electrical stimulation of the peribrachial region (PBR) of the brain-stem. PBR stimulation increased the contrast gain (slope of response versus contrast curve) and the dynamic response range (range between spontaneous activity and maximal firing). Lagged and nonlagged X-cells reached the midpoint of the dynamic response range at lower contrasts during PBR stimulation than in the controls. No comparable change was seen for Y-cells. Only minor changes of threshold contrast were seen. The characteristics of the retinogeniculate transmission were directly studied by comparing the response of dLGN cells with their retinal input (slow potentials, S-potentials). With increasing contrast there was a marked increase in the transfer ratio (proportion of impulses in the input that generates action potentials in the dLGN cell). The transfer ratio seemed to be primarily determined by the firing rate of the retinal input. The transfer ratio increased with increasing input rates from low values near threshold to values that could approach 1 at high-input firing rates. PBR stimulation increased the transfer ratio, particularly at moderate input firing rates. The increased transfer ratio, caused by increasing input firing rates, enhanced the response versus contrast characteristics through an increase in contrast gain and dynamic response range. The modulatory input from the PBR further enhanced these characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00241496
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  • 12
    Electronic Resource
    Electronic Resource
    The auditory pathway in cat corpus callosum (1995)
    Springer
    Experimental brain research 104 (1995), S. 534-540 
    Details
    ISSN: 1432-1106
    Keywords: Corpus callosum ; Auditory pathway ; Primary auditory field ; Tonotopy ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The cortical auditory fields of the two hemispheres are interconnected via the corpus callosum. We have investigated the topographical arrangement of auditory callosal axons in the cat. Following circumscribed biocytin injections in the primary (AI), secondary (AII), anterior (AAF) and posterior (PAF) auditory fields, labelled axons have been found in the posterior two-thirds of the corpus callosum. Callosal axons labelled by small individual cortical injections did not form a tight bundle at the callosal midsagittal plane but spread over as much as one-third of the corpus callosum. Axons originating from different auditory fields were roughly topographically ordered, reflecting to some extent the rostro-caudal position of the field of origin. Axons from AAF crossed on average more rostrally than axons from AI; the latter crossed more rostrally than axons from PAF and AIL Callosal axons originating in a discrete part of the cortex travelled first in a relatively tight bundle to the telo-diencephalic junction and then dispersed progressively. In conclusion, the cat corpus callosum does not contain a sector reserved for auditory axons, nor a strictly topographically ordered auditory pathway. This observation is of relevance to neuropsychological and neuropathological observations in man.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231988
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  • 13
    Electronic Resource
    Electronic Resource
    Depression of transmission from group II muscle afferents by electrical stimulation of the cuneiform nucleus in the cat (1995)
    Springer
    Experimental brain research 105 (1995), S. 25-38 
    Details
    ISSN: 1432-1106
    Keywords: Cuneiform nucleus ; Synaptic transmission ; Spindle afferents ; Spinal cord ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of short trains of electrical stimuli applied within the cuneiform nucleus and the subcuneiform region were examined on transmission from group I and group II muscle afferents to first-order spinal neurons. Variations in the effectiveness of transmission from these afferents were assessed from changes in the sizes of the monosynaptic component of extracellular field potentials evoked following stimulation of muscle nerves. Field potentials evoked from group II muscle afferents in the dorsal horn of the midlumbar and sacral segments and in the intermediate zone of the midlumbar segments were reduced when the test stimuli applied to peripheral nerves were preceded by conditioning stimulation of the cuneiform nucleus or the subcuneiform region. The depression occurred at conditioning-testing intervals of 20–400 ms, being maximal at intervals of 32–72 ms for dorsal horn potentials and 40–100 ms for intermediate zone potentials. At the shortest intervals, both group II and group I field potentials in the intermediate zone were depressed. Conditioning stimulation of the cuneiform nucleus depressed group II field potentials nearly as effectively as conditioning stimulation of the coerulear or raphe nuclei. We propose that the nonselective depression of transmission from group I and II afferents at short intervals is due to the activation of reticulospinal pathways by cells or fibers stimulated within the cuneiform area. We also propose that the selective depression of transmission from group II afferents at long intervals is mediated at least partly by monoaminergic pathways, in view of the similarity of the effects of conditioning stimulation of the cuneiform nucleus and of the brainstem monoaminergic nuclei and by directly applied monoamines (Bras et al. 1990). In addition, it might be caused by primary afferent depolarization mediated by non-monoaminergic fibers (Riddell et al. 1992).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242179
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  • 14
    Electronic Resource
    Electronic Resource
    Distribution of vestibulospinal synaptic input to cat triceps surae motoneurons (1995)
    Springer
    Experimental brain research 107 (1995), S. 1-8 
    Details
    ISSN: 1432-1106
    Keywords: Deiters' nucleus ; Vestibulospinal system ; Motoneurons ; Synaptic input ; Synaptic currents ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We applied supramaximal, repetitive stimulation to the lateral vestibular nucleus (Deiters' nucleus, DN) at 200 Hz to evoke steady-state synaptic potentials in ipsilateral triceps surae motoneurons of the cat. The effective synaptic currents underlying these potentials were measured using a modified voltage-clamp technique. The steady-state effective synaptic currents evoked by activating DN were generally small and depolarizing (mean±SD 2.5±2.6 nA). DN stimulation generated hyperpolarizing synaptic currents in 2 of the 34 triceps motoneurons studied. The effective synaptic currents from DN tended to be larger in putative type F motoneurons than in putative type S cells (type F mean 3.0±3.1 nA; type S mean 1.8±1.0 nA). There was a statistically significant difference between the inputs to putative type FF and putative type S motoneurons (mean difference 2.8 nA, t=2.87, P〈0.01). The synaptic input from DN to medial gastrocnemius motoneurons had approximately the same mean amplitude as that from homonymous la afferent fibers. However, the distribution of DN input with respect to putative motor unit type was the opposite of that previously reported for Ia afferent input. Thus, the synaptic input from DN might act to compress the range of recruitment thresholds within the motoneuron pool and thereby increase the gain of its input-output function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228010
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  • 15
    Electronic Resource
    Electronic Resource
    Non-length-tuned cells in layers II/III and IV of the visual cortex: the effect of blockade of layer VI on responses to stimuli of different lengths (1995)
    Springer
    Experimental brain research 104 (1995), S. 12-20 
    Details
    ISSN: 1432-1106
    Keywords: Visual cortex ; Layer VI to layer IV ; Non-length-tuned cells ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have previously shown, using a local inactivation technique, that layer VI provides a facilitatory input to the majority of hypercomplex cells located in layer IV above, and hence to layers II/III, which in many cases enhances length selectivity. However, many cells in these layers are not tuned for stimulus length, being equally responsive to long and short stimuli. Thus it is important to know whether layer VI can influence the responses of these cells. We have now used a similar paradigm of iontophoretic application of GABA to examine the effect of blockade of layer VI on the length tuning profiles of these cells in layers II–IV. During the blockade of layer VI, the most common effect, seen in 41% of the cells, was inhibition of visual responses, (i.e. commensurate with loss of a facilitatory input). An increase in response magnitude was found in 21% of the population, and responses were unaffected in 36% of cells tested. This suggests that the predominant influence of local regions of layer VI on this cell type, located in layers II/III and IV, is facilitatory, with a smaller proportion of cells receiving an inhibitory input. Such effects were seen even with the shortest lengths tested, suggesting once more that elements of layer VI are responsive to stimuli much shorter than was previously accepted. Thus these data suggest that layer VI plays a role in the generation of the response dynamics of non-length-tuned cells in overlying layers II/III and IV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229851
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  • 16
    Electronic Resource
    Electronic Resource
    On-line compensation of gaze shifts perturbed by micro-stimulation of the superior colliculus in the cat with unrestrained head (1995)
    Springer
    Experimental brain research 106 (1995), S. 196-204 
    Details
    ISSN: 1432-1106
    Keywords: Gaze shifts ; Dynamic feedback ; Superior colliculus ; Microstimulation ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Prior studies have led to the gaze feedback hypothesis, which states that quick orienting movements of the visual axis (gaze shifts) are controlled by a feedback system. We have previously provided evidence for this hypothesis by extending the original study of Mays and Sparks (1980) to the cat with unrestrained head (Pélisson et al. 1989). We showed that cats compensated for a stimulation-induced perturbation of initial gaze position by generating, in the dark, an accurate gaze shift towards the remembered location of a flashed target. In the present study, we investigate goal-directed gaze shifts perturbed “in flight” by a brief stimulation of the superior colliculus. The microstimulation parameters were tuned such that significant perturbations were induced without halting the movement. The ambient light was turned off at the onset of the gaze shift, suppressing any visual feedback. We observed that, following stimulation offset, the gaze shift showed temporal and spatial changes in its trajectory to compensate for the transient perturbation. Such compensations, which occurred “on-line” before gaze shift termination, involved both eye and head movements and had dynamic characteristics resembling those of unperturbed saccadic gaze shifts. These on-line compensations maintained gaze accuracy when the stimulation was applied during the early phase of large and medium (about 60 and 40°) movements. These results are compatible with the notion of a gaze feedback loop providing a dynamic gaze error signal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00241115
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  • 17
    Electronic Resource
    Electronic Resource
    Analysis of potentials induced in red nucleus neurones from the somaesthetic pathway stimulated at the bulbar level (1995)
    Springer
    Experimental brain research 106 (1995), S. 377-390 
    Details
    ISSN: 1432-1106
    Keywords: Motor control ; Somaesthesia ; Magnocellular red nucleus ; Intracellular recording ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A somaesthetic pathway to the magnocellular red nucleus (RNm) via relays other than corticoor cerebello-rubral relays was previously found to exist in the cat. At the brainstem level, the ascending spinorubral fibres follow the medial lemniscus (LM). The present paper aims at describing in detail and evaluating the quantitative importance of the short-latency responses in RNm cells after microstimulation performed in the LM through a monopolar electrode. The RNm cells, tested intracellularly in cats anaesthetized with α-choralose and placed in a stereotaxic device, were identified by their antidromic activation to stimulation of the rubrospinal tract in the cervical cord. It was established that single-shock stimulation below 100 μA current delivered to the LM induced short-latency postsynaptic potentials (PSPs) in 87% of all the rubrospinal cells tested. The responses were indeed due to activation of LM fibres, as demonstrated by different tests: the location of the electrode tip in the LM was verified by recording, with the same electrode, the potentials evoked by stimulating the dorsal columns of the cord. The site was later confirmed histologically. The absence of stimulus spread from the LM to the underlying pyramidal tract was systematically checked by simultaneously recording the responses evoked in RNm cells and in the motor cortex. Monosynaptic excitatory responses (EPSPs) were evoked in RNm cells with a minimum stimulating current of less than 20 μA in the LM and a mean threshold of 42 μA. Disynaptic inhibitory potentials (IPSPs) were evoked in 23% of these cells with single-pulse stimulation. These latter responses showed a temporal facilitation with short trains of three pulses, which indicated that they were transmitted through inhibitory interneurones. Recordings were also performed from presumed LM fibre terminals running inside the RNm. The results therefore confirm the existence of strong lemniscal projections to RNm and demonstrate that they transmit both excitatory and inhibitory messages to rubrospinal cells. As the somaesthetic pathway to the RNm was previously found to come from the spinal cord, where it is located in the ventral portion, the present results also confirm that the LM is composed of fibres originating not only from neurones in the dorsal column nuclei, but also from cells placed at the segmental levels of the cord. The presumed sensorimotor function of this ascending pathway is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231061
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  • 18
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    Electronic Resource
    Functional relation between corticonuclear input and movements evoked on microstimulation in cerebellar nucleus interpositus anterior in the cat (1995)
    Springer
    Experimental brain research 106 (1995), S. 365-376 
    Details
    ISSN: 1432-1106
    Keywords: Climbing fibres ; Rubrospinal tract ; Motor control ; Motor learning ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The functional relation between receptive fields of climbing fibres projecting to the C1, C3 and Y zones and forelimb movements controlled by nucleus interpositus anterior via the rubrospinal tract were studied in cats decerebrated at the pre-collicular level. Microelectrode tracks were made through the caudal half of nucleus interpositus anterior. This part of the nucleus receives its cerebellar cortical projection from the forelimb areas of these three sagittal zones. The C3 zone has been demonstrated to consist of smaller functional units called microzones. Natural stimulation of the forelimb skin evoked positive field potentials in the nucleus. These potentials have previously been shown to be generated by climbing fibre-activated Purkinje cells and were mapped at each nuclear site, to establish the climbing fibre receptive fields of the afferent microzones. The forelimb movement evoked by microstimulation at the same site was then studied. The movements usually involved more than one limb segment. Shoulder retraction and elbow flexion were frequently evoked, whereas elbow extension was rare and shoulder protraction never observed. In total, movements at the shoulder and/or elbow occurred for 96% of the interpositus sites. At the wrist, flexion and extension movements caused by muscles with radial, central or ulnar insertions on the paw were all relatively common. Pure supination and pronation movements were also observed. Movements of the digits consisted mainly of dorsal flexion of central or ulnar digits. A comparison of climbing fibre receptive fields and associated movements for a total of 110 nuclear sites indicated a general specificity of the input-output relationship of this cerebellar control system. Several findings suggested that the movement evoked from a particular site would act to withdraw the area of the skin corresponding to the climbing fibre receptive field of the afferent microzones. For example, sites with receptive fields on the dorsum of the paw were frequently associated with palmar flexion at the wrist, whereas sites with receptive fields on the ventral side of the paw and forearm were associated with dorsiflexion at the wrist. Correspondingly, receptive fields on the lateral side of the forearm and paw were often associated with flexion at the elbow, whereas sites with receptive fields on the radial side of the forearm were associated with elbow extension. The proximal movements that were frequently observed also for distal receptive fields may serve to produce a general shortening of the limb to enhance efficiency of the withdrawal. It has previously been suggested that the cerebellar control of forelimb movements via the rubrospinal tract has a modular organisation. Each module would consist of a cell group in the nucleus interpositus anterior and its afferent microzones in the C1, C3 and Y zones, characterised by a homogenous set of climbing fibre receptive fields. The results of the present study support this organisational principle, and suggest that the efferent action of a module is to withdraw the receptive field from an external stimulus. Possible functional interpretations of the action of this system during explorative and reaching movements are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231060
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  • 19
    Electronic Resource
    Electronic Resource
    Stimulation of the group I extensor afferents prolongs the stance phase in walking cats (1995)
    Springer
    Experimental brain research 103 (1995), S. 20-30 
    Details
    ISSN: 1432-1106
    Keywords: Ib afferent ; Locomotion ; Walking ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Group I afferents in nerves innervating the lateral gastrocnemius-soleus (LG-Sol), plantaris (P1), and vastus lateralis/intermedius (VL/VI) muscles were stimulated during walking in decerebrate cats. The stimulus trains were triggered at a fixed delay following the onset of bursts in the medial gastrocnemius muscle. Stimulation of all three nerves with long stimulus trains (〉600 ms) prolonged the extensor bursts and delayed the onset of flexor burst activity. LG-Sol nerve stimulation had the strongest effect; often delaying the onset of flexor burst activity until the stimulus train was ended. By contrast, flexor bursts were usually initiated before the end of the stimulus train to the P1 and VL/VI nerves. The minimum stimulus strength required to increase the cycle period was between 1.3×threshold and 1.6×threshold for all three nerves. Simultaneous stimulation of the P1 and VL/VI nerves produced a larger effect on the cycle period than stimulation of either nerve alone. The spatial summation of inputs from knee and ankle muscles suggests that the excitatory action of the group I afferents during the stance phase is distributed to all leg extensor muscles. Stimulation of the group I afferents in extensor nerves generally produced an increase in the amplitude of the heteronymous extensor EMG towards the end of the stance phase. This increase in amplitude occurred even though there were only weak monosynaptic connections between the stimulated afferents and the motoneurones that innervated these heteronymous muscles. This suggests that the excitation was produced via oligosynaptic projections onto the extensor motoneuronal pool. Stimulation with 300 ms trains during the early part of flexion resulted in abrupt termination of the swing phase and reinitiation of the stance phase of the step cycle. The swing phase resumed coincidently with the stimulus offset. Usually, stimulation of two extensor nerves at group I strengths was required to elicit this effect. We were unable to establish the relative contributions of input from the group 1a and group 1b afferents to prolonging the stance phase. However, we consider it likely that group Ib afferents contribute significantly, since their activation has been shown to prolong extensor burst activity in reduced spinal preparations. Thus, our results add support to the hypothesis that unloading of the hindlimb during late stance is a necessary condition for the initiation of the swing phase in walking animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00241961
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  • 20
    Electronic Resource
    Electronic Resource
    Effects of eye position on auditory localization and neural representation of space in superior colliculus of cats (1995)
    Springer
    Experimental brain research 104 (1995), S. 402-408 
    Details
    ISSN: 1432-1106
    Keywords: Superior colliculus ; Sensory integration ; Auditory localization ; Eye movement ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The maps of visual and auditory space within the superior colliculus are in approximate register both with each other and with the underlying motor maps associated with orienting responses. The fact that eyes and ears can move independently poses a problem for the sensorimotor organization of these two modalities. By monitoring eye and pinna positions in alert, head-fixed cats, we showed that the accuracy of saccadic eye movements to auditory targets was little affected by eye eccentricity (range ±15 deg) at the onset of the sound. A possible neural basis for this behavioral compensation was suggested by recordings from superior colliculus neurons. The preferred sound directions of some neurons in the deep layers of this midbrain nucleus exhibited a shift with the direction of gaze, while in others the response throughout the auditory receptive field was either increased or decreased, suggesting that changes in eye position alter the gain of the auditory response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231975
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  • 21
    Electronic Resource
    Electronic Resource
    Effect of reversible dorsal cold block on the persistence of inhibition generated by spinal reflexes (1995)
    Springer
    Experimental brain research 107 (1995), S. 205-214 
    Details
    ISSN: 1432-1106
    Keywords: Motoneuron ; Stretch reflex ; Cutaneous ; Contralateral ; Spinal ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of bilateral focal cooling of dorsolateral thoracic spinal cord on segmental reflex pathways to the triceps surae muscles were assessed in decerebrate cats from the reflex forces produced by single shocks or trains of electrical stimuli applied to the ipsilateral caudal cutaneous sural and the contralateral tibial nerves. The validity of the dorsal cold block technique as a substitute for acute surgical dorsal hemisection was established by showing that focal cooling reliably reproduced the stretch-induced “clasp knife” inhibition of triceps surae reflexive force seen following dorsal hemisection. Under control (warm) conditions, the inhibitory components of electrically evoked ipsilateral sural and contralateral tibial reflexes faded rapidly during sustained trains, with a resultant production of large-amplitude reflex force as measured from either the entire triceps surae or from the medial gastrocnemius muscle alone. Dorsal cold block greatly reduced the amplitude of reflexive force evoked by sustained electrical stimulation of either nerve. Indeed, the cold block completely reversed the sign of train-evoked reflexes to a net inhibition of reflex force output in one-half of the sural and one-half of the contralateral tibial stimulation experiments. Peak transient forces evoked by single shocks to the sural or contralateral tibial nerves were also sometimes reduced, but this result was more variable than for prolonged nerve stimulation. The persistence of activity in segmental inhibitory pathways during dorsal cold block, as indicated by instances of reflex sign reversal, suggests that descending bulbospinal pathways traversing the dorsolateral funiculi may be responsible for “fading” of segmental inhibitory reflex components in decerebrate cats with intact spinal cords during sustained afferent input. The possibility that the enhanced magnitude and duration of segmental inhibition during cold block will increase the likelihood of disruption of the size principle for motoneuron recruitment is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230042
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  • 22
    Electronic Resource
    Electronic Resource
    Differences in the temporal dynamics of the visual ON and OFF pathways (1995)
    Springer
    Experimental brain research 104 (1995), S. 171-176 
    Details
    ISSN: 1432-1106
    Keywords: Visual channels ; Lateral geniculate nucleus ; Visual cortex ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The temporal structure of spike trains recorded from optic fibers and single units of the lateral geniculate nucleus (LGN) and primary visual cortex of the cat was studied with a novel method of inter-spike interval analysis. ON type relay cells of the LGN exhibited a multimodal interval distribution preferring a distinct interval (fundamental interval) and its multiples during the sustained light response, whereas most OFF cells showed a broad, unimodal distribution. The general pattern of the interval distribution was relatively independent of stimulus size and contrast and the degree of light adaptation. Simultaneously recorded S-potentials originating from the retinal input generally produced only a single peak at the fundamental interval length. Therefore, the multimodal interval distribution of LGN cells seems to be a result of intra-geniculate inhibition. Cortical cells also showed a weak tendency to fire with spike intervals similar to LGN cells. Therefore, the regular firing pattern observed at peripheral stages of the visual pathway can persist at higher levels and might promote the occurrence of oscillatory activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229868
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  • 23
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    Electronic Resource
    The effects of baclofen on the stretch reflex parameters of the cat (1995)
    Springer
    Experimental brain research 104 (1995), S. 287-296 
    Details
    ISSN: 1432-1106
    Keywords: Baclofen ; Stretch reflex ; Muscle stiffness ; Spinal cord ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Experiments were done in cats decerebrated at the precollicular postmammillary level to determine how a tonic increase of presynaptic inhibition of the intraspinal terminals of muscle spindle afferents changes the mechanical properties of the soleus stretch reflex (s.r.). Baclofen, a specific GABAB receptor agonist, was injected i.v. (1–2 mg/kg) so as to induce a tonic increase in presynaptic inhibition. The effects of baclofen on the stiffness and threshold of the s.r. were determined, respectively, from plots of stiffness vs background force and force vs length (length-tension plot). Baclofen, at these doses, had no effect on the excitation-contraction coupling properties of muscle or on the intrinsic stiffness-force relation. Changes of the soleus background force, required to obtain the stiffness vs force plots, were produced by stimulation of the contralateral common peroneal nerve or the posterior tibial nerve and occasionally by electrical stimulation in the area of the red nucleus. The stiffness of the s.r. as a function of the background force level was determined by stretching the muscle with a square pulse of 1–2 mm amplitude and 200–300 ms duration. The stiffness at each force level was calculated by dividing the change in force by the change in length, at a point where the force trace had stabilized. The length-tension relation of the s.r. was determined by stretching the muscle 12–17 mm at a constant rate of 1–2 mm/s. At all force levels, baclofen produced a significant decrease (40% or more) in the s.r. stiffness, within 10–15 min of injection as determined from the stiffness-force plots. The length-tension plots revealed that the decrease of s.r. stiffness was always accompanied by an increase in the s.r. threshold (typically 2–3 mm). It is suggested, therefore, that the s.r. threshold is not an independent variable, depending on the membrane potential of the α- motoneurons, and additionally on the level of presynaptic inhibition of the muscle spindle afferent terminals. The present results also imply that it may be possible for the CNS to adaptively modify the s.r. stiffness via presynaptic inhibition of the intraspinal terminals of muscle afferents. However, any such change of s.r. stiffness will be accompanied by a change in the s.r. threshold.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242014
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  • 24
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    Electronic Resource
    Effects of eye position on saccadic eye movements and on the neuronal responses to auditory and visual stimuli in cat superior colliculus (1995)
    Springer
    Experimental brain research 103 (1995), S. 227-242 
    Details
    ISSN: 1432-1106
    Keywords: Vision ; Audition ; Superior colliculus ; Saccade ; Multisensory convergence ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Many neurons in the deeper layers of the superior colliculus (SC) respond to multiple sensory inputs — visual, auditory, and somatic — as well as provide signals essential for saccadic eye movements to targets in different modalities. When the eyes and pinnae are in primary position, the neural map of auditory space is in rough topographic alignment with the map of visual space, and if the auditory map is based solely on head-pinna coordinates, any changes in eye position in the orbit will cause misalignment of the maps. We investigated the effects of eye position on the response of sound-sensitive neurons in the SC of cats because previous work on cats and on monkeys had suggested the possibility of species differences in the representation of auditory signals in the SC. We also investigated the effects of eye position on the accuracy of saccades to auditory, visual, and bimodal stimuli. All studies were conducted in alert, trained cats with the head restrained in a fixed position. Neuronal and behavioral responses were studied during periods when the eyes were steadily directed to different positions relative to the position of the sound. Cats showed partial compensation for eye position in making saccades, regardless of the modality of the target, and they showed similar patterns of error in saccades to auditory and visual targets. These behavioral data are consistent with coding the location of visual and auditory targets in the same coordinate system. In the vast majority of intermediate-layer neurons, eye position significantly affected the number of spikes evoked by sound stimuli. For most of these neurons, changes in eye position produced significant shifts in the speaker location producing maximal response. In some neurons, eye position significantly facilitated the magnitude of neuronal response evoked by sounds from a variety of speaker locations. Because few pinna movements could be detected, it is unlikely that these changes in neuronal response could be due to changes in the position of the pinnae. Our results indicate that the deep layers of the SC contain an eye-centered representation of sound location. Because eye position did not affect the percentage of neurons exhibiting multimodal integration, visual and auditory maps appear to remain integrated in the SC even when the eyes are directed eccentrically. Examination of the effects of eye position on neuronal responses to visual stimuli revealed that a substantial minority of neurons showed quantitative changes in the magnitude of response to visual stimuli when the retinal locus of stimulation was held constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231709
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  • 25
    Electronic Resource
    Electronic Resource
    Encoding of jaw movements by central trigeminal neurons with cutaneous receptive fields (1995)
    Springer
    Experimental brain research 104 (1995), S. 363-375 
    Details
    ISSN: 1432-1106
    Keywords: Cutaneous ; Jaw movements ; Vi ; Kinesthesia ; Trigeminothalamic ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Neurons with orofacial cutaneous receptive fields that responded to jaw movements were recorded in the trigeminal subnucleus interpolaris of the cat. Movement-related neuronal activity was identified by imposing passive ramp and hold stretches of the jaw at four different rates. Thirty-nine neurons with hair (26), skin (9), or convergent (4) receptive fields were studied. Thalamic projection neurons were identified by antidromic stimulation of the ventroposteromedial nucleus of the thalamus. The receptive fields of movement-related hair units included multiple hairs located mainly around the angle of the jaw and chin. The receptive fields of movement-related skin units were smaller than those of hair units and they were located primarily around the angle of the mouth. The convergent units had more than one receptive field that usually included hair or skin. All of the hair units were activated both during opening and closing jaw movements. They typically responded with short bursts of action potentials. Four units with skin receptive fields exhibited similar responses. The five skin units that did not show bursting activity included two that were active during both opening and closing of the jaw, two that were active only during opening, and one that was tonically active during maintained open position. All of the convergent units showed biphasic responses, and three responded with bursts. The maximum discharge rate, the mean discharge rate (mean bursting rate for units with bursting responses), and the total number of spikes per movement were measured. Statistical analysis was performed on these variables to assess functional properties of each unit. The results were used to classify units as velocity, speed, direction, or transient motion detectors. Thirty-three percent of the neurons were trigeminothalamic neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231972
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  • 26
    Electronic Resource
    Electronic Resource
    Latency variability of responses to visual stimuli in cells of the cat's lateral geniculate nucleus (1995)
    Springer
    Experimental brain research 105 (1995), S. 7-17 
    Details
    ISSN: 1432-1106
    Keywords: Lagged cells ; Nonlagged cells ; Visual system ; Thalamus ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We constructed average histograms from responses evoked by flashing stimuli and noted previously described variations in the shape of the response profile, particularly with respect to sharpness of the peak. To express this variable, we measured the half-rise latency, which is the latency from stimulus onset required to reach half the maximum response. A short half-rise latency, which is characteristic of nonlagged cells, is associated with a brisk response and sharp peak; a long half-rise latency, characteristic of lagged cells, is associated with a sluggish response and broad peak. Nonlagged cells were readily seen; we attempted to identify cells with long latencies as lagged, but we were unable to do so unambiguously due to failure to observe lagged properties other than latency. We thus refer to these latter cells as having “lagged-like” responses to indicate that we are not certain whether these are indeed lagged cells. In addition to the histograms, we analyzed the individual response trials that were summed to create each histogram, and we used spike density analysis to estimate the initial response latency to the flashing spot for each trial. We found that lagged-like responses were associated with more variability in initial response latency than were nonlagged responses. We then employed an alignment procedure to eliminate latency variation from individual trials; that is, responses during individual trials were shifted in time as needed so that each had a latency equal to the average latency of all trials. We used these “aligned” trials to create a second, “aligned” response histogram for each cell. The alignment procedure had little effect on nonlagged responses, because these were already well aligned due to consistent response latencies amongst trials. For lagged-like responses, however, the alignment made a dramatic difference. The aligned histograms looked very much like those for nonlagged responses: the responses appeared brisk, with a sharply rising peak that was fairly high in amplitude. We thus conclude that the slow build up to a relatively low peak of firing of the lagged-like response histogram is not an accurate reflection of responses on single trials. Instead, the sluggishness of lagged-like responses inferred from average response histograms results from temporal smearing due to latency variability amongst trials. We thus conclude that there is relatively little difference in briskness between nonlagged and lagged-like responses to single stimuli.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242177
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  • 27
    Electronic Resource
    Electronic Resource
    Integration in trigeminal premotor interneurones in the cat (1995)
    Springer
    Experimental brain research 104 (1995), S. 449-461 
    Details
    ISSN: 1432-1106
    Keywords: Premotor interneurones ; Subnucleus oralis-γ ; Trigeminal motor nucleus ; Spike-triggered averaging ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A population of last-order interneurones within the rostrodorsal part of the oral nucleus of the spinal trigeminal tract (NVspo-γ) has been investigated in 21 chloralose anaesthetised cats. The neurones were identified by their antidromic (AD) response to microstimulation (median current 9 μA, range 3–39 μA) of the ipsior the contralateral masseteric subnucleus of the trigeminal motor nucleus. Fifty-one of 113 interneurones tested were discharged from the ipsilateral and eight from the contralateral motor nucleus. The average conduction time was 0.50 ms from the ipsilateral and 0.74 ms from the contralateral motoneurone pool. Conduction velocities of the axons ranged from 2.0 to 14.0 ms. The pattern of primary afferent input onto the selected neurones was analysed by graded electrical stimulation of dissected trigeminal nerves. Low-threshold afferents innervating the intraoral mucosa including the tongue and the perioral skin of the lower lip were the most effective inputs, as judged from both the frequency of occurrence and from the latencies of the evoked spike discharges. Ninety-six percent of the neurones responded to stimulation of the inferior alveolar nerve (Alv inf) and 83% responded to stimulation of the lingual nerve (Ling). The median threshold strength required to evoke the Alv inf and the Ling responses was 1.7 T (range 1.0–3.6 T) and 1.3 T (range 1.0–5.0 T), respectively. The median latency to spike discharges evoked by the Alv inf was 2.0 ms (range 1.3–4.8 ms) and to the Ling it was 2.5 ms (range 1.4–7.0 ms). Action potentials elicited by stimulation of the masseteric and digastric nerves were observed in 40% and 10% of the neurones, respectively. These responses, which had median latencies of more than 8 ms (range 4.7–16.0 ms), were only seen at stimulation intensities above 2 T (range 2.5–25 T). An input from the maxillary whisker nerve was seen in only one case. Postspike averages of the extracellular field potentials within the trigeminal motoneurone subnuclei evoked by interneuronal spikes were made in a subsample of 51 NVspo-γ neurones activated by iontophoresis of L-glutamic acid. Excitatory synaptic effects within the masseteric subnucleus were observed in eight cases. An inhibitory effect was seen in one case. One specific neurone gave an excitatory extracellular field potential within the digastric motoneurone subnucleus. This interneurone was AD activated from the digastric, but not from the masseteric subnucleus. The physiological properties of the NVspo-γ-mass interneurones are discussed in relation to their suggested roles in the phase-dependent control of the trigeminal motoneurones during oro-facial masticatory behaviours.
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    URL: http://dx.doi.org/10.1007/BF00231979
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  • 28
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    Electronic Resource
    An in vivo electrophysiological investigation of group Ia afferent fibres and ventral horn terminations in the cat spinal cord (1995)
    Springer
    Experimental brain research 106 (1995), S. 403-417 
    Details
    ISSN: 1432-1106
    Keywords: Spinal Ia terminations ; Myelinated fibres ; Action potentials ; Primary afferent depolarization ; Transmitter release ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract An extracellular microstimulation technique has been used to investigate and compare the properties of group I primary afferent myelinated fibres in the dorsal column and group Ia unmyelinated terminations in the lumbar spinal cord of cats anaesthetised with pentobarbitone sodium. Fibres were distinguished from terminations on the basis of location, anodic blocking factor and sensitivity to GABAA mimetics. The recovery curves of threshold following an orthodromic impulse provided an estimate of both action potential duration and rate of repolarization. The action potentials of group Ia terminations were of briefer duration (by a factor of approximately 2) with more rapid rates of repolarization (factor of approximately 3) than those of the myelinated fibres. The prolongation of termination but not fibre action potentials by microelectrophoretic tetraethylammonium and 4-aminopyridine indicated the presence of voltage-activated potassium channels in the termination membrane. Differences in the effects on Ia termination action potentials of depolarizations (reductions in threshold) associated with a preceding action potential, synaptically released GABA, microelectrophoretic piperidine-4-sulphonic acid or dl-homocysteic acid suggest that an increase in termination membrane conductance is the major factor in the reduction of transmitter release during the activation of presynaptic GABAA receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231063
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  • 29
    Electronic Resource
    Electronic Resource
    Evidence for high-velocity smooth pursuit in the trained cat (1995)
    Springer
    Experimental brain research 106 (1995), S. 509-512 
    Details
    ISSN: 1432-1106
    Keywords: Eye movement ; Smooth pursuit ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It is generally accepted that in cats smooth pursuit velocity of the eye never exceeds a few degrees per second. This is in contrast with observations in primates, where smooth pursuit velocity can reach values as high as 100°/s. Cats were trained to fixate and pursue spots of light appearing on a translucent screen. Spots were moved in the horizontal and vertical planes at different constant velocities up to 80°/s. Eye position was recorded with the sclerai search coil technique. Naive cats did not pursue moving targets with high efficiency. Smooth eye movement velocity saturated at 5°/s. After a few days of training, smooth-pursuit eye velocity increased with target velocity and saturated at 25°/s on average. However, velocities twice as high have been observed frequently. When the target was unexpectedly extinguished, smooth eye movement velocity dropped to values close to 0°/s in approximately 350 ms. After a short training period (usually 5 times the same target presentation), the eye continued to move smoothly until the target reappeared. These data suggest that smooth pursuit eye movements of the cat are qualitatively similar to those of primates, but reach lower velocities and are more variable in their characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231076
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  • 30
    Electronic Resource
    Electronic Resource
    Ozone exposure suppresses epithelium-dependent relaxation in feline airway (1995)
    Springer
    Lung 173 (1995), S. 47-56 
    Details
    ISSN: 1432-1750
    Keywords: Airway hyperresponsiveness ; Ozone ; Airway epithelial cell ; Bronchiole ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We examined the effect of exposure to ozone on the epithelium-dependent relaxation (EpDR) of bronchioles evoked by electrical field stimulation (EFS) in a feline model with hyperresponsive airways induced by exposure to ozone. Airway responsiveness was assessed by measuring the increases in total pulmonary resistance (RL) produced by aerosolized acetylcholine (ACh) in vivo. Airway responsiveness was also measured in vitro in dissected bronchiolar ring preparations. Exposure to ozone (3 ppm, 2 h) significantly increased the airway responsiveness in vivo. The concentration of ACh required increasing R L to 200% of the baseline value, decreased from 1.97 mg/ml (GSEM 1.94) to 0.12 mg/ml (GSEM 1.77, p 〈 0.01) after exposure to ozone. EFS evoked atropine-, guanethidine-, and tetrodotoxin-resistant relaxations in the control bronchiolar rings precontracted by 5-hydroxytryptamine. Such relaxation was significantly suppressed by the mechanical denudation of epithelium, confirming that it was epithelium dependent. The amplitude of EpDR was significantly suppressed in the animals exposed to ozone. These results suggest that EpDR is present in cats, and that its inhibition may contribute to the development of airway hyperresponsiveness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167600
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    Electronic Resource
    Electronic Resource
    Interactions of the subthalamic nucleus and the subpallidal area in oro-facial dyskinesia: role of GABA and glutamate (1995)
    Springer
    Psychopharmacology 119 (1995), S. 20-26 
    Details
    ISSN: 1432-2072
    Keywords: Oro-facial dyskinesia ; Subthalamic nucleus ; Globus pallidus ; GABA ; Glutamate ; Behaviour ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies have shown that lowering the GABAergic activity in the sub-pallidal area (SP) in the cat results in the display of oro-facial dyskinesia (OFD). There exists an intense, mutual anatomical connection between the SP and the subthalamic nucleus and the adjoining lateral hypothalamic area (STH). The present study investigated whether the STH is also involved in OFD. Once this turned out to be true (see below), it was investigated whether the SP-specific OFD is funneled via the STH, or vice versa. Bilateral injections of low doses (50–250 ng) of picrotoxin, a non-competitive GABA antagonist, into the STH were found to elicit OFD. This effect which was quantified in terms of numbers of tongue protrusions, was dose-dependent: a bell-shaped dose-response was found (50–500 ng). The OFD elicited by the most effective dose of picrotoxin (250 ng) was significantly antagonized by muscimol, a specific GABAA agonist, in a dose (50 ng) which itself was ineffective, indicating GABA specificity. In addition, it was found that OFD elicited by local injections of picrotoxin (250 ng) into the STH was significantly attenuated by SP injections of the broad spectrum glutamate antagonist kynurenic acid in a dose (1000 ng) which itself was ineffective, but not by muscimol (100 ng), indicating that the STH-elicited OFD needs an intact and functioning glutaminergic, but not GABAergic, transmission process in the SP for its expression. Finally, it was found that OFD elicited by picrotoxin injections (500 ng) into the SP was significantly attenuated by muscimol injections (50 ng) into the STH, indicating that the SP-elicited OFD needs an intact and functioning GABAergic transmission process in the STH for its expression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02246049
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  • 32
    Electronic Resource
    Electronic Resource
    Horseradish peroxidase in axons of the dorsal funiculi of the cat: distribution after an injection of the enzyme into the dorsal column nuclei (1995)
    Springer
    Cell & tissue research 283 (1995), S. 67-73 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Node of Ranvier ; Axon ; Horseradish peroxidase (HRP) ; Retrograde axonal transport ; Electron microscopy ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Horseradish peroxidase (HRP) was injected into the left dorsal column nuclei of adult cats. Large dorsal funiculi axons of the C3, C5, C8 and L7 segments were searched for HRP-activity after 12, 24, 36 and 48 h using light and electron microscopy. Accumulations of intra-axonal HRP-positive bodies occurred at nodes of Ranvier in the C3–C8 segments at 12, 24 and 36 h and in the L7 segments at 24, 36, and 48 h. The accumulations of HRP in three spatio-temporally different consecutive patterns, noted earlier at nodes of Ranvier in the peripheral nervous system (PNS) portion of feline alpha motor axons for more than 70 h after an intramuscular injection of the enzyme, were not observed in the present material. We suggest that the differences in the modes in which large PNS and CNS axons interact with retrogradely transported HRP are due to differences in the organization of the respective nodal regions. We also emphasize that endocytosis via axon terminals in the CNS normally represents uptake of material from an extracellular space which is controlled and protected by the blood-brain barrier. This is in contrast to endocytosis via axon terminals in a muscle, which represents uptake of material from an extracellular space openly exposed to influx of different substances from the blood stream.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050513
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  • 33
    Electronic Resource
    Electronic Resource
    A monoclonal anticarbohydrate antibody detecting superfast myosin in the masseter muscle (1995)
    Springer
    Cell & tissue research 283 (1995), S. 85-92 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Masseter muscle ; Limb muscles ; Superfast fibres ; Myosin heavy chains ; Glycosylation ; Galactose ; ATPase ; Cat ; Dog ; Macaca fascicularis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Superfast-contracting muscle fibres (II M) were identified by ATPase staining and after incubation with an antiserum raised against myosin type II M and with an antibody raised against the Galα1–3Galβ1–4GlcNAc structure. II M fibres were present in masseter muscles from cat, dog and Macaca fascicularis but not in limb muscles from the same animals and not in masseter muscles from rat, pig, cow or man. Electrophoresis and staining of blots from myosin preparations showed that the anticarbohydrate antibody detected myosin heavy chains from cat masseter but not myosin heavy chains from cat biceps. The α-galactose specific lectin Griffonia simplicifolia isolectin B4 (GS I B4) did not stain muscle fibres or myosin heavy chains. Therefore, the epitope on myosin heavy chains defined by the anticarbohydrate antibody is presumably not Galα1–3Galβ1–4GlcNAc although the antibody staining was strongly inhibited after absorption by 10 mM of this trisaccharide. Antibody staining of the muscle fibres was totally inhibited by adding 10 mM p-nitrophenyl β-D-glucuronide to the incubation medium. The results thus imply that an anticarbohydrate antibody distinctively detects a carbohydrate epitope specific for myosin in superfast contracting muscle fibres from jaw-closing muscles and confirm that this epitope is not present in other muscle fibre types. This appears to be the first report on differentiated glycosylation among myosin isoforms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050515
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    Electronic Resource
    Electronic Resource
    A new combination of methods for the localization, identification, and three-dimensional reconstruction of the sensory endings of articular afferents characterized by electrophysiology (1995)
    Springer
    Cell & tissue research 281 (1995), S. 283-294 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Articular afferents ; Corpuscular endings ; Free nerve endings ; Morpho-functional examination ; Three-dimensional reconstruction ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. A combination of methods is described to identify and reconstruct corpuscular and non-corpuscular sensory endings of group II and group III nerve fibers following functional examination by electrophysiology. Afferent units activated by electrical stimulation of the medial articular nerve of the cat’s knee were analyzed by single fiber recordings and characterized by their responsiveness to mechanical stimuli. The receptive fields of the units were closely demarcated by fine needles when the responses elicited by insertion of the needles were being recorded. After fixation, the tissue around the demarcated field was dissected and histologically processed. Series of semithin sections were cut from the embedded tissue blocks containing the receptive fields. Corpuscular endings of group II fibers and peripheral myelinated group III nerve fibers, presumably corresponding to the characterized units, were identified by light microscopy of semithin sections and localized within the demarcated area. Non-corpuscular endings were identified by electron microscopy of ultrathin sections cut in alternation with, or after re-embedding of, semithin sections. Morphometric analysis of ultrathin section series allowed the measurement of parameters such as the mean axon diameter and the organelle content of the sensory endings. The methods described are appropriate for collecting data that correlate the structural and functional characteristics of sensory endings in deep tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050425
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  • 35
    Electronic Resource
    Electronic Resource
    Association of immune cells with neuroepithelial bodies in the lungs of neonatal dogs, cats and hamsters (1995)
    Springer
    Cell & tissue research 282 (1995), S. 519-522 
    Details
    ISSN: 1432-0878
    Keywords: Lungs ; Chemoreceptors ; Mast cells ; Eosinophils ; Neutrophils ; Newborns ; Dog ; Cat ; Golden hamster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A close topographical association between neuroepithelial bodies and immune cells is occasionally observed in the lungs of various neonatal mammalian species. The immune cells concerned are mast cells and neutrophil or eosinophil granulocytes. In the lungs of newborn puppies having undergone left lung autotransplantation, mast cells are particularly numerous in the airway mucosa of both right and left lungs and their association with neuroepithelial bodies is highly significant. Several of the substances known to be synthesized by the neuroepithelial bodies have a chemoattractive effect on immune cells. Thus, our observations indicate that intrapulmonary neuroepithelial bodies contribute to the local immune response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318884
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  • 36
    Electronic Resource
    Electronic Resource
    Association of immune cells with neuroepithelial bodies in the lungs of neonatal dogs, cats and hamsters (1995)
    Springer
    Cell & tissue research 282 (1995), S. 519-522 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Lungs ; Chemoreceptors ; Mast cells ; Eosinophils ; Neutrophils ; Newborns ; Dog ; Cat ; Golden hamster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. A close topographical association between neuroepithelial bodies and immune cells is occasionally observed in the lungs of various neonatal mammalian species. The immune cells concerned are mast cells and neutrophil or eosinophil granulocytes. In the lungs of newborn puppies having undergone left lung autotransplantation, mast cells are particularly numerous in the airway mucosa of both right and left lungs and their association with neuroepithelial bodies is highly significant. Several of the substances known to be synthesized by the neuroepithelial bodies have a chemoattractive effect on immune cells. Thus, our observations indicate that intrapulmonary neuroepithelial bodies contribute to the local immune response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050503
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  • 37
    Electronic Resource
    Electronic Resource
    A new combination of methods for the localization, identification, and three-dimensional reconstruction of the sensory endings of articular afferents characterized by electrophysiology (1995)
    Springer
    Cell & tissue research 281 (1995), S. 283-294 
    Details
    ISSN: 1432-0878
    Keywords: Articular afferents ; Corpuscular endings ; Free nerve endings ; Morpho-functional examination ; Three-dimensional reconstruction ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A combination of methods is described to identify and reconstruct corpuscular and non-corpuscular sensory endings of group II and group III nerve fibers following functional examination by electrophysiology. Afferent units activated by electrical stimulation of the medial articular nerve of the cat's knee were analyzed by single fiber recordings and characterized by their responsiveness to mechanical stimuli. The receptive fields of the units were closely demarcated by fine needles when the responses elicited by insertion of the needles were being recorded. After fixation, the tissue around the demarcated field was dissected and histologically processed. Series of semithin sections were cut from the embedded tissue blocks containing the receptive fields. Corpuscular endings of group II fibers and peripheral myelinated group III nerve fibers, presumably corresponding to the characterized units, were identified by light microscopy of semithin sections and localized within the demarcated area. Non-corpuscular endings were identified by electron microscopy of ultrathin sections cut in alternation with, or after re-embedding of, semithin sections. Morphometric analysis of ultrathin section series allowed the measurement of parameters such as the mean axon diameter and the organelle content of the sensory endings. The methods described are appropriate for collecting data that correlate the structural and functional characteristics of sensory endings in deep tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583397
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  • 38
    Electronic Resource
    Electronic Resource
    Intraretinal analysis of electroretinogram with K+ microelectrodes during acute intraocular pressure elevation (1995)
    Springer
    Documenta ophthalmologica 91 (1995), S. 129-139 
    Details
    ISSN: 1573-2622
    Keywords: Cat ; C-wave ; Electroretinogram ; Intraocular pressure ; Potassium ion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We examined the effects of acute intraocular pressure elevation on the intraretinal electroretinogram in the cat dark-adapted eye. Perfusion pressure of the eye (mean arterial pressure minus intraocular pressure) was regulated within the range of 25–75 mm Hg by increasing the intraocular pressure, which was adjusted by changing the height of the reservoir of balanced salt solution perfused into the eye through a needle placed in the anterior chamber. The vitreal electroretinogram, transepithelial c-wave, slow PIII and light-evoked decrease in extracellular K+ concentration were recorded during intraocular pressure elevation in the darkadapted retina. The c-wave increased in amplitude between 40 and 75 mm Hg of perfusion pressure and decreased below 40 mm Hg in some cases. These changes were unrelated to the standing potential. The transepithelial c-wave, slow PIII and light-evoked decrease in extracellular K+ concentration were larger in the range of perfusion pressure examined. These suggest that some factor induces electroretinographic changes that are not readily explained by hypoxia or pH changes alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01203692
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  • 39
    Electronic Resource
    Electronic Resource
    Characterisation of the Intermediate C2H4…Cl2 in a Gaseous Mixture of Ethene and Chlorine by Rotational Spectroscopy: A Weak π-Type Complex (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 17-25 
    Details
    ISSN: 0947-6539
    Keywords: chlorine complexes ; ethene complexes ; intermediates ; rotational spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complex of ethene and Cl2 has been characterised in the gas phase. Rotational spectra of the isotopomers C2H4…35Cl2, C2H4…35Cl37Cl and C2H4…37Cl35Cl were recorded by using a fast-mixing nozzle in an FT microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl nuclear quadrupole coupling constants. χgg (Cl) are reported in each case. The complex is of the π-donor-acceptor type and has a C2v geometry in which Cl2 lies along the C2 axis perpendicular to the plane of the C2H4 nuclei. The binding is weak, and only small changes in the χgg (Cl) attend complex formation. A simple model attributes these changes to a transfer of around 0.02e from the inner to the outer Cl nucleus, thus confirming that the complex is of the Mulliken outer type. Similarities in the properties of C2H4… Cl2 and C2H4… HCl indicate that the angular geometry is in both cases determined mainly by the electrostatic part of the interaction. The distance from the π-bond midpoint to Cl decreases from C2H4… HCl to C2H4… Cl2; this suggests that Cl2 is “snub-nosed”.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010107
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  • 40
    Electronic Resource
    Electronic Resource
    5,10,15,20-Tetraphenylsapphyrin-Identification of a Pentapyrrolic Expanded Porphyrin in the Rothemund Synthesis (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 68-73 
    Details
    ISSN: 0947-6539
    Keywords: porphyrinoids ; Rothemund synthesis ; sapphyrin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Rothemund-type condensation of pyrrole and benzaldehyde yields, apart from 5,10,15,20-tetraphenylporphyrin (TPPH2) and inverted tetraphenylporphyrin 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (CTPPH2), a unique pentapyrrolic macrocyclic molecule with the aromatic nucleus of sapphyrin, namely, 5,10,15,20-tetraphenylsapphyrin (TPSH3). Its unorthodox structural skeleton with an inverted pyrrole ring lying opposite to the bipyrrole unit accounts for the spectroscopic properties of the novel sapphyrin. The diprotonation of TPSH3 acts as a trigger for a structural transformation involving a flip of the pyrrole units, which relocates the 27-NH pyrrolic nitrogen from the periphery into the center of the macrocycle. The formation of 5,10,15,20-tetraphenylsapphyrin proves that the pentapyrrolic product is accessible by the mechanism of the Rothemund synthesis.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010111
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  • 41
    Electronic Resource
    Electronic Resource
    A Tale of Two Complexes, [PtMen(RN=CH—CH=NR)] (n = 2 and n = 4, R = Cyclohexyl): Why do PtII and PtIV Complexes Exhibit Virtually Identical Redox Behavior and Colors? (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 95-99 
    Details
    ISSN: 0947-6539
    Keywords: charge transfer ; EPR spectroscopy ; organometallic compounds ; platinum compounds ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In spite of their very similar cyclic voltammograms, absorption spectra, and solvatochromic behavior, the two 1,4-diazabutadiene title complexes exhibit markedly different photoreactivities and underlying electronic structures, as evident from absorption and EPR spectra of the persistent anion radical forms. The lowest excited state of the nonphotoreactive PtII system [(CyN=CH—CH=NCy)-PtMe2] has MLCT (metal-to-ligand charge-transfer, 5d → π*) character, and the EPR spectrum of the corresponding anion radical at 〈g〉 = 2.016 exhibits sizable metal/ligand orbital mixing. On the other hand, the structurally characterized PtIV complex [(CyN=CH—CH=NCy)-PtMe4] (C2/c; a = 2021.6(2), b = 805.3(1), c = 1254.2(1) pm; β = 111.05(1)°; V = 1905.7(4) × 106 pm3; Z = 4) has a lowlying photoreactive LLCT (ligand-to-ligand charge-transfer, σPt—C → π*) excited state in which the axial Pt—C bonds are activated, as already suggested by the longer Pt—C(ax) bonds (214.0(8) pm) relative to Pt—C(eq) in the ground state (204.5(5) pm). The anion radical of the PtIV complex has lost the long-wavelength absorption band in the visible; it shows a well-resolved EPR spectrum at 〈g〉 = 1.9945 with π-ligand and 195Pt hyperfine structure and a small g anisotropy. A qualitative MO scheme is presented to account for the similar frontier-orbital energy differences despite dissimilar underlying electronic structures.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010114
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  • 42
    Electronic Resource
    Electronic Resource
    Linear and Cyclic Platinum σ-Acetylide Complexes of Tetraethynylethene (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 111-117 
    Details
    ISSN: 0947-6539
    Keywords: alkyne complexes ; carbon networks ; macrocycles ; platinum compounds ; tetraethynylethene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of the first organometallic mono- and dinuclear platinum complexes bearing the tetraethynylethene unit as an η1-ligand are reported. Structural characterization of two of the trans σ-bis(acetylide) derivatives by X-ray crystallography reveals coplanarity of the acetylenic π-ligands and indicates possible electronic delocalization across the metal center. This notion is further supported by comparing the electronic absorption spectra of the platinum-containing compounds with those of related tetraethynylethene derivatives without metals. The solidstate structure of a dinuclear complex with two iodoplatinum fragments attached to one set of geminal acetylenes of tetraethynylethene was also investigated by X-ray diffraction. Hay coupling of a mononuclear species leads to the incorporation of the σ-bis(acetylide) moiety into a diplatinated metallacycle. This macrocyclic compound represents a novel structural motif in the design of a transition metal linked carbon network based on tetraethynylethene.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010204
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  • 43
    Electronic Resource
    Electronic Resource
    Asymmetric Control of 1,3-Dipolar Cycloaddition Reactions with Azomethine Ylides by Means of Proline Esters as Chiral Auxiliary Groups (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 150-154 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; azomethine ylides ; chiral auxiliaries ; cycloadditions ; pyrrolidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Upon treatment with triethylamine or DBU in the presence of LiBr, aromatic and aliphatic imines of amino acid esters are converted to N-metalated azomethine ylides. These 1,3-dipoles undergo highly stereoselective cycloadditions with N-acryloyl-(S)-proline esters in THF at -78 to -40°C to afford highly substituted pyrrolidines with complete regiocontrol and good to excellent diastereomeric ratios. The chiral auxiliary groups can readily be removed from the cycloadducts by simple acid hydrolysis. To rationalize the observed stereoselectivity a transition-state model is proposed in which the lithium cation is coordinated to both the 1,3-dipole and the dipolarophile.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010209
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  • 44
    Electronic Resource
    Electronic Resource
    Synthesis of a Methyl Heptaglucoside with Phytoalexin Elicitor Activity Based on Oxidative Coupling of Glucals (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 161-164 
    Details
    ISSN: 0947-6539
    Keywords: block synthesis ; epoxidations ; glycosylations ; oligosaccharides ; selenoglycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several suitable building blocks for the construction of the phytoalexin elicitor α-methyl-32, 34-di-β-D-glucopyranosylgentiopentaoside (2) were readily accessible by oxidative coupling of glucals. Block coupling of trimeric phenylseleno- and ethylthioglucosyl donors 17 and 18 with tetrasaccharide 16 in the presence of the thiophilic promoter N-iodosuccinimide and catalytic trifluoromethanesulfonic acid furnished the desired heptaglucan 2 in high overall yield.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010304
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  • 45
    Electronic Resource
    Electronic Resource
    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010401
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  • 46
    Electronic Resource
    Electronic Resource
    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010403
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  • 47
    Electronic Resource
    Electronic Resource
    Asymmetric syn-Selective Michael Addition of Enolates to Chiral 8-Phenylmenthyloxy Vinyl Chromium Carbene Complexes (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 236-242 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; enol ethers ; Fischer carbenes ; Michael additions ; syn diastereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Michael addition reactions of ketone and ester lithium enolates to optically active Fischer vinylcarbene complexes derived from (-)-8-phenylmenthol take place with high syn selectivity and high levels of asymmetric induction. The initial Michael adducts can be further elaborated through diastereoselective addition of organometallic reagents to ketones and aldol reactions. Removal of the metal fragment and chiral auxiliary group leads to cyclic enol ethers with three or five contiguous stereogenic centers and of high enantiomeric purity.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010407
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  • 48
    Electronic Resource
    Electronic Resource
    Synthesis of a Fullerene[60] Cryptate and Systematic Langmuir-Blodgett and Thin-Film Investigations of Amphiphilic Fullerene Derivatives (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 243-251 
    Details
    ISSN: 0947-6539
    Keywords: amphiphiles ; C-glycosides ; cryptates ; fullerenes ; ionophores ; Langmuir-Blodgett films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the first fullerene cryptate 7 with a sodium ion bound to a benzo[2.2.2]cryptand covalently attached to a methanofullerene[60] is described. The amphiphilic properties of 7 as well as of a variety of other covalent fullerene derivatives with polar functional groups and the ability of these compounds to form Langmuir monolayers at the air-water interface were investigated in a systematic study. Among these derivatives are Diels-Alder adducts of C60 and methanofullerenes, four of which are fullerene C-glycosides. The films at the water surface were characterized by their surface pressure versus molecular area isotherms, compression and expansion cycles, and optical light microscopy. UV/Vis spectroscopy and small-angle X-ray diffraction (SAXS) were employed for LB film characterization on solid substrates. Parameters influencing the spreading and monolayer character include (a) polarity, (b) balance of hydrophobicity to hydrophilicity, (c) size and bulkiness of the polar groups attached to the fullerene, and (d) presence of aromatic residues in these groups.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010408
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  • 49
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    Light-Triggered Molecular Devices: Photochemical Switching Of optical and Electrochemical Properties in Molecular Wire Type Diarylethene Species (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 275-284 
    Details
    ISSN: 0947-6539
    Keywords: diarylethenes ; molecular devices ; nonlinear optics ; photochromes ; redox switches ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organic photochromic systems represent a starting point for the elaboration of light-triggered molecular switching devices. The novel bispyridinium and bispyridine compounds 12+ and 6 were synthesized as their uncyclized isomers from 3,5-dibromo-2-methylthiophene in overall yields of 43 and 44%, respectively. The diarylethene photochromes 2 and 10-13, substituted with electron donors and acceptors, were prepared from 5-methylthiophene-2-carboxaldehyde in 21-32% overall yield. All of the compounds were found to exhibit pronounced photochromic properties. Irradiation with UV light resulted in essentially complete photocyclization of the open forms to the intensely coloured closed isomers which could, in turn, be reconverted back to the open state with visible light of γ〉600 nm. The absorption maxima of the described compounds in their closed forms are shifted far towards, and even into, the near-IR region. Whereas no thermochromic properties were observed for the open isomers, the rates of thermal decolouration of the cyclized forms was found to be highly dependent on the nature of the substituents on the thiophene rings. It was demonstrated that reversible photochemical interconversion between the two photochromic states could be used to effectively switch a number of physical properties. Thus, the molecules 12+ and 12 represent two kinds of redox switches, the former in reduction and the latter in oxidation, in which electron conduction is switched on in the closed state and off in the open state. Compound 12 may also be considered to be a photoswitchable analogue of tetrathiafulvalene type substances. On the other hand, compound 2 displays a marked increase in nonlinear optical activity on conversion from the open to the closed form. Such systems are prototypes of photoswitchable molecular wires where electron conduction and push-pull interaction can be reversibly modulated by an external stimulus, namely, irradiation by light.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010504
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  • 50
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    A Dual-Mode Molecular Switching Device: Bisphenolic Diarylethenes with Integrated Photochromic and Electrochromic PropertiesDedicated to Professor George Just on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 285-293 
    Details
    ISSN: 0947-6539
    Keywords: diarylethenes ; electrochromes ; molecular devices ; optical memory ; photochromes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bisphenolic dithienylethene molecules 1a and 1b were synthesized in overall yields of 45% from 4-bromoanisole and 44% from 2.6-di-tert-butyl-4-iodophenol, respectively. The corresponding extended quinones 3a and 3b were also prepared. Photochemical studies showed that compounds 1 are photochromic; the open forms 1 could be converted with UV light of 312nm to the closed coloured forms 2 with photostationary states lying at essentially complete conversion (〉 98%). The 1a-2a system was found to exhibit good resistance to photofatigue and thermal stability for both photoisomers. Cyclic voltammetry studies involving the 2/3 couples showed that whereas 2b undergoes irreversible oxidation at + 0.85 V (vs. SCE in THF), the hydroquinone 2a is reversibly oxidized at an E1/2 of + 0.72V (in MeCN, quasi-reversibly in THF at + 0.81 V); this reflects the differences in deprotonation behaviour of the generated QH2/2+ species. The large difference in oxidation potential between 1a and 2a allows the photochemical switching of redox properties. In a complementary fashion, redox switching of the photochromic properties within the 2a-3a pair is possible since 3a is stable to visible light. Owing to this unique behaviour, the triad consisting of 1-3a represents a novel molecular device with mutually regulating photo- and electrochromic behaviour. In addition, the ability to interconvert between the three stable states makes the system well-suited as the basis for an optical memory system with multiple storage and nondestructive readout capacity through a write-lock-read-unlock-erase cycle.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010505
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  • 51
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010603
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  • 52
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    Diastereo- and Enantioselective Synthesis of L-threo- and D-erythro-SphingosineDedicated to Professor Peter Paetzold on the occasion of his 60th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 382-388 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; alkenylations ; SAMP/RAMP hydrazones ; selenyl aldehydes ; sphingosine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: L-threo-sphingosine and its D-erythro isomer (1) are subunits of many glycosphingolipids, gangliosides and ceramides. This paper describes the highly diastereo- and enantioselective synthesis of both isomers (de, ee 〉 98%). The key steps in the synthesis are the aldol reaction of the SAMP hydrazone (S)-2 with racemic α-phenylselenylpentadecanal 3, the diastereoselective triacetoxyborohydride reduction of ketone 5 and exclusive (E) C—C double bond formation in the elimination of hydroxyl and selenyl moieties promoted by methanesulfonyl chloride. Mesylate 8 was then readily converted via the 1,3-O-acetonide-protected azidosphingosine 9 to L-threo-sphingosine. Conversion to the known 1-O,2-N-diacetyl-protected sphingosine 13 with subsequent Mitsunobu inversion of the C3—OH centre afforded the D-erythro-sphingosine epimer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010609
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  • 53
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    Potential Linear-Chain Organic Ferromagnets (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 403-413 
    Details
    ISSN: 0947-6539
    Keywords: conjugation ; ferromagnetism ; helices ; magnetic properties ; polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structures of conjugated polymers containing methyl radicals, carbenes, and nitrogen-based radicals coupled in various ways through benzene rings are examined, employing band-structure calculations in the extended Hückel approximation. The structural and electronic properties of polymers with a para-phenylene or meta-phenylene coupling unit are compared. In the polymer with methyl radicals coupled through a para-phenylene unit, a pairing or Peierls distortion occurs to remove the degeneracy at the Fermi level. The resulting bandgap is nevertheless relatively small; we conclude that such polymers are likely to exhibit high electrical conductivity upon doping, very much like polyacetylene. On the other hand, in the polymers with a meta-phenylene coupling unit, striking symmetry-determined, halfoccupied narrow bands appear at the Fermi level and contribute to the stability of the ferromagnetic state. The relation of a potential ferromagnetic state to metallic, CDW, and SDW states is discussed from the viewpoint of orbital interactions in extended systems. We suggest novel 3- and 4-fold helical structures for the meta-phenylene-coupled polymers.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010704
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  • 54
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    Reversibility in the Reaction of Cyclohexadienyl Radicals with Oxygen in Aqueous Solution (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 423-429 
    Details
    ISSN: 0947-6539
    Keywords: kinetics ; peroxyl radicals ; pulse radiolysis ; radicals ; superoxide radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroxyl radicals were generated radiolytically and reacted with a number of benzene derivatives (PhH). In the presence of oxygen, the hydroxycyclohexadienyl radicals thus formed were converted into their corresponding peroxyl radicals. Pulse radiolysis has shown the oxygen addition (forward reaction, f) to be reversible (reverse reaction, r) [Eq. (1)]. The peroxyl radicals can eliminate HO2· to yield phenols, alongside some ring-fragmentation products (product-forming reaction, p). The rate constants for the forward and reverse reactions (kf and kr) and the corresponding stability constants K (= kf/kr) were determined for the hydroxy-cyclohexadienyl radicals derived from anisole, toluene, fluorobenzene, benzene, chlorobenzene, benzyl chloride, benzoate ion, phenylalanine, and terephthalate ion. The constants kf lie between 8 × 108 (anisole) and 1.6 × 107 dm3 mol-1 s-1 (terephthalate ion), and kr between 7.5 × 104 (toluene) and 3.4 × 103 s-1 (terephthalate ion). The stability constants lie between 2.6 × 104 (benzene) and 3.3 × 103 dm3 mol-1 (phenylalanine). The rate constants for the product-forming reactions kp are between 5.5 × 103 (anisole) and 3.4 × 102 s-1 (benzoate). For the peroxyl radical derived from phenylalanine, a bond dissociation energy of 5.5 kcal mol-1 has been derived. A number of hydroxy-cyclohexadienyl radicals (e.g., those derived from benzoic acid, ethylbenzoate, benzonitrile, and nitrobenzene) react too slowly to allow the equilibrium constant to be determined by means of pulse radiolysis. These reactions have rate constants kf in the order of 5 × 106 dm3 mol-1 s-1, except for nitrobenzene where the reaction is too slow for measurement. The rate constants kr are below 500 s-1, and the product-forming reaction is too slow to be detected by pulse radiolysis. γ-Radiolysis of N2O/O2(4:1)-saturated aqueous solutions of benzonitrile gave dimeric compounds (e.g., dicyanobiphenyls) in low yield, alongside the three isomeric phenols; this again proves the low reactivity of its hydroxycyclohexadienyl radical toward oxygen.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010706
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    Semiconductor-Catalysed Photoaddition of Olefins and Enol Ethers to 1,2-Diazenes: A New Route to AllylhydrazinesHeterogeneous Photocatalysis XIII. Part XII: H. Kisch. J. Prakt. Chem. 1994, 336, 635Dedicated to Professor Hans-Dieter Scharf on the occasion of his 65th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 441-448 
    Details
    ISSN: 0947-6539
    Keywords: allylhydrazines ; cadmium compounds ; catalysis ; photochemistry ; zinc compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Suspensions of zinc or cadmium sulfide powders in a protic solvent catalyse the linear addition of enol ethers and olefins to 1,2-diaryl- and 1-aryl-2-alkyl-1,2-diazenes, producing allylhydrazine derivatives. Relative quantum yields decrease sharply when the 1,2-diazene is more difficult to reduce, while their relationship to the oxidation potential of the enol ether/olefin is complicated. Reduction to 1,2-diarylhydrazine and concomitant dehydrodimerization of the enol ether occurs as a side reaction. It is favoured by increasing light intensity and becomes the major reaction path when platinized (5 mol%) photocatalysts are employed. It is proposed that the photogenerated electron-hole pair in a proton-coupled electron transfer reduces the diazene to a hydrazyl radical and oxidizes the olefin/enol ether to a radical cation. The allylic radical obtained from the latter by deprotonation then undergoes C—N coupling with the hydrazyl radical to afford the allylhydrazine. Diarylhydrazine formation occurs by disproportionation of the hydrazyl radical or by a successive proton-coupled reduction. Thus photoaddition can be classified as a 1 e-/1 h+ process while 2e-/2h+ are necessary for the reduction.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010709
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    Masthead (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010802
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  • 57
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    Stereoselective Homologation-Amination of Aldehydes by Addition of Their Nitrones to C-2 Metalated Thiazoles - A General Entry to α-Amino Aldehydes and Amino Sugars (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 505-520 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general method for the homologation of aldehydes to α-amino aldehydes (aminohomologation) has been developed, which employs nitrones as iminium derivatives of the aldehydes. Key operations include a) the addition of a thiazole metalated at C-2 to the N-benzylnitrone derived from the aldehyde, b) the reductive dehydroxylation of the resultant thiazolyl N-benzylhydroxylamine, and c) the unmasking of the formyl group from the thiazole ring. The homologation sequence was studied by employing nitrones derived from various chiral polyalkoxy aldehydes and dialdoses. The addition of 2-lithiothiazole to these nitrones was syn-selective, whereas the reaction with the same nitrones precomplexed with Lewis acids was anti-selective. Hence, from each nitrone a pair of diastereoisomeric hydroxylamines was obtained. These compounds were then converted by the above sequence into α-epimeric α-amino aldehydes. Model elaborations of some of these products afforded the amino sugars D-glucosamine, D-mannosamine, D-nojirimycin, and advanced intermediates for the synthesis of destomic acid and lincosamine.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010804
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    The Alkenyl Mechanism for Fischer-Tropsch Surface Methylene Polymerisation; the Reactions of Vinylic Probes with CO/H2 over Rhodium Catalyst (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 549-556 
    Details
    ISSN: 0947-6539
    Keywords: alkenyl ; Fischer-Tropsch synthesis ; labelling studies ; rhodium compounds ; vinyl ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results consistent with the participation of vinyls in the initiation and of alkenyl species in the propagation steps of the Fischer-Tropsch reaction are reported. Substantial incorporation of 13C2 into the alkene and alkane (C3-C7) hydrocarbon products occurred when doubly labelled vinyls (13C2H3Br. (13C2H3)4Si, or 13C2H4) were added as molecular probes to the hydrogenation of carbon monoxide over rhodium/ceria/silica catalysts (1 atm, 220°C). There was, by contrast, no significant incorporation of 13C1 into any of the organic products; thus cleavage of the C2 probe did not occur. The degree of 13C2 incorporation decreased with increasing molecular mass of the hydrocarbon; this indicates that the probe molecule initiated but did not propagate. A mathematical model based on polymerisation of surface methylenes initiated by a vinyl, propagated by alkenyls and terminated by reaction with a surface hydrogen or by coupling has been developed to explain the 13C2 incorporation data. Under the conditions of the experiments, the relative ability of the probes to initiate is: vinyl bromide (60%)〉tetravinylsilane (30%)〉ethene (15%). Substantial formation of 13C4 products also occurred when vinyl bromide or tetravinylsilane were used as probes; this arises from a dimerisation of the vinyl on the surface, a process which has been modelled in homogeneous systems and also by other workers in studies on single crystal surfaces. There was no significant 13C incorporation into the oxygenates (methanol, ethanol, acetaldehyde); these products are formed by a different path.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010809
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  • 59
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    Masthead (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010902
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  • 60
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    A Novel Low Molecular Weight Chiral Gelator for Apolar Organic Solvents (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 594-597 
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    ISSN: 0947-6539
    Keywords: electron microscopy ; gels ; helices ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, molecular structure, and properties of a new chiral gelforming agent 1 are described. Key structural features in 1 are a γ-alkoxybutyro-lactone tetralin moiety and an angular phenylsulphone unit. The new low molecular weight gelator 1 can reversibly form stable gels in low concentrations (e.g., 1:800 for n-hexane) with isopropanol and a variety of apolar organic solvents. The gels were studied with differential scanning calorimetry and a combination of electron microscopy techniques, which revealed a highly ordered three-dimensional network of entangled fibers. X-ray analysis showed that the aggregation of 1 leads to a helical structure in the solid state. Nonchiral analogues 2 and 3 were unable to initiate gel formation.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010905
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    Editorial (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 3-3 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010104
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  • 62
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    Hexaalkyl Terpyrrole: A New Building Block for the Preparation of Expanded Porphyrins (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 56-67 
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    ISSN: 0947-6539
    Keywords: amethyrin ; orangarin ; porphyrinoids ; terpyrroles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new, general synthesis of the first β-substituted tetra- and hexaalkyl terpyrroles is described. Also described are two new classes of expanded porphyrins derived from the hexaalkyl terpyrrole. The key step in the terpyrrole formation is the copper(II)-mediated oxidative coupling of the LDA-derived enolates of α-keto pyrroles. The first new expanded porphyrin reported here, the so-called “orangarin”, contains five pyrrolic subunits and two bridging carbon atoms, and is formally a 20π-electron nonaromatic macrocycle. The second new class of expanded porphyrins, the “amethyrins”, are 24π-electron nonaromatic macrocycles containing six pyrrole units. Both of these new macrocycles, as well as one of the new terpyrrolic precursors have been structurally characterized by single crystal X-ray diffraction analysis.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010110
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    Ninth European Symposium on Organic Chemistry. Warsaw, Poland. June 18-23, 1995 (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 100-100 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010115
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    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010201
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  • 65
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    In3Ti2Br9: Jahn-Teller Unstable Indium(I) and Antiferromagnetically Coupled Titanium(III) Atoms (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 118-123 
    Details
    ISSN: 0947-6539
    Keywords: antiferromagnetic exchange ; crystal structure ; indium compounds ; Jahn-Teller distortion ; titanium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dark green crystals of In3Ti2Br9 have been synthesized from elemental Ti and molten InBr3 at 450°C. The X-ray diffractional characterization by means of single-crystal and powder Rietveld refinement reveals a hexagonal crystal structure (a = 738.2(2), c = 1813.9(3) pm; P63/mmc, Z = 2) of Cs3Cr2Cl9 type, containing Ti2Br3-9 dimers and univalent indium cations. Self-consistent, semiempirical band structure calculations show the structural distortions of the two monovalent indium cations to arise from a second-order Jahn-Teller instability. The new compound's magnetic susceptibility and microscopic antiferromagnetic exchange are analyzed by using a Bleaney-Bowers ansatz.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010205
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    Synthesis, Structure, and Reactivity of Chiral Rhenium N-Pyrrolyl Complexes Regiochemistry of Electrophilic Addition and Unprecedented Rearrangements to Carbon-Ligated Species (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 294-303 
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    ISSN: 0947-6539
    Keywords: electrophilic additions ; N-pyrrolyl complexes ; rearrangements ; rhenium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of [{Re}(OTf)] (1; {Re}  -  (η5-C5H5)Re(NO)(PPh3) and potassium pyrrolide gives the N-pyrrolyl complex 2, 88%). Reactions of 2 with (CF3CO)2O/N(C2H5)3 and CH3O2CC=CCO2CH3 give 3- and 2-substituted pyrrolyl complexes respectively (3, R/R′ = H/COCF3, 77%; 5, R/R′ = C(CO2CH3)=CHCO2CH3/H, 69-87%). Free pyrrole is much less reactive towards these reagents. Reactions of 2 and TfOH or HBF4·OEt2 give the 2H-pyrrole adducts +X- (7+X-; 89-83%). At 0-25°C in CH2Cl2, these rearrange to the carbon-ligated tautomers +X-(8+X-) and then +X-; (9+X-; 72-96 h, 90-96%). Reaction of 1 and pyrrole in refluxing toluene gives 8+TfO- and then 9-TfO- (92%). However, 1 and pyrrole react too slowly in CH2Cl2 to be intermediates in the conversion of 7+TfO- to 9+TfO-. Reaction of 9+ TfO- and KH gives the C-pyrrolyl complex (68%), which adds TfOH to give 9+TfO-. Mechanistic aspects of the preceding reactions are discussed. The crystal structures of 2 and 9+TfO- are determined, and the NC4Hx ligand conformations analyzed with extended Hückel MO calculations.
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    URL: http://dx.doi.org/10.1002/chem.19950010506
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    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010601
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    Total Synthesis of RapamycinA list of abbreviations used in this article is given in ref. [49]. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 318-333 
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    ISSN: 0947-6539
    Keywords: rapamycin ; stannylethenes ; Stille coupling ; vinyl iodides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Details of the total synthesis of rapamycin (1) are reported. The synthesis required the preparation of intermediates 4 - 9 in nonracemic form; key coupling reactions included a chromium-mediated addition of vinyl iodide 8 to aldehyde 7 and an Evans aldol reaction to couple fragments 62 and 9. Intermediates 4 and 6 were joined through an amide bond formation to afford advanced intermediate 71. Swern oxidation of the diol in 71 was followed by a selective removal of the TES groups and a second Swern oxidation. Finally, removal of the remaining silyl protecting groups provided fully deprotected, penultimate intermediate 2 in which all carbons were in their proper oxidation state. Macrocyclization was achieved through a tandem inter/intramolecular palladium-mediated Stille coupling reaction between distannylethene 3 and bis(vinyl iodide) 2. This latter process accomplished in one step the installation of the remaining two carbons of the natural product and the completion of its total synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010509
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    New Coordinatively Unsaturated Lutetium Mono- and Bis(alkyl) Complexes with a Bis(ortho)-Chelating Aryldiamine Ligand - Crystal Structures of [LuCl2{2,6-(Me2NCH2)2C6H3}(μ-Cl)(μ-Li(thf)2)]2 and [Lu(μ-Cl){2,6-(Me2NCH2)2C6H3}(CH2SiMe3)]2 (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 343-350 
    Details
    ISSN: 0947-6539
    Keywords: ate complexes ; intramolecular coordination ; lutetium complexes ; organometallic compounds ; yttrium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New complexes of lutetium and yttrium containing the monoanionic, terdentate ligand [2,6-(Me2NCH2)2C6H3]- (NCN) have been synthesized by substitution reactions starting from MCl3 (M = Lu, Y). Reaction of MCl3 (M = Y, Lu) with one equivalent of (NCN)Li affords the ate complexes [(NCN)MCl2(μ-Cl)(μ-Li(thf)2)]2) (M = Lu (1a), Y (1b)) in which the terdentate ligand is bound in mer fashion and all three chloride atoms are retained in the product. Crystals of 1a are monoclinic (space group P21/n, a =10.4559(4), b = 21.6150(9), c=12.1700(7) Å, β = 105.294(4)°, Z = 2, final R = 0.039 for 3695 observed reflections [I〉2.50σ(I)]). Attempted substitution of chloride in the yttrium complex 1b by Me3SiCH2- leads to decomposition. However, reaction of 1a with Me3SiCH2Li gives the monoalkyl complex [(NCN)Lu-(μ-Cl)(CH2SiMe3)]2 2, 30% yield), in which the terdentate ligand is bound in a pseudo-facial manner. Crystals of 2 are triclinic (space group P1, a = 9.8575(7), b = 10.0171(7), c = 11.1460(14) Å, α = 75.096(8). β = 78.092(8), γ =77.474(6)°, Z = 1, final R1 = 0.11 for 1361 reflections [I 2σ(I)]). Substitution of the chloride ions in 2 by Me3SiCH2- is possible and affords quantitatively the bisalkyl complex [(NCN)Lu(CH2SiMe3)2] (3). The lutetium complexes 2 and 3 are formally coordinatively unsaturated complexes, which are moisture-sensitive and thermally stable for several weeks when dissolved in aromatic solvents. However, they decompose rapidly in aliphatic solvents such as hexane, and a decomposition route involving the formation of carbene species is proposed.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010604
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    Masthead (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010702
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  • 71
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    Biologically Induced Reduction in Symmetry: A Study of Crystal Texture of Calcitic Sponge Spicules (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 414-422 
    Details
    ISSN: 0947-6539
    Keywords: biomineralization ; calcite ; crystal morphology ; mosaic structure ; symmetry reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organisms can exert a remarkable degree of control over crystal growth. One way of achieving this is by the adsorption of specialized macromolecules on specific planes of the growing crystals. With continued growth of the crystal, the macromolecules are incorporated inside the crystal bulk. Their presence does not change the crystal structure, but creates discontinuities in the perfect lattice. Here we study in detail three unusual cases of reduction in symmetry at the level of crystal domain shapes, induced by this controlled intercalation. We examined sponge spicules, which are single crystals of Mg-bearing calcite. They were specifically chosen for this study, because their morphologies do not reflect the hexagonal symmetry of calcite. Their crystal textures (coherence lengths and angular spreads) were characterized by high-resolution X-ray diffraction with well-collimated synchrotron radiation. The results are compared to analogous studies of synthetic calcite and Mg-bearing calcite. In all the selected spicules reduction in symmetry is observed in the coherence lengths among symmetry-related crystallographic directions. The reconstructed shapes of the domains of perfect structure closely match the specific spicule morphologies. The synthetic crystals show no such reduction in symmetry. Although the manner by which such exquisite control is achieved is not known, we envisage it involving a combination of oriented nucleation with either physical or stereochemically driven adsorption.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010705
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  • 72
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    Asymmetric Synthesis of Carboranyl Amino Acids with Potential use in BNCT (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 430-435 
    Details
    ISSN: 0947-6539
    Keywords: amino acids ; asymmetric synthesis ; BNCT ; carboranes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two α-amino acids containing the 1,2-dicarba-closo-dodecaborane (12) cage, namely, 5-(1,2-dicarba-closo-dodecaboran (12)-1-yl)-2-aminopentanoic acid (1) and 5-(2-methyl-1,2-dicarba-closo-dodecaboran (12)-1-yl)-2-aminopentanoic acid (2), were prepared by asymmetric synthesis (e.p. 〉 98%) by using the chiral glycine equivalent, imidazolidinone 3, introduced by Seebach, and Oppolzer's camphor-derived sultam derivative 4. The dextrorotatory enantiomers (sodium D line in methanol) of the amino acids 1 and 2 were both shown to have (S) configuration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010707
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  • 73
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    Ab initio Study of the Coordination Modes of the Tetrahydroborato Ligand: Structure of the [Cu(BH4)(PH3)n] (n = 1, 2, 3) Complexes (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 436-440 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; copper compounds ; organometallic compounds ; tetrahydroborato ligand ; theoretical chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All-electron ab initio calculations (MP4/MP2 level) have been performed on [Cu(BH4)(PH3)n] (n = 1, 2, 3) complexes. Full-geometry optimizations were carried out in each case, and the stationary points were characterized by the diagonalization of the analytically calculated Hessian matrix. The η2 coordination mode, with a tetrahedral arrangement around the copper atom, is the most stable structure for n = 2, while for n = 3 a strongly nonlinear η1 coordination mode is preferred. These results are in agreement with the experimental data available on related complexes. For n = 1, for which there is no experimental data, the η3 structure turns out to be the most stable. The energy differences associated with some changes in the coordination mode (η1 → η2 for n = 3 and η3 → η2 for n = 1) are small. Finally, a mechanism for the exchange between terminal and bridging hydrogen atoms is proposed for each complex under study.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010708
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  • 74
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    Total Synthesis of Balanol and Designed Analogues (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 454-466 
    Details
    ISSN: 0947-6539
    Keywords: antitumour agents ; balanol ; enzyme inhibitor ; natural product ; total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total synthesis of balanol, a potent protein kinase C inhibitor isolated from the fungus Verticillium balanoides, is described. The hexahydroazepine fragment was prepared from D-serine through a sequence of reactions including the diastereoselective allylboration of a derived amino aldehyde and a base-induced 7-exo-tet ring closure as key steps. The benzophenone fragment was secured through the initial coupling of the two functionalised aromatic components through an ester linkage, followed by intramolecular nucleophilic attack of an aryl lithium derivative to form the desired ketone bridge. After coupling of the two balanol domains, the adoption of benzylderived protecting groups for the latent functionalities then allowed the liberation of balanol in a single step by catalytic hydrogenolysis. Finally, the newly developed synthetic strategy was applied to the synthesis of a variety of designed balanol analogues for biological evaluation.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010711
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  • 75
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010803
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  • 76
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    New PF3 and Carbonyl Chemistry of TantalumHighly Reduced Organometallics, Part 37. Part 36: M. Jang, J. E. Ellis, Angew. Chem. 1994, 106, 2036; Angew. Chem. Int. Ed. Engl. 1994, 33, 1973.Dedicated to Professor Fausto Calderazzo on the occasion of his 65th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 521-527 
    Details
    ISSN: 0947-6539
    Keywords: carbonyl ligands ; organometallic compounds ; phosphorus ligands ; tantalum compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of [TaCl5] by six equivalents of alkali metal naphthalenide in 1,2-dimethoxyethane at -60°C followed by treatment with gaseous PF3 provides the first homoleptic phosphane complex containing tantalum in the -1 oxidation state, [Ta(PF3)6]-. This can be protonated by concentrated sulfuric acid to yield the previously unknown highly acidic and volatile hydride [HTa(PF3)6]. An improved normal-pressure synthesis of [Ta(CO)6]- is described. Reduction of the latter species by sodium in liquid ammonia gives the carbonyl trianion [Ta(CO)5]3- which undergoes monoprotonation and stannylation to form [HTa(CO)5]2- and [Ph3SnTa(CO)5]2-, respectively. The hydride is a useful precursor to [(Ph3PAu)3Ta(CO)5], the only known gold cluster of tantalum.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010805
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  • 77
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    The Reduction of [Fe(CO)2L2X2] (L = P(OMe)3, P(OiPr)3, PEt3; X = Br, I) - From Iron(II) to Iron(0) via Stable Iron(I) Intermediates (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 541-548 
    Details
    ISSN: 0947-6539
    Keywords: dinitrogen complexes ; EPR spectroscopy ; iron compounds ; reductions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of [Fe(CO)2-L2X2] (L = P(OMe)3 X = Br (1a), I (1b); L = P(OiPr)3, X = Br (2a), I (2b); L = PEt3, X = Br (3a), I (3b)) with Zn in dioxane (1a,b-2a,b) or PhLi in ether (3a,b) led to formation of the corresponding dicarbonyl(halo)bis(phosphorus donor)iron(I) complexes (L = P(OMe)3, X = Br (4a), I (4b); L = P(OiPr)3, X = Br (5a), I (5b); L = PEt3, X = Br (6a), I (6b)). Slightly contaminated 5a,b and pure 6a,b were isolated as stable crystalline blue or blue-green complexes. Complexes 4a,b were obtained, with only minor impurities, by comproportionation of 1a,b and the dicarbonyl(halo)bis-(trimethylphosphite)ferrate anions 7a,b and characterized in THF solution. The comproportionation products 5a,b-6a,b were obtained in high yields by reaction of 2a,b-3a,b with the dinitrogen complexes 13-15. Further reduction of 4a,b-6a,b or exhaustive reduction of 1a,b-3a,b with sodium amalgam or iBuLi in THF afforded the nonisolable dicarbonyl-(halo)bis(phosphorus donor)ferrate(o) anions (7a,b-9a,b). The latter were characterized by acidification with trifluoroacetic acid or acetic acid yielding stable dicarbonyl (halo) hydridobis (phosphorus donor)iron(II) complexes (L = P(OMe)3, X = Br (10a), I (10b); L = P(OiPr)3, X = Br (11a), I (11b);L = PEt3, X = Br (12a), I (12b)). In the presence of N2, 8a was transformed into dinitrogen complex [Fe(CO)2{P(OiPr)3}2N2] (13). With 9a,b the reaction led to formation of [Fe-(CO)2(PEt3)2)2N2] (14) and [{Fe(CO)2-(PEt3)2}2(μ-N2)] (15). In solution at low temperature (-90 to 0°C), the dinitrogen complexes 14 and 15 are in equilibrium with each other. Complexes 13, 14, and 15 were characterized by IR, 1H, 13C, 31P, and 15N NMR spectroscopy. The structures of 5a, 6b, 14, and 15 were determined by X-ray diffraction studies.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010808
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  • 78
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010903
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  • 79
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    The Design of Selective Chelating Agents: 1,3,5-Trideoxy-1,3,5-tris-(dimethylamino)-cis-inositol, a Powerful Ligand for Hard and Highly Charged Metal Ions1,3,5-Triamino-1,3,5-trideoxy-cis-inositol, a Ligand with a Remarkable Versatility for Metal Ions, Part 7. Part 6: K. Hegetschweiler. M. Ghisletta, T. F. Fässler, R. Nesper, Angew. Chem. Int. Ed. Engl. 1993, 32, 1426. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 74-88 
    Details
    ISSN: 0947-6539
    Keywords: chelate ligands ; hydrogen bonds ; ligand design ; mass spectrometry ; stability constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of compounds containing the mononuclear complexes [M(tdci)2]3+ (tdci = 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol, M = Al, Fe, Ga, In) and [M(tdci)2]4+ (M = Ti, Ge, Sn) was prepared and characterized by elemental analysis, NMR spectroscopy, and FAB mass spectrometry. Characteristic fragmentation reactions in the mass spectra were elucidated. X-ray analysis of the AlIII, FeIII, GaIII, and InIII complexes revealed that two neutral, zwitterionic tdci ligands coordinate to the metal cation exclusively through deprotonated alkoxo groups. The six coordinated oxygen donors and the six N—H protons form a hydrophilic pocket, whereas the two cyclohexane rings and the twelve methyl groups form two hydrophobic shells. The hydrophilic pocket is filled with twelve water molecules, which are arranged as a second and a third coordination sphere around the metal cation. The reactivity in aqueous solution was investigated by potentiometric measurements. The bis complexes proved to be stable at pH 7. The evaluated formation constants show an increase of stability in the order AlIII〈InIII〈GaIII〈FeIII. The measurements established that tdci is one of the most effective tridentate ligands for small (r ≤ 0.8Å) and highly charged cations. The different chelating properties of tdci and of the unmethylated 1,3,5-triamino- 1,3,5-trideoxy-cis-inositol are discussed in terms of different steric requirements and different types of solvation of the corresponding complexes in aqueous solution.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010112
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  • 80
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    The Stereochemistry of Carbenoid Cyclopropanation ReactionsChiral Organometallic Reagents, Part XV. For Part XIV, see ref. [1]. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 619-624 
    Details
    ISSN: 0947-6539
    Keywords: alkenes ; carbenoids ; carbolithiations ; cyclopropanations ; mechanistic studies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical course of the intramolecular carbenoid cyclopropanation reaction has been studied for the epimeric carbenoids 12a and 12b. In these reactions the tert-butyldimethylsilyloxy substituent serves as an internal stereochemical reference point. It was found that 12b cyclizes rapidly at -110°C in a complexation-assisted concerted process to give the bicyclo[3.1.0]hexane 16. The diastereomer 12a cyclizes more slowly at -100°C to give both 16 and 17; the former is probably formed by a complexation-assisted carbolithiation pathway.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010909
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  • 81
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    The Role of Porphyrin-to-Porphyrin Linkage Topology in the Extensive Modulation of the Absorptive and Emissive Properties of a Series of Ethynyl- and Butadiynyl-Bridged Bis- and Tris(porphinato)zinc Chromophores (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 645-651 
    Details
    ISSN: 0947-6539
    Keywords: conjugation ; connectivity ; electronic coupling ; metalloporphyrins ; photosynthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method for the regulation of the photophysical properties of highly conjugated porphyrin arrays is described. The absorptive and emissive signatures of such supramolecular structures can be modulated to an impressive degree by regulation of: i) the extent of the steric interactions that define the barrier to rotation about the conjugated bridge between the porphyrin chromophores, and ii) the magnitude of ground state chromophore-chromophore electronic communication within the supermolecule. The power of this approach is illustrated by the straightforward synthesis as well as the electronic and emission spectra of eight different porphyrin arrays in which (5,10,15,20-tetraphenylporphinato)zinc(11) and (10,20-diphenylporphinato)zinc(11) complexes are joined by ethyne or butadiyne groups. The points of connectivity of these bridges between the chromophoric building blocks are systematically varied to produce a series of supramolecular structures with meso-to-meso, meso-to-β, or β-to-β linkage topologies. These variations allow excellent control of the ground- and excited-state characteristics of the arrays in the series by regulating the degree of both excitonic and electronic porphyrin-to-porphyrin coupling. Our approach shows the precision with which photophysical properties can be engineered in appropriately designed supramolecular systems.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010913
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  • 82
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    Synthesis, Reactions, and Molecular Structures of Ethylzinc Enolates of Chiral N-Substituted β-Carbonyl Sulfoximines (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 312-317 
    Details
    ISSN: 0947-6539
    Keywords: aggregates ; asymmetric syntheses ; stereochemistry ; sulfoximines ; zinc enolates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation, structural characterization, and reactivity of ethylzinc-containing enolates and organometallics derived from β-carbonyl sulfoximines are reported. X-ray crystal structures show significant differences between aggregated species obtained from β-keto and β-amido sulfoximines. Whereas the former gives an O-metalated ethylzinc enolate, the latter crystallizes as C-metalated carbonyl species. NMR investigations reveal the presence of chelated zinc enolates in solution. The relationship between structure and reactivity is demonstrated by the reaction profiles of the ethylzinc-containing compounds. A high diastereoselectivity (〉 90% de) was observed in the aldol reaction between the metalated β-amido sulfoximine and benzaldehyde in the presence of trimethylsilyl chloride.
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    URL: http://dx.doi.org/10.1002/chem.19950010508
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  • 83
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    Phase Relationships in the N2O3/N2O4 System and Crystal Structures of N2O3 (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 389-393 
    Details
    ISSN: 0947-6539
    Keywords: crystal structure ; differential thermal analysis ; nitrogen oxides ; phase transitions ; twinning ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixtures of N2O3 and N2O4 have been prepared from measured volumes of NO and O2. Phase relationships in the system N2O3/N2O4, which depend on the composition of the samples and on the temperature, were studied by the Guinier technique and differential thermal analysis. Single crystals of phases A and B of N2O3 were grown in situ on a diffractometer and studied at temperatures between -107 and -170°C by X-ray diffraction. The structure analysis of A-N2O3 (tetragonal, space group I41/a, T = -170°C, a = 1625.57 (16), c = 880.49(13) pm, Z = 32, R1 = 0.051 for 1030 unique reflections) is hampered by twinning and additional disorder of one of two crystallographically independent molecules. B-N2O3 is nicely ordered with one molecule in the asymmetric unit (orthorhombic, space group P212121, T = -160°C, a = 506.86(4), b = 647.96(5), c = 863.26(6) pm, Z = 4, R1 = 0.023 for 1352 unique reflections). The most interesting features of the N2O3 molecule are its planarity and the extraordinarily long N—N bond (189.0(1) pm).
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010610
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  • 84
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010703
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  • 85
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    Mono- and Bis(pentaisopropylcyclopentadienyl) Cobalt and Rhodium Sandwich Complexes and Other Decabranched Cyclopentadienyl ComplexesDedicated to Professor Henri Brunner on the occasion of his 60th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 374-381 
    Details
    ISSN: 0947-6539
    Keywords: cobalt compounds ; cyclopentadienyl ligands ; metallocenes ; peralkylations ; rhodium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acidity of methyl protons in the 18-electron cationic complexes [MCp*Cp]1PF6- and [MCp2*]+PF6- (M = Co or Rh, Cp = η5-C5H5, Cp* = η5- C5Me5) has been used for novel syntheses of starburst organometallic complexes. [CoCp*Cp]+PF6- was deprotonated at -30 °C with Si2Me6NK (1 equiv) in THF to give the fulvene complex [CoICp(η4-C5Me4CH2)]. This was not stable at 20°C, but was characterized by 1H and 13C NMR at -30 °C. The complexes [MCp*Cp]+PF6- (M = Co or Rh) reacted with excess base (KOH or tBuOK) and alkyl halides (RX = CH3I, C2H5I, CH2=CHCH2Br, or PhCH2Br) to give decasubstituted complexes (i.e., two hydrogens of each methyl group are replaced by two R groups). Distinct endo and exo alkyl groups are observed in the new complexes by NMR at room temperature. Coalescence occurs at higher temperatures; this indicates that the bulky alkyl groups are rotating. The calculated activation parameters (ΔG≠) are 71.3±0.8, 70.3±0.8, and 81.0±0.8 kJmol-1 for [Co(C5iPr5)Cp]+PF6-, [Rh(C5iPr5)-Cp]+PF6- (in C6D5NO2), and [Co{C5-(CHEt2)5}Cp]+PF6 (in o-C6H4Cl2), respectively. The single directionality of these ligands is confirmed by the X-ray crystal structure of [Co(C5iPr5)Cp]+PF6. This structure clearly shows the “paddle wheel” conformation adopted in the C5iPr5 ligand, due to steric hindrance between adjacent isopropyl groups and the staggered conformation of the two rings. The relative E° values measured by cyclic voltammetry show that the electron-donating properties of the new C5(CHR2)5 ligand are between those of C5H5 and C5Me5- With the decamethylcobalticinium salt [CoCp2*]+PF6-, the permethylation reactions with base and CH3 I did not go to completion, even under forcing conditions and with repeated reaction (the maximum number of methyl groups introduced was 14). On the other hand, [RhCp2*]+PF6-, in which the distance between rings is larger than in the Co analogue, reacted with excess KOH and CH3I to give [Rh(C5iPr5)2]+PF6 in 55% yield; only one diastereoisomer was detected by NMR (ΔG≠ = 85.5±0.8 kJ mol-1 in C6D5NO2). The C5iPr5 sandwich complexes are extremely robust, even at the 19-electron (CoII) stage. The 20-electron K+ salt of the CoI anion was regiospecifically protonated by H2O at the Cp ligand to give [Co(C5iPr5)(η4-C5H6)] and was decomplexed at 190°C to K+(C5iPr5)-.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010608
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  • 86
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    The Systematic Definition of Organic Reactions (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 449-453 
    Details
    ISSN: 0947-6539
    Keywords: computer chemistry ; databases indexing ; reaction organization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A logical system is presented to describe organic reactions. It is based on the net structural change in a reaction, rather than on substructure searching. This system rigorously provides a place for any reaction. It is very simple to use by hand, but, since it is also numerical, it provides a basis for organizing and retrieving reactions in a database by computer. The effectiveness of a program, COGNOS, written to implement and test the system on a large database, lends confidence in this logic for organizing reactions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010710
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  • 87
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    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010801
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  • 88
    Electronic Resource
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    Synthesis of Zaragozic Acid A/Squalestatin S1 (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 467-494 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric ; syntheses ; enzyme inhibitors ; squalestatins ; total syntheses ; zaragozic acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel synthetic approach to the construction of the zaragozic acids, which was used for the asymmetric synthesis of zaragozic acid A/squalestatin S1 (1), is described. Fragment 5, representing the tricarboxylic acid core portion, is assembled in three key steps: 1) Stille coupling to establish the carbon framework; 2) enantioselective dihydroxylation to introduce the absolute stereochemistry; and 3) diastereoselective dihydroxylation to complete the required carbon-oxygen connectivity. The convergency of this synthesis is demonstrated by the dithiane addition of a variety of C 1 side chains (e.g., 78) to advanced intermediate 5. A multi-event acid-catalyzed rearrangement yielded the zaragozic acid core 86, which was converted to an intermediate obtained from degradation of zaragozic acid A. A second-generation synthesis of the core of the zaragozic acids is also described. When aldehyde 90 was used instead of 5, both the yield and diastereoselectivity of the dithiane addition reaction were improved, although the degree of convergency was slightly lower.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010712
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  • 89
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    Synthesis of (R)-tert-Leucinol by Classical Resolution of the Racemic MixtureAmino Acid Transformations, Part 12. Part 11: ref. [1].Dedicated to Dr. Wilhelm Schuler on the occasion of his 80th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 538-540 
    Details
    ISSN: 0947-6539
    Keywords: amino alcohols ; asymmetric syntheses ; chiral auxiliaries ; enantiomeric resolution ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optically active tert-leucinol is an important building block in asymmetric synthesis. However, the (R) enantiomer particularly has so far remained difficult to obtain, mainly because of the laborious synthesis of the precursor amino acid, (R)-tert-leucine. Here we present a new, classical resolution of racemic tert-leucinol, which allows straightforward preparation of each, but especially the (R) enantiomer, in good yields and high optical purities. The feasibility of the synthesis of useful derivatives is demonstrated by transformation into the corresponding (R)-4-tert-butyl-2-oxazolidinone.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010807
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  • 90
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    Transfer Hydrogenation of Nitro-, Nitroso- and Azoarenes by Homolytic RetrodisproportionationDedicated to Prof. Dr. Manfred Schulz on the occasion of his 65th birthdayBimolecular Formation of Radicals by H Transfer, Part 8; Part 7; see ref. [1]. The present paper is taken from the diploma thesis of M. Coellen, University of Freiburg 1994. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 564-567 
    Details
    ISSN: 0947-6539
    Keywords: aniline ; aromatization ; hydrogen transfer ; mechanistic studies ; radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nitro-, nitroso- and azobenzene are reduced almost quantitatively to aniline when heated to 230-300°C with 9,10-dihydroanthracene (DHA), xanthene or tetralin. From the effect of polar substituents and polar solvents on the reactivity and from the isotope effect kH/kD ≍ 2.4 (280°C), a hydrogen-atom transfer from the H donor to the acceptor (retrodisproportionation) is proposed as the rate-determining step. The lower reactivity of xanthene compared with 9,10-dihydroanthracene eliminates the possibility of a rate-determining hydride transfer. The observation of an intense ESR signal of 9-xanthyl radicals during the reaction in diphenyl ether and the typical products support the proposed homolytic mechanism.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010811
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  • 91
    Electronic Resource
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    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010901
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  • 92
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    An Enantioselective Synthesis of cis-4-tert-Butoxycarbamoyl-1-methoxycarbonyl-2-cyclopentene - A Useful, General Building Block (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 568-572 
    Details
    ISSN: 0947-6539
    Keywords: allylic substrates ; amidinomycin ; asymmetric syntheses ; carbanucleosides ; palladium catalysts ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The amino acid derivative in the title represents an important building block for the synthesis of a number of biologically important targets such as the antiviral carbanucleosides and amidinomycin. By using asymmetric palladium-catalyzed desymmetrization of meso-2-ene-1,4-diols, cis-1,4-dibenzoyloxy-2-cyclopentene can be converted to the enantiomerically pure title compound in only four steps. Chemoselective ester reduction allows entry into the domain of carbanucleosides, whereas double-bond reduction provides the precursor for amidinomycin. In an ancillary study, a facile diastereoselective cis-hydroxylation provides aminocyclopentitols, compounds that have proven to be potent glycosidase inhibitors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010812
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  • 93
    Electronic Resource
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    Bimolecular Gas-Phase Reactions of d-Block Transition-Metal Cations With Dimethyl Peroxide: Trends Across the Periodic Table (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 608-613 
    Details
    ISSN: 0947-6539
    Keywords: gas-phase chemistry ; mass spectrometry ; periodic trends ; peroxides ; transition-metal ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bimolecular gas-phase reactions of d-block transition-metal cations M+ with dimethyl peroxide were screened by means of Fourier transform ion cyclotron resonance mass spectrometry. The rich chemistry can be classified into four types of reactions: i) Oxygen-atom transfer to generate MO+, ii) elimination of radicals, mostly CH3O·, iii) intramolecular redox reaction of dimethyl peroxide to form CH3OH, CH2O and CO, and iv) charge transfer from the metal cation to produce CH3OOCH3+. Some general trends became apparent from this study. For example, the “early” transition metals almost exclusively induce oxygen transfer to generate MO+, in line with the notoriously high oxophilicities of these metals, and electron transfer is only observed for Zn+ and Hg+. Both the radical loss and the disproportionation reaction emerge from a rovibrationally highly excited insertion intermediate (CH3O)2M+, and for the first-row metals the branching ratio of the competing processes seems to be affected by the M+—OR bond strengths as well as the electronic groundstate configurations of M+. For the 4d and 5d cations Ru+—Ag+ and Pt+—Au+, respectively, products resulting from intramolecular redox reactions dominate; this probably reflects the higher propensity of these metal ions to facilitate β-hydrogen atom shifts.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010907
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  • 94
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    Magnetic and Structural Studies of Copper-Lanthanoid Complexes; the Synthesis and Structures of New Cu3Ln Complexes of 6-chloro-2-Pyridone (Ln = Gd, Dy and Er) and Magnetic Studies on Cu2Gd2, Cu4Gd2 and Cu3Gd Complexes (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 614-618 
    Details
    ISSN: 0947-6539
    Keywords: copper compounds ; exchange coupling ; heterometallic compounds ; lanthanide compounds ; magnetic properties ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and structural characterisation of three copper-lanthanoid complexes are reported. The compounds, of general formula [Cu3M(chp)8(NO3)(S)] [M = Gd, S = H2O in 2; M = Dy, S = H2O in 3; M = Er, S = (H2O)0.5(MeOH)0.5 in 4; chp = anion of 6-chloro-2-pyridone], are made by reaction of [Cu2(chp)4] (1) with the hydrated lanthanoid nitrate salt in methanol. Structural studies reveal the three copper atoms lie in an approximate hemisphere about a central lanthanoid atom. Magnetic studies on 2 and two further Cu-Gd complexes show ferromagnetic coupling between the 3d and 4f metals. Consideration of these results along with magnetic data previously reported for Cu-Gd compounds leads to a correlation between the magnitude of this exchange coupling and the exponential of the Cu…Gd distance. This is the first magneto-structural correlation reported for mixed d-block/f-block metal complexes.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010908
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  • 95
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    Ligand-Field Control and Hydrogen Bonding as Design Elements in the Assembly and Crystallization of Poly(azolyl)borate-Metal Complexes: Chelate Complexes Versus Coordination Polymers and Symmetrical Versus Distorted Grid SheetsDedicated to Prof. Dr. Herbert Schumann on the occasion of his 60th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 637-644 
    Details
    ISSN: 0947-6539
    Keywords: chelate ligands ; coordination ; hydrogen bonds ; ligand fields ; polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1- and 2-D coordination polymers [Mn{HB(C2H2N3)3}2(H2O)2].4H2O (11) and [Ni{H2B(CHN4)2}2-(NH3)2] (13), respectively, and the chelate complex [Ni{H2B(C2H2N3)2}2(H2O)2] · 2H2O (12) were synthesized and structurally characterized. The compounds contain ambidentate poly(azolyl)borato ligands (azolyl = triazolyl or tetrazolyl), which can chelate or bridge metal centers. The metal-ligand structures in 11-13 differ from the known coordination modes of the poly(azolyl)borates towards other metal centers. We describe how a change in the metal and/or the conditions of crystallization affects the ligand-field stabilization energy and favors one type of nitrogen donor atom over the other for the poly(triazolyl)borato ligands. The crystal structures of 11 and 12 contain additional water of crystallization; this leads to hydrogen-bonded solvent substructures. In the case of the bis(triazolyl)borato ligands. The crystal structures of 11 and 12 contain additional water of crystallization; this leads to hydrogen-bonded solvent substructures. In the case of the bis(tetrazolyl)borato ligand the water substructure is shown to function as a “reinforcing bar” that symmetrizes the metal-ligand grid sheet.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010912
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  • 96
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    Ligand Design for Securing Ferromagnetic Exchange Coupling in Multimetallic Complexes (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 528-537 
    Details
    ISSN: 0947-6539
    Keywords: exchange coupling ; ferromagnetic properties ; ligand design ; magnetic properties ; multimetallic complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An approach is suggested for using ligands to control exchange coupling in multinuclear ions. The idea arose from structural, EPR, and magnetic studies of [PPh4]3 (Scheme 1). Ferromagnetic coupling has been found between the CoII and each CoIII in 3 with J = -22 ± 5 cm-1 (JS1 · S2). It is suggested that dominant antiferromagnetic superexchange is absent because of the strong σ-donor capacity of the tetradentate ligand [k4-PAC*]4- (Fig. 1). The ligand interacts at CoIII primarily with a single d orbital; it is thus best able to participate in superexchange. The interaction makes the unique d orbital strongly σ-antibonding and empty for each d6, S = 1, CoIII ion in 3, that is, unavailable for antiferromagnetic coupling, but available for ferromagnetic pathways by a Goodenough-Kanamori mechanism. By corollary, when any [k4-PAC*]4--type ligand with any magnetic ion Ma in the tetradentate site binds any magnetic ion Mb in the bidentate site, ferromagnetic coupling should be favored provided Ma is not a d9 ion.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010806
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  • 97
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    Weak Interactions in Crystals: 4,4′-Di(tert-butyl)-N-N′-bipyridinium Diperchlorate - A Biphenyl Analogue with Perpendicular Pyridine Rings (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 557-563 
    Details
    ISSN: 0947-6539
    Keywords: biphenyls ; bipyridinium salts ; conformation ; semiempirical calculations ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of substituted N-aminopyridinium compounds yields bipyridinium salts. After anion exchange Br- → CIO4-, it was possible to grow single crystals from the 4,4′-di(tert-butyl) derivative. The structure determined at 100 K shows a dihedral angle of 84° between the molecular halves connected by a shortened N—N bond of 143 pm in length. This result is contrary to that expected from the isoelectronic correspondence 〉C—C〈↔〉N—N〈, which would suggest planarity, as has been observed experimentally both in solid biphenyl, and in tetraalkylhydrazine dications and radical cations. Lattice packing analysis, however, reveals the presence of hydrogen bonds C(H)…O between the phenyl rings and the perchlorate anions. AM 1 enthalpy hypersurface calculations for the isoelectronic series H5C5X-YC5H5 (X-Y = C—C, +N—C, +N—N+, -B—N+, B—C, and B—B-) predict single-minimum potentials for both the dication 〉N—N〈 as well as the dianion 〉B—B〈 with the molecular halves twisted perpendicular to each other. In detailed model calculations, counteracting effects of π electron density delocalization vs. H/H repulsion of the ortho ring hydrogens adjacent to the central bond seem to dictate the delicate balance of the biphenyl twisting. For further experimental confirmation, the structure of the isosteric molecule 4,4′-di(tert-butyl)biphenyl has been determined: in contrast to the unsubstituted π hydrocarbon with a latticeenforced dihedral angle of 0°, close to the calculated value, the two molecular halves are twisted by 40° - as in biphenyl in the gas phase.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010810
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  • 98
    Electronic Resource
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    Intrazeolitic Reaction between Transition Metal Ions and Open or Closed Polyamine Ligands (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 144-149 
    Details
    ISSN: 0947-6539
    Keywords: chelate ligands ; dioxygen activation ; EPR spectroscopy ; redox systems ; SQUID ; zeolites ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intrazeolitic transition metals, such as Ni2+ and Co2+, were chelated by open or closed, tetra- or pentadentate polyamine ligands. Their coordination and redox chemistry was studied by IR-Raman, EPR, diffuse reflectance, and magnetic techniques. For pseudo-octahedral complexes with tetradentate ligands, the presence of the zeolite favors cis coordination over the trans form. This is explained by the very low tendency of the zeolite surface to bind as a monodentate ligand to a planar metal complex. However, if trans complexes are formed (as with Ni2+), the axial positions on the complex are available for ligand exchange. Such intracrystalline complex syntheses result in the formation of new redox solids. For example, [CoII-(cyclam)]2+-NaY (cyclam = 1,4,8,11-tetraazacyclotetradecane) is a reversible, high-affinity (p1/2〈1 mbar) and high-capacity (〉90 μmol g-1) dioxygen-sorbing material.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010208
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  • 99
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010303
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  • 100
    Electronic Resource
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    Supramolecular Structure, Physical Properties, and Langmuir-Blodgett Film Formation of an Optically Active Liquid-Crystalline Phthalocyanine (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 171-182 
    Details
    ISSN: 0947-6539
    Keywords: chiral mesophases ; Langmuir-Blodgett films ; liquid crystals ; phthalocyanines ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and physical properties of optically active, metal-free 2,3,9,10,16,17,23,24-octa (S-3,7-dimethyloctoxy)phthalocyanine ((S)-Pc(8,2)) are reported and compared with those of the phthalocyanine with (R,S) side chains (mixture of 43 stereoisomers). Unlike the latter compound, (S)-Pc(8,2) lacks a crystalline phase. A freshly prepared sample is in a distorted mesophase and reorganizes irreversibly to a more ordered phase above 65 °C. X-ray diffraction and circular dichroism studies indicate that the molecules are stacked in columns which have a hexagonal arrangement and a left-handed helical superstructure, that is, a novel chiral Dh* mesophase. Solid state NMR measurements reveal that the phthalocyanine units in the columns begin to vibrate laterally when the temperature is increased. At 111 °C (Dh* → Dr transition) they start to rotate around their columnar axes and at the same time the side chains become liquidlike. Energy migration is very efficient in the chiral Dh* phase and also in the frozen mesophase below 3 °C, as follows from luminescence spectroscopy. Intracolumnar charge transport, studied by the time-resolved microwave conductivity technique, turns out to be slower in the helically distorted columns than in linear columns. (S)-Pc(8,2) forms a very stable bilayer at the air-water interface, which can be transferred to give a high quality Langmuir-Blodgett film. The fact that this phthalocyanine is mesogenic at room temperature is thought to be responsible for this behavior.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010306
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