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  • 1995-1999  (2,580)
  • 1970-1974
  • 1935-1939
  • 1997  (2,580)
  • General Chemistry  (2,015)
  • Industrial Chemistry  (437)
  • Rat
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  • 1995-1999  (2,580)
  • 1970-1974
  • 1935-1939
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  • 101
    Electronic Resource
    Electronic Resource
    Intracerebral penetration of carteolol hydrochloride in rats (1997)
    Springer
    Psychopharmacology 131 (1997), S. 388-393 
    Details
    ISSN: 1432-2072
    Keywords: Key words Carteolol hydrochloride ; β-Blocker ; Penetrability ; Brain ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To elucidate the penetrability of carteolol, a β-adrenoceptor antagonist (β-blocker) into the brain of rats, intracerebral and serum concentrations of the compound were determined in male rats receiving single or repetitive oral administration of carteolol hydrochloride at 30 mg/kg. The time-course of the intracerebral concentration of carteolol following single IV administration of the compound at 10 and 30 mg/kg was also studied in male rats. A high-performance liquid chromatography method was used to determine the intracerebral and serum concentrations. Following single oral dosing, the intracerebral concentration of carteolol reached a maximum of 0.074 μg/g at 2 h postdosing and declined with a half-life of 3.7 h, and the Cmax and AUC of carteolol in the brain were 12.5% and 19.8% of those in serum. The intracerebral and serum concentrations of carteolol were determined in male rats receiving repetitive oral dosing of the compound once daily for 7 days. The concentration of carteolol in the brain and serum at 1 h postdosing varied within a range of 0.059–0.091 μg/g and 0.321–0.443 μg/ml, respectively, throughout the dosing period, showing no changes in the penetrability of the compound into the brain due to repeated dosing. The concentration of carteolol in the brain and serum increased in a dose-dependent manner in rats receiving a single IV administration of the compound. The elimination half-life of carteolol in the serum and brain was 0.6–0.8 h and 1.3–1.7 h, respectively, in rats following single IV dosing of the compound. The half-life in the brain was about twice as long as that in the serum. The brain to serum concentration ratio was 0.306:0.499. From the above results, it was concluded that carteolol is distributed from the circulation to the brain with low penetrability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050307
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  • 102
    Electronic Resource
    Electronic Resource
    Effects of imipramine on raphe nuclei and prefrontal cortex extracellular serotonin levels in the rat (1997)
    Springer
    Psychopharmacology 134 (1997), S. 401-405 
    Details
    ISSN: 1432-2072
    Keywords: Key words Imipramine ; Serotonin ; Raphe nuclei ; Prefrontal cortex ; Microdialysis ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The effect of acute administrations of three doses of imipramine (1, 5 and 10 mg/kg SC), a widely used tricyclic antidepressant, on extracellular levels of serotonin (5-HT) has been studied by intracerebral microdialysis in raphe nuclei and prefrontal cortex of conscious rats. Imipramine 1 mg/kg SC did not change extracellular 5-HT in either raphe nuclei and prefrontal cortex. However, with the dose of 5 mg/kg SC imipramine induced in raphe nuclei, a brief increase of extracellular 5-HT followed by a lowering (55–65% basal release) of the neurotransmitter. The same dose of imipramine decreased (60–70% of basal value) extracellular 5-HT in prefrontal cortex. Imipramine 10 mg/kg SC significantly increased 5-HT levels in both raphe nuclei (190 ± 20% above basal value) and prefrontal cortex (280 ± 15% above basal value). Pretreatment with (-)pindolol (5 mg/kg SC), a non-selective 5-HT1A subtype receptor antagonist, 30 min before imipramine 5 mg/kg, modified the effect of the antidepressant: an increase, instead of a decrease, on prefrontal cortex dialysate 5-HT was observed. (-)Pindolol (10 mg/kg SC) increased extracellular 5-HT in both raphe nuclei (155 ± 20% above basal value) and prefrontal cortex (160 ± 8% above basal value). These data show that acute administration of imipramine modifies extracellular 5-HT at the level of the raphe nuclei and prefrontal cortex. 5-HT1A autoreceptors in the raphe nuclei, which this study suggests to be tonically active, may be stimulated after systemic administration of high doses of imipramine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050477
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  • 103
    Electronic Resource
    Electronic Resource
    Changes in baroreceptor vagal reflex performance in the developing rat (1997)
    Springer
    Pflügers Archiv 434 (1997), S. 438-444 
    Details
    ISSN: 1432-2013
    Keywords: Key words Baroreceptor reflex ; Nucleus tractus solitarii ; Neonatal ; Maturation ; Cardiac vagal tone ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Ontogenesis of both vagal control of heart rate and the baroreceptor vagal reflex were evaluated in rats at postnatal ages (P) of 5/6, 10, 15, 20, 25 and 〉42 days anaesthetised with urethane (1.5 g/kg). Between P5/6 and P25 heart rate rose from 372 ± 12 to 448 ± 20 beats per minute and mean arterial pressure increased from 33.9 ± 3.1 to 74.59 ± 3.25 mm Hg (mean ± SEM, n = 7 and 11 respectively). Cardiac vagal tone was absent at P10 but significant at P20 (P 〈 0.05) as revealed with atropine (0.5–1 mg/kg i.v.). Baroreceptor cardiac reflex sensitivity, tested with phenylephrine (10–50 μg/kg i.v.), was attenuated significantly in P10–20 rats compared with P5/6, P25 and mature animals. In P14–17 rats stimulation of neurones in either the solitary tract or ambiguual nuclei, by microinjection of L-glutamate (100–200 pmol), evoked an atropine-sensitive bradycardia indicating a functional integrity of central and peripheral efferent pathways mediating the baroreceptor reflex. Thus, the baroreceptor vagal reflex is functional in P5/6 rats but becomes attenuated between P10–P20, which is coincident with the maturational rise in arterial pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050418
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  • 104
    Electronic Resource
    Electronic Resource
    Absence of evidence for a powerful tonic baroreflex-mediated inhibition on catechol activity in the rat rostral ventrolateral medulla: in vivo voltammetric evidence during sino-aortic deafferentation (1997)
    Springer
    Pflügers Archiv 434 (1997), S. 599-608 
    Details
    ISSN: 1432-2013
    Keywords: Key words Baroreceptor reflex ; Rostral ventrolateral medulla ; C1 cell group ; In vivo voltammetry ; Sino-aortic deafferentation ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  To test in a catechol-specific and dynamic manner for the existence of a powerful long-lasting inhibition arising from barosensitive afferents that depresses the activity of adrenergic neurons in the rostral ventrolateral medulla (RVLM), in vivo voltammetry was used before and after acute sino-aortic deafferentation. Rats were anaesthetized with pentobarbital or halothane and ventilated with a mixture of air and oxygen. Snares were inserted around the vagus, the glossopharyngeal and the superior laryngeal nerves. After placing the animal prone in the stereotaxic frame and stabilization at a high mean arterial pressure (MAP ≈ 120 mmHg), the snares were rapidly closed to produce complete barodeafferentation, assessed by loss of heart rate responses and changes in renal nerve sympathetic activity in response to vasoactive agents. Recording of a catechol signal was maintained in the RVLM during deafferentation. Under pentobarbital-induced anaesthesia (n = 5), deafferentation did not lead to a significant change in the catechol signal within the deafferented group. Under halothane-induced anaesthesia and phenylephrine-induced high baseline pressure (n = 5), no changes in the catechol signal were observed upon deafferentation (not significant vs sham animals: n = 5). This failure to demonstrate a major increase in catechol activity upon deafferentation does not fit with the hypothesis that a powerful tonic baroreflex-mediated inhibition depresses the activity of adrenergic RVLM barosensitive bulbospinal neurons, even when the baseline MAP is high. Rather, these data are compatible with weak or no inhibition of catechol activity by the baroreceptors and a nonessential role of adrenergic neurons within the baroreceptor reflex arc itself: the adrenergic neurons may not be in series within this arc but in parallel with the arc. This interpretation is in keeping with newer schemas of autonomic core circuitry that are devoid of adrenergic neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050442
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  • 105
    Electronic Resource
    Electronic Resource
    A single administration of d-amphetamine prior to stimulus pre-exposure and conditioning attenuates latent inhibition (1997)
    Springer
    Psychopharmacology 130 (1997), S. 79-84 
    Details
    ISSN: 1432-2072
    Keywords: Key words Latent inhibition ; Conditioned emotional response ; Amphetamine ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of a single administration of d-amphetamine (0.32 mg/kg, SC) upon latent inhibition (LI) in a one-session pre-exposure and conditioning procedure was investigated in rats in a conditioned emotional response paradigm. It was found that amphetamine attenuated LI. The effects could not be attributed to differences in unconditioned suppression nor to differences in response rates between the experimental groups. These results support the observations of Dunn and suggest that the disruption of LI may not depend upon a complex interaction between changes in neuronal processes consequent upon repetitive amphetamine administration and the schedule with which the drug is administered during the experimental procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050213
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  • 106
    Electronic Resource
    Electronic Resource
    Additive deficits in the choice accuracy of rats in the delayed non-matching to position task after cholinolytics and serotonergic lesions are non-mnemonic in nature (1997)
    Springer
    Psychopharmacology 130 (1997), S. 303-312 
    Details
    ISSN: 1432-2072
    Keywords: Key words Working memory ; Motor activity ; Serotonergic ; Muscarinic ; Nicotinic ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The role of serotonin (5-HT) and its interaction with the muscarinic or nicotinic receptor-mediated mechanisms in the modulation of working memory and motor activity was investigated by assessing the effects of 5-HT lesion and cholinergic receptor blockade on the performance of rats in a working memory (delayed non-matching to position, DNMTP) task. A global serotonergic lesion was induced by the intracerebroventricular adminstration of 5,7-dihydroxytryptamine (5,7-DHT). Post-mortem neurochemical analysis revealed that serotonin and 5-hydroxyindoleacetic acid (5-HIAA) levels were reduced in frontal and parieto-occipital cortices and in hippocampi of 5,7-DHT lesioned rats. 5-HIAA levels were also reduced in striatum. 5,7-DHT lesion slightly impaired choice accuracy of rats in the DNMTP task and also transiently reduced motor activity in rats. Even the lower dose of scopolamine (0.075 mg/kg), a muscarinic receptor antagonist, impaired the choice accuracy already at the shortest delay (i.e. not indicative of a working memory impairment per se), and caused a marked disruption of motor activity (lengthened response latencies, increased probability of omissions and decreased trials completed). Furthermore, the quaternary analogue, N-methylscopolamine (0.150 mg/kg), affected the motor activity of rats to the same extent as scopolamine. Mecamylamine (1.0; 3.0 mg/kg) also interfered with motor activity and it slightly decreased the choice accuracy, which was not dependent on the delay. Although mecamylamine disrupted the performance of rats in the DNMTP task, the disruption was not as severe as that seen with scopolamine. Moreover, both scopolamine and mecamylamine augmented the slight impairment on the choice accuracy of 5,7-DHT lesioned rats, but this was non-mnemonic in character. We conclude that there is no evidence for any major interaction between the serotonergic system and muscarinic or nicotinic cholinergic mechanisms in working memory per se, but muscarinic and nicotinic receptor antagonists may act additively with the 5,7-DHT lesion to disrupt the choice accuracy of rats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050244
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  • 107
    Electronic Resource
    Electronic Resource
    (−)Alprenolol potentiates the disrupting effects of dizocilpine on sensorimotor function in the rat (1997)
    Springer
    Psychopharmacology 132 (1997), S. 281-288 
    Details
    ISSN: 1432-2072
    Keywords: Key words Acoustic startle response ; Prepulse inhibition ; Schizophrenia ; Dopamine ; Serotonin ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The β-adrenoceptor antagonist as well as serotonin 5-HT1 receptor antagonist, (−)alprenolol, was found to potentiate the disrupting effect of the non-competitive NMDA receptor antagonist, dizocilpine, on prepulse inhibition (PPI) of the acoustic startle response (ASR) in the rat. The facilitating effect of dizocilpine on ASR amplitude was also potentiated by (−)alprenolol. (−)Alprenolol by itself did not affect either of these measures. These effects did not seem to be related to the unselective β-adrenoceptor antagonist property of (−)alprenolol, since combined pretreatment with the β1- and β2-adrenoceptor antagonists, metoprolol and ICI 118551, did not alter the effects of dizocilpine on startle behaviour. However, a serotonergic influence was suggested by the fact that a facilitating effect of dizocilpine on ASR amplitude was also obtained by pretreatment with the 5-HT precursor, L-5-HTP, in benserazide-pretreated rats. Furthermore, pretreatment with the 5-HT2 selective receptor antagonist, MDL 100907, significantly reduced the (−)alprenolol-induced potentiation of the effects of dizocilpine on startle behaviour, while the 5-HT3 selective receptor antagonist, ondansetron, failed to do that. Finally, the (−)alprenolol-induced potentiation of the effects of dizocilpine was significantly reduced by pretreatment with the atypical antipsychotic, clozapine, and by the potential antipsychotic and selective dopamine D2 receptor antagonist, raclopride. This study suggests that altered 5-HT activity may influence the effects of psychotomimetic drugs such as dizocilpine on sensorimotor function, and this observation may have implications for the pharmacological treatment of schizophrenia in humans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050346
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  • 108
    Electronic Resource
    Electronic Resource
    Neonatal lesions of the rat ventral hippocampus result in hyperlocomotion and deficits in social behaviour in adulthood (1997)
    Springer
    Psychopharmacology 132 (1997), S. 303-310 
    Details
    ISSN: 1432-2072
    Keywords: Key words Hyperactivity ; Hippocampus ; Neonate ; Negative symptoms ; Positive symptoms ; Rat ; Schizophrenia ; Social behaviour
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The neonatal ibotenic acid lesion of the ventral hippocampus in the rat is an animal model of several aspects of schizophrenia. This lesion produces a number of behavioural abnormalities, such as hyperlocomotion and deficits in prepulse inhibition of startle, that present themselves relatively late in development, i.e. after puberty. Some of these abnormalities, which are thought to model the positive symptoms of schizophrenia, can be normalized by chronic treatment with neuroleptics. In the present study, we examined the effects of the neonatal hippocampal lesion on social behaviour. Social withdrawal and isolation are key components of the negative symptoms of schizophrenia that have not been previously addressed in this model. Rats were lesioned on postnatal day 7 (PD7) and tested for social interaction on PD35 and PD65. They were then treated with clozapine (1.9 and 7.4 μmol/kg or 0.63 and 2.5 mg/kg) for 21 days and retested. The results show that although, as previously reported, spontaneous hyperlocomotion emerged in the lesioned rats only after puberty (PD65), social interaction deficits and behaviors that may reflect anxiety were present at both PD35 and PD65. Clozapine normalized locomotion, but did not ameliorate putative anxiety or social interaction deficits in the neonatally lesioned rats. Our results indicate that the neonatal hippocampal lesion in the rat models some aspects of both positive and negative symptoms of schizophrenia. The effects of clozapine appear inconsistent with its putative benefit for negative symptoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050349
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  • 109
    Electronic Resource
    Electronic Resource
    Effects of the AMPA receptor antagonist NBQX on the development and expression of behavioral sensitization to cocaine and amphetamine (1997)
    Springer
    Psychopharmacology 134 (1997), S. 266-276 
    Details
    ISSN: 1432-2072
    Keywords: Key words AMPA ; NBQX ; Behavioral sensitization ; Cocaine ; Amphetamine ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We examined the effect of 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX), an antagonist of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) subtype of glutamate receptor, on the development and expression of behavioral sensitization to amphetamine and cocaine in rats. A single injection of NBQX (12.5 mg/kg) administered 30 min prior to cocaine during the induction phase (days 1–5) prevented the development of cocaine sensitization, assessed by responsiveness to cocaine challenge on day 8. This NBQX regimen did not affect development of amphetamine sensitization. Two pretreatment injections of NBQX, one 20 min before and one 70 min after amphetamine on each day of the induction phase (days 1–6), did not affect sensitization of stereotypy but prevented sensitization of post-stereotypy ambulatory hyperactivity (both assessed by responsiveness to amphetamine challenge on day 8). The effect of NBQX on ambulatory sensitization was dose-dependent (attenuation with 12.5 mg/kg, complete prevention with 25 mg/kg). In contrast to its effects on development, NBQX (25 mg/kg) did not prevent expression of sensitization to cocaine or amphetamine. NBQX itself exerted no significant effects on locomotor activity in either drug-naive rats or rats that had received either NBQX or amphetamine repeatedly. These findings support a requirement for AMPA receptor stimulation in the development of locomotor sensitization to cocaine and amphetamine, but suggest a different mechanism for sensitization of amphetamine stereotypy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050449
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  • 110
    Electronic Resource
    Electronic Resource
    Gamma-vinyl GABA attenuates cocaine-induced lowering of brain stimulation reward thresholds (1997)
    Springer
    Psychopharmacology 133 (1997), S. 383-388 
    Details
    ISSN: 1432-2072
    Keywords: Key words Intracranial self stimulation (ICSS) ; Dopamine ; Rat ; GABA transaminase inhibitor ; Vigabatrin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Gamma-vinyl GABA (GVG, also referred to as vigabatrin), an irreversible inhibitor of GABA transaminase (GABA-T), raises levels of GABA in nerve terminals, inhibits striatal dopamine release, and attenuates cocaine-induced increases in extracellular dopamine in the striatum and nucleus accumbens. In order to determine the action of GVG on dopamine-mediated reward, we examined its effects on the threshold for rewarding brain stimulation in male F-344 rats. GVG dose-dependently raised brain stimulation reward (BSR) thresholds at doses of 200, 300, and 400 mg/kg without significant effects on motor performance as measured by response latencies. In order to determine if GVG had similar modulatory effects on cocaine-induced lowering of BSR thresholds, the effective doses of GVG were co-administered with 2.5 and 5.0 mg/kg cocaine, doses that significantly lower BSR thresholds. The 400 mg/kg dose of GVG significantly blocked the lowering of thresholds seen at each dose of cocaine. Cocaine in combination with 200 or 300 mg/kg GVG, doses of GVG that significantly raise BSR thresholds, resulted in thresholds not significantly different from those obtained with cocaine alone. These data demonstrate that, at the doses tested, GVG is more effective at modulating basal reward thresholds than at modulating thresholds lowered by cocaine, implying that as dopaminergic activity increases, GABAergic activity must also increase in order to exert its inhibitory influence on dopaminergic activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050418
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  • 111
    Electronic Resource
    Electronic Resource
    Behavioral sensitization and extracellular dopamine responses to amphetamine after various treatments (1997)
    Springer
    Psychopharmacology 134 (1997), S. 221-229 
    Details
    ISSN: 1432-2072
    Keywords: Key words Behavioral sensitization ; Dopamine ; Amphetamine ; Rat ; Microdialysis ; Caudate putamen ; Nucleus accumbens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The repeated administration of amphetamine (AMPH) results in a pattern of behavioral changes which includes an augmentation of some behaviors, generally referred to as behavioral sensitization. Some investigators have suggested that an increased dopamine (DA) response to AMPH challenge may underlie behavioral sensitization, while others have reported behavioral sensitization in the absence of an enhanced DA response. Because temporal and dosage parameters of the AMPH pretreatment regimen have been suggested to play a role in the appearance of an enhanced DA response, we utilized a variety of AMPH pretreatment regimens to assess the relationship between pretreatment dose of AMPH, duration of withdrawal and the DA response in caudate-putamen and nucleus accumbens to a subsequent AMPH challenge. Under our experimental conditions, behavioral sensitization was observed after each of these treatments in the absence of an enhanced DA response in either brain region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050445
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  • 112
    Electronic Resource
    Electronic Resource
    Validity, reliability and utility of the chronic mild stress model of depression: a 10-year review and evaluation (1997)
    Springer
    Psychopharmacology 134 (1997), S. 319-329 
    Details
    ISSN: 1432-2072
    Keywords: Key words Animal model of depression Chronic mild stress ; Predictive validity ; Face validity Construct validity ; Reliability ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This paper evaluates the validity, reliability and utility of the chronic mild stress (CMS) model of depression. In the CMS model, rats or mice are exposed sequentially, over a period of weeks, to a variety of mild stressors, and the measure most commonly used to track the effects is a decrease in consumption of a palatable sweet solution. The model has good predictive validity (behavioural changes are reversed by chronic treatment with a wide variety of antidepressants), face validity (almost all demonstrable symptoms of depression have been demonstrated), and construct validity (CMS causes a generalized decrease in responsiveness to rewards, comparable to anhedonia, the core symptom of the melancholic subtype of major depressive disorder). Overall, the CMS procedure appears to be at least as valid as any other animal model of depression. The procedure does, however, have two major drawbacks. One is the practical difficulty of carrying out CMS experiments, which are labour intensive, demanding of space, and of long duration. The other is that, while the procedure operates reliably in many laboratories, it can be difficult to establish, for reasons which remain unclear. However, once established, the CMS model can be used to study problems that are extremely difficult to address by other means.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050456
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  • 113
    Electronic Resource
    Electronic Resource
    A rat model of monitoring liver allograft rejection (1997)
    Springer
    Transplant international 10 (1997), S. 103-108 
    Details
    ISSN: 1432-2277
    Keywords: Key words Liver transplantation ; rat model ; Rat ; liver transplantation ; fine needle aspiration ; Fine needle aspiration ; liver ; rat ; Rejection ; liver ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Rat models are often used to study liver allograft rejection. We have established a model for rat liver allograft rejection, monitored by fine needle aspiration biopsy (FNAB), in the strain combination PVG-to-BN with a mean survival time of 37 ± 20 days. In this model, we observed acute rejection with an intense peak of lymphoid blasts and lymphocyte-dominated inflammation in the FNAB [9.1 ± 3.0 corrected increment units (CIU)], and an eventual increase in macrophages (up to 4.2 ± 4.4 CIU), together with fibrosis and parenchymal necrosis in the graft. Markers of immune activation, such as an increase in IL-2-receptor (from 1 % ± 2 % to 21 % ± 13 %) and class II (from 20 % ± 9 % to 43 % ± 13 %) expressing lymphoid cells and induction of ICAM-1 in the graft, were consistent with the overall cellular response. The FNAB correlated well with parallel graft histology. In this rat model, the atraumatic monitoring makes a close follow-up possible without having to sacrifice the experimental animals. This saves work, animals, and costs in the study of liver rejection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001470050020
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  • 114
    Electronic Resource
    Electronic Resource
    The characterization of reconstituted passenger leukocytes on the induction of tolerance in rat liver transplantation (1997)
    Springer
    Transplant international 10 (1997), S. 350-356 
    Details
    ISSN: 1432-2277
    Keywords: Key words Liver transplantation ; passenger leukocytes ; rat ; Passenger leukocytes ; liver transplantation ; rat ; Rat ; liver transplantation ; passenger leukocytes ; Tolerance ; liver transplantation ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The tolerance induced by orthotopic liver transplantation [DA (RT1a) rats to PVG (RT1c) rats] can be prevented by total body irradiation of the donor rat. Reconstitution of the irradiated donor with DA splenic leukocytes reintroduces this tolerance. To investigate the major histocompatibility complex (MHC) specificity of passenger leukocytes, irradiated DA donors were reconstituted by third-party BN (RT1n) splenic leukocytes. The reconstitution with BN splenocytes re-established DA-specific tolerance in PVG recipients, as confirmed by subsequent DA cardiac allografting, while BN hearts were rejected with second-set tempo. To determine which cell components play an important role in re-establishing liver graft tolerance, DA splenic leukocytes were further purified into three types: T, B, and adherent cells. Only “T-cell-enriched” preparations restored liver graft tolerance in three out of five PVG recipients. These results suggest that passenger leukocytes of differing MHC types can help to induce liver-specific tolerance and that T cells in the liver graft may be essential to regulate tolerance induction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001470050069
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  • 115
    Electronic Resource
    Electronic Resource
    Integrated intestinal capacity and nutritional status following small bowel transplantation (1997)
    Springer
    Transplant international 10 (1997), S. 386-391 
    Details
    ISSN: 1432-2277
    Keywords: Key words Intestinal transplantation ; function ; rat ; Small bowel function ; intestinal transplantation ; rat ; Rat ; small bowel function ; intestinal transplantation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Successful small bowel transplantation requires normal functional capacity of the graft and unaltered metabolism of the host. Weight gain and wet weight of muscle groups and intra-abdominal fat pads were compared between transplanted, sham-operated, short bowel-operated, and normal rats that were fed either standard chow or fat-enriched (15 %) pellets. Weight gain and wet weight of muscle groups and fat pads for the control, transplanted, and sham-operated rats were identical, while short bowel animals showed reduced weight. Transplanted rats receiving fat-enriched food had lower wet weight of fat pads than control animals on the high-fat diet. We conclude that small bowel transplantation makes it possible to overcome the intestinal failure associated with short bowel syndrome, leading to overall normal weight gain and development of the recipient. However, altered fat metabolism, reflected in changed body composition, was observed in transplanted animals on the high-fat diet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001470050075
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  • 116
    Electronic Resource
    Electronic Resource
    Prevention of graft rejection and graft-versus-host reaction by a novel immunosuppressant, FTY 720, in rat small bowel transplantation (1997)
    Springer
    Transplant international 10 (1997), S. 343-349 
    Details
    ISSN: 1432-2277
    Keywords: Key words Immunosuppression ; FTY 720 ; rat ; small bowel transplantation ; FTY 720 ; immunosuppression ; rat ; small bowel transplantation ; Rat ; small bowel transplantation ; FTY 720 ; Small bowel transplantation ; rat ; FTY 720
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In the present study, we examined the immunosuppressive effect of a new drug, FTY 720, on small bowel transplantation (SBT) in rats. Grafts from (LEW × BN) F 1-to-LEW rats treated with FTY 720 at 0.5 mg/kg from day 0 to 14 post-SBT survived significantly longer than untreated grafts. In addition, the administration of FTY 720 combined with cyclosporin (CyA; 5 mg/kg per day) had a synergistic effect on allograft survival. The graft-versus-host reaction (GVHR) that occurred in the LEW-to-F 1 rats was markedly reduced after the administration of FTY 720. FTY 720 combined with a low dose of CyA completely abrogated GVHR without any adverse reaction. FTY 720 treatment resulted in a significant decrease in the number of lymphocytes in the peripheral blood and the spleen, but the number of peripheral neutrophils was unchanged. Thus, FTY 720 would appear to be an ideal drug to combine with CyA in order to control the immune reaction after SBT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001470050068
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    Oxytocin innervation of spinal preganglionic neurons projecting to the superior cervical ganglion in the rat (1997)
    Springer
    Cell & tissue research 287 (1997), S. 481-486 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Oxytocin ; Immunocytochemistry ; Paraventricular nucleus ; Superior cervical ganglion ; Spinal cord ; Sympathetic nervous system ; Retrograde tracing ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The paraventricular nucleus of the hypothalamus is a major integrative nucleus for relaying information from the suprachiasmatic nucleus to the autonomic system. The precise pathway by which this information can influence autonomic functions, such as melatonin synthesis in the pineal gland, is not clear. In the present study, we used a retrograde tracer injected in the superior cervical ganglion to identify spinal preganglionic neurons. One of the main neurotransmitters present in descending projections of the paraventricular nucleus of the hypothalamus, oxytocin, was detected with immunocytochemistry to visualise possible contacts with the neurons located in the intermediolateral column of the spinal cord and projecting to the superior cervical ganglion. Although many appositions could be seen at the light-microscopic level, this abundance could not be confirmed at the electron-microscopic level. The implications of these observations for the overall timing message received by the spinal preganglionic neurons are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050772
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    HSP72 induction of systemic organs of rats after severe burn injury (1997)
    Springer
    European journal of plastic surgery 20 (1997), S. 136-140 
    Details
    ISSN: 1435-0130
    Keywords: Burn injury ; Stress protein ; HSP72 ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to understand the stress response of systemic organs to severe burn injury, the induction of 72-kD heat shock protein (HSP72) in various organs (brain, hypophysis, lung, heart, liver, pancreas, spleen, kidney, adrenal gland, and skeletal muscle) was investigated in rats with severe burns. A full-thickness burn was induced on the rats' skin by immersing the rats in hot water (90° C) for 3 s. At 0, 24, and 48 h after the burn injury, the HSP72 expression of various organs was examined using the Western blot analysis. At 24 h after the burn injury, the level of HSP72 had increased in the hypophysis, lung, heart, and kidney. In all organs examined, the expression of HSP72 had increased at 48 h after the burn injury. The level of HSP72 was highest in the hypophysis (3.3-fold compared to the control), and lowest in the brain and adrenal gland (1.7-fold of the control) at 48 h after the burn injury. These results confirm that severe burn injury causes a stress response in systemic organs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01002047
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    Specific [3H] Glutamate Binding in the Cerebral Cortex and Hippocampus of Rats During Development: Effect of Homocysteine-Induced Seizures (1997)
    Springer
    Neurochemical research 22 (1997), S. 637-646 
    Details
    ISSN: 1573-6903
    Keywords: Rat ; early development ; cerebral cortex ; hippocampus ; homocysteine seizures ; glutamate binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Specific [3H]glutamate binding to synaptic membranes from the cerebral cortex and hippocampus of 7-, 12- and 18-day-old rats was examined, both in control animals and during seizures induced by homocysteine. In the cerebral cortex a transient peak of glutamate binding was observed in 7-day-old group, whereas in the hippocampus it occurred in 12-day-old animals. Total specific [3H]glutamate binding was not influenced by preceding seizure activity in either of the age groups and both the studied regions. NMDA- and QA-sensitive glutamate bindings represent the highest portion of the total binding. Moreover, NMDA-sensitive binding in the cerebral cortex of 7-day-old rats is significantly higher as compared to the two more mature groups. The proportion of individual receptor subtypes on total binding in each age group was not influenced by preceding seizure activity. However, NMDA-sensitive binding in the hippocampus of 12-day-old rats, sacrificed during homocysteine-induced seizures, was significantly increased as compared to corresponding controls. In contrast to the effect of NMDA, AMPA, kainate and quisqualate which displaced to a different extent [3H]glutamate binding, homocysteine had no effect when added to membrane preparations. Similarly, [3H]CPP and [3H]AMPA bindings were not affected in the presence of homocysteine. It thus seems unlikely that homocysteine is an effective agonist for conventional ionotropic glutamate receptors. Its potential activity at some of the modulatory sites at the NMDA receptor channel complex or at metabotropic receptors has to be clarified in further experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022434406400
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    Verhalten postoperativer Adhäsionen nach intraperitonealer Applikation von Fibrinolytika in einem Rattenmodell (1997)
    Springer
    Langenbeck's archives of surgery 382 (1997), S. 33-36 
    Details
    ISSN: 1435-2451
    Keywords: Key words Fibrin ; Fibrinolysis ; Peritoneum ; Adhesions ; Rat ; Schlüsselwörter Fibrin ; Fibrinolyse ; Peritoneum ; Adhäsionen ; Ratte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung In einem Rattenmodell wurde die Beeinflussung der Adhäsionsentstehung nach Laparotomien durch intraperitoneale Applikation verschiedener Fibrinolytika untersucht. Streptokinase und TPA verminderten die sero-serosale Haftung signifikant, nicht aber Urokinase. Die intravasale Gerinnung blieb unbeeinflußt.
    Notes: Abstract In a rat model, the effect of the intraperitoneal application of fibrinolytic agents on the development of adhesions was examined. Streptokinase and TPA reduced sero-serosal adhesions significantly, whereas urokinase did not reduce them. Intravascural coagulation was not affected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008008
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    Rate-dependent prolongation of action potential duration in isolated rat ventricular myocytes (1997)
    Springer
    Basic research in cardiology 92 (1997), S. 123-128 
    Details
    ISSN: 1435-1803
    Keywords: Rat ; ventricular myocyte ; action potential duration ; transient outward current ; 4-aminopyridine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Rate-dependent alterations of action potential duration (APD) in rat ventricular myocytes were investigated. Action potentials of the isolated myocytes were recorded with patch electrodes containing EGTA (11 mM), and showed a marked rate-dependent prolongation in the APD (0.2–5 Hz). This prolongation was significantly inhibited in the presence of 4-aminopyridine (4-AP), a blocker of the transient outward K+ current (Ito). Thus, the rate-dependent decrease in Ito may underlie the change in APD. In contrast, the action potentials recorded from rat ventricular papillary muscles with conventional microelectrodes did not show rate-dependent alterations in the APD, i.e., the APD remained practically unaltered at the frequency range of 0.2–5 Hz. These results suggest that the rate-dependent prolongation of APD (due to rate-dependent blockade of Ito) becomes evident when the intracellular Ca2+ was chelated by the internal application of EGTA via patch pipette. We speculate that the rate-dependent prolongation of APD (via decreases in Ito) is masked in the ventricular papillary muscles, probably due to rate-dependent decreases in the inward current (e.g., electrogenic Na+−Ca2+ exchange current) that is regulated by the intracellular calcium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00788629
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    Ca transport during contraction and relaxation in mammalian ventricular muscle (1997)
    Springer
    Basic research in cardiology 92 (1997), S. 1-10 
    Details
    ISSN: 1435-1803
    Keywords: Rat ; rabbit ; ferret ; shortening ; fluorescence ; cardiac myocyte ; sarcoplasmic reticulum ; cardiac hypertrophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract During relaxation of cardiac muscle four Ca transport systems can compete to remove Ca from the myoplasm. These are 1) the SR Ca-ATPase, 2) the sarcolemmal Na/Ca exchange, 3) the sarcolemmal Ca-ATPase, and 4) the mitochondrial Ca uniporter. Isolated ventricular myocytes loaded with the intracellular fluorescent Ca indicator indo-1 were used to study [Ca]i decline during relaxation. By selective inhibition of the various Ca transporters above the dynamic interaction of these systems during relaxation was evaluated. Quantitatively the SR Ca-ATPase and Na/Ca exchange are clearly the most important (accounting for 〉95% of Ca removal). However, the balance of Ca fluxes between these systems vary in a species dependent manner. For example, the SR is much more strongly dominant in rat ventricular myocytes, where ∼92% of Ca removal is via SR Ca-ATPase and only 7% via Na/Ca exchange during a twitch. In other species (rabbit, ferret, cat, and guinea-pig) the balance is more in the range of 70–75% SR Ca-ATPase and 25–30% Na/Ca exchange. Ferret ventricular myocytes also exhibit a unusually strong sarcolemmal Ca-ATPase. During the normal steady state cardiac contraction-relaxation cycle the same amount of Ca must leave the cell as enters over a cardiac cycle. This implies that 25–30% of the Ca required to activate contraction must enter the cell at each cardiac cycle. Experiments using voltage clamp to measure both Ca current and Na/Ca exchange current demonstrate that this amount of Ca may be supplied by the L-type Ca current. The ability of the SR Ca-ATPase to reduce [Ca]i may also be modified both acutely (e.g. by catecholamines) as well as chronically (e.g. during cardiac hypertrophy and heart failure). Using tissue cultured neonatal rat ventricular myocytes, we studied the effect of chronic arrest or stimulation with phorbol esters (to stimulate protein kinase C). Verapamil-induced arrest increased the SR Ca-ATPase at the level of mRNA, protein expression and functional ability to lower [Ca]i in intact cells. Conversely, stimulation or protein kinase C reduced SR Ca-ATPase at all three of these levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00794062
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    An animal model for external otitis (1997)
    Springer
    European archives of oto-rhino-laryngology and head & neck 254 (1997), S. 115-119 
    Details
    ISSN: 1434-4726
    Keywords: External auditory canal ; External otitis ; Pathogenesis ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract External otitis was produced in 12 Sprague-Dawley rats by mechanical stimulation through a plastic micropipette inserted into the right external auditory canal (EAC). The EAC was later evaluated regarding the color of the skin, swelling and the presence of fluid. Within 1 day all rats developed an external otitis that was characterized by a red, swollen ear canal containing an opalescent fluid. The tympanic membrane and middle ear cavity appeared to be normal. No healed EACs were seen within the initial 10 days of follow-up and 4 of 6 rats still exhibited external otitis at day 21. Light microscopy of biopsy specimens revealed pronounced edema of the dermis of the ear canal. Mast cells were more numerous in the early phase of the otitis present, although very few inflammatory cells were found in tissues despite the marked inflammatory reaction produced. Findings show that this animal model for external otitis can be used to investigate pathogenesis as well as to test various treatment strategies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471273
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    Dose-dependent protective effect of BPC 157 on capsaicin-induced rhinitis in rats (1997)
    Springer
    European archives of oto-rhino-laryngology and head & neck 254 (1997), S. S9 
    Details
    ISSN: 1434-4726
    Keywords: Capsaicin ; Rhinitis ; BPC 157 ; Mastocytes ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Protection of BPC 157 on capsaicin-induced rhinitis was studied in Wistar rats for its effect on mastocyte infiltration, degranulation and inflammatory cell infiltration. Animals were pretreated with 10 μg/kg, 10 ng/kg or 2 ml saline i.p. and capsaicin (0.05 ml/nostril of 1750 nmol/l sol.) was applied intranasally. They were then euthanized at 1, 3 and 12 h after capsaicin provocation. Nasal mucosa was analyzed and scored for mastocyte infiltration, degranulation and inflammatory cell infiltration. BPC 157 pretreatment significantly prevented mastocyte infiltration at 1 h. Polymorphonuclear leukocyte infiltration was significantly reduced in rats pretreated with 10 μg/kg BPC 157. A dose-dependent effect of BPC 157 pretreatment was demonstrated only for polymorphonuclear leukocyte infiltration at 12 h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02439711
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    Inhibition of the development of myringosclerosis by local administration of fenspiride, an anti-inflammatory drug (1997)
    Springer
    European archives of oto-rhino-laryngology and head & neck 254 (1997), S. 425-429 
    Details
    ISSN: 1434-4726
    Keywords: Tympanic membrane ; Myringotomy ; Myringosclerosis ; Fenspiride ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Earlier studies have revealed a relationship between the development of myringosclerosis and oxygen-derived free radicals. The latter can be blocked by the anti-inflammatory drug fenspiride. The present study was undertaken to test the ability of fenspiride to prevent myringosclerosis from developing during healing of the tympanic membrane. Myringotomized rats were treated with either topical applications or intraperitoneal injections of fenspiride for 12 days, after which the tympanic membranes were examined by otomicroscopy and studied histologically by light microscopy. Topically applied fenspiride was found to inhibit the development of sclerotic lesions, whereas intraperitoneal injections were ineffective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02439973
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    Effect of focal cerebral ischemia on nitric oxide synthase expression in rats (1997)
    Springer
    Medical molecular morphology 30 (1997), S. 55-62 
    Details
    ISSN: 1860-1499
    Keywords: Nitric oxide ; Nitric oxide synthase ; Immunohistochemistry ; Rat ; Cerebral ischemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Time- and cell-type-dependent immunohistochemical activity of nitric oxide synthase (NOS) was investigated in rat cerebral cortex following focal ischemia and the local concentration of nitric oxide (NO) was measured. NO concentration increased 2 min after the ischemia. Brain NOS-immunoreactive neurons increased in number 5 min after the ischemia. Endothelial cell NOS immunoreactivity was first detected in vascular endothelial cells and astrocytes 5 min after the ischemia, and it increased again during 60 min to 4 days after the ischemia in reactive astrocytes. Inducible NOS immunoreactivity was detected in astrocytes, vascular endothelium, and microglia/macrophages at the periphery of the ischemic core during 2–4 days after the ischemia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01545082
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    Ultrastructural localization of calcium in rat retina with oxalate pyroantimonate and energy-dispersive X-ray detector (1997)
    Springer
    Medical molecular morphology 30 (1997), S. 76-80 
    Details
    ISSN: 1860-1499
    Keywords: Ultrastructure ; Retina ; Rat ; Oxalate ; Potassium pyroantimonate ; X-ray analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Intracellular calcium plays an important role in the intracellular signal transduction as one of the second messengers. In this study, we examined the ultrastructural distribution of calcium in rat retina, using the oxalate pyroantimonate technique and X-ray microanalysis. Large amounts of precipitates were observed inside the disc of outer segments of photoreceptor cells (OS) and the synaptic vesicles of the inner (IPL) and outer plexiform layer (OPL). Precipitates also were observed in the ribosome-rich regions in the cytoplasm and the euchromatinic part in the cell nuclei of the ganglion, amacrine, and bipolar and horizontal cells. However, few precipitates were found in the inner segment of the photoreceptor cells and the retinal pigment epithelium (RPE). X-ray microanalysis with an energydispersive X-ray detector revealed that these precipitates had a peak of antimony and calcium. Therefore, it was suggested that these precipitates were Ca[Sb(OH)6]2, the reaction products of the oxalate-pyroantimonate technique. Our findings showed that calcium precipitates are abundant in retinal regions that are related to visual transmission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01545085
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    Thermoxidized Palm Oil Induces reproductive Toxicity in Healthy and Malnourished Rats (1997)
    Springer
    Plant foods for human nutrition 51 (1997), S. 159-166 
    Details
    ISSN: 1573-9104
    Keywords: Thermoxidized palm oil ; Rat ; Kwashiorkor ; Fertility ; Fetotoxicity ; Reproduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Repeatedly thermoxidized palm oil (TPO), simulating local culinary practice, was fed for eight weeks at 15% of a balanced basal diet to two sets of male and female weanling albino rats of Wistar strain. The first set of animals were normal and healthy while the second set were kwashiorkoric. Primary controls (PC) of all rats were fed a balanced basal diet of commercial rat pellets while secondary controls (SC) were fed the balanced basal diet supplemented with 15% untreated palm oil. The findings indicate that fertility, as expressed by the pregnancy rate of healthy test rats, was 78% when compared with 80% in PC (p 〈 0.05). Fetotoxicity was additionally observed in that neonatal birth weights and litter size in test rats (4.92 g and 6.70, respectively) were inferior (p 〈 0.05) to both SC and PC (4.96 g and 8.40; 5.38 g and 9.25, respectively). Protein energy malnutrition worsened the observed TPO-induced reproductive toxicities in that reproductive capacities of the rehabilitated animals were inferior to that of the healthy animals. Pregnancy rates in test animals were reduced by as much as 55% (p 〈 0.01) while fetotoxicities were also more pronounced (p 〈 0.05).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007985529125
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    Cover page (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), 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.19970030201
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    Masthead (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997) 
    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.19970030202
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    Graphical abstract (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 179-183 
    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.19970030203
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    Simple Mechanical Molecular and Supramolecular Machines: Photochemical and Electrochemical Control of Switching Processes“Molecular Meccano”, Part 14: for Part 13, see D. B. Amabilino, P. R. Ashton, V. Balzani, C. L. Brown, A. Credi, J. M. J. Fréchet, J. W. Leon, F. M. Raymo, N. Spencer, J. F. Stoddart, M. Venturi, J. Am. Chem. Soc., in press. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 152-170 
    Details
    ISSN: 0947-6539
    Keywords: luminescence ; photochemistry ; redox chemistry ; self-assembly ; self-complexation ; template syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photochemical control of a self-assembled supramolecular 1:1 pseudorotaxane (formed between a tetracationic cyclophane, namely the tetrachloride salt of cyclobis(paraquat-p-phenylene), and 1,5-bis[2-(2-(2-hydroxy)ethoxy)ethoxy]naphthalene) has been achieved in aqueous solution. The photochemical one-electron reduction of the cyclophane to the radical trication weakens the noncovalent bonding interactions between the cyclophane and the naphthalene guest - π-π interactions between the π-electron-rich and π-electron-poor aromatic systems, and hydrogen-bonding interactions between the acidic α-bipyridinium hydrogen atoms of the cyclophane and the polyether oxygen atoms of the naphthalene derivative - sufficiently to allow the guest to dethread from the cavity; the process can be monitored by the appearance of naphthalene fluorescence. The radical tricationic cyclophane can be oxidized back to the tetracation in the dark by allowing oxygen gas into the system. This reversible process is marked by the disappearance of naphthalene fluorescence as the molecule is recomplexed by the tetracationic cyclophane. This supramolecular system can be chemically modified such that the π-electron-rich unit, either a naphthalene derivative or a hydroquinone ring, and the tetracationic cyclophane are covalently linked. We have demonstrated that the π-electron-rich residue in this system is totally “self-complexed” by the cyclophane to which it is covalently attached. Additionally, the self-complexation can be switched “off” and “on” by electrochemical two-electron reductions and oxidations, respectively, of the tetracationic cyclophane component. Thus, we have achieved the construction of two switches at the nanoscale level, one driven by photons and the other by electrons.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030123
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    The Oxide Anion Accelerated Retro-Diels-Alder Reaction (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 187-192 
    Details
    ISSN: 0947-6539
    Keywords: Diels-Alder reactions ; pericyclic reactions ; retro reactions ; oxide anion ; synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The widespread application of the retro-Diels-Alder reaction in synthesis has been hampered by the high temperatures usually required to effect cycloreversion. The discovery of the anionic oxy-Cope reaction was followed by predictions that the accelerating effect of the oxide anion should also be observed with other pericyclic reactions. Recently, such predictions have been confirmed for the retro-Diels-Alder reaction, which often proceeds rapidly at room temperature by oxide anion rate acceleration. Such mild retro-Diels-Alder reactions have now been employed in the synthesis of a range of molecular targets, including temperature-sensitive enediynes.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030204
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    Heterosupramolecular Chemistry: Self-Assembly of an Electron Donor (TiO2 Nanocrystallite)-Acceptor (Viologen) Complex〈Dedicated to Dr. Satoshi Ushioda on the occasion of his 65th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 202-207 
    Details
    ISSN: 0947-6539
    Keywords: electron transfer ; heterosupermolecules ; self-assembly ; titanium oxide ; viologens ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A TiO2 nanocrystallite has been modified to recognise and selectively bind, by complementary hydrogen bonding, a uracil substrate incorporating a viologen moiety. Band-gap excitation of the self-assembled donor (TiO2 nanocrystallite)-acceptor (viologen) complex results in electron transfer. Some implications of these findings for the self-assembly of functional nanostructures containing both condensed phase and molecular components are considered.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030206
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    A Triangular Iron(III) Complex Potentially Relevant to Iron(III)-Binding Sites in Ferreascidin (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 193-201 
    Details
    ISSN: 0947-6539
    Keywords: EPR spectroscopy ; exchange coupling ; iron ; Moessbauer spectroscopy ; O ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An asymmetric triangular FeIII complex has been synthesized by an unusual FeII-promoted activation of salicylaldoxime. Formation of the ligand 2-(bis(salicylideneamino)methyl)phenol in situ is believed to occur through the reductive deoximation of salicylaldoxime by ferrous ions. The trinuclear ferric complex has been characterized on the basis of elemental analysis, IR, variable-temperature magnetic susceptibility, and EPR and Mössbauer spectroscopies. The molecular structure established by X-ray diffraction consists of a trinuclear structure with a [Fe3(μ3-O)(μ2-OPh)]6+ core. Two iron ions are in a distorted octahedral environment having FeN2O4 coordination spheres, and the five-coordinated third iron ion, with an FeNO4 coordination sphere, is in a trigonal bipyramidal environment. The magnetic susceptibility measurements revealed an St = 5/2 ground state with the antiparallel exchange interactions J = - 34.3 cm-1, J' = - 4.7 cm-1, and D = - 0.90 cm-1. The EPR results are consistent with a ground state of S = 5/2 together with a negative D5/2 value. The Mössbauer isomer shifts together with the quadrupole splitting also provide evidence for the high-spin state of the three ferric sites. Magnetic Mössbauer spectra lead to the conclusion that the internal magnetic fields possibly lie in the plane of the three ferric ions.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030205
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  • 136
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    Hexabromotricyclobutabenzene and Hexabromohexaradialene: Their Nickel-Mediated One-Pot Syntheses and Crystal Structure (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 208-210 
    Details
    ISSN: 0947-6539
    Keywords: crystal structure ; cyclobutenes ; nickel ; radialenes ; radical reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of hexakis(dibromomethyl)benzene with [(Bu3P)2-Ni(COD)] (COD = 1,5-cyclooctadiene) in DMF at 65-70°C yielded a mixture of the title compounds. The mixture was separated by column chromatography to yield hexabromotricyclobutabenzene (3 a) and hexabromohexaradialene (4) in 24 and 16% yields, respectively. 1H and 13C NMR spectroscopy suggest that 3 is obtained as the syn-all-trans isomer 3 a, and the symmetric anti-all-trans isomer 3 b is not obtained at all. The X-ray structures of 3 a and 4 are reported. The hexaradialene 4 has a chair conformation, and deviates from planarity by 43.6°. Heat or radical impurities cause the clean transformation of 3 a to 4.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030207
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  • 137
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    Theoretical Investigation of the Mechanism of the Baeyer-Villiger Reaction in Nonpolar Solvents (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 210-218 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; Baeyer-Villiger reactions ; migrations ; peroxyacids ; substituent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Baeyer-Villiger reaction of p-anisaldehyde with peroxyacetic acid in nonpolar solvents to give p-anisylformate was examined on the basis of ab initio molecular orbital calculations. To explain the experimental observations, the free-energy change was evaluated for each case in the absence and in the presence of an acid catalyst. It was found that, without catalysts, the rate-determining step corresponds to the carbonyl addition of peroxyacetic acid to p-anisaldehyde and the reaction hardly occurs. Acetic acid was found to catalyze the carbonyl addition and change the rate-determining step from the carbonyl addition to the migration of the carbonyl-adduct intermediate. Trifluoroacetic acid was observed to catalyze both the carbonyl addition and migration, and the carbonyl addition was demonstrated to be a rate-determining step. The results provided a convincing explanation of the complex kinetics seen experimentally. Further calculations were performed for the reaction of benzaldehyde with peroxyacetic acid to give phenylformate. Migratory aptitude was found to depend on the catalyst. Isotope effects were also investigated, and the exceptional isotope effect observed experimentally was shown to be due to the rate-determining carbonyl addition caused by autocatalysis. It is concluded that the mechanism of the reaction varies with catalysis or substituent effects.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030208
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  • 138
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    Terrylenimides: New NIR Fluorescent Dyes (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 219-225 
    Details
    ISSN: 0947-6539
    Keywords: arenes ; C-C coupling ; dyes ; fluorescence ; terrylenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Terrylenimides 3 and 4 represent a new class of blue colorants, exhibiting absorption maxima at 650 to 700 nm and fluorescence emissions in the NIR region (673 to 750 nm). The terrylenimides were synthesized by means of various organometallic coupling reactions, catalyzed by transition metal complexes (Nio, Pdo) and starting from the aromatic bromides, boronic acids, or organotin compounds. The terrylenimides have all the properties expected of excellent fluorescent dyes: high extinction coefficients, high fluorescence quantum yields, and very good thermal, chemical, and photochemical stabilities. Owing to its extended π system, 3 can reversibly accept four negative charges. By varying the substituents, 3 and 4 can be modified to serve either as soluble dyes or as insoluble pigments.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030209
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  • 139
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    Syntheses, Crystal Structures, and Properties of Novel Heterooctametallic Clusters Na2M'2[M3O4(O2CEt)8]2 (M' = Fe, Cr, Mo; M3 = Mo3, MoW2, W3) (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 226-231 
    Details
    ISSN: 0947-6539
    Keywords: chromium ; clusters ; iron ; molybdenum ; tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A mixture of Na2MO4, M(CO)6, FeCl3·6H2O, and (EtCO)2O was heated at 120°C to produce the heterooctanuclear clusters Na2Fe2[M3O4-(O2CEt)8]2 (M = Mo, 1; W, 2). The bioxo-capped clusters Na[M3O2(O2CEt)9] (M3 = MoW2, W3) were treated with Fe-(CO)5, Cr(CO)6, and Mo(CO)6 in (EtCO)2O at 120°C to afford Na2M'2-[MoW2O4(O2CEt)8]2 (M' = Fe, 3; Cr, 4; Mo, 5) and Na2Mo2[W3O4(O2CEt)8]2 (6), respectively. The isomorphous clusters 1, 2, 5, and 6 were characterized by X-ray crystallography. The structures, similar to those of the analogues Na2Cr2[M3O4-(O2CEt)8] (M = Mo, 7; W, 8) and Na2V2[M3O4(O2CEt)8]2 (M = Mo, 9; W, 10), consist of two incomplete cubane-type [M3O4(O2Et)8]4- units centrosymmetrically bridged by two M'(III) metal ions through μ-oxo and propionate groups; the resulting cluster dianions are linked by Na+ ions into infinite chains. Clusters 1-10 do not dissolve in water and common organic solvents at room temperature. Unlike the chromium(III) clusters 7 and 8, the iron(III) and vanadium(III) clusters 1 and 9 are soluble in aqueous acid solution, as a result of their decomposition into isolated [Mo3O4]4+ cluster units. Temperature-dependent magnetic susceptibilities of 1, 2, and 7-10 were measured over the range 2-200 K and modeled by means of the spin-Hamiltonian H = - 2JS1S2 to give spin exchange coupling constants J/k of -0.60, -0.72, -1.76, -1.31, -4.80, and -1.46 K, respectively. These figures show that antiferromagnetic spin exchange coupling interactions between the magnetic, bridging M'(III) ions are very weak. These species show characteristic bands in the IR spectra at 740-820 cm-1, which can probably be assigned to ṽ(M-μ-O).
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030210
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  • 140
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    The Thiazole Ylide: A Frequently Invoked Intermediate Is a Stable Species in the Gas Phase (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 232-236 
    Details
    ISSN: 0947-6539
    Keywords: carbenes ; density functional calculations ; mass spectrometry ; thiamin ; ylides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1, 2-hydrogen shift isomers of neutral (singlet and triplet) thiazole (1) and its radical cation have been investigated by a combination of mass spectro-metric experiments and hybrid density functional theory calculations. The latter were used to probe the structures and stabilities of selected C3H3NS and C3H3NS.+ isomers and transition state structures. Although 3H-thiazole-2-ylidene (2) is less stable than 1, by 31.5 kcalmol-1, it is expected to be capable of independent existence, since the 1, 2-hydrogen shift from carbon to nitrogen involves a very large energy barrier of 72.4 kcalmol-1. The other 1, 2-hydrogen shift reaction from C(2) leads not to the expected cyclic 1H-thiazole-2-ylidene structure (3), which is apparently unstable, but rather to the ring-opened species HSCH=CHNC (4), which is 34.5 kcalmol-1 higher in energy than 1. The barrier in this case is lower but still large (54.9 kcalmol-1). The triplet ground states of 1, 2 and 4 are considerably destabilised (69.5, 63.2 and 58.7 kcalmol-1) relative to their singlet states. Interestingly, in addition to 2.+ and 4.+, the cyclic radical cation 3.+ is predicted to be stable although it is substantially higher in energy than ionised thiazole 1.+ (by 53.9 kcalmol-1), whereas 2.+ and 4.+ are much closer in energy (only 10.2 and 27.0 kcalmol-1 higher, respectively). Dissuading 2.+ and 3.+ from isomerising to 1.+ are energy barriers of 52.6 and 15.3 kcalmol-1, respectively. Experimentally, dissociative ionisation of 2-acetylthiazole enabled the generation of 2.+, which could be differentiated from 1.+ by collisional activation mass spectrometry. Reduction of the ylide ion 2.+ in neutralisation-reionisation mass spectrometry experiments yielded the corresponding neutral molecule 2. This direct observation of a thiazolium ylide provides support for postulates of such species as discrete intermediates in a variety of biochemical transformations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030211
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  • 141
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    Edge-sharing SiN4 Tetrahedra in the Highly Condensed Nitridosilicate BaSi7N10 (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 249-252 
    Details
    ISSN: 0947-6539
    Keywords: high-temperature synthesis ; network structures ; nitridosilicates ; silicon ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel nitridosilicate BaSi7N10 was obtained by the reaction of barium metal with Si(NH)2 in a special high-frequency furnace at 1650 °C. The single-crystal structure determination (a = 687.29(3), b = 671.29(3), c = 963.28(4) pm, β = 106.269(3)°, PC, Z = 2, R1 = 0.0497, wR2 = 0.0924) reveals a network structure of connected SiN4 tetrahedra. BaSi7N10 is the first nitridosilicate with both corner and edge-sharing SiN4 tetrahedra. Unlike the situation in normal oxosilicates, vertex-sharing of SiN4 tetrahedra is not exclusively favored over edge-sharing. With a Si:N molar ratio of 7:10, BaSi7N10 is the most highly condensed multinary nitridosilicate known and has almost the same degree of condensation as binary Si3N4.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030213
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  • 142
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    The Vinylketene-Acylallene Rearrangement: Theory and Experiment (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 237-248 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; allenes ; ketenes ; matrix isolation ; rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkoxyvinylketenes4are generated by flash vacuum thermolysis (FVT) or photolysis of 3-alkoxycyclobutenones3. The thermal interconversion of4and allene carboxylic acid esters5under FVT conditions is demonstrated by Ar matrix FTIR spectroscopy. In addition, ethoxy-vinylketene4bundergoes thermal elimination of ethene with formation ofs-cis-ands-trans-acetylketene(8). An analogous aminovinylketene-to-allenecarbox-amide conversion is observed on FVT of 3-dimethylaminocyclobutenone3c. A facile 1, 3-chlorine migration in 2, 3-buta-dienoyl chloride(5d)is also reported. Consistent with the experimental observations, 1, 3-methoxy, 1, 3-chloro, and 1, 3-dimethylamino migrations in vinylketene are calculated (G2(MP2, SVP) level) to have moderate barriers of 169, 157, and 129 kJ mol-1, respectively, significantly less than the corresponding 1, 3-H shift barrier (273 kJ mol-1). The stabilization of the four-center transition structures is rationalized in terms of the donor-acceptor interaction between the lone pair electrons of the migrating donor substituent and the vacant central carbon p orbital of the ketene LUMO. The predicted migratory aptitude in the series of substituted vinylketenes, R-C(=CH2)-CH=C=O, is in the order N(CH3)2〉SCH3〉SH〉Cl〉NH2〉OCH3〉OH〉F〉H〉CH3, and correlates well with the electron-donating ability of the R group.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030212
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  • 143
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    Evidence for Direct trans Insertion in a Hydrido-Olefin Rhodium Complex - Free Nitrogen as a Trap in a Migratory Insertion Process (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 253-260 
    Details
    ISSN: 0947-6539
    Keywords: dinitrogen ; hydrido complexes ; insertions ; olefins ; rhodium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of the hydrido chloride complex [Rh(H)Cl{CH3C(CH2CH2-P(tBu)2)2}] (4) with NaH under a nitrogen atmosphere results in formation of two products: the dinitrogen complex [Rh(N2)-{CH3C(CH2P(tBu)2)2}] (2) and the unusual low-valent hydrido-olefin complex, [RhH{CH2=C(CH2CH2P(tBu)2)2}] (3). In the presence of N2, complexes 2 and 3 are in equilibrium in solution; 2 is about 2.9kcalmol-1 more stable than 3 + N2. Both complexes co-crystallize in the solid state; they occupy the same crystallographic site in the crystal lattice (P2-(1)/c; Z = 4; a = 12.173(2), b = 14.121 (3), c = 15.367 (3); α = 90, β = 106.50(3), γ = 90°). The mechanism of the reversible interconversion of 2 and 3 has been studied in detail. Complex 3 undergoes rapid olefin insertion/β-hydrogen elimination processes. The insertion rates were measured at different temperatures by saturation transfer NMR experiments, providing evidence for a highly organized late transition state (δS≠≈ - 40 e.u.), which can be caused by a concerted “trans migration”. This theoretically unfavorable process is assisted by a distortion from the ideal square-planar configuration, including a decrease of the P-Rh-P angle and some bias of the double bond toward the hydride as indicated by the X-ray crystal structure of 3. Under a nitrogen atmosphere, the intermediate formed upon olefin insertion is slowly trapped by free dinitrogen to form complex 2. The dinitrogen dissociation from 2 was found to be the rate-determining step for the overall interconversion of 2 and 3 (δG≠298 = 24.1 kcalmol-1).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030214
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  • 144
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    On the Role of Structural Zinc in Bis(Cysteinyl) Protein SequencesZinc complexes of amino acids and peptides, part 10. part 9, ref. [1]. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 261-267 
    Details
    ISSN: 0947-6539
    Keywords: NMR spectroscopy ; peptides ; protein structures ; structure elucidation ; zinc ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Besides its functional role in many hydrolytic metalloenzymes, zinc acts as a structural component by being attached to bis(cysteinyl) protein sequences in some of the same enzymes, and in other metalloproteins and zinc fingers, and by being an essential constituent in metallothioneins. It is not always obvious whether the zinc-binding proteins are pre-organized for the incorporation of the metal or whether the zinc ion provides the structurizing power and stability for the observed peptide conformations. We have addressed the coordination chemistry aspects of this question by synthesizing zinc complexes of small model peptides and by determining their structures in solution by 2D NMR spectroscopy. The peptides chosen were of the terminally protected bis(cysteinyl) type: Cys-Cys, Cys-Gly-Cys, Cys-Phe-Cys, and Cys-Gly-Ile-Cys. The zinc ions fold these peptides into structures that can be superimposed on those of the natural proteins.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030215
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  • 145
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    Structural Effects in the Reductive Activation of (Indenyl)RhL2 Complexes: The Reduction of [Rh(η5-C9H7)(η4-cod)] (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 279-285 
    Details
    ISSN: 0947-6539
    Keywords: electron transfer ; indene ; kinetics ; rhodium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of the indenyl complex [Rh(η5-C9H7)(η4-cod)] has been investigated in the context of structural effects induced by the transfer of one electron. The reduction of this complex occurs in two steps, leading first to the radical anion and then to the highly frangible dianion. Both species eliminate the indenyl anion. In the presence of free cyclooctadiene, the related cleavage leading to the indenyl anion and bis-cyclooctadiene rhodium fragments now follows a Michaelis-Menten-type mechanism involving precoordination of one extra COD ligand to the initial radical anion. These results suggest the modification of the hapticity of the indenyl ligand in connection with 17- and 19-electron metalcentered intermediates.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030217
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  • 146
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    Nickel Complexes of 21-Oxaporphyrin and 21, 23-Dioxaporphyrin (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 268-278 
    Details
    ISSN: 0947-6539
    Keywords: heterocycles ; heteroporphyrins ; nickel ; porphyrinoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nickel(I) and nickel(II) complexes of 5,20-bis(p-tolyl)-10, 15-diphenyl-21-oxaporphyrin (ODTDPPH) and 5,10,15,20-tetraphenyl-21, 23-dioxaporphyrin (O2TPP) have been investigated. These oxa analogues of 5,10,15,20-tetraarylporphyrin, where one or two pyrrole rings are replaced by a furan moiety, have been synthesized by condensation of the respective precursors, namely 2,5-bis(arylhydroxymethyl)furan, pyrrole, and arylaldehyde. Insertion of nickel(II) into ODTDPPH or O2TPP yielded high-spin five- and six-coordinate ([(ODTDPP)NiIICl] and [(O2TPP)NiIICl2]) complexes, which can be reduced with moderate reducing reagents. The EPR spectra of [(ODTDPP)NiI] and [(O2TPP)NiICl] revealed the NiI oxa(dioxa)porphyrin rather than a NiI anion radical electronic structure. In the structures of [(ODTDPP)NiIICl], [(O2TPP)NiIICl2], and [(ODTDPP)NiI], determined by X-ray diffraction, the furan ring is planar and coordinates in the η1 fashion through the trigonal oxygen atom; the nickel ion lies in the furan plane for the latter two complexes, but slightly outside it in [(ODTDPP)NiIICl]. The Ni-N and Ni-O bond lengths decrease upon reduction of high-spin five-coordinate [(ODTDPP)NiIICl] to four-coordinate [(ODTDPP)NiI]. The pattern of downfield pyrrole resonances in 1H NMR spectra of [(ODTDPP)NiIICl] and [(O2TPP)-NiIICl2] has been established. The downfield positions of furan resonances are unusual for NiII heteroporphyrins; they have been accounted for by the nearly in-plane coordination of the furan moiety as opposed to the side-on coordination found for thiophene- or selenophene-containing heteroporphyrins. An example of ion-pair formation, [(O2TPPH)2][NiIICl4], was produced from [(O2TPP)NiIICl2] by acidification with HCl.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030216
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  • 147
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    A Joint Experimental and Theoretical Study of the Interaction between Aluminum and Electroluminescent Polymers: Cyano Derivatives of Poly(p-phenylene vinylene) (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 286-293 
    Details
    ISSN: 0947-6539
    Keywords: light-emitting diodes ; polymers ; semiempirical calculations ; electroluminescence ; polymer/metal interface ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The early stages of metal/polymer interface formation between aluminum and poly(2,5,2′,5′-tetrahexyloxy-8,7′-dicyanodi-p-phenylenevinylene) or their ring-substituted derivatives have been studied theoretically by using quantum-chemical calculations as well as experimentally by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. This class of conjugated polymer is of interest in the development of organic light-emitting diodes. The theoretical and experimental results indicate that aluminum preferentially reacts with the polymer by forming covalent bonds with the nitrogen and carbon atoms of the cyano groups. When the side chains of the phenylene rings include carbonyl groups, however, the theoretical results indicate that the carbonyl moiety is another preferred site of interaction.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030218
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  • 148
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    Extended-Core Discotic Liquid Crystals Based on the Intramolecular H-Bonding in N-Acylated 2,2′-Bipyridine-3,3′-diamine Moieties (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 300-307 
    Details
    ISSN: 0947-6539
    Keywords: bipyridines ; discotic liquid crystals ; hydrogen bonds ; liquid crystals ; mesophases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new type of disc-shaped molecule (1 a-c) has been synthesised and characterised. The molecules were built up by linking three lipophilic, N-monoacylated 2,2′-bipyridine-3,3′-diamine wedges to a central 1,3,5-benzenetricarbonyl unit. They show liquid crystalline behaviour, as shown by DSC, polarisation microscopy and X-ray diffraction. In all cases the mesophase was characterised as a Dho phase. From 1H NMR results it was shown that the interior of compounds 1 a-c preferentially adopts a C3 symmetrical conformation owing to strong intramolecular H-bonding, which gives rise to an extended core. This large core induces strong interactions between molecules, leading to mesophases of enhanced thermal stability.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030220
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  • 149
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    Quantum-Chemical Investigations of Stabilizing Interactions in μ-Diborylcarbene Dicobalt Complexes with a Planar Tetracoordinate Carbon AtomDedicated to Professor Gerhard Herberich on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 294-299 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; cobalt ; planar carbon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum-chemical methods have been employed to study the nature of stabilization in dinuclear cobalt complexes of the general formula [{(C5H5)Co}2(μ-CR12BCBR2R3)] (6) as well as the “antivan't Hoff-Le Bel” configuration of the planar tetracoordinate carbon (ptC) atom of the bridging diborylcarbene ligand 9. Extended Hückel and ab initio Hartree-Fock calculations have been carried out for the model compounds 6b (R1 = R2 = R3 = H) and 6c (R1 = R2 = H; R3 = C6H5). Ab initio electron deformation density maps and natural population analysis calculations show that complexes 6 are stabilized through push-pull effects by which the ptC experiences π electron density delocalization and σ electron density accumulation. The calculated electronic configuration of the ptC in the free ligand 9b is σ2.978π1.501, and in 6b σ3.944π1.356. Electron density donation from one cobalt atom to an aryl group on the bridging ligand further contributes to the stabilization of the complexes 6.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030219
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    Cover page (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), 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.19970030301
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    Masthead (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997) 
    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.19970030302
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  • 152
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    Phenoxyl Radical Complexes of Gallium, Scandium, Iron and Manganese (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 308-319 
    Details
    ISSN: 0947-6539
    Keywords: gallium ; iron ; scandium ; spectroelectrochemistry ; manganese ; phenoxyl radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hexadentate macrocyclic ligands 1,4,7-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane (LCH3H3), 1,4,7-tris(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane (LBuH3) and 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triazacyclononane (LOCH3-H3) form very stable octahedral neutral complexes LMIII with trivalent (or tetravalent) metal ions (GaIII, ScIII, FeIII, MnIII, MnIV). The following complexes have been synthesized: [LBuM], where M = Ga (1), Sc (2), Fe (3); [LBuMnIV]PF6 (4′); [LOCH3M], where M = Ga (1 a), Sc (2 a), Fe (3 a); [LOCH3MnIV]PF6 (4 a'); [LCH3M], where M = Sc (2 b), Fe (3 b), MnIII (4 b); [LCH3MnIV]2(ClO4)3(H3O)(H2O)3 (4 b'). An electrochemical study has shown that complexes 1, 2, 3, 1 a, 2 a and 3 a each display three reversible, ligand-centred, one-electron oxidation steps. The salts [LOCH3FeIII]ClO4 and [LOCH3GaIII]ClO4, have been isolated as stable crystalline materials. Electronic and EPR spectra prove that these oxidations produce species containing one, two or three coordinated phenoxyl radicals. The Mössbauer spectra of 3 a and [3 a]+ show conclusively that both compounds contain high-spin iron(III) central ions. Temperature-dependent magnetic susceptibility measurements reveal that 3 a has an S = 5/2 and [3a]+ an S = 2 ground state. The latter is attained through intramolecular antiferromagnetic exchange coupling between a high-spin iron(III) (S1 = 5/2) and a phenoxyl radical (S2 = 1/2) (H = - 2JS1S2; J = - 80 cm-1). The manganese complexes undergo metal- and ligand-centred redox processes, which were elucidated by spectroelectrochemistry; a phenoxyl radical MnIV complex [MnIVLOCH3]2+ is accessible.
    Additional Material: 17 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030221
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    Graphical abstract (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 327-331 
    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.19970030303
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  • 154
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    Hemoprotein Models Based on a Covalent Helix-Heme-Helix Sandwich: 1. Design, Synthesis, and Characterization (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 340-349 
    Details
    ISSN: 0947-6539
    Keywords: helical structures ; heme proteins ; iron ; peptides ; synthesis design ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we describe the design, synthesis, and spectroscopic characterization of a covalent helix-heme-helix sandwich named FeIII mimochrome I. It contains deuterohemin bound through both propionyl groups to two identical N-and C-terminal protected nonapeptides as α-helical scaffolds. Each peptide moiety bears a His residue in the central position, which acts as axial ligand to the metal ion. The newly developed synthetic strategy is based on a combination of solution and solid-phase methodologies. It represents a powerful method for obtaining a large variety of analogues containing two symmetric or unsymmetric peptide chains covalently bound to the deuteroporphyrin ring. UV/Visible spectroscopic characterization in buffered 2,2,2-trifluoroethanol/water solution proves low-spin bis(his-tidine) iron(III) coordination; circular dichroism (CD) measurements show an α-helical conformation for the peptide moieties. Thus, all the data are in agreement with the designed hypothetical model regarding both the iron(III) coordination and the peptide chain structural organization.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030305
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  • 155
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    Hemoprotein Models Based on a Covalent Helix-Heme-Helix Sandwich: 2. Structural Characterization of CoIII Mimochrome I δ and δ Isomers (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 350-362 
    Details
    ISSN: 0947-6539
    Keywords: cobalt ; helical structures ; heme proteins ; NMR spectroscopy ; por-phyrinoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: FeIII mimochrome I is the prototype of a new class of hemoprotein models characterized by a covalent helix-heme-helix sandwich. It contains deuterohemin bound through two propionyl groups to two identical N- and C-terminal protected α-helical nonapeptides, each of which bears a His residue (a potential axial lig-and of the iron ion) in the central position. In order to understand better the three-dimensional structure of FeIII mimochrome I and its correlation with spectral properties, we have characterized the fully diamagnetic parent compound CoIII mimochrome I by UV/visible, CD, and NMR spectroscopy, coupled with conformational energy calculations. CoIII mimochrome I is a highly water-soluble compound present in solution as two isomers, which slowly interconvert only at very low pH values. These isomers were isolated and separately characterized. Their UV/visible spectral properties are very similar, while their CD spectral properties differ markedly in both the far UV and Soret regions. The isomers were identified by 1H NMR spectroscopy as diastereomers of the δ and δ type. This is the first example of an accurate three-dimensional structure determination in solution of a hemoprotein mimetic that allows a straightforward correlation between structure and spectral properties.
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030306
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  • 156
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    Optical Detection and Manipulation of Single Molecules in Room-Temperature Solutions (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 335-339 
    Details
    ISSN: 0947-6539
    Keywords: single-molecule detection ; single-molecule manipulation ; laser-induced fluorescence ; optical trapping ; confocal fluorescence microscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the tight focus of a gaussian laser beam, single molecules in solution at room temperature can be trapped and detected by observation of fluorescent photons. The focus defines an ultrasmall probe volume on the order of 1 femtoliter, and the electric field gradient associated with this focus enables an individual molecule to be trapped and manipulated.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030304
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  • 157
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    The Reaction of a Triorganochloroindate with Dioxygen (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 568-572 
    Details
    ISSN: 0947-6539
    Keywords: cesium ; indium ; layered compounds ; metalla(crown ethers) ; pi interactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of CsCl with In(CH2Ph)3 yields the triorganochloroindate Cs[(PhCH2)3InCl] (1). Treatment of In(CH2Ph)3 with dry O2 gives the alkoxide [(PhCH2)2InOCH2Ph]2 (2), whereas the reaction of 1 with O2 leads to Cs2[O{PhCH2In(OCH2Ph)2}4] (3). According to X-ray structural investigations, 1 contains Cs2Cl2 four-membered rings as basic structural motif. The dimers are connected by Cs-π-electron interactions to form a layer structure. Compound 3 can be described as a metalla(crown ether) fragment coordinating two Cs+ ions. Additional shielding of the Cs centers by weak Cs-π-electron contacts was observed.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030412
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  • 158
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    Kinetic and thermodynamic study of the mechanism of reversible intermolecular electron-transfer reactions between horse heart cytochrome c and a series of cobalt imine complexes (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 39-46 
    Details
    ISSN: 0947-6539
    Keywords: cobalt ; cytochrome c ; electron transfer ; kinetics ; volume profile ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Kinetics and Thermodynamics of the Reversible Outer-Sphere Electron-Transfer Reactions between Horse Heart Cytochrome cII/III and [Co(phen)3]3+/2+ and [Co(bpy)3]3+/2+ were studied in detail, in particular as a function of temperature and pressure. It was possible to construct a volume profile for both reactions from the pressure data. The transition state was found to be halfway between the reactant and product states on a volume basis in all studied systems. This is in agreement with the λ≠ parameter estimated from the Marcus theory. For all the systems investigated, the differences in the activation volumes are in good agreement with the reaction volumes determined from spectrophotometric and electrochemical measurements at elevated pressure, and from the difference in the partial molar volumes of the metal complexes. The activation and reaction volumes of the bipyridine system are significantly smaller than those of the corresponding phenanthroline and terpyridine systems. A detailed mechanistic analysis is presented. The results show that the different kinetic and thermodynamic techniques employed complement one another.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030108
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    Acid-Base Properties of Adenosine 5′-O-Thiomonophosphate in Aqueous SolutionAbbreviations: Ado, adenosine; AMP2-, adenosine 5′-monophosphate; AMPS2-, adenosine 5′-O-thiomonophosphate, also known as adenosine 5′-O-monophosphorothioate or adenosine 5′-[α-thio]monophosphate; ATP4-, adenosine 5′-triphosphate; ATPγS4-, adenosine 5′-O-[γ-thio]triphosphate; En, ethylenediamine (=1, 2-diaminoethane); RibMP2-, D-ribose 5-monophosphate. Species which are named in the text without a charge either do not carry one or represent the species in general (i.e., independent of their degree of protonation); which of the two-applies is always clear from the context. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 29-33 
    Details
    ISSN: 0947-6539
    Keywords: acidity ; adenosinephosphates ; adenosinethiophosphates ; protonated isomers ; semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acidity constants of H2-(AMPS)± were determined by potentiometric pH titrations in aqueous solution at 25°C and I=0.1M (NaNO3). Titrations with a combined single-junction glass electrode were hampered in the presence of AMPS by a “poisoning” effect; the problem could be avoided by use of two separated electrodes. The values of the acidity constants PKHH2(AMPS) = 3.72 ± 0.03 and pKHH2(AMPS) = 4.83 ± 0.02 are relatively close to each other; the buffer regions of the two equilibria overlap, and therefore a micro acidity constant scheme was developed and the constants for the various sites calculated. It is concluded that the thiophosphateprotonated species (AMPS⋅H)- dominates at about 75% occurrence, while the form (H⋅AMPS)-, with the proton at the N1 site of the adenine residue, occurs at about 25%. Semiempirical AM1 and PM3 calculations including water as a solvent locate the proton in (AMPS⋅H)- mainly on the terminal oxygen atoms rather than the sulfur. The acid-base properties of H2(AMPS)± are considerably more complicated than those of the parent nucleotide, H2(AMP)±; for the latter the two (intrinsic) acidity constants are well separated and consequently practically all protons have left the N1 site before deprotonation at the monoprotonated phosphate group occurs. Finally, an estimate for the acidity constants of H2(ATPγS)2- is given.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030106
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  • 160
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    Interaction of Acetonitrile with Olefins and Alcohols in Zeolite H-ZSM-5: In situ Solid-state NMR Characterization of the Reaction ProductsDedicated to the Memory of Professor K. I. Zamaraev (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 47-56 
    Details
    ISSN: 0947-6539
    Keywords: alcohols ; nitriles ; NMR spectroscopy ; olefins ; zeolites ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction products and intermediates from the interaction of acetonitrile with olefins (oct-1-ene) or alcohols (tert-butyl alcohol) in zeolite H-ZSM-5 at 296 K have been characterized with 13C and 15N solid-state NMR. It has been shown that coadsorption of acetonitrile and olefin on H-ZSM-5 gives rise to the intermediate N-alkylnitrilium cation represents a persistent species inside a zeolite under anhydrous conditions. Upon admittance of water to the pores of the zeolite, the N-alkylnitrilium cation slowly converts into N-alkylamide in accordance with the classic Ritter reaction. In the case of acetonitrile and alcohol, just after coadsorption both the intermediate N-alkylnitrilium cation and the final N-alkyl-amide are identified simultaneously; the former slowly disappears over a few days. Thus, 1) it has been shown that the Ritter reaction can occur not only in liquid acidic media but also on a solid acid catalyst, zeolite H-ZSM-5; 2) N-alkylnitrilium cations have been detected and characterized with solid-state NMR as persistent intermediates in the Ritter reaction for the first time while the reaction proceeds.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030109
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  • 161
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    Novel inorganic cage structures based on ass ligands and cyclopentadienylruthenium groups (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 57-61 
    Details
    ISSN: 0947-6539
    Keywords: clusters ; ruthenium ; sandwich complexes ; arsenic sulfides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [Cp(*)2Ru2-(CO)4] [a: Cp(*) = Cp* (η5-C5Me5); b: Cp(*) = Cpx (η5-C5Me4Et)] with β-realgar in boiling n-decane gives [Cp(*)2Ru2-As4S4] (1a,b). in good yields along with some [Cp(*)2Ru2-As4S2] (2a,b). According to X-ray diffraction analyses of 1b and 2a, their structures belong to two different types of inorganic clusters. Whereas 1b has a cage structure in which the [Cp(*)2Ru2 unit is inserted into the As4S4] cradle, 2a has a sandwich structure in which two coplanar η2-As4S ligands and the Cp* ligands are oriented parallel to one another. Analysis of the As-S connectivity in the core of 1 b reveals a structural relationship to the extremely rare form of arsenic sulfide As4S4(II), and not to the metastable high-temperature form β-As4S4 used in the synthesis. At lower temperatures (60, 115°C) formation of CO-containing products is observed.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030110
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    Total syntheses of the slime mold alkaloid arcyriacyanin APigments from Fungi, Part 67; Part 66: G. Mayer, G. Wille, W. Steglich, Tetrahedron Lett.1996, 26, 4483-4486. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 70-74 
    Details
    ISSN: 0947-6539
    Keywords: alkaloids ; Heck reactions ; heterocycles ; indoles ; total syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Arcyriacyanin A (1) has been synthesized by three different routes. In the first synthesis the bisbromomagnesium salt of 2,4′-biindole (5) was treated with dibromomaleimide (6) to yield arcyriacyanin A (1). The second approach used an intramolecular Heck reaction for the cyclization of a 4-(triflyloxy)arcyriarubin 8 to N-methylarcyriacyanin A (2). Thirdly, compound 2 was obtained by a domino Heck reaction between 3-bromo-4-[1-(tert-butoxycarbonyl)indol-3-yl]-1-methylmaleimide (9) and 4-bromoindole (10). The N-methyl derivative 2 could be transformed into arcyriacyanin A (1) by standard methods.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030112
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  • 163
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    Chain Conformation and Metal…Metal Contacts in Dimers and Stacks of d8-ML4 Complexes: Electronic EffectsThe abbreviations used in this paper are given in the Appendix. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 655-664 
    Details
    ISSN: 0947-6539
    Keywords: band theory ; electronic structure ; stacking interactions ; square-planar complexes ; one-dimensional complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A qualitative theoretical study is presented of the ligand effects on the strength of the M…M nonbonded interaction in dimers and stacks of 8-ML4 chains. It is found that π-acidic ligands enhance and π-basic ligands weaken the M…M bonding interaction. A large amount of structural data can be rationalized with the help of a simple orbital model. Other features of the crystal structures of such compounds are correctly accounted for by semiempirical molecular orbital and electronic band calculations (extended Hückel level). Electronic effects control the deviation from linearity of stacks of complexes with mixed ligands, whereas coupled electronic and steric effects determine the conformational preference. The predictive capability of theoretical band calculations is found to be good.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030422
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    Nitridosilicates-A Significant Extension of Silicate Chemistry (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 679-683 
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    ISSN: 0947-6539
    Keywords: high-temperature synthesis ; materials science ; nitridosilicates ; nitrogen ; silicon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Because of its low chemical reactivity Si3N4 has hardly been used as a starting material for the preparation of multinary silicon nitrides or nitridosilicates, but has gained increasing importance as a nonoxidic material for high-performance applications. A novel synthetic approach is presented, which starts from silicon diimide (Si(NH)2) and makes available a large variety of novel nitridosilicates. The structures of these nitridosilicates represent a significant extension from those found in the family of oxosilicates. Because of their outstanding chemical and physical stability, nitridosilicates might be of particular interest for the development of novel inorganic nitridic materials.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030505
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    Dendritic Bipyridine Ligands and Their Tris(Bipyridine)Ruthenium(II) Chelates - Syntheses, Absorption Spectra, and Photophysical Properties (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 706-712 
    Details
    ISSN: 0947-6539
    Keywords: bipyridine ligands ; dendrimers ; dioxygen quenching ; luminescence ; ruthenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several synthetic strategies have been explored to prepare dendrimers having the [Ru(bpy)3]2+ complex as their core (bpy = 2,2′-bipyridine). Dendritic ligands have been synthesized by attaching branches in the 4,4′-positions of bpy. The largest dendritic bipyridine ligand contains 54 peripherical methylester units. Four RuII dendritic complexes have been prepared. Their absorption and emission spectra are very similar to those of the unsubstituted parent RuII-bipyridine complexes. The large dendritic complexes, however, exhibit a more intense emission and a longer excited-state lifetime than [Ru(bpy)3]2+ in aerated solutions. This is due to the shielding effect of the dendrimer branches on the Ru-bipyridine core, which limits the quenching effect of molecular oxygen. For the largest dendritic complex, which contains 54 peripherical methylester units, the excited-state lifetime in aerated acetonitrile solution is longer than 1 μs, and the rate constant for dioxygen quenching is twelve times smaller than for [Ru(bpy)3]2+.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030509
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    Synthesis of (R)-Sulforaphane Using [cpru(R, R)-CHIRAPHOS)]+ as Chiral AuxiliaryEnantioselective organic syntheses using chiral transition metal complexes, part 3. For part 2 see ref. [1]. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 713-716 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric synthesis ; dioxiranes ; ruthenium ; sulforaphane ; sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new enantioselective (80% ee) synthesis of (R)-sulforaphane and its epimer (S)-sulforaphane is described, which makes use of the pseudo-tetrahedral complex fragment [CpRu-(CHIRAPHOS)]+ as a chiral auxiliary. Reaction of the chloride complexes [CpRu(L-L)Cl] [L-L = 1,-bis(diphenylphosphino)ethane (dppe), (2S,3S)-and (2R,3R)-bis(diphenylphosphino)-butane ((S,S)- and (R, R)-CHIRAPHOS, respectively)] with phthalimidobutyl methyl sulfide gives the thioether complexes [CpRu(L-L)(MeSC4H8NPhth)]PF6. Oxygen transfer from dimethyldioxirane (DMD) produces the corresponding sulfoxide complexes in high yield and high diastereoselectivity. Cleavage of the phthaloyl group with aqueous hydrazine and subsequent reaction with thiophosgene yields the sulforaphane complexes [CpRu(L-L)(MeS(O)C4H8NCS)]PF6. Treatment of these with sodium iodide finally liberates the sulforaphane without noticeable racemization.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970030510
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    New Evidence for Conformational Flexibility in Cyclodextrins from Vibrational Raman Optical Activity (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1292-1298 
    Details
    ISSN: 0947-6539
    Keywords: carbohydrates ; conformation analysis ; cyclodextrins ; inclusion compounds ; Raman optical activity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational flexibility in cyclodextrins (CDs) as a function of methylation, solvent interaction and the extent of inclusion complex formation has been studied by using vibrational Raman optical activity (ROA). The work exploited the sensitivity of ROA to skeletal mobility by comparing the intensity of the glycosidic ROA couplet between about 850 and 970 cm-1 in maltoheptose (MH), β-cyclodextrin (β-CD), heptakis(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) and heptakis(2,3,6-tri-β-methyl)-β-cyclodextrin (TM-β-CD) in buffered aqueous solution, in DMSO and with sodium benzoate and benzoic acid as guests in buffered aqueous solution. Increases in couplet signal strength were interpreted in terms of a reduction in conformational flexibility of the CD ring. In buffered aqueous solution the ROA intensity order MH 〈 TM-β-CD 〈 β-CD 〈 DM-β-CD was observed. The linear molecule MH is expected to be the most flexible of the four oligosaccharides studied, while the changes registered for the three CD macrocycles may be related to the degree of intramolecular hydrogen bond formation and its influence on conformational flexibility. In DMSO, the same ROA intensity order is observed, but with an approximately constant increase relative to the values obtained in aqueous solution. This can be explained by the tighter binding of DMSO in the CD cavities compared with H2O. For the inclusion complexes, our results indicate that the tighter the guest is bound, the larger is the reduction in the conformational flexibility of the CD macrocycle. The residual mobility sensed by ROA in CDs is similar to that sensed in proteins; this provides further insight into their analogous ligand-binding and catalytic properties.
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    URL: http://dx.doi.org/10.1002/chem.19970030817
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    5-exo-trig Versus 6-endo-trig Cyclization of Alk-5-enoyl Radicals: The Role of One-Carbon Ring Expansion (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 376-387 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; cyclizations ; cycloketones ; radicals ; ring expansions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alk-5-enoyl radicals were made to cyclize in exo and endo modes to give the corresponding cycloketone radicals, which are related through one-carbon ring expansion. Relative kinetic data were determined for the ring closure of the 2-methylhept-5-enoyl radical generated by the reaction of the corresponding phenylseleno ester with Bu3SnH over the temperature range 233-323 K. The conversion to absolute rates provided Arrhenius expressions for the 5-exo-trig and 6-endotrig cyclizations. Ab initio and semiempirical (AM1) calculations were performed on the hex-5-enoyl and hept-5-enoyl radicals, respectively, and the outcomes aided in the rationalization of the preexponential factors and activation energies. Both 1,5-and 1,6-ring closure occur via a lower energy “chairlike” transition state. The observed high regioselectivity is due to favorable entropic and enthalpic factors associated with the formation of the smaller ring. The stereoselectivity was higher in the 1,6-ring closure (70:30) than in the 1,5-ring closure (55:45), the trans isomer being predominant in both. For the onecarbon ring expansion studies, the radicals of interest were obtained by deoxygenation of suitable alcohols via the O-phenyl thiocarbonates with (TMS)3-SiH. The one-carbon ring expansion in the cyclopentanone series for the secondary alkyl radicals was studied over the temperature range 343-413 K by means of free-radical clock methodology and yielded the Arrhenius expression. The rate constant was 4.2 x 103 s-1 at room temperature and the reverse reaction (ring contraction) was found to be at least 10 times slower. Since the intermediacy of acyl radicals can be excluded, the reaction must occur via 3-membered cyclic intermediate radicals (or transition states).
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    URL: http://dx.doi.org/10.1002/chem.19970030309
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  • 169
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    A Novel Palladium-Catalyzed Asymmetric Cyclocarbonylation of Allylic Alcohols to γ-Butyrolactones (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 417-423 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric synthesis ; butyrolactones ; carbonylations ; catalyst system ; palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A catalyst system based on [Pd2(dba)3]·CHCl3/(-)-BPPM has been found to effect asymmetric cyclocarbonylation of certain prochiral allylic alcohols to produce good yields of optically enriched γ-butyrolactones. The reaction was performed under an atmosphere of H2 (400 psi) and CO (400 psi) at 100°C in methylene chloride for 48 hours. Asymmetric cyclocarbonylation of allylic alcohols with aliphatic substituents proceeded with moderate enantioselectivities (ee = 25-43%). However, enantiomeric excesses of up to 83% were obtained for substrates containing aromatic substituents, in which case the ee was found to be more sensitive to steric, rather than to electronic factors. Recrystallization of the lactones containing an aromatic group from a mixture of CH2Cl2/Et2O/hexanes (0.5/1.0/8.5), by slow evaporation of the solvent or at low temperature, improved the enantiopurities to 〉98% ee on a reproducible basis. The asymmetric center of the aromatic lactones was assigned the (S)-configuration based on the X-ray crystal structure analysis of enantiopure (S)-(+)-3,3-dimethyl-2-(2′-methylphenyl)-γ-butyrolactone (2k). A hydridopalladium intermediate is believed to play a key role in this reaction. Enantioselectivity is thought to be brought about by the preferential formation of 6b. The carbon skeleton of 6b fits into the chiral scaffold of (-)-BPPM.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030313
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  • 170
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    A New Strategy for Oligosaccharide Assembly Exploiting Cyclohexane-1,2-diacetal Methodology: An Efficient Synthesis of a High Mannose Type Nonasaccharide (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 431-440 
    Details
    ISSN: 0947-6539
    Keywords: carbohydrates ; glycoproteins ; HIV oligosaccharides ; protecting groups ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The high-mannose nonasaccharide 1 is part of the glycoprotein gp 120 of the viral coat of HIV-1. The mannan portion of this triantennary glycan was prepared by a number of consecutive glycosidation steps without the need for any protecting-group manipulation. This was achieved by carefully tuning the reactivity of the glycosyl donors by employing our cyclohexane-1,2-diacetal (CDA) methodology. The method was further extended with one-pot procedures for oligosaccharide synthesis, thus reducing the number of steps to form the protected nonasaccharide 21 from the monosaccharide building blocks to five.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030315
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  • 171
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    The N3 Position of N9-Substituted Adenine as a Metal Ion Binding Site: Structural and Solution Studies with PdII and PtII Complexes of N6′, N6′,N 9-Trimethyladenine (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 388-398 
    Details
    ISSN: 0947-6539
    Keywords: acid-base equilibria ; adenine palladium ; platinum ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Steric blockage of the N1 and N7 sites of 9-methyladenine for metal complexation is achieved by twofold methylation of the exocyclic amino group. With 6′,6′,9-trimethyladenine (TrimeA), binding of MII(dien) (M = Pt, Pd) as well as of trans-[Pt(NH3)2Cl]+ therefore takes place through N 3. X-ray crystal structure determinations and NMR spectroscopic studies of three compounds are reported, and the effects of PtII and PdII on the geometry and the acid-base properties of the TrimeA ligand have been measured and compared with those of the free base. TrimeA has a very pronounced self-stacking tendency in water (K=85M-1 according to the isodesmic model of indefinite noncooperative self-association). Acidity constants derived from potentiometric pH titrations, spectrophotometry, and NMR shift experiments display excellent agreement with each other. Twofold protonated TrimeA, that is H2(TrimeA)2+, carries protons at the N7 and N1 sites; the acidity constants are pKHH2(TrimeA) = - 0.75 and pKHH(TrimeA) = 4.15. These values compare well with those of other adenine residues. Protonation of [Pt(dien)-(TrimeA-N3)]2+ occurs at the N7 position, as shown by spectrophotometry and NMR spectroscopy. The acidity constant of the H+ (N7) site in this complex is low, that is pKHH[Pt(dien)(TrimeA)] = 0.3 (as determined by spectrophotometry), but it is not as low as that for the same site when a proton resides at N1 of unmetalated TrimeA. The pKa of the doubly protonated complex, pKHH2[Pt(dien)(TrimeA)], in which the second acidic proton is situated at N1, is about-1.2 ± 0.3. These findings indicate that upon metalation of N3, the sequence of adenine protonation is reversed. While the N7 site still displays basic properties, the N1 site has undergone a dramatic loss in basicity.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030310
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  • 172
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    Olefin Cross-Metathesis with Monosubstituted Olefins (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 441-444 
    Details
    ISSN: 0947-6539
    Keywords: alkenes ; allylsilanes ; C-C coupling ; cross-metathesis ; jasmonates ; molybdenum ; ruthenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The applicability of olefin cross-metathesis for the synthesis of different unsymmetrically substituted functionalized olefins is described. The coupling of different functionalized olefins in the presence of Grubbs' ruthenium catalyst or Schrock's molybdenum catalyst afforded the crossed products in good yields and with very high selectivities. Derivatives of jasmonic acid and functionalized allylsilanes were prepared by this catalytic method for carbon-carbon double bond formation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030316
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  • 173
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    Organic Approaches to Endohedral Metallofullerenes: Cracking Open or Zipping Up Carbon Shells? (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1009-1016 
    Details
    ISSN: 0947-6539
    Keywords: alkynes ; cobalt ; endohedral metallofullerenes ; fullerenes ; macrocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have been investigating the synthesis of endohedral metallofullerenes since we successfully opened an orifice on the framework of C60 in the form of a cobalt complex having the metal sitting on top of the opening. A second approach aims at the synthesis of spherically-shaped acetylenic macrocycles, which are expected to rearrange to endohedral metal complexes of fullerenes in a controlled process analogous to the gas-phase coalescence of mono- and polycyclic polyynes during fullerene formation by the graphite evaporation method. Since the potential benefits from obtaining endohedral metal complexes of C60 are enormous, both approaches are being actively pursued in our group.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030705
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  • 174
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    Design and Synthesis of Sugar-Responsive Semiartificial Myoglobin Triggered by Modulation of Apoprotein-Cofactor Interactions (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1025-1031 
    Details
    ISSN: 0947-6539
    Keywords: boronic acids ; heme proteins ; molecular recognition ; myoglobin ; saccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenylboronic acid groups as sugar recognition sites were successfully introduced into native myoglobin by a cofactor-reconstitution method. Spectrophotometric pH titration demonstrated the sugar-induced pKa shift of the H2O coordinated to the heme center of the semisynthetic myoglobin bearing phenyl-boronic acids (met-Mb(PhBOH)2). By means of circular dichroism (CD) and paramagnetic 1H NMR spectroscopies, it was proven that sugars that were bound to phenylboronic acid sites induced the rearrangement of the heme crevice to reinforce the heme cofactor-apoprotein interactions. The structural changes that were induced by the binding of sugars subsequently enhanced the dioxygen storage activity of Mb(PhBOH)2. Such sugar-induced structural and functional changes did not occur for other modified Mbs that had no sugar-recognition units. Interestingly, a randomly modified Mb with phenylboronic acid units did not show any sugar response. In Mb(PhBOH)2, the information from the sugar-binding event was efficiently transmitted to the active center, so that the activity was efficiently altered upon sugar binding. In conclusion, the active site specific incorporation of molecular recognition units as nonnatural functional molecules can provide a novel strategy for the design of stimuli-responsive semisynthetic proteins.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030707
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  • 175
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    Allylsilanes as Carbon Nucleophiles in the Palladium-Catalyzed 1,4-Oxidation of Conjugated Dienes (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 482-490 
    Details
    ISSN: 0947-6539
    Keywords: allylsilanes ; catalysis ; cyclizations ; oxidations ; palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Palladium-catalyzed oxidation of cyclic 1,3-dienes 3, 5, 9, 11, and 13, with an allylsilane group in the side chain, led to an intramolecular 1,4-syn-addition to the conjugated diene through a carbocyclization. Acyclic trienesilanes 7 also underwent analogous 1,4-oxidations. The reaction was carried out in acetone-acetic acid (2:1) with a slight excess of LiCl. p-Benzoquinone was employed as the oxidant and Li2PdCl4 as the catalyst. The reaction proceeds through an intramolecular trans addition of the allylsilane to a (π-diene)palladium complex to produce a bicyclic (π-allyl)palladium intermediate. Subsequent trans attack by chloride at the π-allyl intermediate gives the product. The intermediate (π-allyl)palladium complex was isolated and fully characterized. It was unambiguously demonstrated that the allylsilane had attacked the coordinated double bond trans to palladium (trans-carbopalladation). The use of CuCl2 as the oxidant, instead of p-benzoquinone, gave a less stereoselective addition, but interestingly, with the opposite stereochemistry.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030320
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  • 176
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    Studying the Stability of a Helical β-Heptapeptide by Molecular Dynamics Simulations (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1410-1417 
    Details
    ISSN: 0947-6539
    Keywords: helical structures ; molecular dynamics simulations ; NMR spectroscopy ; peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Peptides consisting entirely of homochiral β-amino acids R-CH(NH2)-CH2CO2H form 31-helices in solution, as shown previously by NMR analysis of pyridine and methanol solutions. The stability of the helical secondary structure of one such β-peptide (H-β-HVal-β-HAla-β-HLeu-(S,S)-β-HAla(αMe)-β-HVal-β-HAla-β-HLeu-OH, 1) has been investigated by molecular dynamics simulations using the GROMOS 96 molecular model and force field (962 methanol molecules; T = 298, 350, 400 K; with and without NOE distance restraints). The restraints derived from the NMR studies were equally well satisfied by both the restrained and the unrestrained room-temperature molecular dynamics simulations. The 31-helical conformation of 1 was shown to be so stable that it was restored spontaneously within 400 ps after unfolding had been induced by a sudden increase of the temperature from 298 to 350 K.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030907
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  • 177
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    The Role of Backbone Oxygen Atoms in the Organization of Nucleic Acid Tertiary Structure: Zippers, Networks, Clamps, and C-H…O Hydrogen Bonds (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1400-1404 
    Details
    ISSN: 0947-6539
    Keywords: DNA structures ; hydrogen bonds ; nucleic acids ; RNA ; tertiary structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tight packing between structural elements is a prerequisite for molecular recognition and catalysis. In proteins, α-helices and β-sheets present the amino acid side chains on the surface while the polar amide bonds are buried. The opposite is found in double- and polystranded nucleic acids, where negatively charged phosphates occupy the surface and the side chains are hydrogen bonded in the core. Thus the question arises: How do densely packed nucleic acid molecules achieve close approach, despite the repulsion between phosphates that would appear to preclude tight contacts? One obvious answer is by mediating interstrand contacts through coordinated cations that can screen the negative charges. In this contribution, however, we highlight a variety of alternative direct interactions involving atoms of the sugar-phosphate backbone that can promote tight packing of RNA and DNA into functional molecules. We have analyzed the existing nucleic acid crystal structures in terms of the presence of close contacts between backbone regions. In RNA, ribose 2′-hydroxyl groups were observed to mediate such contacts in the majority of cases. However, their absence in DNA does not prevent oligodeoxynucleotides from packing tightly, aided by various interactions between backbone atoms.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030905
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  • 178
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    π-Electron Ring-Current Effects in Multiple Adducts of 3He@C60 and 3He@C70: A 3He NMR Study (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1071-1076 
    Details
    ISSN: 0947-6539
    Keywords: fullerenes ; endohedral helium complexes ; NMR spectroscopy ; ring currents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis- to hexakisadducts of C60 (1-6) and mono- to tetrakisadducts of C70 (7-13) containing 3He atoms (endo-hedral helium complexes) were prepared and studied by 3He NMR spectroscopy to determine the influence of degree of functionalization and addition pattern on the chemical shift of the 3He atom. In the series of C60 derivatives, which included the previously measured 6-6 monoadduct 3He@C61H2, the 3He resonance was shifted considerably upfield relative to that of 3He@C60 (δ = -6.36) up to the bisadduct 1 (δ = -11.45). The resonances of the higher adducts 3-6, however, were shifted only slightly further up-field and all appeared in a rather narrow spectral range between δ = -11.84 and -12.26. The absence of further substantial upfield shifts was rationalized in terms of the compensation of deshielding due to the functionalization-induced decrease in the diamagnetic π-electron ring currents that extend around the fullerene sphere by the shielding that results from the weaker pentagonal-ring paramagnetic currents and the increased number of localized benzenoid substructures in 3-6. In contrast, all 3He resonances of the C70 adducts are shifted downfield relative to the signal of 3He@C70 (δ = -28.81). A monotonic relationship exists between the chemical shift and the degree of functionalization, whereby the 3He chemical shifts steadily decrease from monoadduct 7 (δ = -27.53) to the isomeric tetrakisadducts 12 (δ = -21.09) and 13 (δ = -20.68). This deshielding was explained by the reduction of the strong diamagnetic ring currents extending along the polar corannulene perimeters as a result of the functionalization at α- and β-type polar bonds in 7-13. In both series, the addition pattern was also found to have a distinct influence on the 3He chemical shift.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030714
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  • 179
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    Dicyanopolyynes: A Homologuous Series of End-Capped Linear sp Carbon (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1105-1112 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; alkynes ; carbon allotropes ; electronic structure ; semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, isolation, spectroscopic characterization, and computational investigations of the rod-shaped dicyanopolyynes 1-6 (C2nN2, n = 4-9), which are model substances for the hypothetical one-dimensional carbon allotrope carbyne sp-C∞, are described. Based on the trends in the spectroscopic behavior of 1-6 with increasing chain length, the electronic as well as the NMR properties of carbyne are predicted. For the investigation of the synthetic potential of this compound class, a first selected series of regioselective derivatizations is presented with the synthesis of the [4+2] and [3+2] cycloadducts 7-12.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030718
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  • 180
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    Molecular and Supramolecular Synthesis with Dibenzofuran-Containing SystemsMolecular meccano, part 18; for Part 17, see D. B. Amabilino, P. R. Ashton, S. E. Boyd, M. Gómez-López, W. Hayes, J. F. J. Org. Chem. 1997, 62, 3062-3075. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1136-1150 
    Details
    ISSN: 0947-6539
    Keywords: crystal engineering ; dibenzofuran ; molecular quadrilaterals ; supra-molecular chemistry ; template synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The template-directed syntheses of two new tetracationic cyclophanes, cyclobis(paraquat-2,8-dibenzofuran) and cyclobis(paraquat-3,7-dibenzofuran), incorporating dibenzofuran subunits has been accomplished. Initially, the cyclophanes were self-assembled around a macrocyclic polyether template, bis-p-phenylene[34]crown-10 (BPP34C10), to form catenanes: the mechanical bond order of the catenane formed determined the requisite “amacrocyclic” templates for synthesis of the free cyclophane. X-ray crystallography shows that both of the cyclophanes possess rectangular covalent frameworks. Furthermore, these cyclophanes form self-assembled tapes in the solid state, since the dibenzofuran moieties have a tendency to associate with each other through crossed ∞-∞ stacks. The dibenzofuran-containing catenanes also form two-dimensional supramolecular arrays in the solid state on account of extended ∞-∞ stacking interactions. In addition, the serendipitous discovery of a plerotopic tecton (consisting of a dibenzofuran nucleus covalently linked from the 2- and 8-positions by methylene groups to 4,4′-pyridylpyridinium (hydrogen bond acceptor) and protonated bipyridinium (hydrogen bond donor) units) has been made. The tecton dimerizes in the solid state to form a supramolecular macrocycle, since its complementary hydrogen bonding sites are oriented in a horseshoelike fashion by the 2,8-disubstituted dibenzofuran unit. However, this superstructure is not retained in the 1:1 complex of the tecton with BPP34C10: cocrystallization of the tecton with this crown ether opens the macrocyclic two-component supermolecule to afford a hydrogen-bonded pseudopolyrotaxane.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030720
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  • 181
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    The C60 Core: A Versatile Tecton for Dendrimer Chemistry (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 561-567 
    Details
    ISSN: 0947-6539
    Keywords: conformation ; dendrimers ; fullerenes ; molecular dynamics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, complete characterization and molecular dynamics simulations of dendrimers 4-8 involving [60]fullerene as core tecton and first- to thirdgeneration benzyl-ether-based dendrons as branches is described. In dendrimer 7 a core branching multiplicity of 12, the highest known to date, is realized for the first time with a Th-symmetrical C60 core having an octahedral addition pattern. This unique structural type of core building block is only possible on the base of C60 and has no precedent in organic chemistry. NMR investigations as well as molecular modelling studies show that, owing to high core branching multiplicity, dendrimer 7 and to a minor extent the mixed adduct 8 already represent globular and densely packed macromolecules, although only first-generation dendrons are involved in their construction.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030411
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    Adsorption of Ionophores and of Their Cation Complexes at the Water/Chloroform Interface: A Molecular Dynamics Study of a [2.2.2]Cryptand and of Phosphoryl-Containing Podands (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 552-560 
    Details
    ISSN: 0947-6539
    Keywords: extraction ; interfaces ; ionophores ; molecular dynamics ; counterion effect ; solvation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report molecular dynamics simulations on ionophores of different topologies and on their complexes with alkali and alkaline-earth cations, with or without counterion, at the water/chloroform interface. As ionophores we consider two phosphoryl-containing podands (the “chainlike” monopodand MP and the “octopuslike” tripodand TP) and the bicyclic cryptand 222. We find that all the solutes behave as surfactants: they remain adsorbed at the interface, without migrating to bulk phases. Their precise location and solvation depend on the nature and conformation of the ionophore, of the cation and of the counterion. Schematically, two types of solutes can be distinguished, depending on their hydrophilic/hydrophobic character. The first type (cryptand 222 and its complexes, or the [MP⋅K+] complex), which have a hydrophobic exterior, stay on the chloroform side of the interface and are partially hydrated by “water fingers”. The second type (free MP and TP, [MP⋅K+]Pic- and [MP⋅Sr2+](Pic-)2 complexes), which are more hydrophilic, are partitioned to a greater extent between the two liquid phases. The status of the ion pairs at the interface depends on the interplay between cation … anion and anion … solvent interactions. When cation-anion interactions are strong enough (as in [MP⋅Sr2+](Pic-)2), the ion pairs remain intimate. Otherwise they dissociate, leading to solvent-separated ion pairs adsorbed at the interface (in the [222⋅K+] Pic- complex) or to the migration of the anion to the water phase (in the [222⋅K+] Cl- complex).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030410
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    Functionalized Lipid Tubules as Tools for Helical Crystallization of Proteins (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 620-625 
    Details
    ISSN: 0947-6539
    Keywords: helical structures ; lipids ; liposomes ; self-assembly ; tubules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of functional supramolecular devices built by self-assembly of elementary molecules and with bioactive properties arouses considerable interest in the field of nanotechnology and new materials. We report here the formation of a new class of lipid tubules exhibiting both properties of molecular recognition and crystal formation for the protein streptavidin. These lipid tubules, made of biotin-containing dioctadecylamine molecules, are straight hollow cylinders with a constant diameter of 27 nm and variable length up to several micrometers. They are unilamellar with an inner diameter of about 16 nm, as shown by cryoelectron microscopy. Streptavidin binds to the biotinylated tubules and assembles spontaneously into ordered helical arrays at the tube surface. These crystals exhibit regular order up to about 1.5 nm resolution. In addition, the helical streptavidin arrays act as functionalized supramolecular devices that bind a wide variety of biotinylated objects, as demonstrated here with proteins and liposomes.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030419
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    Masthead (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997) 
    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.19970030502
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  • 185
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    Calix[4]arene-Based (Hemi)carcerands and Carceplexes: Synthesis, Functionalization, and Molecular Modeling Study (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 639-654 
    Details
    ISSN: 0947-6539
    Keywords: calixarenes ; carcerands ; inclusion compounds ; molecular devices ; resorcinarenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 11 calix[4]arene-based carceplexes obtained by solvent or doped inclusion is reported. Carceplexes with amides, for example, DMF, NMP, and 1,5-dimethyl-2-pyrrolidinone, and sulfoxides, for example, DMSO and thiolane-1-oxide, were obtained by solvent inclusion. In these cases the yield of the carceplex decreases with increasing guest size. Potential guests that do not form carceplexes by solvent inclusion, such as 2-butanone and 3-sulfolene, could be incarcerated by doped inclusion with 1,5-dimethyl-2-pyrrolidinone as a solvent “doped” with 5-15 vol% of potential guest. The amide bridges of the carceplexes were converted into thioamide bridges in essentially quantitative yield by means of Lawesson's reagent in refluxing xylene. The dynamic properties of the incarcerated guests were examined by 2D NMR spectroscopy. Whereas for most guests a preference for one orientation inside the calix[4]arene-based (thia)carcerands was observed, for DMA, NMP, and ethyl methyl sulfoxide inside calix[4]arene-based (thia)carcerands two different orientations were present. The energy barriers for interconversion between the various orientations of DMA, NMP, and ethyl methyl sulfoxide inside calix[4]arene-based (thia)-carcerands were determined with 2D EXSY NMR. The energy barriers are higher for the thiacarcerands than for the corresponding carcerands with amide bridges. This may be due to the stronger hydrogen-bond-donating character of the thioamide group. Furthermore, molecular modeling simulations indicate that in case of the thiacarcerand the cavity is smaller as a result of a smaller diametrical distance between the NH atoms. Our results demonstrate that molecular modeling can be used to estimate the energy barriers for interconversion; the calculated activation energies showed good quantitative agreement with the experimental values.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030421
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  • 186
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    Control of the Helical Chirality in Octahedral Complexes by a Chiral Macrobicyclic Cavity Possessing Six Convergent Hydroxyl Groups (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 969-973 
    Details
    ISSN: 0947-6539
    Keywords: chirality ; coordination modes ; macrocyclic ligands ; octahedral complexes ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The (aR, aR, aR) and (aS, aS, aS) enantiomers of a chiral macrobicyclic ligand with a bicapped tris(binaphthol) structure were synthesized. Complexation of gallium(III), chromium(III) and iron(III) centres in the chiral cavities of these two ligands yielded exclusively one octahedral configuration in each case: the (aR, aR, aR) enantiomer gave a A complex and the (aS, aS, aS) enantiomer a complex. These assignments were established by CD spectroscopy for chromium and iron centres and by molecular modelling.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030619
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  • 187
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    Cover page (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030701
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  • 188
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    Graphical abstract (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 999-1003 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030703
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  • 189
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    Synthesis of Glycodendrimers by Modification of Poly(propylene imine) DendrimersSynthetic carbohydrate dendrimers, part 3. For part 2, see: P. R. Ashton, S. E. Boyd, C. L. Brown, N. Jayaraman, J. F. Stoddart, Angew. Chem. Int. Ed. Engl. 1997, 36, issue 7. A list of abbreviations used in this paper is given in ref. [37]. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 974-984 
    Details
    ISSN: 0947-6539
    Keywords: carbohydrates ; dendrimers ; glycosides ; neoglycoconjugates ; polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of preformed poly-(propylene imine) dendrimers (DAB-dendr-(NH2)x) for the rapid and facile construction of high molecular weight carbohydrate-coated dendrimers (glyco-dendrimers) is presented. An efficient attachment of spacer-armed derivatives of D-galactose and lactose to the primary amino end groups of DAB-dendr-(NH2)x has been achieved by means of amide bond formation, using the N-hydroxysuccinimide coupling procedure. Acetate protecting groups have been employed in order to avoid side reactions at the coupling stage. Deacetylation leads to the target glycodendrimers. The reactivity of all the available DAB-dendr-(NH2)x (generations 1-5) has been investigated and a series of homologous carbohydrate-coated dendrimers have been synthesized. In addition, the attachment of larger saccharide moieties has been demonstrated by the condensation of a trisgalactoside cluster with DAB-dendr-(NH2)x carrying both four and eight primary amino groups. The regularity of the glycodendrimers has been proven by NMR spectroscopy, and the molecular weights of the low-generation carbohydrate-coated dendrimers have been determined by mass spectrometry. Modifications of DAB-dendr-(NH2)x with biologically active carbohydrates affords a new and simple approach to high molecular weight compounds that may be considered as neoglycoconjugates with perfectly symmetrical structures and that offer much promise as multivalent ligands involved in carbohydrate-protein interactions.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030620
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  • 190
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    Trapping of Radicals in the Coordination Spheres of Metals (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1005-1008 
    Details
    ISSN: 0947-6539
    Keywords: alkali metals ; calcium ; ketyl radicals ; radicals ; samarium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of hexamethylphosphoramide (HMPA) or other sterically demanding groups as stabilizing ligands allows the successful isolation of a series of structurally characterizable complexes of ketyl radicals with alkali, alkaline earth, and lanthanide metal. It has been demonstrated that the stability and reactivity of the ketyl radicals strongly depend on both the nature of the metals to which they are bound and the steric and electronic properties of the ancillary ligands, as well as the structure of their parent ketones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030704
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  • 191
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    Indium-Mediated Reactions of Enamines in the Presence of Acid (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1064-1070 
    Details
    ISSN: 0947-6539
    Keywords: allylations ; enamines ; iminium salts ; indium ; zinc ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of enamines with allyl bromide and metallic indium in THF to afford homoallylamines was greatly accelerated by the addition of one equivalent of a suitable carboxylic acid, such as acetic acid. It was established that the likely mechanism consists of a nucleophilic addition of an indium sesquihalide to the iminium salt formed by protonation of the enamine. Substituted allyl bromides also reacted with complete allylic transposition (γ-addition). In contrast to indium-mediated allylation of carbonyl compounds in which only two of the three allyl groups of the sesquihalide are involved, all three allyl groups are involved in the reaction with enamines. As a result only 2/3 equiv of indium are required. This allylation was also performed with zinc, tin, bismuth, and aluminum in the presence of a catalytic amount of InCl3 instead of indium. However, these reactions invariably gave lower yields. The analogous reaction of methyl bromoacetate instead of allyl bromide was also studied. This “Reformatsky-type” process was also greatly accelerated by the addition of one equivalent of acetic acid. In this case, the yields remained moderate for both indium and zinc.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/chem.19970030713
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  • 192
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    Effect of Melamine-Amphiphile Structure on the Extent of Two-Dimensional Hydrogen-Bonded Networks Incorporating Barbituric Acid (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1077-1082 
    Details
    ISSN: 0947-6539
    Keywords: amphiphiles ; barbituric acid ; hydrogen bonds ; melamines ; molecular recognition ; monolayers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four alkyl melamine amphiphiles each containing identical triads of hydrogen-bonding sites (hydrogen donor, acceptor, and donor) but different numbers of alkyl chains were examined in order to determine their monolayer properties and binding behavior towards barbituric acid (BA). Their structural organization in supramolecular assemblies at the air-water interface was affected by the bulkiness of the hydrophobic part of the amphiphile. Aqueous BA and amphiphiles with two or three alkyl chains formed a 1:1 alternate network structure. In contrast, a melamine amphiphile with four alkyl chains formed a 2:1 (BA:amphiphile) complex rather than a 1:1 alternate network structure. The 2:1 complex appears to behave like an independent molecular entity without further networking. The results point to the importance of size matching between the hydrophobic part of the monolayer and the underlying hydrogen-bonded network in order to maintain the overall supramolecular structure.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030715
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  • 193
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    Synthesis and Properties of O-Glycosyl Calix[4]Arenes (Calixsugars)This trivial name refers to calixarene derivatives in which one or more mono- or oligosaccharide moieties are bound to either the upper or lower rim by O-or C-glycosidic bond. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1774-1782 
    Details
    ISSN: 0947-6539
    Keywords: calixarenes ; carbohydrates ; glycosylations ; host-guest chemistry ; Mitsunobu reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Model O-glycosylation reactions at either rim of calix[4]arenes are described with the aim of providing access to a new family of carbohydrate-containing calixarene derivatives named calixsugars. One or two sugar moieties (D-mannofuranose and D-glucopyranose) were introduced at the lower rim of the parent calix[4]arene by glycosylation of the phenolic hydroxyl groups by means of a Mitsunobu reaction. Tetrapropoxy calix[4]arenes bearing two or four hydroxymethyl groups at the upper rim were coupled with perbenzoylated thioethyl D-galactoside and D-lactoside in the presence of the thiophilic promoter copper(III) triflate. In this way β-linked bis- and tetrakis-O-galactosyl calix[4]arenes were obtained in good yield, the latter showing some solubility in water. For the O-lactosyl derivatives only the bis-substituted compound could be obtained because of the competing formation of an intramolecular ether linkage between 1,3-hydroxymethyl groups. Preliminary binding studies showed some affinity of the galactose-containing calixsugars toward charged carbohydrates and dihydrogen phosphate anion.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031108
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  • 194
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    Synthesis, Structure and Hydrolysis Studies of Dimethyltris(Trimethylsilyl)Methylmetallanes of Aluminium and GalliumDedicated to Professor Manfred Weidenbruch on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1783-1792 
    Details
    ISSN: 0947-6539
    Keywords: aluminium ; gallium ; hydrolyses ; Si ligands ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of [(Me3Si)3CLi2thf] with Me2MCl (M = Al, Ga) afford the mixed trialkylmetallanes [(Me3Si)3-CAlMe2·thf] (1) and [(Me3Si)3 CGaMe2·thf] (2) in high yields. The coordinated THF molecule of compound 2 can be removed by sublimation in vacuo to yield the solvent-free product [(Me3Si)3-CGaMe2] (3). Hydrolysis of compound 2 with one equivalent of water at 0°C gives the trimeric hydroxide [{(Me3Si)3CGaMe(μ-OH)}3] (4), while the reaction with two equivalents of water at room temperature yields the unusually stable gallium hydroxide-water complex [{(Me3Si)3CGaMe(OH)(μ-OH)MeGaC(SiMe3)3) H2O·2thf] (6). On heating, compound 6 is converted to the hydroxide [{(Me3Si)3C}4Ga4(μ-O)2(μ -OH)4] (5), which has a heteroadamantane-like core. The hydrolysis of compound 1 with one equivalent of water at - 25°C gives the dimeric hydroxide [{(Me3Si)3CAlMe(μ-OH)}2·2thf] (7), while the reaction with two equivalents of water results in the formation of the novel hydroxide [{(Me3Si)3C}4Al4(μ-O)2 (μ-OH)4] (8), which is isostructural to the gallium compound 6 with the adamantane-like structure. The molecular structures of compounds 1, 2, 4, 5·3THF, 6, 7 and 8·0.5 THF have been determined by X-ray structure analysis. Compound 7 is the first structurally characterised aluminium hydroxide containing methyl groups, and 8 is the smallest structurally characterised galloxane hydroxide described in literature.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031109
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  • 195
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    Intermediates in the Catalytic Dehydrogenative Coupling of Arylgermanes (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1793-1796 
    Details
    ISSN: 0947-6539
    Keywords: dehydrogenative coupling ; germanium ; platinum ; reaction mechanisms ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of a new electron-withdrawing germane, H2Ge[3,5-(CF3)2C6H3]2 (3), has facilitated the isolation and characterization of three new complexes implicated in the dehydrogenative coupling of bisarylgermanes by Pt0-phos-phane complexes. The intermediates include a digermyl species, trans-[(Et3P)2Pt{GeH(Ar)2}2] (7), a bound digermane showing the first stage of Ge-Ge catenation, cis-[(Et3P)2Pt(H){Ge(Ar)2-GeH(Ar)2}] (8), and the Ge-H activated form of this product, [(Et3P)2HPtGe(Ar)2-Ge(Ar)2PtH(PEt3)2] (6). Complexes such as 6 and 8 have not previously been isolated as intermediates in dehydrogenative coupling reactions. An X-ray crystal structure was determined for complex 6, confirming the cis geometry of the hydrogen and germanium ligands; this provides yet another example of the stability of germyl hydrides towards reductive elimination. A similar cis geometry was observed for complex 8. Performing the dehydrogenative coupling reaction under a CO2 atmosphere failed to yield any products containing trapped germylene species.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031110
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  • 196
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    Two New Closely Related MoV Hydroxymonophosphates Built Up of Cd[Mo6P4O25(OH)6]2 And Cd[Mo6P4O26(OH)5]2 ClustersDedicated to Professor H. G. von Schnering on the occasion of his retirement (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1797-1800 
    Details
    ISSN: 0947-6539
    Keywords: cadmium ; crystal structure ; hydrothermal synthesis ; hydroxyphosphate ; molybdenum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new molybdenum(v) hydroxyphosphates have been synthesized hydrothermally, Na2Cd3(Mo2O4OH)6-(PO4)2(PO3OH)6[N(CH3)4]4·10H20 (1) and Cd9(Mo2O4OH)12(PO4)6(PO3OH)10-[N(CH3)4]8·15H2O (2). Their structures have been determined from single-crystal X-ray diffraction. The water molecules and hydroxyl groups have been deduced from valence calculations. Both compounds crystallize in the triclinic space group P1, with the cell parameters for 1 a = 12.340(2), b = 12.596(1), c = 14.717(2) Å, α = 107.24(1)°, β = 89.83(1)°, γ = 114.31(1)°, V = 1972.3(4) Å3, and for 2 a = 11.942(1), b = 13.339(2), c = 26.765(3) Å, α = 85.33(1)°, β = 86.87(1)°, γ = 64.08(1)°, V = 3821.3(9) Å3. The two frameworks can be described on the basis of similar [Mo6P4X31]n- (X = O, OH) anionic clusters, but 1 is a tridimensional structure, whereas 2 exhibits a monodimensional structure.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031111
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  • 197
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    Aggregation, Reaggregation and Degradation of a Trifunctional Thallium(I) Amide Induced by Weak TlI ⃛ TlI AttractionDedicated to Professor Mary McPartlin on the occasion of her 65th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1801-1806 
    Details
    ISSN: 0947-6539
    Keywords: aggregations ; amides ; metal-metal interactions ; subvalent compounds ; thallium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal exchange of the solvated tripodal lithium amide [H3CC{CH2N(Li-solv)SiMe3}3] (1, solv = ether solvent) with thallium(I) chloride leads to the previously reported pentametallated dimeric thallium amide [{H3CC(CH2NSiMe3)3}2(H)Tl5] (2) in high yield. That the redox-induced partial demetallation of the amide presumably occurs at an intermediate stage of the metal exchange is inferred from the isolation and structural characterization of the mixed Tl-Li amide [H3CC{CH3N(Tl) SiMe3}3][H3CC{CH2NSiMe3}3(H)(Tl)(Li-thf)]·(toluene) (3), which has a crystal structure closely related to that of 2. In both cases the central structural motif, defined by weakly attractive Tl⃛ Tl contacts, is a tetrahedral metal array in which a triangular thallium triamide unit is capped by an exposed Tl atom of a second building block. Compound 3 may be converted to 2 by metal exchange with TlCl. The two supramolecular components of 2 reaggregate upon recrystallization in a nonpolar solvent such as pentane to yield the dimeric aggregate of the fully metallated thallium amide [H3CC{CH2N(Tl)-SiMe3}3]2 (4). An X-ray crystallographic study of 4 established the existence of dimeric aggregation through Tl ⃛ Tl interactions leading to a more open dimeric form than 2 and 3, which is interpreted as being due to a structural mismatch of the building blocks. Compound 4 may be thermally degraded by prolonged stirring in toluene at ambient temperature to yield the previously reported mixed-valence TlITlII amide [H3CC(CH2NSiMe3)3Tl2] (5).
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031112
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    Biomimetic Crystallization of Calcium Carbonate Polymorphs by Means of Collagenous Matrices (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1807-1814 
    Details
    ISSN: 0947-6539
    Keywords: aragonite ; biomineralization ; calcite ; crystal growth ; peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crosslinked gelatin films with entrapped poly-L-aspartate were used to induce the crystallization of calcite and aragonite polymorphs. Calcite with high degrees of isomorphous substitution (up to 12mol% magnesium) has been obtained. The morphology and layered organization of magnesium calcite crystals grown inside the crosslinked gelatin films with entrapped poly-L-aspartate resemble some structural features of radial calcitic ooids. The concentration of entrapped poly-L-aspartate and the uniaxial deformation of the films control the growth of aragonite aggregates inside the films. Such aggregates grown inside uniaxially deformed films consist of parallel rods with an architectural assembly similar to that found in some marine organisms. The crystals' aggregation and the control of calcium carbonate polymorphism are related to the modelling of the nucleation sites by poly-L-aspartate structure and concentration, local supersaturation and microenvironment shape. The results indicate that the collagenous matrices with entrapped polyelectrolytes are versatile systems which can contribute to the elucidation of strategies for biomimetic materials chemistry.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031113
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  • 199
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    Calix[4]Arene Podands and Barrelands Incorporating 2,2″-Bipyridine Moieties and Their Lanthanide Complexes: Luminescence Properties (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1815-1822 
    Details
    ISSN: 0947-6539
    Keywords: calixarenes ; lanthanides ; luminescence ; molecular dynamics ; N ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new family of cone-shaped podands and barrel-shaped cryptands based on calix[4]arenes incorporating 5,5′-substituted 2,2′-bipyridine subunits were prepared and characterized. The Eu3+ and Tb3+ complexes of the podands bearing two, three, or four bipyridine chromophores could be isolated. High molar absorption coefficients (εmax = 39 600M-1 cm-1 for Eu4 and 26 700M-1 cm-1 for Eu3) and high metal luminescence quantum yields (16% for Eu4 and 15% for Eu3) were obtained. Molecular dynamics simulations on Eu4 showed that the bipyridine arms wrap around the lanthanide cation, efficiently shielding the cation from solvent molecules. In the presence of chloride counter-ions the fourth bipyridine arms does not coordinate the lanthanide ion. Ligands bearing two bipyridine units and two additional functional groups - ethyl butyrate or N-propylpyrrole - did not give stable lanthanide complexes. The barre-land containing two calix[4]arene moieties and four bipyridine groups did not form complexes with lanthanide ions, most probably because of the rigidity of the ligand.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031114
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  • 200
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    Noncovalent Assembly of Functional Groups on Calix[4]Arene Molecular Boxes (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1823-1832 
    Details
    ISSN: 0947-6539
    Keywords: calixarenes ; hydrogen bonds ; molecular boxes ; noncovalent assembly ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calix[4]arenes diametrically substituted at the upper rim with two melamine units spontaneously form well-defined box-like assemblies in the presence of two equivalents of 5,5-diethylbarbituric acid. These assemblies, consisting of nine different components, are held together by 36 hydrogen bonds and are stable in apolar solvents at concentrations of up to 10-4M. This paper reports the first X-ray crystal structure, and the MALDI TOF mass spectra together with the complete 1H NMR spectroscopic characterization of these hydrogen-bonded assemblies. The crystal structure clearly shows that the assemblies are stereogenic, as a result of the antiparallel orientation of the two rosette motifs. Furthermore, the synthesis of twelve new 1,3-bis(melamine)calix[4]arenes carrying different numbers and types of functionalities at the upper rim is described. Detailed 1H NMR spectroscopic studies on the assembly behavior of these functionalized calix[4]arenes shows that 1) polar substituents (e.g. nitro, cyano) hardly affect the stability of the hydrogen-bonded assembly; 2) hydrogen bond donating or accepting groups, like amino and acetamido, can disturb assembly of the boxes under certain conditions by destabilizing the calix[4]arene pinched cone conformation as a result of intramolecular hydrogen bond formation; and 3) sterically bulky groups (e.g. tBu) can significantly inhibit the formation of the hydrogen-bonded assembly, but this effect very much depends on the exact positions of the groups.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19970031115
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