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  • 1995-1999  (6,967)
  • 1998  (6,967)
  • Chemistry  (5,970)
  • Polymer and Materials Science  (2,108)
  • Life and Medical Sciences  (565)
  • Analytical Chemistry and Spectroscopy  (163)
  • Magnetic resonance imaging  (133)
  • Nuclear reactions
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Years
  • 1995-1999  (6,967)
Year
Keywords
  • 101
    Electronic Resource
    Electronic Resource
    Magnetic resonance imaging of the bone marrow in hematological malignancies (1998)
    Springer
    European radiology 8 (1998), S. 1335-1344 
    Details
    ISSN: 1432-1084
    Keywords: Key words: Hematology ; Bone marrow ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Despite its lack of specificity, magnetic resonance imaging (MRI) of the bone marrow has the potential to play a role in the management of patients with primary neoplastic disorders of the hematopoietic system, including lymphomas, leukemias and multiple myeloma. In addition to its use in the assessment of suspected spinal cord compression, bone marrow MRI could be used as a prognostic method or as a technique to assess the response to treatment. The current review addresses the common patterns of bone marrow involvement observed in primary neoplasms of the bone marrow, basic technical principles of bone marrow MRI, and several applications of MRI in selected clinical situations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003300050548
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  • 102
    Electronic Resource
    Electronic Resource
    MR imaging of a malignant schwannoma and an osteoblastoma with fluid-fluid levels. Report of two new cases (1998)
    Springer
    European radiology 8 (1998), S. 1359-1362 
    Details
    ISSN: 1432-1084
    Keywords: Key words: Bone neoplasms ; Soft tissue neoplasms ; Magnetic resonance imaging ; Osteoblastoma ; Schwannoma ; Neurilemmoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. One case of malignant schwannoma of the sacrum and another of occipital osteoblastoma were evaluated by MR imaging. Both tumors showed fluid-fluid levels with different signal intensities in the sequences performed. Pathologic examination revealed hemmorhagic fluid in both tumors. Malignant schwannoma and osteoblastoma should be included in the list of bone and soft-tissue with fluid-fluid levels. Our data confirm the non-specificity of this finding, which only suggests the presence of previous intratumoral hemorrhage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003300050552
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  • 103
    Electronic Resource
    Electronic Resource
    MRI of the rectum: non-neoplastic disease (1998)
    Springer
    European radiology 8 (1998), S. 3-8 
    Details
    ISSN: 1432-1084
    Keywords: Key words: Rectum ; Diagnosis ; Magnetic resonance imaging ; Congenital disorders ; Inflammatory diseases ; Vascular
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The rectum has become the most successful area of the gastrointestinal tract to be studied with MRI. Its anatomical location, fixed in the pelvic fat, and its lack of peristalsis, make it an ideal organ to be scanned with MRI. In addition, MRI allows a direct sagittal and coronal display, of key importance to colorectal surgeons whose terminology and approach are based on the coronal plane. The sagittal plane allows the depiction of the relation of the rectum to the sacrum, uterus and prostate, with detail not available by other imaging techniques, and the use of endorectal coils allows excellent demonstration of the rectal wall. Although MRI has been used primarily to study rectal carcinoma, other diseases, congenital, inflammatory and vascular in origin, can be studied using the correct technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003300050328
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  • 104
    Electronic Resource
    Electronic Resource
    Gadolinium-DTPA enhancement of symptomatic nerve roots in MRI of the lumbar spine (1998)
    Springer
    European radiology 8 (1998), S. 116-122 
    Details
    ISSN: 1432-1084
    Keywords: Key words: Spine ; Magnetic resonance imaging ; Nerves ; spinal ; Radiculitis ; Contrast media ; paramagnetic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Disc prolapse presenting with sciatica may be associated with enhancement of the symptomatic nerve root following magnetic resonance imaging (MRI) with intravenous gadolinium (Gd)-DTPA. Previous studies have shown, however, that this does not occur in all cases. The aim of this study was to assess the incidence of nerve root enhancement in patients with sciatica and disc prolapse and to try to identify any specific features that might be associated with the phenomenon. A total of 227 patients presenting with low back pain and/or sciatica underwent a MRI study of the lumbar spine with intravenous contrast enhancement. Nineteen of 81 (23.5 %) patients with disc prolapse demonstrated nerve root enhancement. Nerve root enhancement had a highly significant association with sequestrated disc lesions (13/19, 68 %; P 〈 0.0005), and was primarily seen in the symptomatic ipsilateral nerve root (16/19, 84 %). The sensitivity of nerve root enhancement associated with disc prolapse was 23.5 % with a specificity of 95.9 %, a positive predictive value of 76 % and a negative predictive value of 69.3 %. Nerve root enhancement may be indicative of the symptomatic level but its poor sensitivity negates the routine use of Gd-DTPA in MRI for sciatica.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003300050350
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  • 105
    Electronic Resource
    Electronic Resource
    Laryngeal embryonal rhabdomyosarcoma in a child: MRI appearance (1998)
    Springer
    European radiology 8 (1998), S. 1251-1253 
    Details
    ISSN: 1432-1084
    Keywords: Key words: Rhabdomyosarcoma ; Magnetic resonance imaging ; Larynx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. We report a rare case of a young girl with an embryonal rhabdomyosarcoma of the right aryepiglottic fold. Local disease recurrence, occurring 7 years after subtotal resection and adjuvant chemotherapy, was studied with plain radiography, CT and MRI. To the best of our knowledge, this is the first report illustrating the MRI characteristics of a laryngeal embryonal rhabdomyosarcoma in a child.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003300050544
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  • 106
    Electronic Resource
    Electronic Resource
    Intraosseous lipomata of adjacent vertebral bodies (1998)
    Springer
    European spine journal 7 (1998), S. 344-347 
    Details
    ISSN: 1432-0932
    Keywords: Key words Lipoma ; Computed tomography ; Magnetic resonance imaging ; Radiography ; Vertebral
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Osseous lipomata of vertebral bodies are rare. We present a very unusual case where adjacent vertebrae are involved and the plain radiographic and scintigraphic appearances gave cause for some concern. The findings on plain films, scintigraphy, computed tomography and magnetic resonance imaging are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005860050086
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  • 107
    Electronic Resource
    Electronic Resource
    A kindred affected by cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) (1998)
    Springer
    Journal of neurology 245 (1998), S. 217-222 
    Details
    ISSN: 1432-1459
    Keywords: Key words Vascular dementia ; Dominant inheritance ; Cognition ; Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We report a 2-year prospective neuropsychological study of five asymptomatic subjects with magnetic resonance imaging (MRI) abnormalities from an Italian kindred affected by cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). These subjects completed tests for attention capacities, processing speed, abstract thinking, short-term memory, learning and constructional praxis. Seven normal subjects matched for age and education, belonging to the same pedigree and not having MRI hyperintensities were examined as controls. The results did not show significant differences between asymptomatic subjects and normal controls. Cognitive performance of asymptomatic subjects did not deteriorate during a 2-year follow-up. Our findings suggest that, at this stage of the disease process, the presence of diffuse leukoencephalopathy does not imply subtle cognitive defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050208
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  • 108
    Electronic Resource
    Electronic Resource
    The role of morpho-volumetric and memory correlations in the diagnosis of early Alzheimer dementia (1998)
    Springer
    Journal of neurology 245 (1998), S. 525-530 
    Details
    ISSN: 1432-1459
    Keywords: Key words Alzheimer dementia ; Magnetic resonance imaging ; Temporal lobe ; Amygdala ; High ; signal lesions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of the present study was to assess selective atrophy of the temporal lobe and amygdala in the early stages of Alzheimer dementia (AD). Magnetic resonance imaging (MRI) measurements and the presence of highsignal lesions (HSL) were analysed in 31 patients with mild to moderate probable AD and 22 controls. In the AD group, MRI findings were compared with cognitive variables and specific features of memory functions. Alzheimer patients showed a significant reduction in volumetric measurement compared with controls in the total volume (P 〈 0.01), temporal lobe (P 〈 0.01) and amygdala (P 〈 0.05). The temporal lobe/brain volume ratio was also significantly reduced in AD subjects (P 〈 0.05). Atrophy of temporal structures was significantly related to the degree of episodic and semantic memory impairment according to a material-specific effect. No significant correlations between amygdala and cognitive variables were found. The results of our study confirm the usefulness of measures of temporal lobe atrophy assessed with MRI in the diagnosis of AD. In contrast, HSL are relatively common in AD patients (12/31 cases) and were not related to volumetric findings, severity of dementia or functional disability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050237
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  • 109
    Electronic Resource
    Electronic Resource
    Postpartum magnetic resonance imaging in a case of placenta accreta with intrauterine abscess formation (1998)
    Springer
    Archives of gynecology and obstetrics 262 (1998), S. 91-94 
    Details
    ISSN: 1432-0711
    Keywords: Key words: Placenta accreta ; Uterine abscess ; Magnetic resonance imaging ; CT scan ; Ultrasound
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The postpartum magnetic resonance imaging (MRI) appearance of a patient with placenta accreta and abscess formation is presented here and compared to the ultrasound and CT findings. The diagnosis was confirmed on histopathologic examination and cultures of the hysterectomy specimen. On MRI, the T1-weighted acquisitions showed an enlarged uterus of mildly heterogeneous but predominantly low signal intensity. The T2-weighted images demonstrated a heterogenous area of predominantly bright signal within the uterine body and fundus. In this case, MRI was more informative than ultrasound and non-contrast CT scan in the postpartum diagnosis of placenta accreta with abscess formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004040050234
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  • 110
    Electronic Resource
    Electronic Resource
    IV ventricle astrocytomas in childhood: clinicopathological features in 21 cases (1998)
    Springer
    Child's nervous system 14 (1998), S. 537-546 
    Details
    ISSN: 1433-0350
    Keywords: Key words Fourth ventricle ; Brain stem ; Cerebellum ; Astrocytoma ; Brain neoplasms ; Craniotomy ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The authors conducted a study of 21 children with benign astrocytomas in the IV ventricle treated with radical tumor resection from 1982 through 1991. The purposes of this study were to identify the tumor origin and neural involvement, and to determine the natural history following surgical resection. Pathological studies showed that 18 were pilocytic astrocytomas (pure pilocytic in 12, mixed in 6), 2 fibrillary, and 1 gemistocytic. In the IV ventricle, 12 patients had a transependymal involvement of the floor (brain stem), 6 had an involvement of the wall (cerebellar peduncle), and 3 had involvement of both floor and wall. A gross total resection was performed in 9 patients, and the remaining 12 patients underwent a subtotal resection. All patients were followed without radiation therapy (RT) or chemotherapy. During a follow-up period of 6.5–15 years, all patients were alive. Eight patients suffered recurrence between five months and 66 months after diagnosis. Of these, five received RT for recurrence and had a complete response in all cases. The remaining 13 patients showed no evidence of disease and one had a stable residual tumor. The recurrence-free 5-year and 10-year survival rates were 62.5% and 57% respectively. Patients without brainstem involvement, with total resection, or with pure pilocytic astrocytoma had a better outcome than those with brain stem involvement, with subtotal resection, or with nonpilocytic or mixed histology. In summary, a great majority of benign IV ventricle astrocytomas involve the floor of the IV ventricle. It is often difficult to determine the origin of these tumors in most cases. Benign IV ventricle astrocytomas may not recur even after incomplete resection, and close observation without RT is recommended, although RT appears to be effective for these tumors when they recur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003810050269
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  • 111
    Electronic Resource
    Electronic Resource
    Optic atrophy as the first symptom in Hallervorden-Spatz syndrome (1998)
    Springer
    Child's nervous system 14 (1998), S. 135-138 
    Details
    ISSN: 1433-0350
    Keywords: Key words Hallervorden-Spatz syndrome ; Optic atrophy ; Basal ganglia ; Iron deposits ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A 16-year-old boy with the classic or postinfantile type of Hallervorden-Spatz syndrome is described. Bilateral optic atrophy with visual loss but without retinal changes was the only presenting symptom. Mild cognitive impairment, behavioural disturbances and insidious extrapyramidal involvement appeared later. MRI showed marked symmetrical hypointensity of the globi pallidi and substantia nigra. This new observation suggests that the occurrence of optic atrophy in a patient with Hallervorden-Spatz syndrome should be regarded as noncoincidental and stresses the importance of an accurate neurological work-up in all adolescents with any unusual form of progressive optic atrophy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003810050196
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  • 112
    Electronic Resource
    Electronic Resource
    Slipped capital femoral epiphysis: a physeal lesion diagnosed by MRI, with radiographic and CT correlation (1998)
    Springer
    Skeletal radiology 27 (1998), S. 139-144 
    Details
    ISSN: 1432-2161
    Keywords: Key words Slipped capital femoral epiphysis ; Physis ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Objective. To define and compare early lesions associated with slipped capital femoral epiphysis (SCFE) on magnetic resonance imaging (MRI), computed tomography (CT) and radiography. Design and patients. Thirteen patients with 15 symptomatic hips due to SCFE underwent radiography and MRI; CT was performed in 12 patients. SCFE was graded on radiographs, head/neck angles and qualitative changes were evaluated on CT, and morphologic/signal abnormalities were determined on MRI. Results. Physeal widening, apparent on T1-weighted MRI, was evident in every case of SCFE, including one presumed “pre-slip.” T2-weighted images demonstrated synovitis and marrow edema but obscured physeal abnormalities. CT head/neck angles ranged from 4–57° for symptomatic to 0–14° for asymptomatic hips. Physeal and metaphyseal changes were variably identified on both radiographs and CT in all cases of SCFE, but not in the pre-slip. Conclusion. MRI clearly delineates physeal changes of both pre-slip and SCFE, and demonstrates very early changes at a time when radiographs and CT may appear normal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002560050353
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  • 113
    Electronic Resource
    Electronic Resource
    Parosteal osteoma of the iliac bone (1998)
    Springer
    Skeletal radiology 27 (1998), S. 161-163 
    Details
    ISSN: 1432-2161
    Keywords: Key words Parosteal osteoma ; Iliac bone ; Computed tomography ; Magnetic resonance imaging ; Partial regression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  A 33-year-old patient with a 2-year history of intermittent pain in the right gluteal region and thigh presented with a large sclerotic lesion of the iliac bone. From the findings on radiography, scintigraphy, CT and MRI, a giant parosteal osteoma was suspected. The histological examination confirmed the diagnosis. Since the lesion was extensive it was observed with periodic follow-up examinations. At present, 5 years after the diagnosis, the patient is asymptomatic and imaging studies show that the lesion persists with reduction of sclerosis and size. The tumor was on the surface as well as intramedullary – only one other case with such a distribution is known to us – and it was also in the iliac bone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002560050357
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  • 114
    Electronic Resource
    Electronic Resource
    Subcutaneous granuloma annulare: radiologic appearance (1998)
    Springer
    Skeletal radiology 27 (1998), S. 266-270 
    Details
    ISSN: 1432-2161
    Keywords: Key words Granuloma annulare ; Magnetic resonance imaging ; Soft-tissue tumors ; Rheumatoid nodule ; Pseudo-rheumatoid nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Objective. Granuloma annulare is an uncommon benign inflammatory dermatosis characterized by the formation of dermal papules with a tendency to form rings. There are several clinically distinct forms. The subcutaneous form is the most frequently encountered by radiologists, with the lesion presenting as a superficial mass. There are only a few scattered reports of the imaging appearance of this entity in the literature. We report the radiologic appearance of five cases of subcutaneous granuloma annulare. Design and patients. The radiologic images of five patients (three male, two female) with subcutaneous granuloma annulare were retrospectively studied. Mean patient age was 6.4 years (range, 2–13 years). The lesions occurred in the lower leg (two), foot, forearm, and hand. MR images were available for all lesions, gadolinium-enhanced imaging in three cases, radiographs in four, and bone scintigraphy in one. Results. Radiographs showed unmineralized nodular masses localized to the subcutaneous adipose tissue. The size range, in greatest dimension on imaging studies, was 1–4 cm. MR images show a mass with relatively decreased signal intensity on all pulse sequences, with variable but generally relatively well defined margins. There was extensive diffuse enhancement following gadolinium administration. Conclusion. The radiologic appearance of subcutaneous granuloma annulare is characteristic, typically demonstrating a nodular soft-tissue mass involving the subcutaneous adipose tissue. MR images show a mass with relatively decreased signal intensity on all pulse sequences and variable but generally well defined margins. There is extensive diffuse enhancement following gadolinium administration. Radiographs show a soft-tissue mass or soft-tissue swelling without evidence of bone involvement or mineralization. This radiologic appearance in a young individual is highly suggestive of subcutaneous granuloma annulare.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002560050379
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  • 115
    Electronic Resource
    Electronic Resource
    Orientation-dependent changes in MR signal intensity of articular cartilage: a manifestation of the “magic angle” effect (1998)
    Springer
    Skeletal radiology 27 (1998), S. 306-310 
    Details
    ISSN: 1432-2161
    Keywords: Key words Joints ; Knee joints ; Cartilage ; Magnetic resonance imaging ; Susceptibility effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Objective: To study magnetic resonance (MR) imaging pattern of normal hyaline articular cartilage in the knee joint with regard to the contribution of the “magic angle” effect to the MR signal. Design. Thirty-two healthy volunteers were imaged in a standard supine position in a 1.5-T unit using spin echo and gradient echo sequences. Nine volunteers were reimaged with the knee flexed. The signal behavior of the hyaline cartilage of the femoral condyles was evaluated qualitatively and quantitatively. The extended and flexed positions of the nine volunteers were compared. Results. A superficial and a deep hyperintense layer and a hypointense middle cartilage layer were observed. Segments of increased signal intensity were visible along the condyles; a magic angle effect on signal intensity was evident in the hypointense middle layer with both gradient echo and spin echo images. Conclusion. The MR signal behavior of hyaline cartilage is influenced by the alignment of the collagen fibers within the cartilage in relation to the magnetic field. Failure to recognize this effect may lead to inaccurate diagnosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002560050387
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  • 116
    Electronic Resource
    Electronic Resource
    Cerebellitis presenting as acute hydrocephalus (1998)
    Springer
    Child's nervous system 14 (1998), S. 139-141 
    Details
    ISSN: 1433-0350
    Keywords: Key words Cerebellitis ; Hydrocephalus ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A 14-year-old boy presented acutely with occipital headache, nausea and vomiting. MRI showed obstructive hydrocephalus and marked bilateral cerebellar swelling with increased signal on T2-weighted imaging. Following treatment with oral corticosteroids, the clinical and radiological signs resolved. The clinical course and radiological appearances were consistent with cerebellitis associated with a significant mass effect and hydrocephalus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003810050197
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  • 117
    Electronic Resource
    Electronic Resource
    Diffuse bilateral thalamic astrocytomas as examined serially by MRI (1998)
    Springer
    Child's nervous system 14 (1998), S. 384-388 
    Details
    ISSN: 1433-0350
    Keywords: Key words Diffuse astrocytoma ; Bilateral thalamic astrocytomas ; Computed tomography ; Magnetic resonance imaging ; Hyperfractionated radiotherapy ; Chemotherapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We report the case of a 13-year-old girl with diffuse bilateral thalamic astrocytomas. Incoordination was observed at the onset. Cranial computed tomography (CT) showed enlarged thalami, and magnetic resonance imaging (MRI) revealed these lesions to be symmetrically enlarged with high intensity on the T2-weighted image. Owing to these atypical findings in the neuroimaging studies, we had difficulty in making the correct diagnosis of a brain tumor. After the diagnosis of diffuse bilateral thalamic astrocytomas was obtained, we performed hyperfractionated radiotherapy followed by chemotherapy. Radiation therapy was effective for a while, but the girl's condition deteriorated again and she died 8 months after admission. Although diffuse bilateral thalamic astrocytomas are difficult to diagnose because they do not resemble most other neoplasms on neuroimaging studies, pediatricians should keep this entity in mind in order to arrive at a precise and prompt diagnosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003810050250
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  • 118
    Electronic Resource
    Electronic Resource
    Choroid plexus cyst of the left lateral ventricle with intermittent blockage of the foramen of Monro, and initial invagination into the III ventricle in a child (1998)
    Springer
    Child's nervous system 14 (1998), S. 700-708 
    Details
    ISSN: 1433-0350
    Keywords: Key words Choroid plexus cyst ; Lateral ventricle ; Intraventricular cyst ; Magnetic resonance imaging ; CT-stereoendoscopy ; Diomed 25 laser
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A cyst of the choroid plexus of the left lateral ventricle with intermittent blockage of the foramen of Monro and initially with invagination of the III ventricle in a child is described. In a 6-week-old boy a ventriculoatrial shunt was implanted for correction of an active asymmetrical hydrocephalus of unknown origin. When he was 3 months of age a water-soluble contrast CT ventriculography revealed a noncolloid cyst localised predominantly in the upper portion of the III ventricle. At that time the ventricular catheter obstructed with choroid plexus was removed; new bilateral catheters in a parieto-occipital region were implanted. In the course of the next 4 years, first the atrial catheter had to be extracted and then the peritoneal catheter was changed, in both cases because of obstruction. Periods of normal life alternated with periods of transient and intermittent symptoms of increased intracranial pressure, papilloedema, and myoclonic jerks. Repeated computed tomography (CT) and magnetic resonance imaging (MRI) showed stabilised hydrocephalus with an enlarged left lateral ventricle. When the boy was 16 years old MRI revealed a choroid plexus cyst in the left lateral ventricle 2 cm in diameter, with a ball-valve type of obstruction of the foramen of Monro. CT stereoendoscopic resection of the wall of a large cyst filled with cerebrospinal fluid was performed, and two additional adnexal small cysts were coagulated using the bipolar coagulator, Diomed 25 laser and scissors; the symptoms then regressed, except for superior bilateral altitudinal anopsia. Light and electron microscopy of the cyst wall is reported. The cyst was composed of collagenic connective tissue lined with a basal lamina lacking in epithelial cells. The preoperative and postoperative MRI are presented. Choroid plexus cysts localised in the anterior part of lateral ventricles are very rare, and all reported cases have been in male patients. According to the literature our case is only the third ever described in a child.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003810050301
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  • 119
    Electronic Resource
    Electronic Resource
    Intramedullary brain stem cyst and trapped IV ventricle after infection with Listeria monocytogenes (1998)
    Springer
    Child's nervous system 14 (1998), S. 747-750 
    Details
    ISSN: 1433-0350
    Keywords: Key wordsListeria monocytogenes ; Magnetic resonance imaging ; Intracerebral cyst ; Neonatal ; Pregnancy complications
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We present the rare case of a girl surviving intrauterine listeria brain stem meningoencephalitis, who subsequently developed hydrocephalus, a trapped IV ventricle and an intramedullary cyst. Such cases have been reported only infrequently, and in earlier cases modern imaging studies were not available. Magnetic resonance imaging has been helpful in our patient to delineate the lesions and plan further treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003810050309
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  • 120
    Electronic Resource
    Electronic Resource
    Einfluß des Hirnödems auf das Rezidivwachstum maligner Gliome (1998)
    Springer
    Der Radiologe 38 (1998), S. 948-953 
    Details
    ISSN: 1432-2102
    Keywords: Schlüsselwörter Maligne Gliome ; Hirnödem ; Rezidiv ; Magnetresonanztomographie ; Key words Malignant glioma ; Brain edema ; Tumor recurrence ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Purpose: To assess the influence of initial preoperative brain edema in malignant gliomas on regrowth patterns. Subjects and methods: 79 patients with histologically verified supratentorial malignant glioma were prospectively studied by magnetic resonance imaging (MRI) before and every 2–3 months after surgery. The median follow-up time was 11 months. We correlated the configuration of the initial vasogenic edema on T2-weighted images with tumor regrowth patterns on contrast-enhanced T1-weighted images. Results: 35/47 tumor regrowths (75%) imitated the initial edema configuration, while 11/47 occurred within the initial tumor bed; in one case tumor recurrence was multilocal. Conclusion: In glioblastoma, tumor regrowth patterns correlate positively with the configuration of the initial vasogenic brain edema. The initial, „presurgical” peritumoral edema should thus be considered when planning further treatment.
    Notes: Zusammenfassung Fragestellung: Beeinflussen Form und Größe des präoperativen peritumoralen Hirnödems die Rezidiventwicklung bei malignen supratentoriellen Gliomen? Methodik: Prospektiv wurden 79 Patienten mit einem malignen supratentoriellen Gliom mit einem standardisierten MRT-Protokoll untersucht. MRT-Untersuchungen erfolgten vor der neurochirurgischen Operation, möglichst innerhalb der ersten 3 Tage nach Operation und während der Nachbeobachtungszeit in Abständen von 2–3 Monaten. Die mediane Nachbeobachtungszeit betrug 11 Monate. Die initiale präoperative Ödemkonfiguration auf den T2-gewichteten MRT-Aufnahmen wurde mit der Rezidivtumorkonfiguration auf den Kontrastmittel verstärkten T1-gewichteten Aufnahmen verglichen. Ergebnisse: 47 Patienten entwickelten während der Nachbeobachtungszeit ein Rezidiv. Die Konfiguration des Rezidivtumors imitierte in 35/47 Patienten (75%) die initiale präoperative Ödemkonfiguration. Bei 11/47 Patienten entwickelte sich ein lokales und bei einem Patienten ein multilokales Rezidiv. Schlußfolgerungen: Die präoperative Tumorödemkonfiguration im T2-gewichteten MRT-Bild korreliert mit der Rezidivtumorausdehnung. Zukünftige Therapiestudien sollten daher die Ausdehnung des initalen präoperativen Ödems als zusätzlichen prognostischen Faktor mitberücksichigen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001170050447
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    Decreased brain intracellular pH measured by 31P-MRS in bipolar disorder: a confirmation in drug-free patients and correlation with white matter hyperintensity (1998)
    Springer
    European archives of psychiatry and clinical neuroscience 248 (1998), S. 301-306 
    Details
    ISSN: 1433-8491
    Keywords: Key words. Bipolar affective disorder ; Phosphorus-31 magnetic resonance spectroscopy ; Magnetic resonance imaging ; Mood disorder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The authors have previously reported decreased intracellular pH (pHi) in the frontal lobes in euthymic bipolar patients treated with lithium using 31P-MRS. White matter hyperintensity (WMHI) is frequently seen in bipolar disorder. To examine a possible effect of lithium on pHi and the relationship between pHi and WMHI, seven drug-free euthymic bipolar patients were examined, and T2-weighted MRI were examined in 14 previously reported bipolar patients. Drug-free patients showed significantly lower pHi than controls. WMHI was associated with low pHi and increased phosphodiester peak. These results suggest that decrease of pHi is not an effect of lithium but is instead related to the pathophysiology of illness. Decrease of pHi and increase of the PDE peak may be the biochemical basis of WMHI in bipolar disorder.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004060050054
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    Stellenwert der kernspintomographie bei der epiphysiolysis capitis femoris (1998)
    Springer
    European journal of trauma 24 (1998), S. 214-220 
    Details
    ISSN: 1615-3146
    Keywords: Epiphysenlösung ; Epiphysiolysis capitis femoris ; Hüftkopf ; Kernspintomographie ; Hüfte ; Röntgendiagnostik ; Slipped epiphysis ; Femur head ; Magnetic resonance imaging ; Hip radiography ; Technology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract Diagnosis and determination of severity of chronic slipped capital femoral epiphysis (SCFE) is usually made from clinical history, physical examination and radiographic measurement of the degree of slippage. Aim of the present study is to evaluate the diagnostic impact of magnetic resonance imaging in early detection of SCFE. We evaluated magnetic resonance imaging of the hips of 5 healthy children in comparison to the findings in conventional radiographs and magnetic resonance imaging of 9 patients with suspected SCFE. The growth plate of healthy objects shows homogenous low signal intensity, constant width up to 3 mm, and is clearly defined against the surrounding osseous structures. The adjacent surface appears homogenous. Patients with suspected SCFE showed widened growth plate (〉 3 mm) in 6 of 9 cases. Articular effusion was seen in all cases of clinical suspected disease. Incongruence of the ondulate surfaces was seen. Here we found flattening of denticulation of the growth plate in addition. Growth plate showed increase of signal intensity in 2 cases.
    Notes: Zusammenfassung Die Diagnose der im Jugendalter spontan auftretenden Epiphysiolysis capitis femoris wurde bislang anhand der klinischen Beschwerden sowie der Bestimmung des Abrutschwinkels in konventionellen Aufnahmen (Beckenübersicht, Aufnahme nach Rippstein) gestellt. Für die Diagnose der Frühformen der Epiphysiolysis capitis femoris exsistiert kein allseits akzeptierter Goldstandard. Ziel der vorliegenden Arbeit war es herauszuarbeiten, inwieweit die Epiphysiolysis capitis femoris charakteristische Zeichen in der Kernspintomographie bietet und ob die MRT in der Lage ist, früher Veränderungen als die konventionellen Methoden zu erkennen. Die Kernspintomographien (1,5-T-, T1- und T2-SE-Sequenzen koronar, sagittal, paraaxial, fakultativ STIR-, TIRM-, FLASH-2D-Sequenzen) von fünf gesunden Kindern wurden standardisiert analysiert und mit den magnetresonanztomographischen Untersuchungen von neun Patienten mit vermuteter Epiphysiolysis capitis femoris verglichen. Bei den neun Patienten lagen zusätzlich konventionelle Röntgenaufnahmen nach Rippstein vor. Im Normalkollektiv stellte sich die Epiphysenfuge homogen signalarm bzw. signalfrei dar. Sie wies eine konstante Weite bis zu 3 mm auf und war gegenüber den angrenzenden knöchernen Strukturen scharf abgegrenzt. Das Grenzflächensignal erschien homogen und gezähnelt. Patienten mit vermuteter Epiphysiolysis capitis femoris zeigten eine Erweiterung der Epiphysenfuge auf mehr als 3 mm in sechs von neun Fällen. Bei allen klinisch verdächtigen Fällen konnte ein Gelenkerguß abgegrenzt werden. Es fand sich zusätzlich eine Verschiebung oder Abflachung der Verzähnelung. Ein Signalanstieg im Bereich des Knorpels fand sich kernspintomographisch in nur zwei Fällen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02428387
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    Estimation of absorbed dose for 2-[F-18]fluoro-2-deoxy-d- glucose using whole-body positron emission tomography and magnetic resonance imaging (1998)
    Springer
    European journal of nuclear medicine 25 (1998), S. 565-574 
    Details
    ISSN: 1619-7089
    Keywords: Key words: Absorbed Dose ; S-value ; MIRD phantom ; Whole-body positron emission tomography ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The purpose of this study was to measure the cumulated activity and absorbed dose in organs after intravenous administration of 2-[F-18]fluoro-2-deoxy-d-glucose (18F-FDG) using whole-body positron emission tomography (PET) and magnetic resonance imaging (MRI). Whole-body dynamic emission scans for 18F-FDG were performed in six normal volunteers after transmission scans. The total activity of a source organ was obtained from the activity concentration of the organ measured by whole-body PET and the volume of that organ measured by whole-body T1-weighted MRI. The cumulated activity of each source organ was calculated from the time-activity curve. Absorbed doses to the individuals were estimated by the MIRD (medical internal radiation dosimetry) method using S-values adjusted to the individuals. Another calculation of cumulated activities and absorbed doses was performed using the organ volumes from the MIRD phantom and the ”Japanese reference man” to investigate the discrepancy of actual individual results against the phantom results. The cumulated activities of 18 source organs were calculated, and absorbed doses of 27 target organs estimated. Among the target organs, bladder wall, brain and kidney received the highest doses for the above three sets of organ volumes. Using measured individual organ volumes, the average absorbed doses for those organs were found to be 3.1×10–1, 3.7×10–2 and 2.8×10–2 mGy/MBq, respectively. The mean effective doses in this study for individuals of average body weight (64.5 kg) and the MIRD phantom of 70 kg were the same, i.e. 2.9×10–2 mSv/MBq, while for the Japanese reference man of 60 kg the effective dose was 2.1×10–2 mSv/MBq. The results for measured organ volumes derived from MRI were comparable to those obtained for organ volumes from the MIRD phantom. Although this study considered 18F-FDG, combined use of whole-body PET and MRI might be quite effective for improving the accuracy of estimations of the cumulated activity and absorbed dose of positron-labelled radiopharmaceuticals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002590050257
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    Ictal technetium-99m ethyl cysteinate dimer single-photon emission tomographic findings and propagation of epileptic seizure activity in patients with extratemporal epilepsies (1998)
    Springer
    European journal of nuclear medicine 25 (1998), S. 166-172 
    Details
    ISSN: 1619-7089
    Keywords: Key words: Ictal single-photon emission tomography ; Positron emission tomography ; Magnetic resonance imaging ; EEG-video monitoring ; Epilepsy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Although ictal single-photon emission tomography (SPET) with technetium-99m ethyl cysteinate dimer (ECD) has a well-established role in the diagnostic evaluation of patients with temporal lobe epilepsy who are being considered for epilepsy surgery, its use in cases of extratemporal epilepsy is still limited. We investigated the influence of the propagation of extratemporal epileptic seizure activity on the regional increase in cerebral blood flow, which is usually associated with epileptic seizure activity. Forty-two consecutive patients with extratemporal epilepsies were prospectively evaluated. All patients underwent ictal SPET studies with simultaneous electroencephalography (EEG) and video recordings of habitual seizures and imaging studies including cranial magnetic resonance imaging and positron emission tomography with 2-[18F]-fluoro-2 deoxy-d-glucose. Propagation of epilptic seizure activity (PESA) was defined as the absence of hyperperfusion on ictal ECD SPET in the lobe of seizure onset, but its presence in another ipsilateral or contralateral lobe. Observers analysing the SPET images were not informed of the other results. PESA was observed in 8 of the 42 patients (19%) and was ipsilateral to the seizure onset in five (63%) of these eight patients. The time between clinical seizure onset and injection of the ECD tracer ranged from 14 to 61 s (mean 34 s). Seven patients (88%) with PESA had parieto-occipital epilepsy and one patient had a frontal epilepsy. PESA was statistically more frequent in patients with parieto-occipital lobe epilepsies (58%) than in the remaining extratemporal epilepsy syndromes (3%) (P〈0.0002). These findings indicate that ictal SPET studies require simultaneous EEG-video recordings in patients with extratemporal epilepsies. PESA should be considered when interpreting ictal SPET studies in these patients. Patients with PESA are more likely to have parieto-occipital lobe epilepsy than seizure onset in other extratemporal regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002590050210
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    Solitary fibrous tumor of the parotid gland extending to the parapharyngeal space (1998)
    Springer
    European archives of oto-rhino-laryngology and head & neck 255 (1998), S. 18-21 
    Details
    ISSN: 1434-4726
    Keywords: Key words Parotid gland ; Solitary fibrous tumor ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Solitary fibrous tumors (SFT) arise in the pleura and less commonly in extrapleural sites. Head and neck regions have included the nose and paranasal sinuses, soft palate, epiglottis, thyroid, parotid and submandibular glands, as well as the infratemporal fossa and parapharyngeal space. We report a case of SFT arising from the parotid gland and extending to the parapharyngeal space. To our knowledge, this is the fourth case of SFT originating from the parotid gland and is the largest of its kind among the extrapleural lesions described. The characteristics revealed by computed tomography and magnetic resonance imaging are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004050050015
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    Granulomatous tenosynovitis: A rare musculoskeletal manifestation of tuberculosis (1998)
    Springer
    Clinical rheumatology 17 (1998), S. 166-169 
    Details
    ISSN: 1434-9949
    Keywords: Magnetic resonance imaging ; Tenosynovitis ; Tuberculosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A patient with tenosynovial tuberculosis affecting the extensor tendons of the wrist and hand is presented. This case highlights the clinical and magnetic resonance features of tuberculous tenosynovitis, and seeks to increase awareness of what may represent a resurgent musculoskeletal entity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01452268
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    Efficacy of radiosynovectomy of the knee in rheumatoid arthritis: Evaluation with magnetic resonance imaging (1998)
    Springer
    Clinical rheumatology 17 (1998), S. 277-281 
    Details
    ISSN: 1434-9949
    Keywords: Gadolinium ; Magnetic resonance imaging ; Radiosynovectomy ; Rheumatoid arthritis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The intra-articular injection of a radiopharmaceutical agent (radiosynovectomy) produces a reduction of the synovial inflammatory process. The inflammed synovial membrane can be identified with magnetic resonance imaging after the intravenous administration of gadolinium (MRI-Gd). A 6-month prospective study was carried out in 10 patients with rheumatoid arthritis after radiosynovectomy of the knee. The efficacy was evaluated with clinical parameters and MRI-Gd. A progressive amelioration of synovial effusion, pain, articular range of mobility, total leucocytes count in synovial fluid and synovial membrane thickness through MRI-Gd was observed. The global efficacy was considered to be good in six patients, fair in three and bad in one. The study shows for the first time that MRI-Gd allows the evaluation of the response of the synovial membrane to radiosynovectomy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01451005
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    Evaluation of velopharyngeal pathophysiology and velopharyngeal insufficiency with magnetic resonance imaging (1998)
    Springer
    European journal of plastic surgery 21 (1998), S. 118-123 
    Details
    ISSN: 1435-0130
    Keywords: Key words Velopharyngeal insufficiency ; Magnetic resonance imaging ; Velopharyngeal pathophysiology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The disadvantages and limitations of imaging methods to investigate velopharyngeal incompetence have created some difficulties in the management of this condition. Seven normal volunteers and seven patients who were suffering from a speech disorder were examined using magnetic resonance imaging. The velopharyngeal aperture was evaluated at rest and during phonation. In normal volunteers, the velopharyngeal aperture area had a mean value of 1.632 cm2 while at rest and complete closure was obtained during the phonation of /s/ sound. Detailed information was obtained about the function of the levator palati muscle. In five patients during the phonation of /s/ sound there was an increase in the area of the velopharyngeal aperture when compared to the volunteers. Investigation with magnetic resonance imaging is helpful in the pretreatment evaluation and postopertive follow-up examination of velopharyngeal insufficiency. As a result, this noninvasive method can be used as an alternative to conventional radiological investigations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002380050043
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    Mixing in Stars and the Evolution of the 3He Abundance (1998)
    Springer
    Space science reviews 84 (1998), S. 199-206 
    Details
    ISSN: 1572-9672
    Keywords: Nuclear reactions ; Nucleosynthesis ; Abundances ; Stars:Evolution ; Interior ; Rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We first recall the observational and theoretical facts that constitute the so-called 3He problem. We then review the chemical anomalies that could be related to the destruction of 3He in red giants stars. We show how a simple consistent mechanism can lead to the destruction of 3He in low mass stars and simultaneously account for the low 12C/13C ratios and low lithium abundances observed in giant stars of different populations. This process should both naturally account for the recent measurements of 3He/H in galactic HII regions and allow for high values of 3He observed in some planetary nebulae. We propose a simple statistical estimation of the fraction of stars that may be affected by this process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005027519798
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    Folding type-specific secondary structure propensities of amino acids, derived from α-helical, β-sheet, α/β, and α+β proteins of known structures (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 35-49 
    Details
    ISSN: 0006-3525
    Keywords: folding type-specific secondary structure propensities ; amino acids ; α-helical proteins ; β sheet proteins ; α/β proteins ; α+β proteins ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Folding type-specific secondary structure propensities of 20 naturally occurring amino acids have been derived from α-helical, β-sheet, α/β, and α+β proteins of known structures. These data show that each residue type of amino acids has intrinsic propensities in different regions of secondary structures for different folding types of proteins. Each of the folding types shows markedly different rank ordering, indicating folding type-specific effects on the secondary structure propensities of amino acids. Rigorous statistical tests have been made to validate the folding type-specific effects. It should be noted that α and β proteins have relatively small α-helices and β-strands forming propensities respectively compared with those of α+β and α/β proteins. This may suggest that, with more complex architectures than α and β proteins, α+β and α/β proteins require larger propensities to distinguish from interacting α-helices and β-strands. Our finding of folding type-specific secondary structure propensities suggests that sequence space accessible to each folding type may have differing features. Differing sequence space features might be constrained by topological requirement for each of the folding types. Almost all strong β-sheet forming residues are hydrophobic in character regardless of folding types, thus suggesting the hydrophobicities of side chains as a key determinant of β-sheet structures. In contrast, conformational entropy of side chains is a major determinant of the helical propensities of amino acids, although other interactions such as hydrophobicities and charged interactions cannot be neglected. These results will be helpful to protein design, class-based secondary structure prediction, and protein folding. © 1998 John Wiley & Sons, Inc. Biopoly 45: 35-49, 1998
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    Torsional control of double-stranded DNA branch migration (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 69-83 
    Details
    ISSN: 0006-3525
    Keywords: DNA branched junctions ; branch migration ; superhelical torque ; control of DNA structure ; endonuclease VII ; nanomechanical device ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DNA branched junctions are analogues of Holliday junction recombination intermediates. Partially mobile junctions contain a limited amount of homology flanking the branch point. A partially mobile DNA branched junction has been incorporated into a synthetic double-stranded circular DNA molecule. The junction is flanked by four homologous nucleotide pairs, so that there are five possible locations for the branch point. Two opposite arms of the branched junction are joined to form the circular molecule, which contains 262 nucleotides to the base of the junction. This molecule represents a system whereby torque applied to the circular molecule can have an impact on the junction, by relocating its branch point. Ligation of the molecule produces two topoisomers; about 87% of the product is a relaxed molecule, and the rest is a molecule with one positive supercoil. The position of the branch point is assayed by cleaving the molecule with endonuclease VII. We find that the major site of the branch point in the relaxed topoisomer is at the maximally extruded position in the relaxed molecule. Upon the addition of ethidium, the major site of the branch point migrates to the minimally extruded position. © 1998 John Wiley & Sons, Inc. Biopoly 45: 69-83, 1998
    Additional Material: 9 Ill.
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    Conformational change and aggregation of κ-carrageenan studied by flow field-flow fractionation and multiangle light scattering (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 85-96 
    Details
    ISSN: 0006-3525
    Keywords: conformation ; aggregation ; κ-carrageenan ; flow field-flow fractionation ; multiangle light scattering ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relatively novel combination of flow field-flow fractionation (FFF) and multiangle light scattering (MALS) was employed to study a nondegraded κ-carrageenan in different 0.1M salt solutions. The applicability of the technique was tested, and the effects of salt type and salt composition on the molar mass and radius of gyration were studied. A conformational ordering was induced at room temperature by switching the solvent from 0.1M NaCl (coil form) to 0.1M NaI (helix form). An approximate doubling of the average molar mass and an increase in radius of gyration was then observed, in agreement with results obtained previously using size exclusion chromatography-MALS. This increase in size was attributed to conformational ordering and to the formation of double helices. Severe aggregation was observed above 40% CsI in the 0.1M mixed salt solution of CsI and NaI. This was ascribed to the association of helices into large aggregates. For these large associates, having molar masses of several millions, a reversal of the elution order in flow FFF was detected. © 1998 John Wiley & Sons, Inc. Biopoly 45: 85-96 1998
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    Calculations on the low energy conformers of N-acetyl-D-alanyl-D-alanine (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 119-133 
    Details
    ISSN: 0006-3525
    Keywords: conformations of D-alanyl-D-alanine ; β-lactam ; structural overlay ; AMBER force field ; AM1 ; ab initio ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this article a conformational analysis of the D-alanyl-D-alanine dipeptide, both charged and neutral, has been carried out. The preferred conformations were determined by means of ab initio and semiempirical quantum, together with empirical force field calculations. The AMBER* force field and the 6-31 + G** and 6-31G** ab initio levels give rise to a coincident minimum energy structure, which, on the other hand, differs from that determined by AM1, 3-21 + G, and 3-21G. The solvent effect on the different charged and neutral conformations have been considered through the AMSOL semiempirical method. A quantification regarding the structural similarities between the different dipeptide conformations and the ampicillin has been performed. The results show that the best overlay is attained by the minimum structure energy obtained by using the 6-31 + G** methodology, which presents a planar amidic nitrogen. © 1998 John Wiley & Sons, Inc. Biopoly 45: 119-133, 1998
    Additional Material: 5 Ill.
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    C6-oxidized cellulose: Ion interactions with mono- and divalent cations (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 157-163 
    Details
    ISSN: 0006-3525
    Keywords: chemical oxidation ; cellulose ; conformational transition ; capillary viscosity ; microcalorimetry ; calcium ions ; gels ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational behavior of different molecular weight fractions of a synthetic C6-oxidized derivative of cellulose were investigated by means of capillary viscometry, CD, and microcalorimetric measurements. Experiments were carried out in the presence of either monovalent or divalent counterions.The experimental data indicated that C6-oxidized cellulose can assume an ordered extended conformation at low ionic strength, induced by the intrachain repulsions of negative charges. This conformation was suggested to be very similar to the fully extended structure of cellulose. In addition to this, upon increasing the ionic strength, a conformational transition of the order-to-disorder type occurred. In fact, the screening of the electrostatic repulsions introduced a number of conformational kinks into the cellulosic backbone, which enabled the polymer to assume a more coiled conformation hence producing less viscous aqueous solutions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 157-163, 1998
    Additional Material: 6 Ill.
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    Conformational stability of biological polyelectrolytes: Evaluation of enthalpy and entropy changes of conformational transitions (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 203-216 
    Details
    ISSN: 0006-3525
    Keywords: conformational stability ; biological polyelectrolytes ; enthalpy ; entropy ; conformational transitions ; carrageenan ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method is proposed for the determination of the enthalpy and entropy changes of nonionic origin upon conformational transition of linear biopolyelectrolytes in solution. For all transition midpoints, defined by given temperature and ionic strength, the total free energy change of the system is zero, which means that the nonionic contribution to the free energy change is equal in value and opposite in sign to the polyelectrolytic one. The counterion condensation theory of linear polyelectrolytes provides for the appropriate analytical expression to be used in such calculations. Linear plots of the proper functions of the calculated free energy changes vs the proper functions of temperature allows for the determination of the enthalpic and entropic terms of the nonionic free energy change of transition.The method has been applied to the extensive available data of the ion-induced conformational change of κ-carrageenan, a linear sulfated galactan extracted from seaweeds. The method has proved very successful, with the results showing a remarkable convergency of the enthalpy values for different monovalent counterions. On the other hand, the above approach has made it possible to explain the known effect of counterion specificity on the transition by a small difference in the nonionic entropic contributions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 203-216, 1998
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    UV resonance Raman spectroscopy of DNA and protein constituents of viruses: Assignments and cross sections for excitations at 257, 244, 238, and 229 nm (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 247-256 
    Details
    ISSN: 0006-3525
    Keywords: uv resonance Raman spectroscopy ; Raman cross section ; hypochromism ; DNA ; deoxynucleoside ; protein ; aromatic amino acid ; virus assembly ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ultraviolet resonance Raman (UVRR) spectra of H2O and D2O solutions of the nucleoside (dA, dG, dC, dT) and aromatic amino acid (Phe, Trp, Tyr) constituents of DNA viruses have been obtained with laser excitation wavelengths of 257, 244, 238, and 229 nm. Using the 981 cm-1 marker of Na2SO4 as an internal standard, Raman frequencies and scattering cross sections were evaluated for all prominent UVRR bands at each excitation wavelength. The results show that UVRR cross sections of both the nucleosides and amino acids are strongly dependent on excitation wavelength and constitute sensitive and selective probes of the residues. The results provide a library of UVRR marker bands for structural analysis of DNA viruses and other nucleoprotein assemblies. © 1998 John Wiley & Sons, Inc. Biopoly 45: 247-256, 1998
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    Lumbricus terrestris hemoglobin: A comparison of small-angle X-ray scattering and cryoelectron microscopy data (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 289-298 
    Details
    ISSN: 0006-3525
    Keywords: hemoglobin ; hexagonal bilayer ; Lumbricus ; electron microscopy ; three-dimensional reconstruction ; small-angle x-ray scattering ; three-dimensional models ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quaternary structure of Lumbricus terrestris hemoglobin was investigated by small-angle x-ray scattering (SAXS). Based on the SAXS data from several independent experiments, a three-dimensional (3D) consensus model was established to simulate the solution structure of this complex protein at low resolution (about 3 nm) and to yield the particle dimensions. The model is built up from a large number of small spheres of different weights, a result of the two-step procedure used to calculate the SAXS model. It accounts for the arrangement of 12 subunits in a hexagonal bilayer structure and for an additional central unit of cylinder-like shape. This model provides an excellent fit of the experimental scattering curve of the protein up to h = 1 nm-1 and a nearly perfect fit of the experimental distance distribution function p(r) in the whole range. Scattering curves and p(r) functions were also calculated for low-resolution models based on 3D reconstructions obtained by cryoelectron microscopy (EM). The calculated functions of these models also provide a very good fit of the experimental scattering curve (even at h 〉 1 nm-1) and p(r) function, if hydration is taken into account and the original model coordinates are slightly rescaled. The comparison of models reveals that both the SAXS-based and the EM-based model lead to a similar simulation of the protein structure and to similar particle dimensions. The essential differences between the models concern the hexagonal bilayer arrangement (eclipsed in the SAXS model, one layer slightly rotated in the EM model), and the mass distribution, mainly on the surface and in the central part of the protein complex. © John Wiley & Sons, Inc. Biopoly 45: 289-298, 1998
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    Conformational changes due to vicinal glycosylation: The branched α-l-Rhap(1-2)[β-d-Galp(1-3)]-β-d-Glc1-OMe trisaccharide compared with its parent disaccharides* (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 417-432 
    Details
    ISSN: 0006-3525
    Keywords: conformational changes ; vicinal glycosylation ; branched α-l-Rhap(1-2)[β-d-Galp(1-3)]-β-d-Glc1-OMe trisaccharide ; parent disaccharides ; hydrogen bond ; isotope effect ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformations of the α-l-Rhap(1-2)-β-d-Glc1-OMe and β-d-Galp(1-3)-β-d-Glc1-OMe disaccharides and the branched title trisaccharide were examined in DMSO-d6 solution by 1H-nmr. The distance mapping procedure was based on rotating frame nuclear Overhauser effect (NOE) constraints involving C- and O-linked protons, and hydrogen-bond constraints manifested by the splitting of the OH nmr signals for partially deuteriated samples. An “isotopomer-selected NOE” method for the unequivocal identification of mutually hydrogen-bonded hydroxyl groups was suggested. The length of hydrogen bonds thus detected is considered the only one motionally nonaveraged nmr-derived constraint. Molecular mechanics and molecular dynamics methods were used to model the conformational properties of the studied oligosaccharides. Complex conformational search, relying on a regular Φ,Ψ-grid based scanning of the conformational space of the selected glycosidic linkage, combined with simultaneous modeling of different allowed orientations of the pendant groups and the third, neighboring sugar residue, has been carried out. Energy minimizations were performed for each member of the Φ,Ψ grid generated set of conformations. Conformational clustering has been done to group the minimized conformations into families with similar values of glycosidic torsion angles. Several stable syn and anti conformations were found for the 1→2 and 1→3 bonds in the studied disaccharides. Vicinal glycosylation affected strongly the occupancy of conformational states in both branches of the title trisaccharide. The preferred conformational family of the trisaccharide (with average Φ,Ψ values of 38°, 17° for the 1→2 and 48°, 1° for the 1→3 bond, respectively) was shown by nmr to be stabilized by intramolecular hydrogen bonding between the nonbonded Rha and Gal residues. © 1998 John Wiley & Sons, Inc. Biopoly 46: 417-432, 1998
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    Buffer dependence of refractive index increments of protein solutions (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 489-492 
    Details
    ISSN: 0006-3525
    Keywords: refractive index increment ; proteins ; solvent ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The refractive index increment of a protein solution is a property not only of the protein, but also of the solvent. This is demonstrated theoretically and confirmed experimentally using analytical interferometry. © 1998 John Wiley & Sons, Inc. Biopoly 46: 489-492, 1998
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    Editor's comments (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 1-1 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Conformational behavior of the HAV-VP3(110-121) peptidic sequence and synthetic analogs in membrane environments studied by CD and computational methods (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 479-492 
    Details
    ISSN: 0006-3525
    Keywords: hepatitis A ; synthetic peptides ; CD ; liposomes ; computational study ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present study was undertaken to examine the structural features that may be important to explain the immunogenicity of the (110-121) peptide sequence (FWRGDLVFDFQV) of VP3 capsid protein of hepatitis A virus. A conformational analysis of the preferred conformations by CD and molecular mechanics was carried out. Present results suggest that the interaction with liposomes as biomembrane model induces and stabilizes the amphipathic β-structure of the peptide.To study the contribution of amino acid replacements at the RGD tripeptide as well as the influence of the peptide chain length on peptide conformation, solid-phase peptide synthesis of several peptide analogs was carried out and the peptide conformation was studied using CD spectroscopy. The results show that the RGD sequence is necessary to induce the β-structure in the presence of liposomes. © 1998 John Wiley & Sons, Inc. Biopoly 45: 479-492, 1998
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    Liquid crystal formation in DNA fragment solutions (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 31-37 
    Details
    ISSN: 0006-3525
    Keywords: DNA liquid crystals ; DNA fragments ; screened Coulomb interactions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The critical volume fractions pertaining to the formation of DNA liquid crystals were obtained from polarization microscopy, 31P-nmr, and phase separation experiments. The DNA length (approximately one to two times the persistence length 50 nm), ionic strength, and counterion variety dependencies are reported. The cholesteric-isotropic transition is interpreted in terms of the coexistence equations, which are derived from the solution free energy including orientational entropy and excluded volume effects. With the wormlike chain as reference system, the electrostatic contribution to the free energy is evaluated as a thermodynamic perturbation in the second virial approximation with a Debye-Hückel potential of mean force. The hard core contribution has been evaluated with scaled particle theory and/or a simple generalization of the Carnahan-Starling equation of state for hard spheres. For sufficiently high ionic strengths, the agreement is almost quantitative. At lower amounts of added salt deviations are observed, which are tentatively attributed to counterion screening effects. The contour length dependence agrees with a DNA persistence length 50 nm. © 1998 John Wiley & Sons, Inc. Biopoly 46: 31-37, 1998
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    Gelation of gelatin observation in the bulk and at the air-water interface (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 245-252 
    Details
    ISSN: 0006-3525
    Keywords: gelatin ; gelation ; atomic force microscopy ; interfacial rheology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gelation of gelatin under various conditions has been followed by atomic force microscopy (AFM) with the objective of understanding more fully the structure formed during the gelation process. AFM images were obtained of the structures formed from both the bulk sol and in surface films during the onset of gelation. While gelation occurred in the bulk sol, the extent of helix formation was monitored by measurements of optical rotation, and the molecular aggregation was imaged by AFM. Interfacial gelatin films formed at the air-water interface were also studied. Measurements of surface tension and surface rheology were made periodically and Langmuir-Blodgett films were drawn from the interface to allow AFM imaging of the structure of the interfacial layer as a function of time. Structural studies reveal that at low levels of helical content the gelatin molecules assemble into aggregates containing short segments of dimensions comparable to those expected for gelatin triple helices. With time larger fibrous structures appear whose dimensions suggest that they are bundles of triple helices. As gelation proceeds, the number density of fibers increases at the expense of the smaller aggregates, eventually assembling into a fibrous network. The gel structure appears to be sensitive to the thermal history, and this is particularly important in determining the structure and properties of the interfacial films. © 1998 John Wiley & Sons, Inc. Biopoly 46: 245-252, 1998
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    Ribozyme chemogenetics (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 65-81 
    Details
    ISSN: 0006-3525
    Keywords: nucleotide analogue interference mapping ; phosphorothioate ; group I intron ; interference suppression ; RNA ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this review I will outline several chemogenetic approaches used to determine the chemical basis of large ribozyme function and structure. The term chemogenetics was first used to describe site-specific functional group modification experiments in the analysis of DNA-protein interactions. Within the past few years equivalent experiments have been performed on large catalytic RNAs using both single-site substitution and interference mapping techniques with nucleotide analogues. While functional group mutagenesis is an important aspect of a chemogenetic approach, chemical correlates to genetic revertants and suppressors must also be realized for the genetic analogy to be intellectually valid and experimentally useful. Several examples of functional group revertants and suppressors have now been obtained within the Tetrahymena group I ribozyme. These experiments define an ensemble of tertiary hydrogen bonds that have made it possible to construct a detailed model of the ribozyme catalytic core. The model includes a functionally important monovalent metal ion binding site, a wobble-wobble receptor motif for helix-helix packing interactions, and a minor groove triple helix. © 1998 John Wiley & Sons, Inc. Biopoly 48: 65-81, 1998
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    Design, synthesis, and analysis of conformationally constrained nucleic acids (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 83-96 
    Details
    ISSN: 0006-3525
    Keywords: nucleic acid ; disulfide cross-link ; structure ; dynamics ; stability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this review I discuss straightforward and general methods to modify nucleic acid structure with disulfide cross-links. A motivating factor in developing this chemistry was the notion that disulfide bonds would be excellent tools to probe the structure, dynamics, thermodynamics, folding, and function of DNA and RNA, much in the way that cystine cross-links have been used to study proteins. The chemistry described has been used to synthesize disulfide cross-linked hairpins and duplexes, higher order structures like triplexes, nonground-state conformations, and tRNAs. Since the cross-links form quantitatively by mild air oxidation and do not perturb either secondary or tertiary structure, this modification should prove quite useful for the study of nucleic acids. © 1998 John Wiley & Sons, Inc. Biopoly 48: 83-96, 1998
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    On the role of magnesium ions in RNA stability (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 113-135 
    Details
    ISSN: 0006-3525
    Keywords: divalent cations ; magnesium ; RNA ; ion binding ; RNA folding ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Divalent cations, like magnesium, are crucial for the structural integrity and biological activity of RNA. In this article, we present a picture of how magnesium stabilizes a particular folded form of RNA. The overall stabilization of RNA by Mg2+ is given by the free energy of transferring RNA from a reference univalent salt solution to a mixed salt solution. This term has favorable energetic contributions from two distinct modes of binding: diffuse binding and site binding. In diffuse binding, fully hydrated Mg ions interact with the RNA via nonspecific long-range electrostatic interactions. In site binding, dehydrated Mg2+ interacts with anionic ligands specifically arranged by the RNA fold to act as coordinating ligands for the metal ion. Each of these modes has a strong coulombic contribution to binding; however, site binding is also characterized by substantial changes in ion solvation and other nonelectrostatic contributions. We will show how these energetic differences can be exploited to experimentally distinguish between these two classes of ions using analyses of binding polynomials. We survey a number of specific systems in which Mg2+-RNA interactions have been studied. In well-characterized systems such as certain tRNAs and some rRNA fragments these studies show that site-bound ions can play an important role in RNA stability. However, the crucial role of diffusely bound ions is also evident. We emphasize that diffuse binding can only be described rigorously by a model that accounts for long-range electrostatic forces. To fully understand the role of magnesium ions in RNA stability, theoretical models describing electrostatic forces in systems with complicated structures must be developed. © 1999 John Wiley & Sons, Inc. Biopoly 48: 113-135, 1998
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    Three-dimensional structure of the ion-chanel forming peptide trichorzianin TA VII bound to sodium dodecyl sulfate micelles (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 75-88 
    Details
    ISSN: 0006-3525
    Keywords: 1H-nmr ; molecular modeling ; peptaibol ; peptide-lipid interaction ; sodium dodecyl sulfate micelles ; trichorzianin TA VII ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trichorzianin TA VII, Ac0 U1 A2 A3 U4 J5 Q6 U7 U8 U9 S10 L11 U12 P13 V14 U15 I16 Q17 Q18 Fol19, is a nonadecapeptide member of the peptaibol antibiotics biosynthesized by Trichoderma soil fungi, which is characterized by a high proportion of the α,α-dialkylated amino acids, α-aminoisobutyric acid (Aib, U) and isovaline (Iva, J), an acetylated N-terminus and a C-terminal phenylalaninol (Pheol, Fol). The main interest in such peptides stems from their ability to interact with phospholipid bilayers and form voltage-dependent transmembrane channels in planar lipid bilayers. In order to provide insights into the lipid-peptide interaction promoting the voltage gating, the conformational study of TA VII in the presence of perdeuterated sodium dodecyl sulfate (SDS-d25) micelles has been carried out. 1H sequential assignments have been performed with the use of two-dimensional homo- and -heteronuclear nmr techniques including double quantum filtered correlated spectroscopy, homonuclear Hartmann-Hahn, nuclear Overhauser effect spectroscopy, 1H-13C heteronuclear single quantum correlation, and heteronuclear multiple bond correlation. Conformational parameters, such as 3JNHCαH coupling constants, temperature coefficients of amide protons (Δδ/ΔTNH) and quantitative nuclear Overhauser enhancement data, lead to detailed structural information. Ninety-eight three-dimensional structures consistent with the nmr data were generated from 231 interproton distances and six Φ dihedral angle restraints, using restrained molecular dynamics and energy minimization calculations. The average rms deviation between the 98 refined structures and the energy-minimized average structure is 0.59 Å for the backbone atoms. The structure of trichorzianin TA VII associated with SDS micelles, as determined by these methods, is characterized by two right-handed helical segments involving residues 1-8 and 11-19, linked by a β-turn that leads to an angle about 90°-100° between the two helix axes; residues 18 and 19 at the end of the C-terminal helix exhibit multiple conformations. © 1998 John Wiley & Sons, Inc. Biopoly 46: 75-88, 1998
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    Spectroscopic studies of 9-hydroxyellipticine binding to DNA (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 127-143 
    Details
    ISSN: 0006-3525
    Keywords: 9-hydroxyellipticine ; DNA ; CD ; linear dichroism ; resonance light scattering ; intercalation ; drug-drug interactions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of 9-hydroxyellipticine to calf thymus DNA, poly[d(A-T)]2, and poly-[d(G-C)]2 has been studied in detail by means of CD, linear dichroism, resonance light scattering, and molecular dynamics. The transition moment polarizations of 9-hydroxyelliptiycine were determined in polyvinyl alcohol stretched film. Spectroscopic solution studies of the DNA/drug complex are combined with theoretical CD calculations using the final 50 ps of a series of molecular dynamics simulations as input. The spectroscopic data shows 9-hydroxyellipticine to adopt two main binding modes, one intercalative and the other a stacked binding mode involving the formation of drug oligomers in the DNA major groove. Analysis of the intercalated binding mode in poly[d(A-T)]2 suggests the 9-hydroxyellipticine hydroxyl group lies in the minor groove and hydrogen bonds to water with the pyridine ring protruding into the major groove. The stacked binding mode was examined using resonance light scattering and it was concluded that the drug was forming small oligomer stacks rather than extended aggregates. Reduced linear dichroism measurements suggested a binding geometry that precluded a minor groove binding mode where the plane of the drug makes a 45° angle with the plane of the bases. Thus it was concluded that the drug stacks in the major groove. No obvious differences in the mode of binding of 9-hydroxyellipticine were observed between different DNA sequences; however, the stacked binding mode appeared to be more favorable for calf thymus DNA and poly[d(G-C)]2 than for poly[d(A-T)]2, an observation that could be explained by the slightly greater steric hindrance of the poly[d(A-T)]2 major groove. A strong concentration dependence was observed for the two binding modes where intercalation is favored at very low drug load, with stacking interactions becoming more prominent as the drug concentration is increased. Even at DNA : drug mixing ratios of 70:1 the stacked binding mode was still important for GC-rich DNAs. © 1998 John Wiley & Sons, Inc. Biopoly 46: 127-143, 1998
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    Interaction of branched chain polymeric polypeptides with phospholipid model membranes (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 169-179 
    Details
    ISSN: 0006-3525
    Keywords: macromolecular carriers ; drug targeting and delivery ; branched chain synthetic polypeptides ; membrane-synthetic polypeptide interaction ; lipid monolayers/bilayers ; polymer therapeutics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The surface properties at the air/water interface and the interaction of branched chain polymeric polypeptides with a general formula poly[Lys-(DL-Alam-X1)], where X = Π (AK), Ser (SAK), or Glu (EAK), with phospholipids were investigated. Polylysine derivatives with polycationic (SAK, AK) or amphoteric (EAK) were capable to spread and form stable monomolecular layers. The stability of monolayers at the air/water interface was dependent on the side-chain terminal amino acid residue of polymers and can be described by SAK 〈 AK 〈 EAK order. The area per amino acid residue values calculated from compression isotherms were in the same range as compared to those of linear poly-α-amino acids and proteins. Moreover, these polymers interact with phospholipid monomolecular layers composed of dipalmitoyl phosphatidyl choline (DPPC) or DPPC/PG (PG: phosphatidyl glycerol; 95/5, mol/mol). Data obtained from compression isotherms of phospholipids spread on aqueous polymer solutions at different initial surface pressure indicated that insertion into lipid monolayers for SAK or AK is more pronounced than for EAK. The interaction between branched polypeptides and phospholipid membranes was further investigated using lipid bilayers with DPPC/PG and fluorescent probes located either at the polar surface [1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) sodium anilino naphthalene sulfonate (ANS)] or within the hydrophobic core (DPH) of the liposome. Changes in fluorescence intensity and in polarization were observed when TMA-DPH or ANS, but not DPH were used. Comparative data also indicate that all three polymers interact only with the outer surface of the bilayer, but even the most marked penetration of polycationic polypeptide (SAK) did not result in alteration of the ordered state of the alkyl chains in the bilayer. Taken together, data obtained from mono- or bilayer experiments suggest that the interaction between branched polymers and phospholipids are highly dependent on the charge properties (Ser vs Glu) and on the identity (Ser vs Ala) of side-chain terminating amino acids. The binding of polymers to the model membranes could be mainly driven by electrostatic forces, but the significant role of hydrophilic properties in case of SAK cannot be excluded. © 1998 John Wiley & Sons, Inc. Biopoly 46: 169-179, 1998
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    Relationship between conformation and geometry as evidenced by molecular dynamics simulation of Cα,α-dialkylated glycines (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 239-244 
    Details
    ISSN: 0006-3525
    Keywords: Cα,α-dialkylated glycines ; molecular dynamics ; geometry and conformation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relationship between the local backbone conformation and bond angles at Cα of symmetrically substituted Cα,α-dialkylated glycines (Cα,α-dimethylglycine or α-aminoisobutyric acid, Aib; Cα,α-diethylglycine, Deg; Cα,α-di-n-propylglycine, Dpg) has been investigated by molecular dynamics (MD) simulation adopting flat bottom harmonic potentials, instead of the usual harmonic restraints, for the Cα bond angles. The MD simulations show that the Cα bond angles are related to the local backbone conformation, irrespectively of the side-chain length of Aib, Deg, and Dpg residues. Moreover, the N-Cα-C′ (τ) angle is the most sensitive conformational parameter and, in the folded form, is always larger and more flexible than in the extended one. © 1998 John Wiley & Sons, Inc. Biopoly 46: 239-244, 1998
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    Methionine ligation strategy in the biomimetic synthesis of parathyroid hormones (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 319-327 
    Details
    ISSN: 0006-3525
    Keywords: methionine ligation ; parathyroid hormones ; biomimetic ligation ; S-methylation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In biological systems, both proteolysis and aminolysis of amide bonds produce activated intermediates through acyl transfer reactions either inter- or intramolecularly. Protein splicing is an illustrative example that proceeds through a series of catalyzed acyl transfer reactions and culminates at an O- or S-acyl intermediate. This intermediate leads to an uncatalyzed acyl migration to form an amide bond in the spliced product. A ligation method mimicking the uncatalyzed final steps in protein splicing has been developed utilizing the acyl transfer amide-bond feature for the blockwise coupling of unprotected, free peptide segments at methionine (Met). The latent thiol moiety of Met can be exploited using homocysteine at the α-amino terminal position of a free peptide for transthioesterification with another free peptide containing an α-thioester to give an S-acyl intermediate. A subsequent, proximity-driven S- to N-acyl migration of this acyl intermediate spontaneously rearranges to form a homocysteinyl amide bond. S-methylation with excess p-nitrobenezensulfonate yields Met at the ligation site. The methionine ligation is selective and orthogonal, and is usually completed within 4 h when performed at slightly basic pH and under strongly reductive conditions. No side reactions due to acylation were observed with any other α-amines of both peptide segments as seen in the synthesis of parathyroid hormone peptides. Furthermore, cyclic peptide can also be obtained through the same strategy by placing both homocysteine at the amino terminus and the thioester at the carboxyl terminus in an unprotected peptide precursor. These biomimetic ligation strategies hold promise for engineering novel peptides and proteins. © 1998 John Wiley & Sons, Inc. Biopoly 46: 319-327, 1998
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    Modeling the free solution electrophoretic mobility of short DNA fragments (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 359-373 
    Details
    ISSN: 0006-3525
    Keywords: boundary element method ; DNA electrophoresis ; electrophoretic mobility of DNA ; free solution electrophoretic mobility of DNA ; ion relaxation, DNA electrophoresis ; modeling electrophoresis of polyions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Boundary element methods are used to model the free solution electrophoretic mobility of short DNA fragments. The Stern surfaces of the DNA fragments are modeled as plated cylinders that reproduce translational and rotational diffusion constants. The solvent-accessible and ion-accessible surfaces are taken to be coincident with the Stern surface. The mobilities are computed by solving simultaneously the coupled Navier-Stokes, Poisson, and ion-transport equations. The equilibrium electrostatics are treated at the level of the full Poisson-Boltzmann equation and ion relaxation is included. For polyions as highly charged as short DNA fragments, ion relaxation is substantial. At .11 M KCl, the simulated mobilities of a 20 base pair DNA fragment are in excellent agreement with experiment. At .04 M Tris acetate, pH = 8.0, the simulated mobilities are about 10-15% higher than experimental values and this discrepancy is attributed to the relatively large size of the Tris counterion. The length dependence of the mobility at .11 M KCl is also investigated. Earlier mobility studies on lysozyme are reexamined in view of the present findings. In addition to electrophoretic mobilities, the effective polyion charge measured in steady state electrophoresis and its relationship to the preferential interaction parameter γgG is briefly considered. © 1998 John Wiley & Sons, Inc. Biopoly 46: 359-373, 1998
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    Aggregation of dermorphin and L-Ala dermorphin examined by light scattering at sub-NMR concentrations (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 341-346 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Correlation between rate of enzyme-substrate diffusional encounter and average Boltzmann factor around active site (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 355-360 
    Details
    ISSN: 0006-3525
    Keywords: diffusional encounter ; Brownian dynamics ; average Boltzmann factor ; acetylcholinesterase ; Poisson-Boltzmann ; electrostatics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The utility of the average Boltzmann factor around the active site of an enzyme as the predictor of the electrostatic enhancement of the substrate binding rate is tested on a set of data on wild-type acetylcholinesterase and 18 charge mutants recently obtained by Brownian dynamics simulations. A good correlation between the average Boltzmann factors and the substrate binding rate constants is found. The effects of single charge mutations on both the Boltzmann factor and the substrate binding rate constant are modest, i.e., 〈5 fold increase or decrease. This is consistent with the experimental results of Shafferman et al. but does not support their suggestion that the overall rate of the catalytic reaction is not limited by the diffusional encounter of acetylcholinesterase and its substrate. © 1998 John Wiley & Sons, Inc. Biopoly 45: 355-360, 1998
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    Reconstructing the protein-water interface (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 469-478 
    Details
    ISSN: 0006-3525
    Keywords: molecular dynamics ; hydrated proteins ; crystal structures ; density distributions ; globular proteins ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using molecular dynamics simulations of fully hydrated proteins and analysis of crystal structures contained in the Protein Data Bank, we develop a transferable set of perpendicular radial distribution functions for water molecules around globular proteins. These universal functions may be used to reconstruct the unique three-dimensional solvent density distribution around every individual protein with a modest error. We discuss potential applications of this solvent treatment in protein x-ray crystallographic refinements and in theoretical modeling. We also present a fast, grid-based algorithm for construction of the perpendicular solvent density distributions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 469-478, 1998
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    Design strategies for the construction of independently folded polypeptide motifs (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 23-29 
    Details
    ISSN: 0006-3525
    Keywords: independently folded polypeptide motifs ; miniproteins ; natural target domains ; BBA motif ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we present a redesign strategy for the development of uniquely folded polypeptide motifs of less than 40 residues. These mini proteins are based on natural target domains, including the zinc finger domains (BBA motif) Nomenclature corresponds to the defined elements of secondary structure, beginning at the N-terminus of the peptide. Roman lettering refers to a specific motif while Greek characters correspond to the elements of secondary structure within that motif. and the disulfide-rich snake and scorpion toxins (BBB motif). These motifs are designed to act as the molecular framework for the construction of novel functional polypeptides. We will explore the structural determinants of the folded BBA motif, inspired by the zinc finger peptides, in relation to the redesign process. © 1998 John Wiley & Sons, Inc. Biopoly 47: 23-29, 1998
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    Peptide ion channels: Design and creation of function (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 75-81 
    Details
    ISSN: 0006-3525
    Keywords: ion channel ; synthetic peptide ; de novo design ; template-assembled synthetic proteins ; supramolecular assembly ; membrane protein ; planer lipid bilayers ; amphiphilic peptide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To create ion channel function by synthetic peptides is a challenge in the de novo design of artificial membrane proteins. Amphiphilic α-helical motifs of ∼ 20 amino acid residues to span lipid bilayers are most often used for the creation of peptide ion channels. Template molecules to tether helical peptides have been employed to obtain more organized pore structures. Approaches to form molecular assembly of peptides in the membranes by hydrogen bonding have been also investigated. We have developed approaches to assemble helices with individual amino acid sequences to construct artificial helical proteins. Using one of these approaches, four helices corresponding to the voltage sensor segments (S4 in repeat I-IV) of the sodium channel were assembled on a peptide template to give a protein having ion channel activity with rectification. © 1998 John Wiley & Sons, Inc. Biopoly 47: 75-81, 1998
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    Collagen mimetics (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 127-142 
    Details
    ISSN: 0006-3525
    Keywords: collagen mimetics ; triple helix ; peptoid ; template ; biophysics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Collagen peptidomimetics have been synthesized as an alternative to natural collagen. The incorporation of unnatural residues such as peptoids in the collagen sequences can demonstrate potent and specific biological activity and enhance the biostability against enzymatic degradation. Furthermore, the use of achiral peptoids simplifies synthetic strategies by reducing racemization problems. The peptoid residue N-isobutylglycine (Nleu) has been successfully incorporated into a series of collagen mimetics composed of Gly-Pro-Nleu, Gly-Nleu-Pro, and Gly-Nleu-Nleu. The discovery of template-assembled collagen mimetics and metal binding ability has laid the foundation for new opportunities in the design of novel collagen mimetic complexes. This review summarizes the synthesis and integrated biophysical analyses of the structures of these collagen mimetics. Solid phase segment condensation techniques have been utilized for the synthesis of the single chain and template-assembled analogues. The characterization of the collagen-like structures has been established by temperature-dependent optical rotation measurements, CD, NMR spectroscopy, and molecular modelling simulations. © 1998 John Wiley & Sons, Inc. Biopoly 47: 127-142, 1998
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    Syntheses of squarylium-substituted alanine and its peptide, and formation of their thin films onto a poly(3-methylthiophene)/Au electrode (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 179-183 
    Details
    ISSN: 0006-3525
    Keywords: non-natural amino acid ; peptide ; squarylium dye ; thin film ; poly(3-methylthiophene) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We designed a polypeptide that behaves as a photodevice by using a non-natural amino acid with replacement of an α-hydrogen by a squarylium dye and succeeded in syntheses of the non-natural amino acid derivative containing a squarylium and its peptide with trialanine Ala-Ala-Ala. Strong dye-dye interactions were confirmed by absorption and CD spectra for the peptide in 2,2,2-trifluoroethanol solution and in water suspension. The non-natural amino acid derivative could be deposited onto a PMeT/Au electrode by the micelle disruption method. © 1998 John Wiley & Sons, Inc. Biopoly 47: 179-183, 1998
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    Editorial: Protein-protein interactions: Mimics and inhibitors (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 263-263 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    New developments of the electrostatically driven monte carlo method: Test on the membrane-bound portion of melittin (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 117-126 
    Details
    ISSN: 0006-3525
    Keywords: electrostatically driven Monte Carlo method ; cluster analysis ; global energy minimum ; perturbed conformations ; conformational space ; lowest energy conformations ; polypeptide chain ; melittin, membrane-bound portion ; Empirical Conformational Energy Program for Peptides 3 ; annealing methods ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrostatically driven Monte Carlo (EDMC) method has been greatly improved by adding a series of new features, including a procedure for cluster analysis of the accepted conformations. This information is used to guide the search for the global energy minimum. Alternative procedures for generating perturbed conformations to sample the conformational space were also included. These procedures enhance the efficiency of the method by generating a larger number of low-energy conformations.The improved EDMC method has been used to explore the conformational space of a 20-residue polypeptide chain whose sequence corresponds to the membrane-bound portion of melittin. The ECEPP/3 (Empirical Conformational Energy Program for Peptides) algorithm was used to describe the conformational energy of the chain. After an exhaustive search involving 14 independent runs, the lowest energy conformation (LEC) (-91.0 kcal/mol) of the entire study was encountered in four of the runs, while conformations higher in energy by no more than 1.8 kcal/mol were found in the remaining runs with the exception of one of them (run 8). The LEC is identical to the conformation found recently by J. Lee, H.A. Scheraga, and S. Rackovsky [(1998) “Conformational Analysis of the 20-Residue Membrane-Bound Portion of Melittin by Conformational Space Annealing,” Biopolymers, Vol. 46, pp. 103-115] as the lowest energy conformation obtained in their study using the conformational space annealing method. These results suggest that this conformation corresponds to the global energy minimum of the ECEPP/3 potential function for this specific sequence; it also appears to be the conformation of lowest free energy. © 1998 John Wiley & Sons, Inc. Biopoly 46: 117-126, 1998
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    Renaturation of condensed DNA studied through a decoupling scheme (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 195-200 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Band broadening in gel electrophoresis: Scaling laws for the dispersion coefficient measured by FRAP (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 201-214 
    Details
    ISSN: 0006-3525
    Keywords: band broadening ; dispersion ; DNA ; gels ; electrophoresis ; fluorescence recovery ; photobleaching ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We determined quantitatively the band broadening effect during gel electrophoresis by measuring the longitudinal dispersion coefficient Dx, with a fluorescence recovery after photobleaching setup, coupled to an electrophoretic cell. We carried out measurements as a function of the electric field, the average pore size, and the molecular length of DNA fragments. Our results are in good agreement with the predictions of the biased reptation model with fluctuations described by T. A. Duke et al. [(1992) Physics Review Letters, vol. 69, pp. 3260-3263]. This agreement is observed on single-stranded DNA [persistence length ≅ 4 nm; B. Tinland et al. (1997) Macromolecules, vol. 30, pp. 5763-5765] in polyacrylamide gels and on double-stranded DNA (persistence length ≅ 50 nm) in agarose gels, two systems where the ratio between the average pore size and the Kuhn length is larger than 1. © 1998 John Wiley & Sons, Inc. Biopoly 46: 201-214, 1998
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    Inherent DNA curvature and flexibility correlate with TATA box functionality (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 403-415 
    Details
    ISSN: 0006-3525
    Keywords: molecular dynamics ; DNA curvature ; DNA flexibility ; TATA box functionality ; TATA box binding protein (TBP) ; TBP recognition ; TBP binding ; TBP transcriptional activation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four 1.5 ns molecular dynamics (MD) simulations were performed on the d(GCTATAAAAGGG) · d(CCCTTTTATAGC) double helix dodecamer bearing the Adenovirus major late promoter TATA element and three iso-composition mutants for which physical and biochemical data are available from the same laboratory. Three of these DNA sequences experimentally induce tight binding with the TATA box binding protein (TBP) and induce high transcription rates; the other DNA sequence induces much lower TBP binding and transcription. The x-ray crystal structures have previously shown that the duplex DNA in DNA-TBP complexes are highly bent. We performed and analyzed MD simulations for these four DNAs, whose experimental structures are not available, in order to address the issue of whether inherent DNA structure and flexibility play a role in establishing these observed preferences. A comparison of the experimental and simulated results demonstrated that DNA duplex sequence-dependent curvature and flexibility play a significant role in TBP recognition, binding, and transcriptional activation. © 1998 John Wiley & Sons, Inc. Biopoly 46: 403-415, 1998
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    The solution structure of small peptides: An IR CD study of aqueous solutions of (L-Ala)n [n = 3, 4, 5, 6] at different temperatures and ionic strengths (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 455-463 
    Details
    ISSN: 0006-3525
    Keywords: vibrational CD ; solution conformation ; alanine oligopeptides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution conformation of a number of small, linear alanine oligomers was investigated via ir (or vibrational) CD (VCD). We find that these oligopeptides assume distinct solution conformations that depend primarily on chain lengths, and to a lesser degree on temperature, ionic strength, and pH. As expected, the longer chain oligomers exhibit more distinct VCD features and, presumably, more stable solution structures. At the level of the hexamer, however, aggregation of the peptide occurs. The fast time scale of VCD allows solution structures to be detected that may not be observable using slower techniques such as various forms of nmr spectroscopy. The VCD results reported here confirm that it is generally possible to obtain conformational information for small, linear homo- and heterooligopeptides via VCD spectroscopy. In this respect, the sensitivity of VCD is similar to that of electronic CD. Furthermore, the temperature dependence of the VCD results indicate that at elevated temperatures, the increasing number of conformational states results in a loss of discernible conformers, and consequently, a broadening and weakening of the VCD features. © 1998 John Wiley & Sons, Inc. Biopoly 46: 455-463, 1998
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    Miniaturized hemoproteins (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 5-22 
    Details
    ISSN: 0006-3525
    Keywords: hemoproteins ; model systems ; miniaturized proteins ; mimochromes ; helix structures ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present paper highlights and reviews current research in the field of hemoprotein models. Hemoproteins have been extensively studied in order to understand structure-function relationships, and to design new molecules with desired functions. A wide number of synthetic analogues have been developed, using quite different approaches. They differ in molecular structures, ranging from simple meso-substituted tetraaryl-metalloporphyrins and peptide-porphyrin conjugates.In this paper we summarize the state of the art on peptide based hemoprotein models. We also report here the approach used by us to develop a new class of molecules, named mimochromes. They can be regarded as miniaturized hemoproteins, because mimochromes are low molecular weight compounds with some structural and functional properties common to those of the parent high molecular weight protein. The basic structure of mimochromes is a deuteroporphyrin ring covalently linked to two helical peptide chains. Two molecules of this series have been fully characterized. All the information derived from their structural analysis has been applied to the design of new analogues with additional functions. © 1998 John Wiley & Sons, Inc. Biopoly 47: 5-22, 1998
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    An electrostatic model for the dielectric effects, the adsorption of multivalent ions, and the bending of B-DNA (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 503-516 
    Details
    ISSN: 0006-3525
    Keywords: discrete charge model of DNA ; dielectric cylinder in water ; effective dielectric constant ; salt effects ; Debye shielding factor ; potential variations in DNA surface ; Boltzmann averaged bending angles ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have studied electrostatic properties of DNA with a discrete charge model consisting of a cylindrical dielectric core with a radius of 8 Å and a dielectric constant Di = 4, surrounded by two helical strings of phosphate point charges at 10 Å from the axis, immersed in an aqueous medium with dielectric constant Dw = 78.54. Eliminating the dielectric core makes potentials in the phosphate surface less negative by about 0.5 kT/e. Salt effects are evaluated for the model without a dielectric core, using the shielded Coulomb potential. Smearing the phosphate charges increases their potential by about 2.5 kT/e, due mostly to the self-potential of the smeared charge. Potentials in the center of the minor and major grooves vary less than 0.02 kT/e along their helical path. The potential in the center of the minor groove is from 1.0 to 1.7 kT/e, more negative than in the center of the major groove, depending on dielectric core and salt concentration. So multivalent cations and also larger cationic ligands, such as some antibiotics, are likely to adsorb in the minor groove, in agreement with earlier computations by A. and B. Pullman. Dielectric effects on the surface potential and the local potential variations are found to be relatively small. Bending of DNA is studied by placing a multivalent cation, MZ+, in the center of the minor or major groove, curving DNA around it for a certain length, and calculating the free energy difference between the bent and the straight configuration. Boltzmann averaged bending angles, 〈β〉, are found to be maximal in 0.03M monovalent salt, for a length of about 50 or 25 Å of curved DNA when an MZ+ ion is adsorbed in the minor or the major groove, respectively. When the dielectric constant of water is used throughout the calculation, we find maximal bends of 〈β〉 = 11° for M2+ and 〈β〉 = 16° for M3+ in the minor groove, 〈β〉 = 13° for M3+ in the major groove. The absence of bends in DNA adsorbed to mica in the presence of Mg salts supports the role of Mg2+ in “ion bridging” between DNA and mica. The treatment of the effective dielectric constant between two points outside a dielectric cylinder in water is appended. © 1998 John Wiley & Sons, Inc. Biopoly 46: 503-516, 1998
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    Protein design: On the threshold of functional properties (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 63-73 
    Details
    ISSN: 0006-3525
    Keywords: protein de novo design ; novel macromolecules ; topological templates ; Template Assembled Synthetic Proteins (TASP) ; biosensors ; protein folding ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ultimate goal in protein de novo design is the creation of novel macromolecules with tailor-made receptor, sensory, and catalytic functions. Despite considerable progress in understanding basic rules of secondary structure formation and protein stability, the well-known protein folding problem is still far from being solved and, in general, only a limited number of designed proteins are folded uniquely. In this article the state-of-the-art in protein design is demonstrated on some selected examples, indicating that the construction of protein-like macromolecules mimicking some essential features of natural proteins seems to be within reach. Thus, protein design and mimicry has become an interdisciplinary challenge with most intriguing perspectives. © 1998 John Wiley & Sons, Inc. Biopoly 47: 63-73, 1998
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    Mode of action of linear amphipathic α-helical antimicrobial peptides (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 451-463 
    Details
    ISSN: 0006-3525
    Keywords: bacteria ; antibiotics ; linear amphipathic α-helical antimicrobial peptides ; peptide-lipid interactions ; membrane permeation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The increasing resistance of bacteria to conventional antibiotics resulted in a strong effort to develop antimicrobial compounds with new mechanisms of action. Antimicrobial peptides seem to be a promising solution to this problem. Many studies aimed at understanding their mode of action were described in the past few years. The most studied group includes the linear, mostly α-helical peptides. Although the exact mechanism by which they kill bacteria is not clearly understood, it has been shown that peptide-lipid interactions leading to membrane permeation play a role in their activity. Membrane permeation by amphipathic α-helical peptides can proceed via either one of the two mechanisms: (a) transmembrane pore formation via a “barrel-stave” mechanism; and (b) membrane destruction/solubilization via a “carpet-like” mechanism. The purpose of this review is to summarize recent studies aimed at understanding the mode of action of linear α-helical antimicrobial peptides. This review, which is focused on magainins, cecropins, and dermaseptins as representatives of the amphipathic α-helical antimicrobial peptides, supports the carpet-like rather the barrel-stave mechanism. That these peptides vary with regard to their length, amino acid composition, and net positive charge, but act via a common mechanism, may imply that other linear antimicrobial peptides that share the same properties also share the same mechanism. © 1999 John Wiley & Sons, Inc. Biopoly 47: 451-463, 1998
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    Modified oligoribonucleotides as site-specific probes of RNA structure and function (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 39-55 
    Details
    ISSN: 0006-3525
    Keywords: modified nucleotides ; site-specific probes ; RNA structure ; RNA function ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modified nucleotides can be incorporated site specifically into RNA by the use of total chemical synthesis as well as by use of a variety of recombinant RNA techniques. The range of nucleotide analogues includes modifications to base, sugar, and phosphate for structure-function analysis and for cross-linking studies as well as to answer specific mechanistic questions in RNA catalysis. We describe how RNA containing site-specific modifications are prepared, concentrating in particular on routes involving chemically synthesized oligoribonucleotides, and give examples of their application in studies of the hammerhead and hairpin ribozymes. © 1998 John Wiley & Sons, Inc. Biopoly 48: 39-55, 1998
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    Dressed for success: Realizing the catalytic potential of RNA (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 29-37 
    Details
    ISSN: 0006-3525
    Keywords: amide synthase ; catalytic antibodies ; Diels-Alderase ; ideal catalyst platform ; in vitro selection ; Lewis acid ; modified uridines ; modified RNA ; ribozymes ; SELEX ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this manuscript the catalytic ability of RNA is examined and compared to other biopolymers. Despite having considerably fewer catalytically enabling properties when compared to proteins, the power of in vitro selection has allowed for RNA and DNA catalysts to be isolated. RNA catalysis has been expanded by incorporating modified bases to enrich the structural and functional diversity of RNA. Successful examples of new RNA chemistry using base modifications include carbon-carbon bond forming reactions and creation of highly specific active sites that are capable of recognizing small organic molecules without the need for nucleic acid templating or intercalation. In fact, the scope of functional modifications available for use in the RNA platform may eventually surpass those that are found in proteins and there are already hints that well chosen modifications allow nucleic acid catalysts to take advantage of mechanisms not available to selected protein catalysts for similar reactions. The chemical versatility of RNA is just emerging and future research directions will likely entail more creative methods for functional modification that will lead to new catalysts. © 1998 John Wiley & Sons, Inc. Biopoly 48: 29-37, 1998
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    New developments in structure determination of pseudoknots (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 137-153 
    Details
    ISSN: 0006-3525
    Keywords: RNA ; pseudoknot ; Turnip Yellow Mosaic Virus ; Mouse Mammary Tumor Virus ; Beet Western Yellows Virus ; Simian Retrovirus type-1 ; Hepatitis Delta Virus ; translational frameshifting ; ribozyme ; nmr ; x-ray diffraction ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recently, several high-resolution structures of RNA pseudoknots have become available. Here we review the progress in this area. The majority of the structures obtained belong to the classical or H-type pseudoknot family. The most complicated pseudoknot structure elucidated so far is the Hepatitis Delta Virus ribozyme, which forms a nested double pseudoknot. In particular, the structure-function relationships of the H-type pseudoknots involved in translational frameshifting have received much attention. All molecules considered show interesting new structural motifs. © 1999 John Wiley & Sons, Inc. Biopoly 48: 137-153, 1998
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    Structure and Dynamics of Hydrogen Chelates. Part 1. NMR-spectroscopic studies in the quinazoline-2-acetonitrile series (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 236-250 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To get informations on both the structure and dynamics of hydrogen chelates 1 of heteroaromatic systems, a great variety of quinazoline-2-acetonitrile chelates were synthesized (see 2-4). Similarly to the situation of the corresponding H-chelates in the pyrimidine-2-acetonitrile series, the investigation of these new derivatives 2-4 by NMR spectroscopic methods (DNMR, COSY, NOESY, ROESY, EXSY, HMQC, HMBC) confirms the presence of an equilibrium of the two possible H-chelate structures (two ‘rotamers’ I and II, i.e., (E)/(Z) isomers; see Scheme). The corresponding equilibria I ⇌ II were determined by complete 1H-NMR signal assignment at low temperatures (after freezing the rotational processes). In addition, the tautomer equilibria A ⇌ B (relative energies of the two minima of the nonsymmetrical double-well potential) for both ‘rotamers’ are ascertained by H,H and C,H couplings. The results are an important basis for the interpretation of both the UV/VIS absorptions and the dependence of fluorescence and fluorescence quantum yields on temperature.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810206
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    Stereoselective Reactions of Phthalimido-Substituted Radicals Derived from (±)-Threonine: A comparison with reactions of N-phthaloyliminium ions (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 268-284 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective reactions of phthalimido-substituted radicals derived from (±)-threonine with different radical traps are reported (Scheme 3, Table 1). A strong influence of the nature of the radical trap on the stereoselectivity was noticed. Small nucleophilic radical traps gave preferentially the syn products. The observed selectivities are explained with the A1,3 strain model and depend on steric and electronic effects (Fig. 2). Reactions with electrophilic radical traps such as diphenyl diselenide gave the anti diastereoisomers with moderate stereocontrol, presumably due to stereoelectronic effects. The same stereochemical outcome, i.e., preferential formation of the anti products, was observed for the reactions of the related N-phthaloyliminium ion (Scheme 5, Table 2). The stereochemistry of the ionic reaction is rationalized by a Felkin-Anh model (Fig. 3).
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    URL: http://dx.doi.org/10.1002/hlca.19980810208
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    Cyclopalladation of 1,1′-Azonaphthalene (= Di(naphthalen-1-yl)diazene): Isolation and characterization of two isomeric complexes (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 307-316 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cyclopalladation of 1,1′-azonaphthalene (= di(naphthalen-1-yl)diazene; 2) with bis(hexafluoroacetyl-acetonato)palladium(II) (3; [Pd(hfa)2]) yields the ortho-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[1-(naphthalen-1-ylazo-κN2)naphthalen-2-yl-κC2]palladium(II) (4) as well as the peri-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[8-(naphthalen-1-ylazo-κN2)naphthalen-1-yl-κC1]-palladium(II) (5); their structures were corroborated by X-ray analyses. The formation of the novel peri-metallated product 5 containing a six-membered palladacycle strongly depends upon the reaction conditions.
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    URL: http://dx.doi.org/10.1002/hlca.19980810211
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  • 176
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    The Photoisomerization Behavior of the (4-Hydroxycinnamoyl)-spermidines (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 342-352 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photoisomerization behavior of three mono[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 1, 2, and 3, and three bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 4, 5, and 6, are investigated. The synthetic product (E)-1 could be almost quantitatively (〉 96%) converted into its isomer (Z)-1 under UV light irradiation. In the cases of (E)-2 and (E)-3, a mixture of (E)/(Z) ca. 1:2 was obtained, when the same conditions were applied. The comparison of their UV spectra provides the possible explanation for these different behaviors. Furthermore, it was noticed that the (Z) → (E) isomerization of the C=C bond took place during the purification by reverse-phase high-performance liquid chromatography (RP-HPLC), and the (E)/(Z)-mixture is thus inseparable. The same feature could be observed during the isolation of the (Z,Z)-N,N′-bis[3-(4-hydroxyphenyl)prop-2-enoyl]-spermidines, (Z,Z)-4, (Z,Z)-5, and (Z,Z)-6. Nevertheless, the fractions of (Z,Z)-5 and (Z,Z)-6 were in almost pure state collected, and their 1-NMR spectra are presented.
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    URL: http://dx.doi.org/10.1002/hlca.19980810215
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    Preparation and Absolute Configuration of (-)-(E)-α-trans-Bergamotenone (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 153-162 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, absolute configuration, and olfactive evaluation of (-)-(E)-α-trans-bergamotenone (= (-)-(1′S,6′R,E)-5-(2′,6′-dimethylbicyclo[3.1.1]hept-2′-en-6′-yl)pent-3-en-2-one; (-)-1), as well as its homologue (-)-19 are reperted. The previously arbitrarily attributed absolute configuration of 1 and of (-)-α-trans-bergamotene (= (-)-(1 S,6R)-2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1. 1]hept-2-ene; (-)-2), together with those of the structurally related aldehydes (-)-3a,b and alcohols (-)-4a,b, have been rigorously assigned.
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    New Synthesis and Chirality of (-)-4,4,4,4′,4′,4′-Hexafluorovaline (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 182-186 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (-)-(R)-4,4,4,4′,4′,4′-Hexafluorovaline hydrochloride ((R)-5) of 98% ee is prepared from β,β-bis(trifluoromethyl)acrylic acid (= benzyl 4,4,4-trifluoro-3-(trifluoromethyl)but-2-enoate; 1) in 4 steps with an overall yield of 9.6%. Key step is the separation of the TsOH salts of the diastereoisomers obtained by anti-Michael addition of (+)-(R)-1-phenylethylamine (2) to 1 (→ (R,R)-3). In contrast to the published (S)-chirality, the X-ray structure analysis of (R,S)-6 reveals, that (R)-chirality has to be assigned to the levorotatory (-)-4,4,4,4′,4′,4′-hexafluorovaline hydrochloride.
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    URL: http://dx.doi.org/10.1002/hlca.19980810117
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  • 179
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    Tripodal Dodecadentate Ligands with Salicylamide and bipyridine binding sites for iron(II) and iron(III) coordination (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 207-218 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterization of tripodal dodecadentate ligands with salicylamide and bipyridine binding sites for iron(II) and iron(III) are presented.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810203
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  • 180
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    N,N-Dialkylcarbamato Complexes of the d10 cations of copper, silver, and gold (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 219-230 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of CuO'Bu with CO2, and iPr2NH in the presence of PPh3, gives the dialkylcarbamato complex [Cu(O2CNiPr2)(PPh3)2] (1). The CO2/R2NH system (R = Me, Et) in an appropriate organic medium reacts with Ag2O giving the corresponding N,N-dialkylcarbamato complexes of analytical formula [Ag(C2CNR2)] (R = Me, 2; R = Et, 3). The methyl derivative 2 was characterized by X-ray diffraction methods. Crystal data of 2: for [Ag2(O2CNMe2)2], C6H12Ag2N2O4, mol. wt. 391.9; monoclinic, space group P21/c, a = 12.08(1), b = 3.797(2), c = 11.316(7) Å, β = 113.37(6)°, V = 476.3 Å3, Z = 2, Dc = 2.732 g cm-3; μ(MoKα) = 40.64 cm-1, F(000) = 376.0; R = 0.059, Rw = 0.067; g.o.f. 1.27. The structure consists of dinuclear [(Ag2OCNMe2)2] units with slightly distorted linearly two-coordinated Ag-atoms containing bridging carbamato groups to form a substantially planar eight-membered ring with an intra-annular Ag—Ag distance of 2.837(2) Å; the dinuclear units are further joined by Ag—O bonds to form an infinite array. Compound 3, which is presumably dinuclear, as suggested by cryoscopic measurements in benzene, undergoes a structural fission with PPh3, giving the mononuclear triphenylphosphine derivative [Ag(O2CNEt2)(PPh3)2] (4). The amine-catalyzed conversion of Ag2O into Ag2CO3, in the presence of the iPr2NH/CO2 system, is also reported. Cl-Exchange from [AuCl(PPh3)] with [Ag(O2CNEt2)] (3) gives the first N,N-dialkylcarbamato complex of gold, namely [Au(O2CNEt2)(PPh3)] (5), which crystallizes in the monoclinic system: C23H25AuNO2P · 0.5 C7H16, mol. wt. 625.5, space group P21/c; a = 13.212(5), b = 12.25(1), c = 16.795(6) Å, β = 109.09(2)°, V = 2568(2) Å3, Z = 4, Dc, = 1.618 g cm-3; μ(AgKα) = 31.40 cm-1, F(000) = 1236.0; R = 0.058; Rw = 0.064; g.o.f. 2.121. The compound contains two-coordinated Au-atom, namely to the P-atom and to the O-atom of the monodentate carbamato group, the P—Au—O bond angle being 174.7(3)°. The reaction with MeI showed these compounds to react predominantly at the carbamato O-atom giving the corresponding urethanes R2NCO2Me. Evidence was gathered for the transient coordination of CO to Ag in 3.
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    1,3-Oxathiole and Thiirane Derivatives from the Reactions of Azibenzil and α-diazo amides with thiocarbonyl compounds (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 285-302 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of α-diazo ketones 1a,b with 9H-fluorene-9-thione (2f) in THF at room temperature yielded the symmetrical 1,3-dithiolanes 7a,b, whereas 1b and 2,2,4,4-tetramethylcyclobutane-1,3-dithione (2d) in THF at 60° led to a mixture of two stereoisomeric 1,3-oxathiole derivatives cis- and trans-9a (Scheme 2). With 2-diazo-1,2-diphenylethanone (1c), thio ketones 2a-d as well as 1,3-thiazole-5(4H)-thione 2g reacted to give 1,3-oxathiole derivatives exclusively (Schemes 3 and 4). As the reactions with 1c were more sluggish than those with 1a,b, they were catalyzed either by the addition of LiClO4 or by Rh2(OAc)4. In the case of 2d in THF/LiClO4 at room temperature, a mixture of the monoadduct 4d and the stereoisomeric bis-adducts cis- and trans-9b was formed. Monoadduct 4d could be transformed to cis- and trans-9b by treatment with 1c in the presence of Rh2(OAc)4 (Scheme 4). Xanthione (2e) and 1c in THF at room temperature reacted only when catalyzed with Rh2(OAc)4, and, in contrast to the previous reactions, the benzoyl-substituted thiirane derivative 5a was the sole product (Scheme 4). Both types of reaction were observed with α-diazo amides 1d,e (Schemes 5-7). It is worth mentioning that formation of 1,3-oxathiole or thiirane is not only dependent on the type of the carbonyl compound 2 but also on the α-diazo amide. In the case of 1d and thioxocyclobutanone 2c in THF at room temperature, the primary cycloadduct 12 was the main product. Heating the mixture to 60°, 1,3-oxathiole 10d as well as the spirocyclic thiirane-carboxamide 11b were formed. Thiirane-carboxamides 11d-g were desulfurized with (Me2N)3P in THF at 60°, yielding the corresponding acrylamide derivatives (Scheme 7). All reactions are rationalized by a mechanism via initial formation of acyl-substituted thiocarbonyl ylides which undergo either a 1,5-dipolar electrocyclization to give 1,3-oxathiole derivatives or a 1,3-dipolar electrocyclization to yield thiiranes. Only in the case of the most reactive 9H-fluorene-9-thione (2f) is the thiocarbonyl ylide trapped by a second molecule of 2f to give 1,3-dithiolane derivatives by a 1,3-dipolar cycloaddition.
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    URL: http://dx.doi.org/10.1002/hlca.19980810209
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    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810301
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  • 183
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    Synthesis of Chiral C2-Symmetric Binucleating Ligands (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 491-506 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a series of chiral enantiomerically pure C2-symmetric binucleating ligands is reported. Ligands of type 1-4, which consist of a phenolic or heterocyclic unit bridging two chiral dihydrooxazole rings. are readily accessible from chiral amino alcohols. Ligands 5a and 5b are composed of a cyclic urea or thiourea unit, respectively, and two 3,4-dihydro-2H-pyrrole rings containing a stereogenic center next to the N-atom. Compounds of this type are readily assembled from ethane-1,2-diamine and an imidothioic ester derived from pyroglutamic acid. These new ligands, which can coordinate two metals in close proximity to each other, are of interest regarding possible applications in asymmetric catalysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810304
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  • 184
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    Stability and Lability of Dicopper Double-Stranded Helicates in Solution (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 548-557 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stability constants have been measured for a series of ligands based on a 2,2′-(pyridine-2,6-diyl)bis[1H-benzimidazole] unit which forms dinuclear double-stranded helical complexes with copper(I). Variation of different structural parameters confirms the importance of the coordinate bond, the stacking interactions, and the weakly bridging pyridine units observed by X-ray crystallography. The stabilities of the complexes depend strongly on the solvent, and in MeCN, which is a good solvent for copper(I), the complexes are less stable and assemble in a stepwise manner. The interconversion of the enantiomers may be followed by 1H-NMR and takes place on a millisecond time scale around room temperature. The trends in lability are similar to those found for the stability of the complexes.
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  • 185
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    7-Deazapurine Oligodeoxyribonucleotides: The effects of 7-deaza-8-methylguanine on dna structure and stability (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 570-583 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligodeoxyribonucleotides containing 7-deaza-2′-deoxy-8-methylguanosine (m8c7Gd; 2b) were prepared. For this purpose, the phosphonate 3a and the phosphoramidite 3b were synthesized and employed in solidphase oligodeoxyribonucleotide synthesis. The structures and the thermodynamic data of duplex formation of oligodeoxyribonucleotides containing 2b were investigated by temperature-dependent CD and UV spectra and compared with those containing 7-deaza-2′-deoxy-7-methylguanosine (m7c7Gd) or 7-deaza-2′-deoxy-guanosine (c7Gd; 2a). In general, compound 2b reduces the duplex stability. In case of the sequence d(m8c7G-C)4 (18), the B → Z transition was facilitated by the incorporation of 2b. Moreover, a single 7-deaza-8-methylguanine residue present in an oligodeoxyribonucleotide tract of guanine residues destabilizes the dG quadruplex significantly. This destabilization is more pronounced than in the case of 7-deazaguanine or 7-deaza-7-methyl-guanine.
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    URL: http://dx.doi.org/10.1002/hlca.19980810310
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  • 186
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    Absolute rate Constants for the Addition of Malonyl Radicals to Alkenes in Solution (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 770-780 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate constants and their Arrhenius parameters are obtained for the addition of a cyclic malonyl radical derived from Meldrum's acid to 20 mono- or 1,1-disubstituted alkenes in (±)-propylene oxide and for the addition of the open-chain di(tert-butyl)malonyl radical to six mono- or 1,1-disubstituted alkenes in 1,1,2-trichloro-1,2,2-trifluoroethane by time-resolved electron spin resonance spectroscopy. At room temperature, the radicals add at the unsubstituted C-atoms with rate constants ranging from 1.1. 105 M-1S-1 (acrolein) to 2.4. 106 M-1S-1 (1,1-diphenylethene). The frequency factors are in the narrow ranges of log (A/M-1S-1) = 8.7 ± 0.1 for the cyclic and log (A/M-1S-1) = 8.2 ± 0.2 for the open-chain malonyl species, whereas the activation energies vary from 12.9 kJ/mol (1,1-diphenylethene) to 21.7 kJ/mol (acrylonitrile). They correlate with the alkene ionization potentials and, more weakly, with the reaction enthalpy. No correlation was found between the activation energies and the alkene electron affinities. Hence, the results confirm and quantify the electrophilic nature of malonyl radicals in addition reactions.
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    Synthesis of the Spermidine Alkaloid (-)-(4R)-Dihydroisomyricoidine (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1303-1318 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An asymmetric synthesis of (-)-(4R)-dihydroisomyricoidine (28), a 13-membered amino lactam of type A, was performed by a diastereoselective Michael addition between the spermidine derivative 3 and the commercially available optically active ethyl carboxylate 4, and the cyclization of the resulting ω-amino acid 7 using diethyl phosphorocyanidate ((EtO)2POCN), followed by a Wittig reaction to introduce the (Z)-side chain. Some side reactions are also discussed.
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    URL: http://dx.doi.org/10.1002/hlca.19980810541
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  • 188
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    New Types of Potentially Antimalarial Agents: Epidioxy-substituted norditerpene and norsesterpenes from the marine sponge Diacarnus levii (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1285-1292 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Natural free carboxylic acids from the hadromerid sponge Diacarnus levii (Kelly-Borges and Vacelet) were esterified to yield the new cyclic norditerpene peroxides ent-muqubilin benzyl ester (= (αR,3S,6R)-α,6-dimethyl-6-[(E)-4-methyl-6-(2,6,6-trimethyl-cyclohex-1-en-1-yl)hex-3-enyl]-1,2-dioxan-3-acetic acid benzyl ester; 6, diacarnoate B methyl ester(= (αS,3R,6R)-α,6-dimethyl-6-{2-(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-3-oxo-2,5,5,8a-tetramethylnaphthalen-1-yl)ethyl}-1,2-dioxan-3-acetic acid methyl ester; 9), and deoxydiacarnoate B benzyl ester (= (αS,3R,6R)-α,6-dimethyl-6-{2-[(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-2,5,5,8a-tetramethyl-1-naphthalenyl]ethyl}-1,2-dioxan-3-acetic acid benzyl ester; 10), which were isolated following extensive chromatography. The relative configuration of the peroxide/α-methylacetate moiety of 6, 9, and 10, was directly determined from their NMR spectra. The absolute configurations of the peroxide/α-methylacetate moiety was deduced from comparative 1H-NMR data of the (S)- and (R)-phenylglycine methyl ester derivatives 7 and 8 as well as 11/13 and 12/14, all obtained from a mixture of the precursors of 3, 6, and 10. The absolute configuration at the carbobicyclic moiety of enone 9 and of 10, is identical, as established by chemical interconversion, 9 and 10 belong to the normal labdane series according to empirical CD rules, applied either directly to 9 or to the parent (+)-sclareolide-derived enone 20. In contrast, molar rotation additivity rules suggest the ent-labdane configuration for 9 and 10. The epidioxides 1-3, 6, and 10 proved active in vitro against the malaria parasite Plasmodium falciparum; especially the previously isolated methyl 3-epinuapapuanoate (2) was active against a chloroquine-resistant strain, and this with a good security index.
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    URL: http://dx.doi.org/10.1002/hlca.19980810539
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    3-Hydroxy-2-cyanoalk-2-enamides, and 2-Cyano-2-(tetrahydrofuran-2-ylidene)- and 2-Cyano-2-(tetrahydropyran-2-ylidene)acetamides: Synthesis, structure, and solvent-dependent (Z)/(E)-isomerismDedicated to Professor D. Seebach on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1319-1328 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3-Hydroxy-2-cyanoalk-2-enamides, and 2-cyano-2-(tetrahydrofuran-2-ylidene)- and 2-cyano-2-(tetrahydropyran-2-ylidene)acetamides with N-alkyl and N-aryl substituents have been synthesized in three steps from cyanoacetic acid. Their conformations were investigated by X-ray crystallography and 1H-NMR ROESY spectroscopy at room temperature. The enolic compounds 1-3 adopt an extended conformation stabilized by a strong intramolecular O—H … O=C bond both in the solid state and in (D6)DMSO solution. In contrast, the structure of the cyclic derivatives 5a,b-8a,b is solvent-dependent. In the solid state and in CDCl3 solution, the compounds adopt an extended conformation of type I or III, while, in (D6)DMSO solution, their structures undergo time-dependent (Z)/(E)-isomerization structures (of type II or IV). This observation is compatible with a dipolar transition state of rotation. The kinetics of the isomerization are controlled by the N-substituent, the N-(t-Bu) derivatives 7a and 7b having the highest barrier of rotation around the C=C bond. The whole body of experimental evidence together with the results of molecular-mechanics calculations with I-IV, indicate that, in DMSO, two (E)/(Z)-isomers with two conformations are present, and that they undergo interconversion at room temperature with four different constants. The very fast exchange rates kI,II and kIII,IV in the NMR time-scale might be responsible for the detection of only two isomers.
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    URL: http://dx.doi.org/10.1002/hlca.19980810542
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    Monoterpene Dimers from Lisianthius seemannii (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1393-1403 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new acylated dimeric secoiridoid glycoside, seemannoside A (2), has been isolated from the aerial parts of Lisianthius seemannii (GRISEB) O. KUNTZE (Gentianaceae). The structure was established by spectroscopic analysis (UV, MS, 1H- and 13C-NMR, and 2D-NMR experiments) and chemical reactions as (E-4′-O-p-coumaroyl)lisianthioside. The structure of the (Z)-isomer (seemannoside B, 3), also present in the plant, was confirmed by LC/UV/1H-NMR analysis. The active principle, 6, responsible for the antifungal activity of the apolar extract against Cladosporium cucumerinum, has been isolated. Its structure has been established by NMR spectroscopy and X-ray crystallographic analysis as a rare type of aglycone monoterpene dimer.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810548
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  • 191
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    Asymmetric synthesis of pentono- and 6-deoxyhexono-δ-lactams via hetero-Diels-Alder reactions with nitroso dienophile (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1417-1428 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Asymmetric Diels-Alder reaction of the pentadienoic and hexadienoic acids 2a,b with the chiral chloronitroso derivative 3 gave the primary adducts 4a,b with good-to-excellent enantioselectivity. Subsequent as- or trans-dihydroxylation and hydrogenolytic cleavage of the N—O bond led to the 5-amino-5-deoxypentono-δ-lactams 13a, 14, 15a, and 16 in the D-ribose, L-arabinose, D-xylose, and L-lyxose series, respectively, and to the 5-amino-5,6-dideoxyhexono-δ-lactams 13b and 15b in the D-allose and D-glucose series, respectively.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810550
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  • 192
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    Distamycin-NA: A DNA Analog with an Aromatic Heterocyclic Polyamide Backbone. Part 1. Synthesis and structural analysis of monomers and dimers containing the nucleobase uracil (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 14-34 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the monomeric building block 13 and its constitutional isomer 12 of a new type of DNA analog, distamycin-NA, is presented (Schemes 1 and 2). This building block consists of a uracil base attached to a thiophene core unit via a biaryl-like axis. Next to the biaryl-like axis on the thiophene chromophore, a carboxy and an amino substituent are located allowing for oligomerization via peptide coupling. The proof of constitution and the conformational preferences about the biaryl-like axis were established by means of X-ray analyses of the corresponding nitro derivatives 10 and 11. Thus, the uracil bases are propeller-twisted relative to the thiophene core, and bidentate H-bonds occur between two uracil bases in the crystals. The two amino-acid building blocks 12 and 13 were coupled to give the dimers 15 and 16 using dicyclohexylcarbodiimide (DCC) in THF/LiCl and DMF, respectively. While the dimer 15 showed no atropisomerism on the NMR time scale at room temperature, its isomer 16 occurred as distinct diastereoisomers due to the hindered rotation around its biaryl-like axis. Variable-temperature 1H-NMR experiments allowed to determine a rotational barrier of 19 ± 1 kcal/mol in 16. The experimental data were complemented by AM1 calculations.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810103
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  • 193
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    [2+3] Cycloadditions of ‘Thiocarbonyl Ylides’ (= (Alkylidenesulfonio)methanides) and diazoalkanes with N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole])Part of the planned Ph.D. Thesis of T.G., University of Łódź.Dedicated to Professor Romuald Bartnik (University of Łódź) on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 66-77 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heating of a mixture of N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole]; 1) and 2,5-dihydro-1,3,4-thiadiazole 2a or 2b gave the 1,3-dithiolanes 4a and 4b, respectively, via a regiospecific 1,3-dipolar cycloaddition of the corresponding ‘thiocarbonyl methanides’ 3a,b onto the C=S group of 1 (Schemes 1 and 2). The adamantane derivative 4b was not stable in the presence of 1H-imidazole and during chromatographic workup. The isolated 1,3-dithiole 5 is the product of a base-catalyzed elimination of 1H-imidazole from the initial cycloadduct 4b. The formation of the S,N-acetal 6 can be rationalized by a protonation of the ‘thiocarbonyl ylide’ 3b followed by a nucleophilic addition of 1H-imidazole. With the diazo compounds 8a-e (Scheme 3) 1 underwent a regiospecific 1,3-dipolar cycloaddition to give the corresponding 2,5-dihydro-1,3,4-thiadiazole derivatives 9, which spontaneously eliminated 1H-imidazole to yield (1H-imidazol-1-yl)-1,3,4-thiadiazoles 10. The structures of 10a and 10d were established by X-ray crystallography. In the case of diazodiphenylmethane (8f), the initial cycloadduct 9f decomposed via a ‘twofold extrusion’ of N2 and S to give 1,1′-(2,2-diphenylethenylidene)bis[1H-imidazole] (11; Scheme 3).
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810108
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  • 194
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    Synthesis of New Nucleosides by coupling of chloropurines with 2- and 3-deoxy derivatives of N-methyl-D-ribofuranuronamide (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 145-152 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of new deoxyribose nucleosides by coupling chloropurines with modified D-ribose derivatives is reported. The methyl 2-deoxy-N-methyl-3-O-(p-toluoyl)-α-D-ribofuranosiduronamide (α-D-8) and the corresponding anomer β-D-8 were synthesized starting from the commercially available 2-deoxy-D-ribose (1) (Scheme 1). Reaction of α-D-8 with the silylated derivative of 2,6-dichloro-9H-purine (9) afforded regioselectively the N9-(2′-deoxyribonucleoside) 10 as anomeric mixture (Scheme 2), whereas β-D-8 did not react. Glycosylation of 9 or of 6-chloro-9H-purine (17) with 1,2-di-O-acetyl-3-deoxy-N-methyl-β-D-ribofuranuronamide (13) yielded only the protected β-D-anomers 14 and 18, respectively (Scheme 3). Subsequent deacetylation and dechlorination afforded the desired nucleosides β-D-11, β-D-12,15, and 16. The 3′-deoxy-2-chloroadenosine derivative 15 showed the highest affinity and selectivity for adenotin binding site vs. A1 and A2A adenosine receptor subtypes.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810113
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  • 195
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    Asymmetric Synthesis of (S)-5,5,5,5′,5′,5′,5′-Hexafluoroleucine (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 174-181 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (S)-5,5,5,5′,5′,5′-Hexafluoroleucine ((S)-13) of 81 % ee is prepared from hexafluoroacetone (l) and ethyl bromopyruvate (= ethyl 2-oxopropanoate) in 7 steps with an overall yield of 18% (Schemes 1 and 2). Key step in this sequence is the highly enantioselective reduction of the carbonyl group in α-keto ester 4 either by bakers' yeast (91 % ee) or by ‘catecholborane’ 6 utilizing an oxazaborolidine catalyst, yielding hydroxy ester (R)-5 with 99% ee. The absolute configuration was determined by X-ray analysis of the HCl adduct (S,R)-9b of (2S)-N-[(R)- l-phenylethyl]-5,5,5,5′,5′,5′-hexafluoroleucine ethyl ester.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810116
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  • 196
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    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810201
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  • 197
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    Preparation of N-Fmoc-Protected β2- and β3-Amino Acids and their use as building blocks for the solid-phase synthesis of β-peptidesPartially published in a preliminary communication [1]; β2 means that the NH2, group ist at C(3)(= C(β)) and the side chain at C(2) of the amino acid, and β3 indicates that both the NH2 group and the side chain are at C(3)( = C(β)). Fmoc = (9H-Fluoren-9-ylmethoxy)carbonyl.Dedicated to Professor A. I. Meyers, University of Colorado, Fort Collins, on the occasion of his 65th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 187-206 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Fmoc-Protected (Fmoc = (9H-fluoren-9-ylmethoxy)carbonyl) β-amino acids are required for an efficient synthesis of β-oligopeptides on solid support. Enantiomerically pure Fmoc-β3-amino acids β3: side chain and NH2 at C(3)(= C(β)) were prepared from Fmoc-protected (S)- and (R)-α-amino acids with aliphatic, aromatic, and functionalized side chains, using the standard or an optimized Arndt-Eistert reaction sequence. Fmoc-β2- Amino acids (β2 side chain at C(2), NH2 at C(3)(= C(β))) configuration bearing the side chain of Ala, Val, Leu, and Phe were synthesized via the Evans' chiral auxiliary methodology. The target β3-heptapeptides 5-8, a β3- pentadecapeptide 9 and a β2-heptapeptide 10 were synthesized on a manual solid-phase synthesis apparatus using conventional solid-phase peptide synthesis procedures (Scheme 3). In the case of β3-peptides, two methods were used to anchor the first β-amino acid: esterification of the ortho-chlorotrityl chloride resin with the first Fmoc-β-amino acid 2 (Method I, Scheme 2) or acylation of the 4-(benzyloxy)benzyl alcohol resin (Wang resin) with the ketene intermediates from the Wolff rearrangement of amino-acid-derived diazo ketone 1 (Method II, Scheme 2). The former technique provided better results, as exemplified by the synthesis of the heptapeptides 5 and 6 (Table 2). The intermediate from the Wolff rearrangement of diazo ketones 1 was also used for sequential peptide-bond formation on solid support (synthesis of the tetrapeptides 11 and 12). The CD spectra of the β2- and β3-peptides 5, 9, and 10 show the typical pattern previously assigned to an (M) 31 helical secondary structure (Fig.). The most intense CD absorption was observed with the pentadecapeptide 9 (strong broad negative Cotton effect at ca. 213 nm); compared to the analogous heptapeptide 5, this corresponds to a 2.5 fold increase in the molar ellipticity per residue!
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810202
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  • 198
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    Photoaddition of Ethyl 2,2-Dimethyl-5-oxo-5,6-dihydro-2H-pyridine-1-carboxylate to 2,3-dimethylbut-2-ene (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 303-306 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On irradiation (350 nm) in the presence of excess 2,3-dimethylbut-2-ene, the newly synthesized title compound 5 affords as main products the unexpected cyclopropylpyrrolidine 10 (50%) and the spiro-oxetane 9 (25%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810210
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  • 199
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    Influence of Lewis Acids on the [4 + 2] Cycloaddition of N,N′-Fumaroylbis[(2R)-bornane-10,2-sultam] to Cyclopentadiene and application to various dienes (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 324-329 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Among seventeen different Lewis acids, TiCl4 was found to be the best catalyst for the [4 + 2] cycloaddition of cyclopentadiene to N,N′-fumaroylbis[(2R)-bornane-10,2-sultam] ((-)-1). Independently of the TiCl4 molar concentration, almost constant and complete (98-89% d.e.) diastereofacial π-selection was achieved in the Diels-Alder addition of (-)-1 to cyclopentadiene, cyclohexadiene, isoprene, and 2,3-dimethylbuta-1,3-diene.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810213
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  • 200
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    N,Se-Acetals: Preparation and use in diastereoselective radical reactionsFor a preliminary communication of this work, see [1]. (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 353-373 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new facile synthesis of N,S- and N,Se-acetals starting from aldehydes and primary amines is presented (Schemes 3-5). These acetals are used as precursors for stereoselective radical deuteration and allylation reactions (Schemes 6 and 7, Tables 1 and 2). The stereochemical outcome of the reactions depends on the radical trap and the substituents at the N-atom. Deuterations give always anti products with moderate to high selectivities. The allylation reactions give either syn or anti products with low to moderate selectivities. The observed stereoselectivities can be explained with a model based on minimization of A1,3 strain and are controlled by steric and stereoelectronic effects.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810216
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