bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of polyhydroxyalkaloids in Lonchocarpus extracts by GC‐MS of acetylated derivatives
Authors: Magalhães Aderbal F. , Santos Celira C. , Magalhães Eva G. , Nogueira Marisa A.
Published: September 2002

The methanol extracts of the roots of Lonchocarpus cultratus, L. latifolius and L. subglaucescens, species native to Brazil, were all active in the brine shrimp lethality test. Fractions rich in polyhydroxylated alkaloids were obtained from these extracts and, following acetylation, were analysed by GC‐MS leading to the identification of acetylated derivatives of 2,5‐trans‐dihydroxymethyl‐3,4‐trans‐dihydroxypyrrolidine (1), 1‐deoxymannojirimycin, 1‐deoxynojirimycin, fagomine and homonojirimycin. Only from L. subglaucescens could a compound with the constitution and relative configuration expected for the penta‐acetate of 1 be isolated, and its molecular structure was determined for the first time through extensive spectral data analysis. Copyright © 2002 John Wiley & Sons, Ltd.
High‐performance liquid chromatographic analysis of genistein and other isoflavonoids from heartwood of Ougeinia dalbergioides
Authors: Bala Shashi , Uniyal G. C.
Published: September 2002

A simple binary gradient HPLC method employing a Symmetry® C18 column is described for the analysis of genistein, ougeinin, homoferririn, 2′,4′,5,7‐tetrahydroxy‐6‐methyl isoflavone and 2′,4′,8‐trihydroxy‐6‐methoxy‐7‐methyl isoflavone present in heartwood extract of Ougeinia dalbergioides. Copyright © 2002 John Wiley & Sons, Ltd.
Early ultrasound diagnosis of Neu–Laxova syndrome
Authors: Rode Martha E. , Mennuti Michael T. , Giardine Rose M. , Zackai Elaine H. , Driscoll Deborah A.
Published: September 2002

We report the mid‐trimester prenatal diagnosis of Neu–Laxova syndrome (NLS) in two at risk families utilizing serial sonographic examinations. Ultrasound and pathologic findings from seven affected pregnancies, the largest case series of NLS to date, are presented. One fetus had anencephaly and incomplete rachischisis, an anomaly that has not been previously reported in association with NLS. Ultrasonographic detection of severe intrauterine growth restriction (IUGR), abnormally postured limbs, microcephaly, and edema allowed prenatal diagnosis of NLS in five of these at risk pregnancies during the mid‐trimester. Growth curves derived from serial sonograms reveal abnormalities of all standard biometric measurements. The growth discrepancy was most pronounced in the measurements of the biparietal diameter, which were consistently less than two standard deviations below the mean across all gestational ages. This case series confirms that aberrant growth and anomalies may be detected sufficiently early in gestation to permit prenatal diagnosis of NLS. Copyright © 2001 John Wiley & Sons, Ltd.
First trimester screening for Down syndrome and assisted reproduction: no basis for concern
Authors: Wøjdemann K. R. , Larsen S. O. , Shalmi A. , Sundberg K. , Christiansen M. , Tabor A.
Published: September 2002

In pregnancies obtained after assisted reproduction the false‐positive rate of second trimester Down syndrome (DS) screening is increased by 1.5–3‐fold. This may cause an increase in the number of amniocenteses and the fetal loss rate. The present study for the first time examined whether assisted reproductive technologies affect the results of first trimester screening. The markers PAPP‐A, free β‐hCG and the nuchal translucency (NT) thickness were examined at 12–14 weeks' gestation. Screening markers in 47 in vitro fertilisation (IVF), 63 ovulation induction (OI) and 3026 spontaneously conceived singleton pregnancies were compared. The MoM (multiples of the median) value in the IVF pregnancies was 1.02 (95% CI: 0.85–1.22) for PAPP‐A, 1.14 (95% CI: 0.95–1.37) for β‐hCG and 0.97 (95% CI: 0.89–1.05) for NT; the MoM value in the OI pregnancies was 0.89 (95% CI: 0.76–1.05) for PAPP‐A, 1.08 (95% CI: 0.93–1.25) for β‐hCG and 1.02 (95% CI: 0.95–1.11) for NT. The first trimester marker values in assisted reproductive pregnancies and spontaneously conceived pregnancies were not significantly different. Estimated false‐positive rates for a risk cut‐off of 1:400 varied from 4.7% in IVF pregnancies to 5.1% in OI pregnancies. Therefore the false‐positive rate in Down syndrome screening should be independent of the method of conception. Copyright © 2001 John Wiley & Sons, Ltd.
Prenatal diagnosis of a familial complex chromosomal rearrangement involving chromosomes 5, 10, 16 and 18
Authors: Lee M. H. , Park S. Y. , Kim Y. M. , Kim J. M. , Han J. Y. , Kim M. Y. , Ryu H. M.
Published: September 2002

We report one case of a familial complex chromosomal rearrangement (CCR) involving four different chromosomes 5, 10, 16 and 18. The CCR was detected prenatally at 20 weeks' gestation because of advanced maternal age and history of recurrent miscarriages. Cytogenetic analysis of cultured amniotic fluid cells with GTG banding showed a 46,XX,t(5;16;10;18)(q13;q22;q11.2;q21) karyotype. Parental cytogenetic study revealed that the mother has the same CCR. RBG banding, high‐resolution banding and fluorescence in situ hybridization (FISH) were used to characterize further and confirm the conventional banding data. No physical abnormalities were shown in the targeted fetal ultrasonography examination. The parents decided to continue the pregnancy. The child is now 2 years old and has neither congenital anomalies nor evidence of delayed psychomotor development. The fetal targeted ultrasound and FISH analysis helped us reassure fetal status. Copyright © 2002 John Wiley & Sons, Ltd.
Prenatal diagnosis of partial tetrasomy 14: a case study
Authors: George Alice M. , Hallam Lavinia , Oei Paul , McGaughran Julie
Published: September 2002

Prenatal specimens were received from a fetus with abnormalities noted on ultrasound. A supernumerary marker chromosome (SMC) was detected: 47,XY,+mar. Fluorescence in situ hybridisation (FISH) further classified this to be partial tetrasomy for chromosome 14. We compare this finding with other cases of SMC (14) and further classify phenotype with karyotype. Copyright © 2002 John Wiley & Sons, Ltd.
Achondrogenesis type II with normally developed extremities: a case report
Authors: Kocakoc Ercan , Kiris Adem
Published: September 2002

We present a case of achondrogenesis type II with normally developed extremities that was confirmed with postmortem ultrasonographic and radiographic examination. The length of the long bones may vary and the diagnosis of achondrogenesis should not be ruled out with normally developed extremities. Intrauterine sonographic examination of the vertebrae is very important and the absence of vertebral body ossification may be the unique finding of achondrogenesis type II. Axial ultrasonographic images and postmortem plain radiographs are useful to clarify the pathology. Copyright © 2002 John Wiley & Sons, Ltd.
Second trimester two‐step trisomy 18 screening using maternal serum markers
Authors: Muller Françoise , Sault Corinne , Lemay Catherine , Roussel‐Mizon Nathalie , Forestier François , Frendo Jean‐Louis
Published: September 2002

Trisomy 21 maternal serum marker screening has led to screening for other anomalies, including trisomy 18. Trisomy 18 is generally prenatally diagnosed because of major morphological defects. However, in up to 30% of cases ultrasound signs are unclear, and in most cases diagnosis is performed late in pregnancy. Of the different maternal serum markers, PAPP‐A is now considered as the best for trisomy 18 screening. However, pregnancy‐associated plasma protein A (PAPP‐A) is of value in first trimester screening for trisomy 21, but not in the second trimester. We therefore propose a two‐step screening strategy. Based on 45 trisomy 18 cases, we confirm the values of alpha‐fetoprotein (AFP) (median 0.61 MoM), free β‐human chorionic gonadotrophin (β‐hCG) (median 0.24 MoM) and of PAPP‐A (median 0.08 MoM). In the first step, a 0.5 MoM cut‐off for AFP or for free β‐hCG resulted in detection of 37/45 trisomy 18 cases (82%) with a 10% false‐positive rate. The second step consisted of the measurement of PAPP‐A for all these false‐positive cases. Using a PAPP‐A cut‐off of 0.5 MoM, all the 37 trisomy 18 cases were detected, but now with a 0.1–0.2% false‐positive rate. Amniocentesis was only offered to these few patients. This two‐step second trimester screening will be of value for patients who have not been included in first trimester screening based on nuchal translucency (NT) measurement combined with the first trimester markers, PAPP‐A and free β‐hCG. Copyright © 2002 John Wiley & Sons, Ltd.
Intraventricular haemorrhage in a fetus with cerebral cytomegalovirus infection
Authors: Nigro Giovanni , La Torre Renato , Sali Eleonora , Auteri Maura , Mazzocco Manuela , Maranghi Luca , Cosmi Erich
Published: September 2002

Cytomegalovirus (CMV) is the leading infectious cause of prenatal neurological damage, which is particularly severe when primary maternal infection occurs during the first 16 weeks of gestation, at the time of organ development and neuronal migration. Vascular involvement has been suggested to be among thepossible pathogenic mechanisms of virus‐induced pathology, in addition to direct viral effects. We report on a fetus with cerebral CMV infection, which had intraventricular haemorrhage, together with oligohydramnios and hyperechogenic bowel, following maternal primary CMV infection. Copyright © 2002 John Wiley & Sons, Ltd.
Prenatal diagnosis of complete sole trisomy 1q
Authors: Pettenati Mark J. , Berry Margaret , Shashi Vandana , Hartley Bowen J. , Harper Margaret
Published: September 2002

The prenatal diagnosis of a complete trisomy of the long arm of chromosome 1 is reported. Major ultrasound findings included: nuchal thickening, bi‐temporal narrowing, a single choroid plexus cyst, andmild ventriculomegaly. There was a mass in the chest and abdomen, pleural effusion, ascites and a hyperechoic bowel. Skin edema was present. The fetus died at 26 weeks' gestation. A literature review is presented of 17 de novo and two inherited cases with only trisomy 1q. Of note is the fact that 3/5 prenatally detected 1q trisomies have teratomas. A review of the literature reveals a dismal outcome fortrisomy 1q cases if the duplication involves bands 1q25→q32. Copyright © 2001 John Wiley & Sons, Ltd.
Maternal serum levels of dimeric inhibin A in pregnancies affected by trisomy 21 in the first trimester
Authors: Spencer Kevin , Liao Adolfo W. , Ong Charas Y. T. , Geerts Lut , Nicolaides Kypros H.
Published: September 2002

Dimeric inhibin A was measured in maternal serum samples from 45 pregnancies affected by trisomy 21 and 493 samples from unaffected pregnancies at 10–14 weeks of gestation. Inhibin A levels in affected pregnancies were compared with levels of free β‐hCG and PAPP‐A in the same series. In the trisomy 21 group, the median multiple of the median (MoM) inhibin A was not significantly elevated (1.28 vs 1.00) with only 15.5% being above the 95th centile. In contrast, the median MoM free β‐hCG was significantly increased (2.05 vs 1.00) with 36% above the 95th centile and PAPP‐A was significantly reduced (0.49 vs 1.00) with 42% below the 5th centile. Inhibin A levels in the trisomy 21 group were significantly correlated with gestational age such that median levels rose from 1.04 at 11 weeks to 1.30 at 12 weeks and 1.67 at 13 weeks. These findings suggest that first trimester biochemical screening for trisomy 21, which is currently optimised using maternal serum free β‐hCG and PAPP‐A and fetal nuchal translucency, will not benefit from the inclusion of inhibin A. Copyright © 2001 John Wiley & Sons, Ltd.
The Rydel Seiffer tuning fork: an inexpensive device for screening diabetic patients with high‐risk foot
Authors: Vijay V. , Snehalatha C. , Seena R. , Ramachandran A.
Published: September 2002

Considering the simple and inexpensive nature of the graduated tuning fork, we evaluated its usefulness in screening for vibratory sensation loss in non‐diabetic and diabetic subjects, compared with the values obtained with biothesiometer. The vibration perception scores were tested in 195 non‐diabetic healthy control subjects (n=195, M:F, 80:115, Mean±SD, age 50.3±10.4 (years), in 455 Type 2 diabetic subjects who had signs and symptoms of sensory neuropathy and abnormal biothesiometric readings (reading>25V), (n=455, M:F 326:129, Mean Age 58.1±7.7 years, HbA1c 10.1±2.4%) and in 471 diabetic patients with no evidence of neuropathy by biothesiometry. (M:F 299:172, Mean Age 48.0±7.5 years, HbA1c 9.5±2.2%). Patients with neuropathy had a lower mean score of 4.5±2.6 compared with the non‐neuropathy cases (7.7±0.5, P<0.001). Among the 455 patients identified as having neuropathy by abnormal biothesiometric values, 235 had an abnormal tuning fork score of ≤4.0. Tuning fork scores were normal in all the 471 non‐neuropathy cases, thus giving a specificity of 100%. This study shows that the graduated tuning fork has a high specificity and a fairly good sensitivity in the diagnosis of diabetic foot problems. Copyright © 2001 John Wiley & Sons, Ltd.
Short‐term safety and tolerability of antihypertensive agents in Korean patients: an observational study
Authors: Kim Young Sik , Park Hye Soon , Sunwoo Sung , Byeon Jai Jun , Song Yun Mi , Seo Hong Gwan , Kim Cheol Hwan , Cheon Kyeong Soo , Yoo Sun Mi , Lee Jung Kwon
Published: September 2002

Purpose

In order to assess the short‐term safety and tolerability of newly prescribed antihypertensive monotherapies in Korean patients, a prospective study was carried out.

Methods

A total of 1181 patients were observed from July 1997 to August 1999. At 2, 4, 8 and 12 weeks after initiation of antihypertensive monotherapy, the patients were evaluated for whether treatment was to be continued and the development of any adverse reactions.

Results

During the first 12 weeks, the percentage of subjects continuing with their initial angiotensin converting enzyme inhibitors (ACEI) (40.7%) was substanti ally lower than that of subjects continuing with angiotensin II receptor antagonists (ARA) (66.2%), α‐blockers (63.0%), calcium channel blockers (CCB) (61.3%), β‐blockers (55.8%), and diuretics (53.5%), respectively (P< 0.01). The following adverse reactions were detected: cough (7.5%), headache (6.1%), dizziness (3.9%), flushing (3.7%) and impotence (2.4%). Cough, headache, and flushing were more frequent in women, and impotence and loss of libido were more frequent in men (P< 0.05). The incidence of cough associated with ACEI (27.9%) was higher than that associated with the other classes of drugs (P< 0.01).

Conclusions

The tolerability of antihypertensive medication was highest in Korean patients treated with ARAs, followed by CCBs, β‐blockers, diuretics, α‐blockers, and ACEIs. The incidences of adverse reactions were different by sex, age and drug class. Copyright © 2000 John Wiley & Sons, Ltd.
Elasticity of hexagonal liquid crystals
Authors: Derbel N , Raïs K , Tounsi N , Othman T , Gharbia M , Gharbi A , Nguyen H T , Malthête J
Published: September 2002

An investigation of the elastic properties of hexagonal phases of typical liquid crystal samples on an ordered hexagonal discotic hexa‐n‐octyloxytriphenylene (C8HET), a disordered one a triphenylene hexa‐n‐dodecanoate (C11HAT) and a hexacatenar phasmid was carried out. Characterization of their mechanical stability and analysis of light scattering were used; the same results were obtained for the three samples in spite of the differences in their molecular shapes and molecular orders in columns. From the instability of undulating columns submitted to a dilative strain normal to columns, we deduced an anomalously large value of the correlation lengthm(m ≈ 0.1 µm), compared to that of the smectic liquid crystals (m ≈ 20 Å). Results from depolarized Rayleigh scattering showed that, although consisting of one‐dimensional liquid‐like structures, the studied samples in their hexagonal phases behaved elastically like three‐dimensional solids. Considering the differences in molecular shapes and orders, this elastic behaviour was attributed to regular defects. Therefore, one can probably generalize this elastic behaviour as being due to the columnar hexagonal structure.

© 2001 Society of Chemical Industry
Relation between microstructure and glass transition temperature of poly[(methyl methacrylate)‐co‐(ethyl acrylate)]
Authors: Nguyen Giao , Nicole Daniel , Matlengiewicz Marek , Roizard Denis , Henzel Norbert
Published: September 2002

The glass transition temperature of a series of samples of the poly[(methyl methacrylate)‐co‐(ethyl acrylate)] copolymer, synthesized at low conversion, were calculated theoretically using the equations of Barton and Johnston. The values obtained are more precise when the probabilities of the compositional diads are derived from the 13C NMR data instead of the classical method utilizing reactivity ratios. This can be observed more clearly when the copolymer samples are synthesized at high conversion. Introduction of configuration (tacticity) at the diad level confirms the above observations and slightly improves the calculated values of Tg compared to the initial formulae which were only taking into account the compositional sequences of the copolymer.

© 2001 Society of Chemical Industry
Influence of heat treatment on the space charge within an epoxy resin polymer material
Authors: Guermazi Hajer , Smaoui Hichem , Agnel Serge , Mlik Youssef , Toureille Alain , Schué François
Published: September 2002

The influence of heat treatment on the appearance and the evolution of the space charge repartition within an epoxy resin polymer material is investigated. The space charge measurements were made using the thermal step method (TSM) and the thermally stimulated depolarization currents (TSDC) method. The results obtained show the behaviour of the space charge density after heat treatment and, in particular, it can be concluded that the charges are stabilized in deep levels.

© 2001 Society of Chemical Industry
Synthesis and characterization of poly(ether ketone ketone) (PEKK)/sodium sulfonated poly(arylene ether ketone) (S‐PAEK) block copolymers
Authors: Gan Daoji , Lu Shiqiang , Wang Zhijian
Published: September 2002

A series of well‐defined poly(ether ketone ketone) (PEKK)/sodium sulfonated poly(aryl ether ketone) (S‐PAEK) block copolymers of high molecular weights was prepared by direct nucleophilic polymerization of hydroquinone with sodium 5,5′‐carbonylbis(2‐fluorobenzene sulfonate) (1) and PEKK oligomer (2). Varying the ratio of 1 to 2 used in polymerization can be used to control the degree of polymer sulfonation, which correspondingly affects the polymer solubility in solvents. Increasing content of 1 in the copolymers, slightly decreases their thermal stability which is nevertheless thermally stable up to 400 °C. Two Tg values, or one broad Tg, were observed in the DSC measurements of the block copolymers, indicating the existence of phase separation, which was further proved by phase‐separated morphologies as shown in atomic force microscopy images.

© 2001 Society of Chemical Industry
Influence of temperature on lattice spacings of melt‐crystallized poly(iminosebacoyl iminodecamethylene)
Authors: Yang Xiaoniu , Kong Xiaohua , Tan Susheng , Li Gao , Zhou Enle
Published: September 2002

The variation of lattice spacings of poly(iminosebacoyl iminodecamethylene) (nylon‐10,10) with temperature was studied by wide‐angle X‐ray diffraction (WAXD) during both heating and cooling processes, which demonstrates a gradual and continuous transition with temperature. However, the crystal melts before the two peaks merge completely. Both WAXD and differential scanning calorimetry show that crystallization from molten sample results directly in the triclinic form. Additionally, this transition is thermodynamically reversible.

Comparison of this transition with that of nylon‐6,6, suggests that no hydrogen‐bonded network is formed during or after the transition. We prefer to attribute this transition to asymmetrical thermal expansion in the nylon‐10,10 crystals rather than to a true first‐order phase transition.

© 2001 Society of Chemical Industry
Experimental testing of a random medium optical model of porous silicon for photovoltaic applications
Authors: Abouelsaood A. A. , Ghannam M. Y. , Stalmans L. , Poortmans J. , Nijs J. F.
Published: September 2002

We have developed a model for light propagation in porous silicon (PS) based on the theory of wave propagation in random media. The low porosity case is considered, with silicon being the host material assuming randomly distributed spherical voids as scattering particles. The specular and the diffuse part of the light could be determined and treated separately. The model is applied to the case in which porous silicon would be used as a diffuse back reflector in a thin‐film crystalline silicon solar cell realized in an ultrathin (1–3 μm) epitaxially grown Si layer on PS. Three layer structures (epi/PS/Si) have been fabricated by atmospheric pressure chemical vapor deposition (APCVD) of 150–1000 nm epitaxial silicon layers on silicon wafers of which 150–450 nm of the surface has been electrochemically etched. An excellent agreement is found between the experimentally measured reflection data in the 400–1000 nm wavelength range and those calculated using the proposed model. The values of the layer thickness agree, within a reasonable experimental error, with those obtained independently by cross sectional transmission electron microscopy (XTEM) analysis. This provides an experimental verification of the random medium approach to porous silicon in the low porosity case. The analysis shows that the epitaxial growth process has led to appreciable porosity decrease of an initially high porosity layer from about 60% to 20–30%. Copyright © 2001 John Wiley & Sons, Ltd.
Measures used to protect people exposed to a PV generator: ‘univer project’
Authors: Vidal P. G. , Almonacid G. , Pérez P. J. , Aguilera J.
Published: September 2002

Many of the solutions to integrate PV in buildings have the special feature of placing the generator in transit areas where people can have access to inside zones of the installation (metalworks, modules, junction boxes, etc.). In these cases, if we also need a higher level of generation voltage, due to the generator size and efficiency reasons, the risk of electrical damage to people rises due to imprudences or installation faults. In this paper, we present a system of people protection designed and installed in a PV generator integrated in a parking and building area at Jaén University Campus. This PV generator has a high risk level of electric shock to humans due to its location and voltage generator level (range 500 VDC). We include both the theoretical design of the protection subsystem and also the experimental tests and measures to check its functionality and security level reached in the installation. Copyright © 2001 John Wiley & Sons, Ltd.
Solar cell efficiency tables (version 17)
Authors: Green Martin A. , Emery Keith , King David L. , Igari Sanekazu , Warta Wilhelm
Published: September 2002

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since July 2000 are reviewed. Copyright © 2001 John Wiley & Sons, Ltd.
The effect of oxygen on interface microstructure evolution in CdS/CdTe solar cells
Authors: Albin D.S. , Yan Y. , Al‐Jassim M.M.
Published: September 2002

Microstructural changes at the CdS/CdTe solar cell interface where close‐spaced sublimation (CSS) is used as the growth technique to deposit thep‐type CdTe absorber layer are studied by systematic layer characterization at various stages during heterojunction growth. CdS layers grown by both chemical bath deposition (CBD) and CSS provide a basis for determining the effects of CdS crystallinity, grain size, and oxygen content on the subsequent CdTe layer. As‐grown CBD CdS films exhibit small grains and variations in optical properties attributed to film impurities. In contrast, CSS yields CdS films with good crystallinity, larger grains, and nearly ideal optical properties. The hexagonal nature of CSS‐grown CdS is seen to nucleate hexagonal CdTe during the initial stages of CdTe film growth. Cubic CdS deposited by CBD in contrast promotes cubic CdTe nucleation. Oxygen anneals in the latter case can aid hexagonal CdTe nucleation. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) of the CdS/CdTe interface show CdS‐dependent differences in interdiffusion at the interface. This interdiffusion appears to be determined by the oxygen level in the CdS. When low‐oxygen‐containing CSS CdS films are used, sulfur diffusion is substantial, leading to significant consumption of the CdS layer. When these same films are annealed in oxygen, the consumption is reduced. Te diffusion into the CdS layer is also observed to decrease with oxygen anneals. Optical modeling shows that Te alloying with the CdS layer can greatly reduce the short‐circuit current of CdS/CdTe devices. Copyright © 2002 John Wiley & Sons, Ltd.
Solar Cell Efficiency Tables (Version 20)
Authors: Green Martin A. , Emery Keith , King David L. , Igari Sanekazu , Warta Wilhelm
Published: September 2002

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since January, 2002 are reviewed. Copyright © 2002 John Wiley & Sons, Ltd.
Possible effects on the polyethene chain structure of trimethylaluminum coordination to zirconocene catalysts
Authors: Liu Jianke , Støvneng Jon Andreas , Rytter Erling
Published: September 2002

Ethene was polymerized with the catalytic systems L2ZrCl2/MAO/TMA (where L = Cp, Me5Cp, or Me4Cp; Cp = η5‐cyclopentadienyl; MAO = methylaluminoxane; and TMA = trimethylaluminum) at 60 °C, 2 bar, and AlTMA/Zr ratios of 0–2700. The polymerization activity was reduced with the addition of TMA for L = Cp but was almost unaffected for the methyl‐substituted catalysts. Increasing the TMA concentration resulted in a lower molecular weight of the polymer, with the largest effect for L = Me5Cp. A gel permeation chromatography analysis of the polymers revealed a high molecular weight shoulder and a nearly bimodal distribution for L = Me5Cp at high TMA concentrations. A possible explanation of such a shoulder in terms of long‐chain branching was ruled out by dynamic viscosity measurements. The origin of this effect more likely stemmed from competition between chain transfer to aluminum and β‐hydrogen transfer reactions at two different sites, one TMA‐sensitive and one TMA‐insensitive. Polymerizations at various pressures and temperatures substantiated this assumption. A clue to the underlying mechanism came from investigations of chain transfer to TMA studied with density functional calculations. Complexation of Me3Al to Zr was much stronger for L = Cp than for L = Me5Cp. However, the overall chain‐transfer barrier was much higher for L = Cp. These results agreed both with the reduced activity for L = Cp and with the strongly reduced molecular weight for L = Me5Cp observed with the addition of TMA. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3566–3577, 2001
Synthesis and characterization of novel polyimides containing stilbene unit in the side chain and their controllability of nematic liquid crystal alignment on the rubbed surfaces
Authors: Park J. H. , Jung J. C. , Sohn B.‐H. , Lee S. W. , Ree M.
Published: September 2002

Four polyimides containing hexylene spacer and a fluorostilbene unit in the side chains were prepared in thin‐film form by two‐step condensation of 3,3′‐bis[(4′‐fluoro‐4‐stilbenyl)oxyhexyloxy]‐4,4′‐biphenyldiamine (FS6B) with pyromellitic dianhydride (PMDA), benzophenone‐3,3′,4,4′‐tetracarboxylic dianydride (BTDA), 4,4′‐oxydi(phthalic anhydride) (ODPA), and 4,4′‐hexafluoroisopropylidenedi(phthalic anhydride) (6FDA), respectively, and their controllability of liquid crystal (LC) alignment on rubbed surfaces was investigated. Pretilt angles of LCs were achieved in the 2–9° range, depending on the rubbing density and backbone structures. The effect of the mesogenic stilbene group on the pretilting of LCs was distinctive in FS6B‐PMDA. Contact‐angle measurements on thin films annealed at 120 °C revealed that FS6B‐PMDA potentially had the better alignment stability than FS6B‐6FDA. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3622–3632, 2001
Synthesis and properties of oxygen‐, methylene‐, and alkylene‐bridged poly(dithiafulvene)s
Authors: Marathe Sujata , Uemura Takashi , Naka Kensuke , Chujo Yoshiki
Published: September 2002

Polymerization by cycloaddition between aldothioketene and its alkynethiol tautomer (derived in situ from a diyne) leading to the formation of dithiafulvene unit‐linked polymers has been studied. Two aromatic diynes [bis(4‐ethynyldiphenyl)methane (1a) and 4,4′‐diethynyldiphenyl ether) (1b)] were used as starting materials with the aim of obtaining non‐π‐conjugated methylene‐ and oxygen‐bridged aromatic poly(dithiafulvene)s. The poly(dithiafulvene) derived from bis(4‐ethynyldiphenyl)methane can be considered as an interesting precursor to a small band‐gap polymer having alternating aromatic and quinonoid moieties. Further, two aliphatic diynes [1,7‐octadiyne (3a) and 1,9‐decadiyne (3b)] were subjected to cycloaddition polymerization to obtain aliphatic poly(dithiafulvene)s containing localized electron‐rich dithiafulvene units. The polymers obtained were characterized by IR, 1H NMR, gel permeation chromatography, and cyclic voltammetry. The electron‐donating property of the polymers was evident from the charge‐transfer (CT) complex formation with an electron acceptor 7,7,8,8‐teracyanoquinodimethane. The CT complexes were characterized by IR, 1H NMR, and ultraviolet–visible spectroscopies. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3593–3603, 2001
Synthesis of epoxy monomers that undergo synergistic photopolymerization by a radical‐induced cationic mechanism
Authors: Crivello James V. , Ortiz Ricardo Acosta
Published: September 2002

A series of novel, cycloaliphatic, cationically photopolymerizable epoxide monomers bearing benzyl ether groups were prepared. These monomers display a considerable enhancement in the rate of their cationic ring‐opening polymerizations in comparison with monomers that do not contain such groups. In this article, a synergistic free‐radical mechanism is proposed that accounts for this effect, and supporting evidence is offered for its verification. During UV irradiation of an onium salt cationic photoinitiator, the aryl radicals that are generated abstract labile benzyl hydrogens present in such monomers to generate the corresponding carbon‐centered radicals. Subsequently, these radicals are oxidized to benzyl carbocations by the onium salt via a nonphotochemical chain process. The observed increase in the rate and extent of the cationic ring‐opening polymerization of the epoxide monomers is due to the aforementioned mechanism, which effectively increases the number of reactive cationic species present during polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3578–3592, 2001
Preparation of monolithic polymers with controlled porous properties for microfluidic chip applications using photoinitiated free‐radical polymerization
Authors: Yu Cong , Xu Mingcheng , Svec Frantisek , Fréchet Jean M. J.
Published: September 2002

A broad variety of monolithic macroporous polymers with both controlled chemistry and porous properties was prepared using UV‐initiated free‐radical polymerization. The chemistry of the monoliths is defined by the composition of the monomer mixture used for the polymerization. The use of functional methacrylate monomers such as glycidyl methacrylate, 2‐hydroxyethyl methacrylate, butyl methacrylate, 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid, and [2‐(methacryloyloxy) ethyl] trimethylammonium chloride enabled the preparation of monoliths with reactive, hydrophilic, hydrophobic, and ionizable functionalities, respectively. The porous properties of these monoliths were mainly affected by the choice of the porogenic solvent system. Because the UV polymerization was carried out at room temperature, even low molecular weight alcohols and other low boiling point solvents could safely be used to create a versatile series of binary porogenic mixtures. Monoliths were prepared in spatially defined positions using the photolithographic technique within a fused silica capillary and on microfluidic chips, and the former was demonstrated with the separation of derivatized amines by means of capillary electrochromatography in the reversed‐phase mode. Similarly, a monolith prepared in the microchip format was used to demonstrate a microextraction with enrichment of a solution of green fluorescent protein by a factor of 1000. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 755–769, 2002; DOI 10.1002/pola.10155
Complex formation of polyethyleneimine with copper(II), nickel(II), and cobalt(II) ions
Authors: Kislenko V. N. , Oliynyk L. P.
Published: September 2002

An influence of the structure of a globule of polyethyleneimine on the complex formation of one with the copper(II), nickel(II), and cobalt(II) ions is described. A change of the coordination number from the pH of solution for complexes of ethylenediamine, diethylenetriamine, and polyethyleneimine with metal ions was found. The fraction of monomer links, bound with metal ions, depends on the volume of the globule of macromolecule as well as the condition of the proceeding reaction. The reaction of complex formation is controlled by the diffusion of metal ions into the polymer globule in solution. The effective equilibrium constants of complex formation were found. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 914–922, 2002; DOI 10.1002/pola.10157
New synthetic method for aromatic polyketones from bis(arylsilane)s and aromatic dicarboxylic acid chlorides
Authors: Takeuchi Hisashi , Kakimoto Masa‐aki , Imai Yoshio
Published: September 2002

A new synthetic method for aromatic polyketones was developed through Friedel–Crafts polycondensation of bis(arylsilane) monomers with aromatic dicarboxylic acid chlorides. The solution polycondensation of these monomer pairs in the presence of aluminum chloride in 1,2‐dichloroethane readily afforded aromatic polyketones having inherent viscosities up to 0.37 dL/g with the elimination of chlorotrimethylsilane. The polycondensation proceeded through aromatic electrophilic ipso substitution, the mechanism of which is very similar to that of normal Friedel–Crafts acylation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2729–2735, 2002
Kinetic study of the stable free‐radical copolymerization of styrene with butyl methacrylate
Authors: Cuervo‐Rodriguez Rocio , Fernández‐Monreal Carmen , Madruga Enrique López
Published: September 2002

The radical copolymerization of styrene and n‐butyl methacrylate mediated by 1‐phenyl‐1‐(2′,2′,6′,6′‐tetramethyl‐1′‐piperidinyl‐oxy)ethane in bulk at 125 °C has been analyzed over a wide range of conversions and monomer feed compositions. Monomer reactivity ratios have been determined, and the Mayo–Lewis terminal model provides excellent predictions for the variations of the intermolecular structure over the entire conversion range. The kinetic analysis of this copolymerization system indicates an apparent propagation rate coefficient independent of the monomer feed composition as well as a limiting conversion that decreases as the styrene monomer feed decreases. This fact is attributed to side reactions leading to unsaturated end groups and the accumulation of nonactive adducts of n‐butyl methacrylate. The number‐average molecular weights linearly increase with conversion, and the copolymers present narrow molecular weight distributions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2750–2758, 2002
Influence of the amine structure on the polymerization of methyl methacrylate photoinitiated by aromatic ketone/amine
Authors: Valderas C. , Bertolotti S. , Previtali C. M. , Encinas M. V.
Published: September 2002

The polymerization of methyl methacrylate photoinitiated by 2‐chlorothioxanthone in the presence of amines of different structures has been investigated. The photoinitiation efficiency of these systems is highly dependent on the structure of the amine. The polymerization rate increases with the amine concentration, reaching a constant value in an amine concentration range of 10–30 mM. At these amine concentrations, aliphatic hydroxyalkyl amines are more efficient photoinitiators than the corresponding alkyl‐substituted compounds. Dimethylanilines with electron‐acceptor substituents in the 4‐position give higher polymerization rates than electron‐donor‐substituted anilines. The photophysics of these photoinitiation systems has been studied in the polymerization medium. These data show that the singlet and triplet excited states of thioxanthones are efficiently deactivated by the amine. Rate constants are well correlated to the oxidation potential of the amine. These studies have allowed us to simulate the dependence of the photoinitiation efficiency with the amine concentration and indicate that the active radicals are produced from the interaction of the ketone triplet with the amine. Also, photochemical studies have allowed us to establish that the dependence of the polymerization rate on structural features of amines is mainly due to differences in the fraction of produced active radicals that add to the monomer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2888–2893, 2002
Unusual contributions of molecular architecture to rheology and flow birefringence in hyperbranched polystyrene melts
Authors: Kharchenko Semen B. , Kannan Rangaramanujam M. , Cernohous Jeff J. , Venkataramani Shivshankar , Babu Gaddam N.
Published: September 2002

With the increase in sophisticated synthesis methods, it appears that polymer architecture may be a tunable property. Therefore, the role of architecture in rheological and processing properties has received renewed attention, mainly because of dendrimer synthesis and metallocene‐catalyst technology. Linear polymers and hyperbranched polymers represent two ends of branching complexity. Some previous studies have suggested that hyperbranched polymers may behave like unentangled polymers, whereas others have proposed that they exhibit the properties of soft colloids. In an effort to compare the responses of linear and hyperbranched polymers, we synthesized starlike hyperbranched polystyrenes (HBPSs) of various branch lengths and numbers of branches. The HBPSs used in this study were unentangled or weakly entangled, allowing us to study the effect of branch density more readily. Two linear polystyrene (L‐PS) melts and two HBPSs were studied. Using a custom‐built rheooptical apparatus, we characterized the rheology and flow birefringence of these materials. To our knowledge, these are the first flow birefringence measurements on highly branched polymer melts. Our results suggest that the flow behavior of HBPS is significantly different from that of L‐PS: (1) HBPS shows nonterminal behavior in the low‐frequency rheological response; (2) when the stress‐optical rule (SOR) holds, the stress‐optical coefficient of HBPS is much lower than those of analogous linear polymers; and (3) when the branch density is high and the branch length is sufficiently low, the SOR fails for these homopolymer melts. A significant increase in the birefringence for a given amount of stress in the low‐frequency region suggests that there may be a soft core in these materials due to the strong preferential radial orientation of chain segments near the center of a molecule versus those near the periphery. The predominantly elastic response of the soft structures may be responsible for the enhanced form birefringence. Our preliminary results indicate that these materials may exhibit both polymeric and soft‐colloid natures. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2562–2571, 2001
Nanocomposites of poly(ethylene terephthalate‐co‐ethylene naphthalate) with organoclay
Authors: Chang Jin‐Hae , Park Dae‐Keun
Published: September 2002

Poly(ethylene terephthalate‐co‐ethylene naphthalate) (PETN)/organoclay was synthesized with the solution intercalation method. Hexadecylamine was used as an organophilic alkylamine in organoclay. Our aim was to clarify the intercalation of PETN chains to hexadecylamine–montmorillonite (C16–MMT) and to improve both the thermal stability and tensile property. We found that the addition of only a small amount of organoclay was enough to improve the thermal stabilities and mechanical properties of PETN/C16–MMT hybrid films. Maximum enhancement in both the ultimate tensile strength and initial modulus for the hybrids was observed in blends containing 4 wt % C16–MMT. Below a 4 wt % clay loading, the clay particles could be highly dispersed in the polymer matrix without a large agglomeration of particles. However, an agglomerated structure did form in the polymer matrix at a 6 wt % clay content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2581–2588, 2001
Ionic poly(p‐phenylene terephthalamide)s: Preparation and characterization
Authors: Chen W. C. , Sauer J. A. , Hara M.
Published: September 2002

The preparation and characterization of two types of ionic poly(p‐phenylene terephthalamide) (PPTA) is described. A sufficient number of ionic groups were added to render modified PPTA soluble in dimethylsulfoxide (DMSO). In one type, a hydrogen atom of the amide group was replaced by an ionic propanesulfonate group. In the other type, one of the hydrogen atoms on the phenylene ring was replaced by an ionic sulfonate group. The ionic PPTAs in DMSO showed an upturn in viscosity at very low concentrations that was characteristic of the polyelectrolyte behavior. Fourier transform infrared spectra of these samples were also studied. When the ionic group was attached at the end of the short propane side chain, the intensity of both the free and hydrogen‐bonded NH stretching mode was reduced compared with that of PPTA. Depending on the location of the ionic group, there were some changes in the intensity and wave number of the asymmetric and symmetric vibrations of the ionic SO group and the stretching mode of the carbonyl group. In both ionic PPTAs, there was an upward shift in the frequency of the symmetric vibrations of the sulfonate ion when the counterion, having been monovalent, became divalent. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2653–2663, 2001
Structured disorder and conformational selection
Authors: Tsai Chung‐Jung , Ma Buyong , Sham Yuk Yin , Kumar Sandeep , Nussinov Ruth
Published: September 2002

Traditionally, molecular disorder has been viewed as local or global instability. Molecules or regions displaying disorder have been considered inherently unstructured. The term has been routinely applied to cases for which no atomic coordinates can be derived from crystallized molecules. Yet, even when it appears that the molecules are disordered, prevailing conformations exist, with population times higher than those of all alternate conformations. Disordered molecules are the outcome of rugged energy landscapes away from the native state around the bottom of the funnel. Ruggedness has a biological function, creating a distribution of structured conformers that bind via conformational selection, driving association and multimolecular complex formation, whether chain‐linked in folding or unlinked in binding. We classify disordered molecules into two types. The first type possesses a hydrophobic core. Here, even if the native conformation is unstable, it still has a large enough population time, enabling its experimental detection. In the second type, no such hydrophobic core exists. Hence, the native conformations of molecules belonging to this category have shorter population times, hindering their experimental detection. Although there is a continuum of distribution of hydrophobic cores in proteins, an empirical, statistically based hydrophobicity function may be used as a guideline for distinguishing the two disordered molecule types. Furthermore, the two types relate to steps in the protein folding reaction. With respect to protein design, this leads us to propose that engineering‐optimized specific electrostatic interactions to avoid electrostatic repulsion would reduce the type I disordered state, driving the molten globule (MG) → native (N) state. In contrast, for overcoming the type II disordered state, in addition to specific interactions, a stronger hydrophobic core is also indicated, leading to the denatured → MG → N state. Proteins 2001;44:418–427. © 2001 Wiley‐Liss, Inc.
Computational study of lipid‐destabilizing protein fragments: Towards a comprehensive view of tilted peptides
Authors: Lins L. , Charloteaux B. , Thomas A. , Brasseur R.
Published: September 2002

Tilted peptides are short sequence fragments (10–20 residues long) that possess an asymmetric hydrophobicity gradient along their sequence when they are helical. Due to this gradient, they adopt a tilted orientation towards a single lipid/water interface and destabilize the lipids. We have detected those peptides in many different proteins with various functions. While being all tilted‐oriented at a single lipid/water interface, no consensus sequence can be evidenced. In order to better understand the relationships between their lipid‐destabilizing activity and their properties, we used IMPALA to classify the tilted peptides. This method allows the study of interactions between a peptide and a modeled lipid bilayer using simple restraint functions designed to mimic some of the membrane properties. We predict that tilted peptides have access to a wide conformational space in membranes, in contrast to transmembrane and amphipathic helices. In agreement with previous studies, we suggest that those metastable configurations could lead to the perturbation of the acyl chains organization and could be a general mechanism for lipid destabilization. Our results further suggest that tilted peptides fall into two classes: those from proteins acting on membrane behave differently than destabilizing fragments from interfacial proteins. While the former have equal access to the two layers of the membrane, the latter are confined within a single lipid layer. This could be in relation with the organization of lipid substrate on which the peptides physiologically act. Proteins 2001;44:435–447. © 2001 Wiley‐Liss, Inc.
A conserved helix‐unfolding motif in the naturally unfolded proteins
Authors: Zetina Carlos R.
Published: September 2002

Among the naturally unfolded proteins there are many polypeptides that retain an extended conformation in the absence of any apparent signal. Using sequence alignment and secondary structure prediction tools, a conserved (LS/SL)(D/E)(D/E)(D/E)X(E/D) motif is uncovered in the vicinity of the N‐terminus of their unfolded helices. A comparison of these data with published observations allows one to propose that the (LS/SL)(D/E)(D/E)(D/E)X(E/D) motif is a helix‐unfolding signal. Furthermore, the strong similarity between this motif and the STXXDE casein kinase II phosphorylation site suggests a regulatory mechanism for the naturally unfolded proteins within the cell. Proteins 2001;44:479–483. © 2001 Wiley‐Liss, Inc.