bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of solvent contents on the rubber‐phase particle size distribution of high‐impact polystyrene
Authors: Lee Seong Jae , Jeoung Han Gyun , Ahn Kyung Hyun
Published: July 2003

High‐impact polystyrene (HIPS) was prepared by the bulk or low‐solvent polymerization of styrene in the presence of dissolved rubber and characterized to measure the dispersed particle size of the rubber phase. Before preparation, the prepolymerization time was established by measuring the evolution of particle size distribution of the dispersed phase as a function of reaction time. The measurement technique by laser light scattering was found to be efficient enough not only to lead to the right prepolymerization time but also to predict rubber‐phase particle size distribution. Polymerization experiments were then conducted to investigate the effect of solvent contents on the particle size distribution of the rubber phase, in which ethylbenzene was introduced as a solvent at levels of 0, 3, 10, and 15%. As the solvent content increased, the size of rubber‐phase particles initially increased, reaching a maximum, and then decreased. It is speculated that a decrease in the molecular weight of the matrix, a decrease in the viscosity ratio between polybutadiene to polystyrene phases, and a change in rubber morphology all contributed to the change in the rubber particle size of HIPS. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3672–3679, 2003
Preparation and properties of polyethylene/montmorillonite nanocomposites by in situ polymerization
Authors: Yang Feng , Zhang Xuequan , Zhao Haichao , Chen Bin , Huang Baotong , Feng Zhiliu
Published: July 2003

Polyethylene (PE)/montmorillonite (MMT) nanocomposites were prepared by in situ coordination polymerization using a MMT/MgCl2/TiCl4 catalyst activated by Al(Et)3. The catalyst was prepared by first diffusing MgCl2 into the swollen MMT layers, followed by loading TiCl4 on the inner/outer layer surfaces of MMT where MgCl2 was already deposited. The intercalation of MMT layers by MgCl2 and TiCl4 was demonstrated by the enlarged interlayer spacing determined by WAXD. The nanoscale dispersion of MMT layers in the polyethylene matrix was characterized by WAXD and TEM. As a consequence, the crystallinity of the nanocomposite decreased sharply, whereas the tensile strength was significantly improved compared to that of virgin polyethylene of comparable molecular weight. The confinement of the nanodispersed MMT layers to molecular chain and the strong interaction between the nanoscale MMT layers and the resin matrix were thought to account for the decrease of crystallinity and the remarkable enhancement of strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3680–3684, 2003
Investigations of heat transfer and pressure drop between parallel channels with pseudoplastic and dilatant fluids
Authors: Park Simsoo , Lee Dong‐Ryul
Published: July 2003

Central to the problem of heat exchangers design is the prediction of pressure drop and heat transfer in the noncircular exchanger duct passages such as parallel channels. Numerical solutions for laminar fully developed flow are presented for the pressure drop (friction factor times Reynolds number) and heat transfer (Nusselt numbers) with thermal boundary conditions [constant heat flux (CHF) and constant wall temperature (CWT) ] for a pseudoplastic and dilatant non‐Newtonian fluid flowing between infinite parallel channels. A shear rate parameter could be used for the prediction of the shear rate range for a specified set of operating conditions that has Newtonian behavior at low shear rates, power law behavior at high shear rates, and a transition region in between. Numerical results of the Nusselt number [constant heat flux (CHF) and constant wall temperature (CWT) ] and the product of the friction factor and Reynolds number for the Newtonian region were compared with the literature values showing agreement within 0.36% in the Newtonian region. For pseudoplastic and dilatant non‐Newtonian fluids, the modified power law model is recommended to use because the fluid properties have big discrepancies between the power law model and the actual values in low and medium range of shear rates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3601–3608, 2003
Study on rheological behavior of polypropylene/clay nanocomposites
Authors: Li Jian , Zhou Cixing , Wang Gang , Zhao Delu
Published: July 2003

Polypropylene/montmorillonite nanocomposites (PPCN) were prepared by melt intercalation with maleic anhydride modified low isotactic polypropylene as the compatibilizer. The linear and nonlinear rheological properties of polypropylene/montmorillonite nanocomposites were studied. The deviation from linear behavior occurred at a strain of 100 that was quite less than that for the polymer matrix. The results of dynamic frequency scan showed that the percolation threshold of PPCN was near 3 wt %. Having been subjected to steady preshear, the tactoids could be oriented preferentially in the shear direction, and the percolation network was ruptured. The magnitudes of the stress overshoots observed in the reverse flow experiments were strongly dependent on the rest time, which indicated that the ruptured network could be reorganized even under quiescent conditions. Furthermore, PPCN displayed a strain‐scaling stress response to the startup of steady shear. The maxima of the stress overshoots appeared at the stain of 100, which was consistent with the strain where the deviation of linear viscoelastic behavior started. It might imply that subjected to the deformation less than 100, the network structure could be regard as elastic one. Additionally, the analogous strain‐scaling stress response to the startup steady shear elucidated the structural analogy between PPCN and liquid crystal polymer solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3609–3617, 2003
Thermal stability and kinetics analysis of rubber‐modified epoxy resin by high‐resolution thermogravimetric analysis
Authors: Gu Aijuan , Liang Guozheng
Published: July 2003

A dynamic heating rate mode of high‐resolution thermogravimetric analysis was used to study the thermal and thermal‐oxidative stability, as well as kinetics analyses, of a model liquid rubber‐modified epoxy resin, Ep/CTBN, made up of bisphenol A diglycidyl ether‐based epoxy and carboxyl‐terminated butadiene acrylonitrile rubber (CTBN). Results show that the thermal degradation of Ep/CTBN resin in nitrogen and air consists of two and three independent steps, respectively. Moreover, Ep/CTBN has a higher initial degradation temperature and higher activation energy than those of pure epoxy resin in both gases, indicating that the addition of CTBN to epoxy can improve the thermal and thermal‐oxidative stability of pristine epoxy resin. Kinetic parameters such as activation energy, reaction order, and preexponential factor of each degradation step of both Ep/CTBN and pure epoxy resins in air and nitrogen were calculated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3594–3600, 2003
Mechanical, thermal, and microstructural properties of polypropylene/polyamide‐6/styrene‐ethylene‐butadiene‐styrene polymer alloys
Authors: Taşdemir Münir
Published: July 2003

Interfacial agents as compatibilizers have recently been introduced into polymer blends to improve the microstructure and mechanical properties of thermoplastics. In this way, it is possible to prepare a mixture of polymeric materials that can have superior mechanical properties over a wide temperature range. In this study, an incompatible blend of polypropylene (PP) and polyamide‐6 (PA6) were made compatible by the addition of 10% styrene–ethylene–butadiene–styrene copolymer (SEBS). The mixing operation was conducted by using a twin‐screw extruder. The morphology and the compatibility of the mixtures were examined by SEM and DSC techniques. Furthermore, the elastic modulus, tensile and yield strengths, percentage elongation, hardness, melt flow index, Izod impact resistance, heat deflection temperature (HDT), and Vicat softening point values of polymer alloys of various ratios were determined. It was found that the addition of SEBS to the structures decreased the tensile strength, yield strength, elastic modulus, and hardness, whereas it increased the Izod impact strength and percentage elongation values. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3485–3491, 2003
Stem cells from midguts of Lepidopteran larvae: Clues to the regulation of stem cell fate
Authors: Loeb Marcia J. , Clark Edward A. , Blackburn Michael , Hakim Raziel S. , Elsen Kim , Smagghe Guy
Published: July 2003

Previously, we showed that isolated stem cells from midguts of Heliothis virescens can be induced to multiply in response to a multiplication protein (MP) isolated from pupal fat body, or to differentiate to larval types of mature midgut cells in response to either of 4 differentiation factors (MDFs) isolated from larval midgut cell‐conditioned medium or pupal hemolymph. In this work, we show that the responses to MDF‐2 and MP in H. virescens stem cells decayed at different time intervals, implying that the receptors or response cascades for stem cell differentiation and multiplication may be different. However, the processes appeared to be linked, since conditioned medium and MDF‐2 prevented the action of MP on stem cells; MP by itself appeared to repress stem cell differentiation. Epidermal growth factor, retinoic acid, and platelet‐derived growth factor induced isolated midgut stem cells of H. virescens and Lymantria dispar to multiply and to differentiate to mature midgut cells characteristic of prepupal, pupal, and adult lepidopteran midgut epithelium, and to squamous‐like cells and scales not characteristic of midgut tissue instead of the larval types of mature midgut epithelium induced by the MDFs. Midgut stem cells appear to be multipotent and their various differentiated fates can be influenced by several growth factors. Arch. Insect Biochem. Physiol. 53:186–198, 2003. Published 2003 Wiley‐Liss, Inc.
Distinctions between c‐Rel and other NF‐κB proteins in immunity and disease
Authors: Liou Hsiou‐Chi , Hsia Constance Y.
Published: July 2003

c‐Rel is a proto‐oncogene first identified as the cellular counterpart of the v‐Rel oncogene derived from the avian reticuloendotheliosis retrovirus (REV‐T). It was subsequently discovered that c‐Rel belongs to the NF‐κB/Rel transcription factor family whose members share a common DNA recognition motif and similar signaling pathways. Despite the similarities, however, each NF‐κB/Rel member possesses unique properties with regard to tissue expression pattern, response to receptor signals and target gene specificity. These differences are fairly evident from the non‐redundant phenotypes exhibited by individual NF‐κB/Rel knockout mice. Hence the work described in this review will compare and contrast the various physiological functions of c‐Rel to those of other NF‐κB members, particularly with respect to the regulation of proliferation, survival and effector functions in multiple hematopoietic and immunological cell types. The study of c‐Rel knockout mice in several disease models will also be discussed as they reveal an important role for c‐Rel in response to allergens, auto‐antigens, allo‐antigens and pathogenic infection. BioEssays 25:767–780, 2003. © 2003 Wiley Periodicals, Inc.
Left/right, up/down: The role of endogenous electrical fields as directional signals in development, repair and invasion
Authors: Robinson Kenneth R. , Messerli Mark A.
Published: July 2003

A fundamental aspect of biological systems is their spatial organization. In development, regeneration and repair, directional signals are necessary for the proper placement of the components of the organism. Likewise, pathogens that invade other organisms rely on directional signals to target vulnerable areas. It is widely understood that chemical gradients are important directional signals in living systems. Less well recognized are electrical fields, which can also provide directional information. Small, steady electrical fields can directly guide cell movement and growth and can generate chemical gradients of charged macromolecules against the leveling action of diffusion. At the site of a lesion in an ion‐transporting epithelium, for example, a substantial electrical field is instantly generated and may extend over many cell diameters. There are numerous other situations in which relatively long‐range electrical fields have been shown to exist naturally. Recently, there has been substantial progress in identifying specific processes that are controlled, to some extent, by these endogenous electrical fields. This review highlights these recent data and discusses possible mechanisms by which the fields might affect biological processes. BioEssays 25:759–766, 2003. © 2003 Wiley Periodicals, Inc.
The polarisation of the anteroposterior axis in Drosophila
Authors: López‐Schier Hernán
Published: July 2003

The polarisation of the embryonic anteroposterior (AP) axis requires the establishment of positional cues with spatial information, and often involves complex intercellular communications, cell adhesion and cell movement. Recent work on several fronts has begun to shed light on how the initial asymmetries are established and maintained. In this review, I discuss the polarisation of the AP axis during Drosophila oogenesis, focusing on the function of the Notch signalling pathway and its relationship to the activation of the epidermal growth factor receptor. I make special reference to some aspects of Notch activity regulation during oogenesis that appear to depart from the canonical pathway. Finally, I hypothesise on possible similarities between these activities of Notch signalling during Drosophila oogenesis and vertebrate somitogenesis. BioEssays 25:781–791, 2003. © 2003 Wiley Periodicals, Inc.
The formation of sense organs in Drosophila: A logical approach
Authors: Ghysen Alain , Thomas René
Published: July 2003

The genetic analysis of development has revealed the importance of small sets of interacting genes in most morphogenetic processes. The results of gene interactions have so far been examined intuitively. This approach is largely sufficient when one deals with simple interactions, a feedback circuit for example. As more components become involved, however, it is difficult to make sure that the intuitive approach gives a comprehensive view of the behaviour of the system. In this paper, we illustrate the use of a logical approach to describe the genetic circuit that underlies the singling out of sense organ precursor cells in Drosophila. We show how to apply logical modelling to a realistic problem, and how this approach allows an easy assessment of the dynamic properties of the system, i.e., of its possible evolutions and of its reactions to fluctuations and perturbations. BioEssays 25:802–807, 2003. © 2003 Wiley Periodicals, Inc.
From Eden to a hell of uniformity? directed evolution in humans
Authors: Brosius Jürgen
Published: July 2003

For the first time during evolution of life on this planet, a species has acquired the ability to direct its own genetic destiny. Following 200,000 years of evolution, modern man now has the technologies not only to eradicate genetic disease but also to prolong life and enhance desired physical and mental traits. These technologies include preimplantation diagnosis, cloning, and gene therapy in the germline on native chromosomes or by adding artificial ones. At first glance, we should all be in favor of eliminating genetic diseases and enhancing genetic traits. Evolutionary considerations, however, uncover hidden dangers and suggest caution against the total embracement of such actions. The first major concern is that the genome will never be a completely reliable crystal ball for predicting human phenotypes. This is especially true for predictions concerning the performance of alleles in future generations whose populations might be subjected to different environmental and social challenges. The second, and perhaps more important, concern is that the end result of germline intervention and genetic enhancement will likely lead to the impoverishment of gene variants in the human population and deprive us of one of our most valued assets for survival in the future, our genetic diversity. BioEssays 25:815–821, 2003. © 2003 Wiley Periodicals, Inc.
Cooperative interactions between epigenetic modifications and their function in the regulation of chromosome architecture
Authors: Weissmann Frank , Lyko Frank
Published: July 2003

Epigenetic information is encoded by DNA methylation and by covalent modifications of histone tails. While defined epigenetic modification patterns have been frequently correlated with particular states of gene activity, very little is known about the integration level of epigenetic signals. Recent experiments have resulted in the characterization of several epigenetic adaptors that mediate interactions between distinct modifications. These adaptors include methyl‐DNA binding proteins, chromatin remodelling enzymes and siRNAs. Complex interactions between epigenetic modifiers and adaptors provide the foundation for the stability of epigenetic inheritance. In addition, they also provide an explanation for the long‐range effects of epigenetic mechanisms. We propose that a major aspect of epigenetic regulation lies in the modification of chromosome architecture and that local changes in gene expression would be secondary consequences. This view is consistent with many results from recent genomic analyses. BioEssays 25:792–797, 2003. © 2003 Wiley Periodicals, Inc.
Human genetic diversity: Lewontin's fallacy
Authors: Edwards A.W.F.
Published: July 2003

In popular articles that play down the genetical differences among human populations, it is often stated that about 85% of the total genetical variation is due to individual differences within populations and only 15% to differences between populations or ethnic groups. It has therefore been proposed that the division of Homo sapiens into these groups is not justified by the genetic data. This conclusion, due to R.C. Lewontin in 1972, is unwarranted because the argument ignores the fact that most of the information that distinguishes populations is hidden in the correlation structure of the data and not simply in the variation of the individual factors. The underlying logic, which was discussed in the early years of the last century, is here discussed using a simple genetical example. BioEssays 25:798–801, 2003. © 2003 Wiley Periodicals, Inc.
The quest for the function of simple epithelial keratins
Authors: Owens Dewi W. , Lane E. Birgitte
Published: July 2003

Simple epithelial keratins K8 and K18 are components of the intracellular cytoskeleton in the cells of the single‐layered sheet tissues inside the body. As members of the intermediate filament family of proteins, their function has been a matter for debate since they were first discovered. Whilst there is an indisputable case for a structural cell‐reinforcing function for keratins in the mutilayered squamous epithelia of external barrier tissues, some very different stress‐protective features now seem to be emerging for the simple epithelial keratins. Even the emerging evidence of pathological mutations in K8/K18 looks very different from mutations in stratified epithelial keratins. K8/K18‐like keratins were probably the first to evolve and, whilst stratified epithelial (keratinocyte) keratins have diversified into a large group of keratins highly specialised for providing mechanical stability, the simple epithelial keratins have retained early features that may protect the internal epithelia from a broader range of stresses, including osmotic stress and chemical toxicity. BioEssays 25:748–758, 2003. © 2003 Wiley Periodicals, Inc.
Are poly(ADP‐ribosyl)ation by PARP‐1 and deacetylation by Sir2 linked?
Authors: Zhang Jie
Published: July 2003

Poly(ADP‐ribose) polymerase‐1 (PARP‐1) safeguards genomic integrity by limiting sister chromatid exchanges. Overstimulation of PARP‐1 by extensive DNA damage, however, can result in cell death, as prolonged PARP‐1 activation depletes NAD+, a substrate, and elevates nicotinamide, a product. The decline of NAD+ and the rise of nicotinamide may downregulate the activity of Sir2, the NAD+‐dependent deacetylases, because deacetylation by Sir2 is dependent on high concentration of NAD+ and inhibited by physiologic level of nicotinamide. The Sir2 deacetylase family has been implicated in mediating gene silencing, longevity and genome stability. It is conceivable that poly(ADP‐ribosyl)ation by PARP‐1, which is induced by DNA damage, could modulate protein deacetylation by Sir2 via the NAD+/nicotinamide connection. The possible linkage of the two ancient pathways that mediate broad biological activities may spell profound evolutionary roles for the conserved PARP‐1 and Sir2 gene families in multicellular eukaryotes. BioEssays 25:808–814, 2003. © 2003 Wiley Periodicals, Inc.
NTE: One target protein for different toxic syndromes with distinct mechanisms?
Authors: Glynn Paul
Published: July 2003

Epidemics of organophosphate‐induced delayed neuropathy (OPIDN) have paralysed thousands of people. This syndrome of nerve axon degeneration is initiated by organophosphates which react with neuropathy target esterase (NTE). Dosing experiments with adult chickens raise the possibility that OPIDN is initiated by a gain‐of‐function mechanism. By contrast, loss of NTE function by mutation causes massive apoptosis in Drosophila brain. Now, Winrow et al. show that nte−/− mice die by mid‐gestation, but nte+/− mice appear hyperactive and are more sensitive than wild‐type mice to a fatal form of OP toxicity.1 Thus, different toxic syndromes may be initiated via a single target protein. BioEssays 25:742–745, 2003. © 2003 Wiley Periodicals, Inc.
Male genes: X‐pelled or X‐cluded?
Authors: Rogers David W. , Carr Martin , Pomiankowski Andrew
Published: July 2003

Two recent studies by Parisi et al.1 and Ranz et al.,2 catalogue sex differences in gene expression across the whole genome of the fruit fly Drosophila melanogaster. Both report striking associations of sex‐biased gene expression with the X chromosome. Genes with male‐biased expression are depauperate on the X chromosome, whereas genes with female‐biased expression show weaker evidence of being in excess. A number of evolutionary hypotheses for the expulsion or exclusion of male‐biased genes from the X chromosome have been suggested. None is entirely consistent with the available evidence. BioEssays 25:739–741, 2003. © 2003 Wiley Periodicals, Inc.
Animal allure and health linked by plant pigments
Authors: Hõrak Peeter , Saks Lauri
Published: July 2003

Darwin1 introduced the idea that ornamental secondary sexual traits have evolved in response to female preferences for showy males. Among such traits, yellow and red carotenoid‐based ornaments have been considered as particularly good candidates for explaining why and how females would benefit from mating with showy partners. Because carotenoids can be used for promotion of both health and appearance, colourful male ornaments should honestly reveal the vigour of the bearers. Two recent experiments with birds2,3 now show how allocation of bodily carotenoids to sexual signalling is traded off against the use of carotenoids for boosting immune function. BioEssays 25:746–747, 2003. © 2003 Wiley Periodicals, Inc.
Study of degradation pathways of Amadori compounds obtained by glycation of opioid pentapeptide and related smaller fragments: Stability, reactions, and spectroscopic properties
Authors: Jakas Andreja , Horvat Štefica
Published: July 2003

Reactions between biological amines and reducing sugars (the Maillard reaction) are among the most important of the chemical and oxidative changes occurring in biological systems that contribute to the formation of a complex family of rearranged and dehydrated covalent adducts that have been implicated in the pathogenesis of human diseases. In this study, chemistry of the Maillard reactions was studied in four model systems containing fructosamines (Amadori compounds) obtained from the endogenous opioid pentapeptide leucine‐enkephalin (Tyr–Gly–Gly–Phe–Leu), leucine‐enkephalin methyl ester, structurally related tripeptide (Tyr–Gly–Gly), or from amino acid (Tyr). The degradation of model compounds as well as their ability to develop Maillard fluorescence was investigated under oxidative conditions in methanol and phosphate buffer pH 7.4 at two different temperatures (37 and 70°C). At 37°C, glycated leucine‐enkephalin degraded slowly in methanol (t1/2 ∼13 days) and phosphate buffer (t1/2 ∼ 9 days), producing a parent peptide compound as a major product throughout a three‐week incubation period. Whereas fluorescence slowly increased over time at 37°C, incubations off all studied Amadori compounds at 70°C resulted in a rapid appearance of a brown color and sharp increase in AGE (advanced glycation end products)‐associated fluorescence (excitation 320 nm/emmision 420 nm) as well as in distinctly higher amounts of fragmentation products. The obtained data indicated that the shorter the peptide chain the more degradation products were formed. These studies have also helped to identify a new chemical transformation of the peptide backbone in the Maillard reaction that lead to β‐scission of N‐terminal tyrosine side chain and p‐hydroxybenzaldehyde formation under both aqueous and nonaqueous conditions. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 421–431, 2003
Small angle x‐ray scattering of the hemoglobin from Biomphalaria glabrata
Authors: Arndt Márcio H. L. , Oliveira Cristiano L. P. de , Régis Wiliam C. B. , Torriani Iris L. , Santoro Marcelo M.
Published: July 2003

The hemoglobin from Biomphalaria glabrata is an extracellular respiratory protein of high molecular mass composed by subunits of 360 kDa, each one containing two 180 kDa chains linked by disulfide bridges. In this work, small angle x‐ray scattering (SAXS) measurements were performed with the hemoglobin at pH 5.0 and 7.5. Radii of gyration of 98.6 ± 0.5 and 101.8 ± 0.2 Å and maximum diameters of 300 ± 10 and 305 ± 10 Å, respectively, were obtained from Guinier plot extrapolation and analytical curve fitting. The pair distance distribution functions p(r) corresponded to globular particles with a somewhat anisotropic shape for both preparations. Computer analysis of the low angle part of the scattering curve led to the determination of the low resolution envelope of the protein, revealing a P222 symmetry. Shape reconstruction from ab initio calculations using the complete scattering curve furnished a compact prolate three‐dimensional (3D) bead model for the protein. Hydrodynamic parameters were obtained from experiments and theoretical calculations using the 3D model. The results of the structural and biochemical studies reported herein indicate that the multisubunit structure of this hemoglobin is compatible with a tetrameric arrangement. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 470–479, 2003
Viscoelastic and light scattering studies on thermally induced sol to gel phase transition in fish myosin solutions
Authors: Kouchi Sawa , Kondo Shingo , Ooi Kazuko , Ichikawa Hisashi , Dobashi Toshiaki
Published: July 2003

Viscoelastic (VE) and dynamic light scattering (DLS) analyses of fish (white croaker) myosin solutions were performed at myosin concentrations of 30mg/mL for VE and 0.1 mg/mL for DLS at 0.6M KCl and pH 7.0 to clarify thermally induced gelation. The hydrodynamic radius Rh considerably decreased around 30–35°C. The shear modulus G was constant below 25°C and increased by incubating the sample at 30°C. G further increased as the temperature of the incubated sample decreased. The curves of G vs T for different time courses showed a sharp peak around 35°C and a moderate peak around 60°C in the heating process, while a stepwise increase in G was observed around 30°C in the cooling process when the temperature was elevated to not more than 60°C. No distinct stepwise change was observed once the temperature of the sample exceeded 60°C. The absolute value of G strongly depended on the maximum elevated temperature and the incubation time at that temperature. The corresponding behavior of the viscosity η was observed for each time course. Based on these results, the mechanism of thermally induced gelation of myosin solutions is discussed in view of SS bridge formation in the head and tail portions and unwinding/rewinding of coiled‐coil α‐helices in the tail portion. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 498–507, 2003
Nonsequence‐specific arginine interactions in the nucleosome core particle
Authors: García‐Pérez Maria , Pinto Marta , Subirana Juan A.
Published: July 2003

We have analyzed the relative orientation of basic amino acid side chains towards DNA in the nucleosome core particle. The electric field created by DNA phosphates has no apparent preferential orientation: no favored orientation of the arginine guanidinium group is found. Arginine may be either directly hydrogen bonded to a phosphate oxygen or stabilized in the minor groove by van der Waals contacts and the local negative electric field. On the other hand, the phosphate oxygen atoms hydrogen bonded to arginines are always found close to the plane defined by the guanidinium group. Thus it can be concluded that the interactions of arginine are strongly directional, those of phosphate are not. We also find that a highly charged fragment of histone H2B, which is placed between two DNA turns, has a very variable conformation. An increase in protein positive charge density apparently allows multiple nonspecific protein conformations when interacting with DNA. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 432–439, 2003
Fourier transform infrared spectroscopy suggests unfolding of loop structures precedes complete unfolding of pig citrate synthase
Authors: Severcan Feride , Haris Parvez I.
Published: July 2003

Pig citrate synthase (PCS) can be used as a model enzyme to gain some insight into the structural basis of protein thermostability. The thermal unfolding characteristics of the specific secondary structure elements within PCS were monitored in detail by following changes in its amide I band components. The result of our study indicates that PCS undergoes irreversible thermal denaturation. Detailed analysis reveals that the different secondary structures display a multistep transition with a major and a minor transition at different temperatures and a very small initial transition at the same temperature (30°C). A plot of temperature‐induced changes in 1H–2H exchange, the decrease in the absorbance of the α‐helical structures, and the increase in the absorbance of aggregated structures all have in common a multistep transition, the minor one centered at 45°C and the major one around 59°C. In contrast, a band that is tentatively assigned to loop structures displays these same minor and major transitions but at lower temperatures (39 and 52°C, respectively). The transition, which occurs at 39–45°C, is not associated with the appearance of aggregated structures. This transition may reflect a change in the tertiary structure of the protein. However, the final transition, which occurs at a higher temperature (52–59°C), reflects unfolding and aggregation of the polypeptide chains. The Fourier transform infrared (FTIR) analysis suggests that PCS has a thermolabile region that unfolds first, some 7°C below the main unfolding of the protein. We propose that this reflects the unfolding of the highly flexible loop segments, which in turn triggers the unfolding of the predominantly helical core structure of PCS. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 440–447, 2003
Translational diffusion coefficient of cycloamylose in aqueous sodium hydroxide
Authors: Nakata Yasushi , Amitani Keiji , Norisuye Takashi , Kitamura Shinichi
Published: July 2003

Seven cyclic (1 → 4)‐α‐D‐glucan (cycloamylose) samples ranging in weight‐average molecular weight from 5 × 103 to 1.8 × 104 and γ‐cyclodextrin have been studied by sedimentation equilibrium in dimethylsulfoxide (at 25°C) and by dynamic light scattering in 0.5 N aqueous sodium hydroxide (at 25°C), a good solvent for linear amylose. The measured translational diffusion coefficients D in the aqueous NaOH agree fairly closely with previous Monte Carlo results for cyclic (1 → 4)‐α‐D‐glucan chains with excluded volume, when correction is made for the effects of bead diameter and fluctuating hydrodynamic interaction (HI) on the Kirkwood theory on which the computation of D was based. These D data are also explained almost quantitatively by Yamakawa and Fujii's expression for the associated KP ring (based on the Kratky–Porod wormlike chain) with the molecular parameters for linear amylose if the fluctuating HI and excluded‐volume effects are taken into account. It is concluded that the translational diffusion behavior of cycloamylose in the aqueous NaOH is consistent with the conformational characteristics derived from the conformational energy of maltose and dilute‐solution data for linear amylose. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 508–516, 2003
DNA interaction with Mn2+ ions at elevated temperatures: VCD evidence of DNA aggregation
Authors: Andrushchenko Valery , van de Sande Hans , Wieser Hal
Published: July 2003

Interaction of natural calf thymus DNA with Mn2+ ions was studied at room temperature and at elevated temperatures in the range from 23°C to 94°C by means of IR absorption and vibrational circular dichroism (VCD) spectroscopy. The Mn2+ concentration was varied between 0 and 1.3M (0 and 10 [Mn]/[P]). The secondary structure of DNA remained in the frame of the B‐form family in the whole ion concentration range at room temperature. No significant DNA denaturation was revealed at room temperature even at the highest concentration of metal ions studied. However at elevated temperatures, DNA denaturation and a significant decrease of the melting temperature of DNA connected with a decrease of the stability of DNA induced by Mn2+ ions occurred. VCD demonstrated sensitivity to DNA condensation and aggregation as well as an ability to distinguish between these two processes. No condensation or aggregation of DNA was observed at room temperature at any of the metal ion concentrations studied. DNA condensation was revealed in a very narrow range of experimental conditions at around 2.4 [Mn]/[P] and about 55°C. DNA aggregation was observed in the presence of Mn2+ ions at elevated temperatures during or after denaturation. VCD spectroscopy turned out to be useful for studying DNA condensation and aggregation due to its ability to distinguish between these two processes, and for providing information about DNA secondary structure in a condensed or aggregated state. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 529–545, 2003
Application of the Suzuki‐Miyaura cross‐coupling reaction for the modification of phenylalanine peptides
Authors: Kotha Sambasivarao , Lahiri Kakali
Published: July 2003

We have demonstrated an exceptionally simple and a useful methodology for modification of unusual phenylalanine peptides by adapting the building block approach using the Suzuki‐Miyaura cross‐coupling reaction as a key step. This strategy gave a good overall yield of various modified tri‐ and pentapeptides that may be useful to prepare various biologically active peptides in a short period of time. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 517–528, 2003
Application of NMR, molecular simulation, and hydrodynamics to conformational analysis of trisaccharides
Authors: Dixon Ann M. , Venable Richard , Widmalm Göran , Bull T.E. , Pastor Richard W.
Published: July 2003

The preferred conformations and conformational flexibilities of the trisaccharides α‐D‐Glcp‐(1→2)‐β‐D‐Glcp‐(1→3)‐α‐D‐Glcp‐OMe (I) and α‐D‐Glcp‐(1→3)[β‐D‐Glcp‐(1→4)]‐α‐D‐Glcp‐OMe (II) in aqueous solution were determined using nuclear magnetic resonance (NMR) spectroscopy, molecular dynamics (MD) and Langevin dynamics (LD) simulations, and hydrodynamics calculations. Both trisaccharides have a vicinal substitution pattern in which long range (nonsequential) interactions may play an important role. LD simulation at 600 K indicated that the all‐syn conformation predominated, though other conformations were apparent. NOE data and MD and LD simulations at 298 K all indicated that trisaccharide I is a single all‐syn conformer in solution. Given that previous studies showed evidence of anti‐conformers in β‐D‐Glcp‐(1→2)‐β‐D‐Glcp‐(1→3)‐α‐D‐Glcp‐OMe, this result provides an example of how changing the anomeric configuration of one residue from β to α can make an oligosaccharide more rigid. Discrepancies in inter‐ring distances obtained by experiment and by simulation of the all‐syn conformer suggest the presence of an anti‐ψ conformation at the β‐(1→4)‐linkage for II. A combined analysis of measured and calculated translational diffusion constants and 13C T1 relaxation times yield order parameters of 0.9 for each trisaccharide. This implies that any interconversion among conformations is significantly slower than tumbling. Anisotropies of approximately 1.6 and 1.3 calculated for I and II, respectively, are consistent with the observed relatively flat T1 profiles because the tumbling is not in the motional narrowing regime. Published 2003 Wiley Periodicals, Inc. Biopolymers 69: 448–460, 2003
Molecular mechanisms of Fe2+‐induced β‐lactoglobulin cold gelation
Authors: Remondetto Gabriel E. , Subirade Muriel
Published: July 2003

To get more insight into the mechanisms of cold gelation of β‐lactoglobulin (β‐lg), macroscopic and molecular structural changes during Fe2+‐induced gelation of β‐lg were investigated using Fourier transform‐infrared (FTIR) spectroscopy and rheological methods. The FTIR spectroscopy results show that, upon the preheating treatment (first step of gel process), native globular proteins are denatured and aggregated molecules are found in solution. The spectra are similar to those of gels obtained in the second step of the process upon incorporation of Fe, which suggests that aggregated molecules formed during the preheating treatment constitute the structural basis of the aggregation. However, the rheological data show that the aggregation is achieved via two molecular mechanisms, both of which are modulated by the iron concentration. At 30 mM of iron, gel formation is essentially controlled by van der Waals interactions, while at 10 mM of iron, hydrophobic interactions predominate. At the two concentrations, disulfide bonds contribute to gel consolidation, the effect being more pronounced at 10 mM of iron. These mechanisms lead to the formation of gels of different microstructures. At the highest iron concentration, a strong and rapid decrease in the repulsion forces is produced, resulting in random aggregation. At the lowest iron concentration, the iron diminishes the superficial charge of both molecules and aggregated molecules, facilitating the interaction among hydrophobic regions and leading to the growth of the aggregation in the preferential direction and to filamentous gel formation. This study provides a comprehensive view of the different modes of gelation. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 461–469, 2003
Conformational analysis of the exopolysaccharide from Burkholderia caribensis strain MWAP71: Impact on the interaction with soils
Authors: Vanhaverbeke Cécile , Heyraud Alain , Mazeau Karim
Published: July 2003

The strain MWAP71 of Burkholderia caribensis produces a branched charged exopolysaccharide (EPS) that is responsible for soil aggregation. Understanding the conformational properties of the isolated polysaccharide is a prerequisite for proper investigation of the interactions between the polysaccharide and the soil at the atomic level. The aim of this study is first to have an overall view of the flexibility of the backbone and then to ascertain the role played by side groups in the conformational properties of the main chain. Conformational analysis of each oligomeric segment of the polysaccharide has been performed by means of adiabatic mapping of the backbone glycosidic torsion angles using the MM3(92) force field. Substitution by an acetyl group or by a Kdo unit has only a slight effect on the potential energy surfaces of the fragment model compounds. Calculated partition functions, however, indicate that the overall flexibility is slightly larger for the substituted oligomers than for the unsubstituted ones. Prediction of selected average interproton distances from the AB and BC potential energy surfaces allows comparison between modeling results and NMR measurements performed on the ABC fragment. Agreement between the experimental and the predicted data suggests that the established surfaces correctly reflect the observed conformational behavior of such fragments and validate the modeling protocol. The above results have been extended to regular and disordered long polymer chains, differing in Kdo content. It is found that Kdo affects the helical conformations of the polysaccharide. The number of stable helices is considerably larger with Kdo than without Kdo. On the contrary, Kdo has only a moderate effect on unperturbed disordered conformations of the polysaccharide. Predicted persistence length of 70 Å suggests that the polymer is semirigid with moderate extension. A further validation of the modeling results is obtained by the good concordance between this predicted value and the experimental one of 95 Å, measured from light scattering and viscosity experiments. The results lead to an understanding of the interactions of this polysaccharide with soils. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 480–497, 2003
Preliminary study on application of impregnated synthetic peptide TLC stationary phases for the pre‐screening of 5‐HT1A ligands
Authors: Zajdel PaweŁ , Bojarski Andrzej J. , Byrtus Hanna , ChŁoń‐Rzepa Grażyna , Obniska Jolanta , Chevallet Pierre , Martinez Jean , PawŁowski Maciej
Published: July 2003

Chromatographic parameters (ΔRf), defined as a difference in the migration of tested compound on the control and peptide impregnated silica gel TLC plates, were determined for 42 arylpiperazine derivatives. An amino acid sequence of the peptide used for impregnation was derived from the III transmembrane segment of the 5‐HT1A receptor in the close vicinity of aspartic acid (Asp 166) residue. It was found that the ΔRf values obtained in a model employing tetrapeptide P4LA (ADVL), as well as the calculated logP correlate with 5‐HT1A receptor affinity of the studied compounds. Copyright © 2003 John Wiley & Sons, Ltd.
Liquid chromatographic separation of the enantiomers of β‐amino acids on a ligand exchange chiral stationary phase
Authors: Hyun Myung Ho , Han Sang Cheol , Whangbo Sung Hee
Published: July 2003

A liquid chromatographic ligand exchange chiral stationary phase (CSP) derived from (S)‐leucinol was applied in the separation of the enantiomers of 12 β‐amino acids. The resolution was quite successful especially for the enantiomers of β‐amino acids containing aromatic functional group in the side chain. The chromatographic resolution behaviors were dependent on the organic modifier and Cu(II) concentration in aqueous mobile phase and the column temperature. Copyright © 2003 John Wiley & Sons, Ltd.
The benefit of the retrofitting of a conventional LC system to micro LC: a practical evaluation in the field of bioanalysis with fluorimetric detection
Authors: Roy S. , Rieutord A. , Zhou J.Y. , Baillet A. , Prognon P. , Chaminade P.
Published: July 2003

The interests in liquid micro‐chromatography (higher column efficiencies, increase in sensitivity) are now well established. The enhancement of fluorimetric response induced by the reduction of the inner diameter of columns (4.6, 3.0, 1.0 and 0.3 mm respectively) coupled with adapted detection cells to control the loss of efficiency (8 µL for the two first columns and 100 nL for the two smaller ones) has been studied in the bioanalytical field, using the plasma determination of native fluorescent antibacterial agents: fluoroquinolones. Ten‐fold enhancement of the signal can easily be obtained when substituting a 0.3 mm i.d. column and 100 nL detection cell for a 4.6 mm i.d. column, and 8 µL detection cell. In addition to inner diameter reduction, the detection cell geometry appears to be an essential parameter to obtain the best enhancement of the recorded signal. Hence, the enhancement of signal with micro‐chromatography with fluorimetric detection appears to be a compromise between column inner diameter and flow cell volume reduction. Copyright © 2003 John Wiley & Sons, Ltd.
Thin layer chromatographic resolution of some 2‐arylpropionic acid enantiomers using L‐(−)‐serine, L‐(−)‐threonine and a mixture of L‐(−)‐serine and L‐(−)‐threonine‐impregnated silica gel as stationary phases
Authors: Aboul‐Enein Hassan Y. , El‐Awady Mahmoud I. , Heard Charles M.
Published: July 2003

Impregnated silica TLC plates with L‐(−)‐serine and L‐(−)‐threonine and a mixture of L‐(−)‐serine and L‐(−)‐threonine (1:1) as chiral selectors were prepared to use as chiral stationary phases (CSPs) in thin layer chromatography. The resolution of the enantiomers of 2‐arylpropionic drugs, including ibuprofen, ibuproxam, ketoprofen, pranoprofen, benoxaprofen, flurbiprofen and tiaprofenic acid was investigated on these CSPs. A mobile phase system of acetonitrile–methanol–water (16:4:0.5, v/v/v) was used. The spots were detected with iodine vapours and the detection limits were found to range between 0.25 and 0.5 µg/mL for all racemic compounds investigated. The effect of temperature, pH and concentration of the impregnating chiral selectors on resolution has been studied. Copyright © 2003 John Wiley & Sons, Ltd.
Estimation of the lipophilicity of antiarrhythmic and antihypertensive active 1‐substituted pyrrolidin‐2‐one and pyrrolidine derivatives
Authors: Kulig Katarzyna , Malawska Barbara
Published: July 2003

The lipophilicity of some antiarrhythmic and antihypertensive active 1‐[2‐hydroxy‐ or 1‐[2‐acetoxy‐3‐(4‐aryl‐1‐piperazinyl)propyl]pyrrolidin‐2‐one derivatives (1–12) has been investigated. Their lipophilicity (RMO and log k′) was determined by reversed‐phase thin‐layer chromatography and reversed‐phase high‐performance liquid chromatography with mixtures of acetonitrile and Tris buffer as mobile phases. The partition coefficients of compounds 1–12 (log PScilogP) were also calculated with the ScilogP program. Comparison of RMO, log k′ and calculated log D7.0 ScilogP values enabled calculation of clog D7.0 TLC and clog D7.0 HPLC values. Preliminary quantitative structure–activity relationship studies indicated that for active compounds there is a dependence between affinity for α2‐adrenoceptors and their clog D7.0 HPLC values. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of three effective components in Fructus corni and its preparations by micellar electrokinetic capillary chromatography
Authors: Wang Shu Fang , Chen Xing Guo , Hu Zhi De , Ju Yong
Published: July 2003

An efficient micellar electrokinetic capillary chromatography method was developed to analyze three major active components including morroniside, loganin and gallic acid in Fructus corni and its six preparations for the first time. The factors that could affect the separation were studied, such as the pH of the buffer, concentrations of SDS, organic modifier and β‐CD, and the applied voltage. The optimum analysis conditions were 10 mmol/L NaH2PO4–5 mmol/L Na2B4O7 (pH 6.8) buffer containing 140 mmol/L SDS, 1 mmol/L β‐CD, 5% (v/v) methanol and 12.5 kV applied voltage. The linearity between the peak‐areas and the concentrations of the analytes were investigated, and they exhibit excellent linear behavior over the concentration ranges (correlation coefficients 0.9953–0.9995). In addition, the pKa of gallic acid was determined using capillary zone electrophoresis. The result was consistent with that reported by the literature. Copyright © 2003 John Wiley & Sons, Ltd.