bluuebunny/crossref_metadata_2025_split huggingface dataset:
Classical cationic polymerization of styrene in a spinning disc reactor using silica‐supported BF3 catalyst
Authors: Boodhoo Kamelia V. K. , Dunk William A. E. , Vicevic Marija , Jachuck Roshan J. , Sage Valerie , Macquarrie Duncan J. , Clark James H. 
Published: March 2006

AbstractThe carbo‐cationic polymerization of styrene has been studied in a Spinning Disc Reactor (SDR) and the results were compared to those observed in a conventional Stirred Tank Reactor (STR). Addition of styrene to a slurry of silica‐supported boron trifluoride (BF3/SiO2) in 1,2‐dichloroethane led to uncontrollable reactions in the STR at monomer concentrations > 25%w/w and initial temperatures of 20–25°C. By comparison, monomer concentrations of 75% w/w were safely and controllably polymerized in the SDR at 40°C to yield polymers with molecular weights comparable to those reported in the literature for polymer prepared at −60°C. Exceptional heat transfer rates achieved in the SDR are sufficient to deal with the heat evolved when styrene is polymerized at concentrations as high as 75% w/w, the reaction proceeding under essentially isothermal conditions. In the present study, the effects of monomer/solvent feed rates, monomer concentrations, disc size, and disc speed on monomer conversions, polymer molecular weights, and polydispersities achieved in the SDR are investigated. Speculative explanations of the observed results are presented in terms of enhanced mixing effects on the polymerization mechanisms in the SDR. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 8–19, 2006
Study on blooming of tetrabromobisphenol a bis(2,3‐dibromopropyl ether) in blends with polypropylene
Authors: Li Xiang‐Mei , Yang Rong‐Jie 
Published: March 2006

AbstractBlends of polypropylene/tetrabromobisphenol A bis(2,3‐dibromopropyl ether) (PP/TBAB) were prepared by twin‐screw extruder, and then were molded into PP/TBAB plaques. Blooming of TBAB on the surface of PP/TBAB plaques were studied through heat aging test and theoretical calculation. The heat aging test at 70°C for 45 days was performed. Mass of the blooming TBAB on the surface of the plaque was measured every day in the period. Based on Fick's second law of diffusion, a mathematical method was developed to achieve concentration profile of TBAB dependent on time in the PP/TBAB plaques. Diffusion coefficients of TBAB were calculated by using the set concentration equation of TBAB with the experimental data. It was obtained that the diffusion coefficient of TBAB in PP/18 wt % TBAB is larger than that in PP/45 wt % TBAB. For the sample of PP/18 wt % TBAB, diffusion of TBAB reached an equilibrium after the heat aging for 40 days at 70°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 20–24, 2006
Vulcanization kinetic of styrene–butadiene rubber by sulfur/TBBS
Authors: Marzocca A. J. , Mansilla M. A. 
Published: March 2006

AbstractTorque curves, measured with a moving die rheometer at temperatures between 413 and 473 K, were used to characterize the vulcanization of styrene–butadiene rubber with different cure systems based on sulfur and TBBS (N‐t‐butyl‐2‐benzothiazole sulfenamide). Several compounds were prepared varying the amount of sulfur and accelerator between 0.5 and 2.5 phr in the formulation. By means of normalized torque curves, the kinetic of cure of these samples was evaluated considering the model of isothermal curing proposed by Kamal and Sourour. In this frame, the parameters of the kinetic model were obtained. The effect of the amount of sulfur and accelerator in the compound on the kinetic parameters was investigated and a maximum of the rate parameter k for the compound with formulation with 1.0 phr of sulfur and 2.0 phr of accelerator was found. A marked decrease in the activation energy of the cure process of the elastomer was observed at higher levels of TBBS in the compound. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 35–41, 2006
High temperature zone‐drawing of nylon 66 microfiber prepared by CO2 laser‐thinning
Authors: Suzuki Akihiro , Hasegawa Toshinori 
Published: March 2006

AbstractA high temperature zone‐drawing method was applied to a nylon 66 microfiber, obtained by using CO2 laser‐thinning, to develop its mechanical properties. The microfiber used for the high temperature zone‐drawing was prepared by winding at 150 m min−1 the microfiber obtained by irradiating the laser at 4.0 W cm−2 to an original fiber with a diameter of 50 μm, and had a diameter of 9.6 μm and a birefringence of 0.019. The high temperature zone‐drawing was carried out in two steps; the first drawing was carried out at a temperature of 230°C at supplying and winding speeds of 0.266 and 0.797 m min−1, the second at 250°C at supplying and winding speeds of 0.266 and 0.425 m min−1, respectively. The diameter of the microfiber decreased, and its birefringence increased stepwise with the processing. The high temperature zone‐drawn microfiber finally obtained had a diameter of 4.2 μm, a birefringence of 0.079, total draw ratio of 4.8, tensile modulus of 12 GPa, and tensile strength of 1.0 GPa. The wide‐angle X‐ray diffraction photograph of the drawn microfiber showed the existence of highly oriented crystallites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 42–47, 2006
An investigation on wear mechanism of POM/LLDPE blends
Authors: Chen Jinyao , Cao Ya , Li Huilin 
Published: March 2006

AbstractThe friction and wear properties of polyoxymethylene/linear low‐density polyethylene/ethylene‐acrylic acid (POM/LLDPE/EAA) blends are investigated on a MM‐200 wear tester. The results show that the addition of LLDPE and EAA obviously improves the friction and wear properties of POM. The friction coefficient and wear scar width of POM/LLDPE/EAA blends are much lower than those of pure POM. SEM analysis reveals that POM appears to wear by thermal softening and melting of worn surface when sliding against the stainless steel, while no severe damage but wear debris can be observed on the worn face of POM/LLDPE/EAA blend. Long‐time sliding causes the removal of molten POM from the worn surface, while the formation of the lubricated layer occurs on the worn surface for POM/LLDPE/EAA blend. DSC analysis shows that the melting temperature and the crystallinity of the worn surface for POM are improved after a long‐time sliding. Molecular orientation on the worn surface of POM is affirmed by WAXD. For POM/LLDPE/EAA blend, the improvement of the friction and wear properties is mainly owed to wear debris and lubricant layer existing between the contact surfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 48–53, 2006
Cleavage and survival of Xenopus embryos exposed to 8 T static magnetic fields in a rotating clinostat
Authors: Eguchi Yawara , Ueno Shoogo , Kaito Chikara , Sekimizu Kazuhisa , Shiokawa Koichiro 
Published: March 2006

AbstractIn this study, we examined cleavage and survival of fertilized Xenopus embryos exposed to 8 T static magnetic fields (SMFs). We investigated fertilized Xenopus embryos exposed to magnetic field either in static chamber or in a rotating culture system. Our results showed that the exposure to the strong magnetic field of 8 T changed the third cleavage furrow from the usual horizontal one to a perpendicular one; however, when the direction of gravity was randomized by exposing embryos to magnetic field in a rotating culture system, the third cleavage furrow were formed horizontally, a finding which suggests that the observed distortion of the third cleavage furrow in magnetism‐exposed embryos was accomplished by altering gravity effects which were elicited by diamagnetic force due to high gradient magnetic field. Our results also showed that the exposure to the strong magnetic field did not damage survival. These results demonstrate that SMF and altering gravity cause distortion of the third cleavage furrow and show that effects of exposing cleavage embryos to magnetic field were transient and did not affect the post‐cleavage development. We also showed that strong magnetic field is not hazardous to the cleavage and blastula‐gastrula transition of developing embryonic cells. Bioelectromagnetics 27:307–313, 2006. © 2006 Wiley‐Liss, Inc.
Bayesian Analysis for the Meiosis I Non‐disjunction Fraction in Numerical Chromosomal Anomalies
Authors: Loschi Rosangela H. , Franco Glaura C. 
Published: March 2006

AbstractThe main causes of numerical chromosomal anomalies, including trisomies, arise from an error in the chromosomal segregation during the meiotic process, named a non‐disjunction. One of the most used techniques to analyze chromosomal anomalies nowadays is the polymerase chain reaction (PCR), which counts the number of peaks or alleles in a polymorphic microsatellite locus. It was shown in previous works that the number of peaks has a multinomial distribution whose probabilities depend on the non‐disjunction fraction F . In this work, we propose a Bayesian approach for estimating the meiosis I non‐disjunction fraction F in the absence of the parental information. Since samples of trisomic patients are, in general, small, the Bayesian approach can be a good alternative for solving this problem. We consider the sampling/importance resampling technique and the Simpson rule to extract information from the posterior distribution of F . Bayes and maximum likelihood estimators are compared through a Monte Carlo simulation, focusing on the influence of different sample sizes and prior specifications in the estimates. We apply the proposed method to estimate F for patients with trisomy of chromosome 21 providing a sensitivity analysis for the method. The results obtained show that Bayes estimators are better in almost all situations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Simple Imputation Method for Longitudinal Studies with Non‐ignorable Non‐responses
Authors: Wang Molin , Fitzmaurice Garrett M. 
Published: March 2006

AbstractMissing data are a common problem in longitudinal studies in the health sciences. Motivated by data from the Muscatine Coronary Risk Factor (MCRF) study, a longitudinal study of obesity, we propose a simple imputation method for handling non‐ignorable non‐responses (i.e., when non‐response is related to the specific values that should have been obtained) in longitudinal studies with either discrete or continuous outcomes. In the proposed approach, two regression models are specified; one for the marginal mean of the response, the other for the conditional mean of the response given non‐response patterns. Statistical inference for the model parameters is based on the generalized estimating equations (GEE) approach. An appealing feature of the proposed method is that it can be readily implemented using existing, widely‐available statistical software. The method is illustrated using longitudinal data on obesity from the MCRF study. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conformational studies of vasopressin analogues modified with N‐methylphenylalanine enantiomers in dimethyl sulfoxide solution
Authors: Sikorska Emilia , Ślusarz Magdalena J. , Lammek Bernard 
Published: March 2006

AbstractThe conformations of [Arg8]vasopressin (AVP) analogues substituted at positions 2 and 3 with N‐methylphenylalanine (MePhe) enantiomers were earlier investigated by using nuclear magnetic resonance (NMR) spectroscopy in aqueous solution. A comparison of the results obtained in H2O/D2O (9:1) and DMSO‐d6 has shown the structures in the first solution to be more flexible than those in DMSO‐d6. This is manifested by a higher percentage of minor conformations in H2O/D2O. The largest differences between the NMR spectra in both solvents were noticed for [MePhe2, D‐MePhe3]AVP (II) and [D‐Cys1,MePhe2,D‐MePhe3]AVP (III). Namely, in the ROESY spectra in aqueous solution, the cis/trans isomerization between MePhe2–DMePhe3 and D‐Cys1–MePhe2 for II and III, respectively, is observed, while in DMSO‐d6, the appropriate cross peaks indicate isomerization across the Cys6–Pro7 peptide bond. In the case of the remaining peptides, the position of cis/trans isomerization is the same in aqueous solution and in dimethyl sulfoxide. [D‐MePhe2,MePhe3]AVP (V) displays low antiuterotonic and antipressor activities, while [D‐MePhe2,3]AVP (IV) is a weak but selective blocker of oxytocin (OT) receptors in the uterus. The former shows similar conformational preferences as another antagonist of V1a and OT receptors—namely, [Acc2,D‐Arg8]VP (Acc: 1‐aminocyclohexane‐1‐carboxylic acid)—investigated by us. In the case of IV, the cis peptide bond between residues at positions 2 and 3 might be the reason for selectivity. © 2006 Wiley Periodicals, Inc. Biopolymers 82: 603–614, 2006This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Proton transfer pathways in the mutant His‐64–Ala of human carbonic anhydrase II
Authors: Roy Arijit , Taraphder Srabani 
Published: March 2006

AbstractWe have investigated the possible proton transfer pathways from the surface of the protein to the zinc‐bound water molecule in the mutant His‐64–Ala of human carbonic anhydrase II. Starting with an input of known crystallographic structures of the mutant, we model the proton pathways as hydrogen‐bonded networks of proton conducting groups and bound solvent molecules. No proton path is detected in the mutant, in close agreement with the experimental observation of a 20‐fold decrease in its catalytic efficiency compared to the wild‐type enzyme. We also investigate in detail changes in hydration structure at the active site of the mutant and the resulting proton paths in the presence of an exogenous proton donor 4‐methylimidazole (4‐MI). The proton transfer pathways thus detected are correlated to the observed chemical rescue of catalytic activity by 4‐MI. © 2006 Wiley Periodicals, Inc. Biopolymers 82: 623–630, 2006This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Conformational Fluctuations versus Constraints in Amino Acid Side Chains: The Evolution of Information Content from Free Amino Acids to Proteins
Authors: Bojarski Andrzej J. , Nowak Mateusz , Testa Bernard 
Published: March 2006

AbstractLike all other complex biological systems, proteins exhibit properties not found in free amino acids (i.e., emergent properties). Here, we explore top‐down constraints experienced by the residue side chains in proteins compared to amino acids in increasingly complex molecular environments: free amino acids, end‐capped amino acids, and the central residue in an α‐helical nonapeptide. The crystalline structure of the contractile protein profilin Ib and the enzyme trypsin were chosen as objects of study, and submitted to 10 ns molecular dynamics (MD) simulations. The results revealed increased conformational constraints on the side chains when going from the simpler to the more complex compounds. A Shannon entropy (SE) analysis of the conformational behavior of the side chains showed in most cases a progressive and marked decrease in the SE of the χ1 and χ2 dihedral angles. This is equivalent to stating that conformational constraints on the side chain of residues increase their information content and, hence, recognition specificity compared to free amino acids. In other words, the vastly increased information content of a protein relative to its free monomers is embedded not only in the tertiary structure of the backbone, but also in the conformational behavior of the side chains. The postulated implication is that both backbone and side chains, by virtue of being conformationally constrained, contribute to the protein's recognition specificity toward other macromolecules and ligands.
Synthesis and Characterization of a C(6) Nucleoside Analogue for the in vivo Imaging of the Gene Expression of Herpes Simplex Virus Type‐1 Thymidine Kinase (HSV1 TK)
Authors: Johayem Anass , Raić‐Malić Silvana , Lazzati Katia , Schubiger Pius A. , Scapozza Leonardo , Ametamey Simon M. 
Published: March 2006

AbstractThe synthesis and biological evaluation of ‘6‐(1,3‐dihydroxyisobutyl)thymine’ (DHBT; 1), which corresponds to 6‐[3‐hydroxy‐2‐(hydroxymethyl)propyl]‐5‐methylpyrimidine‐2,4(1H,3H)‐dione, is reported. DHBT (1) was designed as a new substrate for herpes simplex virus type‐1 thymidine kinase (HSV1 TK). The compound was found to be exclusively phosphorylated by HSV1 TK, and to exhibit good binding affinity (Ki = 35.3±1.3 μM). Cell‐proliferation assays with HSV1‐TK‐transduced human osteosarcoma cells (143B‐TK+‐HSV1‐WT) and with both human‐thymidine‐kinase‐1‐negative (143B‐TK−) and non‐transduced parental (MG‐63) cells indicate that 1 is less cytotoxic than the standard drug Ganciclovir. Thus, DHBT (1) represents a promising precursor of a nontoxic reporter probe for the monitoring of HSV1 TK gene expression by means of positron‐emission tomography (PET).
Thermal Stability of Dehydrophenylalanine‐Containing Model Peptides as Probed by Infrared Spectroscopy: a Case Study of an α‐Helical and a 310‐Helical Peptide
Authors: Gupta Alka , Mehrotra Ranjana , Klimov Evgueni , Siesler Heinz Wilhelm , Joshi Ratanmani M. , Chauhan Virander Singh 
Published: March 2006

AbstractThe temperature‐dependent secondary‐structural changes in the two known helical model peptides Boc‐Val‐ΔPhe‐Ala‐Leu‐Gly‐OMe (1; α‐helical) and Boc‐Leu‐Phe‐Ala‐ΔPhe‐Leu‐OMe (2; 310‐helical), which both comprise a single dehydrophenylalanine (ΔPhe) residue, were investigated by means of FT‐IR spectroscopy (peptide film on KBr). Both the first‐order and the better‐resolved second‐order derivative IR spectra of 1 and 2 were analyzed. The ν(NH) (3240–3340 cm−1), the Amide‐I (1600–1700 cm−1), and the Amide‐II (1510–1580 cm−1) regions of 1 and 2 showed significant differences in thermal‐denaturation experiments (22°→144°), with the 310‐helical peptide (2) being considerably more stable. This observation was rationalized by different patterns and strengths of intramolecular H‐bonds, and was qualitatively related to the different geometries of the peptides. Also, a fair degree of residual secondary‐structural elements were found even in the ‘denatured’ states above 104° (1) or 134° (2).
Synthesis and Characterization of a New Macrocyclic Copper(II) Complex with an N‐Glycosidic Pendant Arm: in vitro Cytotoxicity and Binding Studies with Calf‐Thymus DNA
Authors: Mathur Suvigya , Tabassum Sartaj 
Published: March 2006

AbstractThe new macrocyclic complex 2‐amino‐2‐deoxy‐N‐[2‐(1,3,5,8,11‐pentaazacyclotridecan‐3‐yl)ethyl]‐β‐D‐glucopyranosylamine copper(II) dichloride (1a) was prepared and thoroughly characterized by various techniques. Molar‐conductance measurements showed that 1a (and its Ni analogue 1b) are ionic in nature. On the basis of spectroscopic data, both complexes were assigned a square‐planar geometry, and found to be highly stabile and hydrolytically robust in H2O over a wide range of pH, as confirmed by cyclic voltammetry (CV). The CuII complex 1a was found to bind to CT‐DNA, with a binding constant Kb of 2.4×103 M−1, as derived by UV/VIS titration, and confirmed by CV, circular dichroism (CD), and viscosity measurements. DNA binding seems to occur mostly via H‐bonding. In an in vitro antitumor MTT assay, 1a exhibited significant anticancer activity against the SY5Y and PC‐12 cell lines, with an estimated IC50 value in the micromolar range for SYSY, similar to the standard drug 5‐fluorouracil.
Synthesis of Fluoro Analogues of 3,4‐(Methylenedioxy)amphetamine (MDA) and Its Derivatives
Authors: Trachsel Daniel , Hadorn Marcel , Baumberger Franz 
Published: March 2006

AbstractThe role of the metabolism of the entactogen 3,4‐(methylenedioxy)methamphetamine (MDMA;1b) in neurotoxic or psychopharmacologic action is widely discussed, but not yet fully understood. To prompt further investigation into the role of MDMA metabolism, six new 3,4‐(difluoromethylenedioxy) analogues of MDMA (1b) were prepared and characterized. Although electronically very different, the fluoro analogues3–5should be sterically very similar to the non‐fluorinated parent compounds. The F‐atoms may prevent the formation of toxic metabolites producedviaa radical pathway (Scheme 1). Different theories regarding MDMA‐induced neurotoxicity are briefly reviewed and discussed. The novel compounds3–5may help to verify the hypothesis that MDMA‐induced neurotoxicity is the result of the formation of metabolites lacking the methylenedioxy bridge.
New Chemical Constituents from the Endophyte Streptomyces Species LR4612 Cultivated on Maytenus hookeri
Authors: Zhao Pei‐Ji , Li Guo‐Hong , Shen Yue‐Mao 
Published: March 2006

AbstractFrom solid cultures of the biologically important endophyte Streptomyces species LR4612, cultivated on Maytenus hookeri, four new and two known compounds were isolated. The new compounds were identified as (2S*,3S*)‐5‐amino‐3‐hydroxy‐5‐oxopentan‐2‐yl 3‐(formylamino)‐2‐hydroxybenzoate (1), N‐[(3R*,4R*)‐3‐amino‐3,4‐dihydro‐4‐methyl‐2,6‐dioxo‐2H,6H‐1,5‐benzodioxocin‐10‐yl]formamide (2), (5β,6α)‐6,11‐dihydroxyeudesmane (3), and 5‐(6,7‐dihydroxy‐6‐methyloctyl)furan‐2(5H)‐one (4); the known compounds were elucidated as sorbicillin (5) and N‐acetyltyramine (6). The structures were established by HR‐ESI‐MS and in‐depth NMR analyses.
Antiviral Flavonoid‐Type C‐Glycosides from the Flowers of Trollius chinensis
Authors: Cai Shao‐Qing , Wang Rufeng , Yang Xiuwei , Shang Mingying , Ma Chaomei , Shoyama Yukihiro 
Published: March 2006

AbstractTwo new flavonoid‐type C‐glycosides, trollisin I (=(1S)‐1,5‐anhydro‐1‐[2‐(3,4‐dihydroxyphenyl)‐5‐hydroxy‐7‐methoxy‐4‐oxo‐4H‐[1]benzopyran‐8‐yl]‐2‐O‐(2‐methylbutanoyl)‐D‐glucitol; 1) and its 2‐O‐benzoyl congener trollisin II (2), were isolated from Trollius chinensis Bunge, together with the two known compounds 2″‐O‐(2′′′‐methylbutanoyl)isoswertisin (3) and vitexin galactoside (4). All compounds were identified by HR‐ESI‐MS and in‐depth NMR‐spectroscopic analyses. In antiviral assays, compound 3 was found to be moderately active towards influenza virus A.
Phylogeny of the Schisandraceae Based on cpDNA mat‐K and rpL16 Intron Data
Authors: Wang Yan‐Han , Zhang Shou‐Zhou , Gao Jian‐Ping , Chen Dao‐Feng 
Published: March 2006

AbstractThe chloroplast mat‐K region and rpL16 intron region were sequenced for 14 species of Schisandraceae, representing both genera Kadsura Kaempf. ex Juss. and Schisandra Michx, to discuss the phylogeny of this family. Analyses were performed both in separate and combined sequence data sets (including the rbc‐L sequence), with Illicium angustispealum A. C. Smith as the out‐group. The results showed that the Schisandraceae are monophyletic. In all the analyses, Schisandra propinqua var. chinensis Oliva and Schisandra plena A. C. Smith were nested within Kadsura, which implies that the genera Kadsura and Schisandra are closely related. They might have originated from a common ancestor, but then evolved via different routes. The result inferred from the combined data showed a greater resolution within Schisandra than those from the two separate data sets. High bootstrap values supported the monophyly of most subgenera according to Law's system (1996). A combination of morphological, anatomical, and chemical analyses indicates that S. chinensis and S. rubriflora may be the primitive taxa in Schisandra.