bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical properties of polystyrene/polyamide 6 blends compatibilized with the ionomer poly(styrene‐co‐sodium acrylate)
Authors: Villarreal M. E. , Tapia M. , Nuño‐Donlucas S. M. , Puig J. E. , González‐Núñez R.
Published: April 2004

The compatibilizing effect of the ionomer, poly(styrene‐co‐sodium acrylate) (PSSAc), on immiscible blends of polystyrene (PS)/polyamide 6 (PA6) was studied by mechanical tests and scanning electron microscopy. The PSSAc acts as an effective compatibilizer because both the deformation at break (%) obtained by tensile stress–strain tests and the impact rupture energy are larger in blends containing small amounts of PSSAc. The morphologies of the fractured surfaces produced by tensile stress–strain tests of blends with or without the ionomer confirm that PSSAc increases the interfacial adhesion between PS and PA6 phases. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2545–2551, 2004
Synthesis and property of hydrogel membranes consisting of fumaramate with phosphorylcholine group
Authors: Oishi Tsutomu , Yamasaki Hirohito , Onimura Kenjiro , Fukushima Toshiyuki , Morihashi Seiji
Published: April 2004

Fumaramate bearing a phosphoryl choline group, isopropyl‐2‐[2′‐(trimethylammonium) ethyl phosphoryl] ethyl fumaramate (IPTPFA), was radically copolymerized with 2‐hydroxyethylmethacrylate (HEMA) in the presence of various crosslinking agents, water, and 2,2′‐azobis(isobutyronitrile) to obtain hydrogel membranes. The obtained hydrogel membranes adsorbed bovine serum albumin (BSA) much less than those of poly(HEMA), and the values of water content (H) were higher than those of poly(HEMA). The values of tensile strength and tensile elongation of the hydrogel were 68.4 g/mm2 and 239%, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2552–2557, 2004
Dependency of thermal and mechanical properties on the composition of mixed‐substituent poly(fluoroalkoxyphosphazenes)
Authors: Maher Andrew E. , Ambler Catherine M. , Powell Eric S. , Allcock Harry R.
Published: April 2004

A series of poly(fluoroalkoxyphosphazenes) containing a mixture of 2,2,3,3,4,4,5,5‐octafluoropentoxy and 2,2,2‐trifluoroethoxy substituents was synthesized. The series included polymers with 25–94% incorporation of the trifluoroethoxy substituent, as well as single‐substituent polymers with 100% octafluoropentoxy or trifluoroethoxy side groups. Polymers were analyzed by multinuclear NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis, and were subjected to limiting oxygen index and microtensile testing. It was found that the Tg and Td values among the cosubstituted polymers varied little with changes in composition, but the mechanical properties varied over a wide range. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2569–2576, 2004
Preparation of composites of polymer liquid crystal/cholesteric liquid crystal and their photochemical switching and memory properties by photoisomerization of a chiral azobenzene molecule
Authors: Kurihara Seiji , Yoshioka Teppei , Zahangir Alam Md , Ogata Tomonari , Nonaka Takamasa
Published: April 2004

A chiral azobenzene compound was synthesized, and mixing the chiral azobenzene compound in a host nematic liquid crystal (LC) induced a cholesteric phase. The twisting power of the trans‐form of the chiral azobenzene compound was larger than that of its cis‐form produced by ultraviolet irradiation. A low molecular weight compensated nematic LC was then prepared by mixing of the chiral azobenzene and a nonphotochromic chiral compound, thus giving mutual opposite helical sense in the host LC. Reversible optical switching between transparent and opaque was achieved by ultraviolet and visible light irradiation. However, the photochemically switched opaque state was not stable even in the dark. Stability of the opaque state was found to be improved by adding polymer LC to the low molecular weight compensated nematic LC. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2577–2580, 2004
Flame retardancy of poly(butylene terephthalate) blended with phosphorous compounds
Authors: Ishikawa Tomoyuki , Maki Ikuhiro , Takeda Kunihiko
Published: April 2004

The thermal degradation and flame retardancy of poly(butylene terephthalate) (PBT) were studied with a focus on the effect of phosphorous compounds. Thermogravimetric analysis, pyrolysis/gas chromatography/mass spectrometry (Py/GC/MS), and elemental analysis were used to analyze the flame retardancy, which were observed by an Underwriters Laboratory UL‐94 test and a cone calorimeter. The 50% degradation temperatures of PBT blends with phosphorous compounds were the same as that of neat PBT. Six scission products were assigned by Py/GC/MS. The burning times of the UL test of several PBT blends were much shorter than that of neat PBT. The relation between flame retardancy and thermal degradation was analyzed with respect to the results of the scission products and the char in burned polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2326–2333, 2004
Enhancement of corrosion protection effect of poly(styrene‐co‐acrylonitrile) by the incorporation of nanolayers of montmorillonite clay into copolymer matrix
Authors: Yeh Jui‐Ming , Liou Shir‐Joe , Lu Hsin‐Jung , Huang Hsi‐Ya
Published: April 2004

A series of polymer–clay nanocomposite (PCN) materials that consisted of poly(styrene‐co‐acrylonitrile) (PSAN) and layered montmorillonite (MMT) clay were successfully prepared by effectively dispersing the inorganic nanolayers of MMT clay into the organic PSAN matrix by a conventional in situ thermal polymerization. First of all, organic styrene and AN monomers at a specific feeding ratio were simultaneously intercalated into the interlayer regions of organophilic clay hosts and followed by a typical free‐radical polymerization with benzyl peroxide as initiator. The as‐synthesized PCN materials were subsequently characterized by FTIR spectroscopy, wide‐angle powder X‐ray diffraction, and transmission electron microscopy. The as‐prepared PCN materials, in the form of coatings, incorporated with low clay loading (e.g., 1 wt %) on cold‐rolled steel, were found to be much superior in corrosion protection over those of bulk PSAN based on a series of standard electrochemical measurements of corrosion potential, polarization resistance, and corrosion current in 5 wt % aqueous NaCl electrolyte. Molecular weights of PSAN extracted from PCN materials and bulk PSAN were determined by gel permeation chromatography with THF as eluant. Effects of the material composition on the molecular barrier and thermal stability of PSAN along with PCN materials, in the form of both membrane and fine powder, were also studied by molecular permeability analysis, differential scanning calorimetry, and thermogravimetric analysis, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2269–2277, 2004
Relation between strain hardening and wear resistance of polymers
Authors: Mergler Y. J. , Schaake R. P.
Published: April 2004

The friction and abrasive wear of blends of polystyrene (PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) were measured. The coefficient of friction decreases only slightly with an increasing PPO fraction, while the abrasive wear decreases largely upon the introduction of increasing amounts of PPO. It is clearly shown that the abrasive wear resistance of the PS/PPO blends increases with an increasing strain hardening modulus of the blend. The wear rate change between 20 and 40 wt % PPO is ascribed to a transition in the failure mechanism from predominantly brittle to predominantly tough. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2689–2692, 2004
Synthesis and lyotropic behavior of mesogen‐linked cellulose acetates
Authors: Wu Changcheng , Gu Qincui , Zhang Rongben , Huang Yong , Chen Shouxi
Published: April 2004

Three aromatic (p‐carboxyl phenyl) esters, 4‐(benzoyloxy) benzoic acid, 4‐(4′‐methylbenzoyloxy) benzoic acid, and 4‐(4′‐chlorobenzoyloxy) benzoic acid, were synthesized and they showed nematic monotropic or thermotropic behavior. The mesogen‐linked cellulose acetates were first prepared by the reaction of aromatic (p‐carboxyl phenyl) esters with cellulose acetate through esterification in the presence of N,N‐dicyclohexylcarbodiimide (DCC) and 4‐dimethylaminopyridine (DMAP). Their degrees of mesogenic unit substitution (DS‐meso) were between 0.27 and 0.41. It was found that they can form cholesteric lyotropic phases in dichloroacetic acid and their critical concentration was about 25 wt %. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2693–2697, 2004
Influence of acrylonitrile–butadiene–styrene (ABS) morphology and poly(styrene‐co‐acrylonitrile) (SAN) content on fracture behavior of ABS/SAN blends
Authors: Yamakawa Roberto S. , Correa Carlos A. , Hage Elias
Published: April 2004

This study attempted to correlate morphological changes and physical properties for a high rubber content acrylonitrile–butadiene–styrene (ABS) and its diluted blends with a poly(styrene‐co‐acrylonitrile) (SAN) copolymer. The results showed a close relationship between rubber content and fracture toughness for the blends. The change of morphology in ABS/SAN blends explains in part some deviations in fracture behavior observed in ductile–brittle transition temperature shifts. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2606–2611, 2004
Surface modification of poly(propylene) by photoinitiators: Improvement of adhesion and wettability
Authors: Castell P. , Wouters M. , de With G. , Fischer H. , Huijs F.
Published: April 2004

Different benzophenone‐type photoinitiators were photografted onto poly(propylene) (PP). The polymer surfaces were analyzed by means of contact angle measurements, UV spectroscopy, and FTIR‐ATR. The modified samples showed a better wettability and higher surface energies, increasing from 26 mN/m for pure PP to 36 mN/m for the modified samples. The UV spectrum of the modified PP films showed two absorption bands that could be related to the grafted initiator. The effect of irradiation time and photoinitiator concentration was investigated. Different acrylates were grafted efficiently onto the modified polymer surfaces. FTIR‐ATR and contact angle measurements confirmed the presence of the grafted chains. The surface energy of the grafted surfaces of samples increased to 70 mN/m, depending on the type of acrylate used. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2341–2350, 2004
Combined experimental and computer simulation study of the kinetics of solute release from a relaxing swellable polymer matrix. I. Characterization of non‐Fickian solvent uptake
Authors: Papadokostaki K. G. , Petrou J. K.
Published: April 2004

This article is concerned with a combined experimental and computer modeling study aimed at the characterization of the non‐Fickian absorption of liquid water by cellulose acetate (CA) matrices (in the form of thin films) on the basis of a strictly limited number of parameters. The observed kinetics exhibited two distinct non‐Fickian features, resulting from short‐term and long‐term viscous structural relaxations of the swelling glassy polymeric matrix. These relaxation processes were modeled by the extension of a previous model of micromolecular diffusion in a polymer subject to a single relaxation process. The successful simulation of the experimental kinetic curves then enabled the determination and cross‐checking of the relevant model parameter values. This work had the dual purpose of providing (1) input related to solvent absorption for the quantitative computer simulation (in part II of this series) of a model monolithic, solvent‐activated, controlled‐release device, consisting of a swellable glassy polymeric matrix (CA) loaded with an osmotically active solute (NaCl), and (2) an example of a general strategy of extracting meaningful values of micromolecular diffusivity in glassy polymers from non‐Fickian absorption kinetic data. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2458–2467, 2004
Effect of chitin addition on injection‐molded thermoplastic corn starch
Authors: Rosa R.C.R. Souza , Andrade C.T.
Published: April 2004

A new type of biodegradable starch‐based composites was prepared by injection‐molding using glycerol and water as plasticizers. Chitin flakes, obtained from shells of Penaeusschmitti, were used as reinforcing phase. The effect of chitin content on the structural and tensile properties of the composite samples was examined after conditioning at 28°C and 80% relative humidity for 30 days. In general, chitin incorporation into the starch matrix resulted in materials with higher modulus and decreased elongation at break. Wide‐angle X‐ray diffraction and differential scanning calorimetry evidenced a significant decrease in crystallinity in the composite samples in relation to the unfilled starch material. Contact angle measurements revealed that the addition of chitin contributes to the improvement of water resistance of the composite samples when compared to injection molded starch alone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2706–2713, 2004
Synthesis and pyrolysis of Ti‐containing precursors for advanced Si/C/N/Ti‐based ceramics
Authors: Zheng Zhimin , Li Yongming , Luo Yongming , Su Shunxing , Zhang Zhijie , Yang Shiyan , Gao Wei , Xie Zemin
Published: April 2004

A new kind of polytitanosilazane (PTSZ) precursor for Si/C/N/Ti‐based ceramic was synthesized from the condensation reaction of silazane lithium salts and titanium tetrachloride (TiCl4). Titanium in the precursors was bonded to silazane compounds in the Si—N—Ti bond. The obtained PTSZs were characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and elemental analyses. The PTSZs were pyrolyzed at 900 to 1300°C under nitrogen, argon, and ammonia atmosphere, respectively, to give amorphous inorganic products. The results indicated that ceramic yields of PTSZs were much higher than that of their corresponding silazane oligomers and ceramic yields increased with the increase in Ti content in PTSZs. Precursors containing reactive vinyl groups gave higher pyrolytic yields. The pyrolytic yield under ammonia is lower than that under nitrogen and argon. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2733–2739, 2004
Are the cometary outbursts caused by impacts with interplanetary vagabonds probable?
Authors: Gronkowski P.
Published: April 2004

The possibility of impacts and their results in relation to the cometary outbursts between comets and other small bodies in the solar system has been investigated. Taking into consideration certain physical features of cometary nuclei and impacting bodies, the probability of impacts of small bodies moving in the main asteroid belt with hypothetical comets which represent three types: Jupiter family comets, Halley family comets and long period comets has been computed. The probability of impacts between comets and meteoroids at large heliocentric distances has also been estimated. Potential consequences of these events in relation to outbursts of the cometary brightness have been discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A calibration map for Wide Field Imager photometry
Authors: Koch A. , Odenkirchen M. , Grebel E.K. , Caldwell J.A.R.
Published: April 2004

We present a prescription to correct large‐scale intensity variations affecting imaging data taken with the Wide Field Imager (WFI) at the MPG/ESO 2.2 m telescope at the European Southern Observatory at La Silla in Chile. Such smoothly varying, large‐scale gradients are primarily caused by non‐uniform illumination due to stray light, which cannot be removed using standard flatfield procedures. By comparing our observations to the well‐calibrated, homogeneous multicolour photometry from the Sloan Digital Sky Survey we characterise the intensity gradients across the camera by secondorder polynomials. The application of these polynomials to our data removes the gradients and reduces the overall scatter.We also demonstrate that applying our correction to an independent WFI dataset significantly reduces its large‐scale variations, indicating that our prescription provides a generally valid and simple tool for calibrating WFI photometry. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The science case of the PEPSI high‐resolution echelle spectrograph and polarimeter for the LBT
Authors: Strassmeier K. G. , Pallavicini R. , Rice J. B. , Andersen M. I. , Zerbi F. M.
Published: April 2004

We lay out the scientific rationale for and present the instrumental requirements of a high‐resolution adaptiveoptics Echelle spectrograph with two full‐Stokes polarimeters for the Large Binocular Telescope (LBT) in Arizona. Magnetic processes just like those seen on the Sun and in the space environment of the Earth are now well recognized in many astrophysical areas. The application to other stars opened up a new field of research that became widely known as the solarstellar connection. Late‐type stars with convective envelopes are all affected by magnetic processes which give rise to a rich variety of phenomena on their surface and are largely responsible for the heating of their outer atmospheres. Magnetic fields are likely to play a crucial role in the accretion process of T‐Tauri stars as well as in the acceleration and collimation of jet‐like flows in young stellar objects (YSOs). Another area is the physics of active galactic nucleii (AGNs) , where the magnetic activity of the accreting black hole is now believed to be responsible for most of the behavior of these objects, including their X‐ray spectrum, their notoriously dramatic variability, and the powerful relativistic jets they produce. Another is the physics of the central engines of cosmic gamma‐ray bursts, the most powerful explosions in the universe, for which the extreme apparent energy release are explained through the collimation of the released energy by magnetic fields. Virtually all the physics of magnetic fields exploited in astrophysics is somehow linked to our understanding of the Sun's and the star's magnetic fields. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New concept for testing General Relativity: the Laser Astrometric Test Of Relativity (LATOR) mission
Authors: Turyshev S.G. , Shao M. , Nordtvedt K.
Published: April 2004

This paper discusses a Fundamental physics experiment that will test relativistic gravity at the accuracy better than the effects of the second order in the gravitational field strength, ∝ G2. The Laser Astrometric Test Of Relativity (LATOR) mission uses laser interferometry between two micro‐spacecraft whose lines of sight pass close by the Sun to accurately measure deflection of light in the solar gravity. The key element of the experimental design is a redundant geometry optical truss provided by a long‐baseline (100 m) multi‐channel stellar optical interferometer placed on the International Space Station (ISS). The spatial interferometer is used for measuring the angles between the two spacecraft and for orbit determination purposes. In Euclidean geometry, determination of a triangle's three sides determines any angle therein; with gravity changing the optical lengths of sides passing close by the Sun and deflecting the light, the Euclidean relationships are overthrown. The geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy. LATOR will not only improve the value of the parameterized post‐Newtonian (PPN) γ to unprecedented levels of accuracy of 1 part in 108, it will also reach ability to measure effects of the next post‐Newtonian order (c−4) of light deflection resulting from gravity's intrinsic non‐linearity. The solar quadrupole moment parameter, J2, will be measured with high precision, as well as a variety of other relativistic effects including Lense‐Thirring precession. LATOR will lead to very robust advances in the tests of Fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Topical disposition of two strengths of a 125I‐rhEGF jelly in rat skin wounds
Authors: Duconge J. , Prats P.A. , Valenzuela C. , Aguilera A. , Rojas I. , Becquer M.A. , Alvarez D. , Estrada L. , Alfonso‐Ortíz S. , Hardy‐Rando E. , García‐Pulpeiro O. , Fernández‐Sánchez E.
Published: April 2004

Growth factors have proved to be an effective therapeutic strategy. However, some controversies have arisen concerning their efficacy in topical wound treatments. Stabilization of epidermal growth factors at the wound site and long‐lasting receptor occupancy are important factors for wound repair. This study evaluated the cumulative profiles of two jellies containing 10 or 20 μg of 125I‐rhEGF per gram of jelly, in a rat full‐thickness skin lesion model. The prolonged time‐courses at the wound sites for both strengths compared with saline solutions previously evaluated using a similar skin lesion model are reported. It seems that these two topical formulations that provide more sustained amounts of 125I‐rhEGF over the period of sampling, would probably achieve the required wound healing response in terms of cell proliferation, collagen deposition and protein synthesis. Further studies need to be developed in order to elucidate whether such an in vivo disposition pattern is consistent with an earlier and stronger promotion of wound healing events. Copyright © 2004 John Wiley & Sons, Ltd.
Effect of intravenous infusion time on the pharmacokinetics and pharmacodynamics of the same total dose of torasemide in rabbits
Authors: Kim Yu C. , Lee Myung G. , Ko Seong‐Hee , Kim So H.
Published: April 2004

The pharmacokinetics and pharmacodynamics of torasemide were evaluated after intravenous administration of the same total dose of torasemide at a dose of 1mg/kg to rabbits with different infusion times, 1 min (treatment I), 30 min (treatment II) and 2 h (treatment III). The loss of water and electrolytes in urine induced by torasemide was immediately replaced with infusion of an equal volume of lactated Ringer's solution. All the pharmacokinetic parameters of torasemide, such as total area under the plasma concentration–time curve from time zero to time infinity (AUC), total body clearance (CL), apparent volume of distribution at steady state (Vss), terminal half‐life and mean residence time (MRT), were independent of infusion times. However, the 8h urine output (235, 534 and 808 ml) and 8h urinary excretion of sodium (24.2, 80.1 and 89.2 mmol) and chloride (27.1, 89.2 and 94.0 mmol) were significantly greater in treatments II and III than those in treatment I, although the total 8 h urinary excretion of unchanged torasemide (1210, 1210 and 1310 µg) were not significantly different among the three treatments. This could be due to the higher diuretic efficiencies in treatments II and III. Copyright © 2004 John Wiley & Sons, Ltd.
Pharmacodynamics of controlled release verapamil in patients with hypertension: an analysis using spline functions
Authors: Aarons Leon , Baxter Claire , Gupta Suneel
Published: April 2004

Aims—To use a nonparametric approach involving longitudinal splines to model the baseline blood pressure profile and investigate the impact of this modelling on the pharmacodynamic analysis for verapamil in patients with angina or hypertension.

Methods—Dose ranging studies were conducted in patients with hypertension and with angina. Subjects received doses of 120, 180, 360 or 540mg racemic verapamil. Pharmacodynamic data were created by subtracting the (systolic) blood pressure following active drug from the placebo response, either by direct subtraction or after modelling the baseline with a longitudinal spline model fitted to the placebo data by nonlinear mixed effects modelling. An Emax model was then used to describe the relationship between change in blood pressure and (R‐)verapamil plasma concentration.

Results—The maximum decrease in systolic blood pressure was found to be 57.6 (±26.1) mm and the C50 was 420 (±349) µg/l for the data obtained by direct subtraction of the placebo data. Similar results were obtained when a cubic spline model was used to describe each individual's placebo response. However, the use of a population spline model only allowed a linear pharmacodynamic model to be fitted to the resulting data. Sparse data were created by randomly removing 66% of the data from the placebo and active phases. The population spline model gave very similar parameter estimates for the linear model applied to the sparse data to those obtained from the complete data set.

Conclusions—The use of a longitudinal spline model together with nonlinear mixed effects modelling to account for baseline blood pressure response can be very powerful in a sparse data environment. Copyright © 2004 John Wiley & Sons, Ltd.
Developmental toxicity of methanol: Pathogenesis in CD‐1 and C57BL/6J mice exposed in whole embryo culture
Authors: Degitz Sigmund J. , Rogers John M. , Zucker Robert M. , Hunter E. Sidney
Published: April 2004

BACKGROUND

Methanol causes axial skeleton and craniofacial defects in both CD‐1 and C57BL/6J mice during gastrulation, but C57BL/6J embryos are more severely affected. We evaluated methanol‐induced pathogenesis in CD‐1 and C57BL/6J embryos exposed during gastrulation in whole embryo culture.

METHODS

Conceptuses with five to seven somites were exposed to 0, 1, 2, 3, 4, or 6 mg methanol/ml culture medium for 24 hr and embryonic morphology was assessed. Cell death was evaluated by histology and LysoTracker red staining, and cell‐cycle distribution was evaluated by flow cytometry.

RESULTS

In C57BL/6J embryos, craniofacial defects were observed at 3 mg methanol/ml and greater. The response for CD‐1 embryos was different, with increased dysmorphology only at 6 mg/ml. However, protein content in CD‐1 embryos was reduced at 3 mg methanol/ml and above, indicating growth retardation. Yolk sac toxicity occurred only at 6 mg methanol/ml in both strains. Methanol caused only small changes in cell‐cycle distribution, while cell death was induced at 4 and 6 mg methanol/ml in both strains after 8 hr. The extent of cell death after 8 hr was greater in C57BL/6J embryos, and increased over time through 18 hr; in contrast, CD‐1 embryos showed less cell death at 18 than at 8 hr, suggesting recovery.

CONCLUSIONS

Cell death plays a prominent role in methanol‐induced dysmorphogenesis, while cell‐cycle perturbation may not. Differences in the extent of cell death between CD‐1 and C57BL/6J embryos correlated with differences in the severity of dysmorphogenesis. Birth Defects Research (Part A), 2004. Published 2004 Wiley‐Liss, Inc.
Pathogenesis of methanol‐induced craniofacial defects in C57BL/6J mice
Authors: Degitz Sigmund J. , Zucker Robert M. , Kawanishi Clinton Y. , Massenburg Gwen S. , Rogers John M.
Published: April 2004

BACKGROUND

Methanol administered to C57BL/6J mice during gastrulation causes severe craniofacial dysmorphology. We describe dysmorphogenesis, cell death, cell cycle assessment, and effects on development of cranial ganglia and nerves observed following administration of methanol to pregnant C57BL/6J mice on gestation day (GD) 7.

METHODS

Mice were injected (i.p.) on GD 7 with 0, 2.3, 3.4, or 4.9 gm/kg methanol, split into two doses. In embryos of mice treated with 0 or 4.9 gm/kg methanol, we used histology and LysoTracker red staining on GD 8 0 hr through GD 8 18 hr to examine cell death and dysmorphogenesis, and we also evaluated cell‐cycle distribution and proliferation using flow cytometry (FCM) and BrdU immunohistochemistry. On GD 10, we evaluated the effect of GD 7 exposure to 0, 2.3, 3.4, or 4.9 gm/kg methanol on cranial ganglia and nerve development using neurofilament immunohistochemistry.

RESULTS

Methanol treatment on GD 7 resulted in reduced mesenchyme surrounding the fore‐ and midbrain, and in the first branchial arches, by GD 8 12 hr. There were disruptions in the forebrain neuroepithelium and optic pit. Neural crest cell emigration from the mid‐ and hindbrain region was reduced in methanol‐exposed embryos. Methanol had no apparent effect on BrdU incorporation or cell‐cycle distribution on GD 8. Cell death was observed in the hindbrain region along the path of neural crest migration and in the trigeminal ganglion on GD 8 18 hr. Development of the cranial ganglia and nerves was adversely affected by methanol. Development of ganglia V, VIII, and IX was decreased at all dosage levels; ganglion VII was reduced at 3.4 and 4.9 gm/kg, and ganglion X was reduced at 4.9 gm/kg.

CONCLUSIONS

These results suggest that gastrulation‐stage methanol exposure affects neural crest cells and the anterior mesoderm and neuroepithelium. Cell death was evident in areas of migrating neural crest cells, but only at time points after methanol was cleared from the embryo, suggesting an indirect effect on these cells. Birth Defects Research (Part A), 2004. Published 2004 Wiley‐Liss, Inc.
Hydrogen‐deuterium exchange in membrane proteins monitored by IR spectroscopy: A new tool to resolve protein structure and dynamics
Authors: Vigano C. , Smeyers M. , Raussens V. , Scheirlinckx F. , Ruysschaert J.M. , Goormaghtigh E.
Published: April 2004

As more and more high‐resolution structures of proteins become available, the new challenge is the understanding of these small conformational changes that are responsible for protein activity. Specialized difference Fourier transform infrared (FTIR) techniques allow the recording of side‐chain modifications or minute secondary structure changes. Yet, large domain movements remain usually unnoticed. FTIR spectroscopy provides a unique opportunity to record 1H/2H exchange kinetics at the level of the amide proton. This approach is extremely sensitive to tertiary structure changes and yields quantitative data on domain/domain interactions. An experimental setup designed for attenuated total reflection and a specific approach for the analysis of the results is described. The study of one membrane protein, the gastric H+,K+‐ATPase, demonstrates the usefulness of 1H/2H exchange kinetics for the understanding of the molecular movement related to the catalytic activity. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Lipid hydration: Headgroup CH moieties are involved in water binding
Authors: Pohle W. , Gauger D. R. , Bohl M. , Mrazkova E. , Hobza P.
Published: April 2004

To explore the interaction potential of phospholipids, we have studied the hydration of diacyl phosphatidylcholine (PC) and methylphosphocholine (MePC), a pertinent model compound, by ir spectroscopy. Related ab initio Hartree—Fock calculations were performed for MePC. Water is considered ideal as a relevant probe molecule. Spectroscopic data for MePC reveal a strong influence of bound hydration water not only on the phosphate groups but also onto the putatively apolar CHn groups. The same could be demonstrated for deuterated dimyristoyl PC taken as a “complete” lipid molecule: both headgroup methyl and methylene moieties are gradually, but remarkably affected by hydration, as evidenced by strong wavenumber upshifts of CH stretching vibration bands. These findings may originate in directed interactions of the CHn groups with bound water molecules, but hydration‐driven conformational changes of PC headgroups could also occur. The results of the ab initio calculations rationalize the first explanation by predicting a substantial contribution of specific CH · · · OH2 interactions, mainly characterized by a dramatic loss of electron density of the σ* antibonding molecular orbitals of CH bonds. Hence, the propensity of the lipid headgroup methyl and methylene groups to act as donor sites in hydrogen bonding must no longer be ignored when considering the interaction potential of PCs. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Dynamics of human serum albumin studied by acoustic relaxation spectroscopy
Authors: Hushcha T. , Kaatze U. , Peytcheva A.
Published: April 2004

Sonic absorption spectra of solutions of human serum albumin (SA) in water and in aqueous phosphate buffer systems have been measured between 0.2 and 2000 MHz at different temperatures (15–35°C), pH values (1.8–12.3), and protein concentrations (1–40 g/L). Several spectra, indicating relaxation processes in the whole frequency range, have been found. The spectra at neutral pH could be fitted well with an analytical function consisting of the asymptotic high frequency absorption and two relaxation contributions, a Debye‐type relaxation term with discrete relaxation time and a term with asymmetric continuous distribution of relaxation times. Both relaxation contributions were observed in water and in buffer solutions and increased with protein concentration. The contribution represented by a Debye‐type term is practically independent of temperature and was attributed to cooperative conformational changes of the polypeptide chain featuring a relaxation time of about 400 ns. The distribution of the relaxation times corresponding to the second relaxation contribution was characterized by a short time cutoff, between about 0.02 and 0.4 ns depending on temperature, and a long time tail extending to microseconds. Such relaxation behavior was interpreted in terms of solute–solvent interactions reflecting various hydration layers of HSA molecules. At acid and alkaline pH, an additional Debye‐type contribution with relaxation time in the range of 30–100 ns exists. It seems to be due to proton transfer reactions of protein side‐chain groups. The kinetic and thermodynamic parameters of these processes have been estimated from these first measurements to indicate the potential of acoustic spectra for the investigation of the elementary kinetics of albumin processes. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
The charge transfer band in horseradish peroxidase correlates with heme in‐plane distortions induced by calcium removal
Authors: Laberge Monique , Szigeti Krisztian , Fidy Judit
Published: April 2004

Horseradish peroxidase C (HRPC) is a class III peroxidase whose structure is stabilized by the presence of two endogenous calcium atoms. Calcium removal has been shown to decrease the enzymatic activity of the enzyme. The spin state of the iron, a mixture of high spin (HS) and mixed quantum spin state (QS) consisting of intermediate spin (IS) 3/2 + (HS) 5/2, is also significantly affected by calcium removal, going from a predominant QS component to a predominant HS component upon removal of one calcium. Removal of both calcium ions, however, results in the appearance of a significant LS contribution, easily monitored in the charge transfer (CT) band region by low‐T absorption. Normal structural decomposition (NSD) calculations of the in‐plane (ip) modes of the heme extracted from HRPC native and Ca2+‐depleted models show that removal of the proximal calcium is associated with perturbed Eu and increased A1g ip distortions of the heme. The effect of complete or distal calcium removal on the heme also results in increased A1g ip distortions, but in significantly decreased Eu distortions. The overall effect is to decrease the nonplanarity of the heme: the total ip distortion of the native HRPC heme is 0.200 and 0.134 Å for the Ca2+‐depleted species. Our NSD results corroborate the role proposed for the protein matrix, namely to fine‐tune the active site by inducing subtle changes in heme planarity and spin state of the iron. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
pH dependence of heme electrochemistry in cytochromes investigated by multiconformation continuum electrostatic calculations
Authors: Hauser K. , Mao J. , Gunner M. R.
Published: April 2004

Cytochromes belong to a diverse family of heme‐containing redox proteins that function as intermediaries in electron transfer chains. They can be soluble, extrinsic, or intrinsic membrane proteins, and are found in different structural motifs (globin, 4‐helix bundles, αβ roll, β sandwich). Measured electrochemical midpoint potentials vary over a wide range even though the basic redox reaction at the heme is the same for all cytochromes. The perturbation of the heme electrochemistry is induced by the protein structure. Also, the pH dependence varies since it depends on the strength of interaction between the heme and surrounding residues as well as the ionization states of these groups. Multiconformation continuum electrostatics (MCCE) has been used to investigate the pH dependence of heme electrochemistry in cytochromes with different folds. Often propionates are the primary contributors for pH dependence especially if they are partially protonated in the reduced heme as it is shown for globin cytochrome c551 P. aeruginosa and cytochrome b5 R. norvegicus (αβ roll). However, if the propionates are already fully ionized at a certain pH they do not contribute to the pH dependence even if they have big interaction with the heme. At pH 7 there is no propionate contribution for cytochrome f C. reinhardtii (β sandwich) and the 4‐helix bundle c′ R. palustris. Other residues can also change their ionization significantly during heme oxidation and therefore be involved in proton release and pH dependence. These residues have been identified for different cytochrome types. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Changes of near‐UV CD spectrum of human hemoglobin upon oxygen binding: A study of mutants at α42, α140, β145 tyrosine or β37 tryptophan
Authors: Jin Yayoi , Sakurai Hiroshi , Nagai Yukifumi , Nagai Masako
Published: April 2004

The deoxy‐form of human adult hemoglobin (Hb A) exhibits a distinct negative CD band at 287 nm that disappears in the oxy‐form. It has been suggested that the negative CD band is due to the environmental alteration of Tyr‐α42 or Trp‐β37 at the α1β2 contact upon deoxygenation. To evaluate the contributions of the aromatic residues at the α1β2 contact and the penultimate tyrosine residues of the α and β subunits (α140 and β145) to the negative CD band, three recombinant (r) Hbs (rHb Ser‐α42, rHb His‐β37, and rHb Thr‐β145) were produced in Escherichia coli, and we compared the near‐uv CD spectra of these three rHbs and Hb Rouen (Tyr‐α140→His) with the spectra of Hb A under the condition in which all mutant Hbs were able to undergo the T→R transition (Hill's n > 2.0). The contributions of Tyr‐α42, Trp‐β37, Tyr‐α140, and Tyr‐β145 to the negative CD band were estimated from changes in the ellipticity of the negative CD band at 287 nm to be 4, 18, 32, and 27%, respectively. These results indicate that environmental alteration of the penultimate tyrosine residues caused by the formation of salt bridges upon the R→T transition is primarily responsible for the negative CD band. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Fourier transform infrared spectroscopic study on the binding of Mg2+ to a mutant Akazara scallop troponin C (E142Q)
Authors: Nara Masayuki , Yumoto Fumiaki , Nagata Koji , Tanokura Masaru , Kagi Hiroyuki , Ojima Takao , Nishita Kiyoyoshi
Published: April 2004

Troponin C (TnC) is the Ca2+‐binding regulatory protein of the troponin complex in muscle tissue. Vertebrate fast skeletal muscle TnCs bind four Ca2+, while Akazara scallop (Chlamys nipponensis akazara) striated adductor muscle TnC binds only one Ca2+ at site IV, because all the other EF‐hand motifs are short of critical residues for the coordination of Ca2+. Fourier transform infrared (FTIR) spectroscopy was applied to study coordination structure of Mg2+ bound in a mutant Akazara scallop TnC (E142Q) in D2O solution. The result showed that the side‐chain COO− groups of Asp 131 and Asp 133 in the Ca2+‐binding site of E142Q bind to Mg2+ in the pseudo‐bridging mode. Mg2+ titration experiments for E142Q and the wild‐type of Akazara scallop TnC were performed by monitoring the band at about 1600 cm−1, which is due to the pseudo‐bridging Asp COO− groups. As a result, the binding constants of them for Mg2+ were the same value (about 6 mM). Therefore, it was concluded that the side‐chain COO− group of Glu 142 of the wild type has no relation to the Mg2+ ligation. The effect of Mg2+ binding in E142Q was also investigated by CD and fluorescence spectroscopy. The on–off mechanism of the activation of Akazara scallop TnC is discussed on the basis of the coordination structures of Mg2+ as well as Ca2+. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Anomalous acceleration of the photocycle in photosynthetic reaction centers inhibited on the acceptor side
Authors: Gerencsér L. , Maróti P.
Published: April 2004

The rate of the photocycle (quinone reduction cycle) was measured under continuous light excitation in an isolated reaction center protein of the photosynthetic bacterium Rhodobacter sphaeroides. The rate is determined by the slowest step of the photocycle, which could be the photochemistry (charge separation), the quinone/quinol and cytochrome c2+/c3+ exchanges, or proton delivery to the secondary quinone. The photocycle was driven by high light intensity of a laser diode (5 W/cm2 at 808 nm) to avoid light limitation of the observed rate. The fast turnover of the reaction center (up to 103 s–1) was slowed down by inhibition of the proton delivery to the secondary quinone by transition metal ions (Cd2+ and Ni2+), by mutation of a key protonatable group (L213Asp → Asn), or by use of low‐affinity ubiquinone (UQ0) to the secondary quinone binding site. Although in all of these cases the rate of turnover was 2–3 orders of magnitude less than that of the primary photochemistry, marked light intensity dependence was observed. The rate of the photocycle increased from 7 s–1 (Ni2+, low light intensity) to 27 s–1 (high light intensity) at pH 8.4. The anomalous reacceleration is due to alternative events on the acceptor side induced by continuous excitation. We argue that the continuous excitation of the protein trapped in the reduced acceptor (QA−QB−) state produces short‐lived reduced bacteriopheophytin (I−) that delivers activation energy to anomalous changes on the acceptor side as second interquinone electron transfer before proton uptake or increase of the quinone dissociation constant. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Identification of stable helical bundles from a combinatorial library of amphipathic peptides
Authors: Boon Chandra L. , Frost David , Chakrabartty Avijit
Published: April 2004

A set of combinatorial amphipathic helical peptides referred to as the KIA series has been screened to identify native‐like helical bundles. The series contains the following consensus sequence: AKAxAAxxKAxAAxxKAGGY, where “x” positions are occupied by either Ala or Ile. The peptide sequences in the series comprise all possible combinations of four Ile residues occupying the six x positions. In each case, Ala occupied the two x positions not occupied by Ile. There are a total of 15 peptides in the KIA series; all of the peptides differ in the number of ridges and grooves formed by the Ile side chains, and two of the KIA peptides possess a canonical knobs‐into‐holes heptad repeat. The structure and stability of these 15 peptides and their pairwise mixtures were evaluated. One peptide in the series formed a stable four‐helix bundle that folded with cooperativity similar to native proteins. Ten peptides assembled into molten globular helical assemblies, two peptides were unstructured, and two peptides assembled into helical filaments that were several micrometers long. One of the helical filament forming peptides could be diverted from forming filaments by the addition of another KIA peptide, and resulted in the formation of a heteromeric six‐helix bundle. This study demonstrates that combinatorial peptides composed of only three types of amino acids can form a diverse array of structures, some of which are native‐like. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2004
Metabolic pathway analysis of yeast strengthens the bridge between transcriptomics and metabolic networks
Authors: Çakir Tunahan , Kirdar Betül , Ülgen Kutlu Ö.
Published: April 2004

Central carbon metabolism of the yeast Saccharomyces cerevisiae was analyzed using metabolic pathway analysis tools. Elementary flux modes for three substrates (glucose, galactose, and ethanol) were determined using the catabolic reactions occurring in yeast. Resultant elementary modes were used for gene deletion phenotype analysis and for the analysis of robustness of the central metabolism and network functionality. Control‐effective fluxes, determined by calculating the efficiency of each mode, were used for the prediction of transcript ratios of metabolic genes in different growth media (glucose–ethanol and galactose–ethanol). A high correlation was obtained between the theoretical and experimental expression levels of 38 genes when ethanol and glucose media were considered. Such analysis was shown to be a bridge between transcriptomics and fluxomics. Control‐effective flux distribution was found to be promising in in silico predictions by incorporating functionality and regulation into the metabolic network structure. © 2004 Wiley Periodicals, Inc.
A new, mild cross‐linking methodology to prepare cross‐linked enzyme aggregates
Authors: Mateo Cesar , Palomo José M. , van Langen Luuk M. , van Rantwijk Fred , Sheldon Roger A.
Published: April 2004

Cross‐linked enzyme aggregates (CLEAs) were prepared from several enzymes (penicillin G acylase, hydroxynitrile lyase, alcohol dehydrogenase, and two different nitrilases) by precipitation and subsequent cross‐linking using dextran polyaldehyde. In most cases, higher immobilization yields were obtained using the latter cross‐linker as compared with the commonly used glutaraldehyde. Active site titration of penicillin acylase CLEAs showed that the higher activity originated from a significantly lower loss in active sites using dextran polyaldehyde as a cross‐linking agent. It is proposed that macromolecular cross‐linkers are too large to penetrate the protein active site and react with catalytically essential amino acid residues. © 2004 Wiley Periodicals, Inc.
Comparison of two‐stage thermophilic (68°C/55°C) anaerobic digestion with one‐stage thermophilic (55°C) digestion of cattle manure
Authors: Nielsen H. B. , Mladenovska Z. , Westermann P. , Ahring B. K.
Published: April 2004

A two‐stage 68°C/55°C anaerobic degradation process for treatment of cattle manure was studied. In batch experiments, an increase of the specific methane yield, ranging from 24% to 56%, was obtained when cattle manure and its fractions (fibers and liquid) were pretreated at 68°C for periods of 36, 108, and 168 h, and subsequently digested at 55°C. In a lab‐scale experiment, the performance of a two‐stage reactor system, consisting of a digester operating at 68°C with a hydraulic retention time (HRT) of 3 days, connected to a 55°C reactor with 12‐day HRT, was compared with a conventional single‐stage reactor running at 55°C with 15‐days HRT. When an organic loading of 3 g volatile solids (VS) per liter per day was applied, the two‐stage setup had a 6% to 8% higher specific methane yield and a 9% more effective VS‐removal than the conventional single‐stage reactor. The 68°C reactor generated 7% to 9% of the total amount of methane of the two‐stage system and maintained a volatile fatty acids (VFA) concentration of 4.0 to 4.4 g acetate per liter. Population size and activity of aceticlastic methanogens, syntrophic bacteria, and hydrolytic/fermentative bacteria were significantly lower in the 68°C reactor than in the 55°C reactors. The density levels of methanogens utilizing H2/CO2 or formate were, however, in the same range for all reactors, although the degradation of these substrates was significantly lower in the 68°C reactor than in the 55°C reactors. Temporal temperature gradient electrophoresis profiles (TTGE) of the 68°C reactor demonstrated a stable bacterial community along with a less divergent community of archaeal species. © 2004 Wiley Periodicals, Inc.