bluuebunny/crossref_metadata_2025 huggingface dataset:
KATP channel openers: Structure‐activity relationships and therapeutic potential
Authors: Mannhold Raimund
Published: December 2003

ATP‐sensitive potassium channels (KATP channels) are heteromeric complexes of pore‐forming inwardly rectifying potassium channel subunits and regulatory sulfonylurea receptor subunits. KATP channels were identified in a variety of tissues including muscle cells, pancreatic β‐cells, and various neurons. They are regulated by the intracellular ATP/ADP ratio; ATP induces channel inhibition and MgADP induces channel opening. Functionally, KATP channels provide a means of linking the electrical activity of a cell to its metabolic state. Shortening of the cardiac action potential, smooth muscle relaxation, inhibition of both insulin secretion, and neurotransmitter release are mediated via KATP channels. Given their many physiological functions, KATP channels represent promising drug targets. Sulfonylureas like glibenclamide block KATP channels; they are used in the therapy of type 2 diabetes. Openers of KATP channels (KCOs), for example, relax smooth muscle and induce hypotension. KCOs are chemically heterogeneous and include as different classes as the benzopyrans, cyanoguanidines, thioformamides, thiadiazines, and pyridyl nitrates. Examples for new chemical entities more recently developed as KCOs include cyclobutenediones, dihydropyridine related structures, and tertiary carbinols. © 2003 Wiley Periodicals, Inc. Med Res Rev, 24, No. 2, 213–266, 2004
Multiple acquisitions with global inversion cycling (MAGIC): A multislice technique for vascular‐space‐occupancy dependent fMRI
Authors: Lu Hanzhang , van Zijl Peter C.M. , Hendrikse Jeroen , Golay Xavier
Published: December 2003

Recently, a new fMRI technique, termed vascular‐space‐occupancy (VASO), was introduced that uses T1‐based blood nulling to detect cerebral blood volume (CBV) changes during brain activity. However, similar to other T1‐preparation methods, this technique is hampered by the fact that there is only one zero‐crossing on the relaxation curve, presently limiting its application to single‐slice studies. A multislice VASO‐fMRI method is presented that employs a series of nonselective 180° pulses to periodically invert the magnetization and maintain it around zero, while acquiring slices in between. The effects of magnetization transfer and signal contamination by stimulated echoes are discussed. Solutions to reduce the effect of T1‐signal decay as a function of slice number are provided. Phantom data show excellent agreement between experiments and numerical simulations. Multislice VASO‐fMRI images of visual stimulation show effective blood nulling in all slices and appropriate functional activations in all volunteers (n = 4). Magn Reson Med 51:9–15, 2004. © 2003 Wiley‐Liss, Inc.
Extended coverage first‐pass perfusion imaging using slice‐interleaved TSENSE
Authors: Kellman P. , Derbyshire J.A. , Agyeman K.O. , McVeigh E.R. , Arai A.E.
Published: December 2003

Parallel imaging applied to first‐pass, contrast‐enhanced cardiac MR can yield greater spatial coverage for a fixed temporal resolution. The method combines rate R = 2 acceleration using TSENSE with shot‐to‐shot interleaving of two slices. The √R SNR loss is largely compensated for by a longer effective repetition time (TR) and increased flip angle associated with slice interleaving. In this manner, increased spatial coverage is achieved while comparable or better image quality is maintained. Single‐heartbeat temporal resolution was accomplished with spatial coverage of eight slices at heart rates up to 71 bpm, six slices up to 95 bpm, and four slices up to 143 bpm. Experiments in normal subjects (N = 6) were performed to assess signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) values. Magn Reson Med 51:200–204, 2004. Published 2003 Wiley‐Liss, Inc.
Self‐gated cardiac cine MRI
Authors: Larson Andrew C. , White Richard D. , Laub Gerhard , McVeigh Elliot R. , Li Debiao , Simonetti Orlando P.
Published: December 2003

The need for ECG gating presents many difficulties in cardiac magnetic resonance imaging (CMRI). Real‐time imaging techniques eliminate the need for ECG gating in cine CMRI, but they cannot offer the spatial and temporal resolution provided by segmented acquisition techniques. Previous MR signal‐based techniques have demonstrated an ability to provide cardiac gating information; however, these techniques result in decreased imaging efficiency. The purpose of this work was to develop a new “self‐gated” (SG) acquisition technique that eliminates these efficiency deficits by extracting the motion synchronization signal directly from the same MR signals used for image reconstruction. Three separate strategies are proposed for deriving the SG signal from data acquired using radial k‐space sampling: echo peak magnitude, kymogram, and 2D correlation. The SG techniques were performed on seven normal volunteers. A comparison of the results showed that they provided cine image series with no significant differences in image quality compared to that obtained with conventional ECG gating techniques. SG techniques represent an important practical advance in clinical MRI because they enable the acquisition of high temporal and spatial resolution cardiac cine images without the need for ECG gating and with no loss in imaging efficiency. Magn Reson Med 51:93–102, 2004. © 2003 Wiley‐Liss, Inc.
Frame‐by‐frame PRESS 1H‐MRS of the brain at 3 T: The effects of physiological motion
Authors: Katz‐Brull Rachel , Lenkinski Robert E.
Published: December 2003

1H‐MRS at high field has been increasingly utilized to study brain metabolism in healthy and pathological states. The aim of this work was to determine the effects of physiological motion on the results of this exam in the presence of the increased susceptibility differences at high field. Single voxel spectra of various regions in the human brain were acquired using frame‐by‐frame PRESS 1H‐MRS at a 0.5 Hz sampling rate. The frame‐by‐frame variations of the FID phase and the frequency and fractional amplitude variations of the residual water‐signal were analyzed. In the human brain the standard deviations of these variations were 3.9 ± 0.5°, 0.83 ± 0.32 Hz, and 0.028 ± 0.013 of the mean amplitude (n = 15). In a motionless phantom, smaller phase and frequency variations were detected in water‐suppressed acquisitions. However, the end effects of physiological motion on PRESS 1H‐MRS of the brain at 3 T were negligible. Magn Reson Med 51:184–187, 2004. © 2003 Wiley‐Liss, Inc.
Visualization and analysis of white matter structural asymmetry in diffusion tensor MRI data
Authors: Zhang Song , Bastin Mark E. , Laidlaw David H. , Sinha Saurabh , Armitage Paul A. , Deisboeck Thomas S.
Published: December 2003

This work presents a method that permits the characterization, quantification, and 3D visualization of white matter structural information contained within diffusion tensor MR imaging (DT‐MRI) data. In this method, regions within the brain are defined as possessing linear, planar, or spherical diffusion. Visualization of this diffusion metric data is realized by generating streamtube and streamsurface models to represent regions of linear and planar diffusion. Quantification of differences in diffusion anisotropy between different regions of interest (ROIs) is then achieved by analyzing 2D barycentric histograms created from the complete distribution of diffusion metric values measured in each region. In four healthy volunteers, there was only a small degree of asymmetry (ε) in the number of linear, planar, or spherical diffusion voxels between the right and left hemispheres (ε ≃ ± 2%). However, in a patient with a metastatic brain lesion there was marked asymmetry in both linear (ε ≃ −10%) and planar (ε ≃ 5%) diffusion between comparable ipsilateral and contralateral regions, with a significant reduction in the number of linear diffusion voxels and an increase in the number of planar diffusion voxels in the tumor‐bearing hemisphere. These results demonstrate the potential of this approach to characterize brain structure in both healthy and diseased subjects. Magn Reson Med 51:140–147, 2004. © 2003 Wiley‐Liss, Inc.
Increase in left ventricular torsion‐to‐shortening ratio in children with valvular aortic stenosis
Authors: Delhaas Tammo , Kotte Jiska , van der Toorn Annet , Snoep Gabriël , Prinzen Frits W. , Arts Theo
Published: December 2003

Perfusion of left ventricular (LV) subendocardium in valvular aortic stenosis (AS) patients is impaired. It was expected that this may lead to a reduction of subendocardial fiber contraction and, consequently, to an increase of LV torsion per amount of ejection. Using MR tagging (MRT), it was investigated whether the torsion‐to‐shortening ratio (TSR) is elevated in valvular AS patients. Six asymptomatic children with valvular AS were investigated using echo Doppler, ECG, exercise test, and MRT. LV torsion and natural strain of the inner diameter were determined from measured tag displacements in two short‐axis slices of the LV. In all AS patients TSR was ∼40% increased (0.62 ± 0.04 rad; mean ± SD) as compared to pediatric (0.44 ± 0.08 rad; n = 5) and adult controls (0.46 ± 0.08 rad; n = 9), indicating subendocardial contractile dysfunction. With other techniques hitherto used this type of dysfunction could not be detected. Magn Reson Med 51:135–139, 2004. © 2003 Wiley‐Liss, Inc.
Simultaneous acquisition of gradient‐echo and asymmetric spin‐echo for single‐shot z‐shim: Z‐SAGA
Authors: Heberlein Keith Arron , Hu Xiaoping
Published: December 2003

This article describes the Z‐SAGA pulse sequence, a technique for recovering susceptibility losses in EPI images for neuroimaging applications. The pulse sequence is based on an asymmetric spin echo EPI sequence and acquires a gradient echo image and an asymmetric spin echo image in a single shot. For one of the images, a z‐shim gradient pulse is applied to compensate for susceptibility‐related field distortions. The two images are combined to form an image with reduced signal loss. This sequence is simple to implement and experimentally demonstrated to be effective for BOLD imaging. Magn Reson Med 51:212–216, 2004. © 2003 Wiley‐Liss, Inc.
Removal of phase artifacts from fMRI data using a Stockwell transform filter improves brain activity detection
Authors: Goodyear Bradley G. , Zhu Hongmei , Brown Robert A. , Mitchell J. Ross
Published: December 2003

A novel and automated technique is described for removing fMRI image artifacts resulting from motion outside of the imaging field of view. The technique is based on the Stockwell transform (ST), a mathematical operation that provides the frequency content at each time point within a time‐varying signal. Using this technique, 1D Fourier transforms (FTs) are performed on raw image data to obtain phase profiles. The time series of phase magnitude for each and every point in the phase profile is then subjected to the ST to obtain a time‐frequency spectrum. The temporal location of an artifact is identified based on the magnitude of a frequency component relative to the median magnitude of that frequency's occurrence over all time points. After each artifact frequency is removed by replacing its magnitude with the median magnitude, an inverse ST is applied to regain the MR signal. Brain activity detection within fMRI datasets is improved by significantly reducing image artifacts that overlap anatomical regions of interest. The major advantage of ST‐filtering is that artifact frequencies may be removed within a narrow time‐window, while preserving the frequency information at all other time points. Magn Reson Med 51:16–21, 2004. © 2003 Wiley‐Liss, Inc.
Scalable multichannel MRI data acquisition system
Authors: Bodurka Jerzy , Ledden Patrick J. , van Gelderen Peter , Chu Renxin , de Zwart Jacco A. , Morris Doug , Duyn Jeff H.
Published: December 2003

A scalable multichannel digital MRI receiver system was designed to achieve high bandwidth echo‐planar imaging (EPI) acquisitions for applications such as BOLD‐fMRI. The modular system design allows for easy extension to an arbitrary number of channels. A 16‐channel receiver was developed and integrated with a General Electric (GE) Signa 3T VH/3 clinical scanner. Receiver performance was evaluated on phantoms and human volunteers using a custom‐built 16‐element receive‐only brain surface coil array. At an output bandwidth of 1 MHz, a 100% acquisition duty cycle was achieved. Overall system noise figure and dynamic range were better than 0.85 dB and 84 dB, respectively. During repetitive EPI scanning on phantoms, the relative temporal standard deviation of the image intensity time‐course was below 0.2%. As compared to the product birdcage head coil, 16‐channel reception with the custom array yielded a nearly 6‐fold SNR gain in the cerebral cortex and a 1.8‐fold SNR gain in the center of the brain. The excellent system stability combined with the increased sensitivity and SENSE capabilities of 16‐channel coils are expected to significantly benefit and enhance fMRI applications. Magn Reson Med 51:165–171, 2004. Published 2003 Wiley‐Liss, Inc.
Stimuli‐responsive polymers. VII. Photomodulated chiroptical switches: Periodic copolyaramides containing azobenzene, phenylene, and chiral binaphthylene main‐chain linkages
Authors: Jaycox Gary D.
Published: December 2003

Conformationally restricted copolyaramides containing a combination of 4,4′‐azobenzene, 1,4‐phenylene, and chiral 2,2′‐binaphthylene main‐chain segments exhibit photoresponsive chiroptical behavior stemming from multiple trans‐cis‐isomerization reactions triggered within their polymer backbones. In contrast to their more randomly constructed counterparts, copolymer variants endowed with periodic backbone structures undergo reversible, wavelength‐dependent inversions in their optical rotations in response to multiple ultraviolet‐light/visible‐light illumination cycles. Similar behavior is also observed for a smaller oligomer fitted with a periodic arrangement of its monomer units. In their present forms, the periodic constructs constitute a new class of solution‐based, photomodulated chiroptical switches that may be suitable for applications in a number of emerging technological areas. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 566–577, 2004
Influence of a cationic polyelectrolyte on the inverse micellar region of the ternary system sulfobetaine/water/alcohol
Authors: Koetz J. , Bahnemann J. , Kosmella S.
Published: December 2003

The influence of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) on structure formation in the inverse micellar region (L2 phase) of the ternary system 3 (N,N‐dimethyldodecylammonio)propanesulfonate/alcohol/water has been investigated. Up to a polymer concentration in the aqueous phase of 10 wt %, an isotropic phase still exists. As the chain length of the alcohol component increases, the isotropic phase region is reduced and shifted in direction to the water corner. The isotropic polyelectrolyte‐modified L2 phase of the heptanol‐based microemulsion has been studied in much more detail by means of conductometric, rheological, and differential scanning calorimetry measurements. The polyelectrolyte‐modified microemulsion phase shows a characteristic low shear viscosity and Newtonian flow behavior. The characteristic features of the nonpercolated microemulsion droplets are the low conductivity and the disappearance of bulk water. One can conclude from the experimental data that the individual nonpercolated polyelectrolyte‐stuffed microemulsion droplets are approximately uniform in size. In addition, the area of the polyelectrolyte‐modified inverse microemulsion phase with heptanol and octanol depends on the temperature. This means that the area of the L2 region can be increased by the temperature being increased from room temperature to 40 °C. This behavior can be explained by a change in the bending elasticity of the surface film induced by Coulombic interactions between the functional groups of the polyelectrolyte and the surfactant head groups. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 742–751, 2004
Uniform polymer in synthetic polymer chemistry
Authors: Hatada Koichi , Kitayama Tatsuki , Ute Koichi , Nishiura Takafumi
Published: December 2003

The preparation of uniform polymers and their use in fundamental polymer chemistry are reviewed. A typical method of preparation is a combination of living polymerization and supercritical fluid chromatography separation. Synthetic uniform polymers allow us to solve ambiguous problems in polymer chemistry due to molecular weight distribution and are of significant importance for studies on structure–property relationships. A close inspection of an isotactic uniform chloral oligomer with a symmetrical chemical structure reveals that oligomers are the first examples of stable atropisomers of aldehyde oligomers and that their chiroptical properties are due only to their helical geometries. A molecular‐level understanding of the mechanism and stoichiometry of the association process of polymer molecules is possible only with uniform polymers, and stereocomplex formation between isotactic and syndiotactic poly(methyl methacrylate)s in acetone has vigorously been studied by size exclusion chromatography (SEC) and NMR. End‐functionalized uniform polymers have enabled us to prepare uniform polymer architectures, such as block, graft, comb, and star polymers. A uniform stereoblock poly(methyl methacrylate) with an isotactic (methyl methacrylate)46‐syndiotactic (methyl methacrylate)46 structure shows a single SEC peak in chloroform but three peaks in acetone, which are ascribable to intermolecularly and intramolecularly associated complexes and nonassociated molecules. A three‐arm star polymer with one isotactic chain and two syndiotactic chains shows a peculiar SEC behavior in acetone due to a braid type of intramolecular stereocomplex formation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 416–431, 2004
Modified poly(ϵ‐caprolactone)s and their use for drug‐encapsulating nanoparticles
Authors: Iojoiu Cristina , Hamaide Thierry , Harabagiu Valeria , Simionescu Bogdan C.
Published: December 2003

Poly(ϵ‐caprolactone) (PCL)‐polydimethylsiloxane diblock and triblock copolymers and poly(ϵ‐caprolactone‐co‐4‐ethylcaprolactone) random copolymers were prepared through the homogeneously catalyzed coordination anionic polymerization of ϵ‐caprolactone (CL) and the copolymerization of CL with 4‐ethyl‐ϵ‐caprolactone (EtCL) in the presence of hydroxy‐terminated polysiloxanes or allyl alcohol as chain‐transfer agents, respectively. Polysiloxane precursors with hydroxypropyl or hydroxyethyl propyl ether end groups were obtained by the hydrosilation of the appropriate unsaturated alcohol with monofunctional or difunctional hydro‐terminated polysiloxanes of different molecular weights. As proven by differential scanning calorimetry analysis, the presence of siloxane blocks and EtCL units determined the diminished copolymer crystallinity, which was shown by the reduced melting temperatures and enthalpy of fusion with respect to those of pure PCL. Both types of copolymers were found to form, in the presence of a poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) emulsifier, monodisperse and stable nanoparticles able to encapsulate different types of bioactive compounds (Vitamin E and indomethacin). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 689–700, 2004
The discovery of isotactic polypropylene and its impact on pure and applied science
Authors: Corradini Paolo
Published: December 2003

This article recalls some aspects of the fascinating history of the discovery by Giulio Natta and his research group of the stereoselective polymerization of propylene and the understanding of the relationships between structure and properties of semicrystalline polymers. The impact of the discovery of isotactic polypropylene and stereoregular polymers on pure and applied science is briefly outlined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 391–395, 2004
Network formation of a phenyl vinyl ketone copolymer with 4‐vinylbenzil and its photodecrosslinking in films
Authors: Mosnáček Jaroslav , Lukáč Ivan , Chromik Štefan , Kostič Ivan , Hrdlovič Pavol
Published: December 2003

The irradiation (λ > 400 nm) in air of a copolymer of phenyl vinyl ketone with 4‐vinylbenzil (VBZ) containing 1.5 wt % VBZ structural units in film, followed by the thermal decomposition of the resulting pendant benzoyl peroxide groups, leads to crosslinking. The subsequent irradiation of the crosslinked polymer at 366 nm results in the cleavage of the poly(phenyl vinyl ketone) chain between the junction points of the polymer network through a Norrish type II reaction. Therefore, poly(phenyl vinyl ketone‐co‐4‐vinylbenzil) represents a novel type of photoresist based on polymer network decrosslinking. The process involves three steps: photogeneration of peroxide, crosslinking by its thermal decomposition, and subsequent photodecrosslinking of the polymer network. This material provides positive‐tone images after UV exposure (λ > 330 nm) and development in an organic medium such as isopropyl methyl ketone. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 765–771, 2004
Novel reaction between cyclic formal and ethylene oxide
Authors: Yamasaki Naoaki , Masamoto Junzo
Published: December 2003

Novel reactions between trioxane and ethylene oxide were discovered, and three novel cyclic formals were isolated and identified. These novel cyclic compounds clarified the initiation mechanism of the copolymerization of trioxane and ethylene oxide. This type of reaction was not limited to the reaction between trioxane and ethylene oxide but was also generalized to the reaction between the cyclic formal and ethylene oxide. Although an NMR method for analyzing the ethylene oxide sequences of the acetal copolymer from trioxane and ethylene oxide has not yet been established, the three newly found novel cyclic compounds, composed of 1 mol of ethylene oxide and 1 mol of trioxane, 2 mol of ethylene oxide and 1 mol of trioxane, and 3 mol of ethylene oxide and 1 mol of trioxane, were useful for analyzing the ethylene oxide sequences. These compounds gave only one consecutive oxyethylene unit, two consecutive oxyethylene units, and three consecutive oxyethylene units in three consecutive oxymethylene units, respectively, and gave different 1H NMR spectra for each oxyethylene unit. Considering these data, we synthesized three polymeric model compounds that had one consecutive oxyethylene sequence, two consecutive oxyethylene sequences, and three consecutive oxyethylene sequences in an oxymethylene main chain. By a linear combination of the 1H NMR spectrum of each oxyethylene unit of the three polymeric model compounds, we succeeded in determining the ethylene oxide sequences by the 1H NMR method for the copolymer from trioxane and ethylene oxide. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 520–533, 2004
Studies of the surface layer structure and properties of poly(styrene/α‐t‐butoxy‐ω‐polyglycidol) microspheres by carbon nuclear magnetic resonance, X‐ray photoelectron spectroscopy, and the adsorption of human serum albumin and γ‐globulins
Authors: Basinska Teresa , Slomkowski Stanislaw , Kazmierski Slawomir , Dworak Andrzej , Chehimi Mohamed M.
Published: December 2003

The composition and properties of the surface layers of poly(styrene/α‐t‐butoxy‐ω‐polyglycidol) [poly(styrene/VB‐polyGL)] microspheres synthesized by the radical copolymerization of styrene and α‐t‐butoxy‐ω‐vinylbenzyl‐polyglycidol (VB‐polyGL) macromonomers [number‐average molecular weight (Mn) = 950 or 2700] were investigated with X‐ray photoelectron spectroscopy, 13C NMR, and the adsorption of human serum albumin and γ‐globulins. The number‐average diameter of the synthesized microspheres was 220 nm. Their surface layers were rich in polyglycidol, with polyglycidol‐to‐polystyrene unit ratios of 0.443 (VB‐polyGL with Mn = 950) and 0.427 (VB‐polyGL with Mn = 2700). In suspensions of poly(styrene/VB‐polyGL) particles in D2O, the polymer chains in the polyglycidol‐rich surface layers were highly mobile, allowing the registration of polyglycidol 13C NMR spectra with standard procedures for polymer solutions. In these spectra, the signals of the relatively immobile polystyrene segments were absent. The spin–lattice relaxation times (T1) measured for polyglycidol in the microsphere surface layers and for VB‐polyGL macromonomers in solution were very close, indicating similar degrees of motion in bound (in particle surface layers) and free (in solution) polyglycidol macromolecules. Studies of protein adsorption revealed that hydrophilic polyglycidol layers were protein‐repellent. It was found that longer polyglycidol chains in particle surface layers were more mobile (higher T1 values) and provided better protection against protein adsorption. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 615–623, 2004
Life—a complex polymer system
Authors: Schurz Josef
Published: December 2003

After a discussion of the different levels of macromolecules, the phenomenon of life is regarded as a complex polymer system. The thermodynamic basis of general system theory is explained as well as the character of system laws. The important notion of emergent system properties is stressed, and life is explained as a system property of a sufficiently complex system. The general applicability of the systemic approach is pointed out, and some examples are provided. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 471–478, 2004
Preparation of polyethylene block copolymers by a combination of postmetallocene catalysis of ethylene polymerization and atom transfer radical polymerization
Authors: Inoue Yoshihisa , Matyjaszewski Krzysztof
Published: December 2003

The synthesis of block copolymers consisting of a polyethylene segment and either a poly(meth)acrylate or polystyrene segment was accomplished through the combination of postmetallocene‐mediated ethylene polymerization and subsequent atom transfer radical polymerization. A vinyl‐terminated polyethylene (number‐average molecular weight = 1800, weight‐average molecular weight/number‐average molecular weight =1.70) was synthesized by the polymerization of ethylene with a phenoxyimine zirconium complex as a catalyst activated with methylalumoxane (MAO). This polyethylene was efficiently converted into an atom transfer radical polymerization macroinitiator by the addition of α‐bromoisobutyric acid to the vinyl chain end, and the polyethylene macroinitiator was used for the atom transfer radical polymerization of n‐butyl acrylate, methyl methacrylate, or styrene; this resulted in defined polyethylene‐b‐poly(n‐butyl acrylate), polyethylene‐b‐poly(methyl methacrylate), and polyethylene‐b‐polystyrene block copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 496–504, 2004
Cellulose structure and biosynthesis: What is in store for the 21st century?
Authors: Brown R. Malcolm
Published: December 2003

This article briefly summarizes historical developments in fundamental research related to the structure and biosynthesis of cellulose. Major advances concerning the structure of cellulose include the discovery of a new suballomorph of cellulose I, the lattice imaging of glucan chains showing no fringe micelle structure, parallel chain orientation in cellulose I, and the discovery of nematic ordered cellulose. Major advances in biosynthesis include the discovery of the terminal synthesizing complex, the isolation and purification of cellulose synthase, the in vitro synthesis of cellulose I, and synthetic cellulose assembly. This article focuses on recent advances in molecular biology with cellulose, including the cloning and sequencing of cellulose synthase genes from bacteria, cyanobacteria, and vascular plants; proof of the terminal synthesizing complex as the site of the catalytic subunit of cellulose synthase; cellulose and callose synthase expression during growth and development; and phylogenetic aspects of cellulose synthase evolution. This article concludes with thoughts about future uses for the accumulating genetic information on cellulose biosynthesis for textiles and forest products and discusses possibilities of new global resources for cellulose production. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 487–495, 2004
Synthesis and characterization of stereoregular poly(methyl methacrylate)–silica hybrid utilizing stereocomplex formation
Authors: Ashok Kumar Achimuthu , Adachi Kaoru , Chujo Yoshiki
Published: December 2003

Stereoregular poly(methyl methacrylate) (PMMA)–silica nanocomposites were prepared using stereocomplex formation between i‐PMMA and s‐PMMA by an in situ method. The methodology adopted here is the simultaneous formation of organic gel and inorganic gel, the so‐called interpenetrating polymer network (IPN) formation. The gelation of i‐ and s‐PMMA were performed by stereocomplex formation with the associated segments forming the crosslinking points in the presence of tetramethoxysilane (TMOS). The effects of the i/s‐ratio, PMMA concentration, molecular weight, and solvent nature on the hybrid materials formation were addressed. The presence of the stereocomplex in the silica matrix was confirmed by DSC and solvent extraction methods. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 785–794, 2004
Phototriggered atmospheric degradation of poly[methyl(phenyl)silanediyl] in the presence of ultraviolet absorbers
Authors: Meszároš O. , Schmidt P. , Pospíšil J. , Nešpůrek S.
Published: December 2003

Oxidative changes in poly[methyl(phenyl)silanediyl] (PMPSi) films exposed in a Weather‐O‐Meter ATLAS Ci 3000+ were monitored by Fourier transform infrared spectroscopy. Increases in absorption in the siloxane, carbonyl, and hydroxyl regions, decreases in absorption in the SiSi region, and changes in the aromatic CH bond region were monitored. Experiments in argon and air indicated the key role of oxygen in the process. The photooxidation of PMPSi was retarded by triazine‐ and oxalanilide‐based ultraviolet absorbers [2‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)‐5‐(hexyloxy)phenol and N‐(4‐tert‐butyl‐2‐ethoxyphenyl)‐N′‐(2‐ethylphenyl)oxalanilide] protecting the polymer by the excited‐state intramolecular proton‐transfer mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 714–721, 2004
Poly(vinyl chloride) on the way from the 19th century to the 21st century
Authors: Braun D.
Published: December 2003

Despite all the technical and economic problems and the public discussions on the environmental dangers and hazards of chlorine chemistry, poly(vinyl chloride) (PVC) is the second most produced plastic (with a worldwide capacity of about 31 million tons), placing after polyolefins and before styrene polymers. Presently, PVC production worldwide is growing at a rate of more than 4% per year. The application of PVC was first described in a patent in 1913, but only after 1930 did a sustained interest in PVC arise in several industrial laboratories. The most remarkable milestones in PVC history and their importance to the development of macromolecular chemistry are briefly described, and some present PVC research and industrial applications, with respect to polymerization, stabilization, bulk property modification, and chemical and material recycling of PVC waste, are discussed. Some actual selected topics include the emulsion polymerization of vinyl chloride with polymeric surfactants and controlled free‐radical polymerization with nitroxyls, whereas ionic and metal organic initiators have not found any technical applications. Chemical reactions offer many possibilities for the modification of PVC, but they have been not used on a technical scale yet. Much work has been done on stabilization with nontoxic or metal‐free systems. The bulk properties of PVC can be influenced by impact modification through the addition of graft copolymers or by blending with other polymers. Also presented are some problems and recent developments in PVC recycling. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 578–586, 2004
Simultaneous introduction of phosphonic and carboxylic acid functions to hydroxylated macromolecules
Authors: Penczek Stanislaw , Pretula Julia , Kaluzynski Krzysztof
Published: December 2003

Novel diblock and dihydrophilic ionic–nonionic copolymers, having phosphonic and carboxylic functions at the same carbon atom in the repeating units of the ionic block, were prepared. The addition of 2‐diethylphosphono‐ethyl acrylate (PC) to hydroxyl groups of the polyglycidol block of the poly(ethylene glycol)‐b‐polyglycidol block copolymer was followed by the dealkylation of phosphonic acid esters and the hydrolysis of carboxylic acid esters. The polymer was characterized by 1H, 13C, and 31P NMR. The kinetics of the PC addition and the hydrolysis of the ethyl carboxylate function were also studied, and a simple bimolecular second‐order reaction was established. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 432–443, 2004
Competition between the formation of excimers and excitons during the photoluminescence of light‐emitting polymer blends
Authors: Lee J. S. , Kim C. H. , Yu J.‐W. , Kim J. K. , Kim D. Y. , Song N. W. , Kim C. Y.
Published: December 2003

Divinylenediethylhexyloxyphenyl and either triphenyltriazine (PTPV) or diphenoxyphenyltriazine (POTPV) were alternately connected to inhibit the dimer emission of the divinylenediethylhexyloxyphenyl unit and to enhance the electron mobility of light‐emitting polymers. A photoluminescence (PL) spectrum of a PTPV film showed characteristics of excimer emissions, whereas POTPV generated a singlet exciton PL emission. A blend of POTPV with poly(vinyl carbazole) (PVK) enhanced the PL intensity of POTPV upon the photoexcitation of PVK, and this indicated efficient energy transfer between the two polymers. Contrary to expectations based on the good overlap of spectra for the PL emission of the donor and the light absorption of the acceptor, the energy transfer from PVK to PTPV was incomplete upon the photoexcitation of the blend at the ultraviolet–visible absorption maximum of PVK. However, the excimer PL emission of PTPV was completely suppressed. The lifetime ratio of the excitations of the donor and the acceptor was proven to be one of the critical factors in the energy transfer, in addition to the Förster energy‐transfer principle. The excimer emission was suppressed by the photoexcitation of the chromophores below a certain critical energy level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 557–565, 2004
Polycationic salts. VI. Synthesis and in vitro studies of 2‐ionene oligomer derivatives of styrene as bile acid sequestering agents
Authors: Zarras Peter
Published: December 2003

Several vinylbenzyltri‐n‐alkylammonium salts were prepared via the Menshutkin reaction in high yields by the reaction of vinyl benzyl chloride (VBC) and tertiary amines. Additional salts based on 2‐ionene oligomers were synthesized via a sequential Menshutkin reaction. The 2‐ionene oligomers were further reacted with VBC to afford the vinyl benzyl chloride‐2‐ionene halide monomers in nearly quantitative yield. The monomers were polymerized in either aqueous or organic solvents with azo initiators in high yield with correspondingly high inherent viscosities. The polymers were measured spectrophotometrically for their bile acid sequestering activity with an in vitro enzymatic reaction. Several of the measured polymers exhibited 15–28% greater activity relative to cholestyramine. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 701–713, 2004
Synthesis, structural analysis, and self‐assembly of phenylene ethynylene oligomers and their F, CF3, and CH3 substituted derivatives
Authors: Percec Simona , Getty Ross , Marshall Will , Skidd Gabriel , French Roger
Published: December 2003

Oligomers consisting of aromatic building blocks separated by alkynyl units were synthesized by Sonogashira cross‐coupling of aryl halides with terminal acetylenes. Strong electron acceptors such as F and CF3 and weak electron donors like CH3 were placed as substituents on one of the benzene rings. Acetyl‐protected sulfhydryl groups were attached to one end of these molecules to promote their self‐organization on gold surfaces. The electron‐transport properties of such self‐assembled monolayers (SAMs) are highly sensitive to the local order of the molecules in the solid state. Single crystals were analyzed by X‐ray diffraction experiments that revealed structural details that could lead to a better understanding of the electron‐transport properties. The unsymmetrical substitution of the aromatic rings by electron‐active groups in the ortho‐, meta‐, or para positions resulted in changes of such molecular parameters as bonding and torsion angles and planarity. These parameters, in turn, can affect the angle of the molecular attachment to a gold substrate and the density of the resulting SAMs. Patterned SAMs of some of these molecules and comparison alkane thiols were obtained on gold by microcontact printing or flooding. The SAM thickness was determined by spectroscopic ellipsometry. Surface potential differences between adjacent SAMs or between SAMs and the gold substrate were measured by scanning surface potential microscopy under ambient conditions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 541–550, 2004
Parallel programming library for molecular dynamics simulations
Authors: Trobec R. , Šterk M. , Praprotnik M. , Janežič D.
Published: December 2003

A parallel programming library for molecular dynamics (MD) simulations is described and applied to the recently proposed split integration symplectic method (SISM) for MD simulation. The results show that for a system of 1024 linear chain molecules with an integration step of 4.5 fs parallel execution of SISM with the particle–particle interactions (PPIs) library on 32 computers gives efficiency of 95.6%. The results also show the parallel simulation of n particles is scalable with the number of processors p and the time requirement is proportional to n2/p for n/p large enough, which guarantees optimal speed‐up. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Generalization of the Kohn–Sham equations with constrained electron density formalism and its time‐dependent response theory formulation
Authors: Casida Mark E. , Wesołowski Tomasz A.
Published: December 2003

The Kohn–Sham equations with constrained electron density (KSCED) embedding formalism of Wesołowski and coworkers was originally developed and is good for the case of two weakly interacting molecular regions with weakly overlapping densities, such as might be expected in describing solvation. A generalization is given here for the case of three molecular regions with strongly overlapping densities with the idea that this generalized theory can offer a better description of embedding in the context of situations that might be encountered in, for example, chemisorption on surfaces or active sites in enzymes. This three‐partition generalization includes the original two‐partition formalism as a special case. Time‐dependent response theory equations are then developed for the two‐ and three‐partition theories for application to the problem of the calculation of polarizabilities and other response properties, including excitation spectra, of embedded molecules or molecular structures. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Theoretical study of the structures and stabilities of AlCn, AlC, and AlC (n = 1–7) monocyclic clusters
Authors: Redondo Pilar , Barrientos Carmen , Largo Antonio
Published: December 2003

A theoretical study of the AlCn, AlC and AlC (n = 1–7) monocyclic clusters has been carried out. Predictions for their electronic structures, dipole moments and vibrational frequencies have been made at the B3LYP/6‐311G(d) and B3LYP/6‐311+G(d) levels. For the AlCn monocyclic clusters the ground state is found to be a doublet in all cases, whereas all corresponding cations have singlet ground states. In the case of the anionic clusters, singlet states are favored up to n = 5, whereas triplet ground states are found for clusters with more carbon atoms. An even–odd parity effect, with n‐even clusters being more stable than n‐odd ones, is found for both the neutral and anionic species, whereas in the case of the cations there is no clear alternation in stability. It is in general observed that n‐even clusters have higher electron affinities and ionization potentials than n‐odd species. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Wave packet calculations for the Cl + H2 reaction
Authors: Skouteris Dimitris , Laganà Antonio , Capecchi Gabriella , Werner Hans‐Joachim
Published: December 2003

Time‐dependent quantum mechanical calculations have been carried out to estimate the convergence with the total angular momentum quantum number J of the reactive cross‐sections for the reaction Cl + H2 using product Jacobi coordinates. The potential energy surface used for the calculations is that of Capecchi and Werner (to be published) developed recently. The theoretical predictions are compared with results of previous theoretical studies. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Reactivity and aromaticity of polyaromatics in radical cyclization reactions
Authors: Van Speybroeck V. , Hemelsoet K. , Waroquier M. , Marin G. B.
Published: December 2003

Theoretical ab initio calculations are presented on cyclization reactions of polyaromatics that occur by a radical mechanism. Such processes are one of the elementary steps for polyaromatic hydrocarbon formation in thermal cracking units and during soot formation. Ring closure can take place at various sites of the polyaromatic surface. It is the aim of this study to obtain insight into the influence of the local structure on the reactivity of the polyaromatics. Aromaticity is a determining factor for the reactivity and can be probed by various magnetic properties such as the diamagnetic susceptibilities, proton chemical shifts, and nucear‐independent chemical shifts. A correlation is established between the magnetic properties and activation energy of the studied reactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Factors affecting reproduction in zoo‐housed geoffroy's tamarins(Saguinus geoffroyi)
Authors: Kuhar Christopher W. , Bettinger Tamara L. , Sironen Alan L. , Shaw James H. , Lasley Bill L.
Published: December 2003

The captive population of Geoffroy's tamarins (Saguinus geoffroyi) has suffered a severe decline over the past 10 years. This population decline is attributed not to a failure to produce offspring, but rather to a failure to successfully rear offspring. To date, no studies have quantitatively examined the behaviors and hormones of this tamarin species in captivity. Therefore, this study was conducted to determine whether there were any discernable factors that could be correlated with failure to rear offspring in S. geoffroyi. Fifteen adult Geoffroy's tamarins (GTs) at the Cleveland Metroparks Zoo (CMZ) were observed by means of instantaneous sampling on a focal animal. In addition, all instances of social behaviors were recorded. A factorial arrangement of treatments was used, as animals were divided between a colony‐housing situation and a non‐colony situation with hand‐reared and mother‐reared animals in both treatments. Repeated‐measures analysis of variance (ANOVA) showed no interactions between the treatments, and no differences between rearing histories for the behaviors studied. However, animals housed in a colony setting exhibited higher levels of aggressive behaviors and lower activity levels compared to those in a non‐colony setting. There also was a trend for colony‐housed animals to huddle, scent‐mark, and exhibit sexual behaviors more often than non‐colony animals. First‐morning‐void urine samples were collected once per week, and assays for E1C and PdG indicated that reproduction was not being suppressed. ANOVA conducted on samples assayed for excreted cortisol showed no differences in mean cortisol concentration by rearing histories or housing conditions. While these physiological indicators reveal no signs of stress, high levels of aggressive and territorial behaviors indicate social unrest in the colony‐housed condition, which may be contributing to the poor reproductive success of those individuals. Zoo Biol 22:545–559, 2003. © 2003 Wiley‐Liss, Inc.
Acquisition of fishes and aquatic invertebrates for zoological collections. Is there a future?
Authors: Thoney D.A. , Warmolts D.I , Andrews C.
Published: December 2003

The majority of the freshwater fishes in the ornamental trade now originate from captive‐bred sources, as do a large proportion of the freshwater species exhibited in public aquariums. In contrast, commercial operators who also supply marine specimens to the ornamental trade remove directly from the wild approximately 98% of the marine fishes and invertebrates exhibited in public aquariums. The common perception prevails that captive propagation is inherently a better alternative to obtaining animals from the wild. Although captive propagation has been shown to have many benefits for terrestrial species, there are a number of features unique to marine species that challenge the idea that every species should be bred in captivity. Some of the key issues relating to the development of widespread conservation‐oriented captive propagation programs include: 1) the high taxonomic diversity in marine animals; 2) the resultant variety in their reproductive methods; 3) their ecological, behavioral, physiological, and nutritional needs; and 4) our general lack of knowledge on their husbandry and medical care. There are several characteristics of marine fish and invertebrate populations that make them suitable candidates for sustainable harvest. For instance, marine teleosts are “r‐selected,” meaning that they have an extremely high fecundity, and most marine teleosts have a wide distribution and the ability to disperse over long distances. In locations considered for fish collection, appropriate management techniques should be employed to ensure that fishes and invertebrates are collected with as little impact on the ecosystem as possible. The collection of marine fishes and invertebrates for public aquariums and the hobby trade should be managed like a fishery to ensure long‐term sustainability. The public aquarium community should support marine organism certification initiatives, such as the Marine Aquarium Council (MAC). Marine organism certification will create market incentives that encourage and support quality and sustainable practices by creating consumer demand and confidence for certified organisms, practices, and industry participants. The creation of refuges that supply propagules to harvested areas, the rotation of areas fished, species‐specific size limits and seasons, and standardization of collecting, handling, and transportation techniques should be used to manage these fisheries and harvest areas. Zoo Biol 22:519–527, 2003. © 2003 Wiley‐Liss, Inc.