bluuebunny/crossref_metadata_2025 huggingface dataset:
Graft copolymers and high‐molecular‐weight star‐like polymers by atom transfer radical polymerization
Authors: Masař Bohumil , Janata Miroslav , Látalová Petra , Netopilík Miloš , Vlček Petr , Toman Luděk
Published: March 2006

Grafting of tert‐butyl acrylate (tBuA), methyl methacrylate (MMA), and styrene (St) monomers (M) by Cu(I)‐mediated ATRP from polystyrene (PSt) macroinitiator (Mn = 5620, polydispersity index, PDI = 1.12), containing initiating 2‐bromopropionyloxy groups (I) (bound to 34% of aromatic cores; 11 groups per backbone), was performed using conditions suitable for the respective homopolymerizations. The preparation of PSt‐g‐PtBuA in bulk using an initial molar ratio [M]0/[I]0 = 140 had a controlled character up to Mn = (132–148) × 103 (PDI = 1.08–1.16). With MMA and St and using the same [M]0/[I]0, preliminary experiments were made; the higher the monomer conversion, the broader was the distribution of molecular weight of the products. Graft copolymerizations of all these monomers at [M]0/[I]0 = 840 or 1680 were successfully conducted up to high conversions. Low‐polydispersity copolymers, with very long side chains, in fact star‐like copolymers, were obtained mainly by tuning the deactivator amount in the reaction mixture. (PSt‐g‐PtBuA, DPn,sc (DP of side chain) = 665, PDI = 1.24; PSt‐g‐PMMA, DPn,sc = 670, PDI = 1.43; PSt‐g‐PSt, DPn,sc = 324, PDI = 1.11). Total suppression of intermolecular coupling was achieved here. However, the low concentrations of initiator required long reaction times, leading sometimes to formation of a small amount (∼5%) of low‐molecular‐weight polymer fraction. This concomitant process is discussed, and some measures for its prevention are proposed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3662–3672, 2006
The morphology and property of ultra‐fine full‐vulcanized acrylonitrile butadiene rubber particles/EPDM blends
Authors: Zhang Liqun , Li Tie , Lu Yonglai , Tang Yuanwang , Qiao Jinliang , Tian Ming
Published: March 2006

A novel UFNBRP/EPDM blend was prepared by compounding ultra‐fine full‐vulcanized acrylonitrile butadiene rubber particles (UFNBRP) with ethylene–propylene–diene monomer (EPDM) matrix. The morphology, dynamic property, and curing property of the blend were discussed in detail. TEM and SEM observations showed that, no matter how high the blend ratio of UFNBRP to EPDM matrix was, UFNBRP particles always kept being in the dispersion phase because of its extremely high viscosity resulting from self‐crosslinking, but were not dispersed as nanosize units, as expected. Dynamic properties, illustrated by DMTA, further demonstrated that two phases exhibited two separate glass transition temperatures, indicating distinct phase separation and weak phase interaction. Rubber processing analyzer results showed that inorganic filler as well as UFNBRP particles in EPDM matrix formed a network and blocked the flow properties of the compound. At the same time, the introduction of UFNBRP particles evidently affected the vulcanization of EPDM, when sulfur was used as a vulcanizing agent, and improved the mechanical properties of EPDM. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3673–3679, 2006
Alternatives for multiobjective optimization of a polymerization process
Authors: Curteanu Silvia , Leon Florin , Gâlea Dan
Published: March 2006

The optimal control policies for a polymerization process, particularly for batch free‐radical polymerization of methyl methacrylate, were determined using a multiobjective optimization technique. The process objectives considered in the optimization include monomer conversion, polydispersity index, polymerization degree, and total reaction time, weighted and combined in a scalar objective function. The decision variables were the initial concentration of the initiator and the temperature represented by isothermal steps. For solving the optimization problem, several methods based on sequential quadratic programming and a genetic algorithm were used and compared. Combining them into a hybrid method (the genetic algorithm provided the initial values for the traditional iterative method) led to the best results. The aims of this study were to develop an approach for optimizing the polymerization process and to describe alternatives for formulating and solving this problem, emphasizing the importance of user decision in choosing solutions based on technological criteria. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3680–3695, 2006
Compatibility of HDPE/postconsumer HDPE blends using compatibilizing agents
Authors: Ramírez‐Vargas E. , Sandoval‐Arellano Z. , Hernández‐Valdez J. S. , Martínez‐Colunga J. G. , Sánchez‐Valdés S.
Published: March 2006

Mechanical properties, molecular weight, X‐ray diffraction, and differential scanning calorimetry (DSC) characterization of blends of virgin high‐density polyethylene (HDPE) with two types of recycled material were investigated. The recycled came from urban plastic waste; one kind was only washed and grounded and the other was extruded and pelletized to remove most of contaminant particles. Starting with the 30/70 virgin/grounded recycled and 50/50 virgin/pelletized recycled blends the recycled content was increased in both blends and compatibilizing agents were used to increase the blend performance. A mixture of phenolic antioxidants and phosphite costabilizers under the name of Recycloblend™, ethylene vinyl acetate (EVA) copolymer, low‐density polyethylene (LDPE), and linear low density polyethylene (LLDPE) were used as compatibilizers. The effect of these additives and the recycled content on the performance of extrusion blow‐molded bottles was determined. The results suggest that blends of virgin/grounded recycled and virgin/pelletized recycled HDPE, in general, were not significantly different among each other and both had a quite similar behavior than the virgin HDPE when compatibilizing agents were used. The addition of compatibilizing agents yielded a material with properties similar to those for the virgin HDPE, helping to reduce the effect of polymers degradation on the rheological and mechanical behavior, with Recycloblend and LLDPE being the most effective for the blends with grounded recycled material, and LLDPE y EVA, for the blends with pelletized recycled. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3696–3706, 2006
Emulsifier‐free synthesis and self‐assembly of an amphiphilic poly(styrene‐co‐acrylic acid) copolymer
Authors: Yan Lifeng , Zhang Guangzao , Liu Guangming , Ji Jing , Li Wan
Published: March 2006

A poly(styrene‐co‐acrylic acid) copolymer was synthesized by surfactant‐free polymerization with the assistance of power ultrasound in water. Fourier transform infrared, NMR, and differential scanning calorimetry measurements revealed that the copolymer was random. Atomic force microscopy and laser light scattering were used to investigate the self‐assembly of the copolymer, and it was found that the copolymer chains formed micelles or other self‐assemble structures in solution. Atomic force microscopy also indicated that the self‐assembled structures developed into nanospheres with a poly(acrylic acid)‐rich or polystyrene‐rich surface in a film, depending on the solvent used for the preparation of the film. In particular, a wheel‐like structure could resulted in a film when the copolymer film was prepared in a moist environment; it resulted from heterogeneous aggregates of poly(acrylic acid) at the rim of water bubbles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:3718–3726, 2006
Studies of the mechanical and thermal properties of cross‐linked poly(methylmethacrylate‐acrylic acid‐allylmethacrylate)‐modified bone cement
Authors: Nien Yu‐Hsun , Chen Jason
Published: March 2006

Bone cement is used as load‐distributing filler between the prosthesis and the bone, as well as a method to anchor prosthesis in orthopedic implants. One of the disadvantages of using polymethylmethacrylate (PMMA) as bone cement is shrinkage of the cement during polymerization. Shrinkage of the cement during polymerization may lose the good load transfer through the interface between the bone and bone cement, and is a source of prosthetic loosening. A crosslinked poly(methylmethacrylate‐acrylic acid‐allylmethacrylate) was applied to bone cement, because it was found that this copolymer exhibits the ability to absorb body fluids and swell in a controlled manner to compensate shrinkage of the cement during polymerization. In this study, the crosslinked poly(methylmethacrylate‐acrylic acid‐allylmethacrylate) modified bone cement was prepared and characterized using tensile analysis and dynamic mechanical analysis. The results show that the modified bone cement is able to enhance the mechanical properties of bone cement. From dynamic mechanical analysis, the transition temperature and the tan δ value of the cement may be affected by prepolymerized crosslinked poly(methylmethacrylate‐acrylic acid‐allylmethacrylate) powder. From the observation of the fracture surfaces of the cements, the modified bone cement may improve fracture toughness. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3727–3732, 2006
Effects of additives with different functional groups on the physical properties of starch/PVA blend film
Authors: Yoon Soon‐Do , Chough Sung‐Hyo , Park Hye‐Ryoung
Published: March 2006

The effects of additives with different functional groups, that is, hydroxyl and carboxyl groups, on the physical properties of starch/PVA blend films were examined. Starch/PVA blend films were prepared by the mixing process. Glycerol (GL) with 3 hydroxyl groups, succinic acid (SA) with 2 carboxyl groups, malic acid (MA) with 1 hydroxyl and 2 carboxyl groups, and tartaric acid (TA) with 2 hydroxyl and 2 carboxyl groups were used as additives. The results of measured tensile strength and elongation verified that hydroxyl and carboxyl groups as functional groups increased the flexibility and strength of the film. The degree of swelling (DS) and solubility (S) of the GL/SA‐added films were low. However, the DS and S of the films with added MA or TA with both hydroxyl and carboxyl groups were comparatively high. When the film was dried at low temperature, the properties of the films evidently improved, probably because hydrogen bonding was activated at low temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3733–3740, 2006
Polyesters from renewable resources: Preparation and characterization
Authors: Bakare I. O. , Pavithran C. , Okieimen F. E. , Pillai C. K. S.
Published: March 2006

Polyesters were synthesized with monoglycerides prepared from rubber seed oil, a renewable resource. Monoglycerides were obtained by an alcoholysis method from the oil, which was neat or modified by treatments with different amounts of maleic anhydride at 230°C. The polyester resins were subsequently prepared by the condensation polymerization of the monoglycerides with phthalic anhydride. The monoglycerides and resins were characterized by spectroscopic analysis and measurements of the physicochemical properties. The chemical resistance of the polyesters was also studied. The results revealed that the polyesters prepared from the modified monoglycerides possessed better properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3748–3755, 2006
A structural model of an accessibility of polycarbonate melt to thermooxidative degradation processes
Authors: Kozlov G. V. , Dolbin I. V. , Zaikov G. E.
Published: March 2006

It is shown that the “accessibility” of a polymer for oxidation is the only structural factor and quantitative estimate within the framework of the fractional derivation. The oxidation rate of the “accessible” part of a macromolecular coil is independent on its structure, which allows to assume its dependence only on the chemical constitution of polymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 3765–3768, 2006
Preparation and properties of some thermosets derived from allyl‐functional naphthoxazines
Authors: Agag Tarek
Published: March 2006

A series of novel naphthoxazine monomers containing allyl functionalities were synthesized from the reaction of 1‐naphthol, 2‐naphthol, and 1,5‐dihdroxynaphthalene with allylamine and formalin. Another series of naphthoxazines were similarly prepared by using aniline instead of allylamine for comparison. The chemical structures of these novel monomers were confirmed by IR, 1H NMR, and elemental analysis. DSC of the aniline‐ based naphthoxazines showed an exotherm due to the ring‐opening polymerization of oxazine. For allylamine‐based naphthoxazines, two exotherms were observed. The first exotherm is attributed to the thermal crosslinking of the allyl group and the second is due to the ring‐ opening polymerization of oxazine. The thermal cure of the allylamine‐based naphthoxazine monomers gave thermoset resins with novel structure comprising of polynaphthoxazine with extended network via the polymerization of allyl functionalities. Dynamic mechanical analyses and thermogravimetric analyses showed that the thermosets derived from allyl‐ functional naphthoxazines have high Tg's and stable storage moduli to higher temperature as well as better thermal stability than that of aniline‐based naphthoxazines. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3769–3777, 2006
Structural and functional classes of multipolar cells in the ventral cochlear nucleus
Authors: Doucet John R. , Ryugo David K.
Published: March 2006

Multipolar cells in the ventral cochlear nucleus (VCN) are a structurally and functionally diverse group of projection neurons. Understanding their role in the ascending pathway involves partitioning multipolar cells into distinct populations and determining where in the brain each sends its coded messages. In this study, we used retrograde labeling techniques in rats to identify multipolar neurons that project their axons to the ipsilateral dorsal cochlear nucleus (DCN), the contralateral CN, or both structures. Three rats received injections of biotinylated dextran amine in the ipsilateral DCN and diamidino yellow in the contralateral CN. Several radiate multipolar neurons (defined by their axonal projections to the ipsilateral DCN and their dendrites that traverse VCN isofrequency sheets) were double‐labeled but over 70% were not. This result suggests two distinct populations: (1) radiate‐commissural (RC) multipolar cells that project to the ipsilateral DCN and the contralateral CN, and (2) radiate multipolar cells that project exclusively (in this context) to the ipsilateral DCN. In a different group of animals, we retrogradely labeled multipolar neurons that project their axons to the contralateral CN and measured the size of their cell bodies. The mean size of this population (266 ± 156 μm2) was significantly smaller than those of RC‐multipolar cells (418 ± 140 μm2). We conclude that the CN commissural pathway is composed of at least two components: (1) RC multipolar cells and (2) commissural multipolar cells that are small‐ and medium‐sized neurons that project exclusively (in this context) to the contralateral CN. These results identify separate structural groups of multipolar cells that may correspond to physiological unit types described in the literature. They also provide protocols for isolating and studying different populations of multipolar cells to determine the neural mechanisms that govern their responses to sound. Anat Rec Part A, 2006. © 2006 Wiley‐Liss, Inc.
Differential representation of speech sounds in the human cerebral hemispheres
Authors: Firszt Jill B. , Ulmer John L. , Gaggl Wolfgang
Published: March 2006

Various methods in auditory neuroscience have been used to gain knowledge about the structure and function of the human auditory cortical system. Regardless of method, hemispheric differences are evident in the normal processing of speech sounds. This review article, augmented by the authors' own work, provides evidence that asymmetries exist in both cortical and subcortical structures of the human auditory system. Asymmetries are affected by stimulus type, for example, hemispheric activation patterns have been shown to change from right to left cortex as stimuli change from speech to nonspeech. In addition, the presence of noise has differential effects on the contribution of the two hemispheres. Modifications of typical asymmetric cortical patterns occur when pathology is present, as in hearing loss or tinnitus. We show that in response to speech sounds, individuals with unilateral hearing loss lose the normal asymmetric pattern due to both a decrease in contralateral hemispheric activity and an increase in the ipsilateral hemisphere. These studies demonstrate the utility of modern neuroimaging techniques in functional investigations of the human auditory system. Neuroimaging techniques may provide additional insight as to how the cortical auditory pathways change with experience, including sound deprivation (e.g., hearing loss) and sound experience (e.g., training). Such investigations may explain why some populations appear to be more vulnerable to changes in hemispheric symmetry such as children with learning problems and the elderly. Anat Rec Part A, 2006. © 2006 Wiley‐Liss, Inc.
Genetics of hearing loss: Allelism and modifier genes produce a phenotypic continuum
Authors: Mchugh Richard K. , Friedman Rick A.
Published: March 2006

Recent genetic and genomic studies have greatly advanced our knowledge of the structure and function of genes involved in hearing loss. We are starting to recognize, however, that many of these genes do not appear to follow traditional Mendelian expression patterns and are subject to the effects of allelism and modifier genes. This review presents two genes illustrative of this concept that have varied expression pattern such that they may produce either syndromic or nonsyndromic hearing loss. One of these genes, cadherin 23, produces a spectrum of phenotypic traits, including presbycusis, nonsyndromic prelingual hearing loss (DFNB12), and syndromic hearing loss as part of Usher syndrome (Usher 1D). Missense mutations in CDH23 have been associated with presbycusis and DFNB12, whereas null alleles cause the majority of Usher 1D. Modifier gene products that interact with cadherin 23 also affect the phenotypic spectrum. Similarly, allelsim in the gene encoding wolframin (WFS1) causes either a nonsyndromic dominant low‐frequency hearing loss (DFNA6/14/38) or Wolfram syndrome. Missense mutations within a defined region are associated with DFNA6/14/38, while more severe mutations spanning WFS1 are found in Wolfram syndrome patients. The phenotypic spectrum of Wolfram syndrome is also hypothesized to be influenced by modifier genes products. These studies provide increasing evidence for the importance of modifier genes in elucidating the functional pathways of primary hearing loss genes. Characterizing modifier genes may result in better treatment options for patients with hearing loss and define new diagnostic and therapeutic targets. Anat Rec Part A, 2006. © 2006 Wiley‐Liss, Inc.
Comparative gene expression analysis reveals a characteristic molecular profile of the superior olivary complex
Authors: Nothwang Hans Gerd , Koehl Alexander , Friauf Eckhard
Published: March 2006

The superior olivary complex (SOC) is a very conspicuous structure in the mammalian auditory brainstem. It represents the first binaural processing center and is important for sound localization in the azimuth and in feedback regulation of cochlear function. In order to define molecular determinants of the SOC, which are of potential functional relevance, we have performed a comprehensive analysis of its transcriptome by serial analysis of gene expression in adult rats. Here, we performed a detailed analysis of the SOC's gene expression profile compared to that of two other neural tissues, the striatum and the hippocampus, and with extraocular muscle tissue. This tested the hypothesis that SOC‐specific or significantly upregulated transcripts provide candidates for the specific function of auditory neurons. Thirty‐three genes were significantly upregulated in the SOC when compared to the two other neural tissues. Thirteen encoded proteins involved in neurotransmission, including action potential propagation, exocytosis, and myelination; five genes are important for the energy metabolism, and five transcripts are unknown or poorly characterized and have yet to be described in the nervous system. The comparison of functional gene classes indicates that the SOC has the highest energy demand of the three neural tissues, yet protein turnover is apparently not increased. This suggests a high energy demand for fueling auditory neurotransmission. Such a demand may have implications on auditory‐specific tasks and relate to central auditory processing disorders. Ultimately, these data provide new avenues to foster investigations of auditory function and to advance molecular physiology in the central auditory system. Anat Rec Part A, 2006. © 2006 Wiley‐Liss, Inc.
Differential expression of cytoskeletal genes in the cochlear nucleus
Authors: Friedland David R. , Popper Paul , Eernisse Rebecca , Ringger Benjamin , Cioffi Joseph A.
Published: March 2006

The relationship between structure and function is clearly illustrated by emerging evidence demonstrating the role of the neuronal cytoskeleton in physiological processes. For example, alterations in axonal caliber, a feature of the cytoskeleton, have been shown to affect reflex arc latencies and are prominent features of several neuropathological disorders. Even in the nonpathologic situation, however, axonal diameter may be a crucial element for the normal function of specialized auditory neurons. To investigate this relationship, we used serial analysis of gene expression and microarray analyses to characterize the expression of cytoskeletal genes in the central auditory system. These data, confirmed by real‐time RT‐PCR, identified differential expression of intermediate neurofilament transcripts (i.e., Nefh, Nef3, and Nfl) among the subdivisions of the cochlear nucleus. In situ hybridization was used to identify specific classes of neurons within the cochlear nucleus expressing these neurofilament genes. Robust neurofilament expression was seen in bushy cells and cochlear nerve root neurons, suggesting an association between cytoskeletal structure and rapid conduction velocities. Gene expression data were also identified for other classes of cytoskeletal and structural genes important in neuronal function. These results may help to explain some causes of hearing loss in hereditary neuropathies and provide an anatomic basis for understanding normal neuronal function in the central auditory system. Anat Rec Part A, 2006. © 2006 Wiley‐Liss, Inc.
Semicircular canal geometry, afferent sensitivity, and animal behavior
Authors: Hullar Timothy E.
Published: March 2006

The geometry of the semicircular canals has been used in evolutionary studies to predict the behaviors of extinct animals. These predictions have relied on an assumption that the responses of the canals can be determined from their dimensions, and that an organism's behavior can be determined from these responses. However, the relationship between a canal's sensitivity and its size is not well known. An intraspecies comparison among canal responses in each of three species (cat, squirrel monkey, and pigeon) was undertaken to evaluate various models of canal function and determine how their dimensions may be related to afferent physiology. All models predicted the responses of the cat afferents, but the models performed less well for squirrel monkey and pigeon. Possible causes for this discrepancy include incorrectly assuming that afferent responses accurately represent canal function or errors in current biophysical models of the canals. These findings leave open the question as to how reliably canal anatomy can be used to estimate afferent responses and how closely afferent responses are related to behavior. Other labyrinthine features, such as orientation of the horizontal canal, which is reliably held near earth‐horizontal across many species, may be better to use when extrapolating the posture and related behavior of extinct animals from labyrinthine morphology. Anat Rec Part A, 2006. © 2006 Wiley‐Liss, Inc.
Structural and functional neural correlates of music perception
Authors: Limb Charles J.
Published: March 2006

This review article highlights state‐of‐the‐art functional neuroimaging studies and demonstrates the novel use of music as a tool for the study of human auditory brain structure and function. Music is a unique auditory stimulus with properties that make it a compelling tool with which to study both human behavior and, more specifically, the neural elements involved in the processing of sound. Functional neuroimaging techniques represent a modern and powerful method of investigation into neural structure and functional correlates in the living organism. These methods have demonstrated a close relationship between the neural processing of music and language, both syntactically and semantically. Greater neural activity and increased volume of gray matter in Heschl's gyrus has been associated with musical aptitude. Activation of Broca's area, a region traditionally considered to subserve language, is important in interpreting whether a note is on or off key. The planum temporale shows asymmetries that are associated with the phenomenon of perfect pitch. Functional imaging studies have also demonstrated activation of primitive emotional centers such as ventral striatum, midbrain, amygdala, orbitofrontal cortex, and ventral medial prefrontal cortex in listeners of moving musical passages. In addition, studies of melody and rhythm perception have elucidated mechanisms of hemispheric specialization. These studies show the power of music and functional neuroimaging to provide singularly useful tools for the study of brain structure and function. Anat Rec Part A, 2006. Published 2006 Wiley‐Liss, Inc.
Managing déjà vu: Collection building for the identification of nonidentical duplicate documents
Authors: Conrad Jack G. , Schriber Cindy P.
Published: March 2006

As online document collections continue to expand, both on the Web and in proprietary environments, the need for duplicate detection becomes more critical. Few users wish to retrieve search results consisting of sets of duplicate documents, whether identical duplicates or close variants. The goal of this work is to facilitate (a) investigations into the phenomenon of near duplicates and (b) algorithmic approaches to minimizing its deleterious effect on search results. Harnessing the expertise of both client‐users and professional searchers, we establish principled methods to generate a test collection for identifying and handling nonidentical duplicate documents. We subsequently examine a flexible method of characterizing and comparing documents to permit the identification of near duplicates. This method has produced promising results following an extensive evaluation using a production‐based test collection created by domain experts.
Dosimetric assessment of an exposure system for simulating GSM and WCDMA mobile phone usage
Authors: Bahr Achim , Dorn Hans , Bolz Thomas
Published: March 2006

An exposure system for investigation of volunteers during simulated GSM and WCDMA mobile phone usage has been designed. The apparatus consists of a dual band antenna with enhanced carrying properties that enables exposure for at least 8 h a day. For GSM a 900 MHz pulse modulated carrier was used. The QPSK modulated WCDMA signal at 1966 MHz comprises a power control scheme, which was designed for investigations of biological effects. The dosimetry of the exposure system by measurements and calculations is described in detail within this paper. It is shown that the SAR distribution of the antenna shows similar characteristics to mobile phones with an integrated antenna. The 10 g averaged localized SAR, normalized to an antenna input power of 1 W and measured in the flat phantom area of the SAM phantom, amounts to 7.82 mW/g (900 MHz) and 10.98 mW/g (1966 MHz). The simulated SAR10g in the Visible Human head model agrees with measured values to within 20%. A variation of the antenna rotation angle results in an SAR10g change below 17%. The increase of the antenna distance by 2 mm with respect to the human head leads to an SAR10g change of 9%. Bioelectromagnetics 27:320–327, 2006. © 2006 Wiley‐Liss, Inc.
Conformational differences in protein disulfide linkages between normal hair and hair from subjects with trichothiodystrophy: A quantitative analysis by Raman microspectroscopy
Authors: Schlücker S. , Liang C. , Strehle K. R. , DiGiovanna J. J. , Kraemer K. H. , Levin I. W.
Published: March 2006

Raman spectra of normal hair shafts and hair shafts from patients exhibiting trichothiodystrophy (TTD) were obtained using line focus laser illumination. Because hair from TTD patients has a significant decrease in the content of the sulfur‐containing amino acids in comparison to normal hair, the 550–500 cm−1 disulfide stretching mode region of the Raman spectrum was examined in detail. A quantitative spectral analysis demonstrates significant increases in the two energetically less favored gauche–gauche–trans (g‐g‐t) and trans–gauche–trans (t‐g‐t) forms. These observations suggest that the increased amounts of these less stable disulfide conformers are contributing factors to or associated with the hair brittleness observed for this congenital disorder. Structure–spectra correlations for the three dominant disulfide conformers are confirmed by quantum chemical calculations using modern density functional theory (DFT). © 2006 Wiley Periodicals, Inc. Biopolymers 82: 615–622, 2006

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Synthesis of Aminooxy‐Functionalized Lanthanide(III) Chelates for Carbonyl‐Group Conjugation
Authors: Hovinen Jari
Published: March 2006

The syntheses of three new aminooxy‐tethered lanthanide(III) chelates, compounds 1–3, incorporating DOTA (=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid), DTPA (=diethylenetriaminepentaacetic acid), or a substituted terpyridine (2,2′,2″,2′′′‐[2,2′: 6′,2″‐terpyridine‐6,6″‐diylbis(methylenenitrilo)]tetraacetic acid), respectively, are described. Reagents 1–3 can be used for carbonyl ‘labeling’, as shown by the formation of the corresponding oxime‐ether bioconjugates of naltrexone (16) and 2‐deoxy‐β‐D‐glucose (17) (Scheme 4).
13C‐NMR Study of the Ruthenium(II)‐Catalyzed Degradation of Labeled G‐Factor Endoperoxides: Proposal of a Likely Biogenetic Pathway and Evidence for CO2 Release
Authors: André‐Barrès Christiane , Baltas Michel , Massou Stéphane
Published: March 2006

G‐factor endoperoxides are natural products acting as phytohormones and contribute to root inhibition and frost resistance in Eucalyptus grandis and other Myrtaceae. Several (Z)‐ and (E)‐configured cyclopentane‐1,3‐dione metabolites of G‐factors have been found in some Eucalyptus extracts. Interestingly, these probable metabolites are identical to the products obtained by RuII‐catalyzed reduction of G‐factors. In the present work, we, thus, studied the mechanism involved in the formation of these compounds by means of in‐depth NMR distribution analysis of two differently 13C‐labeled G3‐factors. The observed CO2 release is underlined, and a comparison with the corresponding FeII‐induced degradation of G‐factor endoperoxides is made. Also, the type of electron transfer proposed in the two processes is discussed and, tentatively, connected to the role of endoperoxides in plants.
Carotid stenting with distal protection in high surgical risk patients: The BEACH trial 30 day results
Authors: White Christopher J. , Iyer Sriram S. , Hopkins L. Nelson , Katzen Barry T. , Russell Mary E.
Published: March 2006

Background: The BEACH trial evaluated the outcomes of carotid artery stent placement with distal emboli protection, using the Carotid Wallstent® and the FilterWire EX®/EZTM, in patients at high surgical risk for carotid endarterectomy (CEA). Methods: We enrolled 747 patients at high surgical risk for CEA due to prespecified anatomical criteria and/or medical comorbidities. The trial included both symptomatic (>50% carotid artery stenosis) as well as asymptomatic (>80% carotid artery stenosis) high surgical risk patients. Three groups of patients were included in the trial. The Roll‐in (R) group (n = 189/747, [25%]) included up to nine patients per site for familiarization of the device and protocol; the Pivotal (P) group (n = 480/747, [65%]) was intended for presentation to the FDA for consideration of device approval; and a Bilateral (B) registry group (n = 78/747, [10%]) was included because of the need to treat patients with bilateral carotid artery disease. In the 480 Pivotal patients, anatomic criteria represented the most frequent high‐risk surgical category for enrollment (58.8%), followed by prior CEA (34.2%), multivessel (≥2) coronary artery disease (21.7%), and contralateral carotid occlusion (18.1%). Results: The technical success rate for stent deployment and FilterWire EX/EZ deployment and retrieval was 98.2%. The mean postprocedure angiographic diameter stenosis in the Pivotal group was reduced to 10.8%, while the overall procedure success rate (<50% residual diameter stenosis) after stent deployment was 98%. The 30 day composite major adverse event (MAE) rate for the entire cohort of 747 patients (i.e. inclusive of all 3 groups) was 5.8% (all death = 1.5%, all stroke = 4.4%, and all myocardial infarction (MI) = 1.0%). In subgroup analysis, there was no significant difference in the MAE rate between the three groups (P = 5.8%, R = 6.9%, B = 2.6%, P = 0.42). Conclusion: The similarity in periprocedural event rates for the Pivotal and Roll‐in groups suggests a flat learning curve for experienced operators using this carotid stent system. The similarity in event rates for the Bilateral group, when compared with the Roll‐in and Pivotal groups, suggests that staged sequential treatment of bilateral stenoses may be performed at the same risk as for unilateral lesions. The 30‐day safety of this stent and distal emboli protection system is encouraging and compares favorably with other carotid stent trials in high surgical risk patients. © 2006 Wiley‐Liss, Inc.
Dehydrodimerization of Isobutene to 2,5‐Dimethyl‐1,5‐Hexadiene over Bismuth‐(III)‐Oxide and Various Additives
Authors: Taubert T. , Scholz P. , Ondruschka B.
Published: March 2006

Bi2O3 and mixtures with different additives (Cr2O3, MoO3, NH4VO3, SnO2, and V2O5) have been chosen to study the oxidative dehydrodimerization of isobutene. The catalytic performances were investigated by variation of the residence time, isobutene to oxygen molar ratio, and pressure. The best results for 2,5‐dimethyl‐1,5‐hexadiene (DMH) yield (13 %) were achieved with Bi2O3 as the catalyst. The selectivity of DMH reaches values of over 90 %.
Mass Transfer during Solute Extraction from a Droplet with Internal Circulation in the Presence of a Constant Uniform Electric Field
Authors: Elperin T. , Fominykh A.
Published: March 2006

Mass transfer, under the influence of an constant uniform electric field in a ternary system, comprised of a transformed solute, a liquid dielectric continuous phase, and a stationary dielectric droplet, was considered in this study. The solubilities of the solute in the dispersed and continuous phases have the same order of magnitude, and the resistance to mass transfer in both phases is taken into account. The applied electric field causes Taylor circulation around the droplet, while the droplet deformation under the influence of the electric field is neglected. The problem is solved in the approximations of a thin concentration boundary layer in the dispersed and continuous phases. The bulk of a droplet, beyond the diffusion boundary layer, is completely mixed and the concentration of solute is homogeneous and time‐dependent in the bulk. The system of transient coupled equations of convective diffusion for solute transport in the dispersed and continuous phases with time‐dependent boundary conditions is solved by combining a generalized similarity transformation method with Duhamel's theorem; the solution is obtained in the form of a Volterra integral equation of the second kind. Numerical calculations essentially show an enhancement of the rate of mass transfer for dispersed liquid‐liquid systems, under the influence of an electric field.
MD Simulations of Diffusivities in Methanol‐n‐hexane Mixtures Near the Liquid‐liquid Phase Splitting Region
Authors: Krishna R. , van Baten J. M.
Published: March 2006

Molecular Dynamics (MD) simulations have been carried out to determine the self‐diffusivities in binary mixtures of methanol and n‐hexane with varying compositions at four different temperatures of 303.15 K, 307.7 K, 310.7 K, and 313.15 K. The Darken relation was used to determine both the Fick diffusivity and the Maxwell‐Stefan diffusivity. The values of the Fick diffusivity obtained from the simulations are in very good agreement with published experimental data of Clark and Rowley [17]. These diffusivities approach zero near composition regions where liquid‐liquid phase splitting occurs. On the other hand, the Maxwell‐Stefan diffusivity is well‐behaved and appears to be practically insensitive to the complex thermodynamics.
Preparation and Characterization of a Solid Acid Catalyst from Commercial Niobia Hydrate
Authors: Frank B. , Yildiz A. , Habel D. , Schubert H. , Schomäcker R.
Published: March 2006

A commercially available niobia hydrate, which is an industrial intermediate in the production of pure niobia, was prepared, characterized, and tested as a solid acid catalyst. The gas phase esterification of acetic acid with ethanol was used as a simple model reaction for the determination of the acidity and the catalytic activity. The kinetic evaluation of the experiments includes an estimation of mass transport limitation as well as a mechanistic study.
A Hybrid Scheme for the Solution of the Bivariate Spatially Distributed Population Balance Equation
Authors: Attarakih M. M. , Bart H.‐J. , Faqir N. M.
Published: March 2006

The advantages of the generalized fixed pivot technique as extended to mass transfer and the quadrature method of moments are hybridized to reduce the bivariate spatially distributed population balance equation describing the coupled hydrodynamics and mass transfer in liquid‐liquid extraction columns. The key idea in the hybridization technique is to use the available moments furnished by the generalized fixed pivot technique to find the abscissa and weights for the Gaussian‐quadrature based approach, in an attempt to evaluate the integrals over unknown droplet densities. To implement the quadrature method of moments efficiently, an explicit form for the abscissas and weights is derived based on the product‐difference algorithm as described by McGraw [1]. The proposed technique is found to reduce the discrete system of partial differential equations from 2 Mx + 1 to Mx + 2, where Mx is the number of pivots or classes. The spatial variable is discretized in a conservative form using a couple of recently published central difference schemes. The numerical predictions of the detailed and reduced models are found to be almost identical, accompanied by a substantial reduction of the CPU time as a characteristic of the hybrid model.
Mechanistic Studies of the Photocatalytic Oxidation of Trichloroethylene with Visible‐Light‐Driven N‐Doped TiO2 Photocatalysts
Authors: Joung Soon‐Kil , Amemiya Takashi , Murabayashi Masayuki , Itoh Kiminori
Published: March 2006

Visible‐light‐driven TiO2 photocatalysts doped with nitrogen have been prepared as powders and thin films in a cylindrical tubular furnace under a stream of ammonia gas. The photocatalysts thus obtained were found to have a band‐gap energy of 2.95 eV. Electron spin resonance (ESR) under irradiation with visible light (λ ≥ 430 nm) afforded the increase in intensity in the visible‐light region. The concentration of trapped holes was about fourfold higher than that of trapped electrons. Nitrogen‐doped TiO2 has been used to investigate mechanistically the photocatalytic oxidation of trichloroethylene (TCE) under irradiation with visible light (λ ≥ 420 nm). Cl and O radicals, which contribute significantly to the generation of dichloroacetyl chloride (DCAC) in the photocatalytic oxidation of TCE under UV irradiation, were found to be deactivated under irradiation with visible light. As the main by‐product, only phosgene was detected in the photocatalytic oxidation of TCE under irradiation with visible light. Thus, the reaction mechanism of TCE photooxidation under irradiation with visible light clearly differs markedly from that under UV irradiation. Based on the results of the present study, we propose a new reaction mechanism and adsorbed species for the photocatalytic oxidation of TCE under irradiation with visible light. The energy band for TiO2 by doping with nitrogen may involve an isolated band above the valence band.
Highly Enantioselective Addition of In Situ Prepared Arylzinc to Aldehydes Catalyzed by a Series of Atropisomeric Binaphthyl‐Derived Amino Alcohols
Authors: Lu Gui , Kwong Fuk Yee , Ruan Ji‐Wu , Li Yue‐Ming , Chan Albert S. C.
Published: March 2006

The direct addition of in situ prepared arylzinc to aldehydes with chiral binaphthyl‐derived amino alcohols as catalysts can afford optically active diarylmethanols in high yields and with excellent enantioselectivities (up to 99 % ee, ee=enantiomeric excess). By using a single catalyst, both enantiomers of many pharmaceutically interesting diarylmethanols can be obtained by the proper combination of various arylzinc reagents with different aldehydes; this catalytic system also works well for the phenylation of aliphatic aldehydes to give up to 96 % ee.
Bis(oxazoline) Lewis Acid Catalyzed Aldol Reactions of Pyridine N‐Oxide Aldehydes—Synthesis of Optically Active 2‐(1‐Hydroxyalkyl)pyridine Derivatives: Development, Scope, and Total Synthesis of an Indolizine Alkaloid
Authors: Landa Aitor , Minkkilä Anna , Blay Gonzalo , Jørgensen Karl Anker
Published: March 2006

A new, short, and simplified procedure for the synthesis of optically active pyridine derivatives from pro‐chiral pyridine‐N‐oxides is presented. The catalytic and asymmetric Mukaiyama aldol reaction between ketene silyl acetals and 1‐oxypyridine‐2‐carbaldehyde derivatives catalyzed by chiral copper(II)–bis(oxazoline) complexes gave optically active 2‐(hydroxyalkyl)‐ and 2‐(anti‐1,2‐dihydroxyalkyl)pyridine derivatives in good yields and diastereoselectivities, and in excellent enantioselectivities—up to 99 % enantiomeric excess. As a synthetic application of the developed method, a full account for the asymmetric total synthesis of a nonnatural indolizine alkaloid is provided.
Solvent effects on the conformational distribution and optical rotation of γ‐methyl paraconic acids and esters
Authors: Coriani S. , Baranowska A. , Ferrighi L. , Forzato C. , Marchesan D. , Nitti P. , Pitacco G. , Rizzo A. , Ruud K.
Published: March 2006

A computational investigation of the optical rotatory power of cis and trans 2‐methyl‐5‐oxo‐tetrahydro‐3‐furancarboxylic acids and the corresponding methyl and ethyl esters is presented. Solvent effects on both the conformational space and the rotatory power are analyzed by comparing results obtained in vacuo with those computed—using the Polarizable Continuum Model—in methanol. A comparison with experimental observations for the optical rotatory power of the title compounds in methanol is also carried out, in a few cases also for several wavelengths. Agreement between theory and experiment is in all cases excellent, in particular when solvent effects are included both in the geometry optimization and in the calculation of the OR, thus confirming the validity of the computational procedure adopted, even for this challenging family of floppy molecules. Chirality, 2006. © 2006 Wiley‐Liss, Inc.
Direct Epimetallation of π‐Bonded Organic Substrates with Titanium(II) Isopropoxide: Intermediacy of Biradical, Oligomeric Titanium(II) Reagents
Authors: Eisch John J. , Gitua John N. , Doetschman David C.
Published: March 2006

Extensive EPR experiments show that a titanium‐containing molecular triplet state is formed in solution by the reaction of two equivalents of butyllithium with one equivalent of titanium(IV) isopropoxide. At higher concentrations this product, titanium(II) isopropoxide, admixed with two equivalents of lithium isopropoxide, is accompanied by the formation of a variety of nontitanium‐containing side products. The powder EPR spectrum of the molecular triplet state in frozen solution is consistent with an asymmetric molecular chain of three Ti centers on which the unpaired electron centers are three metal atoms apart. Dilution experiments show that at lower concentrations, where the nontitanium‐containing side products have dissipated, the intensity of the molecular triplet spectrum varies approximately linearly with concentration. Thus there is no evidence that the observed triplet molecule is one component in a series of concentration‐dependent oligomerization steps. The bulky isopropoxy substituents and the coordination of the isopropoxide anions from the LiOiPr present appear to prevent closure of the Ti3 centers into an equilateral triangular diamagnetic structure. This steric hindrance, operative at the terminal diisopropoxytitanium centers and preventing closure to a ring, seems not to be observed with TiCl2·2THF, which is diamagnetic and may thus be expected to exist as an equilateral triangular cluster of three units of TiCl2·2THF, a structural model currently under further investigation. The smaller steric demand of the chloro and THF units would seem to permit octahedral coordination about each Ti center in such an equilateral trigonal array of Ti3 atoms. Chemical reactions carried out individually with diphenylacetylene, cis‐stilbene or cis‐stilbene oxide and titanium(II) diisopropoxide provide stoichiometric and stereochemical evidence that the attacking titanium(II) reagent is in fact the trimeric biradical. The role of the lithium isopropoxide byproduct in fostering the course of the previously reported SET reactions of titanium(II) isopropoxide and in determining the detailed structure of the open‐chain Ti trimer biradical has been explicated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Titanium Complexes of Dialkanolamine Ligands: Synthesis and Structure
Authors: Zaitsev Kirill V. , Karlov Sergey S. , Selina Anastasia A. , Oprunenko Yu. F. , Churakov Andrei V. , Neumüller Bernhard , Howard Judith A. K. , Zaitseva Galina S.
Published: March 2006

Synthesis of the title compounds, viz. [RN(CH2CH2O)(CHR1CR2R3O)]Ti(OiPr)2 (13–15) and [RN(CH2CH2O)(CHR1CR2R3O)]2Ti (18–28), by the reaction of one ortwo equivalents of the corresponding dialkanolamines RN(CH2CH2OH)(CHR1CR2R3OH) (1–12) with Ti(OiPr)4 is reported. Other routes to [RN(CH2CH2O)(CHR1CR2R3O)]2Ti, such as the reaction of Ti(CH2Ph)4 with dialkanolamine and the reaction of TiCl4(THF)2 with dialkanolamine/Et3N were also tested. Dimeric titanocane 16, [PhCH2N(CH2CH2O)2Ti(OMe)2]2, was obtained from the reaction of one equivalentof dialkanolamine 3 with CpTi(OMe)3. PhCH2N(CH2CH2O)2Ti(OMenth)2 (17) was prepared from the transalkoxylation reaction of 15 with two equivalents of menthol. The composition and structures of all novel compounds were established by 1H and 13C NMR spectroscopy as well as elemental analysis data. The possible solution structure features of 13–28 are discussed. The single‐crystal X‐ray diffraction study oftitanocane 16 clearly indicates a dimeric structure for this compound in the solid state. According to X‐ray data, compounds [PhCH2N(CH2CH2O)2]2Ti (19), [MeN(CH2CH2O)(CH2CHPhO)]2Ti (20), [MeN(CH2CH2O)(CH2CPh2O)]2Ti (23), erythro‐[MeN(CH2CH2O)(CHPhCHPhO)]2Ti (24), threo‐[MeN(CH2CH2O)(CHPhCHPhO)]2Ti (25), and {MeN(CH2CH2O)[CH(CH2)4CHO]}2Ti (27) possess a monomeric structure with a hexacoordinate titanium atom in the solid state. Among them complexes 19, 20, 23, 25, and 27 are characterized by a cis disposition of the nitrogen atoms in the coordination environment of the Ti atom, while nitrogen atoms in 24 occupy trans positions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)