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Structural Units (structural + unit)
Kinds of Structural Units Selected AbstractsChemInform Abstract: Pentaatomic Tetracoordinate Planar Carbon, [CAl4]2- : A New Structural Unit and Its Salt Complexes.CHEMINFORM, Issue 4 2001Xi Li Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Kinetics Approximation Considering Different Reactivities of the Structural Units Formed by the Anionic Copolymerization of 1,3-Butadiene and Styrene Using Al/Li/Ba as InitiatorMACROMOLECULAR REACTION ENGINEERING, Issue 8 2009José. A. Tenorio López Abstract The copolymerization reaction of butadiene and styrene copolymers prepared by anionic living polymerization using an initiator composed of alkyl aluminum, n -butyl lithium, and barium alkoxide is studied using a kinetic model that considers the reactivity of active sites to be different; this assumption is justified by the varying geometric configurations. With the first-order Markov model, the expressions for the fraction of active sites and dyad distribution are obtained. The rate constants are determined by fitting to the conversion and Bernoulli dyad data using the nonlinear least squares method. The conversion and dyad sequence distribution are correctly predicted, and the experimental results indicate that the microstructure and sequence distribution do not change with the conversion and temperature. [source] Kinetics of the Anionic Polymerization of Buta-1,3-diene Considering Different Reactivities of the cis, trans and vinyl Structural UnitsMACROMOLECULAR REACTION ENGINEERING, Issue 5 2008José A. Tenorio López Abstract The anionic solution polymerization of buta-1,3-diene was modeled, considering the reactivity of the active sites to be different due to varying geometric configurations. With the first-order Markov model, expressions for the fraction of active sites and dyad distribution were obtained. The rate constants were determined by fitting to the conversion and dyad experimental data using the nonlinear least squares method. The kinetic model shows that the microstructure and the dyads do not depend on initiator and butadiene concentration but only on rate constants. Without a modifier, the butadiene addition mechanism is entropic; with a modifier, the mechanism changes to entropic-enthalpic. [source] Boronyls as Key Structural Units in Boron Oxide Clusters: B(BO) - 2 and B(BO) - 3CHEMINFORM, Issue 41 2007Hua-Jin Zhai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Electrophile-Induced Ether Transfer: A New Approach to Polyketide Structural Units.CHEMINFORM, Issue 10 2007Kai Liu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Low-Dimensional Structural Units in Amine-Templated Uranyl Oxoselenates(VI): Synthesis and Crystal Structures of [C3H12N2] [(UO2)(SeO4)2(H2O)2] (H2O) (I), [C5H16N2]2 [(UO2)(SeO4)2(H2O)] (NO3)2 (II), [C4H12N] [(UO2)(SeO4)(NO3)] (III), and [C4H14N2] [(UO2)(SeO4)2(H2O)] (IV).CHEMINFORM, Issue 47 2005Sergey V. Krivocochev Abstract For Abstract see ChemInform Abstract in Full Text. [source] Novel Cyclic 1,2-Diacetals Derived from (2R,3R)-(+)-Tartaric Acid: Synthesis and Application as N,O Ligands for the Enantioselective Alkylation of Benzaldehyde by DiethylzincEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2004M. Teresa Barros Abstract A chiral cyclic 1,2-diacetal derived from tartaric acid was used as the basic structural unit for novel ligands. Monooxazoline carbinols in which the degree of substitution of the alcohol and the nature of the stereocentre in the oxazoline ring were varied were synthesized in moderate to good yields. The influence of these structural factors on asymmetric induction was examined in the enantioselective addition of diethylzinc to benzaldehyde. Up to 60% ee was observed with a secondary or a tertiary alcohol as the metal-chelating group. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Cooling and inferred exhumation history of the Ryoke metamorphic belt in the Yanai district, south-west Japan: Constraints from Rb,Sr and fission-track ages of gneissose granitoid and numerical modelingISLAND ARC, Issue 2 2001Takamoto Okudaira Abstract The Ryoke metamorphic belt in south-west Japan consists mainly of I-type granitoids and associated low-pressure/high-temperature metamorphic rocks. In the Yanai district, it has been divided into three structural units: northern, central and southern units. In this study, we measured the Rb,Sr whole-rock,mineral isochron ages and fission-track ages of the gneissose granodiorite in the central structural unit. Four Rb,Sr ages fall in a range of ca 89,87 Ma. The fission-track ages of zircon and apatite are 68.9 ± 2.6 Ma and 57.4 ± 2.5 Ma (1, error), respectively. Combining the newly obtained ages with previously reported (Th,)U,Pb ages from the same unit, thermochronologic study revealed two distinctive cooling stages; 1) a rapid cooling (> 40°C/Myr) for a period (~7 Myr) soon after the peak metamorphism (~ 95 Ma) and 2) the subsequent slow cooling stage (~ 5°C/Myr) after ca 88 Ma. The first rapid cooling stage corresponds to thermal relaxation of the intruded granodiorite magma and its associated metamorphic rocks, and to the uplift by a displacement along low-angle faults which initiated soon after the intrusion of the magma. Uplift by the later stage deformation having formed large-scale upright folds resulted in progress of the exhumation during the first stage. The average exhumation velocity of the stage is , 2 mm/yr. During the second stage, the rocks were not accompanied by ductile deformation and were exhumed with the rate of 0.1,0.2 mm/yr. The difference in the exhumation velocity between the first and second cooling stages resulted from the difference in the thickness of the crust and in the activity of ductile deformation between the early and later stages of the orogenesis. [source] Alternating copolymerization of propylene oxide with carbon monoxide catalyzed by Co complex and Co/Ru complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2002Daisuke Takeuchi Abstract Co2(CO)8 catalyzes the ring-opening copolymerization of propylene oxide with CO to afford the polyester in the presence of various amine cocatalysts. The 1H and 13C{1H} NMR spectra of the polyester, obtained by the Co2(CO)8,3-hydroxypyridine catalyst, show the following structure [CH2CH(CH3)OCO]n. The Co2(CO)8,phenol catalyst gives the polyester, which contains the partial structural unit formed through the ring-opening copolymerization of tetrahydrofuran with CO. The bidentate amines, such as bipyridine and N,N,N,,N,-tetramethylethylenediamine, enhance the Co complex-catalyzed copolymerization, which produces the polyester with a regulated structure. Acylcobalt complexes, (RCO)Co(CO)n (R = Me or CH2Ph), prepared in situ, do not catalyze the copolymerization even in the presence of pyridine. This suggests that the chain growth involves the intermolecular nucleophilic addition of the OH group of the intermediate complex to the acyl,cobalt bond, forming an ester bond rather than the insertion of propylene oxide into the acyl,cobalt bond. Co2(CO)8Ru3(CO)12 mixtures also bring about the copolymerization of propylene oxide with CO. The molar ratio of Ru to Co affects the yield, molecular weight, and structure of the produced copolymer. The catalysis is ascribed to the RuCo mixed-metal cluster formed in the reaction mixture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4530,4537, 2002 [source] Kinetic Model for Crystallization in White Ceramic GlazesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2001Agustin Escardino Theoretical equations have been developed for crystal growth rate in layers of small frit (glass) particles during firing. Throughout the process, the crystalline and the glassy phases have different compositions; therefore, the system can be considered a pseudo-two-component system consisting of a crystallizable component (structural unit) and a noncrystallizable mixture of several components. The concentration of the crystallizable component decreases in the residual glassy phase during the crystal growth process, on integrating at the surfaces of crystals having the same composition. Throughout the crystal growth process, a concentration gradient of the crystallizable component is therefore produced in the glassy phase, which results in mass transport by diffusion of this component from the bulk residual glassy phase to the surfaces of the crystals. Equations have been derived assuming that the diffusion step of the crystallizable component through the residual glassy phase is the overall crystal growth process rate-controlling step. [source] Structural investigation of GeSb6Te10 and GeBi6Te10 intermetallic compounds in the chalcogenide homologous seriesACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2010Toshiyuki Matsunaga The crystal structures of GeSb6Te10 and GeBi6Te10 were scrutinized using an X-ray powder diffraction method, which revealed that these compounds crystallize in trigonally distorted cubic close-packed structures with a 51-layer period (). Each layer consists of a triangular atomic net; Te atoms occupy their own specific layers, whereas Ge, Sb and Bi atoms are located in the other layers. In these pseudobinary compounds, random atomic occupations of Ge and Sb/Bi are observed and the layers form two kinds of elemental structural blocks by their successive stacking along the c axis. These compounds can be presumed to be isostructural. It is known that the chemical formula of the chalcogenide compounds with the homologous structures found in these pseudobinary systems can be written as (GeTe)n(Sb2Te3)m or (GeTe)n(Bi2Te3)m (n, m: integer); the GeSb6Te10 and GeBi6Te10 investigated in this study, which correspond to the case in which n = 1 and m = 3, naturally have 3,×,l = 51-layer structures according to a formation rule l = 2n + 5m commonly found in the compounds of these chalcogenide systems (l represents the number of layers in the basic structural unit). Calculations based on the density functional theory revealed that these materials are compound semiconductors with very narrow band gaps. [source] Basic Types and Structural Characteristics of Uplifts: An Overview of Sedimentary Basins in ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Dengfa HE Abstract: The uplift is a positive structural unit of the crust It is an important window for continental dynamics owing to its abundant structural phenomena, such as fault, fold, unconformity and denudation of strata. Meanwhile, it is the very place to store important minerals like oil, natural gas, coal and uranium. Giant and large-scale oil and gas fields in China, such as the Daqing Oilfield, Lunnan-Tahe Oilfield, Penglai 19,3 Oilfield, Puguang Gas Field and Jingbian Gas Field, are developed mainly on uplifts. Therefore, it is the main target both for oil and gas exploration and for geological study. The uplift can be either a basement uplift, or one developed only in the sedimentary cover. Extension, compression and wrench or their combined forces may give rise to uplifts. The development process of uplifting, such as formation, development, dwindling and destruction, can be taken as the uplifting cycle. The uplifts on the giant Precambrian cratons are large in scale with less extensive structural deformation. The uplifts on the medium- and small-sized cratons or neo-cratons are formed in various shapes with strong structural deformation and complicated geological structure. Owing to changes in the geodynamic environment, uplift experiences a multi-stage or multi-cycle development process. Its geological structure is characterized in superposition of multi-structural layers. Based on the basement properties, mechanical stratigraphy and development sequence, uplifts can be divided into three basic types , the succession, superposition and destruction ones. The succession type is subdivided into the maintaining type and the lasting type. The superposition type can be subdivided into the composite anticlinal type, the buried-hill draped type, the faulted uplift type and the migration type according to the different scales and superimposed styles of uplifts in different cycles. The destruction type is subdivided into the tilting type and the negative inverted type. The development history of uplifts and their controlling effects on sedimentation and fluids are quite different from one another, although the uplifts with different structural types store important minerals. Uplifts and their slopes are the main areas for oil and gas accumulation. They usually become the composite oil and gas accumulation zones (belts) with multiple productive formations and various types of oil and gas reservoirs. [source] High Pressure Response of Rutile Polymorphs and Its Significance for Indicating the Subduction Depth of Continental CrustACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2008MENG Dawei Abstract: ,-PbO2 -type TiO2 (TiO2 -II) is an important index mineral for ultrahigh-pressure metamorphism. After the discovery of a natural high-pressure phase of titanium oxide with ,-PbO2 -structure in omphacite from coesite-bearing eclogite at Shima in the Dabie Mountains, China, a nano-scale (<2 nm) ,-PbO2 -type TiO2 has been identified through electron diffraction and high-resolution transmission electron microscopy in coesite-bearing jadeite quartzite at Shuanghe in the Dabie Mountains. The crystal structure is orthorhombic with lattice parameters a = 4.58times10,1 nm, b = 5.42times10,1 nm, c = 4.96times10,1 nm and space group Pbcn. The analysis results reveal that rutile {011}R twin interface is a basic structural unit of ,-PbO2 -type TiO2. Nucleation of ,-PbO2 -type TiO2 lamellae is caused by the displacement of one half of the titanium cations within the {011}R twin slab. This displacement reduces the Ti-O-Ti distance and is favored by high pressure. The identification of ,-PbO2 -type TiO2 in coesite-bearing jadeite quartzite from Shuanghe, Dabie Mountains, provides a new and powerful evidence of ultrahigh-pressure metamorphism at 4,7 GPa, 850°C-900°C, and implies a burial of continental crustal rocks to 130,200 kilometers depth or deeper. The ,-PbO2 -type TiO2 may be a useful indicator of the pressure and temperature in the diamond stability field. [source] A Polylinker Approach to Reductive Loop Swaps in Modular Polyketide SynthasesCHEMBIOCHEM, Issue 16 2008Laurenz Kellenberger Dr. Abstract Multiple versions of the DEBS 1-TE gene, which encodes a truncated bimodular polyketide synthase (PKS) derived from the erythromycin-producing PKS, were created by replacing the DNA encoding the ketoreductase (KR) domain in the second extension module by either of two synthetic oligonucleotide linkers. This made available a total of nine unique restriction sites for engineering. The DNA for donor "reductive loops," which are sets of contiguous domains comprising either KR or KR and dehydratase (DH), or KR, DH and enoylreductase (ER) domains, was cloned from selected modules of five natural PKS multienzymes and spliced into module 2 of DEBS 1-TE using alternative polylinker sites. The resulting hybrid PKSs were tested for triketide production in vivo. Most of the hybrid multienzymes were active, vindicating the treatment of the reductive loop as a single structural unit, but yields were dependent on the restriction sites used. Further, different donor reductive loops worked optimally with different splice sites. For those reductive loops comprising DH, ER and KR domains, premature TE-catalysed release of partially reduced intermediates was sometimes seen, which provided further insight into the overall stereochemistry of reduction in those modules. Analysis of loops containing KR only, which should generate stereocentres at both C-2 and C-3, revealed that the 3-hydroxy configuration (but not the 2-methyl configuration) could be altered by appropriate choice of a donor loop. The successful swapping of reductive loops provides an interesting parallel to a recently suggested pathway for the natural evolution of modular PKSs by recombination. [source] Natural alkaloids and synthetic relatives as chiral templates of the Orito's reactionCHIRALITY, Issue 1 2010Emília Tálas Abstract The enantioselective hydrogenation of methyl or ethyl pyruvate over cinchona-platinum catalyst system (Orito's reaction) is one of the most intensively studied heterogeneous catalytic asymmetric hydrogenation reactions. Studies aiming at systematic changes of the chiral template have played a crucial role in creating hypotheses for the mechanism of Orito's reaction. It is very important to clarify which structural unit of the alkaloid takes part in the enantiodifferentiation, and learn about the role of the different structural units of chiral templates. In this article, we made an attempt to describe the behavior of natural alkaloids, their synthetic derivatives, and analogues as chiral templates in the heterogeneous catalytic asymmetric hydrogenation of activated ketones. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] Impact of Kerogen Heterogeneity on Sorption of Organic Pollutants.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2009Abstract The overall goal of the present study was to establish correlations between organic pollutant sorption and physicochemical properties of kerogen materials. Three coal samples, each representing a typical kerogen type, were used as the starting materials. A thermal technique was employed to treat the kerogen materials under seven different temperatures ranging from 200 to 500C to simulate different diagenetic history. These samples were systematically characterized for their chemical compositions, functionalities, physical rigidity, and optical properties. The results showed that the chemical, spectroscopic, and optical microscopic properties of each kerogen series changed consistently as a function of treatment temperature or kerogen maturation. The oxygen-to-carbon atomic ratio decreased from 0.29, 0.12, and 0.07 for the original lignite (XF0), fusinite (HZ0), and lopinite (LP0) samples, respectively, to 0.07, 0.06, and 0.04 for XF7, HZ7, and LP7, respectively, that underwent the highest temperature treatment. The hydrogen-to-carbon atomic ratio exhibited similar reducing trend, which is consistent with the aromaticity increasing from 45 to 58% of the original samples to 76 to 81% of highly mature samples. Under the fluorescence microscope, the organic matrix changed from yellow (original lignite sample) and red-brown (original lopinite sample) to colorless for the samples of higher maturation. The measured reflecting index increased from the original samples to the highly mature samples. Moreover, the original and the slightly matured samples exhibited very different chemical compositions and structural units among the three types due to the difference in their source materials. As the kerogen maturation increased, such differences decreased, indicating highly mature kerogen became homogenized regardless of the source material. [source] Molecular-feature domains with posterodorsal,anteroventral polarity in the symmetrical sensory maps of the mouse olfactory bulb: mapping of odourant-induced Zif268 expressionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2002Koichiro Inaki Abstract Individual glomeruli in the mammalian olfactory bulb presumably represent a single type of odourant receptor. Thus, the glomerular sheet provides odourant receptor maps at the surface of the olfactory bulb. To understand the basic spatial organization of the olfactory sensory maps, we first compared the spatial distribution of odourant-induced responses measured by the optical imaging of intrinsic signals with that detected immunohistochemically by expressions of Zif268, one of the immediate early gene products in juxtaglomerular cells. In the dorsal surface of the bulb, we detected a clear correlation in the spatial pattern between these responses. In addition, the molecular-feature domains and their polarities (spatial shifts of responses with an increase in carbon chain length) that were defined by the optical imaging method could be also detected by the Zif268 mapping method. We then mapped the Zif268 signals over the entire olfactory bulb using a homologous series of fatty acids and aliphatic alcohols as stimulus odourants. We superimposed the Zif268 signals onto the standard unrolled map with the help of cell adhesion molecule compartments. Each odourant typically elicited two pairs of clusters of dense Zif268 signals. The results showed that molecular-feature domains and their polarities were arranged symmetrically at stereotypical positions in a mirror-image fashion between the lateral and the medial sensory maps. The polarity of each domain was roughly in parallel with the posterodorsal,anteroventral axis that was defined by the cell adhesion molecule compartments. These results suggest that the molecular-feature domain with its fixed polarity is one of the basic structural units in the spatial organization of the odourant receptor maps in the olfactory bulb. [source] Ordered Mesoporous Silica Derived from Layered SilicatesADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Tatsuo Kimura Abstract Here, the development of ordered mesoporous silica prepared by the reaction of layered silicates with organoammonium surfactants is reviewed. The specific features of mesoporous silica are discussed with relation to the probable formation mechanisms. The recent understanding of the unusual structural changes from the 2D structure to periodic 3D mesostructures is presented. The formation of mesophase silicates from layered silicates with single silicate sheets depends on combined factors including the reactivity of layered silicates, the presence of layered intermediates, the variation of the silicate sheets, and the assemblies of surfactant molecules in the interlayer spaces. FSM-16-type (p6mm) mesoporous silica is formed via layered intermediates composed of fragmented silicate sheets and alkyltrimethylammonium (CnTMA) cations. KSW-2-type (c2mm) mesoporous silica can be prepared through the bending of the individual silicate sheets with intralayer and interlayer condensation. Although the structure of the silicate sheets changes during the reactions with CnTMA cations in a complex manner, the structural units caused by kanemite in the frameworks are retained. Recent development of the structural design in the silicate framework is very important for obtaining KSW-2-based mesoporous silica with molecularly ordered frameworks. The structural units originating from layered silicates are chemically designed and structurally stabilized by direct silylation of as-synthesized KSW-2. Some proposed applications using these mesoporous silica are also summarized with some remarks on the uniqueness of the use of layered silicates by comparison with MCM-type mesoporous silica. [source] Histomorphometric assessment of bone turnover in uraemic patients: comparison between activation frequency and bone formation rateHISTOPATHOLOGY, Issue 6 2001P Ballanti Histomorphometric assessment of bone turnover in uraemic patients: comparison between activation frequency and bone formation rate Aims:,The histomorphometric assessment of bone formation rate (BFR/BS) in bone biopsies from uraemic patients is of crucial importance in differentiating low from high turnover types of renal osteodystrophy. However, since BFR/BS relies on osteoblasts, activation frequency (Ac.f), encompassing all remodelling phases, has recently been preferred to BFR/BS. This study was carried out to consider whether estimation of Ac.f is superior, in practical terms, to that of BFR/BS in distinguishing between different rates of bone turnover in uraemic patients. Methods and results:,Bone biopsies from 27 patients in predialysis (20 men and seven women; mean age 53 ± 12 years) and 37 in haemodialysis (22 men and 15 women; mean age 53 ± 12 years) were examined. The types of renal osteodystrophy were classified on the basis of morphology. Bone formation rate and Ac.f were evaluated according to standardized procedures. The Ac.f was calculated both as a ratio between BFR/BS and wall thickness (W.Th) and as a reciprocal of erosion, formation and quiescent periods (EP, FP and QP). Patients were affected by renal osteodystrophy with predominant hyperparathyroidism (two predialysis and 16 dialysis), predominant osteomalacia (three predialysis and seven dialysis) or that of advanced (nine predialysis and five dialysis) or mild (seven predialysis and four dialysis) mixed type or adynamic type (six predialysis and five dialysis). Activation frequency, which with either formula requires the measurement of W.Th, i.e. the thickness of bone structural units (BSUs), was not calculated in three dialysis patients with severe hyperparathyroidism and in one predialysis and four dialysis patients with severe osteomalacia, because only incomplete BSUs were found. In dialysis, EP was higher in the adynamic than in the other types of osteodystrophy. During both predialysis and dialysis, FP was higher in osteomalacia than in the other forms of osteodystrophy, and in adynamic osteopathy than in hyperparathyroidism or in advanced and mild mixed osteodystrophy. During predialysis and dialysis, QP was higher in the adynamic than in the other forms of osteodystrophy. Correlations were found between BFR/BS and Ac.f, during predialysis (r=0.97) and dialysis (r=0.95). Conclusions:,The superiority of Ac.f in assessing bone turnover, in comparison to BFR/BS, is conceptual rather than practical. The highest values for FP in osteomalacia and for QP in adynamic bone allow a clearer characterization of these low turnover conditions. [source] Fluorescence spectra of Pr3+ ions in phosphate materials calculated by the DVME methodINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2009Y. Kowada Abstract Recently, fluorescence spectra of rare-earth ions in oxide materials are very attractive for the applications of the optical amplification in optical fiber communications, white LED, etc. However, it has been difficult to calculate the fluorescence spectra of rare-earth ions by the first principle method. In this study, we used the relativistic discrete-variational multielectron (DVME) method, which is a configuration-interaction (CI) calculation program using the molecular orbitals obtained by the relativistic DV-X, method. We applied this method for the calculation of the fluorescence spectrum of the Pr3+ ions in phosphate materials. The transition probability of the fluorescence was calculated in the same manner of the absorption. The obtained theoretical fluorescence spectrum was in good agreement with the experimental one, though the intensity of each peak was deeply dependent on the configuration of the surrounding structural units. The results suggested that the DVME method was useful for the calculation of not only absorption but also fluorescence spectra of rare-earth ions in oxide materials. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Structural motifs in ,-pyridyl- and ,-furylcinnamic acid assemblies, A molecular modeling studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2001I. Pálinkó Abstract The aggregation properties of stereoisomeric 2-(3,-furyl)-3-phenylpropenoic acids (FU3E, FU3Z, ,-furylcinnamic acids) and 2-(4,-pyridyl)-3-phenylpropenoic acids (PY4E, PY4Z, ,-pyridylcinnamic acids) were studied by the PM3 semiempirical quantum chemical method. Calculations revealed that (aromatic)CH,N(O) hydrogen bonds made possible the attachment of dimer units; thus, virtually infinite chains can be built out of FU3Z, PY4E, and PY4Z. The energy-minimized structure had zig-zag configuration. PY4Z dimers allowed the formation of ribbonlike network; however, the number of structural units could not be increased infinitely. One of the furyl derivatives (FU3E) could not be stabilized either in the ribbon or the chain form; however, (aromatic)CH,, or (aromatic),,(aromatic), interactions contribute to the packing pattern of the two dimers. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 269,275, 2001 [source] Structure of Sumatra and its implications for the tectonic assembly of Southeast Asia and the destruction of PaleotethysISLAND ARC, Issue 1 2009Anthony J. Barber Abstract It is now generally accepted that Southeast Asia is composed of continental blocks which separated from Gondwana with the formation of oceanic crust during the Paleozoic, and were accreted to Asia in the Late Paleozoic or Early Mesozoic, with the subduction of the intervening oceanic crust. From east to west the Malay peninsula and Sumatra are composed of three continental blocks: East Malaya with a Cathaysian Permian flora and fauna; Sibumasu, including the western part of the Malay peninsula and East Sumatra, with Late Carboniferous,Early Permian ,pebbly mudstones' interpreted as glaciogenic diamictites; and West Sumatra, again with Cathaysian fauna and flora. A further unit, the Woyla nappe, is interpreted as an intraoceanic arc thrust over the West Sumatra block in the mid Cretaceous. There are varied opinions concerning the age of collision of Sibumasu with East Malaya and the destruction of Paleotethys. In Thailand, radiolarites have been used as evidence that Paleotethys survived until after the Middle Triassic. In the Malay peninsula, structural evidence and the ages of granitic intrusions are used to support a Middle Permian to Early Triassic age for the destruction of Paleotethys. It is suggested that the West Sumatra block was derived from Cathaysia and emplaced against the western margin of Sibumasu by dextral transcurrent faulting along a zone of high deformation, the Medial Sumatra Tectonic Zone. These structural units can be traced northwards in Southeast Asia. The East Malaya block is considered to be part of the Indochina block, Sibumasu can be traced through Thailand into southern China, the Medial Sumatra Tectonic Zone is correlated with the Mogok Belt of Myanmar, the West Burma block is the extension of the West Sumatra block, from which it was separated by the formation of the Andaman Sea in the Miocene, and the Woyla nappe is correlated with the Mawgyi nappe of Myanmar. [source] Subdivision of the Sanbagawa pumpellyite,actinolite facies region in central Shikoku, southwest JapanISLAND ARC, Issue 3 2008Masumi Sakaguchi Abstract The mineral assemblages of the pumpellyite,actinolite facies such as pumpellyite + actinolite + epidote + chlorite or actinolite + epidote + hematite + chlorite occur in the Sanbagawa low-grade metamorphic region, central Shikoku, southwest Japan. Chemical compositions of these minerals from the eight newly studied areas were analyzed in order to evaluate the areal extent and thermal structure of the region. In the buffered assemblage of pumpellyite + actinolite + epidote + chlorite, the Fe3+/(Fe3+ + Al) values of epidote decrease slightly with decreasing Fe2+/(Fe2+ + Mg) values for chlorite. The changes in these values show a general correlation with temperature. The presence of this relationship implies that the Fe3+/(Fe3+ + Al) values of epidote can be used to divide the Sanbagawa low-grade metamorphic region into low-, medium- and high-grade subzones. The areal distribution of these subzones indicates that: (i) the temperature seems to decrease in the same sense as envisaged by the zonal mapping of the higher-grade pelitic schists; and (ii) there is no significant gap of metamorphic conditions through the boundary between the two structural units (Besshi and Oboke units). It follows that the Sanbagawa low-grade metamorphic region decreases in temperature going up the structural section, and tectonic discontinuities have not affected the thermal structure. [source] Cooling and inferred exhumation history of the Ryoke metamorphic belt in the Yanai district, south-west Japan: Constraints from Rb,Sr and fission-track ages of gneissose granitoid and numerical modelingISLAND ARC, Issue 2 2001Takamoto Okudaira Abstract The Ryoke metamorphic belt in south-west Japan consists mainly of I-type granitoids and associated low-pressure/high-temperature metamorphic rocks. In the Yanai district, it has been divided into three structural units: northern, central and southern units. In this study, we measured the Rb,Sr whole-rock,mineral isochron ages and fission-track ages of the gneissose granodiorite in the central structural unit. Four Rb,Sr ages fall in a range of ca 89,87 Ma. The fission-track ages of zircon and apatite are 68.9 ± 2.6 Ma and 57.4 ± 2.5 Ma (1, error), respectively. Combining the newly obtained ages with previously reported (Th,)U,Pb ages from the same unit, thermochronologic study revealed two distinctive cooling stages; 1) a rapid cooling (> 40°C/Myr) for a period (~7 Myr) soon after the peak metamorphism (~ 95 Ma) and 2) the subsequent slow cooling stage (~ 5°C/Myr) after ca 88 Ma. The first rapid cooling stage corresponds to thermal relaxation of the intruded granodiorite magma and its associated metamorphic rocks, and to the uplift by a displacement along low-angle faults which initiated soon after the intrusion of the magma. Uplift by the later stage deformation having formed large-scale upright folds resulted in progress of the exhumation during the first stage. The average exhumation velocity of the stage is , 2 mm/yr. During the second stage, the rocks were not accompanied by ductile deformation and were exhumed with the rate of 0.1,0.2 mm/yr. The difference in the exhumation velocity between the first and second cooling stages resulted from the difference in the thickness of the crust and in the activity of ductile deformation between the early and later stages of the orogenesis. [source] Analysis of scattering from polydisperse structure using Mellin convolutionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2006Norbert Stribeck This study extends a mathematical concept for the description of heterogeneity and polydispersity in the structure of materials to multiple dimensions. In one dimension, the description of heterogeneity by means of Mellin convolution is well known. In several papers by the author, the method has been applied to the analysis of data from materials with one-dimensional structure (layer stacks or fibrils along their principal axis). According to this concept, heterogeneous structures built from polydisperse ensembles of structural units are advantageously described by the Mellin convolution of a representative template structure with the size distribution of the templates. Hence, the polydisperse ensemble of similar structural units is generated by superposition of dilated templates. This approach is particularly attractive considering the advantageous mathematical properties enjoyed by the Mellin convolution. Thus, average particle size, and width and skewness of the particle size distribution can be determined from scattering data without the need to model the size distributions themselves. The present theoretical treatment demonstrates that the concept is generally extensible to dilation in multiple dimensions. Moreover, in an analogous manner, a representative cluster of correlated particles (e.g. layer stacks or microfibrils) can be considered as a template on a higher level. Polydispersity of such clusters is, again, described by subjecting the template structure to the generalized Mellin convolution. The proposed theory leads to a simple pathway for the quantitative determination of polydispersity and heterogeneity parameters. Consistency with the established theoretical approach of polydispersity in scattering theory is demonstrated. The method is applied to the best advantage in the field of soft condensed matter when anisotropic nanostructured materials are to be characterized by means of small-angle scattering (SAXS, USAXS, SANS). [source] Isolation and chemical structure characterization of enzymatic lignin from Populus deltoides woodJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Ali Abdulkhani Abstract Cellulytic enzymes were used for the isolation and structural characterization of Populus deltoides wood lignin as a fast growing and important species in wood processing technology. The isolation was based on the hydrolysis and partial solubilization of wood xylan and cellulose using combination of Thricoderma lanuginosus xylanase, Aspergillus sp. plus, A. niger cellulase, and almond glycosidase, followed by lignin purification using Bacillus licheniformis alkaline protease (for hydrolysis of cellulase contamination). The structure of enzymatic lignin (EL) was elucidated using chemical analysis, Py-GC/MS, FTIR, and quantitative 13C-NMR techniques. Different lignin structures of acetylated and nonacetylated lignin preparation were calculated. P. deltoides EL has been determined to have an h : g : s ratio of 5 : 60 : 35. Also, P. deltoides EL contained 0.59/Ar of ,-O-4 moieties with small amounts of other structural units such as pino/syringyresinol (0.05/Ar), phenylcoumaran (0.05/Ar), and spirodienone (0.01/Ar). The degree of condensation was estimated at 20%. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Method for preparing polyaluminocarbosilaneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Guomei He Abstract Polyaluminocarbosilane (PACS) was synthesized directly by the one-pot reaction of polydimethylsilane (PDMS) with aluminum acetylacetonate [Al(acac)3] in an autoclave. In this closed system, all the aluminum in Al(acac)3 was converted into PACS. Therefore, the content of aluminum could be readily controlled quantitatively. On the basis of Fourier transform infrared, 1H-NMR, 13C-NMR, 29Si-NMR, and 27Al magic-angle spinning NMR analysis, the reaction mechanism was proposed as follows: PDMS dissociated during pyrolysis to generate silicon free radicals, and then they reacted with Al(acac)3 to yield PACS containing (SiO)nAl groups (n = 4, 5, or 6). Meanwhile, these reactions resulted in the cleavage of OC and/or OC bonds in Al(acac)3. Some of the free-radical fragments generated by this cleavage continued to react with the silicon free radicals and were incorporated into the structural units of PACS; the rest of them may have been converted into small oxygen-containing compounds, which were removed in the subsequent processing after the reactions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Irreversible Perforations in Vertebral Trabeculae?,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 7 2003X Banse In human cancellous bone, osteoclastic perforations resulting from normal remodeling were generally considered irreversible. In human vertebral samples, examined by backscatter electron microscopy, there was clear evidence of bridging of perforation defects by new bone formation. Hence trabecular perforations may not be irreversible. Introduction: Preservation of the trabecular bone microarchitecture is essential to maintain its load-bearing capacity and prevent fractures. However, during bone remodeling, the osteoclasts may perforate the platelike trabeculae and disconnect the structure. Large perforations (>100 ,m) are generally considered irreversible because there is no surface on which new bone can be laid down. In this work, we investigated the outcome of these perforations on human vertebral cancellous bone. Materials and Methods: Using backscatter electron microscopy, we analyzed 264 vertebral bone samples from the thoracic and lumbar spine of nine subjects (44,88 years old). Nine fields (2 × 1.5 mm) were observed on each block. Several bone structural units (BSUs) were visible on a single trabecula, illustrating a dynamic, historical aspect of bone remodeling. A bridge was defined as a single and recent BSU connecting two segments of trabeculae previously separated by osteoclastic resorption. They were counted and measured (length and breadth, ,m). Results and Conclusion: We observed 396 bridges over 2376 images. By comparison, we found only 15 microcalluses on the same material. The median length of the bridge was 165 ,m (range, 29,869 ,m); 86% being longer than 100 ,m and 35% longer than 200 ,m. Their breadth was 56 ,m (range, 6,255 ,m), but the thinnest were still in construction. Bridges were found in all nine subjects included in the study, suggesting that it is a common feature of normal vertebral bone remodeling. These observations support the hypothesis that perforation could be repaired by new bone formation. and hence, might not be systematically irreversible. [source] Transition metal,boron complexes BnM: From bowls (n = 8,14) to tires (n = 14)JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2006Si-Dian Li Abstract Transition metal,boron complexes BnM have been predicted at density functional theory level to be molecular bowls (n = 8,14) hosting a transition metal atom (M) inside or molecular tires (n = 14) centered with a transition metal atom. Small Bn clusters prove to be effective inorganic ligands to all the VB,VIIIB transition metal elements in the periodic table. Density functional evidences obtained in this work strongly suggest that bowl-shaped fullerene analogues of Bn units exist in small BnM complexes and the bowl-to-tire structural transition occur to the first-row transition metal complexes BnM (M = Mn, Fe, Co) at n = 14, a size obviously smaller than n = 20 where the 2D-3D structural transition occurs to bare Bn. The half-sandwich-type B12Cr (C3v), full sandwich-type (B12)2Cr (D3d), bowl-shaped B14Fe (C2), and tire-shaped B14Fe (D7d) and B14Fe, (C7v) are the most interesting prototypes to be targeted in future experiments. These BnM complexes may serve as building blocks to form extended boron-rich BnMm tubes or cages (m , 2) or as structural units to be placed inside carbon nanotubes with suitable diameters. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2006 [source] Synthesis and characterization of new alternating, amphiphilic, comblike copolymers of poly(ethylene oxide) macromonomer and N -phenylmaleimideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2005Luminita Cianga Abstract A surface-active p -vinyl benzyloxy-,-hydroxy-poly(ethylene oxide) macromonomer containing 22 pendant structural units of ethylene oxide (St,PEO22) was synthesized with an initiation method. Because of its solubility in a large variety of solvents, the free-radical copolymerization with electron-acceptor N -phenylmaleimide (NPMI) was performed at 60 °C in benzene and tetrahydrofuran (THF) as isotropic media and in a water,THF mixture or water as a heterogeneous medium. Oil-soluble 2,2,-azobisisobutyronitrile and water-soluble 4,4,-azobis(4-cyanovaleric acid) were used as the initiators at fixed concentrations. Two different St,PEO22/NPMI comonomer ratios (1/1 and 3/7) at a fixed total comonomer concentration in the polymerization system were used. The structures, compositions, and microstructure peculiarities of the obtained alternating, amphiphilic, comblike copolymers were determined by NMR analysis. For the copolymers synthesized in hydrophilic media, differential scanning calorimetry showed, near the endothermic peak attributed to the melting of the poly(ethylene oxide) side chains, the presence of a second peak due to the partially ordered phase that could exist between the crystalline state and the isotropic melt. Also, the thermal stability of the obtained copolymers was studied with thermogravimetric analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 479,492, 2005 [source] | |||||||||||||||||||||||||||||||||||||||||||