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Chemical States (chemical + states)

Distribution by Scientific Domains
Polymers and Materials Science37%
Chemistry25%

Selected Abstracts

Effect of monomer composition on crystal growth by resin containing bioglass

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2010
Masanori Hashimoto
Abstract This study evaluated the effect of resin monomer composition on crystal growth at the interface between the resin/bioglass composites and water. Light-cured resin that contained 2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl], 2-hydroxyethyl methacrylate, and triethylene glycol dimethacrylate with different compositions were used. Resin/bioglass composites were prepared with 40 mass% bioglass and 60 mass% resin. The resin/bioglass composites were stored in deionized distilled water for 24 h (control group) or 3,12 months (experimental groups). After water storage, the disk surfaces were examined by light- and scanning electron microscopy. Chemical states of the crystals were analyzed by laser-Raman spectroscopy and micro-X-ray diffractometry. The microscopic analysis showed crystal on the resin disks surface after six months of water storage for hydrophilic resins. However, there was no crystal formation in the control and the experimental groups of specimens of hydrophobic resins. Raman analysis showed the chemical states of the crystals formed on the resin matrix and bioglass to be different. The micro-X-ray analysis of crystals on resin disks identified them to be calcium carbonate. This crystal formation occurred in water instead of simulated body fluid. In conclusion, the resin monomer compositions affected the ability to induce crystal growth on the surfaces of disks containing bioglass. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source]

Reaction characteristics of a tooth-bleaching agent containing H2O2 and NaF: in vitro study of crystal structure change in treated hydroxyapatite and chemical states of incorporated fluorine

INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2005
Y. Tanizawa
This in vitro study was performed to elucidate the reaction mechanism of sodium fluoride (NaF), which is added to tooth-bleaching agents to lessen the adverse effect of hydrogen peroxide (H2O2) on teeth. Both hydroxyapatite (HAP) and dihydrated dicalcium phosphate (DCPD), model substances for dental hard tissues, dissolved easily in a simple H2O2 solution. In the H2O2/NaF solutions, however, fluorine compounds that could not be identified by X-ray diffraction (XRD) due to the smallness of the products were formed on the surface of the HAP. X-ray photoelectron spectroscopy (XPS) studies demonstrated that fluoridated hydroxyapatite (FHAP) was formed on HAP, and that calcium fluoride (CaF2) formation was accelerated by increasing the concentrations of fluorine and H2O2 along with the partial dissolution of HAP. In H2O2/NaF solution, DCPD also transformed easily to FHAP and CaF2, which are favorable to the remineralization process on the tooth surface. Thus, the mechanism of NaF was elucidated, and its use together with H2O2 for tooth bleaching was proved to be effective. Methodologically, the XPS two-dimensional plot made it possible for the first time to directly estimate the ratio of FHAP and CaF2 in the reaction products, in contrast to the conventional wet-analytical method, which is simply based on the difference in solubility of the two components. [source]

Reaction characteristics of a tooth-bleaching agent containing H2O2 and NaF: in vitro study of crystal structure change in treated hydroxyapatite and chemical states of incorporated fluorine

INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 4 2005
Y. Tanizawa
This in vitro study was performed to elucidate the reaction mechanism of sodium fluoride (NaF), which is added to tooth-bleaching agents to lessen the adverse effect of hydrogen peroxide (H2O2) on teeth. Both hydroxyapatite (HAP) and dihydrated dicalcium phosphate (DCPD), model substances for dental hard tissues, dissolved easily in a simple H2O2 solution. In the H2O2/NaF solutions, however, fluorine compounds that could not be identified by X-ray diffraction (XRD) due to the smallness of the products were formed on the surface of the HAP. X-ray photoelectron spectroscopy (XPS) studies demonstrated that fluoridated hydroxyapatite (FHAP) was formed on HAP, and that calcium fluoride (CaF2) formation was accelerated by increasing the concentrations of fluorine and H2O2 along with the partial dissolution of HAP. In H2O2/NaF solution, DCPD also transformed easily to FHAP and CaF2, which are favorable to the remineralization process on the tooth surface. Thus, the mechanism of NaF was elucidated, and its use together with H2O2 for tooth bleaching was proved to be effective. Methodologically, the XPS two-dimensional plot made it possible for the first time to directly estimate the ratio of FHAP and CaF2 in the reaction products, in contrast to the conventional wet-analytical method, which is simply based on the difference in solubility of the two components. [source]

Effect of monomer composition on crystal growth by resin containing bioglass

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2010
Masanori Hashimoto
Abstract This study evaluated the effect of resin monomer composition on crystal growth at the interface between the resin/bioglass composites and water. Light-cured resin that contained 2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl], 2-hydroxyethyl methacrylate, and triethylene glycol dimethacrylate with different compositions were used. Resin/bioglass composites were prepared with 40 mass% bioglass and 60 mass% resin. The resin/bioglass composites were stored in deionized distilled water for 24 h (control group) or 3,12 months (experimental groups). After water storage, the disk surfaces were examined by light- and scanning electron microscopy. Chemical states of the crystals were analyzed by laser-Raman spectroscopy and micro-X-ray diffractometry. The microscopic analysis showed crystal on the resin disks surface after six months of water storage for hydrophilic resins. However, there was no crystal formation in the control and the experimental groups of specimens of hydrophobic resins. Raman analysis showed the chemical states of the crystals formed on the resin matrix and bioglass to be different. The micro-X-ray analysis of crystals on resin disks identified them to be calcium carbonate. This crystal formation occurred in water instead of simulated body fluid. In conclusion, the resin monomer compositions affected the ability to induce crystal growth on the surfaces of disks containing bioglass. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source]

An efficient algorithm for multistate protein design based on FASTER

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 5 2010
Benjamin D. Allen
Abstract Most of the methods that have been developed for computational protein design involve the selection of side-chain conformations in the context of a single, fixed main-chain structure. In contrast, multistate design (MSD) methods allow sequence selection to be driven by the energetic contributions of multiple structural or chemical states simultaneously. This methodology is expected to be useful when the design target is an ensemble of related states rather than a single structure, or when a protein sequence must assume several distinct conformations to function. MSD can also be used with explicit negative design to suggest sequences with altered structural, binding, or catalytic specificity. We report implementation details of an efficient multistate design optimization algorithm based on FASTER (MSD-FASTER). We subjected the algorithm to a battery of computational tests and found it to be generally applicable to various multistate design problems; designs with a large number of states and many designed positions are completely feasible. A direct comparison of MSD-FASTER and multistate design Monte Carlo indicated that MSD-FASTER discovers low-energy sequences much more consistently. MSD-FASTER likely performs better because amino acid substitutions are chosen on an energetic basis rather than randomly, and because multiple substitutions are applied together. Through its greater efficiency, MSD-FASTER should allow protein designers to test experimentally better-scoring sequences, and thus accelerate progress in the development of improved scoring functions and models for computational protein design. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]

Proofs of the Coexistence of Two Magnetic Contributions in Pure and Doped CaCu3Ti4O12 Giant Dielectric Constant Ceramics

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009
José Francisco Fernández
Fe3+ - or Nb5+ -doped CaCu3Ti4O12 (CCTO) ceramics show higher values of both room-temperature (RT) grain conductivity and dielectric constant than undoped ceramics. Microstructural and structural characterization combined with magnetic properties reveal the coexistence of two components that seem relevant for the dielectric behavior of the material. The grain possesses a nanostructure characterized by layered domains with thicknesses <80 nm. The formation of the layered domains is associated with the evidence of different chemical states as Cu2+/Cu+ and Ti4+/Ti3+ that are present in the material. The magnetic contribution is related to two coupled effects: the antiferromagnetic (AFM) response with TN=25 K ascribed to Cu2+, and a paramagnetic-like contribution attributed to Ti3+ cations. The coexistence of two coupled magnetic contributions could explain the proposed unusual coupling of the AFM Cu2+ superexchange interaction through the nonmagnetic Ti4+ rather than via the usual oxygen coupling. The lower the paramagnetic-like contribution at RT, the larger the conductivity and the dielectric constant of the material are. Below 150 K, the increase of the paramagnetic-like contribution is correlated with the low transition temperature of the CCTO. [source]

Chemical natures and distributions of metal impurities in multicrystalline silicon materials

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2006
T. Buonassisi
Abstract We present a comprehensive summary of our observations of metal-rich particles in multicrystalline silicon (mc-Si) solar cell materials from multiple vendors, including directionally-solidified ingot-grown, sheet, and ribbon, as well as multicrystalline float zone materials contaminated during growth. In each material, the elemental nature, chemical states, and distributions of metal-rich particles are assessed by synchrotron-based analytical x-ray microprobe techniques. Certain universal physical principles appear to govern the behavior of metals in nearly all materials: (a) Two types of metal-rich particles can be observed (metal silicide nanoprecipitates and metal-rich inclusions up to tens of microns in size, frequently oxidized), (b) spatial distributions of individual elements strongly depend on their solubility and diffusivity, and (c) strong interactions exist between metals and certain types of structural defects. Differences in the distribution and elemental nature of metal contamination between different mc-Si materials can largely be explained by variations in crystal growth parameters, structural defect types, and contamination sources. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Self-assembled Monolayers of n -Hexadecanoic Acid and ,-Hydroxyl n-Hexadecanoic Acid on Titanium Surfaces

CHINESE JOURNAL OF CHEMISTRY, Issue 12 2002
Hai-Gang Chen
Abstract n -Hexadecanoic acid (HA) and ,-hydroxyl n -hexadecanoic add (HHA) are shown to spontaneously assemble on Si-supported titanium surfaces. Contact angle measurements, reflection absorbance IR, AFM and XPS characterizations are performed to examine the physical and chemical states of attached monolayers. The results show that the two amphiphiles tend to form disordered monolayers on titanium surfaces. The HHA headgroups are believed to form polydentate coordination with Ti, which is more chemically stable than the bidentate coordination of HA. All the facts of characterization indicate that HHA monolayer has more surface coverage than HA monolayer. [source]