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Effect of copper ions on the degradation of thiram in aqueous solution: identification of degradation products by HPLC–MS/MS

Filipe, Olga M. S.; Santos, Sónia A. O.; Domingues, M. Rosário M.; Vidal, Maria. M.; Silvestre, Armando J. D.; Santos, Eduarda B. H.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
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The aim of this work was to examine the effect of Cu(II) on the degradation of thiram (Thi) in aqueous solutions, since the literature focused on this effect is scarce and copper based fungicides can be applied together with thiram or during the same season to agricultural crops. The effect of Cu(II) on the degradation of thiram was followed by both UV–vis and HPLC–MS/MS. When thiram is dissolved in pure water its degradation occurs very slowly, being negligible during the first 7 days. However, the presence of Cu(II) has a strong influence on the thiram degradation in aqueous solutions along time. In the presence of an excess of Cu(II), a [CuThi]2+ complex is initially formed which degrades into a complex formed between the dimethyldithiocarbamate anion (DMDTC) and Cu(II) ion, [Cu(DMDTC)]+. This complex further degrades leading to other copper complexes which were identified for the first time, by MSn. The results obtained in the present work also demonstrated that a redox reaction involving DMDTC anions and Cu(II) ions gives rise to the formation of a Thi–Cu(I) complex. Finally, some of the complexes resulting from the degradation of [CuThi]2+ are quite persistent in solution for long periods of time (>1 month).

Photophysics and photostability of adenine in aqueous solution: A theoretical study

LUDWIG, Valdemir; COSTA, Zelia M. da; AMARAL, Marcos Serrou do; BORIN, Antonio Carlos; CANUTO, Sylvio Roberto Accioly; SERRANO-ANDRES, Luis
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
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The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission processes from the lowest-lying pi pi * and n pi * excited states of 9H-adenine in aqueous solution. It is found that conical intersections connecting the pi pi* and n pi* states with the ground state are also present in solution, whereas the barriers for the deactivation paths are significantly smaller on solvated conditions. The large destabilization of the n pi* state found in solution possibly prevents its involvement in the deactivation photophysics and explains the change from a bi- to a mono-exponential decay for the molecule in the gas phase and solution, respectively. (C) 2010 Elsevier B.V. All rights reserved.; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Spanish MEC/FEDER [CTQ2007-61260, CSD2007-0010, CTQ2010-14892]

Formation of SnO2 gels from dispersed sols in aqueous colloidal solutions

Satoshi Hiratsuka, Renato; Helena Pulcinelli, Sandra; Valentim Santilli, Celso
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 76-83
ENG
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Transparent SnO2 gels were obtained from SnCl4 aqueous solution. The sol formation from tin oxihydroxy peptization in different concentrations and by electrolyte addition in solution was measured. It was verified that the residual presence of chloride ions compromises the colloidal system stability. The sol-gel transition was investigated as a function of the quantity of solid particles in the aqueous environment and of aging time at 60°C by infrared spectroscopy and rheological measurements. The transition from plastic to pseudoplastic flow observed with the increase in loading suggests that a continuous and three-dimensional network formation is closely related to hydrogen bridges and/or hydrogen clusters, culminating in the gel formation. © 1990.

The thermodynamically stable state of myelin basic protein in aqueous solution is a flexible coil.

Gow, A; Smith, R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/01/1989 EN
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Conformational studies of myelin basic protein (MBP) in solution generally have used protein purified in organic solvents and acid. The use of such conditions raises the possibility that the secondary structure reported for the basic protein represents a denatured state. Therefore we have purified this protein by using a procedure that avoids denaturants. Bovine myelin was extracted with 0.2 M-CaCl2 and the protein was purified from the supernatant by chromatography on Sephadex G-75. The conformation of the basic protein was characterized by using c.d. and 1H-n.m.r. spectroscopy. In solution, it appeared to be predominantly randomly coiled, with only small segments of persistent structure. However, in the presence of myristoyl lysophosphatidylcholine the secondary structure of MBP became more ordered, and sedimentation-velocity experiments showed that MBP aggregated. Comparison of our results with published data indicates that Ca2+-extracted basic protein behaves similarly to the protein purified by traditional methods with respect to its ordered conformation in solution in the absence and in the presence of lipid and with respect to its self-association. Thus its thermodynamically stable structure in aqueous solution appears to be a highly flexible coil.

Competing interactions contributing to alpha-helical stability in aqueous solution.

Bodkin, M. J.; Goodfellow, J. M.
Fonte: Cold Spring Harbor Laboratory Press Publicador: Cold Spring Harbor Laboratory Press
Tipo: Artigo de Revista Científica
Publicado em /04/1995 EN
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The stability of a 15-residue peptide has been investigated using CD spectroscopy and molecular simulation techniques. The sequence of the peptide was designed to include key features that are known to stabilize alpha-helices, including ion pairs, helix dipole capping, peptide bond capping, and aromatic interactions. The degree of helicity has been determined experimentally by CD in three solvents (aqueous buffer, methanol, and trifluoroethanol) and at two temperatures. Simulations of the peptide in the aqueous system have been performed over 500 ps at the same two temperatures using a fully explicit solvent model. Consistent with the CD data, the degree of helicity is decreased at the higher temperature. Our analysis of the simulation results has focused on competition between different side-chain/side-chain and side-chain/main-chain interactions, which can, in principle, stabilize the helix. The unfolding in aqueous solution occurs at the amino terminus because the side-chain interactions are insufficient to stabilize both the helix dipole and the peptide hydrogen bonds. Loss of capping of the peptide backbone leads to water insertion within the first peptide hydrogen bond and hence unfolding. In contrast, the carboxy terminus of the alpha-helix is stable in both simulations because the C-terminal lysine residue stabilizes the helix dipole...

Simulating Monovalent and Divalent Ions in Aqueous Solution Using a Drude Polarizable Force Field

Yu, Haibo; Whitfield, Troy W.; Harder, Edward; Lamoureux, Guillaume; Vorobyov, Igor; Anisimov, Victor M.; MacKerell, Alexander D.; Roux, Benoît
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
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An accurate representation of ion solvation in aqueous solution is critical for meaningful computer simulations of a broad range of physical and biological processes. Polarizable models based on classical Drude oscillators are introduced and parametrized for a large set of monoatomic ions including cations of the alkali metals (Li+, Na+, K+, Rb+ and Cs+) and alkaline earth elements (Mg2+, Ca2+, Sr2+ and Ba2+) along with Zn2+ and halide anions (F−, Cl−, Br− and I−). The models are parameterized, in conjunction with the polarizable SWM4-NDP water model [Lamoureux et al., Chem. Phys. Lett. 418, 245 (2006)], to be consistent with a wide assortment of experimentally measured aqueous bulk thermodynamic properties and the energetics of small ion-water clusters. Structural and dynamic properties of the resulting ion models in aqueous solutions at infinite dilution are presented.

Supercharging Protein Complexes from Aqueous Solution Disrupts their Native Conformations

Sterling, Harry J.; Kintzer, Alexander F.; Feld, Geoffrey K.; Cassou, Catherine A.; Krantz, Bryan A.; Williams, Evan R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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The effects of aqueous solution supercharging on the solution- and gas-phase structures of two protein complexes were investigated using traveling-wave ion mobility-mass spectrometry (TWIMS-MS). Low initial concentrations of m-nitrobenzyl alcohol (m-NBA) in the electrospray ionization (ESI) solution can effectively increase the charge of concanavalin A dimers and tetramers, but at higher m-NBA concentrations, the increases in charge are accompanied by solution-phase dissociation of the dimers and up to a ~22% increase in the collision cross section (CCS) of the tetramers. With just 0.8% m-NBA added to the ESI solution of a ~630 kDa anthrax toxin octamer complex, the average charge is increased by only ~4% compared to the “native” complex, but it is sufficiently destabilized so that extensive gas-phase fragmentation occurs in the relatively high pressure regions of the TWIMS device. Anthrax toxin complexes exist in either a pre-channel or a transmembrane channel state. With m-NBA, the prechannel state of the complex has the same CCS/charge ratio in the gas phase as the transmembrane channel state of the same complex formed without m-NBA, yet undergoes extensive dissociation, indicating that destabilization from supercharging occurs in the ESI droplet prior to ion formation and is not a result of coulombic destabilization in the gas phase as a result of higher charging. These results demonstrate that the supercharging of large protein complexes is the result of conformational changes induced by the reagents in the ESI droplets where enrichment of the supercharging reagent during droplet evaporation occurs.

A Fiber-Optic Sensor Using an Aqueous Solution of Sodium Chloride to Measure Temperature and Water Level Simultaneously

Yoo, Wook Jae; Sim, Hyeok In; Shin, Sang Hun; Jang, Kyoung Won; Cho, Seunghyun; Moon, Joo Hyun; Lee, Bongsoo
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 10/10/2014 EN
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A fiber-optic sensor system using a multiplexed array of sensing probes based on an aqueous solution of sodium chloride (NaCl solution) and an optical time-domain reflectometer (OTDR) for simultaneous measurement of temperature and water level is proposed. By changing the temperature, the refractive index of the NaCl solution is varied and Fresnel reflection arising at the interface between the distal end of optical fiber and the NaCl solution is then also changed. We measured the modified optical power of the light reflected from the sensing probe using a portable OTDR device and also obtained the relationship between the temperature of water and the optical power. In this study, the water level was simply determined by measuring the signal difference of the optical power due to the temperature difference of individual sensing probes placed inside and outside of the water. In conclusion, we demonstrate that the temperature and water level can be obtained simultaneously by measuring optical powers of light reflected from sensing probes based on the NaCl solution. It is anticipated that the proposed fiber-optic sensor system makes it possible to remotely monitor the real-time change of temperature and water level of the spent fuel pool during a loss of power accident.

Self-assembly of triblock copolymers in aqueous solution; Self-assembly of triblock copolymers in aqueous solution

Fonte: Sociedad Chilena de Química Publicador: Sociedad Chilena de Química
Tipo: Artículo de revista
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Resumen: The aggregation of PE4VP-b-PS-b-PE4VP block copolymers was studied in aqueous solution. Triblock copolymers P4VP-b-PS-b-P4VP were synthesized by sequential anionic polymerization of poly(styrene) and poly(4-vinylpirydine) using sodium naphthalene as a bifunctional initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PE4VP-b-PS-b-PE4VP block copolymers. Both star and crew-cut micelles were formed. The concentrations at which micelles are formed cmc were determined, by steady-state and time-resolved fluorescence probing methods, as a function of quatemization degree. The results indicate that cmc of crew-cut micelles increases with increasing charge density of the PE4VP blocks. For star micelles there is not a clear dependency of cmc with the percentage of quatemization. The lifetime of pyrene fluorescence and the ratio I1/I3 were determined at concentrations of copolymers well above the cmc, and the results show that the location of pyrene into the micelle changes with the charge density of the micelle corona. The micropolarity sensed by pyrene decreases with increasing quatemization degree. The presence of aggregates was confirmed by transmission electronic microscopy.

Certification Report - The certification of equivalent diameters of a mixture of silica nanoparticles in aqueous solution: ERM®-FD102

KESTENS Vikram; ROEBBEN Gert
Fonte: Publications Office of the European Union Publicador: Publications Office of the European Union
Tipo: EUR - Scientific and Technical Research Reports Formato: Online
ENG
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This report describes the production of ERM®-FD102, silica nanoparticles in an aqueous solution certified for different equivalent diameters. The material was produced following ISO Guide 34:2009. The certified reference material (CRM), which has been produced by the Institute for Reference Materials and Measurements (IRMM) of the European Commission's Joint Research Centre (JRC), is a mixture of two monomodal populations of silica nanoparticles with distinct nominal particle sizes of 20 nm and 80 nm. These nominally 20 nm and 80 nm particle populations are further referred to as size class A and size class B, respectively. The CRM was prepared from two commercially available silica sols, moderately diluted in an aqueous solution and bottled in 10 mL pre-scored amber glass ampoules. Between unit-homogeneity was quantified and stability during dispatch and storage were assessed in accordance with ISO Guide 35:2006. The minimum sample intake for the different methods was determined from the results and information provided by the laboratories that participated in the interlaboratory comparison (ILC) exercises of the characterisation study. The material was characterised, for size classes A and B, by an intercomparison amongst laboratories of demonstrated competence and adhering to ISO/IEC 17025. Technically invalid results were removed but no outlier was eliminated on statistical grounds only. Uncertainties of the certified values were calculated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) and include uncertainty contributions related to possible inhomogeneity and instability and to characterisation. The material is intended for quality control and assessment of method performance. As any reference material...

Host–guest chemistry of linked β-cyclodextrin trimers and adamantyl substituted poly(acrylate)s in aqueous solution; Host-guest chemistry of linked beta-cyclodextrin trimers and adamantyl substituted poly(acrylate)s in aqueous solution

Nguyen, T.; Pham, D.T.; Lincoln, S.; Wang, J.; Guo, X.; Easton, C.; Prud'homme, R.
Fonte: RSC Publications Publicador: RSC Publications
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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1 H NMR spectroscopy, isothermal titration calorimetry and rheological studies show that the β-cyclodextrin (β-CD) groups of two linked β-cyclodextrin trimers, β-CD3bz and β-CDen3bz complex the adamantyl substituents and their tethers in 3.0 ± 0.1% substituted poly(acrylate)s to form intra- and inter-poly(acrylate) strand cross-links in aqueous solution. The structures of the linked-β-cyclodextrin trimers and the length of the tether between the adamantyl substituent and the poly(acrylate) backbone have substantial effects on the complexation constants, K, and the associated thermodynamic parameters. This is partially shown for the complexation by β-CD3bz of the adamantyl substituents as tether length varies from –CONH– (3.45 × 104) through –CONH(CH2)nNHCO– where n = 2 (2.09 × 105), 6 (3.17 × 105) or 12 (7.46 × 104) in 0.13–0.37 wt% substituted poly(acrylate) solutions and the figures in brackets are the K in dm3 mol−1 at 298.2 K. For the same sequence of substituted poly(acrylate)s the variation of viscosity is: 0.03, 3.78, 3.48, and 2.03 Pa s−1 at 500 s−1 shear rate at 298.2 K for 5.0 wt% substituted poly(acrylate) solutions in which the β-CD groups of β-CD3bz and the adamantyl substituents are equimolar at 1.5 × 10−2 mol dm−3. The eight data sets for the β-CD3bz and β-CDen3bz systems are discussed in terms of host–guest interactions between the host β-CD groups and the guest adamantyl substituents of the substituted poly(acrylate)s and are compared with those for the analogous β-CD systems.; Hanh-Trang Nguyen...

Complexation of dodecyl-substituted poly(acrylate) by linked β-cyclodextrin dimers and trimers in aqueous solution

Pham, Duc-Truc; Nguyen, Hanh-Trang; Lincoln, Stephen F.; Wang, Jie; Guo, Xuhong; Easton, Christopher J.; Prud'homme, Robert K.
Fonte: Wiley Publicador: Wiley
Tipo: Artigo de Revista Científica
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Two-dimensional NOESY ¹H NMR, isothermal titration calorimetric (ITC), and rheological studies of host-guest complexation by β-cyclodextrin, β-CD, and the β-CD groups of the linked β-CD dimers, β-CD2ur and β-CD2su and trimers, β-CD3bz and β-CDen3bz, of the dodecyl, C12, substituents of the 3.0% substituted poly(acrylate), PAAC12, in aqueous solution are reported. Complexations by β-CD, β-CD2ur, β-CD2su, β-CD3bz, and β-CDen3bz of the C12 substituents of PAAC12 in 0.2 wt % solution exhibit complexation constants 10⁻⁴K11 (298.2 K)0.83, 5.80, 4.40, 15.0, and 1.50 dm3 mol⁻¹, respectively. (The corresponding ΔH11 and TΔS11 show a linear relationship.) The rheologically determined zero-shear viscosities of 3.3 wt % aqueous solutions of PAAC12 alone and in the presence of β-CD, β-CD2ur, β-CD2su, β-CD3bz, and β-CDen3bz (where the β-CD groups and C12 substituents are equimolar) are 0.016, 0.03, 0.12, 0.25, 0.12, and 0.08 Pa s (298.2 K), respectively, and show PAAC12 to form interstrand cross-links through complexation.; We are grateful for support of this research by the AustralianResearch Council through Discovery Project DP110103177 andby the National Science Foundation of China through Grants20774028 and 20774030.

Insights into perfluorooctane sulfonate photodegradation in a catalyst-free aqueous solution

Lyu, Xian-Jin; Li, Wen-Wei; Lam, Paul K. S.; Yu, Han-Qing
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 23/03/2015 EN
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Photodegradation in the absence of externally added chemicals could be an attractive solution for the removal of perfluorooctane sulfonate (PFOS) in aqueous environment, but the low decomposition rate presents a severe challenge and the underlying mechanisms are unclear. In this study, we demonstrated that PFOS could be effectively degraded in a catalyst-free aqueous solution via a reduction route. Under appropriate pH and temperature conditions, a rapid PFOS photodegradation, with a pseudo-first-order decomposition rate constant of 0.91 h−1, was achieved. In addition, hydrated electrons were considered to be the major photo-generated reductive species responsible for PFOS photodegradation in this system. Its production and reduction ability could be significantly affected by the environmental conditions such as pH, temperature and presence of oxidative species. This study gives insights into the PFOS photodegradation process and may provide useful information for developing catalyst-free photodegradation systems for decomposing PFOS and other persistent water contaminants.

The photochemistry of purine components of nucleic acids. I. The efficiency of photolysis of adenine and guanine derivatives in aqueous solution.

Ivanchenko, V A; Titschenko, A I; Budowsky, E I; Simukova, N A; Wulfson, N S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1975 EN
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It has been shown that the quantum yield of the photochemical conversion of adenine and the corresponding nucleosides and nucleoside 5'-phosphates in liquid (pH 5.6 and 2.0) and frozen aqueous solutions do not exceed 10(-4). The quantum yield of the photoconversion of guanine-containing nucleosides and nucleoside 5'-phosphates in liquid aqueous solution (pH 5.6) after removal of oxygen by passing through nitrogen and in the frozen state do not exceed 0.3 x 10(-4). The quantum yield in oxygen-containing liquid aqueous solutions increase to 0.3 x 10(-3), i.e. to values commensurate with the quantum yield of pyrimidine photolysis.

The photochemistry of d(T-A) in aqueous solution and in ice.

Bose, S N; Kumar, S; Davies, R J; Sethi, S K; McCloskey, J A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 25/10/1984 EN
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When d(T-A) is irradiated at 254 nm in aqueous solution an internal photoadduct is formed between its constituent adenine and thymine bases. The resultant photoproduct, designated TA*, arises from a singlet excited state precursor; a similar photoreaction is not observed with d(C-A) or d(T-G). In contradistinction, irradiation of d(T-A) in frozen aqueous solution yields a dimeric photoproduct in which two d(T-A) molecules are coupled together by a (6-4) photoadduct linkage between their respective thymine bases. Both photoproducts have been extensively characterised by a combination of electron impact and fast atom bombardment mass spectrometry, UV, CD, 1H NMR and fluorescence spectroscopy. Acid treatment of TA* gives 6-methylimidazo[4,5-b]pyridin-5-one whose identity was established by an independent chemical synthesis involving photorearrangement of 6-methyl-imidazo[4,5-b]pyridine N(4)-oxide. A tentative mechanism is presented to account for the acid degradation of TA*. The structure of the dimeric ice photoproduct follows from its cleavage, by snake venom phosphodiesterase, to 5'-dAMP and the (6-4) bimolecular photoadduct of thymidine; on acid hydrolysis it gives adenine and 6-(5'-methyl-2'-oxopyrimidin-4'-yl) thymine.

Semiempirical SCF-MO calculations on the tautomeric equilibrium of histamine in gas phase and in aqueous solution

Parra Mouchet, Julia; Olea Azar, Claudio
Fonte: Sociedad Chilena de Química Publicador: Sociedad Chilena de Química
Tipo: Artículo de revista
EN
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The potential energy surface of hstamine monocation is calculated by MNDO types methodologies and by the Reaction Field model at CNDO/2 level, in order to rationalize the experimental findings about the relative abundance of histamine monocation tautomers in gas phase and in aqueous solution, respectively. The results indicate that the most stable form in gas phase exhibits an intramolecular H-bonding between the imidazolic and the amino N atoms. The corresponding proton transfer potential energy function across the H-bridge calculated in vacuum, consists of an asymmetric double well curve favoring the form which the proton is mainly bonded to the aromatic N atom. The influence of the solvent polarity on the H-bridge structure consists on an inversion of the minima in the proton transfer curve, together with a lowering of the torsional energy barrier of the side chain respect to the aromatic ring. Finally, a mechanism involving an intramolecular proton transfer, which explains the tautomeric equilibrium of histamine from gas phase to aqueous solution is proposed. The mechanism is rationalized in terms of charges distribution and HOMOs characterization.

Spectroscopic Evidence for the Specific Na+ and K+ Interactions with the Hydrogen-bonded Water Molecules at the Electrolyte Aqueous Solution Surfaces

Feng, Ran-ran; Bian, Hong-tao; Guo, Yuan; Wang*, Hong-fei
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/12/2008
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Sum frequency generation vibrational spectra of the water molecules at the NaF and KF aqueous solution surfaces showed significantly different spectral features and different concentration dependence. This result is the first direct observation of the cation effects of the simple alkali cations, which have been believed to be depleted from the aqueous surface, on the hydrogen bonding structure of the water molecules at the electrolyte solution surfaces. These observations may provide important clue to understand the fundamental phenomenon of ions at the air/water interface.; Comment: 15 pages, 2 figures

Thermodynamic Oxidation and Reduction Potentials of Photocatalytic Semiconductors in Aqueous Solution

Chen, Shiyou; Wang, Lin-Wang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/03/2012
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We introduce an approach to calculate the thermodynamic oxidation and reduction potentials of semiconductors in aqueous solution. By combining a newly-developed ab initio calculation for compound formation energy and band alignment with electrochemistry experimental data, this approach can be used to predict the stability of almost any compound semiconductor in aqueous solution. 30 photocatalytic semiconductors have been studied, and a graph (a simplified Pourbaix diagram) showing their valence/conduction band levels and oxidation/reduction potentials is produced. Based on this graph, we have studied the stabilities and trends against the oxidative and reductive photocorrosion for compound semiconductors. We found that, only metal oxides can be thermodynamically stable when used as the n-type photoanodes. All the non-oxides are unstable due to easy oxidation by the photogenerated holes, but they can be resistant to the reduction by electrons, thus stable as the p-type photocathodes.

Mechanism for the Phase Transition of a Genetically Engineered Elastin Model Peptide (VPGIG)_(40) in Aqueous Solution

Yamaoka, Tetsuji; Tamura, Takumi; Seto, Yuuki; Tada, Tomoko; Kunugi, Shigeru; Tirrell, David A.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 10/11/2003
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The concentration dependence of the pressure- and temperature-induced cloud point transition (P_c and T_c, respectively) of aqueous solutions of an elastin-like polypeptide with a repeating pentapeptide Val−Pro−Gly−Ile−Gly sequence (MGLDGSMG(VPGIG)_(40)VPLE) was investigated by using apparent light scattering, differential scanning calorimetry, and circular dichroism methods. In addition, the effects of salts and surfactants on these properties were investigated. The P_c and T_c of the present peptide in aqueous solution were strongly concentration dependent. The calorimetric measurements showed that the enthalpy of transitions was 300−400 kJ/mol, i.e., 7−10 kJ/mol per VPGIG pentamer. The T_c of the (VPGIG)_(40) solution was highly affected by the addition of inert salts or SDS. The effects of salts were consistent with those observed in the lyotropic series or Hoffmeister series. The CD spectrum at low peptide concentrations indicated that the present peptide forms type II β-turn-like structure(s) at higher temperatures, but the temperature dependence of random coil diminishment (195 nm) and β-turn formation (210 nm) were not exactly coincident. A hypothetical mechanism of the (VPGIG)_(40) phase transition that could account for these observations was postulated. Observations suggest that the temperature-responsive properties of the elastin model peptides occur via a mechanism involving conformational change−association−aggregation and that the first two are strongly interactive.

In vitro dentin permeability after application of Gluma® desensitizer as aqueous solution or aqueous fumed silica dispersion

Ishihata, Hiroshi; Finger, Werner J; Kanehira, Masafumi; Shimauchi, Hidetoshi; Komatsu, Masashi
Fonte: Universidade de São Paulo. Faculdade de Odontologia de Bauru Publicador: Universidade de São Paulo. Faculdade de Odontologia de Bauru
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 01/04/2011 ENG
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OBJECTIVES: To assess and to compare the effects of Gluma® Desensitizer (GDL) with an experimental glutaraldehyde and HEMA containing fumed silica dispersion (GDG) on dentin permeability using a chemiluminous tracer penetration test. MATERIAL AND METHODS: Twenty disc-shaped dentin specimens were dissected from extracted human third molars. The dentin specimens were mounted in a split chamber device for determination of permeability under liquid pressure using a photochemical method. Ten specimens were randomly selected and allocated to the evaluation groups Gluma® Desensitizer as aqueous solution and glutaraldehyde/HEMA as fumed silica dispersion, respectively. Dentin disc permeability was determined at two pressure levels after removal of smear with EDTA, after albumin soaking, and after application of the desensitizing agents. Two desensitizer-treated and rinsed specimens of each group were examined by scanning electron microscopy (SEM) for surface remnants. RESULTS: Comparatively large standard deviations of the mean EDTA reference and albumin soaked samples permeability values refected the differences of the dentin substrates. The mean chemiluminescence values of specimen treated with GDL and GDG, respectively, were signifcantly reduced after topical application of the desensitizing agents on albumin-soaked dentin. The effects of GDL and GDG on permeability were not signifcantly different. Treated specimens showed no surface remnants after rinsing. CONCLUSIONS: The experimental desensitizer gel formulation reduced dentin permeability as effectively as the original Gluma® Desensitizer solution.