共查询到20条相似文献,搜索用时 0 毫秒
1.
J. Kopoldová V. Vlasáková M. Weingart 《Journal of Radioanalytical and Nuclear Chemistry》1985,96(4):363-372
Gamma radiolysis of 10–2M aqueous oxygen-free tryptophan solutions irradiated at various pH values and in a N2O atmosphere was investigated. The values of the radiation losses of tryptophan and the yields of NH3 were determined. Using HPLC with an electrochemical detector the formation of hydroxylated radiation products of tryptophan was followed and the effect of pH on the radiolysis course discussed. 相似文献
2.
Srivastava A Ghorai S Bhattacharjya A Bhattacharya S 《The Journal of organic chemistry》2005,70(17):6574-6582
A novel low-molecular mass tetrameric sugar derivative containing azobenzene core, 1, showed pronounced hydrogelation at micromolar concentration. Based on this observation, four related azobenzene based tetrameric sugar derivatives, 4-7, and three tetrameric sugar derivatives with a bis-terephthalamide core, 9-11, were also synthesized. However, none of these closely related analogues of the compound 1 showed effective gelation. The gel formed from 1 was characterized extensively using melting temperature analysis, UV-vis, FT-IR, circular dichroism spectroscopy, and scanning electron microscopy. The resultant gel exhibited impressive tolerance to the pH variation of the aqueous phase and gelated water in the pH range of 4-10. While UV-vis and CD spectroscopy indicated that pronounced aggregation of the azobenzene chromophores in 1 was responsible for gelation, FT-IR studies showed that hydrogen bonding is also a contributing factor in the gelation process. The melting of gel was found to depend on the pH of the aqueous medium in which gel was formed. The gel showed considerable photostability to UV irradiation, indicating tight intermolecular packing inside the gelated state that rendered azobenzene groups in the resultant aggregate refractory to photoisomerization. The electron micrographs of the aqueous gels of 1 showed the existence of spongy globular aggregates in such gelated materials. Addition of salts to the aqueous medium led to a delay in the gelation process and also caused remarkable morphological changes in the microstructure of the gel. 相似文献
3.
Yu. L. Moreva N. S. Alekseeva Yu. M. Chernoberezhskii 《Russian Journal of Applied Chemistry》2010,83(7):1281-1283
The size distribution of kraft lignin particles in aqueous solutions in a wide pH range (9.5−2.0) was studied by filtration through track membranes. 相似文献
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Temperature gradient focusing (TGF) has previously been shown to be a practical technique for simultaneous concentration and separation of a variety of samples. In this paper, we demonstrate that TGF can be conducted at a wide range of pH values. Techniques for first-order prediction of the suitability of a given BGE for focusing are discussed. Buffer suitability for TGF is assessed experimentally by simultaneously concentrating and separating a pair of fluorescent analytes. One analyte is held at constant concentration for use as an internal standard while the concentration of the other dye is varied. Peak area is shown to vary linearly with the input dye concentration. A high degree of resolution (R(s) >3) of fluorescein and carboxyfluorescein, as well as for two LysoSensor-based dyes, is also observed. Foucusing and separation by TGF was successfully conducted quantitatively in BGE solutions of pH from 3.0 to 10.5. 相似文献
6.
Conformational changes in humic acids in two different aqueous solutions (NaCl and NaOH) are studied by means of high resolution ultrasound spectrometry. The method is based on the measurement of parameters of ultrasonic waves propagating through the sample. The attenuation describes the decay of the amplitude of the ultrasonic wave with the distance travelled. The velocity is the speed of this wave and is related to the wavelength and the frequency of oscillation of the deformation. It is determined by the density and elasticity of the sample, which is strongly influenced by the molecular arrangement. The minimal velocity of ultrasound was observed at 1 g dm?3 for lignitic humic acids and at 0.5 g dm?3 for IHSS Leonardite standard. The values of compressibility as computed are almost constant up to humic acids?? content corresponding to the minimum velocity of ultrasound and then decrease with the increase in concentration. This shows that the organisation of particles in diluted and concentrated humic acids sols is different. The decrease in compressibility points to the formation of a more rigid structure, which could lead to the decrease in humic acids?? binding ability. It was confirmed that the method employed was very sensitive and could be utilised as an indicator of conformational changes in humic acids in solutions with varying concentrations. 相似文献
7.
N. I. Baram Kh. L. Ziyaev B. Khodzhaniyazov A. I. Ismailov 《Chemistry of Natural Compounds》1999,35(1):29-32
The results are given of a study of the hydrolysis of alkyl- and heterylimines of gossypol at various pH values.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 162 70 71. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 38–41, January–February, 1999. 相似文献
8.
Thereza Christina Vessoni Penna Marina Ishii Adalberto Pessoa Junior Olivia Cholewa 《Applied biochemistry and biotechnology》2004,114(1-3):469-483
The thermal stability of the recombinant green fluorescent protein (GFPuv) expressed by Escherichia coli cells and isolated by three-phase partitioning extraction with hydrophobic interaction chromatography was studied. The GFPuv
(3.5–9.0 μg of GFPuv/mL) was exposed to various pH conditions (4.91–9.03) and temperatures (75–95°C) in the 10 mM buffers: acetate (pH 5.0–7.0), phosphate (pH 5.5–8.0), and Tris-HCl (pH 7.0–9.0). The extent of protein denaturation (loss
of fluorescence intensity) was expressed in decimal reduction time (D-value), the time exposure required to reduce 90% of the initial fluorescence intensity of GFPuv. For pH 7.0 to 8.0, the thermostability
of GFPuv was slightly greater in phosphate buffer than in Tris-HCl. At 85°C, the D-values (pH 7.1–7.5) ranged from 7.24 (Tris-HCl) to 13.88 min (phosphate) The stability of GFPuv in Tris-HCl (pH>8.0) was
constant at 90 and 95°C, and the D-values were 7.93 (pH 8.38–8.92) and 6.0 min (pH 8.05–8.97), respectively. The thermostability of GFPuv provides the basis
for its potential utility as a fluorescent biologic indicator to assay the efficacy of moist-heat treatments at temperatures
lower than 100°C. 相似文献
9.
Hiroshi Murata Iwao Satake Katumitu Hayakawa Masaru Tanokura 《Colloid and polymer science》2006,284(7):725-732
The conformation of poly(l-lysine) (PLL) was investigated in sodium alkanesulfonate CnSO3Na (n=8, 7) at various temperatures by circular dichroism spectrum measurements. C8SO3Na induced a double-step conformational change from a coil, to a β-sheet, and then to an α-helix, in which C7SO3Na induced a single-step coil-to-helix conformational change. Binding isotherms of C8SO3Na by PLL were constructed from the potentiometry of equilibrium concentration of the surfactant using a surfactant ion-selective electrode. The curves indicated the cooperative binding characteristic and were analyzed by a linear lattice model using the Bethe approximation. The thermodynamic parameters obtained from the model revealed that the binding of C8SO3Na by PLL was an entropy-driven process. The conformational change was observed at nearly full binding, presumably due to the surfactant clustering of the ordered conformation. 相似文献
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Malgorzata Wszelaka-Rylik W. Zielenkiewicz 《Journal of Thermal Analysis and Calorimetry》2007,87(1):85-89
Calorimetric and volumetric investigations of ovalbumin salting by sodium
chloride, lithium chloride, potassium chloride, lithium sulfate and ammonium
sulfate buffered solutions in the range of concentrations of about 0.2–1.2
M of salts are reported. The evolution of enthalpies and apparent molar volumes vs. salts concentration was investigated using ITC
MicroCal titration microcalorimeter and Anton Paar DMA 60/602 digital densimeter.
It was found that the changes in enthalpies of salting and apparent molar
volumes follow a similar trend. Conclusions about the ability of salts: to
precipitate ovalbumin solution are presented. 相似文献
12.
G. K. Elyashevich N. G. Bel’nikevich S. A. Vesnebolotskaya 《Polymer Science Series A》2009,51(5):550-553
The swelling kinetics of sodium polyacrylate gels has been studied in media with different pH values. The pH dependence of the degree of equilibrium swelling shows a maximum at pH 6. The degree of swelling decreases with an increase in the crosslink density, and this dependence follows an S-shaped pattern for all examined gels. When a gel swollen in media with pH 3–13 is dried in air, its contraction is reversible, while in the case of the gel swollen in acidic media at pH < 3, the process is irreversible owing to the replacement of sodium ions with protons. 相似文献
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B M Michov 《Electrophoresis》1989,10(10):686-689
A theory for discontinuous electrophoresis in a polyacrylamide gel is presented for one buffer at two pH values. It is shown that polyions stack between identical leading and trailing ions, and resolve in a gel of constant polyacrylamide concentration. The theory is illustrated by the separation of serum protein polyions in a Tris-glycinate buffer of pH 8.19 in the well-forming gel, and pH 9.16 in the resolving gel. The selected concentrations and electrolyte ionization degrees of Tris and glycine have values at which the serum protein polyions stack between the resolving and electrode buffers, followed by separation in the resolving gel. 相似文献
16.
The lifetime of zwitterionic, neutral, oxo, and hydroxy tautomeric forms of thymine and 5-chlorouracil is calculated with regard to intermolecular proton transfer in dimers. Time characteristics of picosecond spectra of aqueous solutions at different values are interpreted. 相似文献
17.
Thereza Christina Vessoni Penna Marina Ishii Juliana Sayuri Kunimura Olivia Cholewa 《Applied biochemistry and biotechnology》2005,122(1-3):501-527
The stability at room temperature (25°C) of recombinant green fluorescent protein (GFPuv), expressed by Escherichia coli cells and isolated by three-phase partitioning extraction with hydrophobic interaction column, was studied. The GFPuv was diluted in buffered (each 10 mM: Tris-HCl, pH 8.0; phosphate, pH 6.0 and 7.0 and acetate, pH 5.0) and in unbuffered (water for injection [WFI]; pH 6.70 ± 0.40) glucose solutions (from 1.5 to 50%). By assaying the loss of fluorescence intensity as a measure of denaturation, the stability of GFPuv in these solutions was evaluated relative to glucose concentration, pH, osmolarity, density, conductivity, and viscosity. The extent of protein denaturation (loss of fluorescence intensity) was expressed in decimal reduction time (D-value), the time required to reduce 90% of the initial fluorescence intensity of GFPuv. The D-value between 56 and 83 h of GFPuv at 1.5–15% glucose in WFI was equivalent to 20–30% glucose in a phosphate. The stability of GFPuv in 50% glucose was similar for all buffers studied and four times higher than in WFI. By the convenient measure of fluorescence intensity, GFPuv can be used as an indicator to report the extent of denaturation rates of other proteins in glucose solutions. 相似文献
18.
Trotsenko O Roiter Y Minko S 《Langmuir : the ACS journal of surfaces and colloids》2012,28(14):6037-6044
Conformations of cationic polyelectrolytes (PEs), a weak poly(2-vinylpyridine) (P2VP) and a strong poly(N-methyl-2-vinylpyridinium iodide) (qP2VP), adsorbed on mica from saline solutions in the presence of counterions of different valences are studied using in situ atomic force microscopy (AFM). Quantitative characteristics of chain conformations are analyzed using AFM images of the adsorbed molecules. The results of the statistical analysis of the chain contour reveal collapse of the PE coils when ionic strength is in a range from tens to hundreds of millimoles per kilogram and re-expansion of the coils with a further increase of ionic strength up to a region of the saturated saline solutions. The competition between monovalent and multivalent counterions simultaneously present in solutions strongly affects conformations of PE chains even at a very small fraction of multivalent counterions. Shrinkage of PE coils is steeper for multivalent counterions than for monovalent counterions. However, the re-expansion is only incremental in the presence of multivalent counterions. Extended adsorbed coils at low salt concentrations and at very high concentrations of monovalent salt exhibit conformation corresponding to a 2D coil with 0.95 fraction of bound segments (segments in "trains") in the regime of diluted surface concentration of the PE. Shrunken coils in the intermediate range of ionic strength resemble 3D-globules with 0.8 fraction of trains. The incrementally re-expanded PE coils at a high ionic strength remain unchanged at higher multivalent salt concentrations up to the solubility limit of the salt. The formation of a strong PE complex with multivalent counterions at high ionic strength is not well understood yet. A speculative explanation of the observed experimental result is based on possible stabilization of the complex due to hydrophobic interactions of the backbone. 相似文献
19.
Deo P Deo N Somasundaran P Jockusch S Turro NJ 《The journal of physical chemistry. B》2005,109(44):20714-20718
Structural changes of pyrene-labeled and unlabeled poly(maleic acid/octyl vinyl ether) (PMAOVE) and poly(maleic acid/methyl vinyl ether) (PMAMVE) with changes in pH have been investigated in this study. The changes in the photophysical properties of pyrene are interpreted to investigate uncoiling or swelling of the polymeric chains with pH. The vibrational fine structure of the pyrene fluorescence (I(3)/I(1)) and the ratio between excimer and monomer fluorescence (I(e)/I(m)) of both pyrene-labeled and unlabeled PMAMVE and PMAOVE suggest that, at pH 4, the polymers are in the coiled form and PMAOVE forms hydrophobic nanodomains. An increase in pH ionizes a number of COOH groups on both PMAMVE and PMAOVE, which leads to the stretching or swelling of the polymers. 相似文献
20.
L. A. Dunn 《Journal of solution chemistry》1974,3(1):1-14
The temperature variation of the limiting partial molar volumes of a number of electrolytes in aqueous solution has been examined in terms of solvent electrostriction. The Desnoyers, Verrall, and Conway theory has been modified and extended to cover the temperature range 0–100°C. It has been shown that electrostriction effects alone cannot account for the observed maxima in the V° –T plots for various electrolytes. It is concluded that solvent structural changes over this temperature range may well be important. 相似文献