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51.
S. Magaz F. Migliardo D. Barreca E. Bellocco G. Lagan 《Journal of Molecular Structure》2007,840(1-3):114-118
Among disaccharides, trehalose, a naturally-occurring glass-forming disaccharide, is particularly effective in terms of its ability to preserve several organisms under stress conditions. The present work is aimed to investigate the bioprotective action of trehalose on lysozyme as a function of temperature. In order to extract quantitative information about the dimensional changes of the proteins, we performed Small Angle Neutron Scattering measurements on lysozyme/D2O solutions in absence and in presence of the disaccharide. The findings emphasise the capability of trehalose to stabilise the protein, activating aggregation processes. 相似文献
52.
研究了水质、滤膜、溶液浓度、糖液pH值、混浊度的变化与白砂糖色值的关系。研究结果表明,溶液的pH变化影响最严重。不调整糖液pH与用HCl或NaOH调整糖液pH对比所得白砂糖色值的结果是满意的。标准偏差112~186,相对标准偏差116%~225%,调pH使结果偏高,导致产生系统误差。因此:测定白砂糖色值不宜调整糖液的pH。 相似文献
53.
We studied the adsorption behaviour at the liquid/air and liquid/solid interface of a new anionic surfactant derived from sugar, the sodium decyl galacturonate. The surface tension of aqueous solutions, measured in equilibrium and as a function of time, is particularly affected by the presence of decanol, synthesis residue, which amount ranges between about 0 and 13%. The surface tension lowering is accelerated in presence of decanol, owing to its rapid diffusion to the interface or/and because it affects the mobility and adsorption process of the anionic surfactant molecules. The wetting power of surfactant solutions were also investigated in relation with textile treatment applications. We measured the kinetics of absorption of surfactant solutions in a piece of standard cotton and compared it to the absorption of pure decanol, a completely wetting liquid and to the absorption of an alkylpolyglucoside. The time at which the fabric piece is saturated appears to be related to the adsorption of surface-active molecules on the fibers at the advancing liquid front/fabric contact line. Decanol was found to promote absorption and micellar life-time seem to reflect the differences observed at high concentration. This study shows the importance of controlling the amount of surface-active residues which may alter the kinetics of surfactant adsorption, particularly in industrial processes where equilibrium conditions are not reached. 相似文献
54.
Compared to the general ionic liquids (ILs), a significant deviation of the binary mixtures of 1-decyl-3-methylimidazolium tri(hexafluoroacetylaceto)-copper(II) ([C10mim][Cu(hfacac)3]) with methanol was found, indicating the way methanol interacts with ILs might be governed by the special structure of the chelating anion. IR results showed that the (C2-H) of 1-decyl-3-methylimidazolium hexafluoroacetylacetonate ([C10mim][hfacac]) blue-shifted more significantly than that of [C10mim][Cu(hfacac)3], meanwhile the (C=O) red-shifted in [C10mim][Cu(hfacac)3], which is contrast with that in [C10mim][hfacac]. Two-dimensional correlation analysis of the FTIR spectra indicated that the chelating cavity has little effect on the sequence of the ILs sites that interact with methanol. Combined with small angle X-ray scattering (SAXS) results, the picture of mixing processes in these two systems were proposed. Methanol interacts directly with the anion followed by the cation in [C10mim][hfacac], while methanol preferentially enters the chelating cavity and enhances the packing effect in the [C10mim][Cu(hfacac)3] system. 相似文献
55.
The standard potentialss
E
o of M/M+ (M=Li, Na, K, Rb, and Cs) electrodes in aqueous urea solutions containing 12, 20, 30 and 37% by weight of urea have been determined at 25°C from emf measurements on the cell M(Hg)/MCl (m), solvent/AgCl–Ag, from the activities of metals in amalgams by use of a similar type of cell in water, and from the values ofs
E
o of the Ag/AgCl electrode determined earlier. The standard free energies of transfer of MCl, G
t
o
(MCl), from water to the mixed solvents, computed by use of these values and those for the Ag–AgCl electrode, rise sharply from Li+ to Na+ but fall from Na+ to K+ and rather sharply from K+ to Cs+ with a maximum at Na+ in all the solvent compositions. This has been attributed to the superimposition of soft-soft interactions on the electrostatic interactions between the ions and the negative charge centers of the possible hydrogen-bonded solvent complexes in the mixed solvents. Comparison of G
t
o
(i) values for individual ions, obtained by a simultaneous extrapolation procedure, with those in aqueous mixtures of methanol,t-butanol, and dimethyl sulfoxide leads to the conclusion that the solvation of these ions in all these solvents is chiefly dictated by the acid-base type of ion-solvent interactions. 相似文献
56.
Rongbin Qi Yujun Wang Jiding Li Changwei Zhao Shenlin Zhu 《Journal of membrane science》2006,280(1-2):545-552
Worldwide concerns over environment have stimulated increasing interest both in academic and industry for deep desulfurization of gasoline. Polydimethylsiloxane (PDMS) composite membrane was used to separate the binary and multicomponent alkane/thiophene mixtures by pervaporation. Effect of carbon number and concentration of alkane, and of feed temperature, on the separation efficiency of alkane/thiophene mixtures was investigated experimentally. Experimental results of binary mixtures indicated that the total fluxes for different alkane/thiophene mixtures decrease with increase of carbon number in the alkanes. Corresponding activation energies of permeation for alkanes in PDMS membrane increase with increase of carbon number in the alkanes. Differences of molecular size and structure of the alkanes lead to various selectivities thereof within PDMS membrane. In addition, the permeability and activation energy of thiophene in various systems differ from each other due to coupling effect which should be taken into consideration when dealing with multicomponent systems. Pervaporation results of ternary systems indicated that, the increase of content of lighter alkane in feed would result in a larger total flux, but a smaller selectivity to thiophene simultaneously. A quaternary system, the mixture of n-heptane, n-octane, n-nonane and thiophene, was employed to simulate the desulfurization process of gasoline. With the membrane having a PDMS layer of 11 μm, the total flux was measured to be about 1.65 kg/m2 h, with the corresponding enrichment factor of thiophene 3.9 at 30 °C. 相似文献
57.
Herein, we discuss the analyses and quantification of the different components in porphyrin mixtures, prepared from p-anisaldehyde, p-tolualdehyde, and 5-(4-bromophenyl)-dipyrromethane with acid catalysis, using NMR and HPLC. The advantages and disadvantages of these analytical methods are emphasized. Due to the similar size of a bromine atom and a methyl group it was possible to grow crystals suitable for X-ray crystallographic studies from a mixture of porphyrins, where the 4-position of the meso-phenyl rings was either substituted with methyl groups or bromine atoms. We also show that X-ray studies are inferior to NMR analysis for determining the components in a porphyrin mixture. 相似文献
58.
The adsorption isotherms of the binary mixtures of ethanol/n-Octane, ethanol/n-hexadecane and n-octane/n-hexadecane onto the activated carbon TA 95 were measured at 278 K, 288 K, 298 K and 308 K and described with mathematical functions. About 300 experimental values of the adsorption excess of the ternary mixture ethanol/n-octane/n-hexadecane onto activated carbon TA 95 at 298 K were measured by gas chromatography inside the ternary triangle. The ternary miscibility gap was determined at three temperatures. A good representation of the ternary data and the calculated activity coefficients (using the UNIFAC model) in three-dimensional space was possible with the help of transformation of coordinates. It was possible, too, by utilization of the conception of the quasi two-component representation of the mole fractions with and without miscibility gap. Several influencing factors on ternary adsorption isotherms were discussed for the system ethanol/n-octane/n-hexadecane/TA 95. 相似文献
59.
Enthalpies of solution of sodium benzoate, potassium benzoate, and potassium halo-substituted benzoates are reported at 298.15°K
in water and in nine water-tert-butyl alchol mixtures. Transfer enthalpies from water to the mixed solvent go through a maximum for about 0.055 mole fraction
of alcohol. Additivity of ionic contributions in the enthalpies of transfer is verified. Substituent effects on the transfer
enthalpies of benzoates are discussed in terms of size of the solutes and cohesion of the solvent mixtures.
For Part V, see ref. 1. 相似文献
60.
Alfonso Loaiza Dan Borchardt Francisco Zaera 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2481-2493
13C NMR at 125.76 MHz with 1H and 2H decoupling, 2H NMR at 76.77 MHz with 1H decoupling, and 1H NMR at 500.14 MHz with 2H decoupling were employed as analytical tools to study the complex mixtures of deuterated ethanes resulting from the catalytic H–D exchange of normal ethane with gas-phase deuterium in the presence of a platinum foil. Reference samples consisting of 1:1 binary mixtures of pure normal ethane and ethane-dn (n=1–6) were used to identify the peak positions in the 13C, 2H, and 1H NMR spectra due to each individual isotopomer, and the effect of isotopic substitution on the chemical shifts was determined in each case. While the NMR of all three nuclei worked well for the identification of the individual components of the 1:1 standard mixtures, both 1H and 2H NMR suffered from inadequate resolution when studying complex reaction mixtures because of the broadening of the lines due to 1H–1H (1H NMR) and 2H–2H (2H NMR) couplings. 13C NMR was therefore determined to be the method of choice for the quantitative analysis of the reaction mixtures. Using the 13C NMR results, a correlation that takes into account the primary and secondary isotope substitution effects on chemical shifts was deduced. This equation was used for the identification of the individual components of the mixtures, and integration of the individual observed resonances was then employed for quantification of their composition. This study shows that 13C NMR with 1H and 2H decoupling is a viable procedure for studying mixtures of deuterated ethanes. Furthermore, the additivity of the isotopic effects on chemical shifts and the transferability of the values obtained with ethane to other molecules makes this approach general for the analysis of other isotopomer mixtures. 相似文献