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1.
《Microchemical Journal》1987,36(2):245-252
A systematic spectrophotometric study on the complexation of uranyl ions with ascorbic acid (vitamin C) is carried out. Factors influencing the sensitivity or selectivity of uranyl ascorbate are studied, and adequate elimination or control of the procedure is suggested. Results of the absorbance of uranyl ascorbate developed in HNO3, HCl, and H2SO4 acid media within the concentration range (1.0–8.0) × 10−N show a marked dependence on the nature and concentration of the acid used. The observed decrease in color intensity at higher acidities is explained on the basis of the decomposing effect of hydrogen ions on uranyl ascorbate and the complexing effect on uranyl ions. Study of the stoichiometry of uranium:ascorbic acid complex in acid medium by continuous variation and molar ratio methods indicated the formation of 1:1 and 1:2 complexes. The formation constant of the 1:1 complex as calculated by these two methods was found to be 4.8 × 104 and 5.0 × 104, respectively. Best suitable conditions for stabilizing and increasing the color intensity of uranyl ascorbate, dependent on the nature of the medium and pH of the solution, are suggested for the determination of ascorbic acid in pharmaceutical preparations using this method. 相似文献
2.
K. Iida M. Nango H. Yasue K. Okuda M. Okita A. Kashiwada N. Takada M. Maekawa Y. Kurono 《Colloid and polymer science》1998,276(2):152-159
The effect of denaturants such as urea and normal alcohols on the formation of light-harvesting (LH) polypeptides/bacteriochlorophyll
a (BChla) complex (LH1 complex) in n-octyl-β-D-glucopyranoside (OG) micelle was examined to provide an insight into stability of the complex. The stabilities
of the LH1 complex in OG micelle and of the complex in the chromatophore of photosynthetic bacteria were compared by addition
of denaturants. The extent of stability of these complexes was monitored by the change in absorbance of Qy band of BChla in these complexes, resulting generally in the blue-shifting of the Qy band from near 870 nm to about 777 nm upon addition
of these denaturants. Urea and guanidium hydrochloride (Gnd) showed a relatively weak denaturing effect. Normal alcohols showed
stronger denaturing effect, depending on the hydrophobicity of the alcohols. These results imply that the stability of LH1
complex in OG micelle can be largely attributed to the hydrophobic interactions in the complex as well as that of the complex
in the chromatophore of photosynthetic bacteria.
Received: 23 May 1997 Accepted: 13 September 1997 相似文献
3.
Chen HY Yeh SW Hsu SC Kao CL Dong TY 《Physical chemistry chemical physics : PCCP》2011,13(7):2674-2681
The formation of base pair radical anions is closely related to many fascinating research fields in biology and chemistry such as radiation damage to DNA and electron transport in DNA. However, the relevant knowledge so far mainly comes from studies on isolated base pair radical anions, and their behavior in the DNA environment is less understood. In this study, we focus on how the nucleobase sequence affects the properties of the guanine-cytosine (GC) base pair radical anion. The energetic barrier and reaction energy for the proton transfer along the N(1)(G)-H···N(3)(C) hydrogen bond and the stability of GC˙(-) (i.e., electron affinity of GC) embedded in different sequences of base-pair trimer were evaluated using density functional theory. The computational results demonstrated that the presence of neighboring base pairs has an important influence on the behavior of GC˙(-) in the gas phase. The excess electron was found to be localized on the embedded GC and the charge leakage to neighboring base pairs was very minor in all of the investigated sequences. Accordingly, the sequence behavior of the proton-transfer reaction and the stability of GC˙(-) is chiefly governed by electrostatic interactions with adjacent base pairs. However, the effect of base stacking, due to its electrostatic nature, is severely screened upon hydration, and thus, the sequence dependence of the properties of GC˙(-) in aqueous environment becomes relatively weak and less than that observed in the gas phase. The effect of geometry relaxation associated with neighboring base pairs as well as the possibility of proton transfer along the N(2)(G)-H···O(2)(C) channel have also been investigated. The implications of the present findings to the electron transport and radiation damage of DNA are discussed. 相似文献
4.
The effect of initial panipenem (CAS No. 87726-17-8) concentration on its degradation in an aqueous solution was investigated. The degradation of panipenem followed pseudo-first-order kinetics at all the pH values tested. However, in an acidic solution, the degradation rate increased with the initial panipenem concentration. On the other hand, in an alkaline solution, the degradation rate was not affected by its initial concentration. In an acidic solution, the plots of the first-order rate constants versus initial panipenem concentrations showed a linear relationship. Theoretically, the first-order rate constant is independent of the initial concentration, and therefore, the results suggested unusualness. We investigated the results obtained under acidic conditions in detail to find a very complex reaction mechanism: panipenem and its degradation products are factors causing the unusual increase in the degradation rate. Moreover, it was shown that the dissociation of the carboxyl group played an important role in the degradation of panipenem. 相似文献
5.
A. S. Kotovaya S. G. Shova E. I. Melnik Yu. A. Simonov A. P. Gulya E. Pahontu 《Russian Journal of Coordination Chemistry》2013,39(1):23-32
A number of products formed in reactions of cobalt(II) salts with monoethanolamine (HEtm) in a neutral medium were synthesized and studied. X-Ray diffraction study showed that the nitrate and acetate form the dimers [Co(HEtm)3][Co(Etm)3](NO3)3 and [Co(HEtm)3][Co(Etm)3](CH3COO)3 · 8H2O, respectively. In chloride solutions, cobalt is partially oxidized to give the trinuclear complex [CoII{CoIII(Etm)3}2]Cl3 · H2Etm · 2H2O. The reaction of the chelate [Co(Etm)3] · 3H2O with nitric acid is accompanied by complete protonation of the coordinated aminoethanolate ions, and the reaction with formic acid involves complete replacement of the coordinated ligand by acid residue anions and water molecules to give the coordination polymer {Co2(μ-HCOO)4(H2O)4} n . 相似文献
6.
Vlase T. Vlase G. Chiriac A. Doca N. 《Journal of Thermal Analysis and Calorimetry》2003,72(3):847-853
The kinetic of decomposition of copper formate, acetate, propionate and butyrate under non-isothermal conditions was studied.
The support materials were carborundum and silica and the concentrations of the supported compounds were 15, 20, 25 and 30
mass%. In order to avoid the effects of thermal gradients and dilution, a series of parallel samples of carboxylate/support
mixtures with the same concentration were studied. The support effect was estimated by the difference between the isokinetic
temperature of the supported, respectively mixted carboxylate series, and is discussed in connection with the precursor concentration
and the nature of the carboxylate anion. The suggestion of considering the thermodynamic activation function instead of the
Arrhenius parameters for discussion on compensation effect was argued.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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8.
The infrared spectrum of the I(-)-D(2) anion complex is measured in the D(2) stretch region by monitoring production of I(-) photofragments. The rotationally resolved spectrum consists of two overlapping Sigma-Sigma subbands, redshifted by approximately 58 cm(-1) from the free D(2) fundamental vibrational band. These subbands are associated with absorptions by I(-)-D(2) complexes containing ortho and para forms of D(2). The measured rotational constants are consistent with a 3.79 A separation between I(-) and the D(2) center of mass, contracting by 0.08 A when the D(2) subunit is vibrationally excited. Spectroscopic data are used to generate effective radial potential energy curves describing the interaction of ortho and para D(2) with I(-) from which the dissociation energies of I(-)-D(2)(ortho) and I(-)-D(2)(para) are estimated as D(0)=236 and 297 cm(-1), respectively. 相似文献
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10.
本文用分光光度法测定了离子强度为 0.2 至4.2 范围内的离子对CuSO: 和配阴离子Fe(Tiron)- 在各种支持电解质中的稳定性. 在各种支持电解质中, 两个配合物体系的稳定性随离子强度变化的趋势基本一致, 但稳定性的极小值位置则大相同. 稳定性数据表明,B体系在离子强度小于2.0 时适用; 对Fe(Tiron) -体系则完全不能应用. 本文简单地讨论了造成上述情况的原因. 测得CuSo4 和Fe(Tiron)- 在25°C 时的热力学稳定常数logK. 分别为2.17和19.50. 相似文献
11.
John E. Barry Manuel Finkelstein W.Michael Moore Sidney D. Ross Lennart Eberson 《Tetrahedron letters》1984,25(27):2847-2850
Complexes between N-bromosuccinimides and succinimide anions are shown to be intermediates in the reduction of N-bromosuccinimides, and a method for their synthesis as tetra-n-butylammonium salts is described. 相似文献
12.
A luminescent anion sensor based on a europium hybrid complex. 总被引:1,自引:0,他引:1
M Montalti L Prodi N Zaccheroni L Charbonnière L Douce R Ziessel 《Journal of the American Chemical Society》2001,123(50):12694-12695
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14.
One electron paramagnetic parent osazone complex of rhodium of type trans-Rh(L(NHPh)H(2))(PPh(3))(2)Cl(2) (1), defined as an osazone anion radical complex of rhodium(III), trans-Rh(III)(L(NHPh)H(2)(?-))(PPh(3))(2)Cl(2), 1((t-RhL?)), with a minor contribution (~2%) of rhodium(II) electromer, trans-Rh(II)(L(NHPh)H(2))(PPh(3))(2)Cl(2), 1((t-Rh?L)), and their nonradical congener, trans-[Rh(III)(L(NHPh)H(2))(PPh(3))(2)Cl(2)]I(3) ([t-1](+)I(3)(-)), have been isolated and are substantiated by spectra, bond parameters, and DFT calculations on equivalent soft complexes [Rh(L(NHPh)H(2))(PMe(3))(2)Cl(2)] (3) and [Rh(L(NHPh)H(2))(PMe(3))(2)Cl(2)](+) (3(+)). 1 is not stable in solution and decomposes to [t-1](+) and a new rhodium(I) osazone complex, [Rh(I)(L(NHPh)H(2))(PPh(3))Cl] (2). 1 absorbs strongly at 351 nm due to MLCT and LLCT, while [t-1](+) and 2 absorb moderately in the range of 300-450 nm, respectively, due to LMCT and MLCT elucidated by TD-DFT calculations on 3((t-RhL?)), [t-3](+), and Rh(I)(L(NHPh)H(2))(PMe(3))Cl (4). EPR spectra of solids at 295 and 77 K, and dichloromethane-toluene frozen glass at 77 K of 1 are similar with g = 1.991, while g = 2.002 for the solid at 25 K. The EPR signal of 1 in dichloromethane solution is weaker (g = 1.992). In cyclic voltammetry, 1 displays two irreversible one electron transfer waves at +0.13 and -1.22 V, with respect to Fc(+)/Fc coupling, due to oxidation of 1((t-RhL?)) to [t-1](+) at the anode and reduction of rhodium(III) to rhodium(II), i.e., [t-1](+) to electromeric 1((t-Rh?L)) at the cathode. 相似文献
15.
Sadayuki Koizumi T. Imato Nobuhiko Ishibashi 《Analytical and bioanalytical chemistry》1997,357(1):37-43
Potentiometric selectivities of a plasticized poly(vinyl chloride) (PVC) membrane containing a hydrophobic quaternary ammonium
salt and triphenyltin chloride (TPTCl) for several inorganic anions were evaluated by measurements of the membrane potential
of a bi-ionic system (the so-called bi-ionic membrane potential). The addition of TPTCl to the plasticized PVC membrane containing
a quaternary ammonium salt gave rise to selectivity patterns different from the Hofmeister anion series, which is observed
for a membrane containing only the quaternary ammonium salt. The change in the selectivity pattern from the Hofmeister to
the non-Hofmeister was observed under conditions where the TPTCl concentration was higher than the quaternary ammonium salt
in the membrane. Response mechanisms and the selectivity of the TPTCl-based electrode are discussed with respect to the concentration
dependence of TPTCl and quaternary ammonium salt in the membrane.
Received: 6 July 1995/Revised: 2 February 1996/Accepted: 6 February 1996 相似文献
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17.
Observations on the effect of temperature on performance and stability of anion exchange columns in ion chromatography 总被引:1,自引:0,他引:1
Summary The influence of column temperature on elution behaviour of several ions on anion-exchange resin beds of the Dionex Ion Pac
type was investigated. Iodate, bromate, bromide and iodide ions were separated on Ion Pac AS9SC column in the temperature
range of 10°C–55°C, using NaHCO3/Na2CO3 and NaHCO3 eluents. Free energy, enthalpy and entropy changes for respective ion exchange reactions were calculated and compared with
literature data for classical gel type exchangers. In most cases the enthalpy change was a function of temperature. The work
at elevated temperatures caused progressing resin degradation i.e. loss of strongly basic groups, accompanied by formation
of weakly basic groups and also some weakly acidic groups. Similar resin degradation was observed for Ion Pac AS5 column.
Observations on the changes of the plate height with the retention factor and temperature lead to conclusion that in some
circumstances longitudinal diffusion in the resin phase also contributes to the total plate height. 相似文献
18.
Junpei Miyake Keita Fukasawa Masahiro Watanabe Kenji Miyatake 《Journal of polymer science. Part A, Polymer chemistry》2014,52(3):383-389
Five kinds of ammonium groups functionalized partially fluorinated poly(arylene ether) block copolymer membranes were prepared for investigating the structure–property relationship as anion exchange membranes (AEMs). Consequently, the pyridine (PYR)‐modified membrane showed the highest alkaline and hydrazine stability in terms of the conductivity, water uptake, and dry weight. The chloromethylated precursor block copolymers were reacted with amines, such as trimethylamine, N‐butyldimethylamine, 1‐methylimidazole, 1,2‐dimethylimidazole, and PYR to provide the target quaternized poly(arylene ether)s. The structures of the polymers, as well as model compounds and oligomers were well characterized by 1H NMR spectra. The obtained AEMs were subjected to water uptake and hydroxide ion conductivity measurements and stabilities in aqueous alkaline and hydrazine media. The pyridinium‐functionalized quaternized polymers membrane showed the highest alkaline and hydrazine stability with minor losses in the conductivity, water uptake, and dry weight. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 383–389 相似文献
19.
The metal-ligand complex 1 ([Mg (L)] (2+)) (or 2 ([Ca (L)]( 2+))) was demonstrated to selectively bind HSO(4)(-) (or H(2)PO(4)(-)) over other anions by using UV-vis absorption and fluorescence spectroscopy. The studied complex exhibits the remarkable color change and fluorescence quenching upon introducing HSO(4)(-) (or H(2)PO(4)(-)) anion in acetonitrile. Both the mechanism and structure of the secondary complex of complex 1 with anion were proposed on the basis of theoretical computation. 相似文献
20.
The complexation of tetramethylresorc[4]arene with primary and secondary amines in acetonitrile was investigated spectrophotometrically. The stoichiometry of the complexes formed was shown to depend on the amine concentration. Based on the proposed complexation models, the formation constants of the complexes as well as their thermodynamical parameters were determined and discussed. Depending on the amine concentration, two types of solid complexes of tetramethylresorc[4]arene with amines were obtained. The composition of these complexes was confirmed by 1H NMR. 相似文献