The rheological study of the interaction between alkali metal ions and kappa-carrageenan gels

The rheological change in kappa-carrageenan and agarose gels immersed in alkali metal salt solution was studied by the measurement of longitudinal vibrations. The storage modulus of kappa-carrageenan gel increased remarkably by the immersion, while that of agarose gel did not change so much. The reason of this change in kappa-carrageenan was ascribed to the shielding effect of the electrostatic repulsion of sulfate groups by alkali metal ions. As a result of the shielding, the helical structure was thought to become the densely packed state. The difference of the action between the two groups (Li⁺, Na⁺) and (K⁺, Cs⁺) was discussed from the viewpoint that these ions are either structure makers or breakers for the structure of water.     

FTIR spectroscopic study on the interaction between a fluoroionophore and metal ions.

A fluoroionophore sensor, N-[4-(1-pyrene)butyroyl]-L-tryptophan (PLT), has been reported. It can distinguish lead ion from other 12 metal ions via forming a pyrene dimer and it exhibits a very high sensitivity (0.15 microM) in aqueous solution (Chem. Commun., 2006, 2702). When the indole moiety in PLT was changed to benzene, in forming a new fluoroionophore of N-[4-(1-pyrene)butyroyl]-L-phenylalanine (PLP), it could not form a pyrene dimer in response to Pb(2+) in water. The present study describes the spectroscopic clarification of the intrinsic differences of the binding model between PLP and PLT in binding with Pb(2+). The model shows identical chelating bidentate coordination between COO(-) and Pb(2+) both in PLP-Pb and PLT-Pb; however, there is no indication of the interaction between the phenyl ring and the metal ion or the hydrogen bonding between amide groups in PLP-Pb. These differences in the binding model between PLP-Pb and PLT-Pb illustrate that the indole ring in PLT appears to play a crucial role in the high selectivity and sensitivity of PLT to lead(II) ion.     

The synthesis,spectroscopic and thermal study of oxamic acid compounds of some metal(II) ions

Summary The preparation of oxamic acid complexes of general formula M(H₂NCOCOO)₂·xH₂O (M = Mn^II, Co^II, Ni^II, Cu^II or Zn^II; x = 1 for Cu^II, x = 2 for the other metals) is reported. The i.r. and Raman spectra are discussed considering a trans-octahedral structure, formed by five-membered chelate rings with the amide oxygen and one carboxylic oxygen as donor atoms. The apical positions are occupied by water molecules. The thermal degradation process is very similar for the different complexes, first losing H₂O in one or different steps, then the fragments of the organic ligand to give the metal oxide as residue. The thermal degradation of the Cu^II and Zn^II compounds results in the formation of a new polymeric compound by deprotonation of the primary amide function in an endothermic process, the polymer further decomposes to form the metal oxide.     

FT-IR and Raman spectroscopic study of hydrated rubidium (cesium) borates and alkali double borates

FT-IR and Raman spectra of five hydrated alkali borates and five hydrated alkali double borates have been recorded at room temperature in the range 400 to 4000 cm⁻¹, and analyzed. Fundamental vibrational modes have been identified and assignments tentatively made in comparison with the work of Janda and Heller, and Li Jun. The text was submitted by the authors in English.     

Effect of amino acids on the interaction between cobalamin(II) and dehydroascorbic acid

The kinetics of the reaction between one-electron-reduced cobalamin (cobalamin(II), Cb(II)) and the two-electron-oxidized form of vitamin C (dehydroascorbic acid, DHA) with amino acids in an acidic medium is studied by conventional UV–Vis spectroscopy. It is shown that the oxidation of Cbl(II) by dehydroascorbic acid proceeds only in the presence of sulfur-containing amino acids (cysteine, acetylcysteine). A proposed reaction mechanism includes the step of amino acid coordination on the Co(II)-center through the sulfur atom, along with that of the interaction between this complex and DHA molecules, which results in the formation of ascorbyl radical and the corresponding Co(III) thiolate complex.     

Formation and interaction of hydrated alkali metal ions at the graphite-water interface

Ion hydration at a solid surface ubiquitously exists in nature and plays important roles in many natural processes and technological applications. Aiming at obtaining a microscopic insight into the formation of such systems and interactions therein, we have investigated the hydration of alkali metal ions at a prototype surface-graphite (0001), using first-principles molecular dynamics simulations. At low water coverage, the alkali metal ions form two-dimensional hydration shells accommodating at most four (Li, Na) and three (K, Rb, Cs) waters in the first shell. These two-dimensional shells generally evolve into three-dimensional structures at higher water coverage, due to the competition between hydration and ion-surface interactions. Exceptionally K was found to reside at the graphite-water interface for water coverages up to bulk water limit, where it forms an "umbrellalike" surface hydration shell with an average water-ion-surface angle of 115 degrees . Interactions between the hydrated K and Na ions at the interface have also been studied. Water molecules seem to mediate an effective ion-ion interaction, which favors the aggregation of Na ions but prevents nucleation of K. These results agree with experimental observations in electron energy loss spectroscopy, desorption spectroscopy, and work function measurement. In addition, the sensitive dependence of charge transfer on dynamical structure evolution during the hydration process, implies the necessity to describe surface ion hydration from electronic structure calculations.     

Experimental (FT-IR, FT-Raman, H, C NMR) and theoretical study of alkali metal 2-aminonicotinates

The influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of 2-aminonicotinic acid (2-ANA) was studied by the methods of molecular spectroscopy. The vibrational (FT-IR, FT-Raman) and NMR (¹H and ¹³C) spectra of 2-aminonicotinic acid and its alkali metal salts were recorded. Characteristic shifts and changes in intensities of bands along the metal series were observed. The changes of chemical shifts of protons (¹H NMR) and carbons (¹³C NMR) in the series of studied alkali metal 2-aminonicotinates (2-AN) were observed too.Optimized geometrical structures of the studied compounds were calculated by the B3LYP method using the 6-311++G** basis set. Aromaticity indices, atomic charges, dipole moments and energies were also calculated. The theoretical chemical shifts in ¹H and ¹³C NMR spectra and theoretical wavenumbers and intensities of IR and Raman spectra were determined. The calculated parameters were compared to the experimental characteristics of the studied compounds.     

铜、锌离子对齐墩果酸与蛋白质相互作用的影响

使用荧光光谱和紫外吸收光谱研究金属离子存在下对齐墩果酸(OA)与牛血清白蛋白(BSA)相互作用的影响.实验结果表明,生理pH值条件下齐墩果酸对牛血清白蛋白的荧光猝灭可能是一个单一的静态猝灭过程.求得了OA与BSA相互作用的结合常数为6.16×103 L·mol-1.Zn2+或Gu2+存在下,OA对BSA的荧光猝灭类型没...     

Kinetics and mechanism of the alkali metal ions promoted electron transfer between 12-tungstocobaltate(III) and citric acid

The kinetics of the interactions of the Keggin type heteropolyanion [CoW₁₂O₄₀]^5?, with all the molecular and anionic forms of citric acid have been investigated spectrophotometrically in the pH range 0.60–5.45 at 60°C. With the exception of the molecular form of the acid (H₃L), all the other species (H₂L^?, HL^2?, and L^3?) undergo oxidation through an alkali metal ion catalyzed path in addition to the uncatalyzed one. The catalytic power increases with increasing size of the alkali metal ion. The contributions of each path have been evaluated from the kinetic data with the help of the measured dissociation constant values of citric acid. A plausible mechanism involving the formation of a bridged outer-sphere complex of the reacting species with the alkali cation, has been suggested. The observed limiting dependence of k_obs on [citrate] at high concentrations owing to an equilibrium between the reactants preceeding the electron transfer step supports the proposed mechanism. The pH-rate profile gives an excellent fit with the evaluated kinetic parameters.     

The aromatic sidechains of amino acids as neutral donor groups for alkali metal cations

An aromatic residue that can serve as a pi-donor occurs in all known protein sequences about one out of every 11 amino acids. Benzene, phenol, and indole, the sidechains of phenylalanine, tyrosine, and tryptophan, are particularly important in protein structure. Solid state structures confirm the interactions of these neutral arenes, along with double and triple bonds, with sodium and potassium cations.     

UV-vis spectroscopic study of interaction of metal ions with the E(T)(30) dye involving micellar media

Interaction between 3d-transition metal ions (Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) and the E(T)(30) dye, 2,6-diphenyl-4-(2,4,6-triphenyl 1-pyridino)phenolate in aqueous medium have been studied by distributing the dye between the aqueous and micellar phase formed by cationic surfactant cetyltrimethylammonium bromide(CTAB). Values of equilibrium constant K for the dye-metal ion interaction and the partition coefficient of the dye between the micellar and the aqueous phase have been determined. K values show a systematic correlation with ionic potential of metal ions.     

Fluorescence spectroscopic investigation of the interaction between triphenyltin and humic acids

The interaction between triphenyltin (TPT) and humic acid (HA) was investigated using UV-vis and fluorescence spectra techniques. The experimental results showed that the fluorescence quenching of HA by TPT was a result of the interaction of TPT with HA. The binding constant K(b) and corresponding thermodynamic parameters were measured at different temperatures. The binding of TPT molecule to HA is a spontaneous molecular interaction procedure in which entropy increased and Gibbs free energy decreased. Hydrophobic interaction force plays a major role in stabilizing the TPT-HA complex. The three-dimensional fluorescence contour spectra revealed that TPT could enter into the hydrophobic cavities in some domain of HA.     

Comparison of the conformational behavior of amino acids and N-acetylated amino acids: a theoretical and matrix-isolation FT-IR study of N-acetylglycine

Within the structure determination task for peptides, which is of large interest due to the relation between structure and functionality, infrared spectra can provide detailed information on the conformational behavior. The conformational landscape ofN-acetylgycine has been studied by a combined theoretical and matrix-isolation FT-IR study. The acetylation simulates an amino acid a peptide bond. Four stable conformations were found at the MP2/6-31++G** level of theory. Among these, only one contains an intramolecular H-bond that has a small abundance at the considered temperature. Apart from this one, three other different conformations could be detected in an Ar matrix. The experimental rotamerization constants NAG2 ? NAG1 and NAG3 ? NAG1 could be estimated. The values of the rotamerization constants as well as the mean frequency deviation of N-acetylglycine were combined with previously obtained data of other N-acetylated amino acids and they appeared to be similar to the data for nonsubstituted amino acids. This suggests that the used methodology can be in the future applied to investigate small peptides. Analysis of H-bond frequency shifts and distance demonstrates that the intramolecular H-bonds in N-acetylated amino acids are stronger compared to those in nonsubstituted amino acids.     

The UV-VIS spectroscopic study of the interaction between WCl6 and esters of carboxylic acids

The reaction of WCl₆ with methyl 10-undecenoate and methyl palmitate has been studied. The rate constant of the first step of the reaction has been established and compared with that of the WCl₆+(CH₃)₄Sn reaction. On the basis of this comparison the influence of the reaction of WCl₆ + ester on the ester metathesis is discussed.

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WCl₆ -10- -. , WCl₆+(CH₃)₄Sn. WCl₆+ .

     

Fluorescence study of the interaction between metal ions and methyl methacrylate–methacrylic acid copolymers in aqueous solutions: thallium(I), calcium(II), and terbium(III)

 The binding of the cations thallium(I), calcium(II) and terbium(III) to methyl methacrylate– methacrylic acid copolymers with different fractions of acid groups (x) has been studied in aqueous solution at various pH values using the fluorescence of covalently bonded 9-vinyl anthracene as a probe. In all cases, the extent of binding increases as a function of the charge of the polymer with either increasing fraction of carboxylic acids or of pH. However, differences are observed in the behavior of the three cations. With Tl(I), quenching of the anthracene group fluorescence is observed, indicating that the thallium(I) approaches the probe and suggesting that the alkylanthracene is probably in a relatively polar region. Binding constants have been determined from anthracene quenching data and from studies with the fluo-rescent-probe sodium pyrenetetra-sulfonate. Good agreement is obtained between the two methods, and values for the binding constants increase from 250 to 950 M^-1 as x increases from 0.39 to 1. It is suggested that the cation is held in the polyelectrolyte domain, partly by Debye–Hückel effects and partly by more specific interactions. Stronger binding is found with calcium(II) and terbium(III), and in this case increases in fluorescence intensity are observed on complexation due to the anthracene group being in a more hydrophobic region, probably as a result of conformational changes in the polymer chain. In the former case the stoichiometry of the interaction was determined from the fluorescence data to involve two carboxylate groups bound per calcium. Association constants were found using murexide as an indicator of free calcium to vary from 8400 to 37 000 M^-1 as x increases from 0.39 to 1. It is suggested that in this case specific calcium(II)–carboxylate interactions contribute to the binding. With terbium(III), a greater increase in the probe fluorescence intensity was observed than with calcium, and it is suggested that the interaction with the polymer is even stronger, leading to a more pronounced conformational change in the polymer. It is proposed that the terbium(III) interacts with six carboxylic groups on the polymer chain, with three being coordinated and three attracted by electrostatic interactions. Received: 10 June 1997 Accepted: 24 October 1997     

The enthalpies of interaction of strongly basic anionites with amino acid ions

The enthalpies of interaction of strongly basic anionites ARA-1p, AV-17-8, and AV-29-12P with glycine, glutamic acid, and tyrosine anions were determined by microcalorimetry. The interaction of ionites with amino acid anions over the selected concentration range was accompanied by heat release. The value and duration of heat release and the enthalpy of the process depended substantially on the structure of the ionite and the amount of the cross-linking agent and the structure, properties, and concentration of amino acids. An attempt was made to consider the influence of the hydrophobic properties of amino acids on the enthalpy of the process.