Zur Frage der Dissoziation von Komplexen in Salzschmelzen

On the Problem of the Dissociation of Complexes in Salt Melts To interprete experimental enthalpies of mixing of molten salts a semiquantitative model is proposed. The model bases on the assumption of dissociated complex species in the melts. It is possible to estimate the equilibrum constants and the enthalpies of formation of the complex species.     

Acids in dimethylformamide. III. Ionic equilibria of dicarboxylic acids

Dissociation and homoconjugation constants of succinic, malonic, and dimethylmalonic acids have been determined potentiometrically at 25°C. Conductometric studies on the tetraethylammonium salts of the acids permitted the evaluation of the corresponding dissociation constants, which allowed a better fit of calculated curves with experimental data. Homoconjugation of two monovalent anions with a divalent anion was pointed out in all cases. No appreciable homoconjugation of the monovalent anion with the diprotic acids was found. In order to standardize the glass electrode at high paH values, the dissociation constant of diethylbarbituric acid has also been determined.     

Cluster ion formation in laser mass spectrometry of substituted pyridines

Emission of cluster ions occurs during laser irradiation of substituted pyridines even at threshold laser power densities. The clusters generated include dimers and trimers, and appear in both positive-ion and negative-ion laser mass spectra. Fragments of cluster ions are observed and can be rationlized as losses of neutral molecules from (nM ± H)^±. Dissociation of clusters occurs primarily from substituents on the pyridine ring. Laser mass spectrometry of pyridoxine hydrochloride and pyridoxamine-dihydrochloride resulted in the emission of clusters analogous to those observed for nicotinic acid. In contrast to these results, secondary-ion and field-desorption mass spectra of salts contain the ions C_nA_n?1⁺ and C_nA_n+1^?, that were not detected in the laser mass spectra.     

Evaluating Atmospheric pressure Solids Analysis Probe (ASAP) mass spectrometry for the analysis of low molecular weight synthetic polymers

Atmospheric pressure Solids Analysis Probe (ASAP) mass spectrometry has facilitated the ionisation of oligomers from low molecular weight synthetic polymers, poly(ethylene glycol) (PEG: M(n) = 1430) and poly(styrene) (PS: M(n) = 1770), directly from solids, providing a fast and efficient method of identification. Ion source conditions were evaluated and it was found that the key instrument parameter was the ion source desolvation temperature which, when set to 600 °C was sufficient to vapourise the heavier oligomers for ionisation. PS, a non-polar polymer that is very challenging to analyse by MALDI or ESI without the aid of metal salts to promote cationisation, was ionised promptly by ASAP resulting in the production of radical cations. A small degree of in-source dissociation could be eliminated by control of the instrument ion source voltages. The fragmentation observed through in-source dissociation could be duplicated in a controlled manner through Collision-Induced Dissociation (CID) of the radical cations. PEG, which preferentially ionises through adduction with alkali metal cations in MALDI and ESI, was observed as a protonated molecular ion by ASAP. In-source dissociation could not be eliminated entirely and the fragmentation observed resulted from cleavage of the C-C and C-O backbone bonds, as opposed to only C-O bond cleavage observed from tandem mass spectrometry.     

Electrochemical studies of sulfonates in non-aqueous solvents: Part III. Trifluoromethanesulfonic acid as a strong acid in dipolar aprotic solvents and acetic acid

Dissociation of trifluoromethanesulfonic acid in non-aqueous solvents has been investigated mainly by conductometry and compared with that of p-toluenesulfonic, methanesulfonic, fluorosulfuric and perchloric acids. The solvents used are dimethyl sulfoxide, N,N-dimethylacetamide, N,N-dimethylformamide, n-butyronitrile, propylene carbonate, acetonitrile, nitromethane, methyl isobutyl ketone and acetic acid. Trifluoromethanesulfonic acid is completely dissociated in rather basic solvents such as dimethyl sulfoxide, dimethylacetamide and dimethylformamide, while it is associated to some extent in the other solvents, especially in methyl isobutyl ketone and acetic acid. The strength of trifluoromethanesulfonic acid is almost the same as that of perchloric acid in all the solvents. Dissociation constants of the other acids are also obtained.     

Dissociation constants of some organic acids

Dissociation constants of di(nonylphenyl)dithiophosphoric acid, di(nonylphenyl)phosphoric acid and 9-phenyltetracosansulphuric acid, determined by two methods, are reported.     

Dissociation of the ammonium ion in water-urea and water-tert-butyl alcohol mixtures

Dissociation constants for the ammonium ion in water-urea and water-tert-butyl alcohol mixtures (0-40%) have been determined by a potentiometric method.     

Thermodynamics of 1,10-phenanthrolium ion in ethanol—water

Dissociation constants of the 1,10-phenanthrolium ion in different aqueous ethanolic solutions have been determined spectrophotometrically and pH-metrically. Some aspects of the role of the solvent have been discussed.     

Study of dissociation of α-alkyl-substituted dicarboxylic acids

Dissociation of α-alkyl-substituted dicarboxylic acids low-soluble in water was studied by the method of pH-potentiometry titration. Equilibrium constants of the dissociation at 25°C were determined.     

Calculations of dissociation constants of carboxylic acids by empirical and quantum-chemical DFT methods

Dissociation constants of 15 carboxylic acids in water, methanol, and DMSO were calculated by empirical and quantum-chemical DFT methods. The maximal error of the empirical calculation was 1.4%. A comparative analysis of the results obtained was carried out.     

Electrophilic C-H activation at Cp*Ir: ancillary-ligand control of the mechanism of C-H activation

Density functional calculations on the low-temperature cyclometalation of dimethylbenzylamine with [IrCl2Cp*]2/NaOAc have characterized a novel electrophilic activation pathway for C-H bond activation. C-H activation occurs from [Ir(DMBA-H)(kappa2-OAc)Cp*]+, and OAc plays a central role in determining the barrier for reaction. Dissociation of the proximal OAc arm sets up a facile intramolecular deprotonation via a geometrically convenient six-membered transition state. Dissociation of the distal OAc arm, however, leads to a higher energy four-membered (sigma-bond metathesis) transition state, while oxidative addition is even higher in energy. For this Ir3+ system, these three mechanisms appear to lie within a continuum in which the participation of the metal center and an H-accepting ancillary ligand are inversely related. The ability of the ancillary ligand to act as a proton acceptor is the key factor in determining which mechanism pertains.     

混合溶剂中氨基酸热力学性质的研究 IV: 278.15-318.15K下甘氨酸-乙醇-水体系

在混合溶剂中恒定乙醇的质量百分数χ=10%, 应用电动势法测定了无液接电池(A)和电池(B)的电动势。根据电池(A)和电池(B)的电动势, 用传统的Debye-Huckel外推法和我们在前文提出的多项式逼近程序, 确定了甘氨酸有278.15-318.15k范围内5个温度下的第一、第二热力学解离常数, 两种方法所得的结果在实验误差范围内一致。并相应计算了该体系的热力学量。     

Amino-Substituted Gem-Diphosphonic Acids: Dissociation Mechanism,Complex Formation and the Structure of Species in Aqueous Solutions

Dissociation mechanism of acids R 2 N(CH 2 ) n CR'(PO 3 H 2 ) 2 and the structure of their metal complexes depend on R and N. Intramolecular H-bonds stabilize the cyclic conformations of the species.     

Zersetzungsdrücke und Phasengrenzen von Niobnitriden

Dissociation Pressures and Phase Boundaries of Niobium Nitrides Dissociation pressures of niobium nitrides in the region NbN_1.006–NbN_0.45 were measured by a thermogravimetric method at temperatures from 1300 to 1800°C. The results enabled us to make statements on the two phase regions η/δ, δ/γ and δ/β and on the homogeneity ranges of the δ and the β phase. Enthalpies of the conversions η → δ, δ → γ, δ(γ) → β, and of the formation of the δ phase were calculated. A partial three dimensional c,p,T diagram and a proposal for a twodimensional c,T diagram of the Nb? N system have been designed.     

Properties of 2,4-dinitrophenyl derivatives of amino acids as analytical forms for high-performance liquid chromatography

Dissociation constants of 2,4-dinitrophenyl derivatives of α-amino acids in micellar solutions of sodium dodecyl sulfate used as a micellar mobile phase in reversed-phase liquid chromatography were determined. The method of micellar liquid chromatography was used to determine the composition of polypeptide fractions of animal origin.     

Reversible clustering of magnetic nanobiocatalysts for high-performance biocatalysis and easy catalyst recycling

Reversible clusters of nanobiocatalysts are developed via non-covalent interaction among enzyme-bound iron oxide magnetic nanoparticles. Dissociation of the clusters by shaking during biotransformation enables high catalytic performance, and re-clustering by stopping shaking after reaction allows for easy magnetic separation. The novel concept is demonstrated with alcohol dehydrogenase RDR for the enantioselective reduction of 7-methoxy-2-tetralone.     

Determination of some thermodynamic parameters of dissociation of dihydropyrimidine derivatives

Dissociation constant of dihydropyrimidine derivatives has been determined in dimethyl forma-mide—water (60: 40 v/v) system at different temperatures. The data are discussed in terms of the electron nature of the substituents. Further, some thermodynamics parameters such as enthalpy of solution, Gibbs energy change and entropy of solution have also been evaluated for these systems.     

Molecular Dispersion of Chains in the Mixed-Valence Complexes

A way to prepare molecular electronic wires in organic media is the solubilization of one-dimensional mixed-valence complexes with varied metal species through the formation of amphiphilic supramolecular assemblies (see picture). Dissociation and reassembly of the complex was detected as thermochromism in the intervalence (M(II)-->M(IV)) absorption bands.     

A Spectrophotometric Study of the Effect of Cationic Tensides (CPB,CPTB) on The Dissociation Constants of 4-(2-Pyridylazoresorcinol); The Effect of a Strong Electrolyte (Nacl)

Abstract

Dissociation constants pK_a1 and pK_a2 of 4- (2-pyridylazoresorcinol) were determined spectrophotometrically in the presence of CPB and CPTB. The effect of a strong electrolyte, NaCl, was studied.