Yoshiaki Kinjo

Determination of the transfer thermodynamic functions for the zinc(II), cadmium(II), mercury(II) and mercury(I) ions from water to methanol, dimethyl sulfoxide, acetonitrile, pyridine and N,N-dimethylthioformamide and of standard electrode potentials of the M2+/M(s) couples in these solvents

The transfer thermodynamic functions for the zinc, cadmium, mercury(II) and mercury(I) ions from water to methanol, dimethyl sulfoxide, acetonitrile, pyridine and N,N-dimethylthioformamide are reported. The ΔtG⊖ values are calculated from potentiometrically determined standard electrode potentials in the different solvents with a silver reference electrode, and the ΔtH⊖ values are obtained from calorimetrically determined enthalpies of solution of the anhydrous metal trifluoromethylsulfonates. The entropies of transfer, ΔtS⊖, are calculated from the experimentally obtained ΔtG⊖ and ΔtH⊖ values; all of the measurements were performed at 25 °C. The extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption has been applied in order to calculate the contributions from the single ions. The studied ions are more strongly solvated in N,N-dimethylthioformamide, pyridine and dimethyl sulfoxide than in water, while they are more weakly solvated in methanol and acetonitrile. The entropies of transfer are negative for all the systems under study except for the cadmium ion to N,N-dimethylthioformamide.

Thermodynamic study on the transfer of the tin(II), lead(II) and alkaline-earth-metal ions from water to methanol, dimethyl sulfoxide, acetonitrile, pyridine and N,N-dimethylthioformamide

The thermodynamic functions for the transfer reactions of the tin(II), lead(II) and alkaline-earth-metal ions from water to methanol, acetonitrile, dimethyl sulfoxide and pyridine, and of the tin(II) and lead(II) ions to N,N-dimethylthioformamide, are reported. The Gibbs energies of transfer, ΔtG⊖, have been calculated from the standard electrode potentials of the Sn2+/Sn(s) and Pb2+/Pb(s) couples, which have been determined potentiometrically with the Ag(s)/Ag+ electrode as reference in the title solvents, and the Gibbs energies of transfer of the silver ion. The Gibbs energies of transfer of the alkaline-earth-metal ions were calculated from electrode or halfwave potentials of the M2+/M(am) couples in the title solvents and the difference in standard electrode potential between the M2+/M(am) and M2+/M(s) couples reported in the literature. The enthalpies of transfer, ΔtH⊖, have been obtained from calorimetrically determined enthalpies of solution of the anhydrous metal trifluoromethylsulfonates. The entropies of transfer, ΔtS⊖, have been calculated from the experimentally determined ΔtG⊖ and ΔtH⊖ values. All measurements have been carried out at 25 °C. The extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption has been applied in order to calculate the contributions from the single ions. The tin(II) and lead(II) ions are solvated more strongly in dimethyl sulfoxide and N,N-dimethylthioformamide than in water, while they are solvated more weakly in methanol and acetonitrile. The small tin(II) ion is solvated more weakly and the larger lead(II) ion is solvated more strongly in pyridine than in water. The alkaline-earth-metal ions are solvated more strongly in dimethyl sulfoxide than in water, while methanol and the nitrogen donor solvents acetonitrile and pyridine solvate these ions more weakly than water. The enthalpies of transfer for these ions to the solvents studied are exothermic except for the tin(II), calcium and strontium ions to acetonitrile. The entropies of transfer to all solvents are markedly negative except for N,N-dimethylthioformamide where the TΔtS⊖ values are close to zero. The difference in solvation of an ion between two solvents is mainly dependent on the bonding character of the ion–solvate bonds and on the way in which the ion affects the solvent bulk.

Coordination of divalent transition-metal ions to xanthine in aqueous solution

Abstract The stability constants of the 1:1 complexes [M(HL)] + formed between xanthine (H 2 L) and M 2+ = Mn 2+ , Co 2+ , Ni 2+ , Zn 2+ , and Cd 2+ in 0.1 mol dm −3 NaNO 3 aqueous solution were determined at 25°C by potentiometric titrations using glass electrodes. Xanthine was deprotonated at N-1 with pK a = 7.41. The anion (HL − ) displayed a dichotomy for metal-ion binding at N-1 and N-7. The ratios for the metal-ion distribution between these sites were estimated. It was found that Mn 2+ , Ni 2+ and Cd 2+ favored the binding at N-7, while Co 2+ and Zn 2+ showed approximately equal distributions between N-1 and N-7.

Application of Pitzer's equations to dissociation constants of ammonium ion in lithium chloride–sodium chloride mixtures

The Pitzer equations have been used to calculate the dissociation constants of NH+4 ions in concentrated LiCl–NaCl solutions at 25 °C. The calculated values agreed with the observed values within experimental uncertainties provided all the higher-order interaction terms (θS and ψS) concerned were introduced. The θ(NH4Na) and ψ(NH4NaCl) values, which are not available in the literature, were determined from isopiestic measurements of NH4Cl–NaCl solutions.

Coordination of mercury(II) to amino acids under physiological conditions

Abstract The complex formation of mercury(II) with glycine(HL) and β-alanine(HL) was investigated under physiological conditions (at 37°C in 0.15 mol dm−3 NaCl aqueous solution) by glass-electrode potentiometry. From the analysis of the emf data in the two systems by use of computer program MIQUV, it was concluded that the species formed in both the systems are [HgL]+ and [HgL2] and their formation constants in the glycine system are larger than the corresponding ones in the β-alanine system, notwithstanding the lower basicities of the amino and carboxylate groups within glycine than those within β-alanine. The formation constants in the glycine system measured under the present experimental conditions (no data in the β-alanine system is available in the literature) are extremely less than those observed in different ionic media such as KNO3, probably because chloride is bound to mercury(II) with high stability.

Complexation of thiomalic acid with mercury(II) and lead(II) under physiological conditions

The complex formation of thiomalic acid (H3L) with Hg(II) and Pb(II) was investigated under physiological conditions of 37 degrees C and 0.15 mol dm-3 NaCl by potentiometric titrations using glass electrodes. From the analysis of the emf data in the two systems by use of computer program MIQUV it was concluded that the species formed in the two systems are [HgH4L2], [HgH3L]-, [HgH2L2]2-, [HgHL2]3-, [HgHL], [HgL]-, [HgL2]4-, [Hg(OH)L]2-, [Hg(OH)L2]5-, [PbH2L2]2-, [PbH2L]+, [PbHL2]3-, [PbHL], [PbL]-, [Pb(OH)L]2-, and [Pb(OH)2L]3-. The hydrolytic reactions of Hg(II), data on which were used in the analysis of the above system, were also studied by separate potentiometric titrations. Measurements of 13C NMR spectra of [HgL2]4- and [PbL]- and [PbHL2]3- in D2O solutions suggested that the ligand coordinates with both the metal ions through the sulfhydryl group and one of the two carboxylate groups in such a way that the five-membered chelate ring is formed within the complexes.

Evaluation of dissociation constants of ammonium ion in aqueous lithium perchlorate and lithium chloride-sodium chloride mixed solutions

The Pitzer approach has been applied to the evaluation of dissociation constants of ammonium ion in lithium perchlorate and lithium chloride-sodium chloride mixed solutions at 25°C. The calculated values showed good agreement with the observed values, provided all the higher-order interaction terms (θs and Ψs) concerned were introduced. The unknown Ψ(NH4LiClO4) value was determined from the isopiestic measurements of NH4ClO4−LiClO4 mixed solutions. Parameters in the Pitzer formalism for ammonia-ion interactions involved in LiCl and NaCl media were determined by use of the activity coefficients of ammonia measured in LiCl−NaCl mixed solutions by a transpiration method.