Download thermodynamic study of solvation and complex formation in system

THERMODYNAMIC STUDY OF SOLVATION AND COMPLEX
FORMATION IN SYSTEM
Сu(NO3) 2 - β-ALANINE -WATER -ETHANOL AT 298K
V.N. Vandyshev, S.F. Ledenkov, A.S. Molchanov
Institute of solutions chemistry RAS, Ivanovo, Russia.
E-mail: [email protected]
The important problem of solutions chemistry concerns determination of
comprehensive thermodynamic characteristics of the processes in multicomponent
liquid systems. In real biological systems there are complex interactions between amino
acids, peptides, "metals of life» and aqueous solvent. The role of solvation effects and
hydratation in the biochemical interactions remains not clear in many cases. In this
work the influence of properties of water – ethanolic solvent on complex formation of
copper (II) with β-alanine is considered.
Heat effects of mixing of solutions Cu(NO3)2 with triple system of water – ethanol
– β-alanine have been measured by means an isoperibolic microcalorimeter.
Measurements have been carried out in a concentration range EtOH 0,00,8 mol.
fraction, β-alanine 00,02 mol/kg and copper nitrate 00,02 mol/kg.
The transfer enthalpies of sodium alaninate NaAla from water to aqueous ethanol
mixture have been determined. The maximum of endothermicity on the isotherm of
transfer enthalpies NaAla has been found out at concentration 0,05 mol. fraction EtOH.
At the further increase of ethanol concentration we observed change of a sign of
ΔtransH(NaAla) value that is caused by stronger solvation of ion Na+ in mixed solvents.
With use of the published data on transfer enthalpies of Na+ in a binary mixtures water
- ethanol the corresponding enthalpies of alanine anion are calculated.
Small concentration β-alanine in a solution essentially change thermochemical
characteristics of disolution Cu(NO3)2 salt, that is caused by formation of complexes
Cu(II) with β-alanine and also dissociation of amino acid during complexation. The
measured enthalpies of on complex formation are negative at all range water-ethanol
mixtures. At the same time process of dissociation of β-alanine in water solution is
endothermic.
Obtained thermochemical characteristics of processes of complex formation and
solvation allow to carry out the detailed analysis of thermodynamics of interactions of
molecules and ions in a multicomponent system. The environment of a solvated ligand
affects significant on the stability of complex compounds in a solution.
This work was supported by Russian Foundation for Basic Research (grant № 08-03-97527).