Thermodynamics of interaction of imidazole with nucleosides, monophosphates as well as with aromatic amino acids

Abstract

1. 1. Use was made of the microcalorimetric method to determine the enthalpy ( Δ r H° aq) and concentration constants ( K c) of equilibrium upon the complex formation of imidazole with adenosine, guanosine, uridine, cytidine (cytosine) and their monophosphates as well as phenyl-alanine, tryptophan and alanine. 2. 2. The thermodynamic parameters of the complex formation were calculated from the assumption that the reacting substances interact in ratio 1:1. This simplest model is perfect to describe experimental data for the processes under study. 3. 3. The values of enthalpies ( Δ r H° aq) and concentration constants of equilibrium ( K c) upon interaction of imidazole, nucleosides and their monophosphates were found to be: for adenosine Δ r H° aq,aden = −26.0 ± 1.2 kJ/mol ( K c = 0.36 ± 0.05 M −); for AMP Δ rH° aq,AMP =−18.5 ± 1.2 kJ/mol (K c = 0.33 ± 0.05 M t ̄ ) ; for guanosine Δ r H° aq,guan = −14.5 ± 1.2 kJ/mol ( K c = 0.43 ± 0.05 M − ); for GMP Δ r H° aq,GMP = −10.1± 1.2 kJ/mol ( K c =0.51± 0.05 M −); for cyticline Δ r H° aq,cyti = −19.6 ± 1.2 kJ/mol ( K c = 0.17 ± 0.05 M −) and for cytosine Δ r H° aq,cyto = -20.9 ± 1.2 kJ/mol ( K c = 0.14 ± 0.05 M −1).