Protonation Equilibria of Biologically Active Ligands in Mixed Aqueous Organic Solvents

Table 12

Protonation constants () of some α-amino acids in solution containing 50% DMSO at different temperatures and  mol·dm⁻³ NaNO₃ and their thermodynamic parameters^b.

System			20°C	25°C	30°C	35°C	Thermodynamics^d
							Gly	1	1	10.04	9.79	9.53	9.30	−85.71	−100.14	−55.87
1	2	14.14	13.85	13.52	13.22	−21.04		6.87	−23.09
L-Ala	1	1	10.02	9.85	9.69	9.46	−63.51	−24.63	−56.17
	1	2	14.19	13.96	13.75	13.46	−19.34	13.80	−23.46
L-Val	1	1	9.79	9.57	9.49	9.26	−57.69	−9.63	−54.82
	1	2	13.89	13.61	13.47	13.17	−21.75	4.31	−23.03
L-Ser	1	1	9.42	9.12	8.82	8.52	−103.66	−173.88	−52.02
	1	2	13.30	12.95	12.60	12.25	−17.28	15.34	−21.85
L-Isl	1	1	9.72	9.51	9.39	9.20	−58.07	−12.28	−55.74
	1	2	13.81	13.56	13.42	13.19	−11.06	40.55	−23.01
L-Leu	1	1	10.09	9.77	9.45	9.13	−110.57	−184.0	−55.74
	1	2	14.18	13.81	13.42	13.04	−21.07	6.51	−32.01

^aDMSO% (vol/vol), ^bdata taken from reference [87], and are stoichiometric coefficients corresponding to ligand and H⁺ respectively; ^dWith respect to the thermodynamic parameters (, and ) these parameters referred to these reactions (L⁻ + H⁺ LH^±, corresponding to –NH₂ group) and (LH^± + H⁺, corresponding to carboxylate group); The % is expressed as (volume/Volume).