Potentiometric study of vitamin D-3 complexes with manganese(II), iron(II), iron(III) and zinc(II) in water-ethanol medium

Vitamin D-3 (LH) complexes with manganese(II), iron(II), iron(III) and zinc (II) were identified in water-ethanol medium (30/70). Their stability const ants were determined at 298 K and at a constant ionic strength of 0.100 M u sing potentiometric methods. The computerisation of the experimental data s howed the presence of ML (M = metal, L = deprotonated vitamin D-3) and ML, species in all cases; in addition, the ML, iron(III) complex was detected. The calculated overall stability constants beta for (MnL)-L-II, (FeL)-L-II, (FeL)-L-III and (ZnL)-L-II are, respectively, in logarithms, 12.4, 16.5, 2 8.5 and 16.5. Under the experimental conditions, the only protonated specie s MLH detected was with iron(III). (C) 1999 Elsevier Science Inc. All right s reserved.