POTENTIOMETRIC STUDY OF VITAMIN-D-3 COMPLEXES WITH COBALT(II), NICKEL(II) AND COPPER(II) IN WATER-ETHANOL MEDIUM

Vitamin D-3 complexes with cobalt (II), nickel (II) and copper (II) we re identified in water-ethanol medium (30/70). Their stability constan ts were determined at 298 K and at a constant ionic strength of 0.100 mol L(-1)using potentiometric methods. The computerisation of the expe rimental data showed the presence of ML (M = metal, L = deprotonated v itamin D-3) and ML2 species in all cases except for CuL2. The calculat ed overall stability constants beta, for CoL, Nit and Cut are, respect ively, in logarithms, 7.6, 7.8 and 9.3, in harmony with the Irving-Wil liams order of stability. Under the experimental conditions, the only protonated species MLH detected was with copper. (C) 1998 Elsevier Sci ence Inc. All rights reserved.