Abstract
The reaction of 5‐carboalkoxypicolinic acid (5 ROpicH, R=Me, Et, __i__Pr, __s__Bu; 1 a–d) with vanadyl sulfate yielded the complexes [VO(H~2~O)(5 ROpic)~2~], 2 a–d, with H~2~O and one of the picolinato ligands in the equatorial positions, and the second picolinate occupying equatorial (N) and axial (O) positions. Reaction of 1 a with [NH~4~][VO~3~] yielded [NH~4~][VO~2~(5 MeOpic)~2~], [NH~4~]‐3, in which the N functions of the picolinates are trans to the doubly bonded, cis‐positioned oxo groups. Complexes 1 a⋅H~2~O, 1 b, 1 c, 2 a⋅3.5 H~2~O and [NH~4~]‐3⋅4 H~2~O have been structurally characterised. A detailed pH‐potentiometric solution speciation analysis of the system VO^2+^‐1 a revealed a dominance of VO(5 OMepic)~2~ between pH 2 and 6, with the same coordination pattern, evidenced by EPR spectroscopy, as in the crystalline solid state. In ternary systems containing physiological concentrations of the low molecular mass biogenic binders (B) lactate, oxalate, citrate or phosphate, ternary species of general composition VO(5 MeOpic)B dominate at physiological pH, with citrate being the most effective competitor for picolinate. All of the complexes trigger glucose uptake and degradation by simian virus modified mice fibroblasts at non‐toxic concentrations (<100 __μ__M), with 2 a, [VO~2~(pic)~2~]^−^ and [VO~2~(dipic)]^−^ being at least as effective as insulin. Vanadium uptake by the cells is most effective in the case of 2 a. 2 a also effectively inhibits free fatty acid release by rat adipocytes treated with epinephrine, thus mimicking the inhibition of lipolysis by insulin.