Abstract

The complexation of VO²⁺ ion by ten acetamidrazone and 2-phenylacetamidrazone derivatives (L) was studied. Sixteen novel VO²⁺ complexes were synthesised and characterised through the combined application of analytical and spectroscopic (EPR (electron paramagnetic resonance), FT-IR and diffuse reflectance electronic absorption) techniques. Eight are 1:2 species of composition [VOL₂]SO₄ · xH₂O and eight are 1:1 species with formula [VOL(SO₄)]_n · xH₂O. The experimental data suggest a bidentate coordination mode for L with the donor set formed by the imine nitrogen and the carbonyl oxygen. EPR spectra indicate a square-pyramidal geometry for the 1:1 complexes and a penta-coordinated geometry intermediate between the square-pyramid and the trigonal-bipyramid for the 1:2 species. The hyperfine coupling constant along z axis, A_z, of the 1:2 complexes exhibits a marked reduction with respect to the predicted value (~148 × 10⁻⁴ cm⁻¹ vs. ~170 × 10⁻⁴ cm⁻¹). IR spectroscopic evidence supports the presence of sulphate as a counter-ion in the 1:2, and as a bridging bidentate ligand in the 1:1 complexes. Insulin-mimetic tests on modified fibroblasts, based on a modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazoliumbromide) assay, performed on three of the bis-chelated and eight of the mono-chelated derivatives, indicate that they are biologically active. The similar hydro/lipophilicity and the lack of ligand substituents recognizable by cell membrane receptors prevent substantial differentiation in the insulin-mimetic action.

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