Oxidovanadium(IV) Schiff Base Complex Derived from Vitamin B₆: Synthesis, Characterization, and Insulin Enhancing Properties

Abstract

A new Schiff base, [H(4)pydmedpt](2+)·2Cl(-), derived from one of the forms of vitamin B(6) has been synthesized by condensation of pyridoxal hydrochloride with N,N-bis[3-aminopropyl]-methylamine (medpt) and characterized by analytical and spectroscopic methods. The molecular structure is calculated by density functional theory (DFT) procedures, and the donor properties of each individual donor atom are evaluated by calculation of the Fukui function. One pot reaction of pyridoxal and medpt with vanadyl acetylacetonate yields the brown complex [V(IV)O(H(2)pydmedpt)](2+)·2Cl(-)1, which upon recrystallization from water crystallizes as [V(IV)O(pydmedpt)]·5H(2)O 2. The compounds are characterized by analytical and spectroscopic methods, 2 being also characterized by single crystal X-ray diffraction. It displays a slightly distorted octahedral geometry around the vanadium atom involving the coordination of N(amine), two N(imine), and O(phenolato) donors of the ligand. One of the phenolato oxygen donors is positioned trans to the terminal O-oxido atom with relatively short V-O(phenolate) {2.041(3) Å} and long V-O(oxido) {1.625(4) Å} bond distances when compared to other known compounds. The two different pK(a) values (6.0 and 7.9) obtained for 1 are due to protonation of the pyridine ring nitrogen atoms having different basic characters, this being also substantiated by theoretical calculation of the proton affinity of the O- and N- atoms of the molecule. The spin Hamiltonian parameters are obtained from the electron paramagnetic resonance (EPR) spectra, but the A(z) value (ca. 155 × 10(-4) cm(-1)) is lower than expected by applying the additivity rule for the present set of equatorial donor atoms (ca. 162-163 × 10(-4) cm(-1)), this being attributed to the strong trans V-O(phenolate) bond. The UV-vis transitions and EPR spectral parameters are calculated by DFT procedures, and both the calculated electronic transitions and the hyperfine coupling constants agree well with those experimentally observed. The inhibitory effect of 1 on FFA release and % glucose uptake determined with isolated rat adipocyte cells gave IC(50) and EC(50) values lower than for V(IV)OSO(4) and of the same order of magnitude of other reported insulin enhancing vanadium compounds.

Correlation of Insulin‐Enhancing Properties of Vanadium‐Dipicolinate Complexes in Model Membrane Systems: Phospholipid Langmuir Monolayers and AOT Reverse Micelles

“…Numerous vanadium compounds have demonstrated antidiabetic effects1–25 but the in vitro assays that are used have problems predicting the efficacy of the vanadium compounds across oxidation states 8. 11, 14, 21, 23, 26–28 Although their mode of action is not fully understood, it is generally accepted that these compounds are potent phosphatase inhibitors and it is presumed that they act at the active site of protein tyrosine phosphatases such as PP1B and, thus, indirectly exert an effect on signal transduction 4.…”

Thirty years through vanadium chemistry

“…The compounds prepared are slightly to moderately soluble in water and the order of stability of the complexes formed is pyridoxamine b H 2 pyr 2 en b H 2 pyr 2 an. Pyridoxal and pyridoxamine are forms of Vitamin B 6 and are non-toxic metabolites and this work promoted the start of many other studies involving pyridoxal Schiff base (pyr 2 en) and reduced Schiff base derivatives (pyr 2 an) by several groups including ours [155][156][157][158][159].…”

“…[154] were published, either for the preparation and use of vanadium complexes or of other metal ions. As mentioned Schiff bases and reduced Schiff bases derived from pyridoxal have the advantage of being more compatible with solvents containing water, thus they were proposed either as ligands for the preparation of complexes with potential pharmaceutical use, or for homogeneous or supported catalytic systems to be used with water containing solvents [155][156][157][158][159].…”

Inhibition of Acrylamide Formation by Vanadium Salt in French Fries and Potato Chips

“…Vitamin B6- [20] and vitamin E- [24] combined vanadium complexes have been reported to have better antidiabetic activity than vanadium alone. Some foods such as mushrooms, shellfish, black pepper, parsley, dill weed, beer, wine, grain, and grain products have significant levels of vanadium.…”