Biologically relevant metal complexes with mixed O,S donor ligands

Thio analogues of two 3-hydroxy-4-pyrones (Hma, Hema) and two 3-hydroxy-4-pyridinones (Hmpp, Hdpp) have been synthesized as a new class of ligand precursors. Reacting 3-hydroxy-4-pyrones with P2S5 led to the formation of the respective 3 hydroxy-4-pyranthiones (Htma, Hetma) in reasonable yields. One of these pyranthiones, thiomaltol (Htma), was further reacted with aqueous NH4OH and MeNH2 to yield 3-hydroxy-4-pyridinethiones, Hmppt and Hdppt, respectively. During the synthesis of the 3-hydroxy-4-pyridinethiones, their dimeric forms Hmppt-dimer and Hdppt-dimer were also isolated and characterized. Solution studies of the monomeric compounds established that these thio compounds have lower pKa values than the corresponding oxygen analogues, as expected. X-ray crystallographic analyses of Htma and Hetma confirmed that only the carbonyl oxygen (C=O) had been substituted with a sulfur atom and C=S bond lengths in the resulting molecules are longer than the C=O bond lengths in their synthetic precursors. X-ray crystallographic analysis of Hdppt-dimer demonstrated the presence of a disulfide bond in the dimeric organic compounds.; The four monomeric ligand precursors were complexed with vanadium to yield eight complexes: four oxovanadium(IV) and four vanadium(III) complexes. Solution studies (potentiometric and spectrophotometric) of the four oxovanadium(IV) compounds indicated the formation of reasonably stable complexes with (VO)L 2 and (VO)L2(OH) as the dominant species at physiological pH. X-ray crystallographic analysis demonstrated the presence of cis and trans isomers of VO(tma)2. For both isomers, the two ligands are in the equatorial plane with the V=O bond perpendicular to the ligands, forming a square pyramidal structure.; Reaction of the four monomeric ligand precursors with Ga3+ and In3+ ions yielded new tris(bidentate ligand) complexes. X-ray quality crystals of the fac-isomer of Ga(tma) 3 were also obtained; two of the ligated S atoms were found in a cis configuration with respect to each other with the third sulfur atom and one of the oxygen atoms occupying the perpendicular axis. New complexes with a range of lanthanides (Ln3+) were also synthesized with the two pyranthiones, Htma and Hetma. The synthesis reactions yielded complexes of the type LnL3·xH2O and LnL2(OH)·xH 2O, supported by elemental analysis and spectroscopic evidence such as mass spectral data and IR and NMR spectra.