Studies on some novel Schiff-base complexes in solution and solid state

In solution Schiff-base complexes of stoichiometry MAB, MAB₂ or MA₂B₂ have been detected in the Co(II), Ni(II), Cu(II) and Zn(II)-o-vanillin (o-van) [A]-L-valine (val), L-glutamine (gln) and L-histidine (his)(B) systems. The results suggest that in the M-o-van-val/gln systems, the Schiff-base ligand (AB) is tridentate in M(AB) complexes, while (AB) is tetradentate in his systems. MAB₂ species can be represented as M(AB)(B), where the mode of coordination of (AB) would be similar to that in the M(AB) species. The MA₂B₂ complex can be represented as M(AB)₂, where (AB) is tridentate in all the systems. The stabilities of complexes follow the Irwin–Williams order of stability. MAB complexes were isolated and conformed by characterization data. Conductance studies indicate that all complexes are non-ionic. Magnetic susceptibility and electronic spectral data suggest a tetrahedral structure in Co(II) and Ni(II)-o-van-val/gln and Ni(II)-o-van-his systems and square-planar structure in Co(II)-o-van-his and Cu(II)-o-van-val/gln/his systems for the MAB species. The IR spectral data indicate the tri and tetradentate binding of (AB) in the M(AB) complexes, respectively, in M(II)-o-van-val/gln and M(II)-o-van-his systems. Antimicrobial activity of the ligand and its Cu(II) complexes has been studied; Cu(II) complexes have higher activity than that of the ligand and control.     

Reactive oxygen and nitrogen species (RONS) scavenging reactions of o-vanillin: Pulse radiolysis and stopped flow studies

Reactions of peroxyl radicals and peroxynitrite with o-vanillin (2-hydroxy 3-methoxy benzaldehyde), a positional isomer of the well-known dietary compound vanillin, were studied to understand the mechanisms of its free radical scavenging action. Trichloromethylperoxyl radicals (CCl₃O ₂ ^· ) were used as model peroxyl radicals and their reactions with o-vanillin were studied using nanosecond pulse radiolysis technique with absorption detection. The reaction produced a transient with a bimolecular rate constant of approx. 10⁵ M⁻¹s⁻¹, having absorption in the 400–500 nm region with a maximum at 450 nm. This spectrum looked significantly different from that of phenoxyl radicals of o-vanillin produced by the one-electron oxidation by azide radicals. The spectra and decay kinetics suggest that peroxyl radical reacts with o-vanillin mainly by forming a radical adduct. Peroxynitrite reactions with o-vanillin at pH 6.8 were studied using a stopped-flow spectrophotometer. o-Vanillin reacts with peroxynitrite with a bimolecular rate constant of 3 × 10³ M⁻¹s⁻¹. The reaction produced an intermediate having absorption in the wavelength region of 300–500 nm with a absorption maximum at 420 nm, that subsequently decayed in 20 s with a first-order decay constant of 0.09 s⁻¹. The studies indicate that o-vanillin is a very efficient scavenger of peroxynitrite, but not a very good scavenger of peroxyl radical. The reactions take place through the aldehyde and the phenolic OH group and are significantly different from other phenolic compounds.     

邻香兰素对甲苯胺Schiff碱稀土配合物的制备和表征

前文曾报道了香兰素(3-甲氧基-4-羟基苯甲醛)与对甲基苯胺的Schiff碱稀土配合物。本文讨论邻香兰素(2-羟基-3-甲氧基苯甲醛)与对甲基苯胺的Schiff碱稀土配合物[LnL_2Cl·2H_2O]Cl_2(Ln:ce,Pr,Nd,Sm,Eu,Gd,Dy;L:Schiff碱)的制备和表征。 1 实验 1.1 配合物的制备 按文献方法,用等摩尔比的邻香兰素与对甲基苯胺在无水乙醇中先制成Schiff碱,然后按摩尔比1:2将稀土氯化物LnCl_3·nH_2O的无水乙醇溶液滴加到