A new oxovanadium(V) complex of NH 4 VO 3 and tryptophan (TrpH) has been synthesized in aqueous solution at pH 6.0 and characterized by elemental analysis, UV-Vis, FT-IR, 1 H-NMR and mass spectroscopic data. The complex (Na 4 [V 3 O 9 (Trp)]) was diamagnetic in nature as was evident from the electron spin resonance spectroscopy (ESR) and the magnetic susceptibility measurements, in conformity with the presence of vanadium(V) in the structure. The electrochemical behaviour of Na 4 [V 3 O 9 (Trp)] complex was also studied on the hanging mercury drop electrode (HMDE) by using cyclic voltammetry (CV). The cyclic voltammograms of Na 4 [V 3 O 9 (Trp)] complex exhibit two new reduction waves at -0.38 V and -1.01 V in Britton-Robinson buffer (pH 6.0) for the potential range from 0.0 V to -1.2 V.
The interaction of novobiocin (NOV), an aminocoumarin antibiotic, with cysteine was studied by square-wave voltammetry technique on the hanging mercury drop electrode in different pH values. After the addition of NOV into the cysteine solution, the peak current of mercurous cysteine thiolate decreased and its voltammetric peak potential shifted to more positive values. Voltammetric results showed that NOV binds with cysteine forming 1:1 nonelectroactive molecular complex by means of electrostatic and hydrogen-bonding interactions. The binding constants of NOV with cysteine at pHs 5, 7 and 10 were calculated to be 3.06×10 3 , 1.54×10 4 and 1.06×10 5 M -1 , respectively. Furthermore, a possible mechanism of such interaction was also discussed.
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