Synthesis, Characterization and Biological Activity of Oxovanadium(IV) Complexes Containing α-Amino Acid Schiff Bases and 5,6-Dimethyl-1,10-phenanthroline Ligands

Abstract

Five oxovanadium(IV) complexes of the type [VO(L)(DPhen)], containing Schiff base derived from α-amino acid, [where L = 3-hydroxybenzaldehyde-α-alanine (hb-Ala), 3-hydroxybenzaldehyde-DL-phenylalanine (hb-Phe), 3-hydroxybenzaldehyde-leucine (hb-Leu), 3-hydroxybenzaldehyde-glycine (hb-Gly) and 3-hydroxybenzaldehyde-DL-methionine (hb-Met) & DPhen = 5,6-Dimethyl-1,10-phenanthroline] have been synthesized and characterized by some physicochemical properties, molar conductance, magnetic susceptibilities measurements, elemental analysis, UV-Visible, FT-IR and EIS-MS spectral studies. The molar conductance values evidenced the non-electrolytic nature of the complexes. The magnetic moment values of the complexes are in accordance with the d 1 electronic configuration of the V IV O 2+ moiety and indicates the paramagnetic behavior of the complexes. IR spectral data indicates the coordination of tridentate amino acid Schiff base ligands to the vanadyl (VO 2+ ) ion through O, N, O-donor. ESI-MS spectral study confirmed the proposed structure of the complexes. All the analytical data suggested that all the complexes possess to have distorted octahedral geometry. The complexes were screened for their antibacterial activity against four human pathogenic bacteria; two Gram positive Escherichia coli & Pseudomonas aeruginosa and two Gram negative Staphylococcus aureus & Bacillus cereus with Kanamycin (K-30) standard. The result shows that all the complexes have moderate to strong potential antibacterial activity against all the pathogenic bacteria.

Equilibria of complexes in the aqueous cobalt(II)–N-(2-hydroxybenzyl)phenylalanine system and their biological activity compared to analogous Schiff base structures

“…Increasing the hydrophobic ligand shell around the cobalt(II) ion as result of charge delocalization enhances the ability of the complex to penetrate the bacterial cell membranes, limiting growth by disrupting cell respiration and blocking protein synthesis [5] , [18] , [64] .…”

“…Also, a benzyl group in the ligand molecule contributes to the increase of the antimicrobial activity of the complexes by enhancing their lipophilic nature. Bit et al note that the complex with 3-hydroxybenzaldehyde-D L -phenylalanine showed greater activity than other species containing an α-amino acid-derived Schiff base [18] . Interestingly, the Co(II)–PhAlaSal complexes show the same potent inhibitory activity towards H. pylori as free cobalt(II) [66] , whose MIC is comparable to those of some antibiotics commonly used in eradication therapies for these strains [67] .…”

“…Schiff bases, on the other hand, demonstrate high complexation potential with metal ions due to the presence of phenolic, amino and carboxyl groups that support the development of chelating compounds [8] , [15] , [16] , [17] . Schiff base ligands and their transition metal complexes have a variety of applications as antibacterial, antifungal, antitumor, anti-HIV, anti-inflammatory and antiviral agents [18] , [19] , [20] , [21] , [22] , [23] , [24] .

Scheme 1 The N -(2-hydroxybenzyl)phenylalanine (PhAlaSal) structure as zwitter-ionic form [LH 2 ].

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