Synthesis of monosodium salts of N-(5-nitro-salicylidene)-D-amino acid Schiff bases and their iron(III) complexes: spectral and physical characterizations, antioxidant activities

Abstract

Amino acid Schiff bases, [NaL]·nH2O (L = N-(2-hydroxy-5-nitrobenzylidene)alaninate, N-(2-hydroxy-5-nitrobenzylidene)valinate, and N-(2-hydroxy-5-nitrobenzylidene)phenylalaninate), were synthesized as monosodium salts (L1Na–L3Na). The structures of the monosodium salts were confirmed on the basis of elemental analysis, conductivity measurements, UV–vis, FT-IR, and 2D NMR (HMQC) spectroscopies. L1Na was also structurally determined by single-crystal X-ray diffraction. Hydrogen bond between the amino N(2)–H and phenolate O(1) of the salicylidene part of the molecule played important roles in stabilizing the zwitterion crystal structure. The ranges of the D–H…A angles and those of the H…A and D…A distances indicated the presence of short hydrogen bonds in the structure. In addition, the monosodium salts have been evaluated for in vitro antioxidant activity. Iron(III) complexes (L1Fe–L3Fe) have been obtained by reaction of the appropriate ligand with iron(III) chloride in a 2 : 1 M ratio. Fe(III) complexes were characterized by elemental and thermal analysis, conductivity and magnetic susceptibility measurements, UV–vis, FT-IR, and X-ray photoelectron spectroscopy methods.