Synthesis, structural characterization and evaluation of the chelating potential in C. elegans involving complexes of mercury (II) with Schiff-bases derived from amino acids

Two series of neutral mercury(II) complexes have been obtained from the reaction of HgPh(OCOCH3)(1, 2, and 3) or Hg(OCOCH3)(2)(4, 5, and 6) with N-(2-hydroxynaphtalidene)beta-alanine (L1H(2)), N-(5-bromosalicylidene)beta-alanine (L2H(2)), and N-(5-bromo-salicylidene)beta-phenylalanine (L3H(2)), respectively. The complexes were characterized by elemental analysis, IR, NMR (H-1, C-13, and Hg-199) and X-ray crystallography (1 and 2). The elementary analysis showed that the obtained compounds have a high degree of purity and the infrared spectra indicated the shifts of the main functional groups (carboxylate, azomethine and phenol) of the Schiff bases when compared to the respective mercury complexes. X-ray diffraction analyses are similar for complexes 1 and 2, consistent with mononuclear compounds bearing a primarily di-coordinated HgII nucleus with several additional Hg-O interactions, which give rise to supramolecular assemblies. Solution NMR analyses indicate that the primary coordination is retained in DMSO for 1, 2 and 3, but the additional interactions observed in solid state are lost in solution. Complexes 4, 5 and 6 are also mononuclear and all analyses, in both solution and solid state, point to a di-coordinated Hg-II nucleus with a di-anionic Schiff base ligand. The biological evaluation of the Schiff base (L1H(2)) chelating potential was performed by pretreating Caenorhabditis elegans (C. elegans) nematodes with the L1H(2) (1 mM) followed by phenylmercury acetate exposure (LC50 = 290 mu M). The pretreatment with L1H(2) resulted in a significant protection of worm survival against phenylmercury acetate toxicity. Together, these data show that the chelating potential of these ligands is a crucial factor in reducing the toxic effects caused by metals in the worm, suggesting them as promising agents in chelation therapy. (c) 2020 Elsevier B.V. All rights reserved.