Structural studies of Fe(III) and Cu(II) complexes of salycylaldehyde benzoyl hydrazone, a synthetic chelating agent exhibiting diverse biological properties

Abstract

Salicylaldehyde benzoyl hydrazone (SBH) is a Schiff base that can function as a tridentate chelating agent [l-3]. Some thirty years ago, it was shown that this compound has modest bacteriostatic properties when tested in vitro against microorganisms such as Mycobacten’um tuberculosis, Mycobacterium smegmatis, Candida albicans and Aspergillus niger, although these effects were not sufficiently marked to encourage further study at that time [4, 51. Recently, however, interest in the biological properties of SBH has been renewed with the recognrtion that aroylhydrazones of this type are able to induce iron excretion in mammals and thus are potentially of use in the treatment of iron overload on man [6, 71. SBH itself can mobilize iron from iron-loaded reticulocytes in vitro [8] and produces high levels of iron excretion when administered to rats [9] . preliminary studies have also shown that SBH is an unusually potent inhibitor of DNA synthesis in a variety of cultured human and rodent cells and that the complex [CuCl(SBH)]*H,O produces significant inhibition of tumor growth when given to mice bearing a transplanted fibrosarcoma [lo-121. The common mechanism underlying these various biological effects of SBH appears to be an ability to penetrate cell membranes and disrupt the intracellular metabolism of essential metal ions. The exact nature of such disruptions, and the extent to which they may be exploited for therapeutic purposes, require much additional study, including detailed elucidation of the chemical properties of complexes formed between SBH and physiologically-important transition metals. This paper reports single crystal X-ray diffraction studies of two such complexes, [FeCla(SBH)(CHsOH)] and [CuCl(SBH)]~H,O. TABLE I. Selected Bond Distances, in A.