Models for enzyme–copper–nucleic acid interaction: interaction of some copper complexes derived from salicylaldehyde, glycine and α-alanine with cytosine, cytidine and deoxycytidine

Abstract

The interaction of [CuL(H₂O)](H₂L = salicylideneglycine or salicylidene-α-alanine) with cytidine and cytosine has been investigated using UV–VIS, IR, EPR, ¹H NMR line-broadening and electrochemical techniques. Adducts of the type [CuL(B)(H₂O)_n](B = cytosine or cytidine, n= 0 or 1) have been isolated. Infrared spectra of these adducts and a ¹H NMR line-broadening study of the interaction of [Cu(salgly)(H₂O)] with cytidine and deoxycytidine indicate the involvement of the N(3) and O(2) sites in co-ordination. EPR spectra and electrochemical studies show that the extra methyl group in the alanine complex leads to distortion of the co-ordination plane, thereby resulting in stronger interaction with bases. However, cytosine interacts with the glycine complex strongly as the planarity of the latter favours semi-chelation involving the O(2) site. The extent of interaction of the bases with the copper(II) complexes depends on the co-ordinative unsaturation and distortion from the co-ordination plane around Cu^II as well as the basicity and ortho effect of the former. On the other hand, steric effects of the ligands are important in binding to Cu^I.