Interaction of the DNA bases and their mononucleotides with pyridine-2-carbaldehyde thiosemicarbazonecopper(II) complexes.: Structure of the cytosine derivative

Experimental studies of the binding interactions of [CuL(NO3)] and [[CuL'(NO3))(2)] (HL = pyridine-2-carbaldehyde thiosemicarbazone, and HL' = pyridine-2-carbaldehyde 4N-methylthiosemicarbazone) with adenine, guanine, cytosine, thymine and their moncinucleotides (dNMP), 2-deoxyadenosine-5'-monophosphate, (dAMP), 2'-deoxyguanosine-5'-monophosphate, (dGMP), 2'-deoxycytidine-5'-monophpsphate (dCMP), and thymidine-5'-monophosphate (dTMP) have been carried out in aqueous solution at pH 6.0, I= 0.1 M (NaClO4) and T = 25 degrees C. The complexation constants of these compounds, calculated by Hildebrand-Benesi plots for the dye binding, D, ([CuL] or [CuL']) to the nucleobases or nucleotides (P), have shown two linear stretches in adenine, guanine, dAMP and dGMP. The data were analyzed in terms of formation of 1:1 DP and 1:2 DP2 complexes with increasing purine base or nucleotide content. For cytosine and dCMP only 1:1 complexes have been observed, whereas for thymine and dTMP such complex structures were not observed. The [CuL(Hcyt)](ClO4) cytosine derivative has been isolated and characterized. The crystal structure consists of perchlorate ions and [CuL(Hcyt)](+) monomers attached by hydrogen bond, chelate pi-ring and anion-pi interactions. The Cu2+ ions bind to the NNS chelating moiety of the thiosemicarbazone ligand and the cytosine N13 site (N3, most common notation) yielding a square-planar geometry. A pseudocoorchnation to the cytosine 012 site (=O2) can also be considered. (c) 2008 Elsevier Inc. All rights reserved.