ISBN: 978-83-60043-10-3 - eurobic9

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Eurobic9, 2-6 September, 2008, Wrocław, Poland P197. Coordination Ability of Niacin Towards Nickel(II) Ions J. Urbańska and H. Podsiadły Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-3<strong>83</strong> Wrocław, Poland Niacin is a water-soluble type of vitamin B including nicotinic acid and nicotinamide. Nicotinic acid is converted in vivo to nicotinamide and although the two compounds are identical in their vitamin functions, their pharmacologic and toxic effects are different. _____________________________________________________________________ 316 N O OH Nicotinamide is an reactive moiety of two coenzymes with similar structures: nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) which are necessary for enzymatic catalysis of several vitally important redox processes. Metal complexes of biologically important ligands are sometimes more effective than the free ligands. In spite of the great biological importance of nicotinic acid and nicotinamide their interaction with metal ions is rarely studied polarographically. This is probable due to the electrochemical activity of these ligands which reduction waves overlap with the reduction wave of some metal ions or their complexes [1, 2, 3]. In this communication we present the polarographic, potentiometric and spectroscopic (UV-VIS) results on the coordination ability of these ligands towards Ni(II) ions. Ni(II) ions in non-complexing electrolyte undergo reduction process at mercury electrode irreversible at about - 1.0 V. Addition of very small amounts of nicotinamide or nicotinate ions causes the appearence of the new wave (prewave), at less negative potentials (- 0.7 V). This prewave increase with concentration of ligands in the solution, whereas Ni(II) wave decreases and finally disappears. The appearance of this prewave implies the formation of at least one Ni(II)-niacin complex which is reduced at a lower potential than that required for the reduction of aquaion. Detailed analysis polarographic curves on the concentration of reagents (ligands and Ni(II) ions), pH values and mercury drop time allow us to establish the stoichiometry of the complexes reduced at the electrode and those existing in the solution as well as their stability constants. Such a peculiar behaviour of nickel(II) ions at the dropping mercury electrode was already observed in the presence of the other N and N, O donor ligands [4, 5, 6, 7]. Potentiometric and spectroscopic studies display that nicotinic acid and nicotinamide are relatively week ligands towards nickel(II) ions. The complexation occurs in the pH range 3 - 6; at higher pH the formation of poorly soluble species (probably Ni(OH)2) has been observed. The stability constants of complexes determined from potentiometric data are in good accordance with that obtained polarographically. UV-VIS spectroscopy confirms monodentate coordination mode of both ligands to nickel(II) ions, by the nitrogen of pyridine rings. References: [1] L. Campanella, P. Cignini and G. De Angelis, Rev.Roumaine Chim., 18, 1269 (1973). [2] R. Rodriguez-Amaro, R. Perez, V. Lopez and J.J. Ruiz, J. Electroanal. Chem., 278, 307 (1990). [2] E. Mathieu, R. Meunier-Prest and E. Laviron, Electrochim. Acta, 42, 331 (1997). [4] D.R. Crow and M.E. Rose, Electrochimica Acta, 24, 41 (1979). [5] P.K. Aggarwal and D.R. Crow, Electrochimica Acta, 25, 411 (1980). [6] J. Urbańska, H. Kozłowski, A. Delannoy and J. Henion, Anal. Chim. Acta, 207, 85 (1988). [7] J. Urbańska and H. Kozłowski, J.Coord.Chem., 42, 197 (1992). N O NH 2
Eurobic9, 2-6 September, 2008, Wrocław, Poland P198. Enantiomers of a Cr(III) Polypyridyl Complex: Photophysics and DNA Intercalation Studies S. Vasudevan a , S. Quinn a , N. Fletcher b , M. Wojdyla a , J. Kelly a a School of Chemistry, Trinity College, College Green, 2, Dublin, Ireland e-mail: vasudevs@tcd.ie c School of Chemistry and Chemical Engineering, Queens University, University Road, BT7 1NN, Belfast, United Kingdom Transition metal heteroleptic complexes of dipyridophenazine (DPPZ) have acquired wide acclaim as DNAbinding agents due to their strong binding, light-switching and photocleaving effects. The most studied of these are the Ruthenium complexes [1]. However, Kane-Maguire revealed the chromium analogues to be particularly interesting due to their long emission lifetimes, strong oxidising power and higher intercaltion with DNA [2]. In this work, the photophysics of Cr(III) polypyridyl complex, [Cr(phen)2dppz] 3+ has been explored using nanosecond transient absorption and fluorescence lifetime measurements. The single crystal X-ray diffraction studies of the complex revealed two enantiomers, which were successfully separated by means of size-exclusion chromatography. The interactions of these enantiomers with DNA was investigated by emission and optical spectroscopy, including thermal denaturation experiments and circular dichroism studies. References: [1] J. G. Vos, J. M. Kelly; Dalton Trans., 2006, 4869 - 48<strong>83</strong>. [2] N. A. P. Kane-Maguire, J. F. Wheeler; Coord. Chem. Rev., 2001, 145 - 162. _____________________________________________________________________ 317
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ISBN: 978-83-60043-10-3 - eurobic9

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