Molecular diversity in several pyridyl based Cu(II) complexes: biophysical interaction and redox triggered fluorescence switch

Abstract

Variation of pyridyl based receptors around a Cu(II) center results in structural diversity allowing redox triggered Cu(II)/Cu(I) fluorescence switch for intracellular Cu(I) imaging. Single crystal X-ray structures of 2-hydroxy-6-methylnicotinic acid (L1), its mono nuclear Cu(II) complex, viz. [Cu(L1)(2)(H2O)(SO4)]center dot 2H(2)O (C1a), polymeric Cu(II) complex (C1b) and a dinuclear Cu(II) complex of 2-(naphthalen-2-ylmethylsulfanyl)nicotinic acid (L4), viz. [Cu-2(L4)(4)(H2O)(2)]center dot 1.12H(2)O (C4) with a Cu-Cu distance of 2.6028(7) angstrom are reported. Moreover, C1a interacts with calf thymus DNA, which is useful for disruption of normal DNA activity with plausible applications in biology (binding constant, K' = 1.56 x 10(4)). Chemical or electrochemical reduction of C1a generates a fluorescent Cu(I) complex. The lowest detection limit of L1 for Cu(I) is 50 mu M. The association constant of L1 for Cu+ is 7.09 x 10(2). Quenching constants of Cu(II) for L1, L2, L3 and L4 are 4 x 10(5), 4.2 x 10(6), 8.9 x 10(5) and 4.4 x 10(6), respectively. The magnetic behavior of C1b indicates a ferromagnetic one-dimensional solid.