Solid and solution structures and DNA binding properties of [MII(4-CNpy)2(SO4)(H2O)3]·H2O for M = Cu, Co, Ni

Compounds of the type [M(H2O)3(SO4)(4-CNpy)2]·H2O, with M = Co and Ni, display an interesting hydrogen bonded layered structure in the solid state. The copper analog of the above species, [Cu(H2O)3(SO4)(4-CNpy)2]·H2O (1), has now been synthesized as well and is found to be isostructural in the crystallographic sense to the Co (2) and Ni (3) species. The solid and solution phase UV–Vis–NIR spectra of 1, 2, and 3 indicate that species of the type [M(H2O)4(4-CNpy)2]2+ may be present in aqueous solutions of 1, 2, and 3. The DNA binding behavior of the above water-soluble complexes with Calf-Thymus (CT) DNA has been investigated by isothermal titration calorimetry (ITC) to find that the nature and extent of interaction are dependent on the identity of the metal.

Graphical abstractCu(H2O)3(SO4)(4-CNpy)2 and its Co and Ni analogs strongly bind calf thymus DNA with the Cu species showing distinctive binding behavior.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A new complex, [Cu(4-CNpy)2(SO4)(H2O)3]·H2O, has been synthesized and characterized. ► This crystalline species is isostructural with its Co(II) and Ni(II) analogs. ► These complexes exist as [M(4-CNpy)2(H2O)4]2+ in aqueous solution. ► ITC data suggest that all three complexes bind strongly with CT-DNA. ► They bind differently in comparison with their respective metal sulfate salts.