Synthesis, crystal structure, and DNA interaction of magnesium(II) complexes with Schiff bases

A pair of stereoisomers of magnesium Schiff base complexes, [Mg(C18H16N3O2)2·2CH3OH] n (1) (C18H16N3O2: 2-acetylpyridine-l-tryptophan) and [Mg(C18H16N3O2)2·2CH3OH] n (2) (C18H16N3O2: 2-acetylpyridine-d-tryptophan), was synthesized and characterized by IR, UV, elemental analysis, 1H NMR, and X-ray diffraction single crystal analysis. The analyses of the structures indicate that they all crystallize in the tetragonal crystal system, space group P4 3 2 1 2 and P4 1 2 1 2, respectively. The two magnesium complexes have similar crystal structures. Mg(II) is six-coordinate with two nitrogens from C=N, two nitrogens from pyridine, and two carboxylic oxygens in different ligands forming a distorted octahedral geometry. Through N–H···O intermolecular hydrogen bonds a 2-D layer structure was formed. The interaction between 1 and calf thymus DNA was also investigated by UV absorption spectra, fluorescence emission spectra and viscometry. The results indicate that 1 interacts with DNA very strongly (K b = 2.01 × 107 L mol−1 and K sq = 0.195). The nature of the binding seems to be mainly an electrostatic interaction between DNA and the magnesium complex. Other binding modes, such as hydrogen bonds, may also exist.