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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 groupP43212andP41212, 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 between1and calf thymus DNA was also investigated by UV absorption spectra, fluorescence emission spectra and viscometry. The results indicate that1interacts with DNA very strongly (Kb = 2.01 × 107 L mol−1andKsq = 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. [ABSTRACT FROM AUTHOR]