Nickel(II) complexes with Schiff bases derived from 2-acetylpyrazine and tryptophan: synthesis, crystal structures and DNA interactions

A pair of stereoisomers of nickel Schiff base complexes, namely [Ni(C 17 H 15 N 4 O 2 ) 2 ·2CH 3 OH] n ( 1 ) (C 17 H 15 N 4 O 2  = 2-acetylpyrazine- l -tryptophan) and [Ni(C 17 H 15 N 4 O 2 ) 2 ·2CH 3 OH] n ( 2 ) (C 17 H 15 N 4 O 2  = 2-acetylpyrazine- d -tryptophan), were synthesized and characterized by physico-chemical and spectroscopic methods. The X-ray diffraction single-crystal analyses indicate that the structure of 2 is essentially 0D monomeric, while a 2D layer structure is formed through N–H…O intermolecular hydrogen bonds for 1 . The interactions between complex 1 and calf thymus DNA were investigated by spectroscopic and viscometric methods. The results indicate that complex 1 interacts with DNA very strongly ( K b  = 1.01 × 10 7  mol −1  L and K sq  = 1.11). The nature of the binding seems to be mainly an electrostatic interaction between DNA and the complex. However, other binding modes, such as hydrogen bonding, may also be present in this system.