Synthesis, crystal structure, and biological activities of two chiral mononuclear Mn((III)) complexes

Two new chiral mononuclear Mn((III)) complexes, [MnL((R)) Cl (C2 H5 OH)]•C2 H5 OH () and [MnL((S)) (CH3 OH)2 ]Cl•CH3 OH (), {H2 L = (R,R)-or (S,S)-N,N'-bis-(2-hydroxy-1-naphthalidehydene)-cyclohexanediamine} were synthesized and characterized by various physicochemical techniques. Bond valence sum (BVS) calculations and the Jahn-Teller effect indicate that the Mn centers are in a +3 oxidation state. The statuses of the two complexes in the solution were confirmed as a pair of enantiomers by electrospray ionization, mass spectrometry (ESI-MS) spectrum. The binding ability of the complexes with calf thymus CT-DNA was investigated by spectroscopic and viscosity measurements. Both of the complexes could interact with CT-DNA via an intercalative mode with the order of (R-enantiomer) > (S-enantiomer). Under the physiological conditions, the two compounds exhibit efficient DNA cleavage activities without any external agent, which also follows the order of R-enantiomer > S-enantiomer. Interestingly, the concentration-dependent DNA cleavage experiments indicate an optimal concentration of 17.5 μM. In addition, the interaction of the compounds with bovine serum albumin (BSA) was also investigated, which indicated that the complexes could quench the intrinsic fluorescence of BSA by a static quenching mechanism.