Structure-function correlation of mononuclear nonheme copper(II) compounds based on ligand backbone effect and phenoxazinone synthase activity

Abstract

Mononuclear nonheme copper(II) compounds, [Cu(BQEN)(CH3CN)]2+ 1 and [Cu(BQPN)(CH3CN)]2+ 2 (BQEN = N,N'-dimethyl-N,N'-di(quinolin-8-yl)ethaneane-1,2-diamine; BQPN = N,N'-dimethyl-N,N'-di(quinolin-8-yl)propane-1,2-diamine) are synthesised and characterized by elemental analysis, ESI-MS, EPR and single crystal X-ray diffratrometry. Compound 1 crystalises in Pi space group while 2 crystallises in P21/n. Compounds 1 and 2 exhibit distorted square pyramidal geometry which deviate interestingly by 4.8 and 48.0 percent from a regular square pyramidal structure in 1 and 2 respectively. This is attributed to the marginal increase in the carbon chain backbone of ligand in 2. Compounds 1 and 2 have been used in aerial oxidation of 2-aminophenol (H2AP) to 2-amino-phenoxazine-3-one (APX) which revealed phenoxazinone synthase activity. The DFT steric maps were utilized to understand the catalytic activity of 1 (percent Vbur, 71.3 percent) and 2 (percent Vbur, 75.6 percent). The current results clearly demonstrate an interesting structure-function relationship based on the effect of ligand backbone on the geometry.