Examining the binding mechanism of 3,4-dihydro-3-(2-oxo-2-phenylethylidene)-quinoxalin-2(1H)-one and its fragments to Cu²⁺

Abstract

The structure and stoichiometries of the complexes that could be formed between Cu²⁺ and 3,4-dihydro-3-(2-oxo-2-phenylethylidene)-quinoxalin-2(1H)-one (1) were investigated by various spectral techniques such as IR, fluorescence, UV–vis and electron paramagnetic resonance. The results suggest that initially 3 : 1 and 2 : 1 (1/Cu²⁺) complexes are formed at low Cu²⁺ concentration and upon adding more Cu²⁺, 1 : 1 (preferred) and 1 : 2 complexes are generated. Since 1 possesses two possible binding sites, further exploration was done by testing the binding ability of Cu²⁺ to fragments of 1, namely β-enaminoketone derivatives (2–3) and quinoxaline-2-one (4), and by executing calculations of thermodynamic parameters of the reaction between 1 and Cu²⁺ in ethanol, optimized geometries of the possible complexes, and estimation of stability constants at various stoichiometries. Consequently, a step-by-step binding mechanism is suggested for formation of various complexes between 1 and Cu²⁺.

Keywords:

• Quinoxalinone derivatives
• Chelate
• Cu²⁺ binding
• N,O
• Ligands
• Stability constants

Acknowledgments

This work was supported by grants from the National Basic Research Program of China (No. 2009CB930200), The National Key Technology R&D Program (2011BAD23B01), Beijing Natural Science Foundation (No. 7112008) and Beijing City Education Committee (KM201010005009). The authors are thankful to Dr Peter King and Prof. Marcel Maeder for their assistance with the data analysis using ReactLab^TM Equilibria program and to Mrs. E. Solomon for technical assistance. JYB is grateful to (the late) Mrs. Irene Evens for supporting this research.