Redox Chemistry of "Neglected Copper‐Tris" Complex in Presence of Ascorbic Acid and O2.

Sometimes unusual redox chemistry and modulation of enzyme activity Cu‐proteins can be encountered by the presence of a trace amount of Cu−Tris interaction (Tris‐(hydroxymethyl) aminomethane) during vitro studies. Herein, we addressed a redox chemistry of CuII−Tris with variable stoichiometric ratios in the presence of ascorbic acid (H2A) and O2. The redox chemistry of Bs3 (Cu : Tris; 1 : 3) with H2A/O2 was passed through several intermediates with progress on time yielding initially yellow precipitate, (Yp3), then green solution, (Gs3) and finally cyan solution (Cs3). The UV‐Vis spectra of Bs3, Gs3 and Cs3 displayed peaks at 640, 690 and 710 nm respectively suggesting CuII. The redox potential of CuII/CuI in Bs3, Gs3 and Cs3 were −0.18 V, −0.15 V and −0.19 V (vs. Ag/AgCl) respectively. The EPR spectrum of Bs3 showed an axial signal with g∥,⊥=2.483/2.105&A∥=160×10−4 cm−1 whereas Gs3 and Cs3 showed rhombic signal with g1,2,3=2.302/2.063/2.018&A∥=177×10−4 cm−1 and g1,2,3=2.274/2.064/2.016&A∥=164×10−4 cm−1 respectively suggesting a distorted tetragonal geometry. ESI−MS data indicated the probable composition of Bs2‐Bs5, Gs3 and Cs3 in solution. Integration of all spectroscopies data demonstrated the probable composition and redox mechanism. [ABSTRACT FROM AUTHOR]