A Study of the Reaction of Ribose Bis(Thiosemicarbazonato) Copper(II) and Nitric Oxide

Abstract

The acid constant of ribose bis(thiosemicarbazone), RibTSC, and the formation constants of ribose bis(thiosemicarbazonato) copper(II), Cu(RibTSC-2H), and Cu(RibTSC-2H)-(NO)ₓ were determined (where x = 1 or 2). The SPEFO version of the LETAGROP was used to determine both constants, and the graphical method was also used for the first constant. The results show that RibTSC has one isosbestic point at 350 nm and a pKₐ value of 11,08, Cu(RibTSC-2H) has a relatively large average formation constant of 6,188*106, and the logarithm of the formation constants of Cu(RibTSC-2H)-(NO)₁ and Cu(RibTSC-2H)-(NO)₂ were found to be 8,68 +- 0,12 and 11,41 +- 0,09, respectively.

The reaction between aqueous Cu(RibTSC-2H) and saturated aqueous nitric oxide, NO, in a pH 7.4 buffered aqueous solution, at 20°C, was studied using UV-visible. The absorbance of Cu(RibTSC-2H) at 468 nm decreases as portions of NO were successively added to 2 ml of 2,5*10⁻⁵ mol/L of this complex. A graph of ε(Cu(RibTSC-2H)) at 468 nm against [NO], at 20°C, reflects that Cu(RibTSC-2H)-(NO)₂ adduct is formed, which does not decompose when temperature is raised to 60°C. The concentration of 2.10⁻³ molL⁻¹ for saturated aqueous nitric oxide at 20°C was used for all calculations.