Reduction Kinetics of Thionine in Aerobic Condition with D-Galactose

Reduction kinetics of thionine (Th) with D‐galactose (RH) was observed on a UV/Visible 1601 Shimadzu spectrophotometer at λ_max 599 nm. The results showed that the initially slow reduction kinetics got enhanced and proceeded to completion within a few minutes. A pseudo first order kinetics was observed when influence of different parameters like concentration of dye and reductant, ionic strength and temperature was investigated. A significant shift in wave length from 599 to 517 nm was observed at alkaline pH whereas addition of a small amount of acid caused a shift in equilibrium. This resulted in the generation of oxidized form of thionine which was pragmatic in the presence of atmospheric oxygen. Change in ionic strength at elevated temperature lied to decrease in the rate constant. Thermodynamics activation parameters like E_a reflects a high amount of energy required for reduction of Th with RH whereas entropy of activation (ΔS^?) and free energy of activation (ΔG^?) show the highly solvated states of transient complex which was less disorderly arranged than the oxidized form of dye. A mechanism consistent with above findings has been discussed in the relevant section of paper.