Comment on Color Loss in Ethanolic Solutions of Chlorophyll a

Comment on Degradation of Ascorbic Acid in Ethanolic Solutions

“…This thermodynamic and kinetic approach to the study of molecular stability in various ethanol concentrations has been previously used for other molecules in ethanol solutions. , In this paper we show our analysis of the kinetics of degradation of ascorbic acid in ethanolic solutions reported by Hsu et al to provide a thermodynamic explanation for the decrease in activation energy observed in 40% (v/v) ethanolic solutions based on transition-state theory.…”

“…Interestingly, we recognized that the value of Δ H a ° strongly correlates with that of Δ S a ° throughout the ethanolic solutions as the R 2 value of the linear fitting in Figure B has a large value (0.9945). The correlation between enthalpy and entropy changes is possibly due to a phenomenon called enthalpy–entropy compensation, whereby an increase in enthalpy or entropy accompanies a corresponding increase in the other variable, consequently limiting the variation of Gibbs free energy change. ,− Stronger hydrogen bondings between water and ethanol in 40% (v/v) ethanolic solution may result in the decrease in observed enthalpy of the system. Because Δ G a ° remains relatively constant with a relatively large change in Δ H a ° at 40% (v/v) ethanol concentration (Figure C), we can conclude that a corresponding change in Δ S a ° is occurring as a result of enthalpy–entropy compensation.…”

On the Reverse Stability Kinetics of Meat Pigment Oxidation in Aqueous Extract from Fresh Beef

“…In this letter we show our analysis of the data of Frelka et al. () to explain the reverse stability of oxymyoglobin in terms of thermodynamics using transition‐state theory, which has been used in the thermo‐kinetic analysis of chemical reactions in agricultural and food chemicals (Brock, Rosa, & Kang, ; Farhoosh, ; Fisher, Purnell, & Kang, ; Mock & Kang, ; Nayak, Berrios, Powers, & Tang, ; Tang & Skibsted, ). We also discuss an inconsistency found in the original paper and suggest a follow‐up experiment that will allow us to develop a deeper understanding of the oxidation process.…”

Comment on Enhancement of the Catalytic Activity of a 27 kDa Subtilisin-like Enzyme from Bacillus amyloliquefaciens CH51 by in Vitro Mutagenesis

“…This means that ΔΔ H a ° is compensated by T ΔΔ S a °. This phenomenon is called enthalpy–entropy compensation, which is often observed in weakly coupled systems including proteins − and small chemicals. − …”