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Propyl gallate (PG) has been used as an antioxidant in food industry. Because of its widespread use in food industry, the toxicology of PG should be well addressed. In this study, for the first time, we report on the interaction of PG with human serum albumin (HSA) using fluorescence and circular dichroism (CD) spectroscopy. The fluorescence spectroscopy analysis showed significant decrease in the fluorescence intensity of HSA upon increasing concentration of PG.Further, the fluorescence quenching was found to be resultant form the formation of the PG-HSA complex, hence the quenching mechanism was rather a dynamic procedure. The positive values of enthalpy (ΔH), and entropy (ΔS) and the negative value of Gibb's free energy (ΔG) indicated that hydrophobic interactions play major role in the complexation of PG with HSA. To show the impact(s) of PG on the secondary structure of HSA, we capitalized on a CD technique, which showed a significant change in the secondary structure of HSA upon complexation with PG leading to a profound reduction of α-helices content of HSA. Molecular modeling analysis confirmed that the hydrophobic interaction was the major intermolecular forces that stabilize PG-HSA complex. Based on these findings, it can be concluded that PG molecules are dynamically bound to HAS and effectively distributed within the body.

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A copper(II) complex containing aspartame (APM) as ligand, Cu(APM)2Cl2·2H2O, was synthesized and characterized. In vitro binding interaction of this complex with human serum albumin (HSA) was studied at physiological pH. Binding studies of this complex with HSA are useful for understanding the Cu(APM)2Cl2·2H2O-HSA interaction mechanism and providing guidance for the application and design of new and more efficient artificial sweeteners drive. The interaction was investigated by spectrophotometric, spectrofluorometric, competition experiment and circular dichroism. Hyperchromicity observed in UV absorption band of Cu(APM)2Cl2·2H2O. A strong fluorescence quenching reaction of HSA to Cu(APM)2Cl2·2H2O was observed and the binding constant (Kf) and corresponding numbers of binding sites (n) were calculated at different temperatures. Thermodynamic parameters, enthalpy change (∆H) and entropy change (∆S) were calculated to be -458.67 kJ mol(-1) and -1,339 J mol(-1 )K(-1) respectively. According to the van't Hoff equation, the reaction is predominantly enthalpically driven. In conformity with experimental results, we suggest that Cu(APM)2Cl2·2H2O interacts with HSA. In comparison with previous study, it is found that the Cu(II) complex binds stronger than aspartame.