Investigation of the interactions of neohesperidin dihydrochalcone and maprotiline hydrochloride with human serum albumin protein by spectrofluorimetric method

In this study, the interactions of neohesperidin dihydrocalcone (NHD) antioxidant substance and maprotilin hydrochloride (MHC) drug substance with human serum albumin (HSA) protein, the most abundant protein in blood plasma, were investigated by fluorescence and circular dichroism spectroscopy. Fluorescence measurements were carried out at four different temperatures (15 °C, 25 °C, 37 °C and 45 °C) and at physiological pH value of 7.4. It was found from florescence measurements that there was an interaction between HSA and NHD, on the contrary to HSA-MHC system. Stern-Volmer quenching constant, quenching rate constant, binding constant, number of binding site and thermodynamic parameter (?H, ?S and ?G) values were calculated for the binding process of NHD to HSA protein.Static quenching was effective for the quenching mechanism of HSA-NHD system. Binding constants of HSA-NHD system were found to be 4.01x104 M-1, 2.79x104 M-1, 2.11x104 M-1 and 1.16x104 M-1 at 15 °C, 25 °C, 37 °C and 45 °C, respectively. This result indicated that an increase in the temperature led to a decrease in the binding constant value. Furthermore, there was one NHD binding site on HSA protein. Binding process occured spontaneously and was exothermic. Thermodynamic parameter values showed that the main interaction forces between HSA and NHD molecules were the formation of hydrogen bonding and van der Waals forces. In addition, the binding of NHD to HSA caused a change in the secondary structure of protein. Circular dichroism analysis indicated that the amount of ?-helix in HSA protein decreased with increasing NHD concentration.