Combined voltammetric and spectroscopic analysis of small molecule–biopolymer interactions: The levodopa and serum albumin system

Abstract

An analytical method was researched for the simultaneous determination of reactants and products during the binding of important small molecules such as levodopa (LD) with biopolymers such as bovine serum albumin (BSA). Voltammetry and fluorescence spectroscopy were used to obtain the analytical profiles from different reactant mixtures as a function of concentration. This enabled the extraction of the equilibrium constants (KSV) which are reported for the first time. Voltammetric results supported the formation of the LD–BSA complex but not that with dopamine. Further information of the LD–BSA system was unattainable because the measured composite profiles could not be extracted.New information was obtained when the extended data matrix was resolved by the MCR–ALS method. The previously unavailable extracted voltammogram profile of LD–BSA complex indicated that the complex was electroactive; this was unexpected if the LD–BSA system was in its folded state, and hence, it was suggested that the protein must be unfolded. The observation that the drug:BSA stoichiometry was 3:1, i.e. (levodopa)3–BSA, supported this suggestion; these results were obtained from the MCR–ALS extracted concentration profiles for the three reaction components.