Investigation Of The Interaction Between Biological Molecules And Pharmaceutical Determination By Zero Current Potentiometry

It is important to investigate interactions between metal ions or drug molecules and biomolecules. Voltammetry is one of the most common techniques in this field, but the application of it is limited if the research objects have no electrochemical activity or the redox peaks of the both reactants are overlapped with each other. Zero Current Potentiometry, a new kind of electrochemical method, is based on tracking the changing of the interfacial potential when the interactions are at the conducting material surface/substances interface no matter the electroactivity of the research objects. It is used to investigate the molecular interaction in this thesis.Hermodynamics of metal ions with various valences with amino acids, interactions between protein and pharmaceuticals and pharmaceutical determination were investigated. The detailed contents were as follows:(1)Coordination between copper ions with varied valence, Cu2+ and Cu+, with glycine(Gly) was investigated by zero current potentiometry. By applying a specific linear sweep potential Eapp on copper wire(CW), Cu+ or Cu2+ were selectively electro-generated on the CW surface according to the redox characteristic of Cu2+/Cu and Cu+/Cu couples. When Gly was added in buffer solution, Cu+ or Cu2+ bonded with Gly through coordination reaction, resulting in the changing of the interfacial potential at the corresponding interface. The changing of the interfacial potential was tracked by measuring zero current potential(Ezcp) that corresponds to where circuit current I was equal to zero in recorded I-Eapp curve. Zero current potential Ezcp showed linear relationship with-logc(Gly) in both cases. Through their linearity relationships, the stability constants logb and binding ratios m of complexes were calculated respectively. The obtained results showed that the proposed approach has the advantage for studying the coordination equilibrium of metal ions with varied valences, especially the ions that are not stable in solution.(2)Coordination between bovine serum albumin(BSA) with Indomethacin(INM) was investigated by zero current potentiometry. BSA was immobilized on the surface of carbon conducting material(CMC). Immersing BSA-CMC and SCE in aqueous solution containing INM, the interaction of BSA with INM produced a change on interfacial potential at the BSA-CMC/INM interface. The relationship between zero current potential Ezcp and t was recorded to track the dynamics process of INM-BSA interaction; while the changing of zero current potential Ezcp with the concentration of INM was used to to determine the thermodynamic constants of the interaction. The experiment results indicated that dynamics process of INM on the surface of BSA fitted Langmuir model well, and the apparent rate constant ka was 1.16×106(mol·l-1)-1·s-1. The binding ratio of INM with BSA was found to be 1:1 and the stability constant was 1.70×106l·mol-1. The content of INM in tablets was also determined using zero current potentiometry. The detection limit was 5.04×10-8mol·l-1 and the determined result was consistent with the result by UV-vis.(3)Coordination between BSA with Meloxicam(MLX) was investigated by zero current potentiometry. The BSA was immobilized on the surface of CMC. Immersing BSA-CMC and SCE in aqueous solution containing MLX, the interaction of BSA with MLX produced a change on interfacial potential at the BSA-CMC/MLX interface. The relationship between zero current potential Ezcp and t was recorded to track the dynamics process of MLX-BSA interaction; while the changing of zero current potential Ezcp with the concentration of MLX was used to to determine the thermodynamic constants of the interaction. The experiment results indicated that dynamics process of MLX on the surface of BSA fitted Langmuir model well, and the apparent rate constant ka was 1.64×106(mol·l-1)-1·s-1. The binding ratio of MLX with BSA was found to be 1:1 and the stability constant was 3.71×105 l·mol-1; Detection limit was 2.16×10-8mol·l-1, and the determined result was consistent with the result by UV-vis.(4)Lamivudine(LAM) was determined by zero current potentiometry. CMC and SCE were immersed in aqueous solution containing LAM with different concentration, obtaining the relationship between zero current potential Ezcp and logc(LAM). At the same time, the effect of p H in LAM solution was investigated. Results showed that zero current potential Ezcp has a good relationship with-logc(LAM) under the condition of different p H. The interference experiment results revealed that zero current potentiometry could be used for pharmaceutical determination directly.