Study of the Protein Bovine Serum Albumin (BSA) and the Triblock Copolymer P103 Interface By Differential Capacitance

Abstract

Triblock copolymers are considered as non-ionic surfactants due to their self-assembling nature. Triblock copolymers can form structures similar to micelles and larger structures at a certain concentration and temperature. The triblock copolymers used here are biodegradable, water-soluble and are formed by chains of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), which can be arranged as A-B-A or B-A-B; where A are chains of PEO and B chains of PPO. And in this case they are referred by the commercial name Pluronics. The physicochemical properties of these surfactants (Critical micellar temperature (CMT), critical micellar concentration (CMC), density, molecular weight, etc.) depend on their molecular weight, the number of PPO and PEO chains present in the triblock copolymer, on the solvent (polar or no polar) and on the presence of salts in the solution. Applications of triblock copolymers are diverse; for instance, in the field of biotechnology they have been used for the controlled release of drugs, proteins, DNA. However, even when these compounds are already used and applied in several topics, there is a lack in the knowledge concerning to the effect of the interactions of them with other compounds, such as biopolymers. The main interest is to understand the effects of these interactions in the characteristic shape or size of aggregates formed by triblock copolymers. In order to obtain information about this topic, an initial approach is to study the interactions of some triblock copolymer and some well-characterized protein, as bovine serum albumin (BSA). BSA protein is cheap, easy to isolate and purify. In this way, BSA is an excellent option for the interactions study that exist between proteins and triblock copolymers. The objective of this work is to contribute to the knowledge of the interactions of triblock copolymers and proteins through the use of electrochemical techniques to obtain information about the amount of species adsorbed on the electrodes, as well as the size of the interface formed by the interaction of both, protein and triblock copolymers, once they are adsorbed on a metal surface. This information is important in the design of the sensors and is also necessary for the application of drug delibery and other fields of bioengineering and biomedicine. Thus, this investigation is focused on the interaction between BSA and the termosensible triblock copolymer Pluronic® P103 (PEO17-PPO60-PEO17). The interactions are studied by the adsorption of both compounds onto a gold disk electrode immersed in a phosphate buffer solution. Some electrochemical techniques, such as cyclic voltammetry and Differential-capacitance vs. Polarization potential are presented and analyzed in a wide range of temperatures and different P103 and BSA concentration. The thickness of the interface and the effect on the polarization potential are reported.