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Effect of the membrane/protein interaction nature on adsorptive properties of ultrafiltration membranes based on aromatic poly- and copolyamides

Membranes are a science intensive product of interindustry use, without which a breakthrough development of basic and high-technology sectors of economy, development of science as well as effective solution of important goals of the social sphere and problems of environment protections are impossible. Active development of medicine, pharmaceutical industry and biotechnology in the recent years contributed to the growth of scientific and commercial interest in ultrafiltration. The most important characteristic of ultrafiltration membranes is selectivity. According to existing views the basis of the separation mechanism implemented in ultrafiltration is size selectivity. However, such phenomena as concentration polarization and adsorption play a very important role in separation. Investigation of these phenomena is of significant practical interest, because its results in many ways determine the choice of the membrane media, conditions of its recovery, the mode and conditions of filtration. Adsorption of proteins on the surface of porous membranes is a rather complicated process due to the individual mechanism implemented in each specific case. Therefore, the issue of the contribution of various types of interactions into the process of adsorption still remains controversial. To determine the nature of membrane/protein interaction and clarify the factors of its control, the present work involved investigation of sorption of several proteins on a number of synthesized porous membranes based on aromatic polyamides noted for the presence, nature and concentration of ionogenic groups. The investigations were carried out using bovine serum albumin, lysozyme of hen's eggs, myoglobin and bacitracin. Adsorption of proteins by the membranes was investigated in the static mode. The protein concentration was determined using the SF-2000 spectrophotometer  (experimental-design bureau Spektr) by optical density at the wave length λ=278 nm. To mathematically process the experimental data, the two-parameter models by Langmuir, Freundlich, Temkin and the three-parameter model by Langmuir-Freundlich were used. To assess the compliance degree of the experimental data to the selected mathematical models, the values of the coefficient of determination (R2) and sum squares errors (SSE) were used. It has been shown that in the case of the presence of charge in protein macromolecules and the membrane surface the role of electrostatic forces is dominant in the protein adsorption mechanism, however, the contribution of non-electrostatic interactions in the investigated membrane/protein systems is significant.