Monitoring CHAPS self-assembly by EPR spectroscopy and Factor Analysis

P.M.RODI; M.D. BOCCO GIANELLO; A.M. GENNARO

Carlos Paz

Congreso; XLII Reunión Anual de la Sociedad Argentina de Biofísica; 2013

Sociedad Argentina de Biofisica

CHAPS is a zwitterionic synthetic detergent derivative from bile salts. It is a facial detergent, and due to its peculiar characteristics, CHAPS self assembly has been subject of several works in the last years, and there are open discussions regarding the characteristic of the resulting micelles. In this work we obtain EPR spectra of the spin label 12-SASL in CHAPS solutions of a wide range of concentrations. The spectra show strong changes with concentration. Using Principal Factor Analysis we demonstrate that all the spectra can be reproduced as linear combinations of only three fundamental spectra, and obtained their relative weights at each detergent concentration. One of them corresponds to 12-SASL free in water, and the other two correspond to the label in motionally restricted environments. One of the motionally restricted components appears at a concentration coincident with the experimentally reported cmc of CHAPS, and it was assigned to 12-SASL in a ?Type 1? micelle. The relative weight of this component gradually decreases at increasing concentrations, with the rise of the component assigned to a ?Type 2? micelle. Rotational correlation times of the spin labels for each of the micelles were obtained by fitting the spectra with ?slow motion? conditions, and compared with the micelle rotational diffusion times calculated by MD (poster Herrera et al.). This comparison allows us to make estimations about the aggregation number.