Counterion condensation in short cationic peptides: limiting mobilities beyond the Onsager-Fuoss theory.

摘要: We investigated the effect of background electrolyte (BGE) anions on electrophoretic mobilities cationic amino acids arginine and lysine polycationic peptides tetraarginine, tetralysine, nonaarginine, nonalysine. BGEs composed sodium chloride, propane-1,3-disulfonate, sulfate were used. For acids, determination limiting mobility by extrapolation, using Onsager-Fuoss (OF) theory expression, yielded consistent estimates. peptides, however, estimates found to spuriously depend BGE salt. This paradox was resolved molecular modeling. Simulations, all-atom as well coarse-grained levels, show that significant counterion condensation, an not accounted for in OF theory, occurs tetra- nonapeptides, even low concentrations. Including this quantitative estimation removed discrepancy between estimated different salts. The condensation be mainly due electrostatic interactions, with specific ion effects playing a secondary role. Therefore, conclusions are likely generalizable other analytes similar density charged groups is expected fail predictable way such analytes.