Capillary electrophoretic separation of proteins and peptides using Pluronic liquid crystals and surface-modified capillaries

Separation of model mixtures of peptides/proteins carried out in a hydrophi lically coated capillary in 10 mmol/l Tris and 75 mmol/l phosphate buffer c ontaining 7.5% (w/w) Pluronic F127 copolymer (apparent pH 2.9) revealed tha t the separation is predominantly driven by the charge/mass ratio with litt le or no sieving effect. Using a coated capillary helped to remove current fluctuations that are observed in the fused-silica capillaries in the prese nce of the Pluronic copolymer. With peptides bearing distinct positive char ge (polylysine of M-r around 3300) molecular sieving helps more detailed se paration of individual species. Polyamino acids carrying negative charge ca n be brought to the detector window in the reversed polarity mode, however, no detailed separation of the individual species involved was observed und er the conditions used. With a naturally occurring mixture of collagen frag ments released by CNBr treatment of the protein the sequence of emerging pe ptides (positive polarity mode) with no relation to the rel. mel. mass coul d be revealed. It is concluded that separation of proteins/peptides in the presence of Pluronic in the background electrolyte occur on the charge/mass ratio basis with molecular sieving effects acting as a secondary partition mechanism. (C) 2000 Elsevier Science B.V. All rights reserved.