Estimation of the pK(a) of the amine groups of benzhydrylamine resin and its lysyl derivative by measurement of swelling

For better evaluation of the potential of benzhydrylamine resin (BHAR), used as a solid support for peptide synthesis, as a novel anion-exchange resin, the pK(a) of its amine group was estimated by microscopic measurement of the sizes of the dry and swollen beads. Using the volume of the bead occupied by the solvent (as a percentage) as the swelling parameter, a plot of the degree of swelling of BHAR loaded with 2.4 mmol g(-1) amine groups against the pH of the medium produced a decreasing sigmoidal-type curve with increasing pi. By considering the point of inflection of the curve, a pK(a) value of approximately 7.5 was estimated far the amine group of tile BHAR, the same approach was also applied to the lysyl derivative of the BHAR (Lys-BHAR) and pK(a) values around 6.5 and 10.0 were obtained for the alpha and epsilon amine groups, respectively.UNIV São Paulo,CENA,LAB MICROBIOL & BIOL MOL,BR-13400970 PIRACICABA,SP,BRAZILWeb of Scienc