Calcium and thiocyanate interactions with crosslinked albumin microcapsules: influence of the reticulation rate

Ca2+ and SCN- interactions with strongly or lightly crosslinked albumin microcapsules were studied, using 45Ca2+ for a pH range varying from 5.5 to 7.8 and 14SCN- ions for the range 2.15 to 3.0. With strongly crosslinked albumin, the Scatchard plots of equilibrium isotherms indicate a maximum number of binding sites for Ca2+ ions, when N is equal to 12 and an apparent association constant, K' is equal to 7.8 X 10(3) l/mol. For the weakly crosslinked albumin, this constant is equal to 11 X 10(3) l/mol and the variation of calcium absorption with pH has an unusual shape, with a maximum at pH 6.5. The measurement of SCN- ion absorption by lightly crosslinked microcapsules indicates a K' value of 5.4 X 10(3) l/mol and an N value of 7 for pH 2.15. These values are, respectively, 8.3 X 10(3) l/mol and 2 for pH 2.15 when using strongly crosslinked microcapsules.