The adsorption of acidic amino acids and homopolypeptides on hydroxyapatite

Abstract

The adsorption of poly-l-glutamic and poly-l-aspartic acid and their monomers on precipitated nonstoichiometric hydroxyapatite (Ca10-x(PO4)6-x(HPO4)x (OH)2-x·xH2O) were studied under mild basic conditions (∼pH 8). The adsorption isotherms of the amino acids were of the Langmuir type. The spectroscopic results are consistent with an adsorption mechanism in which terminal carboxyl groups are attached to surface calcium ions. These calcium ions are those originally associated with phosphate moieties in the hydroxyapatite surface. On the basis of the infrared spectra at variable relative humidity, a model of poly-l-glutamic chain adsorption is proposed in which chains lie with the majority of their segments on adsorbent surfaces. © 1981.