Electrophoretic mobility hydroxyapatite

The mechanism of interaction of amino acids at solid/ aqueous solution interfaces has been investigated through adsorption and electrokinetic measurements. Isotherms for the adsorption of glutamic acid, proline and lysine from aqueous solutions at the surface of rutile are quite different from those on hydroxyapatite. To delineate the role of the electrical double layer in adsorption behavior, electrophoretic mobilities were measured as a function of pH and amino acid concentrations. Mechanisms for interaction of these surfactants with rutile and hydroxyapatite are proposed, taking into consideration the structure of the amino acid ions, solution chemistry and the electrical aspects of adsorption. 

Only a few systematic studies have been carried out on the mechanism of interaction of organic surfactants and macromolecules. Mishra et al. (12) studied the effect of sulfonates (dodecyl), carboxylic acids (oleic and tridecanoic), and amines (dodecyl and dodecyltrimethyl) on the electrophoretic mobility of hydroxyapatite. Vogel et al. (13) studied the release of phosphate and calcium ions during the adsorption of benzene polycarboxylic acids onto apatite. Jurlaanse et al.(14) also observed a similar release of calcium and phosphate ions during the adsorption of polypeptides on dental enamel. Adsorption of polyphosphonate on hydroxyapatite and the associated release of phosphate ions was investigated by Rawls et al. (15). They found that phosphate ions were released into solution in amounts exceeding the quantity of phosphonate adsorbed. 

Figure 9. The effect of lysine on the electrophoretic mobility of hydroxyapatite.

Lipoprotein-X (Lp-X), an abnormal lipoprotein, occurs in patients with obstructive liver disease or LCAT deficiency. Lp-X floats in the density range of LDL and has the same electrophoretic mobility as LDL. It can be separated from LDL, however, by hydroxyapatite chromatography or by zonal centrifugation. The composition of Lp-X differs from that of LDL, and it does not react with antisera to LDL. The major apoproteins of Lp-X isolated from patients with LCAT deficiency are albumin, apo C, and apo A. Lp-X also contains small amounts of apo D and apo E. Lp-X from patients with obstructive liver disease has been reported to lack apo A-I, a powerful activator of LCAT. The lipid constituents of Lp-X are cholesterol (almost entirely unesterified) and phospholipids. In electron microscopy, negatively stained Lp-X preparations appear as stacks of disk-like structures rouleaux). 

Mishra, R.K., Chander, S., and Fuerstenau, D.W., Effect of ionic surfactants on the electrophoretic mobility of hydroxyapatite. Colloids Surf, 1, 105, 1980. 

Figure 3.1. Experimental examples of the PZC of > Al203, the PZNPC of goethite, the PZSE of hydroxyapatite, and the PZNC of kaolinite. (u is the electrophoretic mobility.)...

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