Hydroxyapatite, adsorption

The inhibition of Streptococcus mutans adherence to hydroxyapatite with combinations of alkyl phosphates and nonionic surfactants was tested. Seven alkyl phosphate derivatives and three nonionic surfactants were examined for their ability to inhibit the adherence of 3H-labeled cells of S. mutans to hydroxyapatite treated with buffer or parotid saliva. No compound by itself effectively hindered binding of bacteria to hydroxyapatite. A combination of certain of the alkyl phosphates, notably a disodium phosphate of 1-octadecanol, and nonionic surfactant at a 1 1 molar ratio gave a strong inhibition of S. mutans adherence. Treatment with this combination resulted in 98% reduction of adherence. Adsorption of the two types of surface-active agents alone and in combinations was studied using 14C-labeled agents. Electrophoretic measure-... 

The precise nature of the adhesion of the polyelectrolyte cements to untreated dental enamel and dentine has yet to be established. The earliest theory was due to Smith (1968) who speculated that the polyacrylate chains of the cement formed a chelate with calcium ions contained in the hydroxyapatite-like mineral in enamel and dentine. Beech (1973) considered this unhkely since it involved the formation of an eight-membered ring. Beech studied the interaction between PAA and hydroxyapatite, identified the formation of polyacrylate and so considered that adsorption was due to ionic attraction. 

Wilson, Prosser Powis (1983) studied the adsorption of polyacrylate on hydroxyapatite using infrared and chemical methods. They observed an exchange of ions and concluded that polyacrylate displaced surface phosphate and calcium, and entered the hydroxyapatite structure itself (Figure 5.2). They postulated that an intermediate layer of calcium and aluminium phosphates and polyacrylates must be formed at the cement-... 

In order to elucidate the mechanism of adhesion of ionomer-carboxylate cements, Wilson and his coworkers have carried out several studies on the adsorption of carboxylates - aliphatic, aromatic and polymeric-on hydroxyapatite (Skinner et al., 1986 Scott, Jackson Wilson, 1990 Ellis et al., 1990). 

Ellis, J., Jackson, A. M., Scott, R. P. Wilson, A. D. (1990). Adhesion of carboxylate cements to hydroxyapatite. III. Adsorption of poly(alkenoic acid)s. Biomaterials, 11, 379-84. 

Pure Ti02 was recently reported to be active in the disinfection of water contaminated by spores of the type Fusarium solani [142], Bacillus anthracis [143], or Cryptosporidium parvum oocysts [144], or when supported as nanocomposites on zeolite H(i for E. coli deactivation [145], and it found applications in water treatment as a replacement for chlorine. Ag-Ti02 immobilized systems were used for inactivation of bacteria, coupling the visible light response of the system and the strong bactericidal effect of Ag [146]. Silver was deposited on hydroxyapatite to form nanocomposites with a high capacity for bacterial adsorption and inactivation [147], or used for airborne bacterial remediation in indoor air [148],... 

Hicks and Riley [287] have described a method for determining the natural levels of nucleic acids in lake and seawaters, which involves preconcentration by adsorption onto a hydroxyapatite, elution of the nucleic acids, and then photometric determination of the ribose obtained from them by hydrolysis. 

Precipitation can occur if a water is supersaturated with respect to a solid phase however, if the growth of a thermodynamically stable phase is slow, a metastable phase may form. Disordered, amorphous phases such as ferric hydroxide, aluminum hydroxide, and allophane are thermodynamically unstable with respect to crystalline phases nonetheless, these disordered phases are frequently found in nature. The rates of crystallization of these phases are strongly controlled by the presence of adsorbed ions on the surfaces of precipitates (99). Zawacki et al. (Chapter 32) present evidence that adsorption of alkaline earth ions greatly influences the formation and growth of calcium phosphates. While hydroxyapatite was the thermodynamically stable phase under the conditions studied by these authors, it is shown that several different metastable phases may form, depending upon the degree of supersaturation and the initiating surface phase. 

Adsorption and Electrokinetic Effects of Amino Acids on Rutile and 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. 

Interest in the nature of interactions between shortchain organic surfactants and large molecular weight macromolecules and ions with hydroxyapatite extends to several fields. In the area of carles prevention and control, surfactant adsorption plays an important role in the Initial states of plaque formation (1-5) and in the adhesion of tooth restorative materials ( ). Interaction of hydroxyapatite with polypeptides in human urine is important in human biology as hydroxyapatite has been found as a major or minor component in a majority of kidney stones ( 7). Hydroxyapatite is used in column chromatography as a material for separating proteins (8-9). The flotation separation of apatite from... 

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. 

Adsorption and Electrokinetic Behavior of Hydroxyapatite. The adsorption densities of glutamic acid and lysine on hydroxyapatite are shown in Flgures b and 7. The change in slope of the adsorption isotherm at 10 M glutamic acid is considered to be due to a... 

Figure 6. The isotherm for adsorption of glutamic acid on hydroxyapatite.

Figure 7. The effect of pH on the adsorption of glutamic acid and lysine on hydroxyapatite.

The adsorption of amino acids on rutile and hydroxyapatite exhibits some characteristics of specific adsorption. The results can be interpreted in terms of electrostatic models of adsorption, however, if reorientation of adsorbed molecules is taken into consideration. The electrokinetic behavior of hydroxyapatite in glutamic acid is complicated because of a chemical reaction, possibly involving calcium ions. The study shows that it is necessary to take into consideration the orientation of adsorbed molecules, particularly for zwitterionic surfactants. 

Humic substances. Analogous to the reactions described above, humic substances (the polymeric pigments from soil (humus) and marine sediments) can be formed by both enzymatic and non-enzymatic browning. High concentrations of free calcium and phosphate ions and supersaturation with respect to hydroxyapatite can sustain in soil, because adsorption of humic acids to mineral surfaces inhibits crystal growth (Inskeep and Silvertooth, 1988). A similar adsorption to tooth mineral in a caries lesion can be anticipated for polycarboxylic polymers from either the Maillard reaction or enzymatic browning. 

J. Lin, S. Raghavan, D.W. Fuerstenau, The adsorption of fluoride ions by hydroxyapatite from aqueous solution. Colloids Surf. 3 (1981) 357-370. 

Anti-adhesive effect. Green and roasted coffee, used in a treatment mixture and as a pretreatment on beads, inhibited the Strep tococcus mutans sucrose-independent adsorption to saliva-coated hydroxyapatite beads. The inhibition of Salmonelb mutans adsorption indicated that coffee-active molecules may adsorb to a host surface, preventing the tooth receptor from interacting with any bacterial adhesions. Among the known tested coffee components, trigonelline and nicotinic and chlorogenic acids are very... 

La is of interest in its relationship to biological hydroxyapatite because of their inhibitory effect on the demineralization of dental enamel. The form of La was not clear, namely surface adsorption or lattice incorporation. In an attempt to clarify it, laser-induced luminescence has been used (Mayer et al. 1999). La " is not luminescent, Gd-containing samples were prepared and studied. Figure 11.1 demonstrates Gd luminescence spectra with 266 nm laser excitation before and after heating at 800 °C. It is clearly seen that luminescence intensity is drastically stronger after thermal treatment. Thus precipitated samples must be heated to 800 °C to enable Gd " " to replace Ca and become luminescent and its incorporation form is surface adsorption. 

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