dilute solutions, and the impact of calcium and phosphate ortho-Phospho-L-serine (H 2 C, where C represents the serineions on the process was not systematically studied.
phosphato ion), a constituent of salivary proteins, seems to play
The ''adsorption'' of o-phospho-L-serine (Fig. 1) from an important role in the mineralization of teeth. To understand aqueous solutions in these studies (10, 11) is an ion-exthe basic mechanism of this interaction, the uptake of o-phosphochange process and as such should be affected by calcium, L-serine from relatively concentrated aqueous solutions (up to 100 phosphate, and hydrogen ions. Therefore, to elucidate any mmol/L) onto synthetic hydroxyapatite was studied. Previous mechanism of adsorption, the concentrations of these chargestudies have shown that in the dilute concentration range (Γ΅12.5 determining ions should be taken into consideration and acmmol/L) the uptake followed a regular Langmuirian adsorption counted for (12)(13)(14)(15)(16)(17)(18)(19). Monitoring of the charge-determining plot. At higher concentrations the uptake curve increased steeply, but no formation of a separate phase in the reacted apatite was ions originating from the substrate and the correlation of discernible, either by optical or by scanning electron microscopy. their concentrations with those of the solute ions may also The dissolution of apatite released phosphate and calcium ions clearly demonstrate the occurrence of a chemical reaction into the solution in amounts linearly related to the uptake of serine or the formation of a separate phase before the reaction with P/C Γ
1 and Ca/C Γ
2. The charge and mass balance of manifests itself in any other manner. The interactions of the reaction can be reconciled with the formation of the surface alizarin red S, chlorhexidine digluconate, and citric acid with complex (shown within brackets):
hydroxyapatite in aqueous solutions (20-22) were demonstrated, in this manner, to involve chemical reactions. Ca 10 (OH) 2 (PO 4 ) 6 / 6H 2 C r [Ca 6 (HC) 2 (HPO 4 ) 2 (PO 4 ) 2 ]
The ''adsorption'' or uptake of o-phospho-L-serine in the / 4Ca 2/ / 2HC 10 / 2C 20 / 2H 2 PO 10 4 / 2H 2 O. dilute concentration range (Γ΅12.5 mmol/L) was restudied with concomitant monitoring of calcium, phosphate, and hy-The formation of two other surface complexes is possible; however, drogen ions in order to establish whether the interaction the complex shown above probably disrupts the apatite lattice the is pure ion-exchange adsorption. To explain the somewhat least. Traces of CaCrH 2 O precipitate out from the filtrates of peculiar ''affinity'' of phosphoserine, as compared to L-serhighly concentrated solutions after 6 days.