Preparation conditions of fibrous hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: HAp) particles were examined by two-step chemical routes: (i) the preparation of fibrous octacalcium phosphate (Ca₈H₂(PO₄)₆・5H₂O: OCP) particles by homogeneous precipitation, using 0.0333-0.0500 mol・dm^-3 Ca(NO₃)₂, 0.0200-0.0300 mol・dm^-3 (NH₄)₂HPO₄, 0.04-0.40 mol・dm^-3 urea ((NH₂)₂CO; precipitant) and conc. HNO₃, and (ii) the microwave-assisted hydrothermal heating of OCP particles at 130°C for 1-3 h. The fibrous HAp particles with the mean long-axis length of 307 μm were obtained when the calcium phosphate solution containing 0.0333 mol・dm^-3 Ca(NO₃)₂, 0.0200 mol・dm^-3 (NH₄)₂HPO₄ and 0.12 mol・dm^-3 (NH₂)₂CO, was heated under flux at 80°C for 24 h, followed by the microwave-assisted hydrothermal heating at 130°C for 3 h. The mean long-axis length decreased down to 255 μm, after the heating under reflux and microwave-assisted hydrothermal heating of the calcium phosphate solution containing 0.050 mol・dm^-3 Ca(NO₃)₂, 0.030 mol・dm^-3 (NH₄)₂HPO₄ and 0.20 mol・dm^-3 (NH₂)₂CO. Instead, the microwave-assisted hydrothermal heating of OCP particles in the HAp-dissolved solution, i.e., the dissolution of HAp powder by bubbling CO₂ gas, helped increasing the mean long-axis length to 437 μm.

View full abstract

Phosphorylation of hydroxyproline (Hyp) has been achieved using inorganic trisodium-cyclo-triphosphate (P_3m) in aqueous solution. In the reaction of Hyp (1.5 M) and P_3m (0.5 M), at pH 11, and 10°C, N-triphosphoryl hydroxyproline (P₃-(N)-Hyp) was synthesized. An intramolecular attack of carboxyl group on a phosphorus atom of P₃-(N)-Hyp yields cyclic phosphate derivative (P₁-(N,O)-Hyp). Hydrolysis of cyclic phosphate derivative occurs simultaneously to form N-phosphoryl hydroxyproline (P₁-(N)-Hyp). Here, we were able to show that Hyp reacts with P_3m to form the intermediates (P₃-(N)-Hyp and (P1-(N,O)-Hyp) and give the final product (P₁-(N)-Hyp). The optimum condition for P₁-(N)-Hyp was Hyp : P_3m = 2(1.0 M) : 1(0.5 M), pH 13, and 25°C. P₁-(N)-Hyp was synthesized by dissolving Hyp and P_3m in H₂O under the optimum conditions for 7 days, and isolated by adding 2-propanol to the reaction solution. The moisture retention of P₁-(N)-Hyp and Hyp alone were compared by measuring amount of water. The moisture retention of the P₁-(N)-Hyp can be increased more effectively than that of Hyp alone.

View full abstract

Catalytically active cerium dioxide is used as light reflection materials for cosmetic applications. Therefore, cosmetics containing this pigment cause oxidation of the skin. From this fact, the substitute for cerium dioxide is required to prepare the cosmetics without catalytic activity. Herein, as novel white pigments for use in cosmetics, cerium phosphate was prepared at various pH values. The chemical composition, powder properties, catalytic activity, color, and smoothness of the cerium phosphate were evaluated. All samples prepared in this work indicated XRD pattern of the cerium phosphate hydrate. The sample prepared at pH 4 had relatively small particles and low static friction resistance. The samples prepared at pH 5, 6, and 7 had no photocatalytic activity. The samples prepared at pH 5 and 6 exhibited high reflectance within the range of visible light.

View full abstract