Liquid-phase synthesis of calcium phosphates in the presence of gallic acid

Abstract

Acid, medium, and basic calcium phosphates were obtained by liquid-phase synthesis from aqueous solutions of calcium chloride and ammonium hydrogen phosphate at Ca/P molar ratios of 1,0-1,67 and pH 5-11 in the presence of a polyphenol compound (gallic acid). Using X-ray phase analysis and IR spectroscopy, it has been shown that brushite is formed in a slightly acidic medium (pH 5-6) at a Ca/P molar ratio of 1,0, the unit cell size of which can decrease in the presence of gallic acid. In an alkaline environment (pH 8-11), the polyphenolic compound chelates calcium ions, which leads to the formation of amorphized calcium phosphate, which after heating at 800°C turns into β-tricalcium phosphate and hydroxyapatite. It was found that the presence of gallic acid promotes the formation of basic calcium phosphate at a lower molar ratio (Ca/P 1,5) than for stoichiometric hydroxyapatite (Ca/P 1,67). It has been shown by thermal analysis that the liquid-phase synthesis of calcium phosphates in the presence of gallic acid promotes the transformation of brushite into calcium pyrophosphate, and amorphized calcium phosphates into tricalcium phosphate and hydroxyapatite, upon high-temperature treatment.

Keywords

• gallic acid
• liquid-phase synthesis
• brushite
• amorphized calcium phosphates
• hydroxyapatite
• tricalcium phosphate
• calcium pyrophosphate