Enzyme-catalyzed synthesis of hydrated calcium oxalate

Calcium oxalate hydrate was prepared by a homogeneous precipitation method using hydrolysis of oxamic acid catalyzed by enzyme. A conventional enzyme screening strategy was adopted to obtain proper hydrolase that hydrolyzes oxamic acid to oxalic acid. Dimethylformamide-water mixed solvent was used to suppress the spontaneous hydrolysis of oxamic acid. The resultant precipitates were characterized by electron microscopy, thermogravimetry, Fourier transform-IR spectroscopy and X-ray diffraction. The calcium oxalate obtained by the enzyme-catalyzed precipitation was trihydrate and fibrous with a length of 50-100 μm while that obtained by a conventional homogeneous precipitation was monohydrate and granular.