Modulation of calcium oxalatecrystallization by commonly consumed green tea

Abstract

In the present work, effects of the extract of green tea, one of the most popular beverages in peoples daily life, on the calcium oxalate (CaOx) crystallization were investigated by using field emission scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The experimental results showed that the tea extract (TE) was effective in directing CaOx crystallization from calcium oxalate monohydrate (COM) to calcium oxalate dihydrate (COD). Unusual morphological COD crystals were obtained in the presence of TE, but the morphological development did not consistently follow a TE concentration-dependent fashion. The complete transformation of gradually roughened COD bipyramids with layered {100} faces into larger porous COD bipyramids was achieved in the presence of the highest TE concentration, suggesting the existence of two different TE-mediated COD crystallization processes. These phenomena have not been reported previously, indicative of the unique impact of phenol-rich TE on CaOx crystallization. It is believed that the hydrogen bonds between the TE and CaOx host crystals play a pivotal role in prohibiting COM formation and in the morphological control of COD crystals. The hydrogen bonding interactions between the phenol groups of TE with the oxalate groups of CaOx were further discussed on the basis of FT-IR data.