Properties of calcium carbonate precipitated in the presence of DPPC liposomes modified with the phospholipase A.sub.2

Small unilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles of average diameter 119 nm were used as a template for calcium carbonate precipitation. The precipitation was carried out from CaCl.sub.2 and Na.sub.2CO.sub.3 solutions at room temperature 25 °C and physiological temperature 37 °C. Moreover, liposomes modified with the enzyme phospholipase A.sub.2 (PLA.sub.2) were also used as an organic matrix. The influence of liposomes on the precipitation of calcium carbonate has been investigated using scanning electron microscopy and X-ray diffraction measurements. The particles surface modification was evidenced using zeta potential measurements and thermogravimetric analysis. The obtained results show that the effect of DPPC vesicles on the CaCO.sub.3 precipitation is concentration dependent. The stability of vaterite increases with the increase in liposomes content in the solutions. At the liposomes concentration equal to 100 mg L.sup.-1 a mixture of precipitated vaterite and calcite is observed. The temperature increase weakens this effect. Moreover, the enzyme PLA.sub.2 action has no significant influence on the calcium carbonate precipitation in the presence of DPPC liposomes at both investigated temperatures.