Crystallization of calcium oxalate monohydrate at dipalmitoylphosphatidylcholine monolayers in the presence of chondroitin sulfate A

The growth and aggregation of calcium oxalate monohydrate (COM) crystals beneath dipalmitoylphosphatidylcholine (DPPC) monolayers in the presence of chondroitin sulfate A (C₄S) was systematically examined under different surface pressure. The results indicated that the addition of C₄S can inhibit the crystal growth and prevent the aggregation of COM crystals. Under a DPPC monolayer, well-defined three-dimensional hexagonal prisms and threedimensional rhombus prisms with sharply angled tips were obtained. The DPPC monolayer at a surface pressure of 10mN/m can match the Ca²⁺ distance of the (101) face of COM better than at 20 mN/m. The addition of C₄S could cooperatively modulate the interaction strength between the monolayer (or itself) with the specific morphology determining faces such as (101) and (0 2 0), and thus results in remarkable stabilization of the (101) faces. The dramatic changes in morphological details were due to the strong electrostatic interactions between the Ca²⁺-rich (101) crystal faces of COM and the polyanionic polysaccharide C₄S together with the negatively charged sites of the zwitterionic DPPC monolayers. The increase of the concentration of C4S can further enhance the stabilization of the (101) face.