Precipitation of calcium oxalate monohydrate at phospholipid monolayers

Studies of calcium oxalate monohydrate (COM) precipitation at Langmuir monolayers of the phospholipids dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylcholine (DPPC), and dipalmitoylphosphatidylserine (DPPS) are reported. The precipitation is heterogeneous and selective, with a majority of crystals orienting with the COM (101) face toward the monolayer interface for each phospholipid. The number density of COM crystals depends on the identity of the phospholipid monolayer, decreasing in the order DPPG > DPPS > DPPC. It was also found that COM precipitation increases as the surface pressure of the monolayer is lowered and with the addition of low levels (<0.1%) of cholesterol. The possibility that changes in monolayer fluidity influence COM attachment is discussed.