Precipitation of calcium oxalate monohydrate at phospholipid monolayers

Studies of calcium oxalate monohydrate (COM) precipitation at Langmuir mono layers of the phospholipids dipalmitoylphosphatidylglycerol (DPPG), dipalmi toylphosphatidylcholine (DPPC), and dipalmitoylphosphatidylserine (DPPS) ar e reported. The precipitation is heterogeneous and selective, with a majori ty of crystals orienting with the COM (10(1) over bar) face toward the mono layer interface for each phospholipid. The number density of COM crystals d epends on the identity of the phospholipid monolayer, decreasing in the ord er DPPG > DPPS > DPPC. It was also found that COM precipitation increases a s the surface pressure of the monolayer is lowered and with the addition of low levels (<0.1%) of cholesterol. The possibility that changes in monolay er fluidity influence COM attachment is discussed.