Cholesterol and phospholipids in membranes: The hydrogen bonding problem

Cholesterol and phospholipids are major components of biological membranes. The role of cholesterol in membranes is not metabolic and is known to be a regulator of membrane fluidity which in turn regulates various biological phenomena. We have studied the nature of cholesterol and phospholipid interaction in artificial membranes using ¹³C NMR spectroscopy. This involved preparation of phospholipids specifically labeled with ¹³C in the ester carbonyl group. Though the chemical shift data did not provide very useful information the T₁ and T₂ measurements indicated that previously proposed H bonding between the ester carbonyl group and hydroxyl group of cholesterol seems unprobable.