Lamellar to hexagonal phase transition in DOPE-DOPC- Alkanol system: X-ray diffraction study

Alkane-1-ols (abbreviation CnOH, n is the number of carbons in alkyl chain) are known as general anesthetics that do not obey the Meyer-Overton rule [1]. Their anesthetic potency increases up to C11OH and then decreases, compounds with n 13 are nonanesthetic, although the molar partition coefficient Kp between the lipid bilayers and aqueous phase increases exponentially in the whole region [2]. Hornby and Cullis [3] have found that alkanols up to butanol stabilize the bilayer arrangement for EYPE (egg phosphatidylethanolamine) whereas longer alkanols induce the formation of hexagonal phase. Gruner and Shyamsunder [4] suggested that the anesthetic action might be coupled to protein function via alteration of the tensions leading to the spontaneous curvature of lipid monolayers. Lamellar phases of phosphatidylcholines (PCs) are maintained by the balance of repulsive and attractive forces acting within the headgroup and hydrocarbon regions of the lipid bilayer. Phosphatidylethanolamines (PEs) destabilize the lamellar (L ) phase of the mambrane bilayer and promote the formation of nonbilayer phases. They adopt hexagonal phase (HII) in liquid crystalline state at physiological temperatures and pH values [5].