Role of head group structure in the phase behavior of amino phospholipids. 2. Lamellar and nonlamellar phases of unsaturated phosphatidylethanolamine analogs

Abstract

Three types of analogues of unsaturated phosphatidylethanolamines (PE) have been prepared: phosphatidyl-omega-amino-1-alkanols, N-alkyl-PE's, and C2-alkyl-PE's, with alkyl substitution of carbon-2 of the ethanolamine head group. The physical properties of dioleoyl, dielaidoyl, and 1-palmitoyl-2-oleoyl phospholipids with these head groups have been examined by calorimetry, 31P NMR, freeze-fracture electron microscopy, and X-ray diffraction. N-Alkylation of PE, or substitution of the ethanolamine moiety by 3-amino-1-propanol or 4-amino-1-butanol, decreases the transition temperature of the hydrated gel phase (Tc) and considerably increases the temperature of the lamellar to hexagonal II transition (TH). The pattern of these effects for various PE analogues suggests that head group size and hydrophobicity as well as hydrogen bonding are important determinants of the phase behavior of these lipids. C2-Alkylated PE analogues exhibit several rather surprising properties, notably the ready formation of a quasi-crystalline "high-melting" solid phase even for di-cis-unsaturated species and substantially lower TH values than are observed for the parent PE species. The behavior of these compounds suggests that "hydration forces" can be more important than considerations of lipid "dynamic shape" in predicting the relative stabilities of lamellar vs. nonlamellar phases for at least some zwitterionic phospholipids.

Monomeric and dimeric anionic surfactants: A comparative study of self-aggregation and mineralization

“…In this respect, alkanolamines can act as organic counterions and are used widely in cosmetic products to replace potassium hydroxide or sodium hydroxide to neutralize fatty acids. Alkanolamines also act as counterions in phospholipids; therefore; they are relevant for the study of cell membranes [16]. Nevertheless, there is not much open literature on alkanolamine surfactants [17][18][19], and to our knowledge, there is no report on alkanolamine dimeric surfactants.…”

Structures of Lipid Assemblies

“…For example, addition of an ethyl group to the methylene next to the nitrogen in the phosphatidylethanolamine headgroup leads to a destabilization of the liquid crystalline lamellar phase and favors the formation of the hexagonal II phase. 11 There is direct evidence for this role of the hydrophobic effect in the structures formed by phosphatidylethanolamine. 12 Chaotropic agents such as guanidine hydrochloride disrupt water structure, reducing the unfavorable nature of the interaction of a hydrophobic species with an aqueous phase.…”

The lipid organisation of the cell membrane

“…In this phase the lipids form tubes with the polar head groups facing out and the fatty acyl chains facing the interior. Phosphatidylethanolamine is a lipid commonly found in cell membranes which can form the H II phase (Brown et al, 1986). In this phase the lipid forms tubes with the polar head groups facing inside and the fatty acyl chains facing outside (inverse of the H I phase).…”