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It was recently shown that oligolamellar vesicles of 3:1 mixtures of dioleoylphosphatidylethanolamine (DOPE) and the photopolymerizable lipid 1,2-bis[10-(2',4'-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphocho line (SorbPC) are destabilized by polymerization of the SorbPC [Lamparski, H., Liman, U., Frankel, D.A., Barry, J.A., Ramaswami, V., Brown, M.F.,O'Brien, D.F. (1992) Biochemistry 31, 685-694]. The current work describes the polymorphic phase behavior of these mixtures in extended bilayers, as studied by 31P NMR spectroscopy and X-ray diffraction. In the NMR experiments, samples with varying degrees of polymerization were slowly raised in temperature, with spectra acquired every 2.5-10 degrees C. In the unpolymerized mixiture, and in those photopolymerized samples where the monomeric SorbPC was decreased by 33% and 51%, an isotropic signal grew progressively until no signal from the lamellar liquid-crystalline (L alpha) phase remained. In the highly polymerized sample with a 90% loss of monomeric SorbPC, less than 20% of the lipids underwent this transition. In none of the samples was an inverted hexagonal phase (HII) observed, under conditions of slow heating to almost 100 degrees C. The X-ray diffraction studies indicated that samples which exhibit the isotropic NMR signal corresponded to a structure exhibiting no well-defined crystalline order, which upon thermal cycling became an inverted cubic phase belonging to either the Pn3m or Pn3 space groups. The temperature of the transition to the cubic precursor decreased as the extent of polymerization increased, demonstrating that photopolymerization of these lipid bilayers can significantly alter the composition and thermotropic phase behavior of the mixture.

Polyunsaturated fatty acids are widely distributed components of biological membranes and are believed to be involved in many biological functions. However, the mechanisms by which they act on a molecular level are not understood. To further investigate the unique properties of omega 3 polyunsaturated phospholipid bilayers, deuterium nuclear magnetic resonance (2H NMR) studies have been made of the liquid-crystalline (L alpha) and gel phases of a homologous series of mixed-chain phosphatidylcholines containing docosahexaenoic acid: (per-2H-n:0)(22:6)PC, where n = 12, 14, 16, and 18. The moments of the 2H NMR lineshapes have been evaluated, and from these the warming and cooling main phase transition temperatures were determined. The transition temperatures of the mixed-chain series were found to be significantly lower than those of the corresponding lipids in the disaturated series, di(per-2H-n:0)PC, with hystereses ranging from 2 to 14 degrees C. Distinct effects of the docosahexaenoyl chain on bilayer order were found, though these effects varied across the mixed-chain series. In evaluating the moment data, an empirical method for normalizing the moments with respect to differences in temperature was applied, in addition to using the reduced temperature method. For the systems studied here, the method of normalization had no significant effect on the interpretation of the moment data.

The configurational properties and dynamics of the arachidonic acyl chains of phospholipid bilayers have been investigated for the first time by solid-state 2H NMR techniques, with the goal of achieving a better understanding of the biological roles of polyunsaturated phospholipids. Vinyl perdeuterated arachidonic acid (20:4 delta 5,8,11,14-d8) was prepared from eicosatetraynoic acid (ETYA) and was esterified with 1-palmitoyl-sn-glycero-3-phosphocholine to yield 1-palmitoyl-2-vinylperdeuterioarachidonoyl-sn-glycero-3-phosphocho line [(16:0)(20:4-d8)PC]. 31P NMR spectra of aqueous dispersions of (16:0)(20:4-d8)PC as well as 1-perdeuteriopalmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine [(per-2H-16:0)(20:4)PC] were characteristic of the lamellar liquid-crystalline state. The dispersions had similar 31P chemical shift anisotropies, with little apparent motional averaging of the lineshapes due to macroscopic reorientation of liposomes or lateral diffusion of phospholipids about their curved surfaces. Comparison to other phosphatidylcholines indicated that both samples comprised the fully hydrated L alpha phase plus excess water. However, the dispersion of (16:0)(20:4-d8)PC yielded relatively narrow powder-type 2H NMR spectra, compared to (per-2H-16:0)(20:4)PC in the liquid-crystalline state. The differences in the 2H NMR powder patterns thus reflect differences in the configurational properties of the polyunsaturated sn-2 arachidonic acyl chain compared to the saturated sn-1 palmitic chain. When the powder-type 2H NMR spectra of the (16:0)(20:4-d8)PC bilayer were dePaked (theta = 0 degrees), they showed three kinds of deuterons upon integration: one with a large splitting (approximately 25-35 kHz), two with intermediate splittings (approximately 10-15 kHz), and the remainder with smaller splittings (approximately 0.3-5 kHz).(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction of divalent and trivalent metal cations, ferricyanide, a lipophilic ion (tetraphenylborate), and a local anesthetic (tetracaine) with the phosphocholine head group of egg lecithin was investigated by using wide-line 14N and 31P NMR. Measurements of the 14N quadrupolar splittings in the presence of a variety of perturbing agents demonstrated that the 14N NMR technique can be used to directly monitor ion or anesthetic binding. The 14N quadrupolar splitting (delta nu Q) is a measure of the order parameter of the C beta-N bond segment, and changes in delta nu Q as large as 3.5 kHz were observed. Moreover, a comparison of the changes in the quadrupolar splittings induced by the binding of ions or anesthetics provided a sensitive method of discriminating between these perturbing agents in their ability to alter the orientational order of the C beta-N bond segment of the phosphocholine moiety. Without exception, addition of metal ions or anesthetics always resulted in a decrease of the 14N delta nu Q. This reduction reflects a change in the average orientation or degree of motional averaging at the C beta-N bond segment position. In the case of metal ion binding, the strength of the interaction increased with the charge of the metal ion in the order Ca2+ less than Ln3+, in agreement with a previous 2H NMR study [Akutsu, H.,Seelig, J. (1981) Biochemistry 20, 7366-7373].(ABSTRACT TRUNCATED AT 250 WORDS)