Generic phase behavior of branched-chain phospholipid monolayers

Monolayers of chemically modified triple-chain phospholipids have been investigated at the air/water interface using pressure-area isotherms. The condensed phases of the lipids were characterized by grazing incidence X-ray diffraction (GIXD). Increasing chain length corresponds to a temperature effect, which was quantified for different lipids, depending on the head group structure using isotherm (two-dimensional systems) and DSC (three-dimensional systems) measurements. The combination of structure investigations revealed generic phase diagrams, which describe the phase behavior of multiple-chain lipids in two dimensions. For the 1-acyl-2-O-alkyl phospholipids, the generic phase diagram exhibits only L(2d), LS and LE phases while the exchange of the position of the branched acyl and the non-branched alkyl chains at the glycerol backbone leads to a much richer polymorphism (L(2h), L(2d), Ov, LS, S, tau, LE). Here we present the first experimental evidence of the unusual tau phase for multiple-chain lipid monolayers. This phase exhibits an undistorted in-plane lattice despite of tilted chains.     

The reproducibility of phospholipid analyses by MALDI-MSMS

The identification of phosphocholine and phosphoethanolamine lipids by MALDI TOF/TOF, including characterisation of the headgroup and delineation of the acyl chain at each position of the glycerol backbone, has been explored using lipids representative of each type. The relative intensities of fragments involving the neutral loss of one or other of the acyl chains from ion adducts of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) were compared. For POPC and POPE, a statistical preference for the loss of the chain from the sn-1 position was observed in the presence of lithium. For OPPC this selectivity was reversed for one of the fragments. In the absence of lithium, fragmentation was favoured at the sn-2 position for all lipids. In all cases, spectra obtained in the presence of lithium yielded more intense product ion peaks. Although Collision Induced Dissociation (CID) could be used for complete lipid characterisation, LIFT? was found to be a better method due to the presence of a greater number of distinguishing product ion peaks and a better shot-to-shot reproducibility of peak intensities.     

Synthesis of modified ether phospholipids

A number of modified ether phospholipids with additional substituents in the 2 position of the C(1)-alkyl chain, 1-O-[2-(R,S)-hydroxyhexadecyl]-2-O-methyl-rac-glycero-3-phosphocholine, 1-O-[2-(R,S)-acetoxyhexadecyl]-2-O-methyl-rac-glycero-3-phosphocholine, 1-O-[2-(R,S)-hydroxyhexadecyl]-2-chloro-2-deoxy-rac-glycero-3-phosphocholine, and 1-O-[2-(R,S)-acetoxyhexadecyl]-2-chloro-2-deoxy-rac-glycero-3-phosphocholine, have been synthesized.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 974–978, May, 1995.We thank Dr. V. S. Pashkov for spectroscopic measurements and Dr. M. V. Anikin for spectroscopic measurements and scientific discussions.This work was partially supported by the Russian Foundation for Basic Research (Project No. 94-03-08166).     

Structure of docosahexaenoic acid-containing phospholipid bilayers as studied by (2)H NMR and molecular dynamics simulations.

Polyunsaturated phospholipids are known to be important with regard to the biological functions of essential fatty acids, for example, involving neural tissues such as the brain and retina. Here we have employed two complementary structural methods for the study of polyunsaturated bilayer lipids, viz. deuterium ((2)H) NMR spectroscopy and molecular dynamics (MD) computer simulations. Our research constitutes one of the first applications of all-atom MD simulations to polyunsaturated lipids containing docosahexaenoic acid (DHA; 22:6 cis-Delta(4,7,10,13,16,19)). Structural features of the highly unsaturated, mixed-chain phospholipid, 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (PDPC), have been studied in the liquid-crystalline (L(alpha)) state and compared to the less unsaturated homolog, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The (2)H NMR spectra of polyunsaturated bilayers are dramatically different from those of less unsaturated phospholipid bilayers. We show how use of MD simulations can aid in interpreting the complex (2)H NMR spectra of polyunsaturated bilayers, in conjunction with electron density profiles determined from small-angle X-ray diffraction studies. This work clearly demonstrates preferred helical and angle-iron conformations of the polyunsaturated chains in liquid-crystalline bilayers, which favor chain extension while maintaining bilayer flexibility. The presence of relatively long, extended fatty acyl chains may be important for solvating the hydrophobic surfaces of integral membrane proteins, such as rhodopsin. In addition, the polyallylic DHA chains have a tendency to adopt back-bended (hairpin-like) structures, which increase the interfacial area per lipid. Finally, the material properties have been analyzed in terms of the response of the bilayer to mechanical stress. Simulated bilayers of phospholipids containing docosahexaenoic acid were less sensitive to the applied surface tension than were saturated phospholipids, possibly implying a decrease in membrane elasticity (area elastic modulus, bending rigidity). The above features distinguish DHA-containing lipids from saturated or monounsaturated lipids and may be important for their biological modes of action.     

Synthesis of cationic ether lipids of alkyl type with short-chain substituents at the 2-position of the glycerol backbone

A series of cationic ether lipids with short-chain substituents at the 2-position and various cationic groups attached directly or through a spacer group to the glycerol backbone was synthesized.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1826–1830, October, 1994.This work was supported by the Russian Foundation for Basic Research (Project No. 94-03-08-166).     

Synthesis and antitumor activity of new amphiphilic alkylglycerolipids substituted with a polar head group, 2-(2-trimethylammonioethoxy)ethyl or a congeneric oligo(ethyleneoxy)ethyl group

A new series of amphiphilic 1-octadecyl glycerolipids (eleven compounds, 1a-k) were designed and synthesized, in which the 3-phosphocholine portion of platelet-activating factor (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF) was replaced by the 2-(2-trimethylammonioethoxy)ethyl group and congeneric groups having oligo(ethyleneoxy)ethyl bridges of various lengths at position 3, together with modification at position 2 (lower alkyl, acetonyl, acetoacetyl, carboxymethyl and pyrimidin-2-yl groups). These ether lipids, characterized by a nonphosphorus lysoglycerolipid structure, showed potent antitumor activity in vitro (human promyelocytic leukemia cells, HL-60, and human epidermoid carcinoma cells, KB) and in vivo (mouse sarcoma S180 and mouse mammary carcinoma MM46). Maximal in vitro potency was obtained with 1-O-octadecyl-2-O-(2-pyrimidinyl)-3-O-[2-(2-trimethylammonioethoxy )ethyl] glycerol (1g; IC50 values for both HL-60 and KB were 0.32 microgram/ml, indicating a higher activity than alkyl-lysophospholipid, ET18-OMe). Several appropriately 2-substituted 1-octadecylglycerolipids with the 3-[2-(2-trimethylammonioethoxy)ethyl] group (e.g., methyl, 1b; butyl, 1f; 2,2,2-trifluoroethyl, 1j; and acetonyl, 1k) showed a potent life-span-prolonging effect on mice with ascites sarcoma S180 and on those with mammary carcinoma MM46, when administered intraperitoneally at 16.5 and 12.5 mg/kg/d, respectively. Compounds 1b and 1k showed definite tumor growth inhibition against solid sarcoma S180 in mice, whether given p.o. or i.v. at 16.5 mg/kg/d. Studies on the structure-activity relationships indicate that the metabolic stability to phospholipase C or related enzymes is at least partly responsible for the potent antitumor activity of this series of ether lipids.     

Dynamic assessment of bilayer thickness by varying phospholipid and hydraphile synthetic channel chain lengths

A library of "hydraphile" synthetic ion channel analogues that differ in overall length from approximately 28-58 A has been prepared. A new and convenient ion-selective electrode (ISE) method was used to assay Na(+) release. Liposomes were formed from three different phospholipids: 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and 1,2-dierucoyl-sn-glycero-3-phosphocholine (DEPC). The acyl chains of the lipids comprise cis-unsaturated 14:1, 18:1, or 22:1 residues, respectively. Sodium release was measured for each liposome system with each of the synthetic channels. Peak activity was observed for shorter channels in liposomes formed from DMPC and for longer channels in DEPC. A separate study was then conducted in DMPC liposomes in the presence of the putative membrane-thickening agents cholesterol and decane. Peak activity was clearly shifted to longer channel lengths upon addition of 20 or 40 mol % cholesterol or n-decane to the liposome preparation.     

Rapid access to phospholipid analogs using thiol-yne chemistry

Phospholipids and glycolipids constitute an essential part of biological membranes, and are of tremendous fundamental and practical interest. Unfortunately, the preparation of functional phospholipids, or synthetic analogs, is often synthetically challenging. Here we utilize thiol-yne click chemistry methodology to gain access to phospho- and glycolipid analogs. Alkynyl hydrophilic head groups readily photoreact with numerous thiol modified lipid tails to yield the appropriate dithioether phospho- or glycolipids. The resulting structures closely resemble the structure and function of native diacylglycerolipids. Dithioether phosphatidylcholines (PCs) are suitable for forming giant unilamellar vesicles (GUV), which can be used as vessels for cell-free expression systems. The unnatural thioether linkages render the lipids resistant to phospholipase A2 hydrolysis. We utilize the improved stability of these lipids to control the shrinkage of GUVs composed of a mixture of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and dioleyl-dithioether PC, concentrating encapsulated nanoparticles. We imagine that these readily accessible lipids could find a number of applications as natural lipid substitutes.     

Efficient synthesis of phospholipids from glycidyl phosphates.

New efficient routes to enantiopure phospholipids, starting from (S)-glycidol, are described. Lysophosphatidic acids and phosphatidic acids were obtained in good overall yields from (S)-glycidol, in only three and four steps, respectively. Moreover, the strategy can also be used to produce phosphatidylcholines in three steps. Using dialkylphosphoramidites, (S)-glycidol was phosphorylated to give (R)-1-O-glycidyl dialkyl phosphates. Regiospecific epoxide opening, using hexadecanol or cesium palmitate, followed by phosphate deprotection, provided lysophosphatidic acids. 2-O-Esterification prior to phosphate deprotection provided 1,2-O-diacyl and 1-O-alkyl-2-O-acyl phosphatidic acids. Phosphorylation of (S)-glycidol using phosphorus oxychloride followed by in situ treatment with choline tosylate produced (R)-glycidyl phosphocholine. Subsequent nucleophilic opening of the epoxide using cesium palmitate produced 1-O-palmitoyl-sn-glycero-3-phosphocholine, which has been used in syntheses of phosphatidylcholines.     

Electrostatic contributions to indole-lipid interactions

The role of electrostatic forces in indole-lipid interactions was studied by (1)H and (2)H NMR in ether- and ester-linked phospholipid bilayers with incorporated indole. Indole-ring-current-induced (1)H NMR chemical shifts of lipid resonances in bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycero-3-phosphocholine, 1,2-di-O-octadecenyl-sn-glycero-3-phosphocholine, and 1,2-di-O-octadecenyl-sn-glycero-3-phosphomethanol show a bimodal indole distribution, with indole residing at the upper hydrocarbon chain/glycerol region of the lipid and near the choline group, when present. (2)H NMR of indole-d(7)-incorporated lipid bilayers reveals that the former site is occupied by about two-thirds of the indole, which adopts a distinct preferred orientation with respect to the bilayer normal. The results suggest that the upper hydrocarbon chain/glycerol location is dictated by many factors, including interactions with the electric charges and dipoles, van der Waals interactions, entropic contributions, and hydrogen bonding. Indole diffusion rates are higher in lipids with ester bonds and lower in choline-containing lipids, suggesting that interactions between indole and carbonyl groups are of minor importance for lipid-indole association and that cation-pi interactions with choline drive the second indole location. Nuclear Overhauser effect spectroscopy cross-relaxation rates suggest a 30-ns lifetime for indole-lipid associations. These results may have important implications for sidedness and structural transitions in tryptophan-rich membrane proteins.     

Two-Dimensional polymerization of supramolecular assemblies: Synthesis and bilayer polymerization of lipids containing α-methylene-substituted acyl chains

Polymerization of lipid assemblies may be usefully employed to alter the properties of the assemblies. The possible locations of the reactive group in the lipids include (1) the chain terminus, (2) the head group, and (3) near the lipid backbone. The third strategy yields polymerized assemblies which retain their head group functionality and lipid chain motion. We have designed and synthesized new members of this later category by the use of 2-methylene-substituted acyl chains. The main transition temperature (T_m) from gel to liquid crystalline phase of hydrated bilayers of 1-palmitoyl-2-(2-methylene)palmitoyl-sn-glycero-3-phosphocholine ( 1 ) and the disubstituted 1,2-bis(2-methylenepalmitoyl)-sn-glycero-3-phosphocholine ( 2 ) were 33.6 and 25.3°C, respectively. The T_m of the mono-substituted 1-oleoyl-2-(2-methylene)palmitoyl-sn-glycero-3-phosphocholine ( 3 ) bilayers was detected in a range from ?15 to ?10°C by x-ray diffraction. Hydrated bilayers of each individual lipid were successfully polymerized with a water-soluble initiator, azobis(2-amidinopropane) dihydrochloride (AAPD). These results indicate the lipid 2-methylene groups are accessible to the water interface. Thermal polymerization of the mono-substituted lipids in aqueous suspensions with AAPD, yielded oligomers. However the bis-2-methylene PC ( 2 ) was successfully polymerized to yield stabilized crosslinked bilayers. © 1994 John Wiley & Sons, Inc.     

Structural characterization of phosphatidyl-<Emphasis Type="Italic">myo</Emphasis>-inositol mannosides from <Emphasis Type="Italic">Mycobacterium bovis</Emphasis> bacillus calmette guérin by multiple-stage quadrupole ion-trap mass spectrometry with electrospray ionization. I. PIMs and lyso-PIMs

We described a multiple-stage ion-trap mass spectrometric approach to characterize the structures of phosphatidylinositol and phosphatidyl-myoinositol mannosides (PIMs) in a complex mixture isolated from Mycobacterium bovis Bacillus Calmette Guérin. The positions of the fatty acyl substituents of PIMs at the glycerol backbone can be easily assigned, based on the findings that the ions arising from losses of the fatty acid substituent at sn-2 as molecules of acid and of ketene, respectively (that is, the [M - H - R(2)CO(2)H](-) and [M - H - R(2)CHCO](-) ions), are respectively more abundant than the ions arising from the analogous losses at sn-1 (that is, the [M - H - R(1)CO(2)H](-) and [M - H - R(1)CHCO](-) ions) in the MS(2) product-ion spectra of the [M - H](-) ions desorbed by electrospray ionization (ESI). Further dissociation of the [M - H - R(2)CO(2)H](-) and [M - H - R(1)CO(2)H](-) ions gives rise to a pair of unique ions corresponding to losses of 74 and 56 Da (that is, [M - H - R(x)CO(2)H - 56](-) and [M - H - R(x)CO(2)H - 74](-) ions, x = 1, 2), respectively, probably arising from various losses of the glycerol. The profile of the ion-pair in the MS(3) spectrum of the [M - H - R(2)CO(2)H](-) ion is readily distinguishable from that in the MS(3) spectrum of the [M - H - R(1)CO(2)H](-) ion and thus the assignment of the fatty acid substituents at the glycerol backbone can be confirmed. The product-ion spectra of the [M - H](-) ions from 2-lyso-PIM and from 1-lyso-PIM are discernible and both spectra contain a unique ion that arises from primary loss of the fatty acid substituent at the glycerol backbone, followed by loss of a bicyclic glycerophosphate ester moiety of 136 Da. The combined structural information from the MS(2) and MS(3) product-ion spectra permit the complex structures of PIMs that consist of various isomers to be unveiled in detail.     

Charge-remote and charge-driven fragmentation processes in diacyl glycerophosphoethanolamine upon low-energy collisional activation: A mechanistic proposal

A mechanistic study of diacyl glycerophosphoethanolamine fragmentation under low energy collision-activated dissociation with electrospray ionization tandem mass spectrometry is reported. The fragmentation pathways leading to the formation of carboxylate anions (RxCO2-) (x = 1, 2) and the formation of the ions representing neutral loss of ketene ([M - H - Rx'CH=C=O]-) are charge-driven processes, which are governed by the gas-phase basicity and the steric configuration of the molecules. The fragmentation pathway for the formation of the [M - H - RxCO2H]- ions, reflecting neutral loss of fatty acid, is a charge-remote process, which involves the participation of the hydrogens at C-1 and C-2 of the glycerol, resulting in [M - H - R2CO2H]- > [M - H - R1CO2H]-. The preferential formations of R2CO2- > R1CO2-, and of [M - H - R2'CH=C=O]- > [M - H - R1'CH=C=O]- are attributed to the findings that charge-driven processes are sterically more favorable at sn-2. The observation of the abundance of [M - H - Rx'CH=C=O]- > [M - H - RxCO2H]- is attributed to the fact that the [M - H]- ions of GPE are basic precursor ions, which undergo preferential loss of ketene than loss of acid. The major pathway for the formation of RxCO2- ions arises from the nucleophilic attack of the anionic charge site of the phosphate on the C-1 or C-2 of the glycerol to render a charge transfer. The sterically more favorable attack on the C-2 than C-2 of the glycerol results in the abundance of R2CO2- > R1CO2-. These features of tandem spectra readily identify and locate the fatty acid substituents of GPE in the glycerol backbone.     

Kinetic properties of pancreatic and intestinal sPLA2 from chicken and mammals using the monomolecular film technique

The interfacial kinetic and binding data for the pancreatic and intestinal sPLA2 from bird and mammals show that these enzymes have dramatically different ability to bind and hydrolyse phospholipids. The main conclusions from our experimental data indicate that phosphatidylcholine monolayers (PC), in contrast to phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), were resistant to the hydrolysis by human intestinal sPLA2. Conversely, chicken intestinal sPLA2 was found to be able to hydrolyse all the phospholipids tested, including PC. The experiments show also that the interfacial penetrating ability of chicken sPLA2 (from intestine and pancreas) was higher than their mammalian's orthologs. This observation is confirmed by the activity of pancreatic chicken PLA2 measured on PC film showing that the interfacial pressure window that permits sPLA2 activity was very large, between 5 and 20 dynes cm(-1), compared with the porcine pancreatic sPLA2-IB which was inactive at pressure above 15 dynes cm(-1). In trying to establish a structure-function relationship, we examined the surface electrostatic potentials of the various sPLA2 from chicken and mammals. We reported in this study that the binding, orientation and persistence of sPLA2 at the lipid-water interface is probably governed by the electrostatic and hydrophobic forces operative at this surface. These variations argue strongly that these enzymes are not isoforms and that they are expected to have functions other than the release of lipid mediators for the biosynthesis of the eicosanoids.     

Synthesis, helicity, and chromism of optically active poly(phenylacetylene)s carrying different amino acid moieties and pendant terminal groups

Functional phenylacetylene derivatives containing l-alanine and l-leucine moieties with chiral menthyl and achiral n-octyl terminal groups {HC[triple bond]C-C6H4-p-CONHCH(R)CO2R': R = CH3, R'= (-)-(1R,2S,5R)-menthyl [1(-)]; R = CH2CH(CH2)3, R' = (-)-(1R,2S,5R)-menthyl [2(-)]; R'= CH2CH(CH2)3, R' = (+)-(1S,2R,5S)-menthyl [2(+)]; R'= CH2CH(CH2)3, R' = (CH2)7CH3 (2o)} are synthesized. Polymerizations of the acetylene monomers are effected by organorhodium catalysts, giving corresponding polymers P1(-), P2(-), P2(+), and P2o of high molecular weights (Mw up to 1.2 x 10(6)) in high yields (up to 89%). The polymers are thermally stable (Td >or= 300 degrees C) and soluble in common organic solvents. The polymer structures are characterized by IR, NMR, UV, and CD spectroscopies. Intense CD signals are observed in the visible spectral region, indicating that the polymer chains are taking a helical conformation with an excess of preferred handedness. The backbone conjugation and chain helicity of the polymers can be tuned by changing their molecular structures [(a)chiral pendant groups] and by applying external stimuli (solvent and pH). Addition of trifluoroacetic acid to the polymer solutions decreases their molar ellipticities and enhances their backbone conjugations, inducing a halochromism with a continuous and reversible color change (yellow <==> red).     

Determination of the fatty acyl profiles of phosphatidylethanolamines by tandem mass spectrometry of sodium adducts

Phosphatidylethanolamines (PEs) are one of the major constituents of cellular membranes, and, along with other phospholipid classes, have an essential role in the physiology of cells. Profiling of phospholipids in biological samples is currently done using mass spectrometry (MS). In this work we describe the MS fragmentation of sodium adducts of 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphatidylethanolamine (POPE) and 2-linoleoyl-1-palmitoyl-sn-glycero-3-phosphatidylethanolamine (PLPE). This study was performed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) using three different instruments and also by matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS). All MS/MS spectra show product ions related to the polar head fragmentation and product ions related to the loss of acyl chains. In ESI-MS/MS spectra, the product ions [M+Na-R1COOH-43]+ and [M+Na-R2COOH-43]+ show different relative abundance, as well as [M+Na-R1COOH]+ and [M+Na-R2COOH]+ product ions, allowing identification of both fatty acyl residues of PEs, and their specific location. MALDI-MS/MS shows the same product ions reported before and other ions generated by charge-remote fragmentation of the C3-C4 bond (gamma-cleavage) of fatty acyl residues combined with loss of 163 Da. These fragment ions, [M+Na-(R2-C2H3)-163]+ and [M+Na-(R1-C2H3)-163]+, show different relative abundances, and the product ion formed by the gamma-cleavage of sn-2 is the most abundant. Overall, differences noted that are important for identification and location of fatty acyl residues in the glycerol backbone are: relative abundance between the product ions [M+Na-R1COOH-43]+ > [M+Na-R2COOH-43]+ in ESI-MS/MS spectra; and relative abundance between the product ions [M+Na-(R2-C2H3)-163]+ > [M+Na-(R1-C2H3)-163]+ in MALDI-MS/MS spectra.     

Synthesis and characterization of carbohydrate-based phospholipids

Novel carbohydrate-based phospholipids containing two saturated C(12) (dilauroyl ribo-phosphocholine) (DLRPC), C(14) (dimyristoyl ribo-phosphocholine) (DMRPC), and C(20) (diarachadonyl ribo-phosphocholine) (DARPC) carboxylic acid chains were synthesized. The physical properties of the supramolecular structures formed by these compounds were compared to those formed by their direct glycerol analogues dilauroyl phosphocholine (DLPC), dimyristoyl phosphocholine (DMPC), and diarachadonyl phosphocholine (DAPC). Modulated differential scanning calorimetry (MDSC) and X-ray diffraction data indicated that with chain lengths < or =14 carbons, the carbohydrate backbone increased the thermal stability of the bilayer below the phase-transition temperature (T(m)) as compared to the glycerol-based lipids. With longer chains (C(20)), the bilayer structure was destabilized as compared to glycerol-based lipids. NMR studies of a DMRPC vesicle dispersion reveal split choline headgroup signals and distinct magnetization transfer effects arising from the "inner" and "outer" surfaces of the bilayer vesicle. Modulated differential scanning calorimetry also demonstrated that glycerol- and carbohydrate-based lipids mix, as evidenced by a single intermediate T(m). In addition, carbohydrate-based lipid/cholesterol mixtures exhibited a decrease in enthalpy with an increase in cholesterol concentration. Unlike glycerol phospholipids, carbohydrate lipids were resistant to enzymatic degradation by phospholipase A(2) (PLA(2)).     

Toward bicelle stability with ether-linked phospholipids: temperature, composition, and hydration diagrams by 2H and 31P solid-state NMR

Phosphorus and deuterium wide line NMR was used to determine diagrams of binary mixtures of 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (DIOMPC) and 1,2-di-O-hexyl-sn-glycero-3-phosphocholine (DIOHPC) ether-phospholipids. By varying the hydration, h, the temperature, T, and the mole fraction, X, of long-chain ether-phospholipids, we delineated the conditions for which such systems are oriented by the magnetic field, in the presence of 100 mM KCl. The 3D domain is found for X = 62-90%, T = 27-50 degrees C, and h = 70-98%. At 80% hydration, the domain shape (X = 70-90% and T = 27-42 degrees C) is close to that already observed for ester-phospholipids mixtures (Raffard, G.; Steinbruckner, S.; Arnold, A.; Davis, J. H.; Dufourc, E. J. Langmuir 2000, 16, 7655-7662) where disc-shaped bicelles of 300-600 A have been found by electron microscopy (Arnold, A.; Labrot, T.; Oda, R.; Dufourc, E. J. Biophys. J. 2002, 83, 2667-2680). Systems made of ether-linked lipids are much more stable on time and acidic conditions than those made of ester lipids. Assuming that the disc-shaped species are also found with ether lipids, their diameter as determined from integration of phosphorus NMR lines ranges from 240 to 440 A +/- 10%; it is generally independent of hydration and temperature but decreases with decreasing long-chain lipid content, X. The structure and the dynamics of water in the DIOMPC-DIOHPC were characterized by (2)H NMR. Water exchanges between the membrane surface where it is bound and a bulk isotropic pool lead to an average ordered state for temperatures in the bicelle region and above, thus offering a larger thermal span for structural studies of dissolved molecules.     

Sterically hindered triacylglycerol analogues as potent inhibitors of human digestive lipases

A novel class of inhibitors of human digestive lipases have been developed. Various sterically hindered triacylglycerols based on 2-methyl- and 2-butylglycerol, and/or 2-methyl fatty acids were synthesized. The triacylglycerol analogues were tested for their ability to form stable monomolecular films at the air/water interface by recording their surface-pressure/molecular-area compression isotherms. The inhibition of human pancreatic and gastric lipases by the sterically hindered triacylglycerol analogues was studied by using the monolayer technique with mixed films of 1,2-dicaprin, which contained variable proportions of each inhibitor. Triolein analogues that contain a butyl group at the 2-position of the glycerol backbone or methyl groups both at the 2-position of glycerol, and the alpha-position of each oleic acid residue were potent inhibitors; this caused a 50% decrease in HPL activity at 0.003 molar fraction.     

Influence of perfluorinated compounds on the properties of model lipid membranes

The influence of selected perfluorinated compounds (PFCs), perfluorooctanoic acid (PFOA) or perfluorooctanesulfonic acid (PFOS), on the structure and organization of lipid membranes was investigated using model membranes-lipid monolayers and bilayers. The simplest model--a lipid monolayer--was studied at the air-water interface using the Langmuir-Blodgett technique with surface pressure and surface potential measurements. Lipid bilayers were characterized by NMR techniques and molecular dynamics simulations. Two phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), characterized by different surface properties have been chosen as components of the model membranes. For a DPPC monolayer, a phase transition from the liquid-expanded state to the liquid-condensed state can be observed upon compression at room temperature, while a DMPC monolayer under the same conditions remains in the liquid-expanded state. For each of the two lipids, the presence of both PFOA and PFOS leads to the formation of a more fluidic layer at the air-water interface. Pulsed field gradient NMR measurements of the lateral diffusion coefficient (DL) of DMPC and PFOA in oriented bilayers reveal that, upon addition of PFOA to DMPC bilayers, DL of DMPC decreases for small amounts of PFOA, while larger additions produce an increased DL. The DL values of PFOA were found to be slightly larger than those for DMPC, probably as a consequence of the water solubility of PFOA. Furthermore, 31P and 2H NMR showed that the gel-liquid crystalline phase transition temperature decreased by the addition of PFOA for concentrations of 5 mol % and above, indicating a destabilizing effect of PFOA on the membranes. Deuterium order parameters of deuterated DMPC were found to increase slightly upon increasing the PFOA concentration. The monolayer experiments reveal that PFOS also penetrates slowly into already preformed lipid layers, leading to a change of their properties with time. These experimental observations are in qualitative agreement with the computational results obtained from the molecular dynamics simulations showing a slow migration of PFCs from the surrounding water phase into DPPC and DMPC bilayers.