Dipalmitoylphosphatidylethanolamine Research Articles

Effect of myelin basic protein on membrane lipid monolayers composed of DPPC and DPPE molecules

By analyzing the Langmuir monolayer surface pressure-mean molecular area ( π -A) curves, the interaction between myelin basic protein (MBP) and dipalmitoylphosphatidyl-choline cell membranes (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE), which are the different head group of lipid molecules, has been systematically studied, respectively. The results showed that: (1) with the MBP concentration in subphase increasing, the isotherm of DPPC and DPPE monolayer moved to lager average molecular area direction when the number of the lipid on the interface was constant; (2) when the surface pressure of the monolayer reached to 10 mN/m, one MBP molecule could combined with (140 ± 3) DPPC and (100 ± 3) DPPE molecules, respectively; as the surface pressure increased, the number of proteins interacted with two kinds of phospholipid molecules inserting the interface decreased; (3) with the increase of protein concentration, the monolayer film formed by the lipid molecules becomes more loose and MBP molecules are easy to insert into DPPE with smaller head; (4) the π-T curves indicated that the presence of protein could make DPPC monolayer surface pressure decreased, and the higher the concentration of protein was, the more for decreasing values of the surface pressure. Then the DPPC was brought into the MBP subphase; (5) for DPPE monolayer, the protein combined with DPPE inserted the membrane interface, causing the increase of surface pressure, and the higher the protein concentration was, the greater change the pressure appeared.

Antimicrobial mechanism of flavonoids against Escherichia coli ATCC 25922 by model membrane study

Abstract Antimicrobial mechanism of four flavonoids (kaempferol, hesperitin, (+)-catechin hydrate, biochanin A) against Escherichia coli ATCC 25922 was investigated through cell membranes and a liposome model. The release of bacterial protein and images from transmission electron microscopy demonstrated damage to the E. coli ATCC 25922 membrane. A liposome model with dipalmitoylphosphatidylethanolamine (DPPE) (0.6 molar ratio) and dipalmitoylphosphatidylglycerol (DPPG) (0.4 molar ratio), representative of the phospholipid membrane of E. coli ATCC 25922, was used to specify the mode of action of four selected flavonoids through Raman spectroscopy and differential scanning calorimetry. It is suggested that for flavonoids, to be effective antimicrobials, interaction with the polar head-group of the model membrane followed by penetration into the hydrophobic regions must occur. The antimicrobial efficacies of the flavonoids were consistent with liposome interaction activities, kaempferol > hesperitin > (+)-catechin hydrate > biochanin A. This study provides a liposome model capable of mimicking the cell membrane of E. coli ATCC 25922. The findings are important in understanding the antibacterial mechanism on cell membranes.

The Structure of Lipid Bilayers Adsorbed on Activated Carboxy-Terminated Monolayers Investigated by Sum Frequency Generation Spectroscopy

The formation and structure of isotopically asymmetric supported bilayer membranes (SBMs) has been investigated using sum frequency generation (SFG) vibrational spectroscopy supplemented by reflection absorption infrared spectroscopy (RAIRS). The bilayers were composed of a proximal and distal leaflet of the phospholipid dipalmitoyl phosphatidylethanolamine (DPPE) supported on a gold surface. The proximal leaflet was chemically tethered to the gold via an 11-mercapto-undecanoic acid (MUA) self-assembled monolayer (SAM) that had been chemically modified to produce an activated succinimidyl ester headgroup using N-hydroxysuccinimide (NHS) and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC). The activation of the MUA and the tethering of the DPPE were monitored and confirmed using SFG and RAIRS. The distal leaflet of the bilayer was added using either vesicle fusion (VF) or Langmuir-Blodgett (LB) deposition. To gain insight into the structure of each layer of the SBM perdeuterated DPPE (d-DPPE) and MUA (d-MUA) were used to create SBMs with a layer that was isotopically distinguishable from the rest. The polar orientation and conformational ordering of the lipids was determined using SFG. It was found that the tethering of the proximal lipid leaflet resulted in an increase in the conformational order of the MUA SAM. Furthermore, by careful analysis and comparison of spectra recorded in both the C-H (2800-3000 cm(-1)) and C-D (2000-2300 cm(-1)) stretching regions it was concluded that a better ordered and more biologically relevant lipid bilayer was formed when the distal leaflet was added using LB deposition. On the other hand the SFG spectra of the SBMs in which the distal leaflet was added by VF showed little evidence of conformational ordering on the time scale of minutes, suggesting the presence of an incomplete monolayer or of multilayer formation.

Use of thermodynamic coupling between antibody–antigen binding and phospholipid acyl chain phase transition energetics to predict immunoliposome targeting affinity

Thermodynamic analysis of ligand-target binding has been a useful tool for dissecting the nature of the binding mechanism and, therefore, potentially can provide valuable information regarding the utility of targeted formulations. Based on a consistent coupling of antibody–antigen binding and gel–liquid crystal transition energetics observed for antibody–phosphatidylethanolamine (Ab–PE) conjugates, we hypothesized that the thermodynamic parameters and the affinity for antigen of the Ab–PE conjugates could be effectively predicted once the corresponding information for the unconjugated antibody is determined. This hypothesis has now been tested in nine different antibody-targeted echogenic liposome (ELIP) preparations, where antibody is conjugated to dipalmitoylphosphatidylethanolamine (DPPE) head groups through a thioether linkage. Predictions were satisfactory (affinity not significantly different from the population of values found) in five cases (55.6%), but the affinity of the unconjugated antibody was not significantly different from the population of values found in six cases (66.7%), indicating that the affinities of the conjugated antibody tended not to deviate appreciably from those of the free antibody. While knowledge of the affinities of free antibodies may be sufficient to judge their suitability as targeting agents, thermodynamic analysis may still provide valuable information regarding their usefulness for specific applications.

Modified phosphatidylethanolamines induce different levels of cytokine expression in monocytes and dendritic cells

Glycation of phosphatidylethanolamine (PE) is a reaction that is known to occur under the chronic hyperglycemic conditions found in diabetes. Glycated phosphatidylethanolamines were found in plasma and atherosclerotic plaques of diabetic patients, and its presence was correlated with increased oxidative stress. Moreover, upregulation of cytokines and other inflammatory mediators can be observed not only in diabetes, but also under oxidized phosphatidylcholine stimulation. In this study, we evaluate the effect of dipalmitoyl-phosphatidylethanolamine (DPPE) and linoleoyl-palmitoyl-phosphatidylethanolamine (PLPE) structural oxidation, glycation and glycoxidation, on monocyte and myeloid dendritic cell stimulation. Expression of cytokines, IL-1β, IL-6, IL-8, MIP-1β and TNF-α, were determined using flow cytometry after cell stimulations with native PEs, oxidized, glycated and glycoxidized PEs. Native PE, PLPE and DPPE, and all modified PEs were able to increase the stimulation levels of monocytes and mDCs. Generally, in monocytes and mDCs stimulation, GluOxPLPE and GluDPPE were the PLPE/DPPE modifications that induced the most pronounced rise in cytokine production. However, GluOxDPPE was the DPPE modification that produced the lowest stimulation levels of mDCs and monocytes. Our results indicate that glycated PE and glycoxidized PE may have an important contribution to the low-grade systemic inflammation associated with diabetes and to the development of diabetic complications.

Drude Model Based Polarizable Force Field for Lipids

Incorporation of electronic polarization of atoms induced by local electric fields in the empirical potential function used to generate molecular dynamics simulations is important for accurate studies of various biological processes such as ion transfer, binding and selectivity. In this work, we present new polarizable force fields for the simulations of zwitterionic lipids membranes based on the classical Drude oscillator model. The lipids considered include: dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC).The parameterization strategy relies on the properties of small model compound analogs of functional groups in the molecules. The polar head group parameters are based on the molecular ions dimethyl phosphate and tetramethyl ammonium, methyl acetate for the glycerol linker region and linear alkanes as well as alkenes for the aliphatic tail of the lipid. The small molecule parameters are optimized and validated against a suite of experimental properties. The resulting lipid force field is applied to the simulation of lipid bilayers and monolayers for each lipid. For the lipid bilayer, the area per lipid, deuterium order parameters and electron density profile, and for the monolayers, the surface pressure and dipole potentials are all found to be in good agreement with experimental data when available. Thus, we have successfully validated our force field for a number of lipids.

Direct determination of phospholipase D activity by infrared spectroscopy

To determine phospholipase D (PLD) activity, an infrared spectroscopy assay was developed, based on the phosphate vibrational mode of phospholipids such as dimyristoylphophatidylcholine (DMPC), lysophosphatidylglycerol (lysoPG), dipalmitoylphosphatidylethanolamine (DPPE), and lysophosphatidylserine (lysoPS). The phosphate bands served to monitor the hydrolysis rates of phospholipids with PLD. The measurements could be performed within less than 20min with 10μl of buffer containing 2 to 40mM DMPC and 10 to 200ng of Streptomyces chromofuscus PLD (corresponding to 350–7000pmol of DMPC hydrolyzed per minute). The limit of sensitivity was approximately 10ng of PLD at 100mM Tris–HCl (pH 8.0) with 10mM Ca2+ and 2.5mgml−1 Triton X-100. Reproducible specific activity of PLD (35±5nmol of hydrolyzed DMPCmin−1μg−1 PLD) measured by the infrared assay remained stable over 50 to 200ng of PLD and over 5 to 40mM DMPC. The feasibility of this assay to determine the hydrolysis rate of other phospholipids such as lysoPG, DPPE, and lysoPS was confirmed. The IC50 of cobalt (800±200μM), a known S. chromofuscus PLD inhibitor, was measured by means of the infrared assay, demonstrating that this assay can be used to screen PLD activity and/or the specificity of its inhibitors.

Nanoclusters of nickel oxide using giant vesicles

Giant unilamellar vesicles (GUVs) of dioleoylphosphatidycholine (DOPC) and dipalmitoylphosphatidylethanolamine (DPPE) containing NiCl2 or NiSO4 have been used as templates to prepare nanoparticles of nickel oxide of 35–75nm size. The GUVs have been studied by steady state fluorescence anisotropy, fluorescence life time measurements, optical microscopy and confocal laser scanning microscopy (CLSM). In general, the GUVs containing the nickel salts show a contraction in size (ranging from 14 to 19μm) compared with pure GUVs (20–30μm). Fluorescence anisotropy values show that GUVs with NiCl2 are better organized compared with those containing NiSO4. Transmission electron microscopy (TEM), and powder XRD studies corroborate these findings. The stacking of the lipids in the presence of Ni2+ leading to contraction in the GUVs has been modeled using Gaussian 03 package. Nickel sulfide formed from mixing these vesicles with Na2S containing vesicles, has been further calcined to obtain nanosized clusters of nickel oxide. Scanning electron micrographs of the nickel oxide formed from GUVs with NiCl2 show smaller sizes (35–45nm) with wider size distributions compared with those from GUVs with NiSO4 (sizes 50–75nm) that have more uniform sizes. Results suggest that by judicious choice of different anions in the metal salts a method to structure and tune the sizes and morphology of the nanoclusters using GUVs as templates is possible.

Liposomal glyco-microarray for studying glycolipid–protein interactions

A microarray enables high-throughput interaction screening of numerous biomolecules; however, fabrication of a microarray composed of cellular membrane components has proven difficult. We report fabrication of a liposomal glyco-microarray by using an azide-reactive liposome that carries synthetic and natural glycolipids via chemically selective and biocompatible liposome immobilization chemistry. Briefly, liposomes carrying anchor lipid dipalmitoylphosphatidylethanolamine (DPPE)-PEG(2000)-triphenylphosphine and ganglioside (GM1 or GM3) were prepared first and were then printed onto an azide-modified glass slide so as to afford a liposomal glyco-microarray via Staudinger ligation. Fluorescent dye release kinetics and fluorescence imaging confirmed successful liposome immobilization and specific protein binding to the intact arrayed glycoliposomes. The liposomal glyco-microarray with different gangliosides showed their specific lectin and toxin binding with different binding affinity. The azide-reactive liposome provides a facile strategy for fabrication of either a natural or a synthetic glycolipid-based membrane-mimetic glycoarray. This liposomal glyco-microarray is simple and broadly applicable and thus will find important biomedical applications, such as studying glycolipid-protein interactions and toxin screening applications.

Headgroup specificity for the interaction of the antimicrobial peptide tritrpticin with phospholipid Langmuir monolayers

We examined the interaction of the cationic antimicrobial peptide (AMP) tritrpticin (VRRFPWWWPFLRR, TRP3) with Langmuir monolayers of zwitterionic (dipalmitoyl phosphatidylcholine, DPPC, and dipalmitoyl phosphatidylethanolamine, DPPE) and negatively charged phospholipids (dipalmitoyl phosphatidic acid, DPPA, and dipalmitoyl phosphatidylglycerol, DPPG). Both surface pressure and surface potential isotherms became more expanded upon addition of TRP3 (DPPE∼DPPC≪DPPA<DPPG). The stronger interaction with negatively charged phospholipids agrees with data for vesicles and planar lipid bilayers, and with AMPs greater activity against bacterial membranes versus mammalian cell membranes. Considerable expansion of negatively charged monolayers occurred at 10 and 30mol% TRP3, especially at low surface pressure. Moreover, a difference was observed between PA and PG, demonstrating that the interaction, besides being modulated by electrostatic interactions, displays specificity with regard to headgroup, being more pronounced in the case of PG, present in large quantities in bacterial membranes. In previous studies, it was proposed that the peptide acts by a toroidal pore-like mechanism [1,2]. Considering the evidence from the literature that PG shows a propensity to form a positive curvature as do toroidal pores, the observation of TRP3's preference for the PG headgroup and the dramatic increase in area promoted by this interaction represent further support for the toroidal pore mechanism of action proposed for TRP3.

Molecular organization of bacterial membrane lipids in mixed systems—A comprehensive monolayer study combined with Grazing Incidence X-ray Diffraction and Brewster Angle Microscopy experiments

To properly design and investigate new antibacterial drugs a detailed description of the organization of bacterial membrane is highly important. Therefore in this work we performed a comprehensive characteristic of the Langmuir monolayers composed of phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) mixed in a wide range of composition and treated as an artificial cytoplasmic layer of bacterial membrane. To obtain detailed information on the properties of these films we combined the analysis of the surface pressure–area curves with the surface potential measurements, Brewster Angle Microscopy studies and Grazing Incidence X-ray Diffraction experiments. It was found that the investigated phospholipids mix nonideally in the monolayers and that the most favorable packing of molecules occurs at their equimolar proportion. This is directly connected with the formation of hydrogen bonds between both types of molecules in the system. All the collected experimental data evidenced that dipalmitoylphosphatidylethanolamine (DPPE) and dipalmitoylphosphatidylglycerol (DPPG) form highly ordered associates of fixed (DPPE:DPPG 1:1) stoichiometry. The obtained results allow one to conclude a nonuniform distribution of lipids in bacterial membranes and the existence of domains composed of the investigated phospholipids. The latter seems to be of great importance in the perspective of further studies on the mechanism of action of antibacterial agents.

Polymeric Micelles of PEG-PE as Carriers of All-Trans Retinoic Acid for Stability Improvement

The topical application of all-trans retinoic acid (ATRA) is an effective treatment for several skin disorders, including photo-aging. Unfortunately, ATRA is susceptible to light, heat, and oxidizing agents. Thus, this study aimed to investigate the ability of polymeric micelles prepared from polyethylene glycol conjugated phosphatidylethanolamine (PEG-PE) to stabilize ATRA under various storage conditions. ATRA entrapped in polymeric micelles with various PEG and PE structures was prepared. The critical micelle concentrations were 97-243 μM, depending on the structures of the PEG and PE molecules. All of the micelles had particle diameters of 6-20 nm and neutral charges. The highest entrapment efficiency (82.7%) of the tested micelles was exhibited by ATRA in PEG with a molecular weight of 750 Da conjugated to dipalmitoyl phosphatidylethanolamine (PEG(750)-DPPE) micelles. The PEG(750)-DPPE micelle could significantly retard ATRA oxidation compared to ATRA in 75% methanol/HBS solution. Up to 87% of ATRA remained in the PEG(750)-DPPE micelle solution after storage in ambient air for 28 days. This result suggests that PEG(750)-DPPE micelle can improve ATRA stability. Therefore, ATRA in PEG(750)-DPPE micelle is an interesting alternative structure for the development of cosmeceutical formulations.

Nimesulide interaction with membrane model systems: Are membrane physical effects involved in nimesulide mitochondrial toxicity?

Nimesulide (NIM), a widely used nonsteroidal anti-inflammatory drug (NSAID), is known to interfere with mitochondrial physiology and to cause idiosyncratic hepatotoxicity. In this study, we characterized the effects of NIM on the physical properties of membrane models containing the main phospholipid classes of the inner mitochondrial membrane: phosphatidylcholine (PC), phosphatidylethanolamine (PE) and cardiolipin (CL). NIM binding/incorporation was observed with the mitochondrial membrane mimicking model composed of dioleoyl PC (DOPC), dioleoyl PE (DOPE) and tetraoleoyl CL (TOCL) at a 1:1:1 M ratio, as well as an increase of membrane permeability, monitored by calcein release, and an increase of lipid disorder, evaluated by fluorescence anisotropy of DPH-PA. Consistently, DSC thermograms of dipalmitoyl PC (DPPC) and a mixture of dipalmitoyl PE (DPPE) and TOCL (7:3 M ratio) showed a NIM-induced decrease of the cooperativity of the phase transition and a shift of the DPPC endotherm to lower temperatures. On the other hand, 31P NMR studies with the ternary lipid model indicated a stabilizing effect of NIM on the lipid bilayer structure. Quenching of the fluorescent probes DPH and DPH-PA revealed a peripheral insertion of NIM in the hydrophobic portion of the bilayer. Our data indicate that NIM may influence mitochondria physiological processes by interfering with membrane structure and dynamics. The relevance of these findings will be discussed in terms of the reported NIM effects on mitochondria transmembrane potential, protonophoresis, and induction of the permeability transition pore.

Penetration behaviour of alkylbetainate chlorides into lipid monolayers

In this paper, the penetration behaviour of the alkylbetainate chloride surfactants (C(n)BC, n=10-16) into lipid monolayers of dipalmitoylphosphatidylserine (DPPS), dipalmitoylphosphatidic acid (DPPA), dipalmitoylphosphatidylethanolamine (DPPE), palmitoyoleoylphosphatidylcholine (POPC) and cholesterol (CHOL) is investigated using the Langmuir trough technique. The penetration of C(n)BC is followed by measurement of the surface pressure increase (Δπ) at a constant surface area after the injection of C(n)BC into the aqueous phase, underneath the lipid monolayer previously spread at the air-water interface at 25°C and at different initial surface pressures (π(i)). The influence of both the lipid head group and the surfactant hydrocarbon chain length on the effectiveness of C(n)BC penetration into these monolayers is discussed. The results have shown that C(n)BC adsorb at the air-water interface giving evidence of their surface-active properties. The adsorption kinetics of C16BC into different lipid monolayers are lipid head charge and lipid head volume-dependent. The magnitude of the surface pressure increase (Δπ) arises in the following order: DPPA>DPPS≫CHOL≈DPPE>POPC. C(n)BC penetration into negatively-charged (DPPS and DPPA) monolayers does not seem to depend on surfactant alkyl-chain length compared to uncharged (CHOL) and zwitterionic (DPPE and POPC) monolayers for which Δπ increases with a larger alkyl-chain length. Electrostatic interactions are mainly involved in the affinity of C(n)BC with monolayers but the hydrophobic effect plays also a role.

Preparation and characterization of polymeric pH-sensitive STEALTH® nanoparticles for tumor delivery of a lipophilic prodrug of paclitaxel

Paclitaxel is an effective and widely used anti-cancer agent. However, the drug is difficult to formulate for parenteral administration because of its low water solubility and Cremophor EL, the expient used for its formulation, has been shown to cause serious side effects. The present study reports an alternative administration vehicle involving a lipophilic paclitaxel prodrug, paclitaxel oleate, incorporated in the core of a nanoparticle-based dosage form. A hydrophobic poly (β-amino ester) (PbAE) was used to formulate the nanoparticles, which were stabilized with a mixture of phosphatidylcholine, Synperonic® F 108, and poly(ethylene glycol)-dipalmitoyl phosphatidyl ethanolamine. PbAE undergoes rapid dissolution when the pH of the medium is less than 6.5 and is expected to rapidly release its content within the acidic tumor microenvironment and endo/lysosome compartments of cancer cells. PbAE nanoparticles were prepared by an ultrasonication method and characterized for particle size and physical stability. The nanoparticles obtained had a diameter of about 70nm and a good physical stability when stored at 4°C. In vitro cellular uptake and release of paclitaxel oleate PbAE nanoparticles were studied in Jurkat acute lymphoblastic leukemia cells. The results were compared with pclitaxel oleate in poly(ɛ-caprolactone) (PCL) particles, that do not display pH-sensitive release behavior, and paclitaxel in PbAE particles. Both uptake and release of the prodrug were faster when administered in PbAE than in PCL, but much slower than those of the free drug in PbAE. Cytotoxicity assay was performed on the formulations at different doses. Paclitaxel and paclitaxel oleate showed almost identical activity, IC50 123 and 128nM, respectively, while that of the prodrug in PCL was much lower with IC50 at 2.5μM. Thus, PbAE nanoparticles with the incorporated paclitaxel prodrug paclitaxel oleate may prove useful for replacement of the toxic Cremophor EL and also by improving the distribution of the drug to the tumor.

Reorganization and Caging of DPPC, DPPE, DPPG, and DPPS Monolayers Caused by Dimethylsulfoxide Observed Using Brewster Angle Microscopy

The interaction between dimethylsulfoxide (DMSO) and phospholipid monolayers with different polar headgroups was studied using "in situ" Brewster angle microscopy (BAM) coupled to a Langmuir trough. For a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer, DMSO was shown to significantly impact the structure of the liquid expanded (LE) and gaseous phases. The domains reorganized to much larger domain structures. Domains in the liquid condensed (LC) phase were formed on the DMSO-containing subphase at the mean molecular area where only gaseous and LE phases were previously observed on the pure water subphase. These results clearly demonstrate the condensing and caging effect of DMSO molecules on the DPPC monolayer. Similar effects were found on dipalmitoyl phosphatidyl ethanolamine, glycerol, and serine phospholipids, indicating that the condensing and caging effect is not dependent upon the phospholipid headgroup structure. The DMSO-induced condensing and caging effect is the molecular mechanism that may account for the enhanced permeability of membranes upon exposure to DMSO.

QM AND AB INITIO INVESTIGATION ON THE HYDROGEN BONDING, NMR CHEMICAL SHIFTS AND SOLVENT EFFECTS ON THE DPPE

The hydrogen bonding effects that were produced from interaction of membrane lipid dipalmitoylphosphatidyl-ethanolamine (DPPE) with 1-5 water molecules, has been theoretically investigated through the quantum mechanical calculations at the Hartree-Fock level of theory and the 3-21G, 6-31G and 6-31G* basis sets with the computational package of Gaussian 98. According to the obtained results of the structural optimization of the isolated DPPE in the gas phase, we can see the evidences of interactions in the head group of this macromolecule (from the molecular point of view we have a proton transfer from the ammonium group to the phosphate oxygen of zwitterionic form. As we know that the hydrogen bonding of DPPE with water molecules which have surrounded its head group plays an important role in the permeability of DPPE. So, in order to understand the microscopic physico-chemical nature of this subject we have analyzed bond and torsion angles of DPPE before and after added water molecules. In this paper we have theoretically studied the complexes DPPE with water molecules which have surrounded its head group. As mentioned before, this theoretically study has been done through Hartree-Fock level of theory by using simple basis sets. Theoretical data shows that the interaction of head group of DPPE with water molecules causes some changes in the geometry of DPPE which were explained by the contribution of zwitterionic form of DPPE macromolecule, and finally hydrated DPPE becomes stable complex. Comparison between theoretical and experimental geometry data of DPPE macromolecule shows that the calculation at the HF/3-21 level of theory produces results which they are in better agreement with the experimental data. Moreover the hydrogen bonding effects on the NMR shielding tensor of selected atoms in the hydrated complexes of DPPE were reported. The ";Gauge Including Atomic Orbitals"; (GIAO) approaches within the SCF-Hartree-Fock approximation have been used in order to investigate the influence of hydrogen bonding of DPPE-water complex on the shielding tensors. Finally, the solvent affects on the stability of DPPE macromolecule, dipole moment and atomic charge of some selected atoms of DPPE molecule was discussed using Onsager model and Merz-Singh-Kolman schema. Keywords : Gauge Including Atomic Orbital, DPPE, hydrogen bonding, solvation, quantum mechanics, ab initio

Sum Frequency Generation (SFG) Vibrational Spectroscopy of Planar Phosphatidylethanolamine Hybrid Bilayer Membranes under Water

Sum frequency generation (SFG) spectroscopy has been used to study the structure of phosphatidylethanolamine hybrid bilayer membranes (HBMs) under water at ambient temperatures. The HBMs were formed using a modified Langmuir-Schaefer technique and consisted of a layer of dipalmitoyl phosphatidylethanolamine (DPPE) physisorbed onto an octadecanethiol (ODT) self-assembled monolayer (SAM) at a series of surface pressures from 1 to 40 mN m(-1). The DPPE and ODT were selectively deuterated so that the contributions to the SFG spectra from the two layers could be determined separately. SFG spectra in both the C-H and C-D stretching regions confirmed that a monolayer of DPPE had been adsorbed to the ODT SAM and that there were gauche defects within the alkyl chains of the phospholipid. On adsorption of a layer of DPPE, methylene modes from the ODT SAM were detected, indicating that the phospholipid had partially disordered the alkanethiol monolayer. SFG spectra recorded in air indicated that removal of water from the surface of the HBM resulted in disruption of the DPPE layer and the formation of phospholipid bilayers.

Isopranoid- and dipalmitoyl-aminophospholipid adjuvants impact differently on longevity of CTL immune responses

The success of lipid membranes as cytotoxic T-cell (CTL) adjuvants requires targeted uptake by antigen-presenting cells (APCs) and delivery of the antigen cargo to the cytosol for processing. To target the phosphatidylserine (PS) receptor of APCs, we prepared antigen-loaded liposomes containing dipalmitoylphosphatidylserine and archaeal lipid liposomes (archaeosomes), containing an equivalent amount of archaetidylserine, and compared their ability to promote short and long-term CTL activity in animals. CTL responses were enhanced by the incorporation of PS into phosphatidylcholine/cholesterol liposomes and, to a lesser extent, into phosphatidylglycerol/cholesterol liposomes, that correlated to the amount of surface amino groups reactive with trinitrobenzoyl sulfonate. Archaeosomes contrasted to the liposome adjuvants by exhibiting higher amounts of surface amino groups and inducing superior shorter and, especially, longer-term CTL responses. The incorporation of dipalmitoyl lipids into archaeosomes induced instability and prevented long-term, but not short-term, CTL responses in mice. The importance of glycero-lipid cores (isopranoid versus dipalmitoyl) to the longevity of the CTL response achieved was shown further by incorporating dipalmitoyl phosphatidylethanolamine (DPPE) or equivalent amounts of synthetic archaetidylethanolamine (AE) into archaeosome adjuvants. Both DPPE and AE at equivalent (5 mol%) concentrations enhanced the rapidity of CTL responses in mice, indicating the importance of the head group in the short term. In the longer term, 5% of DPPE (but not 5% of AE) was detrimental. In addition to head-group effects critical to the potency of short-term CTL responses, the longer term CTL adjuvant properties of archaeosomes may be ascribed to stability imparted by the archaeal isopranoid core lipids.

Photophysical Studies of Novel Ruthenium Metal-Ligand Complexes Incorporated in Model Lipid-Membrane Bilayers

We have designed and synthesized ruthenium metal-ligand complexes (MLCs) with amine- or acyl-reactive functional groups. The MLCs have potential as luminescent probes to investigate bio-macromolecular dynamics on the sub-microsecond-to-microsecond timescale. This timescale is of interest, for example, for analysis of the motions associated with macro-molecular assemblies and interactions of membrane-bound proteins. Here we report the photophysical and structural properties of MLCs (1) [HRu(CO)(4,4′-dicarboxy-bipyridyl)(PPh3)2]+ [PF6]- conjugated to dipalmitoyl-phosphatidyl-ethanolamine (DPPE), (2) [HRu(CO)(bpy) (PPh2C2H4COOH)2]+ [PF6]- conjugated to dimyristoyl-phosphatidyl-ethanolamine (DMPE) and (3) [(CF3CO2)Ru(CO) (5-aminophen)(Ph2PC2H2PPh2)]+ [PF6]- conjugated to DPPE and cholesterol. These conjugates were incorporated in 100nm-diameter-unilamellar lipid-membrane vesicles to investigate the photophysical properties of the probes in a model membrane environment and to evaluate the utility of these probes for investigating the physical properties of lipid membranes. We are also investigating the photophysical behavior of MLCs in Nanodiscs, which are ∼10nm-diameter phospholipid bilayers surrounded by a recombinant scaffold protein. We are using Nanodiscs as a platform for investigating the dynamics of transporter proteins, and we are using the MLCs as tools to characterize the physical properties of the Nanodisc-transporter assembly.