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Hydrated lipid structures, such as liposomes, that display tethered metal-ion-chelating groups have proven useful in peptide and protein binding, as well as 2D protein crystallization through molecular recognition of accessible histidine sites in proteins and peptides. Polymerizable metal-ion-chelating lipids bearing a reactive diacetylene group have been described. These interesting compounds can be polymerized in the solid-analogous phase. Here we describe the design of the first polymerizable metal-ion-chelating lipid that can be used in the fluid, i.e., liquid analogous, phase of lipid bilayers. The synthesis of 1-palmitoyl-2-[8-[(E,E)-2‘,4‘-hexadienoyloxy]octanoyl]-sn-glycero-3-N-[11-[N‘,N‘-bis[carboxymethyl]imino]-3,6,9-trioxaundecanoyl] phosphatidylethanolamine (1) is described. The chelator moiety, iminodiacetate (IDA), was linked to the polymerizable phosphatidylethanolamine (PE) with a terminal 2,4-hexadienoyl (sorbyl) group through an oligo(ethylene glycol)-based spacer. Lipid 1−Cu complex is d...

Hydrated amphiphiles form various phases as a function of molecular structure, temperature, concentration, and pressure.1–4 There appears to be a one-to-one correspondence between the structures observed for hydrated amphiphiles and that for block copolymers.5 Amphiphiles are characterized by having a hydrophilic headgroup attached to at least one hydrophobic tail. The unfavorable interfacial enthalpic interaction between the hydrophobic tail(s) of the amphiphile with the polar water molecules induces the former to aggregate with the hydrophobic tail(s) of other amphiphiles.4 The hydrophilic headgroup therefore separates the water from the tail(s), in much the same way that the A–B junction of a diblock AB copolymer separates the two homopolymer blocks A and B.6 Self-organized arrays of non-covalently associated amphiphiles may exist as self-supported lamellar/vesicular, various bicontinuous cubic, or hexagonal/cylindrical phases. Amphiphiles are also frequently studied as supported assemblies, e.g., monolayers at the air–water interface, LB multilayers, or self-assembled monolayers. During the past two decades or so, the understanding of each of these supramolecular assemblies has advanced significantly. This progress is a consequence of fundamental and applied research in many laboratories. The advent of methods to polymerize supramolecular assemblies—first in monolayers in the 1970s, followed by bilayer vesicles in the early 1980s, and more recently in nonlamellar phases, i.e., cubic and hexagonal phases—has led to the creation of new materials, the development of new methods, and a widening perspective on the potential applications of these novel polymeric materials. These uses include the controlled delivery of reagents and drugs, the preparation of biological membrane mimics, the separation and purification of biomolecules, the modification of surfaces, the stabilization of organic zeolites, and the preparation of nanometer colloids, among others. The concept of an area-minimizing surface has been used extensively to describe the morphologies of amphiphile/water systems.2,7 The free energy of the system is described by the topology of the surfaces. In this analysis, a spontaneous curvature term arises purely as a result of the fact that the dimensions of the microdomain are only a few orders of magnitude greater than that of the constituent molecules. This means that the shape of the interface is influenced by the interactions on a molecular level. In order for a system to achieve equilibrium, the various terms in the free energy expression, chief of which is the mean curvature, must be minimized. This theory has been extended to describe the effects of surface charge8 and branched alkyl chains9 on the formation of nonlamellar assemblies. The distribution of a mixture of lipids in nonlamellar phases has also been investigated.10 The identification of the morphology of amphiphile/water systems traditionally relies on methods such as X-ray and neutron diffraction scattering, differential scanning calorimetry (DSC), NMR spectroscopy (e.g., diffusion, 2H, 31P), and transmission and scanning electron microscopy (TEM, SEM). With the exception of the various electron microscopy methods, the characterizations are usually indirect. Though space-group identification and unit cell dimensions are readily obtained with diffraction methods, exactly how the molecules are organized in the unit cell for the amphiphile/water system has only been recently settled.11 In principle, the polymerization of supramolecular assemblies of amphiphiles could be accomplished by at least two strategies: (a) the formation of the hydrated phase from amphiphiles containing a reactive group, followed by either linear or cross-linking polymerization of all or a portion of the organic region of the phase, or (b) the prepolymerization of the amphiphile in isotropic organic media, followed by solvent removal, polymer purification, then hydration of the linear polymer to form the desired phase. This review will emphasize the first strategy. The second approach was successfully employed for the formation of polymerized monolayers at the air–water interface and their transfer to yield LB multilayers but has been infrequently described as a method for the polymerization of self-supported assemblies of amphiphiles.12,13 This review covers the reports, up to late-2000, of the polymerization of self-supported assemblies. The review emphasizes those publications that appeared since the extensive 1988 review by Ringsdorf et al.14 Less attention is given to the numerous studies of reactive amphiphiles in monolayers or multilayers, except in those cases that aid in the understanding of hydrated amphiphilic phases. The following sections review the various methods to polymerize hydrated amphiphiles in bilayer membranes and in nonlamellar phases. In addition, the characteristics of the resultant polymers and the polymeric materials are described, if they are reported by the authors.

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.

Photoinduced electron transfer (PET) from the hydrophobic triphenylbenzylborate anion to the water-soluble tricationic N,N'-bis [3-(trimethylammonio)propyl]thiadicarbocyanine was investigated in water and in phosphatidylcholine membrane systems. The borate (donor) and dye (acceptor) form a strong complex in water,leading to inefficient PET. In the presence of liposomes, the hydrophobic borate anion is bound deep within a bilayer. The resulting negative surface charge of the liposomes leads to electrostatic binding of the cationic dye within the head group region of the membrane

The interaction of the delta-opioid receptor selective peptides, cyclic [D-Pen2, D-Pen5]-enkephalin [DPDPE] and its acyclic analog, DPDPE(SH)2, with neutral phospholipid bilayer membranes was examined by permeability and calorimetry measurements. The permeabilities were accomplished by entrapping either peptide inside of unilamellar liposomes (composed of a mixture of a molar ratio 65:25:10 phosphatidylcholine/phosphatidylethanolamine/cholesterol) then monitoring the peptide efflux through the bilayer. The initial permeability of DPDPE (first 12 h) averaged over four experiments was (0.91 +/- 0.47).10(-12) cm s-1. In contrast the average permeability of the acylic DPDPE(SH)2 was (4.26 +/- 0.23).10(-12) cm s-1. The effect of these peptides on the phase transition, Tm, of 1,2-dipalmitoylphosphatidylcholine (DPPC) bilayers was examined by high sensitivity differential scanning calorimetry. The Tm, the calorimetric enthalpy, and the van 't Hoff enthalpy of DPPC were not significantly altered by the presence of DPDPE, whereas the calorimetric data for DPPC with DPDPE(SH)2 showed a small, yet significant, increase (0.2 degrees C) in the Tm with a 30% decrease in the cooperative unit. Both the permeability and calorimetry data reveal a stronger peptide-membrane interaction in the case of the more flexible acyclic peptide.

Supramolecular assemblies of amphiphiles include monolayers, bilayers, multilayers, as well as nonlamellar structures. The recent introduction of methods to polymerize supramolecular assemblies has increased the range of chemical and physical stabilities of these new materials. Polymerized supramolecular assemblies offer opportunities to prepare new materials for both biological and materials sciences. Polymerization has proven a valuable probe of the similarities of molecular order within bilayers and multilayers, and to examine the transformation of the first into the latter. It is also possible to initiate the transformation from lamellar to nonlamellar assemblies via polymerization induced processes within the assembly. Examples of each of these types of supramolecular conversions are described.

The use of polymerized lipid bilayers as substrates for microcontact printing (muCP) of protein films was investigated. We have previously shown that vesicle fusion of bis-SorbPC, a dienoate lipid, on glass and silica substrates, followed by redox-initiated radical polymerization, produces a planar supported lipid bilayer (PSLB) that is ultrastable(1a) [Ross, E. E.; Rozanski, L. J.; Spratt, T.; Liu, S.; O'Brien, D. F.; Saavedra, S. S. Langmuir 2003, 19, 1752] and highly resistant to nonspecific adsorption of dissolved proteins [Ross, E. E.; Spratt, T.; Liu, S.; Rozanski, L. J.; O'Brien, D. F.; Saavedra, S. S. Langmuir 2003, 19, 1766].(1b) Here we demonstrate that muCP of bovine serum albumin (BSA) onto a dried poly(bis-SorbPC) PSLB from a poly(dimethylsiloxane) (PDMS) stamp produces a layer of strongly adsorbed protein, comparable in surface coverage to films printed on glass surfaces. Immobilization of proteins on poly(PSLB)s has potential applications in biosensing, and this work shows that direct muCP of proteins is a technically simple approach to create immobilized monolayers, as well as multilayers of different proteins.

We report on the photovoltaic properties of solar cells containing a new discotic liquid crystalline material (DL-CuPc) based on copper phthalocyanine. In addition to being soluble, these materials can self-organize into highly ordered structures which can lead to good transport properties that can potentially be superior to those of amorphous materials. Increase in short-circuit current density and fill factor was obtained by thermal annealing of spin-coated DL-CuPc layer in bi-layer solar cells based on junction between DL-CuPc and C 60 . These improvements are explained by change in structure and morphology upon thermal annealing.

Substrate-supported lipid bilayers have been prepared from bis-diene functionalized phosphorylcholine (PC) lipids and polymerized by UV irradiation. The overall bilayer structure is largely preserved upon removal from water, although significant loss of material occurs from the upper leaflet of the bilayer, likely due to desorption at the air/water interface. The morphology and surface structure of the bilayer, as observed by AFM, indicate a substantially different arrangement of the lipids in the hydrated and dehydrated states, presumably due to the loss of water from the near surface region. These changes have been correlated with infrared spectral shifts sensitive to the conformation of the hydrocarbon chains. Protein adsorption studies show that rehydrated, polymerized bilayers retain a degree of resistance to BSA adsorption intermediate between model hydrophobic and fluid PC lipid bilayer surfaces. The degree of protein adsorption is correlated with desorption of material from the upper leaflet of the bilayer upon drying, which produces voids at which hydrophobically driven protein adsorption occurs.

Bicontinuous cubic phases of monoacylglycerides/Poloxamer 407 (PEO98PPO67PEO98)/water can be dispersed into submicron particles, which are termed “cubosomes”. Technological applications of these nanoparticles may be possible, if their nonlamellar architecture can be rendered more robust. To accomplish this goal, a polymerizable heterobifunctional monoacylglycerol, 3-(2,4,13-(E,E)-tetradecatrienoyl)-sn-glycerol (1), was synthesized and combined with water to form an optically transparent gel. In the presence of Poloxamer 407 and excess water the cubic phase of 1 was dispersed by ultrasonication into 300-nm diameter nanoparticles. The polymerization of these reactive cubosomes could be initiated either by the use of a photoinitiator or with redox chemistry. The polymerized cubosomes remained stable even after the addition of excess Triton X-100, in a manner consistent with executing cross-linking in the nanostructures.

A critical spacer arm length necessary to promote efficient binding of the HIV-1 surface glycoprotein rgp120 to several synthetic galactosyl-conjugated lipids, reconstituted into planar lipid bilayers, was identified. This should aid the design of anti-HIV-1 agents based on membrane-tethered, carbohydrate-based receptors for gp120.

The cross-linking of supramolecular assemblies of hydrated lipids is an effective method to stabilize these assemblies to disruption by surfactants or aqueous alcohol. The heterobifunctional lipids, Acryl/DenPC(16,18) and Sorb/DenPC(18,21), are examples of a new class of polymerizable lipid designed for the creation of cross-linked lipid structures. The robust nature of cross-linked liposomes was demonstrated by lyophilization of the liposomes followed by their essentially complete redispersion in water. The resulting liposomes were compared to the original sample by quasi-elastic light scattering and transmission electron microscopy. There was no major change in the size or structure of the cross-linked liposomes after rehydration of the freeze-dried powder of liposomes. Moreover, the rehydrated cross-linked liposomes continued to be resistant to surfactant solubilization. Neutral cross-linked liposomes were predominantly redispersed after freeze-drying with the aid of bath sonication. The small amount of residual liposome aggregation observed with neutral liposomes could be prevented by incorporating a surface charge into the liposome or attaching hydrophilic polymers, for example, poly(ethylene glycol), onto the liposome.

Hydrated amphiphiles form various phases as a function of molecular structure, temperature, concentration, and pressure.1–4 There appears to be a one-to-one correspondence between the structures observed for hydrated amphiphiles and that for block copolymers.5 Amphiphiles are characterized by having a hydrophilic headgroup attached to at least one hydrophobic tail. The unfavorable interfacial enthalpic interaction between the hydrophobic tail(s) of the amphiphile with the polar water molecules induces the former to aggregate with the hydrophobic tail(s) of other amphiphiles.4 The hydrophilic headgroup therefore separates the water from the tail(s), in much the same way that the A–B junction of a diblock AB copolymer separates the two homopolymer blocks A and B.6 Self-organized arrays of non-covalently associated amphiphiles may exist as self-supported lamellar/vesicular, various bicontinuous cubic, or hexagonal/cylindrical phases. Amphiphiles are also frequently studied as supported assemblies, e.g., monolayers at the air–water interface, LB multilayers, or self-assembled monolayers. During the past two decades or so, the understanding of each of these supramolecular assemblies has advanced significantly. This progress is a consequence of fundamental and applied research in many laboratories. The advent of methods to polymerize supramolecular assemblies—first in monolayers in the 1970s, followed by bilayer vesicles in the early 1980s, and more recently in nonlamellar phases, i.e., cubic and hexagonal phases—has led to the creation of new materials, the development of new methods, and a widening perspective on the potential applications of these novel polymeric materials. These uses include the controlled delivery of reagents and drugs, the preparation of biological membrane mimics, the separation and purification of biomolecules, the modification of surfaces, the stabilization of organic zeolites, and the preparation of nanometer colloids, among others. The concept of an area-minimizing surface has been used extensively to describe the morphologies of amphiphile/water systems.2,7 The free energy of the system is described by the topology of the surfaces. In this analysis, a spontaneous curvature term arises purely as a result of the fact that the dimensions of the microdomain are only a few orders of magnitude greater than that of the constituent molecules. This means that the shape of the interface is influenced by the interactions on a molecular level. In order for a system to achieve equilibrium, the various terms in the free energy expression, chief of which is the mean curvature, must be minimized. This theory has been extended to describe the effects of surface charge8 and branched alkyl chains9 on the formation of nonlamellar assemblies. The distribution of a mixture of lipids in nonlamellar phases has also been investigated.10 The identification of the morphology of amphiphile/water systems traditionally relies on methods such as X-ray and neutron diffraction scattering, differential scanning calorimetry (DSC), NMR spectroscopy (e.g., diffusion, 2H, 31P), and transmission and scanning electron microscopy (TEM, SEM). With the exception of the various electron microscopy methods, the characterizations are usually indirect. Though space-group identification and unit cell dimensions are readily obtained with diffraction methods, exactly how the molecules are organized in the unit cell for the amphiphile/water system has only been recently settled.11 In principle, the polymerization of supramolecular assemblies of amphiphiles could be accomplished by at least two strategies: (a) the formation of the hydrated phase from amphiphiles containing a reactive group, followed by either linear or cross-linking polymerization of all or a portion of the organic region of the phase, or (b) the prepolymerization of the amphiphile in isotropic organic media, followed by solvent removal, polymer purification, then hydration of the linear polymer to form the desired phase. This review will emphasize the first strategy. The second approach was successfully employed for the formation of polymerized monolayers at the air–water interface and their transfer to yield LB multilayers but has been infrequently described as a method for the polymerization of self-supported assemblies of amphiphiles.12,13 This review covers the reports, up to late-2000, of the polymerization of self-supported assemblies. The review emphasizes those publications that appeared since the extensive 1988 review by Ringsdorf et al.14 Less attention is given to the numerous studies of reactive amphiphiles in monolayers or multilayers, except in those cases that aid in the understanding of hydrated amphiphilic phases. The following sections review the various methods to polymerize hydrated amphiphiles in bilayer membranes and in nonlamellar phases. In addition, the characteristics of the resultant polymers and the polymeric materials are described, if they are reported by the authors.

The lateral diffusion coefficient of a probe in hydrated bilayers that were linearly polymerized or crosslinked to different extents was determined. The lipids chosen were the mono- and bis-acryloylphosphatidylcholine. The results reveal a significant decrease in the dynamic motion of small molecules probes in polymerized hydrated bilayers at a composition of about 2:1 mono- and bis-substituted lipids. This first observation oc critical composition behavior in polymerized supramolecular assemblies provides a fresh insight into two-dimensional polymerizations

The concept of an area-minimizing surface has been used extensively to describe the morphologies of hydrated amphiphiles and block copolymers. These morphologies include lamellar, hexagonal, and the more complex bicontinuous cubic phases. In spite of the morphological similarities between certain block copolymers and hydrated amphiphiles there are of course some major differences. The stability of the two systems can be widely different This distinction is now minimized by the successful introduction of methods to polymerize and even crosslink the phases of hydrated amphiphiles to greatly enhance their stability. The presence of the water domains in the polymerized nonlamellar phases, in particular the inverted hexagonal phase, are regions of well defined size and shape. This research is examining methods to create novel materials by selective use of these to (1) deposit metals and minerals or (2) isolate rod-like polymers. The major focus of the ongoing research is to extend the current state of the science to ascertain the potential and limits of a fundamentally new method for the synthesis of high value supramolecular composites.

Modifications of 4,4′ residues of Biphalin have resulted in greater binding selectivity and biological potency for the μ opioid receptor. A higher partition coefficient across the phospholipid bilayer membrane has been achieved by using a β-branched unusual amino acids. Biphalin, a highly potent antinociceptive peptide, has been modified on 4, 4′ positions by using β-branched and aromatic substituted unusual amino acids. For example: (Tyr-D-Ala-Gly-Phe-NH)2 ------> (Tyr-D-Ala-Gly-(2S,3R)β-Me-Phe-NH)2

The cellular uptake of liposomes is generally believed to be mediated by adsorption of liposomes onto the cell surface and subsequent endocytosis. This report examines the effect of liposome surface charge on liposomal binding and endocytosis in two different cell lines: a human ovarian carcinoma cell line (HeLa) and a murine derived mononuclear macrophage cell line (J774). The large unilamellar liposomes were composed of 1, 2-dioleolyl-sn-glycero-3-phosphatidylcholine with and without the addition of either a positively charged lipid, 1, 2-dioleoyl-3-dimethylammonium propanediol (DODAP), or a negatively charged lipid, 1,2-dioleolyl-sn-glycero-3-phosphatidylserine. In some experiments 5 mol % of the anionic PEG2000-PE or a neutral PEG lipid of the same molecular weight was added. HeLa cells were found to endocytose positively charged liposomes to a greater extent than either neutral or negatively charged liposomes. This preference was not lipid-specific since inclusion of a cationic cyanine dye, DiIC18(3), to impart positive charge in place of DODAP resulted in a similar extent of endocytosis. In contrast the extent of liposome interaction with J774 cells was greater for both cationic and anionic liposomes than for neutral liposomes. The greater uptake of positively charged liposomes by HeLa cells was also observed with sterically stabilized liposomes (PEG liposomes). Although the overall amount of endocytosis for all the PEG liposomes examined was attenuated relative to conventional liposomes, the extent of endocytosis was greatest for positively charged PEG liposomes, whereas negatively charged PEG2000-PE liposomes were hardly endocytosed by the HeLa cells. Incorporation of a neutral PEG lipid into liposomes permits the independent variation of liposome steric and electrostatic effects in a manner that may allow interactions with cells of the reticuloendothelial system to be minimized, yet permit strong interactions between liposomes and proliferating cells.

Permeability coefficients of a series of analogues of a potent opioid peptide, c[D-Pen2, D-Pen5]enkephalin, were measured in a model membrane system. The analogues included hydrophobic amino acid substitutions on position 3. Liposomes of a mixed composition consisting of zwitterionic lipids and cholesterol served as the model membranes. The obtained permeability coefficients range between 0.38 x 10(-12) and 2.9 x 10(-12) cm/s. These data were correlated with the hydrophobicity scale of Nozaki and Tanford (J. Biol. Chem. 246, 1971, 2211-2217) (correlation coefficient = 0.9933) and with determinations of lipid order perturbation by differential scanning calorimetry (correlation coefficient = -0.9779). The reasonably good correlation obtained within the family of analogues substituted on position 3 (Gly, Ala, Leu, Phe) indicates that changes in permeabilities are primarily related to increases in the partition coefficient of the peptide. However, Phe residue added on the N-terminal end of the peptide (position 0) does not appear to follow the observed trend, showing stronger lipid perturbation and lower permeability compared to the Phe3 analog. This observation demonstrates that each class of peptide modifications requires a new basis of permeability analysis and predictions.

Lipid assemblies are arrays of noncovalently associated amphiphiles, i.e. supramolecular assemblies. They may be classified as supported or self-supported assmeblies. The advent of methods to polymerize these supramolecular assemblies has opened up opportunities for the creation of new materials. This review emphasizes the interaction of polymerization and lipid domain formation within supramolecular assemblies. The polymerization of amphiphilic assemblies can “lock in” preexisting lipid domains or create lipid domains from random mixtures depending on the nature of the polymerizable amphiphile. Lipid diacetylenes or fluorinated lipids provide a convenient means to form an unpolymerized immiscible mixture of reactive and nonreactive lipids in monolayers or bilayers. In contrast the polymerization of dienoyl-, sorbyl-, or acryloyl-substituted lipids can effectively induce the phase separation of unreactive lipids from the growing polymeric domains. Polymerization-induced lipid domains can endow bilayer vesicles with latent instability sites or can be used to concentrate membrane-associated electron or energy transfer cofactors. These polymeric materials suggest new approaches to the delivery of reagents as well as the transduction of light energy.

The photopolymerization of two-component large unilamellar liposomes (LUV) composed of 3:1 dioleoylphosphatidylethanolamine (DOPE) and either 1,2-bis[10-(2'-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphatidylc holine (bis-SorbPC) or 1-palmitoyl-2-[10-(2'-hexadienoyloxy)decanoyl]-sn- glycero-3-phosphatidylcholine (mono-SorbPC) facilitated liposome fusion. Fusion was characterized by fluorescent assays for lipid mixing, aqueous contents mixing, and aqueous contents leakage. The rate and extent of the liposome fusion was dependent on the extent of photopolymerization, temperature, and the fusion initiation conditions, including the pH and the presence of Mg2+ ions. Examination of the temperature dependence of fusion for unpolymerized and polymerized liposomes showed that an enhancement of the rate of fusion occurred in the temperature range delta TI, which previous NMR studies have identified as the initial appearance of precursors to the formation of the inverted cubic phase [Barry, J. A., et al. (1992) Biochemistry 31, 10114]. The phase behavior and fusion characteristics of the DOPE/bis-SorbPC (3:1) membranes provide unequivocal evidence that liposome fusion is mediated via intermediates associated with the lamellar to QII phase transition rather than the HII phase. Photopolymerization of SorbPC-containing liposomes forms poly-SorbPC, which enhances the lateral separation of the liposome components. The formation of enriched domains of polymorphic lipids, e.g., DOPE, causes isothermal induction of fusion by lowering the critical fusion temperature of the membranes.

The size distribution of phospholipid vesicles prepared by the freeze thaw-extrusion method were determined by the non-perturbing technique of quasi-elastic light scattering (QELS) and compared to latex particles of known size. Multiangle QELS experiments were performed to avoid errors due to the angular dependence of the scattering function of the particles. The experimentally determined autocorrelation function was analyzed by multiple mathematical procedures, i.e. single exponential, CUMULANT, exponential sampling, non-negatively constrained least square and CONTIN, in order to select suitable models for vesicle characterization. The most consistent results were obtained with CUMULANT, non-negatively constrained least square and CONTIN. In many instances single exponential analysis gave comparable results to these procedures, which indicates the vesicles have a narrow distribution of sizes. The influence of filter pore size, extrusion pressure and lipid concentration on the size and size distribution of extruded vesicles was determined. Extrusion through 100-, 200- and 400-nm pore size filters produced a unimodal distribution of vesicles, with somewhat smaller diameters as the extrusion pressure increased. The larger the filter pore size, the more dependent the vesicle size was on applied pressure. The observed vesicle size was independent of the lipid concentration between 0.1 and 10 mg ml −1 .

We discuss here our most recent results with the characterization of epitaxial deposits of various phthalolcyanine dyes formed by vacuum deposition (O/I-MBE) or solution deposition on the surface of metal dichalcogenide semiconductors, such as SnS 2 . Surface electron diffraction techniques used during the vacuum deposition process help to verify the type and extent of long range ordering of these dyes. SnS 2 semiconductor substrates allow for the photoelectrochemical characterization of the dye layers, starting with the deposition of submonolayer amounts of material. High quantum yields per absorbed photon are seen for ultrathin films of InPc-Cl, VOPc, and CuPc on SnS 2 , and the photocurrent spectra suggest similar ordering at the monolayer level, even though multilayer structures are quite different. Ordered Pc thin films are also obtained for a new class of liquid crystalline phthalocyanines (LC-Pc), where the hydrocarbon side chains are attached to the Pc ring by amide linkages. Deposition of ultrathin films of these materials produces photocurrent spectra which are quite similar to those obtained for low coverages of the vacuum deposited Pc. Photocurrent spectra on SnS 2 show that the first monolayer of material may have a completely different surface structure than the bulk of the multilayer LC-Pc thin film. The nature of dye/dye' interfaces and their effect on exciton dissociation events has also been explored using vacuum deposited materials. Superlattices of Pcs were formed by vacuum deposition, where the active dye was sandwiched between various spacer molecules with thicknesses down to a few molecular layers. Transient photocurrent yield spectra from such assemblies suggests that exciton dissociation events in such materials can be confined to within a few molecular layers of the dye/dye' interface.

Three novel polymerizable ether lipids, 1,2-O-bis[10(2',4'-hexadienoyloxy)decyl]-rac, 1,2-O-bis(10,12-tricosadiynyl)-rac, and (-)-2,3-O-bis(10,12-tricosadiynyl)-sn-glycero-1-phosphocholine, were synthesized from 3-O-benzyl-rac, 3-O-trityl-rac and (-)-1-O-trityl-sn-glycerol as starting materials, respectively. All the reactions employed in these multi-step syntheses are straightforward giving an overall yield of 21% for the sorbyl, 42% for the racemic diacetylenic and 44% for the chiral diacetylenic lipid. All the lipids form bilayer assemblies on hydration and show transitions from gel to liquid-crystalline phases at 11.4 degrees, 27.6 degrees and 30.0 degrees C, respectively. Bilayer assemblies of each are photoreactive and are readily polymerized by irradiation with 254 nm light. Tubules of the chiral diacetylenic ether lipid were observed.

The stability of two-component liposomes composed of the polymerizable 1,2-bis-[10-(2',4'-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphati dylcholine (SorbPC) and either a phosphatidylethanolamine (PE) or a phosphatidylcholine (PC) were examined via fluorescence leakage assays. Ultraviolet light exposure of SorbPC-containing liposomes forms poly-SorbPC, which phase separates from the remaining monomeric lipids. If the nonpolymerizable lipids are PE's, then the photoinduced polymerization destabilizes the liposome with loss of aqueous contents. The permeability of the control dioleoylPC/SorbPC membranes was not affected by photopolymerization of SorbPC. The photodestabilization of dioleoylPE/SorbPC (3:1) liposomes required the presence of oligolamellar liposomes. NMR spectroscopy of extended bilayers of dioleoylPE/SorbPC (3:1) showed that the photopolymerization lowers the temperature for the appearance of 31P NMR signals due to the formation of isotropically symmetric lipid structures. These observations suggest the following model for the photoinduced destabilization of liposomes composed of PE/SorbPC; photopolymerization induced phase separation with the formation of enriched domains of PE, which allows the close approach of apposed regions of enriched PE lamellae and permits the formation of an isotropically symmetric structure between the lamellae. The formation of such an interlamellar attachment (ILA) between the lamellae of an oligolamellar liposome provides a permeability pathway for the light-stimulated leakage of entrapped water-soluble reagents.

Patterned thin films of a unique phthalocyanine (Pc), (2,3,9,10,16,17,23,24-oktakis((2-benzyloxy)ethoxy)phthalocyaninato) copper (1), are created by means of capillary flow of chloroform solutions into micrometer-dimension hydrophobic/hydrophilic channels. These channels are created by a combination of microcontact printing of octadecylmercaptan (C18-SH) layers on gold, creating a hydrophobic channel bottom, and oxidative electropolymerization of m-aminophenol (at pH 4), creating hydrophilic channel walls (microcontact printing/electropolymerization, μCP-EP). The polyphenoxide channel walls grow perpendicular to the substrate plane, with excellent retention of structure to thicknesses (ca. 30 nm) far exceeding the height of the C18-self-assembled monolayer (SAM). Doping of the C18-SAM layers with small percentages of 1-phenyldodecane provides for efficient wetting of the channel bottoms with solutions of 1, consistent with recent studies, which have shown the need for phenyl-termination of substrates surfaces to create coherent rod-like aggregate structures. These optimized channels provide for excellent capillary flow conditions for chloroform solutions of 1, yielding 10 μm width Pc films with thicknesses exceeding the height of the polyphenoxide channel walls by up to 10×. We also present evidence for formation of birefringent (ordered) material near the hydrophilic walls.

A critical spacer arm length necessary to promote efficient binding of the HIV-1 surface glycoprotein rgp120 to several synthetic galactosyl-conjugated lipids, reconstituted into planar lipid bilayers, was identified. This should aid the design of anti-HIV-1 agents based on membrane-tethered, carbohydrate-based receptors for gp120.

Etude de l'influence des concentrations en amorceur et en monomere sur le degre de polymerisation des polymeres obtenus par polymerisation radicalaire d'une couche bimoleculaire d'acryloylphosphatidylcholine. Les resultats suggerent que la terminaison des polymerisations de couches bimoleculaires de lipides a lieu surtout par reaction avec des fragments d'amorceur

The efficient formation of polydiacetylenes in cast films demonstrates that a well-ordered multilayer structure can be readily formed by the casting of hydrated bilayer membranes onto solid supports.