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Hydrated amphiphiles can yield quite complex lyotropic liquid crystals such as the lamellar (bilayer) and nonlamellar phases. Lamellar structures can be solidlike or liquid crystalline. An important characteristic of these lamellar phases is the lateral diffusion of the lipids which increases by ca. 102 at the main phase transition, Tm. The rate (Rp) and degree (Xn) of polymerization were determined for polymerizable lipids in these two phases. A determination of the effect of temperature between 25 and 45 °C on the Rp of redox-initiated polymerization of mono-SorbPC bilayers showed a discontinuity near the Tm. The calculated activation energy, Ea, and frequency factor, A, for the polymerization at temperatures below Tm are 10 kcal/mol and 107, respectively. A similar calculation for the polymerization at temperatures above the Tm gave an Ea = 24 kcal/mol and A = 1016. The degree of polymerization, relative to poly(methyl methacrylate) standards, for bilayers of mono-SorbPC at temperatures above and below...

Prostate cancer can be detected using assays for blood-borne prostate-specific antigen (PSA), which is the clinically most useful diagnostic marker of malignant disease. This paper characterizes the 5 -flanking prostate-specific enhancer which controls expression of the human PSA gene This enhancer, located between -5824 and -3738, is androgen-responsive and requires a promoter for activity. Inductions of 12-100-fold activity occur at 1 nM concentrations of the testosterone analog R1881. The enhancer demonstrated tissue specificity as judged by transfections of several human cell lines. Electrophoretic mobility shift assays comparing nuclear extracts from breast cancer cells MCF-7, and prostate cancer cells LNCaP, showed three regions of prostate-specific binding. These three regions are -4168 to -4797 (region I), -4710 to 4479 (region II), and -4168 to -3801 (region III). Region III contained a putative androgen response element at -4136 that markedly affected activity if mutated. These data suggest that prostate-specific gene expression may involve interaction of prostate-specific proteins or protein complexes with the enhancer in addition to binding of the androgen receptor to androgen response elements.

The first chemical syntheses of polymerizable monoacylglycerol and 1,2-diacyl-sn-glycerol are reported. The monodienoylglycerol is obtained in 80% yield from 1,2-O-isopropylidene-sn-glycerol and dienoyl fatty acid. The dienoic acid is accessible in 60% yield from the base-catalyzed hydrolysis of dienoyl ester, which is synthesized from the Wittig−Horner reaction of aldehyde and trimethyl 4-phosphonocrotonate. The acylation is carried out in the presence of 4-(dimethylamino)pyridine and dicyclohexylcarbodiimide. The use of excess protected glycerol relative to fatty acid affords the acylated product in high yield. The final step is the deprotection of isopropylidene group using dilute HCl solution. The 1,2-diacyl-sn-glycerol is synthesized by acylation of 3-(4-methoxybenzyl)-sn-glycerol with dienoyl fatty acid in the presence of 4-(dimethylamino)pyridine and dicyclohexylcarbodiimide. The removal of the 4-methoxybenzyl group by dimethylboron bromide catalyzed hydrolysis is especially useful in the synthesis...

Polymerization of monomeric lipids in an assembly proceeds in a linear or cross-linking manner depending on the number of polymerizable groups per monomeric lipid. Lipids that contain a single reactive moiety in either of the hydrophobic tails or associated with the hydrophillic head group yield linear polymers. Polymerization of lipids with reactive groups in each hydrophobic tail generally yield cross-linked polymeric networks. This report describes three approaches to the characterization of the gel point for polymerizations constrained by the two-dimensional nature of lipid bilayers. The gel point for two-dimensional lipid assemblies was determined by correlation of the onset of significant changes in the physical properties of the polymerized bilayers with the bilayer composition. The properties examined in this study were the lateral diffusion of a small molecule probe of the bilayer, the stability of polymerized bilayer vesicles in the presence of surfactants, and the solubility of lipid polymers i...

A rhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 is reported to increase the aqueous dispersion and biodegradation of petroleum hydrocarbons and to complex heavy metals. These reports indicate the potential for application of rhamnolipids in remediation of contaminated sites. Effective use of rhamnolipids will require understanding of rhamnolipid morphology and the effects of pH and organic and inorganic contaminants on that morphology. We used cryo-transmission electron microscopy to investigate the morphology of vitrified, frozen hydrated suspensions of rhamnolipid over a pH range of 5.5 to 8.0, and to determine the effect of a model alkane, octadecane, and a model heavy metal, cadmium, on rhamnolipid morphology. Micrographs clearly showed that rhamnolipid morphology was a function of pH, changing from lamellar, to vesicular, to micellar as pH increased. The effect of cadmium and octadecane on rhamnolipid morphology was determined at pH 6.8 and 7.0, where maximum cadmium complexation and maximum octadecane dispersion occurs. Cadmium seemed to stabilize rhamnolipid vesicle structures as shown by an increase in vesicle number and a decrease in vesicle diameter. In contrast, octadecane favored the micellar structure as shown by the complete absence of vesicles.

The thermotropic phase behavior of hydrated bilayers of mono- and bis-substituted phosphatidylcholines (PC) containing either acryloyl, methacryloyl, or sorbyl ester groups at the chain terminus was studied by differential scanning calorimetry. Each of these compounds exhibits a single endotherm which occurs at a temperature lower than that of the main phase transition T m of the corresponding linear saturated chain PC. Variation of the chain length of the sorbylPCs results in a pronounced odd/even alternation of the T m . Consideration of the preferred conformation of glycerol ester lipids suggested by the crystal structure of dimyristoylPC dihydrate provides a basis for understanding the odd/even effect reported here

The first chemical syntheses of polymerizable monoacylglycerol and 1,2-diacyl-sn-glycerol are reported. The monodienoylglycerol is obtained in 80% yield from 1,2-O-isopropylidene-sn-glycerol and dienoyl fatty acid. The dienoic acid is accessible in 60% yield from the base-catalyzed hydrolysis of dienoyl ester, which is synthesized from the Wittig−Horner reaction of aldehyde and trimethyl 4-phosphonocrotonate. The acylation is carried out in the presence of 4-(dimethylamino)pyridine and dicyclohexylcarbodiimide. The use of excess protected glycerol relative to fatty acid affords the acylated product in high yield. The final step is the deprotection of isopropylidene group using dilute HCl solution. The 1,2-diacyl-sn-glycerol is synthesized by acylation of 3-(4-methoxybenzyl)-sn-glycerol with dienoyl fatty acid in the presence of 4-(dimethylamino)pyridine and dicyclohexylcarbodiimide. The removal of the 4-methoxybenzyl group by dimethylboron bromide catalyzed hydrolysis is especially useful in the synthesis...

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.

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 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

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 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.

Etude de la photodestabilisation des vesicules de couches bimoleculaires de dioleoyl phosphatidylethanolamine