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Biomedical subjects

S W Hui

Publications and source records attributed to S W Hui.

At least 37 records · Page 2Linked to original sources
PubMed1998

A pulsed electric field enhances cutaneous delivery of methylene blue in excised full-thickness porcine skin.

We used electric pulses to permeabilize porcine stratum corneum and demonstrate enhanced epidermal transport of methylene blue, a water-soluble cationic dye. Electrodes were placed on the outer surface of excised full-thickness porcine skin, and methylene blue was applied to the skin beneath the positive electrode; 1 ms pulses of up to 240 V were delivered at frequencies of 20-100 Hz for up to 30 min. The amount of dye in a skin sample was determined from absorbance spectra of dissolved punch biopsy sections. Penetration depth and concentration of the dye were measured with light and fluorescence microscopy of cryosections. At an electric exposure dose VT (applied voltage x frequency x pulse width x treatment duration) of about 4700 Vs, there is a threshold for efficient drug delivery. Increasing the applied voltage or field application time resulted in increased dye penetration. Transport induced by electric pulses was more than an order of magnitude greater than that seen following iontophoresis. We believe that the enhanced cutaneous delivery of methylene blue is due to a combination of de novo permeabilization of the stratum corneum by electric pulses, passive diffusion through the permeabilization sites, and electrophoretic and electroosmotic transport by the electric pulses. Pulsed electric fields may have important applications for drug delivery in a variety of fields where topical drug delivery is a goal.

Administration, Cutaneous↗
PubMed1997

Grafted poly-(ethylene glycol) on lipid surfaces inhibits protein adsorption and cell adhesion.

Monolayers of dipalmitoyl-phosphatidylethanolamine (DPPE) mixing with various mole percentages of distearoyl-phosphatidylethanolamine (DSPE)-conjugated poly-(ethylene glycol) (PEG m.w. 750-5000) were deposited on DPPE-coated glass surfaces by the Langmuir-Blodgett method. Increasing percentages of grafted PEG in these supported lipid surfaces increasingly inhibit the adsorption of bovine serum albumin (BSA), laminin, and fibronectin. Increasing percentages of grafted PEG also inhibit the adhesion of erythrocytes, lymphocytes, and macrophages to these supported lipid surfaces. The adsorption of proteins on lipid coated glass surfaces were assayed by the fluorescence of FITC-labelled proteins. Cell adhesion was measured mainly by microscopic counting. The concentration of PEG-grafted lipids required for the inhibition of erythrocyte adhesion decreases with increasing molecular weight of the grafted PEG. The inhibitory effects are strongly dependent on the graft density of PEG at low concentrations, but weakly dependent on graft density at higher concentrations. For DSPE-PEG5000, the change of graft density dependency occurs approximately at the complete coverage of the lipid surface by the grafted polymer in the mushroom conformation (0.7 mol%), and the transition to partial brush conformation. The change-overs become less distinctive for grafted PEG of lower molecular weights, probably due to the failure of strictly mushroom and brush models of the polymer. The relative inhibitory efficiency is protein or cell dependent. The implication on the function of stealth liposomes is discussed.

Adsorption↗
PubMed1997

Poly(ethylene glycol)-conjugated surfactants promote or inhibit aggregation of phospholipids.

The calcium-induced aggregation of dilauroyl phosphatidic acid (DLPA) suspensions, with or without added poly(ethylene oxide) (PEO)-conjugated surfactants containing 4 to 30 ethylene oxide subunits, were monitored by turbidity measurement and quasi-elastic light scattering (QLS). The aggregation was inhibited (protected) by the incorporated PEO surfactant for most samples, while a window for promotive effect was found for samples with low surface coverage by the PEO moiety of the incorporated surfactant. Promotion occurs only when the aggregation is slow and at a low level. The promotion is explained by the synergistic effect of PEO and divalent calcium cations when the steric repulsion is weak. The promotion/protection crossover is a display between the PEO/calcium synergistic effect and the steric repulsion.

Calcium↗
PubMed1997

The effect of lipid molecular packing stress on cationic liposome-induced rabbit erythrocyte fusion.

The effect of curvature stress on the efficiency of cationic liposome-induced fusion between rabbit erythrocytes was studied. Multilamellar cationic liposomes containing 1,2-dioleoyl-3-trimethylammoniumpropane (DOTAP) and different PEs (1,2-dilnoleoyl-sn-glycero-3-phosphoethanolamine (dilin-PE), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), and lysophosphatidylethanolamine, egg (lyso-PE)) were used to induce cell-cell fusion. It was found that high cell-cell fusion yield (FY) of about 50% could be achieved in sucrose solution by using cationic liposomes containing 50% DOTAP. Cell-cell fusion was assayed by shape criterion and was verified by fluorescence microscopy, using a membrane dye mixing method. The curvature stress, as a result of mixing unsaturated PEs in cationic liposomes, had a significant effect on cell-cell FY which increased with the degree of acyl chain unsaturation, in the order dilin-PE > DOPE > POPE > lyso-PE. Replacement of dilin-PE, DOPE, or POPE by lyso-PE gradually in cationic liposomes lowered the cell-cell FY from 50% to 1%. Furthermore, cationic liposome induced cell lysis, and fusion between cationic liposomes and cells, as assayed by the N-(lissamine rhodamine B sulfonyl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, triethylammonium salt and N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2- dihexadecanoyl-sn-glycero-3-phosphoethanolamine, triethylammonium salt (Rh-PE/NBD-PE) energy transfer method, followed the same order as that for cell-cell fusion. Fusion between the negatively charged PS liposomes and cationic liposomes also followed the same order. The electric double layer screening by electrolytes in NaCl-containing solution and phosphate buffered saline (PBS) was found to reduce the cell-cell FY and cell lysis. These findings suggest that liposome-induced cell-cell fusion was achieved by cationic liposomes serving as fusion-bridges among cells.

Animals↗
PubMed1997

Effects of lipid headgroup and packing stress on poly(ethylene glycol)-induced phospholipid vesicle aggregation and fusion.

The effect of lipid headgroup and curvature-related acyl packing stress on PEG-induced phospholipid vesicle aggregation and fusion were studied by measuring vesicle and aggregate sizes using the quasi-elastic light scattering and fluorescence energy transfer techniques. The effect of the lipid headgroup was monitored by varying the relative phosphatidylcholine (PC) and phosphatidylethanolamine (PE) contents in the vesicles, and the influence of hydrocarbon chain packing stress was controlled either by the relative amount of PE and PC content in the vesicles, or by the degree of unsaturation of the acyl chains of a series of PEs, e.g., dilinoleoylphosphatidylethanolamine (dilin-PE), lysophosphatidylethanolamine (lyso-PE), and transacylated egg phosphatidylethanolamine (TPE). The PEG threshold for aggregation depends only weakly on the headgroup composition of vesicles. However, in addition to the lipid headgroup, the curvature stress of the monolayer that forms the vesicle walls plays a very important role in fusion. Highly stressed vesicles, i.e., vesicles containing PE with highly unsaturated chains, need less PEG to induce fusion. This finding applies to the fusion of both small unilamellar vesicles and large unilamellar vesicles. The effect of electrostatic charge on vesicle aggregation and fusion were studied by changing the pH of the vesicle suspension media. At pH 9, when PE headgroups are weakly charged, increasing electrostatic repulsion between headgroups on the same bilayer surface reduces curvature stress, whereas increasing electrostatic repulsion between apposing bilayer headgroups hinders intervesicle approach, both of which inhibit aggregation and fusion, as expected.

Acylation↗
PubMed1997

Characterization of biomimetic surfaces formed from cell membranes.

A method for fabricating biomimetic surfaces from intact cell membranes is described. A monolayer of alkanethiol on gold is covered by a second layer derived from the components of erythrocyte membranes either by self-assembly or by Langmuir-Blodgett methods. The resulting asymmetric hybrid layer was characterized by ellipsometry, surface plasmon resonance (SPR), contact angle, capacitance, voltammetry, and electron and atomic force microscopy. The erythrocyte membrane layer was measured to be approximately 30-40 A in thickness. Using SPR, the presence of erythrocyte components on the surface was demonstrated by their selective removal by enzymatic action. The uniform deposition of membranous material on the substrate was shown by electron and atomic force microscopy. Demonstration of acetylcholinesterase (AChase) activity, a membrane-anchored enzyme, on the surface for at least 8 days, suggests that the outer leaflet of the erythrocyte membrane is present in its native form. Cyclic voltammetry demonstrates that enhanced electron transport from a solution redox species accompanies formation of the erythrocyte layer at the surface. This enhanced electron transport is blocked by 4,4'-diisothiocyanate stilbene-2,2'-disulfonic acid, a well known blocker of anion transport, suggesting that an erythrocyte anion transporter protein is incorporated into the surface layer in an active conformation.

Acetylcholinesterase↗
PubMed1997

Characterization of electric-pulse-induced permeabilization of porcine skin using surface electrodes.

We measured the transient and long-term changes of permeability of full-thickness porcine skin after the application of a single or a train of electric pulses, as the basis for optimization of the electrical parameters for enhancing transdermal drug or gene delivery by electroporation. Two electrodes were attached to the stratum corneum of excised skin for transdermal electric pulse delivery and impedance measurement. Both transient and long-term permeabilization were found to be dependent on the electrical exposure dose, i.e., the product of pulse voltage and cumulative pulsing (exposure) time. Skin resistance dropped to about 20% of its prepulsing value when pulsed beyond a critical dosage of 0.4 V-s (with 20-40 V across each skin path), but recovered rapidly within seconds after the pulse. Long-term permeabilization of the skin required repeated pulsing with a minimum potential of 160 V (80 V across each skin path). The maximum long-term resistance drop, to 35% of the initial value, required a dose greater than 200 V-s, recovering slowly and seldom completely in tens of minutes to hours. The decrease and recovery of the resistance were dependent on the frequency and pulse length only for low-dose electrical exposure.

Administration, Cutaneous↗
PubMed1996

Structural study of the interaction between the SIV fusion peptide and model membranes.

It has been shown that there is a correlation between the fusogenecity of synthetic peptides corresponding to the N-terminal segment of wild-type and mutant forms of simian immunodeficiency virus gp32 (SIV) and their mode of insertion into lipid bilayers. Fusogenic activity is only observed when the peptide inserts into the bilayer with an oblique orientation. Since bilayer destabilization is a necessary step in membrane fusion, we investigate how fusion peptides, which insert at different orientations into lipid bilayers, structurally affect model membranes. We use X-ray diffraction to investigate the structural effects of two synthetic peptides on three different lipid systems. One peptide corresponds to the wild-type sequence (SIVwt), which inserts into the membrane at an oblique angle and is fusogenic. The other peptide has a rearranged sequence (SIVmutV), inserts into the membrane along the bilayer normal, and is nonfusogenic. Our results are expressed through different structural effects, which depend on the lipid system: for example, (i) disordering of the L alpha phase as evidenced by the broadening of the diffraction peaks, (ii) morphological convertion of multilamellar vesicles into unilamellar vesicles, (iii) decrease of the hexagonal phase cell parameter when SIVwt is added, and (iv) change in the conditions for the formation of cubic phases as well as its kinetic stability over a range of temperatures. Some of these observations are explicable based on the fact that the SIVwt destabilizes bilayers by inducing a negative monolayer curvature, while the SIVmutV destabilizes bilayers by inducing a positive monolayer curvature. Finally, we present a model which describes how these findings correlate with fusogenic activity and fusion inhibitory activity, respectively.

Amino Acid Sequence↗
PubMed1996

Electrofusion between heterogeneous-sized mammalian cells in a pellet: potential applications in drug delivery and hybridoma formation.

High-efficiency electrofusion between cells of different sizes was achieved by application of fusing electric pulses to cells in centrifuged pellets. Larger target cells (Chinese hamster ovary or L1210 cells) were stacked among smaller human erythrocytes or erythrocyte ghosts by sequential centrifugation at 700 g to form five-tier pellets in a specially designed centrifugation-electrofusion chamber. The membranes of erythrocytes and ghost were labeled with fluorescent membrane dye (1,1' dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine (Dil)), and the contents of ghosts were loaded with water-soluble fluorescent dye (42-kDa fluorescein isothiocyanate dextran (FITC-dextran)), to monitor heterogeneous cell fusion. Fusion efficiency was assayed by the extent of either membrane dye mixing or contents (FITC-dextran) mixing with target cells. Four rectangular electric pulses at 300 V and 80 microseconds each were found to give the optimal fusion results of approximately 80% heterogeneous fusion by the content-mixing assay and approximately 95% by the membrane-dye-mixing assay. Cell viability remained greater than 80% after electrofusion. Because of the electric breakdown of cell membranes at the beginning of the pulse, the pellet resistance and hence the partial voltage across the pellet reduced rapidly during the remaining pulse time. This voltage redistribution favored the survival of fused cells. The limited colloidal-osmotic swelling of cells in pellets enhanced cell-cell contact and increased the pellet resistance after each pulse. As a result, the partial voltage across the pellet was restored when the next pulse was applied. This redistribution of pulse voltage in the pellet system permitted the breakdown of cell membranes at a lower applied voltage threshold than that required for electrofusion of cells in suspension or in dielectrophoretic cell chains. The cell viability and soluble dye retention within cells (FITC-dextran) remained at the same high levels for 3 h when the cells were incubated in respective culture media with serum at 37 degrees C. Viability and dye retention decreased significantly within 30 min when cells were incubated in phosphate-buffered saline without serum. The pellet technique was applied to form hybridomas by fusion of larger SP2/0 murine myelomas with smaller naive mouse lymphocytes. An optimum of 173 +/- 70 hypoxanthine aminopterin thymidine (HAT)-selected clones of the hybridomas was obtained from 40,000 SP2/0 cells and 1.5 x 10(6) lymphocytes used in each trial. This high-efficiency fusion technique may be adapted to mediate drug and gene transfer to target cells ex vivo as well as to form hybrid cells with limited cell sources.

Animals↗
PubMed1996

The role of helper lipids in cationic liposome-mediated gene transfer.

In the procedure for cationic liposome-mediated transfection, the cationic lipid is usually mixed with a "helper lipid" to increase its transfection potency. The importance of helper lipids, including dioleoylphosphatidylcholine (DOPC) and phosphatidylethanolamine (dioleoyl PE), DO was examined. Freeze-fracture electron microscopy of DNA:cationic complexes containing the pSV-beta-GAL plasmid DNA, the cationic lipid dioleoyl trimethylammonium propane, and these helper lipids showed that the most efficient mixtures were aggregates of ensheathed DNA and fused liposomes. PE-containing complexes aggregated rapidly when added to culture media containing polyanions, whereas PC-containing complexes did not. However, more granules of PC-containing complexes were formed on cell surfaces after the complexes were added to Chinese hamster ovary (CHO) cells in transfection media. Pronase treatment inhibited transfection, whereas dilute poly-L-lysine enhanced transfection, indicating that the attachment of DNA:liposome complexes to cell surfaces was mediated by electrostatic interaction. Fluorescence spectroscopy studies confirmed that more PC-containing complexes than PE-containing complexes were associated with CHO cells, and that more PC-containing complexes were located in a low pH environment (likely to be within endosomes) with time. Cytochalasin-B had a stronger inhibitory effect on PC-containing liposome-mediated than on PE-containing liposome-mediated transfection. Confocal microscopic recording of the fluorescently label lipid and DNA uptake process indicated that many granules of DNA:cationic liposome complexes were internalized as a whole, whereas some DNA aggregates were left out on the cell surfaces after liposomes of the complexes fused with the plasma membranes. For CHO cells, endocytosis seems to be the main uptake pathway of DNA:cationic liposome complexes. More PC-containing granules than PE-containing granules were formed on cell surfaces by cytoskeleton-directed membrane motion, after their respective DNA:liposome complexes attached to cell surfaces by electrostatic means. Formation of granules on the cell surface facilitated and/or triggered endocytosis. Fusion between cationic liposomes and the cell membrane played a secondary role in determining transfection efficiency.

Animals↗
PubMed1996

High-efficiency loading, transfection, and fusion of cells by electroporation in two-phase polymer systems.

A method to concentrate drugs, DNA, or other materials with target cells in two-phase polymer systems for high-efficiency electroloading is described. The two-phase polymer system is utilized for cell and loading material selection, as well as for cell aggregation before electrofusion. The phase mixing of several water-soluble polymers is characterized, and the polyethylene glycol-Dextran (PEG m.w. 8,000 + Dextran m.w. 71,000) mixture is selected to illustrate the advantage of the two-phase systems. Fluorescently labeled Dextran or DNA is loaded into Chinese hamster ovary (CHO) and JTL cells, using electroporation in either the two-phase polymer system or the conventional single-phase suspension. The loading efficiency is 4 to 30 times higher for the two-phase system, with the best advantage at lower applied field range. Transfections of CHO, COS, Melan C, and JTL lymphoid cells using pSV-beta-galactosidase (for CHO and COS), pBK-RSV-tyrosinase, and pCP4-fucosidase plasmids, respectively, by electroporation in the two-phase polymer system and the conventional single-phase electroporation method, are compared. The former method is far superior to the latter in terms of efficiency. The threshold and optimal field strengths for the former are significantly lower than those for the latter method, so the former method is more favorable in terms of equipment requirement and safety. Electrofusion efficiency in the two-phase system is comparable to that in polyethylene glycol suspension alone and is a significant improvement from the conventional electrofusion method with dielectrophoresis. The two-phase polymer method is, therefore, a valuable technique for gene delivery to a limited cell source, as in ex vivo gene therapy.

Animals↗
PubMed1996

Tetraoleoylpyrophosphatidic acid: a four acyl-chain lipid which forms a hexagonal II phase with high curvature.

Tetraoleoylpyrophosphatidic acid (bis phosphatidic acid), when hydrated in aqueous buffer, was shown to form an inverted hexagonal phase using 31P NMR. Low-angle x-ray diffraction provided verification of the formation of this phase in dilute aqueous buffer and in 2 M NaCl and permitted comparison of the tube diameter with that of cardiolipin in 2 M NaCl. By using the water cylinder diameters for tetraoleoylpyrophosphatidic acid, bovine cardiolipin, chloroplast monogalactosyl-diglyceride, and dioleoyl phosphatidylethanolamine as a means of estimating the spontaneous curvatures, tetraoleoylpyro-phosphatidic acid was shown to exhibit the greatest curvature of any of the above lipids, equaled only by the calcium salt of cardiolipin. Inverted micelles of hydrated tetraoleoylpyrophosphatidic acid and of cardiolipin in tetradecane were approximately the diameter of the inverted hexagonal tubes. A rationale is given for the differences.

Animals↗
PubMed1995

Interaction of free fatty acids with phospholipid bilayers.

The partition of free fatty acids (FFA) to egg-phosphatidylcholine (egg-PC) and egg-phosphatidylethanolamine (egg-PE) vesicles was studied. Upon the addition of FFA to the suspension of vesicles, the pH of the aqueous phase changed depending on the length and saturation of the FFA hydrocarbon chain, as well as on the vesicle composition. The medium pH decreased faster if FFA was added to egg-PE as compared to egg-PC vesicles. The fluorescent free fatty acid indicator (ADIFAB) was used to measure the amount of FFA remaining in the aqueous phase. Most of the FFA added to the suspension of egg-PE vesicles remained in the aqueous phase, whereas in the presence of egg-PC vesicles the FFA partitioned preferentially into the lipid phase. The amount of FFA incorporated into the lipid bilayers was estimated by measuring the changes of pH at the lipid bilayer surface, using fluorescein-PE. At high surface concentrations of FFA, decreasing pH at the bilayer surface caused the protonation of FFA, and raised the pK of FFA at the bilayer surface from 5 to about 7. The partition of FFA in egg-PE vesicles was an order of magnitude lower than that in egg-PC vesicles. The incorporation amount was determined more by the molecular packing than by the nature of lipid headgroups, because steroylcaprioyl-PE, which preferred the bilayer structure, behaved more like egg-PC than egg-PE. Understanding FFA partition characteristics would help to interpret the hydrolysis measurements of phospholipids, and to explain many biological activities of FFA.

Fatty Acids, Nonesterified↗
PubMed1995

Nucleoside conjugates. 14. Synthesis and antitumor activity of 1-beta-D-arabinofuranosylcytosine conjugates of ether lipids with improved water solubility.

A series of ara-CDP-rac-1-O-alkyl-2-O-acylglycerols (9a-f), analogues of highly active ara-CDP-rac-1-O-hexadecyl-2-O-palmitoylglycerol (1) and Cytoros2 (2), was prepared, and solubility, lipophilicity, and structure-activity relationships of these conjugates were investigated. Conjugates 9a-f containing sn-1 alkyl (< C16) and sn-2 fatty acyl (< C14) and sn-1 alkyl (< C14) and sn-2 fatty acyl (< C16) substituents of the glycerol were water-soluble by shaking, while those with the sn-1 alkyl (> C16) and the sn-2 fatty acyl (> C16) such as conjugate 1 were sparingly soluble. Conjugates 9a-c,e were almost completely solubilized in water by shaking. However, a large portion of conjugates 9d and 9f in water by shaking exist in micelles with mean diameters ranging 7.0-55.2 nm. The partition coefficients (1-octanol/PBS) of the water-soluble conjugates were about 9-18 times greater than that of ara-C. A single dose (300 mg/kg) of conjugates 9d and 9f produced a significant increase in life span (ILS 206 to > 543%) with 17-67% long-term survivors (> 45 days) in mice bearing ip-implanted L1210 lymphoid leukemia. These results were comparable to those of the previous conjugate 1 and Cytoros (2). In contrast, conjugates 9a-c,e at single doses were less effective (ILS 69-178% with no long-term survivors). However, two (qd, 1, 7) or three (qd 1, 5, 9) divided doses of these conjugates were found to be as effective as a single dose of the previous conjugates. The three divided doses (150 mg/kg per day) of conjugates 9d, 9e, and 9f produced a remarkable antitumor activity in L1210 leukemic mice (ILS > 350% with > 50% long-term survivors). Because of the convenient formulation and the significant antitumor activities, the water-soluble conjugates 9d, 9e, and 9f warrant further investigation.

Animals↗
PubMed1995

The structure and stability of phospholipid bilayers by atomic force microscopy.

Atomic force microscopy (AFM) was used to investigate the structure, stability, and defects of the hydrophilic surfaces of Langmuir-Blodgett bilayer films of distearoylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylethanolamine (DPPE) in the solid phase, and dilinoleoylphosphatidylethanolamine (DLPE) in the fluid phase. Their relative resilience to external mechanical stress by the scanning tip and by fluid exchange were also investigated. DPPE monolayers showed parallel ridges at the surface with a period of 0.49 nm, corresponding to the rows of aligned headgroups consistent with the known crystallographic structure. DSPC and DLPE monolayers did not show any periodic order. The solid DSPC and DPPE monolayers were stable to continued rastering by the AFM tip; however, the stability of DLPE monolayers depended on the pH of the aqueous environment. Structural defects in the form of monolayer gaps and holes were observed after fluid exchange, but the defects in DLPE monolayer at pH 11 were stable during consecutive scanning. At pH 9 and below, the defects induced by fluid exchange over DLPE monolayers were more extensive and were deformed easily by consecutive scanning of the AFM tip at a force of 10 nN. The pH dependence of resilience was explained by the increasing bending energy or frustration due to the high spontaneous curvature of DLPE monolayers at low pH. The tangential stress exerted by the AFM tip on the deformable monolayers eventually produced a ripple pattern, which could be described as a periodic buckling known as Shallamach waves.

Biophysical Phenomena↗
PubMed1994

Structure of polymerizable lipid bilayers VII: lateral organization of diacetylenic phosphatidylcholines with short proximal acyl chains.

As an extension of recent results (Rhodes, Xu and Bittman (1992) Biochim. Biophys. Acta 1128, 93; Hui, Xu and Bittman (1992) Langmuir 8, 2724) with a C18 diacetylenic phosphatidylcholine, bilayers of 1,2-bis(pentacosa-4,6-diynoyl)-sn-glycero-3-phosphocholine (C25) were investigated using X-ray diffraction on multibilayers and electron diffraction on Langmuir-Blodgett deposited bilayers. Monolayers of this lipid form solid (gel phase) domains at pi > 14 mN/m. Electron diffraction data indicated that the chain spacing in these domains is 4.25 A and that the chains are tilted at angle of approximately 35 degrees relative to the bilayer plane. Wide angle data from X-ray diffraction experiments indicated a similar spacing and chain tilt. Small angle data showed that the lamellar repeat was 70 A at high humidity and < or = 60 A at low humidity. The bilayer electron density profiles indicated a bilayer structure with no interdigitation. High angle reflections indicate that the principal acyl chain repeat is preserved as a function of hydration but some rearrangement occurs for other reflections. The approximately 10 A reflection corresponding to the headgroup spacing previously observed with C18-diacetylenic phosphatidylcholine bilayers was not observed. The results are interpreted in terms of a packing model and possible limitations or constraints to the polymerization process.

Acetylene↗