Vesicle formation from dimeric surfactants through ion-pairing. Adjustment of polar headgroup separation leads to control over vesicular thermotropic properties

Eight new vesicle-forming dimeric surfactants are synthesized: the polar headgroup separation in such dimeric amphiphiles strongly influences their vesicular thermotropic phase-transition behaviour.

EFFECTS OF METAL-IONS ON THE CONFORMATION OF POLAR HEADGROUP OF SPHINGOMYELIN BILAYER

With the wide application of rare earth in agriculture, medicament, especially the application of Gd-DTPA as nuclear magnetic resonance image reagent in clinical practice([1]), the studies on the toxicology in biological body, as well as the study on the use as informative probes instead of divalent calcium ion in biological and biochemical research have attracted intensive concern([2]). Phospholipids bilayers have served as a model of biomembrane in the last two decades. The effects of metal ions on the conformation of polar headgroup of dipalmitoylphosphatidylcholine (DPPC) bilayers have been reported([3]). Sphingomyelin is major component of several biological tissues such as brain and nerve cells and has identical polar headgroup to DPPC. The interaction of metal ions with sphingomyelin bilayer remains nonrevealed. This note presents the results of the study on this aspect.

Effect of Altered Polar Headgroup of Phosphatidylethanolamines on Transbilayer Aminophospholipid Distribution in Sonicated Vesicles

The transbilayer aminophospholipid distributions in small unilamellar vesicles comprising of phosphatidylethanolamine or its analogs (bearing modifications in the polar headgroup) and egg hosphatidylcholine were ascertained using trinitrobenzenesulfonic acid as external membrane probe. These vesicles, containing 10-30 mol% phosphatidylethanolamine or its analogs, were formed by sonication and fractionated by centrifugation. Phosphatidylethanolamine at low concentrations (10 mol%) preferentially localized in the outer monolayer. This preference appeared to be reversed at higher phosphatidylethanolamine concentrations (30 mol%). Unlike this finding, phosphatidylethanolamine bearing ethyl, phenyl and benzyl substituents at the carbon atom adjacent to the amino group distributed mainly in the outer surface irrespective of their concentrations. Similar results were obtained when the phosphate and amino groups were separated by three methylene residues. These observations suggest that the effective polar headgroup volume and/or hydrogen-bonding capacity of phospholipids are the important factors that determine their distribution in small unilamellar vesicles.

Hybrid Qm/Mm Simulation Of The Hydration Phenomena Of Dipalmitoylphosphatidylcholine Headgroup

The polar headgroup of dipalmitoylphosphatidylcholine (DPPC) molecule both in gas phase and aqueous Solution is investigated by the hybrid quantum mechanical/molecular mechanical (QM/MM) method, in which the polar head of DPPC molecule and the bound water molecules are treated with density functional theory (DFT), while the apolar hydrocarbon chain of DPPC molecule is treated with MM method. It is demonstrated that the hybrid QM/MM method is both accurate and efficient to describe the conformations of DPPC headgroup. Folded structures of headgroup are found in gas phase calculations. In this work, both monohydration and polyhydration phenomena are investigated. In monohydration, different water association sites are studied. Both the hydration energy and the quantum properties of DPPC and water molecules are calculated at the DFT level of theory after geometry optimization. The binding force of monohydration is estimated by using the scan method. In polyhydration, more extended conformations are found and hydration energies in different polyhydration styles are estimated. (C) 2008 Elsevier Inc. All rights reserved.

Synthesis, redox and electrochemical properties of new anthraquinone-attached micelle- and vesicle-forming cationic amphiphiles

Three new cationic amphiphiles bearing anthraquinone moieties at the polar headgroup region were synthesized, The single-chain amphiphile, N,N-dimethyl-N-octadecyl-N-(9,10-dihydro dioxoanthracen-2-ylmethyl)ammonium bromide 1, in the presence of cetyltrimethylammonium bromide upon dispersion in water gave co-micellar aggregates containing covalently attached anthraquinone residues at the polar aqueous interfaces. The other two double-chain amphiphiles, N,N-dioctadecyl-N-methyl-N-(9,10-dihydro-9,10-dioxoanthracen-2-ylmethyl)ammonium bromide 2 and N,N-dimethyl-N-(1,2-bispalmitoyloxypropanyl)-N-(9,10-dihydro-9,10-dioxanthracen-2-ylmethyl)ammonium bromide 3, however, on dispersion in aqueous media produced vesicular aggregates. The critical temperatures for the gel to liquid-crystalline-like phase transition processes for the vesicular systems were determined by following temperature-dependent changes in the ratios of keto-enol tautomeric forms of benzoylacetanilide doped within respective. vesicular assemblies. The redox chemistry of the these supramolecular assemblies was also studied by following the time-dependent changes in the ITV-VIS absorption spectroscopy in the presence of exogenous reducing or oxidizing agents, Electrochemical studies using glassy carbon electrodes reveal that redox-active amphiphiles adsorb on to the glassy carbon surfaces to form electroactive deposits when dipped into aqueous suspensions of either of these aggregates irrespective of the micellar or vesicular nature of the dispersions.

How does spacer length of imidazolium gemini surfactants control the fabrication of 2D-Langmuir films of silver-nanoparticles at the air-water interface?

A series of gemini surfactants based on cationic imidazolium ring as polar headgroup, abbreviated as lm-n-lm], 2Br(-) (n = 2, 5, 6 and 12), was synthesized. Their ability to stabilize silver nanoparticles in aqueous media was investigated. The resulting suspensions were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). They exhibit specific morphologies by adopting different supramolecular assemblies in aqueous media depending on the internal packing arrangements and on the number of spacer methylene units -(CH2)(n)-]. Individual colloids were extracted from the aqueous to chloroform layer and spread at the air/water interface to allow the formation of well-defined Langmuir films. By analysis of the surface pressure-area isotherms, the details about the packing behavior and orientation of the imidazolium gemini surfactant capped silver nanoparticles were obtained. Morphological features of the dynamic process of monolayer compression at the air-water interface were elucidated using Brewster angle microscopy (BAM). These monolayers were further transferred on mica sheets by the Langmuir-Blodgett technique at their associated collapse pressure and the morphology of these monolayers was investigated by atomic force microscopy (AFM). The number of spacer methylene units -(CH2)(n)-] of the gemini surfactants exerted critical influence in modulating the characteristics of the resulting Langmuir films. (C) 2014 Elsevier Inc. All rights reserved.

How does spacer length of imidazolium gemini surfactants control the fabrication of 2D-Langmuir films of silver-nanoparticles at the air-water interface?

A series of gemini surfactants based on cationic imidazolium ring as polar headgroup, abbreviated as Im-n-Im], 2Br(-) (n = 2, 5,6 and 12), was synthesized. Their ability to stabilize silver nanoparticles in aqueous media was investigated. The resulting suspensions were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). They exhibit specific morphologies by adopting different supramolecular assemblies in aqueous media depending on the internal packing arrangements and on the number of spacer methylene units -(CH2)(n)-]. Individual colloids were extracted from the aqueous to chloroform layer and spread at the air/water interface to allow the formation of well-defined Langmuir films. By analysis of the surface pressure-area isotherms, the details about the packing behavior and orientation of the imidazolium gemini surfactant capped silver nanoparticles were obtained. Morphological features of the dynamic process of monolayer compression at the air-water interface were elucidated using Brewster angle microscopy (BAM). These monolayers were further transferred on mica sheets by the Langmuir-Blodgett technique at their associated collapse pressure and the morphology of these monolayers was investigated by atomic force microscopy (AFM). The number of spacer methylene units (CH2)(n)-] of the gemini surfactants exerted critical influence in modulating the characteristics of the resulting Langmuir films. (C) 2014 Elsevier Inc. All rights reserved.

Interaction of scopolamine and cholesterol with sphingomyelin bilayers by FT-Raman spectroscopy

The interaction of scopolamine and cholesterol with sphingomyelin bilayers has been investigated by FT-Raman spectroscopy in head-group region (600-1000 cm(-1)), the C-C stretching (1000-1200 cm(-1)), CH2 deformation (1400-1500 cm(-1)) and the C-H stretching (2800-3000 cm(-1)) mode regions. The results indicate that scopolamine and cholesterol do not change the conformation of O-C-C-N+ backbone in the choline group of sphingomyelin bilayers, the polar headgroup is still extending parallel to the bilayer surface and O-C-C-N+ group is still in its gauche conformer. Scopolamine and cholesterol lower the order of the interface, the interchain, CH2 crystal lattices and the lateral chain-chain packing, and increase their fluidity.

2D NMR and FT-Raman spectroscopic studies on the interaction of lanthanide ions and Ln-DTPA with phospholipid bilayers

The interactions of lanthanide ions and the Ln-DTPA (DTPA = diethylenetriaminepentaacetate) complex with di palmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE) bilayers are studied by 2D NOESY and FT-Raman spectroscopy. Proton NMR spectroscopic results show that lanthanide ions combine with phosphate groups in the polar region of the outer layer of DPPC liposomes, leading to the separation in chemical shift of the proton signal of N(CH3)(3) The conformational change of the O-C-C-N+ backbone from the gauche conformer to the trans one is not found; i.e., the orientation of the polar headgroup is still parallel to the surface of the bilayers. The Ln-DTPA complex at low concentration in a pH 7.4 solution localizes far away from bilayers and thereby has little effect on the structure of bilayers. The FT-Raman spectroscopic results indicate that lanthanide ions affect strongly the fluidity of acyl chains of DPPE bilayers while the Ln-DTPA complex affects it slightly.

NMR and FT-Raman studies on the interaction of lanthanide ions with sphingomyelin bilayers

The interactions of lanthanide ions with sphingomyelin bilayers have been studied by using 2D NOESY spectroscopy and FT-Raman spectroscopy methods. The results indicate that lanthanide ions, as well as divalent calcium, combine mainly to the phosphate group in the polar headgroup and do not change the conformation of O-C-C-N+ backbone in the choline group of sphingomyelin bilayers. The polar headgroup is still extending parallel to the bilayer surface and O-C-C-N+ group is still in its gauche conformer.

A NMR-STUDY OF THE INTERACTION OF SILICA WITH DIPALMITOYLPHOSPHATIDYLCHOLINE LIPOSOMES

The interaction of silica with dipalmitoylphosphatidylcholine (DPPC) liposomes has been studied by detecting H-1 and 2D NOESY NMR spectra and measuring proton spin-lattice relaxation time (T-1). The antagonistic effect of aluminium citrate on silica has also been studied by measuring the proton T-1 values, The results show that silica particles mainly bind to the phosphate moiety of the polar headgroup of DPPC bilayers through hydrogen bonds between Si-OH and O-P groups, but they have no significant effect on the conformation of the choline group of the polar headgroup, The addition of silica particles decreases the mobilities of the hydrocarbon chains slightly, Proton T-1 data also indicate that aluminium citrate reduces the effect of silica, A possible mechanism for the toxicity of silica and the antagonistic effect of aluminium titrate on silica is suggested. (C) 1995 Academic Press Inc.

CHARACTERIZATION OF LYOPHILIZED LIPOSOMES PRODUCED WITH NON-PURIFIED SOY LECITHIN: A CASE STUDY OF CASEIN HYDROLYSATE MICROENCAPSULATION

A commercial casein hydrolysate was microencapsulated in liposomes produced with non-purified soy lecithin, cryoprotected with two different disaccharides and lyophilized. The encapsulation efficiency of casein hydrolysate ranged from 30 to 40%. The powders were analyzed by differential scanning calorimetry (DSC), scanning electron micrography (SEM), infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). DSC data revealed the presence of an exothermal transition in empty lyophilized liposomes, which was ascribed to the presence of a quasicrystalline lamellar phase (intermediary characteristics between the L-beta and L-c phases). The addition of peptides to the liposomal system caused the disappearance of this exothermic phenomenon, as they were located in the polar headgroup portion of the bilayer, causing disorder and preventing the formation of the quasicrystalline phase. Infrared data indicated the presence of the peptides in the lyophilized formulations and showed that the cryoprotectants interacted effectively with the polar heads of phospholipids in the bilayer.

Molecular Dynamics Investigations of PRODAN in a DLPC Bilayer

Molecular dynamics computer simulations have been performed to identify preferred positions of the fluorescent probe PRODAN in a fully hydrated DLPC bilayer in the fluid phase. In addition to the intramolecular charge-transfer first vertical excited state, we considered different charge distributions for the electronic ground state of the PRODAN molecule by distinct atomic charge models corresponding to the probe molecule in vacuum as well as polarized in a weak and a strong dielectric solvent (cyclohexane and water). Independent on the charge distribution model of PRODAN, we observed a preferential orientation of this molecule in the bilayer with the dimethylamino group pointing toward the membrane's center and the carbonyl oxygen toward the membrane's interface. However, changing the charge distribution model of PRODAN, independent of its initial position in the equilibrated DLPC membrane, we observed different preferential positions. For the ground state representation without polarization and the in-cyclohexane polarization, the probe maintains its position close to the membrane's center. Considering the in-water polarization model, the probe approaches more of the polar headgroup region of the bilayer, with a strong structural correlation with the choline group, exposing its oxygen atom to water molecules. PRODAN's representation of the first vertical excited state with the in-water polarization also approaches the polar region of the membrane with the oxygen atom exposed to the bilayer's hydration shell. However, this model presents a stronger structural correlation with the phosphate groups than the ground state. Therefore, we conclude that the orientation of the PRODAN molecule inside the DLPC membrane is well-defined, but its position is very sensitive to the effect of the medium polarization included here by different models for the atomic charge distribution of the probe.

Characterization of lyophilized liposomes produced with non-purified soy lecithin: a case study of casein hydrolysate microencapsulation

A commercial casein hydrolysate was microencapsulated in liposomes produced with non-purified soy lecithin, cryoprotected with two different disaccharides and lyophilized. The encapsulation efficiency of casein hydrolysate ranged from 30 to 40%. The powders were analyzed by differential scanning calorimetry (DSC), scanning electron micrography (SEM), infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). DSC data revealed the presence of an exothermal transition in empty lyophilized liposomes, which was ascribed to the presence of a quasicrystalline lamellar phase (intermediary characteristics between the Lβ and Lc phases). The addition of peptides to the liposomal system caused the disappearance of this exothermic phenomenon, as they were located in the polar headgroup portion of the bilayer, causing disorder and preventing the formation of the quasicrystalline phase. Infrared data indicated the presence of the peptides in the lyophilized formulations and showed that the cryoprotectants interacted effectively with the polar heads of phospholipids in the bilayer.

Oligonucleotide Adsorption Affects Phase Transition but Not Interdigitation of diC14-Amidine Bilayers

Oligonucleotides have been extensively used in basic research of gene expression and function, vaccine design, and allergy and cancer therapy. Several oligonucleotide-based formulations have reached the clinical trial phase and one is already on the market. All these applications, however, are dependent on suitable carriers that protect oligonucleotides against degradation and improve their capture by target cells. The cationic lipid diC14-amidine efficiently delivers nucleic acids to mammalian cells. It was recently shown that diC14-amidine bilayers present an interdigitated phase which strongly correlates with a potent fusogenic activity at low temperatures. Interdigitated phases correspond to very ordered gel phases where the two bilayer leaflets are merged; they usually result from perturbations at the interfacial region such as modifications of the polar headgroup area or dehydration of the bilayer. Interdigitation has been described for asymmetric lipids or mixed-chain lipids of different chain lengths and for lipids with large effective headgroup sizes. It has also been described for symmetric lipids under pressure modifications or in the presence of alcohol, glycerol, acetonitrile, polymyxin B, or ions like thiocyanate. Surprisingly, the role of polyelectrolytes on membrane interdigitation has been only poorly investigated. In the present work, we use dynamic light scattering (DLS), differential scanning calorimetry (DSC), and electron spin resonance (ESR) to explore the effect of a small single-stranded oligonucleotide (ODN) polyelectrolyte on the structure and colloid stability of interdigitated diC14-amidine membranes.