Reversible optical control of monolayers on water through photoswitchable lipids.

We have obtained molecular insights into a monolayer of azobenzene-based photoswitchable lipids self-assembled on water, using the surface sensitive technique vibrational sum-frequency generation spectroscopy in combination with surface pressure measurements. The photolipids can undergo wavelength-dependent, light-triggered cis/trans and trans/cis isomerization, allowing for reversible control of the surface pressure and the molecular ordering of the lipids in the monolayer. If the photoswitchable lipid is embedded in a layer with conventional phospholipids, such as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), we show that the surface pressure and molecular ordering of DPPC can be influenced by switching the azobenzene-based lipid between its two states.

Photochemically induced disturbance of the alkyl chain packing in vesicular membranes.

In previous reports, we presented the synthesis and properties of double-tailed azobenzene-substituted phosphate amphiphiles (Kuiper et al. Synthesis 2003, 695 and Kuiper et al. Langmuir 2004, 20, 1152).

Chain-length and solvent dependent morphological changes in sodium soap fibers.

Sodium soap fibers with varying alkyl chain lengths were studied by cryotransmission electron microscopy and differential scanning calorimetery in water and water-propylene glycol mixtures. The morphology of the lamellar fibers was found to be dependent on the chain length of the alkyl chain and the solvent polarity. Cryoelectron microscopy revealed that short-chain (C10-C14) sodium soaps have the bilayer plane perpendicular to the fiber width, which enables one to see the bilayer striations on the fibers, whereas long-chain (C16-C20) sodium soaps have bilayer planes parallel to the fiber width, and the bilayer striations are not visible.

pH-dependent phase behavior of carbohydrate-based gemini surfactants. The effects of carbohydrate stereochemistry, head group hydrophilicity, and nature of the spacer.

The pH-dependent phase behavior and hydroxide-ion adsorption ability of a series of (reduced) carbohydrate-based gemini surfactants were studied between pH 2 and 12. Static and dynamic light scattering were employed to address transitions in the aggregate morphologies and cryo-electron microscopy was used to provide further evidence for the morphologies present in solution. Changes in aggregate structure as a result of a change in solution pH and an accompanying change in protonation state or a change in molecular structure can be rationalized in terms of the variations in the packing parameter.

pH-dependent phase behavior of carbohydrate-based gemini surfactants. Effect of the length of the hydrophobic spacer.

The phase behavior of a series of carbohydrate-based gemini surfactants with varying spacer lengths was studied using static and dynamic light scattering between pH 2 and 12. Cryo-electron microscopy pictures provide evidence for the different morphologies present in solution. The spacer length of the gemini surfactants was varied from two to 12 methylene units.

Gene delivery by cationic lipid vectors: overcoming cellular barriers.

Non-viral vectors such as cationic lipids are capable of delivering nucleic acids, including genes, siRNA or antisense RNA into cells, thus potentially resulting in their functional expression. These vectors are considered as an attractive alternative for virus-based delivery systems, which may suffer from immunological and mutational hazards. However, the efficiency of cationic-mediated gene delivery, although often sufficient for cell biological purposes, runs seriously short from a therapeutics point of view, as realizing this objective requires a higher level of transfection than attained thus far.

Hydroxide-ion binding to nonionic interfaces in aqueous solution.

The mechanism of hydroxide ion binding to nonionic surfaces is explored by variation of the properties of the water-aggregate interface and by variation of the type of the aggregate.

Lipoplexes formed from sugar-based gemini surfactants undergo a lamellar-to-micellar phase transition at acidic pH. Evidence for a non-inverted membrane-destabilizing hexagonal phase of lipoplexes.

The present study aims at a better understanding of the mechanism of transfection mediated by two sugar-based gemini surfactants GS1 and GS2. Previously, these gemini surfactants have been shown to be efficient gene vectors for transfection both in vitro and in vivo. Here, using Nile Red, a solvatochromic fluorescent probe, we investigated the phase behavior of these gemini surfactants in complexes with plasmid DNA, so-called lipoplexes.

AOT-based microemulsions accelerate the 1,3-cycloaddition of benzonitrile oxide to N-ethylmaleimide.

We studied the 1,3-dipolar cycloaddition of benzonitrile oxide to N-ethylmaleimide in AOT/isooctane/water microemulsions at 25.0 degrees C and found the reaction rate to be roughly 150 and 35 times greater than that in isooctane and pure water, respectively. The accelerating effect of the microemulsion is the combined result of an increase in the local concentrations of the reactants through incorporation into the interface and of the intrinsic rate of the process through electrostatic interactions with the headgroups in the surfactant.

Transfection mediated by pH-sensitive sugar-based gemini surfactants; potential for in vivo gene therapy applications.

In this study, the in vitro and in vivo transfection capacity of novel pH-sensitive sugar-based gemini surfactants was investigated. In an aqueous environment at physiological pH, these compounds form bilayer vesicles, but they undergo a lamellar-to-micellar phase transition in the endosomal pH range as a consequence of an increased protonation state. In the same way, lipoplexes made with these amphiphiles exhibit a lamellar morphology at physiological pH and a non-lamellar phase at acidic pH.

Water in oil microemulsions as reaction media for a Diels-Alder reaction between N-ethylmaleimide and cyclopentadiene.

The Diels-Alder reaction between N-ethylmaleimide and cyclopentadiene in water/AOT/isooctane microemulsions, where AOT denotes sodium bis(2-ethylhexyl)sulfosuccinate, was studied. The rate of the reaction was found to be higher than that obtained in pure isooctane, irrespective of the particular microemulsion composition used. The efficiency of this catalytic action ranged from a factor of 3 at low water contents (viz.

pH-Dependent aggregation properties of mixtures of sugar-based gemini surfactants with phospholipids and single-tailed surfactants.

Sugar-based gemini surfactants (GSs) display rich pH-dependent phase diagrams and are considered to be promising candidates as gene- and drug-delivery vehicles for biomedical applications. Several sugar-based GSs form vesicles around neutral pH. The vesicular dispersions undergo transitions toward wormlike micelles and spherical micelles at acidic pH, whereas flocculation followed by redispersion upon charge reversal is observed at basic pH.

The influence of phenyl and phenoxy modification in the hydrophobic tails of di-n-alkyl phosphate amphiphiles on aggregate morphology.

A series of di-n-alkyl phosphate amphiphiles containing phenyl and phenoxy groups in the hydrophobic tails were synthesised, and their aggregation behaviour was investigated using fluorescence spectroscopy, differential scanning calorimetry, and cryo-electron microscopy. The aggregates displayed a wide variety of aggregate morphologies. The incorporation of a phenyl group into the end or in the middle of the alkyl chain lowered the main phase transition temperature, resulting in closed vesicles only above the phase transition temperature.

Vesicular catalysis of an S(N)2 reaction: toward understanding the influence of glycolipids on reactions proceeding at the interface of biological membranes.

The kinetics of the S(N)2 reaction of a series of aromatic alkylsulfonates with water and bromide ions in membrane mimetic media have been investigated. These media include vesicles formed from only synthetic amphiphiles, vesicles composed only of phospholipids and mixtures of these components. Special focus is placed on the influence of the addition of n-dodecyl-beta-glucoside as a mimic for glycolipids.

Sunfish cationic amphiphiles: toward an adaptative lipoplex morphology.

A detailed physicochemical study is presented on a new class of cationic amphiphiles, Sunfish amphiphiles, recently designed, synthesized, and tested for gene delivery. These materials have two hydrophobic tails, connected to the cationic pyridinium headgroup at the 1- and 4-positions. Two extreme morphologies can be visualized, i.

Activity of water in aqueous systems; a frequently neglected property.

In this critical review, the significance of the term 'activity' is examined in the context of the properties of aqueous solutions. The dependence of the activity of water(l) at ambient pressure and 298.15 K on solute molality is examined for aqueous solutions containing neutral solutes, mixtures of neutral solutes and salts.

Nonbilayer phase of lipoplex-membrane mixture determines endosomal escape of genetic cargo and transfection efficiency.

Cationic lipids are widely used for gene delivery, and inclusion of dioleoylphosphatidylethanolamine (DOPE) as a helper lipid in cationic lipid-DNA formulations often promotes transfection efficacy. To investigate the significance of DOPE's preference to adopt a hexagonal phase in the mechanism of transfection, the properties and transfection efficiencies of SAINT-2/DOPE lipoplexes were compared to those of lipoplexes containing lamellar-phase-forming dipalmitoylphosphatidylethanolamine (DPPE). After interaction with anionic vesicles, to simulate lipoplex-endosomal membrane interaction, SAINT-2/DOPE lipoplexes show a perfect hexagonal phase, whereas SAINT-2/DPPE lipoplexes form a mixed lamellar-hexagonal phase.

H-aggregation of azobenzene-substituted amphiphiles in vesicular membranes.

Photochemical switching has been studied of double-tailed phosphate amphiphiles containing azobenzene units in both tails in aqueous vesicular dispersions and in mixed vesicular systems with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Since the ease of switching depends on the strength of the bilayer packing, particular emphasis has been placed on the occurrence of H-aggregation in the hydrophobic core of the vesicles. UV-vis spectrometry was employed to monitor H-aggregation and showed how this process depends on the ionic strength and on the mode of preparation of the vesicles.

Physisorption of hydroxide ions from aqueous solution to a hydrophobic surface.

We present results from detailed molecular dynamics simulations revealing a counterintuitive spontaneous physical adsorption of hydroxide ions at a water/hydrophobic interface. The driving force for the migration of the hydroxide ions from the aqueous phase is the preferential orientation of the water molecules in the first two water layers away from the hydrophobic surface. This ordering of the water molecules generates an electrical potential gradient that strongly and favorably interacts with the dipole moment of the hydroxide ion.

Kinetics of hydrolysis of 4-methoxyphenyl-2,2-dichloroethanoate in binary water-cosolvent mixtures; the role of solvent activity and solute-solute interactions.

Rate constants are reported for the pH-independent hydrolysis of 4-methoxyphenyl-2,2-dichloroethanoate in aqueous solution as a function of the concentration of added cyanomethane (acetonitrile), polyethylene glycol (PEG 400) and tetrahydrofuran (THF). The concentration of water was varied between ca. 25 and 55.

Polymorphism of pyridinium amphiphiles for gene delivery: influence of ionic strength, helper lipid content, and plasmid DNA complexation.

Two double-tailed pyridinium cationic amphiphiles, differing only in the degree of unsaturation of the alkyl chains, have been selected for a detailed study of their aggregation behavior, under conditions employed for transfection experiments. The transfection efficiencies of the two molecules are remarkably different, especially when combined with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) as helper lipid. The phase behavior of the cationic amphiphile/DOPE mixtures have been studied using (31)P- and (2)H-NMR (on deuterated cationic amphiphiles) as main techniques, to monitor independently the behavior of the two components.

Probing the effect of the amidinium group and the phenyl ring on the thermodynamics of binding of benzamidinium chloride to trypsin.

The effect of the amidinium group and the phenyl ring on the thermodynamics of binding of benzamidinium chloride to the serine proteinase trypsin has been studied using isothermal titration calorimetry. Binding studies with benzylammonium chloride, [small alpha]-methylbenzylammonium chloride and benzamide, compounds structurally related to benzamidinium chloride, showed that hydrogen bonding between the amidinium group and the enzyme is primarily enthalpy-driven. Binding of cyclohexylcarboxamidinium chloride and acetamidinium chloride showed that the hydrophobic binding of the phenyl ring in the S1 pocket is primarily entropy-driven and that a rigid, flat hydrophobic binding site for the inhibitor is favourable.

Lipid-mediated light activation of a mechanosensitive channel of large conductance.

This paper describes the reversible activation of a mechanosensitive channel via a light-sensitive lipid mimic. For these experiments, the mechanosensitive channel of large conductance (MscL) protein from Lactococcus lactis and Escherichia coli was reconstituted in lipid bilayers composed of 80 mol % 1,2-dioleoyl-sn-glycero-3-phosphocholine and 20 mol % di-(5-[[4-(4-butylphenyl)azo]phenoxy]pentyl)phosphate (4-Azo-5P). Light-induced isomerization of the azobenzene moiety of 4-Azo-5P from trans to cis was used to activate MscL.