Search results for "Actant"

Structure, stability, and fragmentation of sodium bis(2-ethylhexyl)sulfosuccinate negatively charged aggregates in vacuo by MD simulations.

2014

Negatively charged supramolecular aggregates formed in vacuo by n bis(2-ethylhexyl)sulfosuccinate (AOT(-)) anions and n + n(c) sodium counterions (i.e., [AOT(n) Na(n+nc)](nc)) have been investigated by molecular dynamics (MD) simulations for n = 1 to 20 and n(c) = -1 to -5. By comparing the maximum excess charge values of negatively and positively charged AOTNa aggregates, it is found that the charge storage capability is higher for the latter systems, the difference decreasing as the aggregation number increases. Statistical analysis of physical properties like gyration radii and moment of inertia tensors of aggregates provides detailed information on their structural properties. Even for …

Solubilisation of Chlorinated oils in triblock copolymers-surfactant mixed aggregates

2006

Reversed-phase liquid chromatography with mixed micellar mobile phases of Brij-35 and sodium dodecyl sulphate: a method for the analysis of basic com…

2015

Micellar liquid chromatography (MLC) is a reversed-phase liquid chromatographic (RPLC) mode, which uses a surfactant as a modifier, with significant changes in retention and selectivity with regard to the classical RPLC mode that employs mixtures of water and organic solvent. The anionic sodium dodecyl sulphate (SDS) is the most usual surfactant in MLC, but it also requires the addition of an organic solvent to decrease the retention times and increase the efficiency. In particular, positively charged basic compounds are strongly retained by the stationary phase modified by adsorption of SDS monomers and require the addition of a strong solvent, such as propanol or pentanol. The non-ionic s…

Surfactant self-assembly in the gas phase: Bis(2-ethylhexyl)sulfosuccinate- alkaline metal ion aggregates

2008

Molecular dynamics (MD) simulations were conducted for systems in vacuo consisting of n AOT anions (bis(2-ethylhexyl)sulfosuccinate ions) and n 1 or n Na+ ions up to n = 20. For n = 15, positively charged systems with Li+, K+, and Cs+ cations were also considered. All systems were observed to form reverse micelle-like aggregates whose centre is occupied by cations and polar heads in a very compact solid-like way, while globally the aggregate has the form of an elongated and rather flat ellipsoid. Various types of statistical analyses were carried out on the systems to enlighten structural and dynamical properties including gyration radius, atomic pair correlation functions, atomic B-factor …

Entrapment of amino acids in gas phase surfactant assemblies: The case of tryptophan confined in positively charged (1R,2S)-dodecyl (2-hydroxy-1-meth…

2017

The ability of positively charged aggregates of the surfactant (1R,2S)‐dodecyl (2‐hydroxy‐1‐methyl‐2‐phenylethyl))dimethylammonium bromide (DMEB) to incorporate D-tryptophan or L-tryptophan in the gas phase has been investigated by electrospray ion mobility mass spectrometry (ESI‐IM‐MS). Strongly impacted by the pH of the electrosprayed solutions, both protonated (T+) and deprotonated (T-) tryptophan are effectively included into the aggregates, whereas, tryptophan in zwitterionic (T0) form is practically absent in singly charged DMEB aggregates but can be found in multiply charged ones. The ability to incorporate tryptophan increases with the aggregation number and charge state of aggr…

ABC A-subclass proteins: Gatekeepers of cellular phospho- and sphingolipid transport

2007

During the past years, available evidence suggests that members of a novel family of structurally highly related multispan proteins, designated ABC A-subclass transporters, exert critical functions in the control of cellular lipid transport processes. Loss-of-function scenarios, thus far, have revealed pivotal roles of individual ABC A-transporters in specialized lipid secretory pathways of the cell including HDL biogenesis (ABCA1), lung surfactant production (ABCA3), retinal integrity (ABCA4/ABCR) and skin lipid barrier formation (ABCA12). Although the specific transporter activities of many members of this novel protein family have not yet been established in detail, available evidence in…

Effect of Cholesterol on Electrostatics in Lipid−Protein Films of a Pulmonary Surfactant

2010

We report the changes in the electrical properties of the lipid-protein film of pulmonary surfactant produced by excess cholesterol. Pulmonary surfactant (PS) is a complex lipid-protein mixture that forms a molecular film at the interface of the lung's epithelia. The defined molecular arrangement of the lipids and proteins of the surfactant film gives rise to the locally highly variable electrical surface potential of the interface, which becomes considerably altered in the presence of cholesterol. With frequency modulation Kelvin probe force microscopy (FM-KPFM) and force measurements, complemented by theoretical analysis, we showed that excess cholesterol significantly changes the electri…

Thermodynamic and kinetic properties of water–oil–surfactant mixtures

1998

Abstract We present experimental data on thermodynamic and kinetic properties of the emulsification failure of a droplet-phase microemulsion, and model them by a bending free energy. In contrast to most other models used to describe water–oil–surfactant mixtures no entropic contributions are included in the present description. Still, there is quantitative agreement between theory and measurements, even though there are no free parameters in our model – only experimentally accessible material constants appear.

Dry adsorbed emulsion: 2. Dissolution behaviour of an intricate formulation

2002

The behaviour of a pharmaceutical form, called dry adsorbed emulsion (DAE), containing a sparingly soluble drug (i.e. theophylline) was studied for dissolution drug release kinetic, in relation with DAE structure characterisation. In vitro dissolution testings were performed under different experimental conditions (medium at pH 1.2 and 7.4, medium with or without surfactant addition, different particle sizes, discrete or densified particles). Discrete DAE particles showed an extended release, in comparison with the native drug powder, depending on both drug solubility in the medium and particle size. The relevance of dissolution data was not improved by surfactant addition (0.1% sodium laur…

Effect of self-assembled surfactant structures on ion transport across the liquid|liquid interface

1999

In this paper, the effect of a coadsorbed polyanion–cationic surfactant system on the transport of tetraethylammonium ion across the water|1,2-dichloroethane interface is studied. It is shown that the change in double-layer structure due to the presence of adsorbed or coadsorbed surfactant can explain the experimental observations, thus concluding that no other effects on ion transfer (e.g., steric hindrance) are relevant under these experimental conditions. The implications of these results are discussed. Keywords: ITIES, Ion transfer, Self-assembled monolayers, Surfactants, Double-layer effects