Quiescent bilayers at the mica–water interface

Speranza, Francesca; Pilkington, Georgia A.; Dane, Thomas G.; Cresswell, Philip T.; Li, Peixun; Jacobs, Robert M.; Arnold, Thomas; Bouchenoire, Laurence; Thomas, Robert K.; Briscoe, Wuge H.

doi:10.1039/c3sm50336d

Cited by 48 publications

(78 citation statements)

References 73 publications

(139 reference statements)

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“…Indeed, it has been observed that the values of onset and end of transition from gel L b 0 to liquid disordered L a phase for mica supported DPPC bilayers shifted to slightly lower temperatures in effect of the force exerted by the AFM tip [12]. It has also been observed that aggregate structures of cationic surfactants on mica surfaces reported by AFM imaging are inconsistent with XRR data for the same systems [40], and this was suggested to be due to the perturbing effect of the tapping AFM tip. Based on these considerations we propose that the XRR data reflects the unperturbed bilayer structure, whereas the AFM images report structures that are affected by interactions with the tip, which in our case lowers the gel to liquid disordered transition temperature.…”

Section: Afm Imagingmentioning

confidence: 81%

The effect of temperature on supported dipalmitoylphosphatidylcholine (DPPC) bilayers: Structure and lubrication performance

Wang

Zander²,

Liu

et al. 2015

Journal of Colloid and Interface Science

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Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and glycoproteins, are the biolubricants that sustain low friction between cartilage surfaces bathed in synovial fluid. In this work we have investigated how the friction force and load bearing capacity of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers on silica surfaces are affected by temperature, covering the temperature range 25-52°C. Friction forces have been determined utilizing the AFM colloidal probe technique, which showed that DPPC bilayers are able to provide low friction forces over the whole temperature interval. However, the load bearing capacity is improved at higher temperatures. We interpret this finding as being a consequence of lower rigidity and higher self-healing capacity of the DPPC bilayer in the liquid disordered state compared to the gel state. The corresponding structure of solid supported DPPC bilayers at the silica-liquid interface has been followed using X-ray reflectivity measurements, which suggests that the DPPC bilayer is in the gel phase at 25°C and 39°C and in the liquid disordered state at 55°C. Well-defined bilayer structures were observed for both phases. The deposited DPPC bilayers were also imaged using AFM PeakForce Tapping mode, and these measurements indicated a less homogeneous layer at temperatures below 37°C.

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Section: Afm Imagingmentioning

confidence: 81%

The effect of temperature on supported dipalmitoylphosphatidylcholine (DPPC) bilayers: Structure and lubrication performance

Wang

Zander²,

Liu

et al. 2015

Journal of Colloid and Interface Science

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“…Moreover, their radius values are comparable to those obtained from experimental data, 47 and to the expected maximum-extension value for the CTA + ion (ca. 2.30 nm), 20 even when different counterions were employed (i.e., Cl − and Br − ). Despite the suitability of the data, a match between the theoretical and experimental values of the micellar radius cannot be used as the sole criterion to choose the best theoretical model.…”

Section: The Micellar Radius and Counterion Dissociation Degreementioning

confidence: 99%

“…19 Indeed, under the previously mentioned conditions, l max plus the length of the polar group is approximately equal to the radius of the spherical micelles. 20 Particularly, we are interested in studying the surfactant cetyltrimethylammonium bromide, [CH 3 (CH 2 21 has applications in DNA extraction, and is widely used in the synthesis of metallic nanoparticles as a stabilizer and growth-driving agent of nanoparticles. 22,23 Its 1 st and 2 nd CMCs in water are 0.92 mM 24 and 0.27 M, 25 respectively, and its Krafft temperature is 298 K. 26 As expected, the counterions (bromide) are located near the external positively charged border of the CTA + aggregates; however, it is important to mention that many assembly properties, such as the morphology, size, charge, and intra-micellar interactions, depend on the nature of the counterion.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations of Cetyltrimethylammonium Bromide (CTAB) Micelles and their Interactions with a Gold Surface in Aqueous Solution

Silva¹,

Dias²,

Hora³

et al. 2017

J. Braz. Chem. Soc.

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Surfactants are molecular structures with remarkable physicochemical properties and applications. Most of their characteristics are due to their ability to promote aggregation and interactions with different interfaces. The scarcity of theoretical studies dedicated to evaluating the forces involved in these interactions prompted us to propose other models capable of reproducing the experimental data in better ways. We carried out molecular dynamics (MD) simulations to obtain a model for cetyltrimethylammonium bromide (CTAB), selected from gromos54a7 force field parameters, that better describes most of its behaviors in aqueous solution (micellar structure, counterion dissociation, etc.) and its adsorption pattern on a gold surface. The parameters adopted for one of the models were able to mimic several characteristics suggested by experimental measurements of the CTAB micelles, as well their adsorption pattern on a gold surface. Indeed, this model was able to obtain quasi-spherical micelles, as well as a pattern of adjacent cylindrical micelles with alkyl chain interactions on a gold surface.Keywords: molecular dynamics, micelles, interface interaction, cetyltrimethylammonium bromide, gold IntroductionSurfactants are a class of compounds containing a polar group, charged or neutral, attached to a long hydrophobic tail.1,2 These are remarkably versatile compounds with a broad variety of important applications in the pharmaceutical, medical, and food industries and for nanomaterial synthesis.3,4 Above a certain temperature in solution (the Krafft temperature), surfactants tend to aggregate to minimize unfavorable interactions between the surfactants and the surrounding environment. 5 The minimum concentration required for surfactant aggregation is defined as the critical micellar concentration (CMC), and most of the characteristics of these aggregates are controlled by factors such as the solvent type, chemical structure of the surfactant, and solution conditions (e.g., concentration, temperature, presence of additives, and ionic strength). 6Variations of these factors yield aggregates with different morphologies such as spherical or ellipsoidal micelles, cylindrical or thread-like micelles, disk-like micelle, membranes and vesicles.7 These self-assembled structures have been characterized by a number of techniques, such as dynamic light scattering (DLS), 8 nuclear magnetic resonance (NMR), 9,10 fluorescence spectroscopy, 11 quasielastic neutron scattering (QENS), 12,13 small-angle X-ray scattering (SAXS), 14,15 and small-angle neutron scattering (SANS). 16,17 Computational simulations have also been employed to explore the structures and dynamical behaviors of micelles for different surfactants. 18Considering that no holes exist within a micelle, its radius is estimated as the maximum extension of a hydrocarbon chain and can be evaluated by using the following equation:where l max is the maximum length in nm and n C is the number of carbon atoms in the chain. 19 Indeed, under the previously mentioned conditions, ...

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“…The incident angle q i was varied in the range 0.06-2 for each of the measurements, corresponding to a momentum transfer Q ¼ 4p sin q i /l range of 0.011-0.345Å À1 . The surface scattering data were collected by X-ray reectivity (XRR), [19][20][21]24,25 using an avalanche photodiode detector in the specular reection plane, but at reection angles q f with a small offset Dq ¼ 0.06 (q f ¼ q i AE Dq) to the incident angle (q i ) to minimise the contribution from the silicon substrate. PM samples on solid silicon substrates were mounted inside a small chamber enclosed with Kapton lms, which allowed a constant ow of helium (He) during the measurements to reduce background scattering and sample damage.…”

Section: Materials Sample Preparation and Experimental Methodsmentioning

confidence: 99%

Insitu X-ray reflectivity studies of molecular and molecular-cluster intercalation within purple membrane films

et al. 2014

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It has been recently demonstrated that molecular and molecular cluster guest species can intercalate within lamellar stacks of purple membrane (PM), and be subsequently dried to produce functional bioinorganic nanocomposite films. However, the mechanism for the intercalation process remains to be fully understood. Here we employ surface X-ray scattering to study the intercalation of aminopropyl silicic acid (APS) or aminopropyl-functionalised magnesium phyllosilicate (AMP) molecular clusters into PM films. The composite films are prepared under aqueous conditions by guest infiltration into preformed PM films, or by co-assembly from an aqueous dispersion of PM sheets and guest molecules/clusters.Our results show that addition of an aqueous solution of guest molecules to a dried preformed PM film results in loss of the lamellar phase, and that subsequent air-drying induces re-stacking of the lipid/ protein membrane sheets along with retention of a 2-3 nm hydration layer within the inter-lamellar spaces. We propose that this hydration layer is necessary for the intercalation of APS molecules or AMP oligomers into the PM film, and their subsequent condensation and retention as nano-thin inorganic lamellae within the composite mesostructure after drying. Our results indicate that the intercalated nanocomposites prepared from preformed PM films have a higher degree of ordering than those produced by co-assembly.

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Quiescent bilayers at the mica–water interface

Cited by 48 publications

References 73 publications

The effect of temperature on supported dipalmitoylphosphatidylcholine (DPPC) bilayers: Structure and lubrication performance

The effect of temperature on supported dipalmitoylphosphatidylcholine (DPPC) bilayers: Structure and lubrication performance

Molecular Dynamics Simulations of Cetyltrimethylammonium Bromide (CTAB) Micelles and their Interactions with a Gold Surface in Aqueous Solution

Insitu X-ray reflectivity studies of molecular and molecular-cluster intercalation within purple membrane films

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