Adsorpton at the liquid surface studied by means of specular reflection of neutrons

9915sites of the Ti02 matrix via the cationic vacancies which are always present inside rutile-type compounds. Both processes formally yield to a final VxTi,,,,02 rutile solid solution.In this paper, the resulting drastic modifications observed by ESR have been analyzed and correlated with these two distinct diffusional mechanisms, ESR thus appears to be a convenient and very sensitive tool to study the diffusion processes which take place in mixed oxide catalysts.The same procedure should be extended to various paramagnetic ions (molybdenum Mov for instance) to allow a more complete discussion to be made taking into account the size and the charge of the diffusing probe. Moreover, it should be interesting to study, via the superhyperfine couplings, the diffusion mechanisms occurring inside supports containing magnetically active species, like tin nuclei (I = in Sn02 for instance. These studies have been performed and will be reported elsewhere.Two systems, representing monolayers of n-hexadecyltrimethylammonium chloride at the akwater interface, but with different periodic units, are investigated by equilibrium molecular dynamics simulations. Model potentials from the literature, augmented by tMls from ab initio ~alculations for the head group, are used. No constraints are applied to the interfacbfonning molecules.The system remains stable for the entire duration of the simulation of several hundred picoseconds. The structure of the interface is analyzed in terms of various distance and angle distribution functions and compared to experimental data from X-ray and neutron studies. The distribution of the head groups is in very good agreement with these experimental findings.

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“…6 A results in a coordination number of 7.8. The position of the maxima of these two g functions implies a local spherical micellar curvature.…”

Section: Resultsmentioning

confidence: 99%

Molecular dynamics simulation of a n-hexadecyltrimethylammonium chloride monolayer

Boecker¹,

Schlenkrich²,

Bopp³

et al. 1992

J. Phys. Chem.

107

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“…Specular reflection of neutrons is a relatively new experimental technique for measuring interfacial structure, but it has already been shown to be applicable to both vapor/liquid (3)(4)(5) and liquid/solid interfaces (6). The intensity of neutrons specularly reflected from a Address correspondence to Dr. Bayerl. surface yields information on the scattering-lengthdensity profile normal to the surface, from which the structure at the interface can be deduced.…”

Section: Introductionmentioning

confidence: 99%

Structure of an adsorbed dimyristoylphosphatidylcholine bilayer measured with specular reflection of neutrons

Johnson

Bayerl

McDermott

et al. 1991

Biophysical Journal

478

407

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Using specular reflection of neutrons, we investigate for the first time the structure of a single dimyristoylphosphatidylcholine bilayer adsorbed to a planar quartz surface in an aqueous environment. We demonstrate that the bilayer is strongly adsorbed to the quartz surface and is stable to phase state changes as well as exchange of the bulk aqueous phase. Our results show that the main phase transition is between the L alpha phase and the metastable L beta'* phase, with formation of the P beta' ripple phase prevented by lateral stress on the adsorbed bilayer. By performing contrast variation experiments, we are able to elucidate substantial detail in the interfacial structure. We measure a bilayer thickness of 43.0 +/- 1.5 A in the L alpha phase (T = 31 degrees C) and 46.0 +/- 1.5 A in the L beta'* phase (T = 20 degrees C). The polar head group is 8.0 +/- 1.5 A thick in the L alpha phase. The water layer between the quartz and bilayer is 30 +/- 10 A for the lipid in both the L alpha and L'* phase. Our results agree well with those previously reported from experiments using lipid vesicles and monolayers, thus establishing the feasibility of our experimental methods.

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“…The neutron scattering length densities of hydrogen and deuterium are very different (−3.7409 × 10 −13 cm vs 6.674 × 10 −13 cm), allowing greatly enhanced contrast by deuterating certain components of the system studied. Because of these advantages neutron reflectivity has been used to study, in situ , adsorption of synthetic polymers and surfactants onto solid−liquid interfaces (Lee et al, 1991; Bradley et al, 1988; Satija et al, 1990). Recently this method has been successfully applied (Fragneto et al, 1995) to study the adsorption of β‐casein and, by our group, to study the adsorption of human serum albumin (Liebmann‐Vinson et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

Neutron and X-ray Reflectivity Studies of Human Serum Albumin Adsorption onto Functionalized Surfaces of Self-Assembled Monolayers

et al. 1997

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Neutron and X-ray reflectivity (NR and XR) have been widely used for the investigation of the structure of thin organic films. Here we demonstrate how these sensitive techniques may be applied to the study of protein adsorption to well-characterized self-assembled monolayers (SAMs) with different chemical functionalities. NR can be used for in situ study, while XR provides complementary information on the initial surfaces and dried layers measured in air after protein has been adsorbed. In situ measurements of adsorption of human serum albumin onto a hydrophilic NH2-terminated monolayer clearly show the presence of a thin layer of adsorbed protein next to the SAM. Adsorption of albumin onto a hydrophobic, deuterated, CD3-terminated SAM causes even bigger changes in the NR. Upon replacing the protein solution with protein-free buffer solution, the reflectivities from both kinds of monolayers do not change, demonstrating that the albumin adsorption is irreversible after several hours of contact with the protein solution. X-ray reflectivity measurements of dried substrates performed ex situ in air provide a lower bound estimate of the amount of protein which must be at the interface in situ. This combination of techniques provides a uniquely sensitive approach for studying changes that occur upon protein adsorption at an interface.

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Adsorpton at the liquid surface studied by means of specular reflection of neutrons

Cited by 41 publications

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Molecular dynamics simulation of a n-hexadecyltrimethylammonium chloride monolayer

Molecular dynamics simulation of a n-hexadecyltrimethylammonium chloride monolayer

Structure of an adsorbed dimyristoylphosphatidylcholine bilayer measured with specular reflection of neutrons

Neutron and X-ray Reflectivity Studies of Human Serum Albumin Adsorption onto Functionalized Surfaces of Self-Assembled Monolayers

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