Search results for "layer"

Bistable Hofmann-Type FeII Spin-Crossover Two-Dimensional Polymers of 4-Alkyldisulfanylpyridine for Prospective Grafting of Monolayers on Metallic Su…

2021

Aiming at investigating the suitability of Hofmann-type two-dimensional (2D) coordination polymers {FeII(Lax)2[MII(CN)4]} to be processed as single monolayers and probed as spin crossover (SCO) junctions in spintronic devices, the synthesis and characterization of the MII derivatives (MII = Pd and Pt) with sulfur-rich axial ligands (Lax = 4-methyl- and 4-ethyl-disulfanylpyridine) have been conducted. The thermal dependence of the magnetic and calorimetric properties confirmed the occurrence of strong cooperative SCO behavior in the temperature interval of 100-225 K, featuring hysteresis loops 44 and 32.5 K/21 K wide for PtII-methyl and PtII/PdII-ethyl derivatives, while the PdII-methyl deri…

Consecutive Selective Adsorption of Pentamidine and Phosphate Biomolecules on a Self-Assembled Layer:  Reversible Formation of a Chemically Selective…

1996

In situ ellipsometric film thickness measurements, FT-IR external reflectance spectroscopy, and potentiometric measurements indicated that the amphiphile pentamidine (PAM), a bisbenzamidine, associated by self-assembly with a preformed self-assembled monolayer of a mercaptoalkanoic acid on gold. The structural properties of PAM and the nature of the substrate were ideal for the formation of a densely packed monolayer. This process was fully reversible, as demonstrated by changing the pH of the surrounding medium. Thus, disassembly−reassembly occurred when the pH was cycled between 8.7 and 3. The bilayer structure, featuring a positively charged amidinium surface, was subsequently used for s…

Identification of the membrane penetrating domain of Vibrio cholerae cytolysin as a β-barrel structure

2005

Summary Vibrio cholerae cytolysin (VCC) is an oligomerizing pore-forming toxin that is related to cytolysins of many other Gram-negative organisms. VCC contains six cysteine residues, of which two were found to be present in free sulphydryl form. The positions of two intramolecular disulphide bonds were mapped, and one was shown to be essential for correct folding of protoxin. Mutations were created in which the two free cysteines were deleted, so that single cysteine substitution mutants could be generated for site-specific labelling. Employment of polarity-sensitive fluorophores identified amino acid side-chains that formed part of the pore-forming domain of VCC. The sequence commenced at…

Monolayers of Bolaform Amphiphiles: Influence of Alkyl Chain Length and Counterions

1994

We have prepared self-assembled monolayers of novel cationic bolaform amphiphiles on negatively charged substrates. Most of these amphiphiles form smooth, defect-free monolayers which can be used to reverse the substrate surface charge and thus allow subsequent adsorption of anionic molecules and construction of multilayers. Atomic force microscopy, surface force measurement, and surface plasmon spectroscopy were combined to probe the molecular orientation and ordering, mechanical properties, and surface electrical properties of the monolayers. In addition, the amphiphile aggregation behavior at an air-water interface was studied by surface tension measurement, and lyotropic phase behavior …

Layer-by-layer deposited multilayer assemblies of polyelectrolytes and proteins: from ultrathin films to protein arrays

2008

We have recently introduced a new method of creating ultrathin films of polyelectrolytes based on the electrostatic attraction between opposite charges. Multilayer assemblies are adsorbed in a layer-by-layer fashion from aqueous solutions of the polymers. The total film thickness can easily be adjusted by varying the ionic strength of the solution. Here, we report on the temperature stability and the water content of the multilayer assemblies. Furthermore, we have extended our concept to the incorporation of protein layers into films of synthetic polyelectrolytes. The well established system biotin/streptavidin was used to construct such multilayers, also by biospecific recognition. Adsorpt…

Chain linear dimensions in the surface-enriched layer of polymer mixtures

1992

We calculate the mean-square end-to-end distances and mean-square gyration radii using the bond fluctuation model for a binary polymer blend in the presence of a wall by Monte Carlo simulation. In the bulk, the size of the minority, low-concentration polymer species is compressed compared to the majority one. In the vicinity of the wall, where the minority polymer concentration is enriched due to attraction from the wall, the dimensions of the two types of polymers are approximately equal and are essentially the same as in an athermal polymer melt. Thus, the geometric constraint is more important to the structure of the polymers than the polymer-polymer and polymer-wall interactions.

Semidilute and Concentrated Polymer Solutions near Attractive Walls:  Dynamic Monte Carlo Simulation of Density and Pressure Profiles of a Coarse-Gra…

1997

Using a bead−spring model of flexible polymer chains, we study polymer adsorption from solutions onto attractive planar walls, varying both the strength of the adsorption potential e and the concentration of the solution over a wide range. Treating the case of good solvents, the profiles of density and pressure are computed and it is shown that thermal equilibrium between the adsorbed layer and the bulk solution is obtained. The case of a wall with purely repulsive potential under otherwise identical conditions is treated for comparison. It is shown that for the strongly adsorbing wall there is a pronounced layering, while a layered structure at the repulsive wall occurs only for high conce…

Fatty Acid Aggregates Simulated using Constant pH Molecular Dynamics with a Coarse-Grained Model

2013

Fatty acids are crucial biomolecules, important for lipid metabolism, signaling, models for protocell membranes, soaps, industrial applications, and drug delivery. Oleic acid has complex phase behavior with respect to the protonation state of the carboxylic head group, which depends on the pH of the solution. Oils form at low pHs, vesicles at intermediate pHs, and micelles at high pHs. We use constant pH molecular dynamics with the MARTINI coarse-grained model to investigate oleic acid aggregates at different pH conditions. We determine titration curves for the oleic acid monomers in different aggregates, and observe a shift in the microscopic pKa. In agreement with experimental results, th…

Cover Feature: Towards Atomically Precise Supported Catalysts from Monolayer‐Protected Clusters: The Critical Role of the Support (Chem. Eur. J. 31/2…

2020

Carotenoids and the Assembly of Light-harvesting Complexes

2006

Carotenoids are constitutive components of all light-harvesting complexes in plants and many such complexes in bacteria. In the crystal structures of several light-harvesting complexes, carotenoids are seen to span the lipid bilayer and connect components of the complex on both membrane surfaces and/or to mediate the interaction of transmembrane protein helices. This important stabilizing function suggests that these pigments are also actively involved in the assembly of light-harvesting complexes. Verification of this notion appears too ambitious a goal at present, as the question of how the pigment-protein complexes of the photosynthetic apparatus are assembled is still open. However, inf…