Search results for "bilayer"
showing 10 items of 391 documents
Ionic iridium complex and conjugated polymer used to solution-process a bilayer white light-emitting diode.
2013
Bilayer white light-emitting devices are prepared from solution, using an ionic orange phosphorescent organometallic complex and a neutral fluorescent conjugated polymer. Because of the very different polarity of the two components, they dissolve in orthogonal solvents, allowing for the direct deposition of the blue emitter on top of the orange emitter without the need of cross-linking or special coating methodology. Fine tuning of the layer thickness of both light-emitting layers allows for the color tuning of different types of white light.
The dynamic orientation of membrane-bound peptides: bridging simulations and experiments.
2007
AbstractThe structural organization in a peptide/membrane supramolecular complex is best described by knowledge of the peptide orientation plus its time-dependent and spatial fluctuations. The static orientation, defined by the peptide tilt and a rotation about its molecular axis, is accessible through a number of spectroscopic methods. However, peptide dynamics, although relevant to understand the functionality of these systems, remains largely unexplored. Here, we describe the orientation and dynamics of Trp-flanked and Lys-flanked hydrophobic peptides in a lipid bilayer from molecular dynamics simulations. A novel view is revealed, where collective nontrivial distributions of time-evolvi…
Self-Assembling of Peptide/Membrane Complexes by Atomistic Molecular Dynamics Simulations
2007
Abstract Model biological membranes consisting of peptide/lipid-bilayer complexes can nowadays be studied by classical molecular dynamics (MD) simulations at atomic detail. In most cases, the simulation starts with an assumed state of a peptide in a preformed bilayer, from which equilibrium configurations are difficult to obtain due to a relatively slow molecular diffusion. As an alternative, we propose an extension of reported work on the self-organization of unordered lipids into bilayers, consisting of including a peptide molecule in the initial random configuration to obtain a membrane-bound peptide simultaneous to the formation of the lipid bilayer. This strategy takes advantage of the…
Calculation of the Phase Behavior of Lipids
1998
The self-assembly of monoacyl lipids in solution is studied employing a model in which the lipid's hydrocarbon tail is described within the Rotational Isomeric State framework and is attached to a simple hydrophilic head. Mean-field theory is employed, and the necessary partition function of a single lipid is obtained via a partial enumeration over a large sample of molecular conformations. The influence of the lipid architecture on the transition between the lamellar and inverted-hexagonal phases is calculated, and qualitative agreement with experiment is found.
Polymer-induced shape changes and capping in giant liposomes
1995
We studied the coupling of a polymeric amphiphile undergoing a transition from an expanded to a collapsed state of the hydrophilic polymer chain upon heating above 29°C with free and solid supported lipid bilayers. Lateral diffusion measurements and studies of vesicle shape-changes confirmed previous calorimetric studies, suggesting that the amphiphile remains incorporated in the giant vesicles and the supported bilayer during the transition. The two-dimensional hydrodynamic radii of the amphiphile in the expanded and collapsed state was measured by making use of the strong quadratic dependence of the diffusion coefficient on the radius of the diffusant (D ∞ r−2) due to the frictional coupl…
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…
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…
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…
The amphipathic peptide mellitin as a tool to study the membrane-dependent activation of tissue transglutaminase
2001
The role of membrane phospholipids on the cross-linking activity of guinea pig liver (tissue) transglutaminase has been investigated using the amphipathic model peptide melittin as glutaminyl substrate and the primary amine monodansylcadaverine as extrinsic amine donor. A marked increase of transglutaminase catalytic activity was observedin vitro assays in the presence of neutral membrane phospholipids. In contrast, activation was abolished in the presence of membranes containing pure anionic lipids. Enzyme activation could be ascribed to a direct binding of the lipid to the protein as demonstrated in enzymatic assays using a non membrane-interacting peptide (Cbz-Gln-Gly). The data obtained…