Search results for "Plastics"
showing 10 items of 2724 documents
Modeling Supramolecular Polymerization: The Role of Steric Effects and Hydrophobic Interactions
2019
We present a combined experimental–simulation study of self-assembly into one-dimensional filaments. Experimentally, we study amphiphilic AuI-metallopeptides in neutral aqueous media. Our model foc...
Molecular Mechanisms Controlling the Self-Assembly Process of Polyelectrolyte Multilayers
1998
The distance dependent interaction between polyelectrolyte-covered mica surfaces in aqueous solution was investigated with the surface forces apparatus. We find the following: (i) The surface charge changes sign, when an oppositely charged polyelectrolyte from a concentrated polyelectrolyte solution is adsorbed. (ii) Tails and loops of the adsorbed polyions dangle into the bulk phase, inducing a small steric force. If polycations and poyanions are adsorbed on top of each other, a strong short range attractive force is seen due to ion-pair formation after crossing a large repulsive electrostatic/steric barrier. (iii) Obviously, after polyelectrolyte adsorption, there are still nonoccupied b…
Local control of antibody binding to hapten-presenting interfaces: Steric and electrostatic interaction
1991
The binding of labeled antibodies to hapten substituted monolayers at the air/water interface has been studied by means of fluorescence microscopy. Haptens with various spacer lengths between the epitope and a hydrocarbon chain, anchoring the molecule to the interface, have been synthesized. With DMPC,a unspecific binding has been shown to predominate over specific binding due to electrostatic interactions. At high surface pressures the bound antibody is detached because of steric interference with the lipid head groups. Due to a reduction of electrostatic interactions, no unspecific binding is observed to monolayers of cholesterol, which carries a small dipole moment. Mixed monolayers of c…
Introducing a 1,1-diphenylethylene analogue for vinylpyridine: anionic copolymerisation of 3-(1-phenylvinyl)pyridine (m-PyPE)
2021
3-(1-Phenylvinyl)pyridine (m-PyPE), prepared by Wittig reaction from the readily available 3-benzoylpyridine, represents a structural analog of 1,1-diphenylethylene (DPE), one phenyl group being replaced by pyridine. The suitability of m-PyPE for the copolymerisation with vinylpyridine is reflected by the 13C NMR shifts of the β-carbon of 2-vinylpyridine (2-VP; 118.32 ppm) and m-PyPE (115.83 ppm, measured in CDCl3), which possess predictive character for carbanionic copolymerisation. In analogy to DPE and its manifold reported derivatives, carbanionic homopolymerisation of m-PyPE was not possible, due to its steric bulk. Copolymers of 2-VP and m-PyPE with varied composition have been synthe…
Macromolecules in ordered media: 4. Poly(2-vinyl pyridine)-liposome association induced by electrostatic interactions
1997
Abstract We have investigated the interaction between vesicles based on dimyristoyl phosphatidic acid (DMPA) and a polymer, such as poly(2-vinyl pyridine) (P2VPy), on the basis of both partition and binding models. The resulting association curves are non monotonous being three regions clearly evidenced. The electrostatic and steric origin of the attractive or repulsive interactions are analyzed as a function of pH, ionic strength and temperature using the fluorescence spectroscopy technique. We emphasize the importance of differentiating the ideal definition of the binding constant from the theoretically evaluated including the activity coefficient, γ, to take into account shifts from the …
Comparison of linear and hyperbranched polyether lipids for liposome shielding by 18F-radiolabeling and positron emission tomography
2018
Multifunctional and highly biocompatible polyether structures play a key role in shielding liposomes from degradation in the bloodstream, providing also multiple functional groups for further attachment of targeting moieties. In this work hyperbranched polyglycerol (hbPG) bearing lipids with long alkyl chain anchor are evaluated with respect to steric stabilization of liposomes. The branched polyether lipids possess a hydrophobic bis(hexadecyl)glycerol membrane anchor for the liposomal membrane. hbPG was chosen as a multifunctional alternative to PEG, enabling the eventual linkage of multiple targeting vectors. Different hbPG lipids (Mn = 2900 and 5200 g mol-1) were examined. A linear bis(h…
On the Adsorption Process in Polymer Brushes: A Monte Carlo Study
1996
The adsorption process of the single polymer chain in a polymer brush of varying surface coverages is studied by means of Monte Carlo simulations of the bond-fluctuation lattice model. Only the end monomers can adsorb at the grafting surface, whereas inner monomers interact repulsively with it. The brush builds up a steric hindrance which forces the penetrating polymer to stretch strongly and which is responsible for small adsorption probabilities at surface coverages close to the overlap density. The final step of the adsorption process is determined by a fluctuation of the end monomer around its average position, which is comparable to the initial step of the desorption process.
Specific interaction of desthiobiotin lipids and water-soluble biotin compounds with streptavidin
1991
As shown for biotin lipids (Ref. 1), the formation of perfect 2-D crystalline streptavidin domains can also be observed in the plane of desthiobiotin lipid monolayers. The binding constant of streptavidin with desthiobiotin (Ka = 5·1013 mol−1) is lower than that with biotin (Ka = 1015 mol−1) (Ref. 2). By adding free biotin into the subphase a competitive replacement and a detaching of the streptavidin domains from the desthiobiotin lipid monolayer takes place. Streptavidin domains built at receptor lipid monolayers are still functional. As could be shown, there are two biotin binding sites at each protein molecule that are fully accessible to biotin (Ref. 1). This can be proven by the inter…
Surface functionalization and surface recognition: Plasmon optical detection of molecular recognition at self assembled monolayers
1991
The synthesis of biotin- functionalized organic mercaptans and their chemisorption on gold surfaces is described. Biotin bound covalently to self assembled monolayers is recognized by streptavidin from aqueous buffer solutions. Spacer length and packing density of the biotin labels on the organic surface determine the docking kinetics. With a flexible and hydrophilic spacer very fast -diffusion controlled-docking is observed. As an alternative method of self assembly the spreading of organic mercaptans on water surfaces is established. Pressure-area diagrams of different functionalized mercaptans and disulfides are shown and their monolayer properties are discussed.
Ligand-receptor interactions directly measured with the surface forces apparatus
1991
Ligand-receptor interactions give rise to very strong bonds due to perfect geometrical fit. Using the Surface Forces Apparatus we have studied the interactions between membrane-bound biotin ligands and streptavidin receptors. We find an unusually strong short-range binding force associated with equally specific molecular rearrangements-both qualitatively and quantitatively unlike anything previously measured.