Biomedical subjects

P Linse

Publications and source records attributed to P Linse.

6 recordsLinked to original sources

PubMed2005

Polyion adsorption onto catanionic surfaces. A Monte Carlo study.

The adsorption of a single and negatively charged polyion with varying flexibility onto a surface carrying both negative and positive charges representing a charged membrane surface has been investigated by using a simple model employing Monte Carlo simulations. The polyion was represented by a sequence of negatively charged hard spheres connected with harmonic bonds. The charged surface groups were also represented by charged hard spheres, and they were positioned on a hard surface slightly protruding into the solution. The surface charges were either frozen in a liquidlike structure or laterally mobile. With a large excess of positive surface charges, the classical picture of a strongly adsorbed polyion with an extended and flat configuration emerged. However, adsorption also appeared at a net neutral surface or at a weakly negatively charged surface, and at these conditions the adsorption was stronger with a flexible polyion as compared to a semiflexible one, two features not appearing in simpler models containing homogeneously charged surfaces. The presence of charged surface patches (frozen surface charges) and the ability of polarization of the surface charges (mobile surface charges) are the main reasons for the enhanced adsorption. The stronger adsorption with the flexible chain is caused by its greater ability to spatially correlate with the surface charges.

Adsorption↗

PubMed2005

Polymer distribution in connected spherical domains.

The distribution of neutral and charged polymers with different flexibilities between two spheres of varying volume connected by a short and narrow cylinder has been investigated by Monte Carlo simulations. The uncharged chain displayed mostly a single-sphere occupancy due to the high conformational entropy penalty of crossing the cylindrical domain, whereas for the charged polymer a double-sphere occupancy was obtained, except for very different spherical volumes. The origin of this different occupancy behavior stems from the counterion entropy. At increasing stiffness, a stronger preference for double-sphere occupancy was predicted.

Journal Article↗

PubMed2003

Phase behavior and structure of an ABC triblock copolymer dissolved in selective solvent.

A mean-field lattice theory is applied to predict the self-assembly into ordered structures of an ABC triblock copolymer in selective solvent. More specifically, the composition-temperature phase diagram has been constructed for the system (C)14(PO)12(EO)17/water, where C stands for methylene, PO for propylene oxide and EO for ethylene oxide. The model predicts thermotropic phase transitions between the ordered hexagonal, lamellar, reverse hexagonal, and reverse cubic phases, as well as the disordered phase. The thermotropic behavior is a result of the temperature dependence of water interaction with EO- and PO-segments. The lyotropic effect (caused by changing the solvent concentration) on the formation of different structures has been found weak. The structure in the ordered phases is described by analyzing the species volume fraction profiles and the end segment and junction distributions. A "triple-layer" structure has been found for each of the ordered phases, with each layer rich in C-, PO-, and EO-segments, respectively. The blocks forming the layers are not stretched. The dependence of the domain spacing on polymer volume fraction and temperature is also considered.

Journal Article↗

PubMed2002

Swelling of cross-linked polyelectrolyte gels.

A model of a cross-linked polyelectrolyte gel has been examined using Monte Carlo simulations. The simple model contained a charged defect-free network represented by linked charged beads and explicit counterions. Pressure-density relations for the polyelectrolyte gel, a corresponding non-ionic polymer gel, and several partly or fully degraded gels have been determined. The polyelectrolyte gel displayed a very large swelling capacity, in agreement with experiments. The swelling mechanism and chain properties are discussed and foundations of current theories on gel swelling are examined.

Journal Article↗

PubMed2001

Effective macroion-macroion potentials in asymmetric electrolytes.

Effective macroion-macroion potentials in solutions of macroions carrying 60 elementary charges and either monovalent or divalent counterions have been calculated at different concentrations by means of Monte Carlo simulations with a consequent inversion of radial distribution functions according to Lyubartsev and Laaksonen [Phys. Rev. E 52, 3730 (1995)]. With monovalent counterions, the effective potentials are essentially of a Yukawa type, whereas with divalent ones, an attractive region appears at short separation. A charge renormalization scheme invoking the cell model and the assumption of a Yukawa-type potential works favorably only in the case of monovalent counterions.

Biophysical Phenomena↗

PubMed1996

Effects of fused tryptophan rich peptides to a recombinant protein. A domain on the partitioning in polyethylene glycol-dextran and Ucon-dextran aqueous two-phase systems.

Genetic engineering has been used to construct fusion proteins with tryptophan containing peptides. The peptides and the fusion proteins have been partitioned in aqueous two-phase systems of poly(ethylene glycol) (PEG)-dextran and Ucon-dextran. The studied model protein was ZZT0, where Z is an engineered domain of domain B of staphylococcal protein A. The specially designed hydrophobic peptides, Ala-Trp-Trp-Pro (T1) and (Ala-Trp-Trp-Pro)2 (T2), have been inserted into ZZT0, to give the peptide-protein fusions ZZT1 and ZZT2. In the experimental studies it was found that T1 and T2 preferred the PEG phase and even more the Ucon phase over the dextran phase. For T2 the partitioning was more one sided than for T1. For the fusion proteins, ZZT1 and ZZT2, the partitioning was enhanced into the PEG or Ucon rich phase as compared to ZZT0. The effects were lower than expected from independent contributions to the partition coefficient from the protein and the peptides. A heterogeneous lattice model was used to calculate theoretical peptide and protein partition coefficients. The calculations could reproduce the qualitative features of the experimental data. The model results suggest that a part of these experimentally observed effects is due to a depletion zone, i.e. a zone of reduced polymer concentration around the protein. The experimental results indicate a further reduction of the partition coefficient, beyond that predicted by the lattice calculations. A possible folding of the inserted peptide is discussed as a plausible mechanism for this further reduction in the partition coefficient.

Dextrans↗