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At least 1,171 records · Page 65Linked to original sources
PubMed2000

Remarkable proteolytic activity of imidazoles attached to cross-linked polystyrene.

The insoluble resins synthesized by attaching imidazoles to poly(chloromethylstyrene-co-divinylbenzene) effectively hydrolyzed albumin with half-life as short as 20 min at pH 7 and 25 degrees C. Thus, peptide hydrolysis was accomplished with imidazole in an artificial system for the first time. The imidazole-based artificial proteinases manifested optimum activity at pH 7-8. The proteolytic activity of the imidazole-based artificial proteinases exceeded that of previously reported organic artificial proteinases including catalytic antibodies. High proteolytic activity was observed when imidazole was attached to the resin through the C-2 atom instead of the N atom. The catalytic activity was greatly reduced when the content of imidazole was lowered. This indicates catalytic cooperation of at least two proximal imidazole moieties attached to the resin. Possible mechanisms for the effective protein hydrolysis by the proximal imidazoles are presented.

Cross-Linking Reagents↗
PubMed2004

Nanostructuring effect of plasma and solvent treatment on polystyrene.

Plasma treatment of polymer surfaces is used to control the generation of topological surface structures: stripes, starlike morphologies, and pinnacles in the range from 100 nm up to several micrometers. These protrusions arise when the plasma-treated polymer surface is exposed to an organic solvent (liquid or vapor phase). The distribution density and the height of the observed structures on the surface are functions of the power density of the plasma reactor and the exposure time to the plasma, the duration of the development process, the type of the polymer, and its manufacturing. We suggest that the structures are generated by selective swelling of less cross-linked areas within the polymer surface and not by rearrangement or dissolution of polymer chain fragments created by plasma, or by amphiphilic moieties due to oxidation as a consequence of plasma treatment.

Gold↗
PubMed2005

SANS study of the interactions among DNA, a cationic surfactant, and polystyrene latex particles.

The compaction of DNA by a cationic surfactant both in the bulk and adsorbed on the surface of latex particles was followed for the first time by SANS. In the bulk, a decrease in the overall size of the DNA coil in the presence of the cationic surfactant was observed at a negative-to-positive charge ratio far below the phase separation region, at a negative-to-positive charge ratio of 18. Additionally, large surfactant aggregates seem to form within the DNA-surfactant complex. On the other hand, DNA adsorbs onto the surface of latex particles, forming a thick layer, as evidenced by the fitting of the SANS data to a core-shell form factor. Addition of a cationic surfactant to the DNA-coated latex particles at a negative-to-positive charge ratio of 38 induces a slight decrease in the size of the particle layer, where the cationic surfactant is evenly distributed within the adsorbed layer. A further decrease of the negative-to-positive charge ratio to 18 induces a dramatic change in the SANS data that suggests significant compaction of the adsorbed layer and the formation of large surfactant aggregates, similar to those detected in the bulk.

Adsorption↗
PubMed2005

Hybrid particles of polystyrene and carboxymethyl cellulose as substrates for copper ions.

The synthesis of hybrid particles was carried out by emulsion polymerization of styrene in complexes formed by carboxymethyl cellulose (CMC), a polyanion, and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). CMC chains with variable molecular weights and degrees of substitution were tested. The polymerization condition chosen was that corresponding to CMC chains fully saturated with CTAB and to the onset of pure surfactant micelle formation, namely, at the critical aggregation concentration. The hybrid particles were characterized by zeta potential and light scattering measurements. The period of colloidal stability in the ionic strength of 2.0 mol L(-)(1) NaCl was observed visually. Upon increasing the CMC chain length, the particle characteristics remained practically unchanged, but the colloid stability was increased. The increase in the CMC degree of substitution led to particles with more negative zeta potential values. The adsorption of copper ions (Cu(2+)) on the surface of hybrid particles could be described by the Langmuir model, as determined by potentiometric measurements. The increase in the mean zeta potential values and X-ray absorption near-edge spectra evidenced the immobilization of Cu(2+) ions on the hybrid particles.

Carboxymethylcellulose Sodium↗
PubMed2006

QCM studies of gel spreading: Kraton gels on polystyrene surfaces.

Contact of a polymer gel made from a styrene/ethylene-butene/styrene triblock copolymer in mineral oil was investigated by bringing the gel into contact with the coated surface of a quartz crystal microbalance (QCM). The experimental apparatus enabled simultaneous measurement of the load, displacement, and contact area, in addition to the resonant frequency and dissipation of the oscillating quartz crystal. The QCM response was determined by the linear viscoelastic properties of the gel at the frequency of oscillation. A geometric correction factor involving the contact area provided a means for quantitatively determining these viscoelastic parameters as the gel spread over the QCM surface. When the gel was removed from the surface, a thin solvent layer was left behind. The thickness of this solvent layer was determined from the QCM response and was compared to predictions from a simple model involving the disjoining pressure of the film and the osmotic pressure of the gel. Qualitative agreement with the model required that tensile, adhesive forces at the perimeter of the gel/QCM contact area were taken into account when calculating the film thickness.

Chemical Phenomena↗
PubMed2007

Blends of poly(epsilon-caprolactone) and intermediate molar mass polystyrene as Langmuir films at the air/water interface.

Poly(epsilon-caprolactone)/polystyrene (PCL/PS) blends, where nonamphiphilic PS is glassy in the bulk state at the experimental temperature of 22.5 degrees C, are immiscible as Langmuir films at the air/water (A/W) interface. Surface pressure-area per monomer isotherm analyses indicate that the surface concentration of amphiphilic PCL is the only factor influencing the surface pressure below the collapse transition. For PS-rich blends, Brewster angle microscopy (BAM) studies at the A/W interface and atomic force microscopy studies on Langmuir-Schaefer films reveal that PS nanoparticle aggregates formed at very low surface pressures can form networks upon further compression. The morphologies seen in PS-rich blends (networklike rings) are consistent with a recent study of a nonamphiphilic polyhedral oligomeric silsesquioxane (POSS), octaisobutyl-POSS, blended with amphiphilic poly(dimethylsiloxane), suggesting that the nonamphiphilic PS aggregates at the A/W interface produce domains with dipole densities that differ from that of pure PCL. In all composition regimes, the amphiphilic PCL phase tends to spread and form a continuous surface layer at the A/W interface, while simultaneously improving the dispersion of nonamphiphilic PS domains. During film expansion, BAM images show a gradual change in the surface morphology from highly continuous networklike structures (PS-rich blends) to broken ringlike structures (intermediate composition) to small discontinuous aggregates (PCL-rich blends). This study provides valuable information on the morphological evolution of semicrystalline PCL-based polymer blends confined in a "two-dimensional" geometry at the A/W interface and fundamental insight into the influence of microstructure (domain size, phase-separated structures, crystalline morphology, etc.) on the interfacial properties of blends as Langmuir films.

Air↗
PubMed2004

Biocidal activity of polystyrenes that are cationic by virtue of protonation.

[structure: see text] Poly(1) kills bacteria (Gram-positive and -negative) and lyses human erythrocytes; this biocidal profile is similar to that of the peptide toxin mellitin. Poly(1) has antibacterial activity comparable to that of a potent derivative of the host defense peptide magainin II, but lacks magainin's selectivity for bacteria over erythrocytes. An analogous N-quaternized polymer, poly(3), is less biocidal than poly(1), suggesting that reversible N-protonation leads to greater biocidal activity than does irreversible N-quaternization.

Anti-Bacterial Agents↗
PubMed2000

Novel hydrazino-carbonyl-amino-methylated polystyrene (HCAM) resin methodology for the synthesis of P1-aldehyde protease inhibitor candidates.

[structure: see text] A new strategy for the synthesis of peptidyl and peptidomimetic P1-aldehydes 3 on HCAM solid support is described. The appropriate C-terminal aldehyde precursors were prepared and anchored to a resin support via a semicarbazone linkage (HCAM resin). After synthetic elaboration, acidic hydrolysis efficiently delivered C-terminal target aldehydes 3a-h in good overall yields and in excellent purity.

Aldehydes↗