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At least 1,261 records · Page 70Linked to original sources
PubMed1987

Effects of a drag-reducing polyelectrolyte of microscopic linear dimension (Separan AP-273) on rat hemodynamics.

Separan AP-273, a polydisperse, high molecular weight (10(5)-10(7) dalton range), anionic polyacrylamide, demonstrates polymer drag reduction (Toms effect) in the flows of several substances including blood. That is, under appropriate conditions, pipe flow can be increased markedly for a given pressure gradient, sometimes threefold or more, by nanomolar concentrations of linear macropolymers. The effect of intact and degraded Separan was tested in the open-chest, anesthetized rat, and left ventricular and carotid pressures, aortic blood flow (electromagnetic flow probe on ascending aorta), and the electrocardiogram were recorded. The results indicate that aortic flow, which in control animals was about half the flow reported for conscious rats, increases markedly after injection of Separan. The effect on blood pressure after an initial fall was variable, but the slope of arterial diastolic pressure was consistently steepened. Electrocardiographic changes were unremarkable except for a slow decline in heart rate. Although secondary reflexes undoubtedly influenced the results, the primary mechanism of the polymer appears to involve a reduced resistance to flow. The results are compatible with the proposal that the Toms effect, or some variant of it, is operative in vivo under favorable conditions. If this view is correct, then Separan and two other chemically different macropolymers with similar hemodynamic effects and physical attributes, i.e., linearity and molecular lengths approaching 100 micron, might be prototypes of a novel category of cardiovascular drugs.

Acrylic Resins↗
PubMed2002

Matrix molecular weight cut-off for encapsulation of carbonic anhydrase in polyelectrolyte beads.

The enzyme bovine carbonic anhydrase (BCA) has been immobilized in the chitosan-alginate system for the first time, to catalyze the conversion of CO2 to HCO3-. Chitosan-coated alginate beads are a biodegradable and environmentally benign matrix, chosen for application of the enzyme in a novel biomimetic CO2 sequestration system. The feasibility of the system and immobilization of the enzyme were demonstrated in our earlier studies. Optimization of the matrix to improve the retention time of the enzyme in an encapsulated form is the subject of the present study. The improvement in the molecular weight cut-off of the beads was accomplished by adjusting the cross-linking conditions, coating composition, and molecular weight of the system. The quantity of enzyme released from the system was measured by a Bio-Rad protein assay. Poly-L-lysine was also used as a coating reagent for comparison purposes. The presence of a coating on the alginate beads was verified by Kjeldahl analyses. The difference in the microstructures of alginate and chitosan/alginate beads was demonstrated by SEM studies. Mineralization of the chitosan/alginate matrix in the presence of CaCO3 was also studied by FT-IR, to assess the possibility of using the beads continuously in a bioreactor.

Alginates↗
PubMed1983

Mechanism of adhesion of polyelectrolyte cements to hydroxyapatite.

The interaction between polyacrylate ions and hydroxyapatite was examined using extraction techniques and infra-red spectroscopy. These studies have shown that polyacrylate ions become irreversibly attached to the surface of hydroxyapatite by displacing existing phosphate ions. The mechanism is not one of simple ion exchange, since calcium ions are displaced by the phosphate ions.

Acrylic Resins↗
PubMed2004

Further investigations on a poly(vinyl alcohol)- polyelectrolyte chemically selective optical film.

The ionomer poly(vinylbenzyltrimethylammonium chloride) has been blended with cross-linked poly(vinyl alcohol) to form optically clear composites that can be covalently linked as thin films to oxide surfaces. Films are characterized using spectroscopic ellipsometry with refractive index (n) and extinction coefficient (k) data presented for wavelengths 300 to 1100 nm. A refractive index of 1.54 and average thickness of 709 nm are typical of an air dry film prepared by spin-coating. Dynamic in situ ellipsometry results for films exposed to 0.1 M KNO(3) and 1.0 mM Fe(CN)(6)(-3) are presented. Upon initial exposure to 0.1 M KNO(3), an air dry film expands by about 160% and stabilizes in size and refractive index at about 18 hours. Ion exchange of film cationic groups with ferricyanide is marked by slight film contraction, presumably due to electrostatic cross-linking by the multivalent anion. These films are useful in the spectroelectrochemical sensor with our newly developed fluorescence detection mode, as demonstrated by results of the reversible incorporation of the fluorescent anion fluorescein.

Journal Article↗
PubMed2006

Direct evidence of multicompartment aggregates in polyelectrolyte-charged liposome complexes.

By means of the combined use of dynamic light scattering and transmission electron microscopy measurements, we provide a direct evidence for the existence of an equilibrium cluster phase in the polyion-induced liposome aggregation, where the liposomes maintain their integrity, with the ability of preserving the aqueous core content from the external medium. We prepared single liposomes containing, in their interior, different CsCl electrolyte solutions at different concentrations (0.1 and 0.01 M, respectively). During the polyion-induced complexation of a mixture of these two differently loaded liposomes, reversible aggregates form, whose multicompartmental structure reveals the simultaneous presence of nonfused liposomes. Clusters composed by mesoscopic-sized vesicles and realized by charged lipids coupled to oppositely charged polyions are playing an increasingly important role as model systems in a variety of phenomena in soft matter and for their potential use in biomedical applications as drug delivery systems. Aggregates of liposomes such as those described in this article, where the electrostatic interactions are the primary driving forces promoting aggregation, may represent a new and interesting class of colloids which give rise to a rich phenomenology with several unusual colloidal behaviors that deserve to be further investigated.

Colloids↗
PubMed1997

Kinetic aspects of polyelectrolyte adsorption: adsorption of chitin derivatives onto liposomes as a model system.

Carboxymethylchitin (CMC) and Carboxymethyl/Glycolchitin (CO) have been adsorbed onto liposomes at physiological ionic strength (I) and pH using phosphate buffer saline (PBS, I = 154 mM, pH = 7.4). Adsorption isotherms at different polymer weight average molecular weights (Mw), for Positive ([+]) or high surface affinity liposomes (DSPC:CHOL:DMTAP, 5:4:1), and Neutral ([N]) or low surface affinity liposomes (DSPC:CHOL, 1:1), have been obtained at T = 25 degrees C. For all CMCs, the adsorbed amount increases with polymer concentration ([P]zero) and no true plateau is observed. The CMC Mw = 4.19 x 10(5) adsorbed on a positive surface fits Langmuir kinetics with maximal coverage gamma max = 325.4 micrograms/mg (polymer/lipid), and inverse of equilibrium constant K* = 4.743 x 10(-4) mg/ml. For all isotherms the predicted amount of polymer needed to coat the entire surface based on the Radius of Gyration (Rg) is inferior to the amount adsorbed. This fact in conjunction with the dependence of gamma max on the number of adsorption shots, suggests that the adsorption is not thermodynamically but kinetically controlled.

Adsorption↗
PubMed1976

[Mechanisms of action of synthetic polyelectrolytes and polyampholytes on the immune response].

We investigated the effect of polyacrilic acid (PAA) on the immune response in mice of various strains on sheep red blood cells and also the influence of poly-2-methyl-5-vinyl-pyridine (PMVY), PAA and their statistical copolymers on antibody-forming cells (AFC) production in cultures of T- and B-lymphocytes in vivo. PAA was seen to increase accumulation of AFC in the spleen of mice depending on their genotypes. PMVP and PAA were found to intensify the cooperating interaction of T- and B-lymphocytes, whereas their copolymers exert quite an opposite effect. The injection of copolymers to the recipients of cooperating T- and B-lymphocytes practically results in the complete elimination of the cooperation effect between T- and B-lymphocytes in the immune response to sheep erythrocytes without cytostatic action of cell proliferation.

Acrylic Resins↗
PubMed2003

Structure-function studies of the lustrin A polyelectrolyte domains, RKSY and D4.

The lustrin superfamily represents a unique group of biomineralization proteins localized between layered aragonite mineral plates (i.e., nacre layers) in mollusk shell. These proteins not only exhibit elastomeric behavior within the mineralized matrix, but also adhesion to the aragonite-containing composite layer. One member of the lustrin superfamily, Lustrin A, has been sequenced; the protein is organized into defined, modular sequence domains that are hypothesized to perform separate functions (i.e., force unfolding, mineral adhesion, intermolecular binding) within the Lustrin A protein. Using nuclear magnetic resonance (NMR) and in vitro mineralization assays, we investigated structure-function relationships for two Lustrin A putative mineral binding domains, the 30 AA Arg, Lys, Tyr, Ser-rich (RKSY) and the 24 AA Asp-rich (D4) sequence regions domain of the Lustrin A protein. The results indicate that both sequences adopt open, unfolded structures that represent either extended or random coil states. Using geologic calcite overgrowth assays and scanning electron microscopic analyses, we observe that the RKSY polypeptide does not significantly perturb calcium carbonate growth. However, the D4 domain does influence crystal growth in a concentration-dependent manner. Collectively, our data indicate that D4, and not the RKSY domain, exhibits structure-function activity consistent with a mineral binding region.

Amino Acid Sequence↗