Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0267964 (PAA)
 2,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Polyelectrolyte brushes were built on mica by anchoring polystyrene-poly(acrylic acid) (PS-b-PAA) diblock copolymers at a controlled surface density in a polystyrene monolayer covalently attached to OH-activated mica surfaces. Compared to physisorbed polymer brushes, these irreversibly attached charged brushes allow the polymer grafting density to remain constant upon changes in environmental conditions (e.g., pH, salt concentration, compression, and shear). The normal interaction and friction forces as a function of surface separation distance and at different concentrations of added salt (NaCl) were investigated using a surface forces apparatus. The interaction force profiles were completely reversible both on loading and receding and were purely repulsive. For a constant polymer grafting density, the influence of the polyelectrolyte charges and the Debye screening effect on the overall interaction forces was investigated. The experimental interaction force profiles agree very well with scaling models developed for neutral and charged polymer brushes. The variation of the friction force between two PAA brushes in motion with respect to each other as a function of surface separation distance appeared to be similar to that observed with neutral brushes. This similarity suggests that the increase in friction is associated with an increase in mutual interpenetration upon compression as observed with neutral polymers. The effect of the PAA charges and added ions was more significant on the repulsive normal forces than on the friction forces. The reversible characteristics of the normal force profiles and friction measurements confirmed the strong attachment of the PAA brushes to the mica substrate. High friction coefficients (ca 0.3) were measured at relatively high pressures (40 atm) with no surface damage or polymer removal.
 ...
PMID:Friction and normal interaction forces between irreversibly attached weakly charged polymer brushes. 1822 26

The salt effect on the complex formation of poly(acrylamide)- block-poly(sodium acrylate) (PAM- b-PAA) as a neutral-anionic block copolymer and dodecyltrimethylammonium bromide (DTAB) as a cationic surfactant at different NaBr concentrations, CNaBr, was investigated by turbidimetric titration, steady-state fluorescence spectroscopy, and dynamic light scattering. At C NaBr < 0.25 M, DTAB molecules may form micelle-like aggregates on PAM- b-PAA chains to form a PAM- b-PAA/DTAB complex above the critical surfactant concentration C critical for the onset of complex formation. In the region of relatively high turbidity, a larger complex is likely to form a core-shell structure, of which the core is a dense and disordered microphase made of surfactant micelles connected by the PAA blocks. The corona was a diffuse shell of PAM chains, and it ensured steric stability. At CNaBr = 0.25 M, a higher electrostatic intermicellar repulsion and intercomplex repulsion induced by a large amount of bound DTAB micelles may lead to a redissolution of large colloidal complexes into intrapolymer complexes. Moreover, a salt-enhancing effect on the complex formation was observed in the PAM- b-PAA/DTAB system; the critical surfactant concentration decreased with increasing salt concentration at CNaBr < 0.10 M. The salt-enhancing effect is due to the larger increase of interaction in comparison to the screening of the interaction.
 ...
PMID:Salt effect on complex formation of neutral/polyelectrolyte block copolymers and oppositely charged surfactants. 1845 24

The adsorption of bovine serum albumin (BSA) in a planar poly(acrylic acid) (PAA) brush layer has been studied by fixed-angle optical reflectometry. The influence of polymer length, grafting density, and salt concentration is studied as a function of pH. The results are compared with predictions of an analytical polyelectrolyte brush model, which incorporates charge regulation and excluded volume interactions. A maximum in adsorption is found near the point of zero charge (pzc) of the protein. At the maximum, BSA accumulates in a PAA brush to at least 30 vol %. Substantial adsorption continues above the pzc, that is, in the pH range where a net negatively charged protein adsorbs into a negatively charged brush layer, up to a critical pH value. This critical pH value decreases with increasing ionic strength. The adsorbed amount increases strongly with both increasing PAA chain length and increasing grafting density. Experimental data compare well with the analytical model without having to include a nonhomogeneous charge distribution on the protein surface. Instead, charge regulation, which implies that the protein adjusts its charge due to the negative electrostatic potential in the brush, plays an important role in the interpretation of the adsorbed amounts. Together with nonelectrostatic interactions, it explains the significant protein adsorption above the pzc.
 ...
PMID:Adsorption of the protein bovine serum albumin in a planar poly(acrylic acid) brush layer as measured by optical reflectometry. 1850 22

We consider a symmetrical poly(styrene- stat-(acrylic acid))- block-poly(acrylic acid), i.e., PSAA- b-PAA, diblock copolymer, with a molar fraction phi AA = 0.42 of acrylic acid, in the more hydrophobic PSAA statistical first block. We investigate its structural behavior at constant concentration in water using small-angle neutron scattering (SANS) by varying (i) the ionization of its acrylic acid motives via the pH by adding NaOH and (ii) the ionic strength of the solution by increasing the NaCl salt concentration c S. We present the resulting morphological phase diagram {pH, c S}, in which we identified two different lamellar phases presenting a smectic long-range order at small-to-intermediate ionizations and a spherical phase with a liquid-like short-range order at larger ionization. In the low-ionization regime, the first lamellar phase comprises a water-free PSAA lamellar core surrounded by a dense poly(acrylic acid) brush swollen with water. Its mostly hydrophobic core still being glassy, this phase is unable to reorganize and is frozen in. A detailed analysis of the SANS data shows the osmotic nature of the polyelectrolyte brush, in which the Na+ counterions are confined so that local electroneutrality is satisfied. Above the pH at which the PSAA statistical block starts ionizing, the PSAA lamellar core melts. The second lamellar phase identified then comprises a PSAA core thinner than that of the frozen-in previous phase, implying a significant increase of the core/water interface and a decrease of the brush surface density. The transition from the first lamellar phase to the second one can be quantitatively shown to result from the balance between the two contributions: (i) the extra interfacial cost between the thinner core and water and (ii) the associated gain in entropy of mixing for the counterions confined inside the brush. At even higher ionization, the diblocks finally form spherical objects with a very small, pH-dependent aggregation number and reach an apparent onset of self-association. When the highest ionization investigated is reached, the cores of these final spherical core-shell objects are found to contain a significant amount of water. We thereby demonstrate that at constant concentration, pH, and ionic strength both trigger a transition from frozen to molten hydrophobic phases as well as unexpected morphological transitions.
 ...
PMID:Double-polyelectrolyte, like-charged amphiphilic diblock copolymers: swollen structures and pH- and salt-dependent lyotropic behavior. 1859 8

Two-dimensional NMR and small-angle neutron scattering experiments were performed on comicelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO, and poly(acrylic acid)-block-poly(acryl amide), PAA-b-PAAm, in aqueous solutions to study whether a transition between a heterogeneous (Janus-type) and homogeneous corona can be observed upon a variation of parameters that are anticipated to affect the miscibility of the PEO and PAAm coronal blocks. Investigated were the effect of a salt-induced decrease in micellar aggregation number, P agg for 1<or=[NaNO3]<or=279 mM, a temperature increase for 25<or=T<or=80 degrees C, a variation of the fraction of EO monomers in the corona, fEO, at a fixed corona block length, N corona, for 0<or=fEO<or=1, a decrease in the PEO block length, N PEO, at a fixed PAAm block length, NPAAm, for 200<or=NPEO<or=450, and finally, upon a decrease in corona block length at NPAAm=NPEO for 100<or=N corona<or=400. These parameters should affect the mixing/demixing transition via their effect on the PEO/PAAm interfacial area (e.g., as in the case of f EO and P agg) or the relevant Flory-Huggins interaction parameters (e.g., as in the case of temperature). None of the above parameters was shown to yield a transition toward a homogeneous corona wherein the polymer chains are randomly mixed; i.e., the segregation of PAAm and PEO chains within the micellar corona of comicelles of PAA-b-PAAm and P2MVP-b-PEO appears to be rather robust.
 ...
PMID:On the transition between a heterogeneous and homogeneous corona in mixed polymeric micelles. 1882 17

Uricase (UOx) and polyelectrolyte were used for preparation of a permselective multilayer film and enzyme multilayer films on a platinum (Pt) electrode, allowing the detection of uric acid amperometrically. The polyelectrolyte multilayer (PEM) film composed of poly(allylamine) (PAA) and poly(vinyl sulfate) (PVS) were prepared via layer-by-layer assembly on the electrode, functioning as H(2)O(2)-selective film. After deposition of the permselective film (PAA/PVS)(2)PAA, UOx and PAA were deposited via layer-by-layer sequential deposition up to 10 UOx layers to prepare amperometric sensors for uric acid. Current response to uric acid was recorded at +0.6 V vs. Ag/AgCl to detect H(2)O(2) produced from the enzyme reaction. The response current increased with increasing the number of UOx layers. Even in the presence of ascorbic acid, uric acid can be detected over the concentration range 10(-6)-10(-3) M. The response current and deposited amount of UOx were affected by deposition bath pH and the addition of salt. The deposition of PAA/UOx film prepared in 2 mg ml(-1) solution (pH 11) of PAA with NaCl (8 mg ml(-1)) and 0.1 mg ml(-1) solution (pH 8.5) of UOx with borate (100 mM) resulted in an electrode which shows the largest response to uric acid. The response of the sensor to uric acid was decreased by 40% from the original activity after 30 days.
 ...
PMID:Amperometric uric acid sensors based on polyelectrolyte multilayer films. 1896 95

Amphiphilic poly(epsilon-caprolactone)-b-poly(acrylic acid) (HS-PCL-b-PAA) with a thiol functionality in the PCL terminal has been prepared in a novel synthetic cascade. Initially, living anionic ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) employing the difunctional initiator, 2-hydroxyethyl 2-bromoisobutyrate, followed by esterification with 2,4-dinitrophenyl- or 4-monomethoxytrityl-protected mercaptoacetic acids (Prot-), provided well-defined PCL macroinitiators capped with protected thiols. The macroinitiators allowed atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) in a controlled fashion by use of NiBr2(PPh3)2 catalyst to produce Prot-PCL-b-PtBA with narrow polydispersities (1.17-1.39). Subsequent mild deprotection protocols provided HS-PCL-b-PAA. Reduction of a gold salt in the presence of this macroligand under thiol-deficient conditions afforded stable, aggregation-free nanoparticles, as evidenced from UV-vis spectroscopy and transmission electron microscopy (TEM), the latter revealed nanoparticles with a mean diameter of 9.0+/-3.1 nm.
 ...
PMID:Gold nanoparticles protected with thiol-derivatized amphiphilic poly(epsilon-caprolactone)-b-poly(acrylic acid). 1905 94

Compression of the polyelectrolyte multilayers has been found previously when they were pressed by a poly(dimethylsiloxane) (PDMS) stamp under a small pressure (Macromolecules 2004, 37, 8836). In this work, we further found that the pattern formation of the poly(diallyldimethylammonium chloride) (PDADMAC) containing multilayers is dependent on the drying time of the multilayers prior to compression. After the poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA)/PDADMAC multilayers were dried at 70% relative humidity and room temperature for 2, 6, and 12 h, compression of the multilayers by a PDMS stamp with linear patterns obtained double strips, high ridges and linear patterns on the multilayers, respectively. These phenomena were independent of the layer number and salt concentration and could be applied to other PDADMAC containing multilayer systems such as poly(styrene sulfonate) sodium salt (PSS)/PDADMAC and poly(acrylic acid, sodium salt) (PAA)/PDADMAC. A model was suggested to depict the process, and the influence of the water content on the multilayer structure and properties was discussed. The stability experiments revealed that the strips and high ridges obtained at shorter drying time could be erased by incubation in water for 5 h, while the compression created patterns were very stable.
 ...
PMID:Influence of drying time of polyelectrolyte multilayers on the compression-induced pattern formation. 1905 63

Several new sugar glasses were investigated for their potential in solid-matrix luminescence. Both solid-matrix fluorescence (SMF) and solid-matrix phosphorescence (SMP) properties were obtained, and two heterocyclic aromatic amines were employed as model compounds. In addition to glucose glasses, which were investigated previously, fructose, ribose, xylose, galactose, maltose, and glucose with poly(acrylic acid) (PAA) were studied. Detailed experimental conditions were obtained for each sugar-glass system. In addition, NaI was investigated as a heavy-atom salt in the sugar-glass systems to enhance the SMP of the heterocyclic aromatic amines. The SMF intensity was the strongest in maltose and glucose with PAA for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and in maltose for 2-amino-9H-pyrido[2,3-b]indole (AalphaC). The largest SMP signals for PhIP with and without NaI were acquired in glucose with PAA. For AalphaC with NaI, the strongest SMP signal was obtained in maltose. Limits of detection were obtained for PhIP in the several sugar-glass systems, and the lowest limit of detection was 0.04pmol/mg of PhIP in maltose with NaI present. An extensive study was carried out using both SMF and SMP to determine if neutral and/or protonated species of PhIP and AalphaC were in the sugar-glass systems. General guidelines such as glass transition temperature and solubility are discussed for selecting a sugar glass as a solid matrix.
 ...
PMID:Solid-matrix luminescence of heterocyclic aromatic amines in several new sugar-glass systems. 1907 93

Free-standing and supported films with a lateral gradient in composition were prepared using blends of poly(acrylic acid) (PAA)/sodium salt and its copolymers with acrylamide (AAm) in an applied electric field. The gradients were stabilized by complexation of carboxylate groups with metal species. To find the favorable conditions and components for successful blending and interaction with Fe and Ce species, we studied blending of the two PAA samples with molecular weights of 2000 and 15 000 Da with two copolymers of AA and AAm (with 10 and 70 wt % of AA units) and interaction of these blends with Fe(III) and Ce(IV) ions. The structure of the hybrid (blend) films was studied using differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, X-ray diffraction, and optical microscopy. To ensure blend miscibility and efficient interaction with metal ions, the copolymer containing 70 wt % AA units has been used. The surface enrichment with metal species was observed at all experimental conditions studied in this work. For lateral gradient film formation, 15 000 Da PAA has been used to avoid uneven distribution of the homopolymer in the film, observed for 2000 Da PAA. The gradient films were characterized by XPS. The lateral gradient of functionality such as COONa group or Fe content has been obtained at different strengths of electric field applied during film formation. The use of lower voltage allows one to prevent NaOH formation and creates more favorable conditions for development of a gradient polymer film. The Ce content gradient was not observed due to formation of large Ce oxide particles (> or = 750 nm), masking the gradient of functionality. For the first time, free-standing films with a lateral gradient in composition were prepared using an applied electric field.
 ...
PMID:Bioinspired gradient materials via blending of polymer electrolytes and applying electric forces. 1910 43


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>