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Query: UMLS:C0267964 (PAA)
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In this study, the formation and disintegration of polyelectrolyte complex micelles is studied by dynamic light scattering titrations with the aim to assess the extent to which these complexes equilibrate. Also, the time evolution of samples at fixed (electroneutral) composition was followed to obtain information about the relaxation time of the complex formation. We find that, in 3.5 mM phosphate buffer with pH 7, polyelectrolyte complex micelles consisting of the positively charged homopolymer PDMAEMA(150), the negatively charged diblock copolymer PAA(42)-PAAm(417) (both having a pH-dependent charge), as well as the positively charged protein lysozyme slowly equilibrate with a relaxation time of about 2 days. The same structures were obtained, independent of the way the polymers and proteins had been mixed. In contrast, polyelectrolyte complex micelles (at the same pH) consisting of (pH-dependent) negatively charged homopolymer PAA(139), the pH-independent positively charged diblock copolymer P2MVP(41)-PEO(205), and the negatively charged protein alpha-lactalbumin did not equilibrate. The way in which solutions containing these macromolecules were mixed yielded different results that did not change over the period of at least a week.
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PMID:Reversibility and relaxation behavior of polyelectrolyte complex micelle formation. 1933 98

The association between a randomly pyrene labeled PAA polymer (PAAMePy55) and a PEO-PPO-PEO triblock copolymer (P123) in aqueous solutions of different NaCl concentrations and pHs has been studied by means of dynamic light scattering (DLS) and steady-state fluorescence spectroscopy at 40 degrees C. At acidic pH values, in the low P123/PAAMePy55 molar ratio regime (i.e., at low P123 concentrations), the relaxation time distributions retrieved from the DLS data analysis were monomodal and very similar to those obtained for the pure PAAMePy55 solution. The apparent hydrodynamic radius of PAAMePy55 at low pH is 18 nm. At higher molar ratios (i.e., at high P123 concentrations), still in the acidic pH regime, bimodal relaxation time distributions were obtained, where the fast relaxation mode is connected to the translational diffusion of free P123 micelles with a hydrodynamic radius obtained at infinite P123 dilution (R(H,P123=0)) of 10-11 nm. This value coincides perfectly with the hydrodynamic radius of the pure P123 micelles at 40 degrees C, which was found to be ca. 10 nm at all pH values. The second mode corresponds to a complex consisting of one PAAMePy55 polymer chain and about 42 P123 micelles and with a R(H,P123=0) between 35 and 36 nm depending on pH. At pH 9, the mixed system also presented bimodal relaxation time distributions. At this high pH, the intermolecular association between PAAMePy55 and P123 is less strong than at acidic pH according to the steady-state fluorescence measurements. The fast mode is also in this case attributed to free P123 micelles whereas the second mode is related to the so-called "slow mode" commonly observed for polyelectrolyte solutions. In this system, it is related to the formation of multichain domains, that is, large domains formed by several PAAMePy55 chains that move in a common electrostatic field (i.e., a structure factor effect). The presence of P123 micelles does not lead to the total disruption of these domains. They may either contain entrapped P123 micelles or hydrophilic diblock impurities (originating from the P123 sample) that associate with the PAAMePy55 chains.
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PMID:Complex formation between a fluorescently-labeled polyelectrolyte and a triblock copolymer. 1935 71

By using absorption and fluorescence (steady-state and time-resolved) techniques, the interaction between a poly(acrylic acid) (PAA), randomly grafted with pyrene (Py) units (PAAMePy55), and a triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) (EO(20)PO(68)EO(20), P123) was investigated. From the fluorescence data, it is shown that upon addition of P123 a decrease of the (pyrene-pyrene, Py-Py) intramolecular association, i.e., a decrease of dynamic and static excimer formation, is observed. Time-resolved fluorescence data reveal the existence of two types of monomers (monomers that are able to form excimer, MAGRE, and isolated monomers) and two excimers. Addition of P123 causes also an increase of the amount of isolated Py monomers. The overall fluorescence data suggest that the PAAMePy55 and the P123 block copolymer associate strongly at low pH, leading to the formation of P123 micelles surrounded by one PAAMePy55 chain, where the pyrene groups are located at the PPO/PEO interface of the P123 micelles. Steady-state fluorescence results also showed that an excess of P123 micelles in solution is required for the association to occur. At high pH (pH 9 and above) the situation is less clear. The steady-state (particularly in the I(1)/I(3) ratio) and time-resolved fluorescence results indicate a contact between the pyrene groups and PEO, which then would imply that there may be an interaction, but much weaker than at low pH.
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PMID:Association of a hydrophobically modified polyelectrolyte and a block copolymer followed by fluorescence techniques. 1935 73

The effect of block sequence on the self-assembly of ABC terpolymers in selective solvent (water/THF) was explored based on two kinds of terpolymers: polystyrene-block-poly(ethylene oxide)-block-poly(acrylic acid) (PS-b-PEO-b-PAA) and PEO-b-PS-b-PAA with the same component, comparable molecular weight, but different block sequence. Copolymer PS-b-PEO-b-PAA has a higher critical water content (CWC) and larger aggregates size than PEO-b-PS-b-PAA. Furthermore, they presented vesicles with hundreds of nanometers at 25% water content which was not observed in the case of PEO-b-PS-b-PAA. It was also found that there was a sharp jump of both the scattering light intensity and average aggregate size for PS-b-PEO-b-PAA. The kinetics of morphological transitions vs the water content was described to explain this phenomenon.
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PMID:Effect of block sequence on the self-assembly of ABC terpolymers in selective solvent. 1936 12

Formation and stabilization of multiresponsive micelles with a mixed poly(ethylene oxide)/polyelectrolyte shell and a temperature-responsive poly(propylene oxide) core were studied. Various poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers were mixed with poly(acrylic acid)-block-poly(propylene oxide)-block-poly(acrylic acid) (PAA-PPO-PAA) or poly(dimethylaminoethyl methacrylate)-block-poly(propylene oxide)-block-poly(dimethylaminoethyl methacrylate) (PDMAEMA-PPO-PDMAEMA) triblock copolymers. The micelles formed by binary mixtures of well-defined compositions at a specific pH were additionally stabilized by loading with pentaerythritol tetraacrylate (PETA), that was polymerized and cross-linked "in situ" with UV assistance. Depending on both the composition of the copolymers and the experimental conditions, either spherical or wormlike "stabilized polymeric micelles with a mixed shell" (SPMMS) were observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The SPMMS that contained PAA blocks in the shell were pH-sensitive, such that a reversible transition from well-dispersed SPMMS to precipitate could be promoted. In contrast, the SPMMS with a PEO/PDMAEMA mixed shell remained well-dispersed in the 2-11 pH range. Finally, SPMMS were successfully exploited as templates for the preparation of Ag nanoparticles (Ag NPs).
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PMID:Stabilized mixed micelles with a temperature-responsive core and a functional shell. 1940 18

Photoactive micelles of a diblock copolymer composed of poly(ethylene oxide) and poly(7-(2-methacryloyloxyethoxy)-4-methylcoumarin) (PEO-b-PCMA) were layer-by-layer assembled with poly(acrylic acid) (PAA) using hydrogen-bonding between the PEO corona of the micelles and the PAA chains (pH < 3). In addition to characterizing the assembly process using a number of techniques, the tunable photo-cross-linking of polymer micelles through dimerization of the coumarin groups was used to generate interesting functions for the multilayer film. On the one hand, the easy tuning of the photo-cross-linking density could be used to control the release rate of hydrophobic guest molecules loaded in the film. On the other hand, after chemical cross-linking of PAA to stabilize the film, the photo-cross-linking of the micelles could be used to restrict the dissolution of PEO-b-PCMA chains in a good organic solvent; this cross-linking-dependent extraction of polymer micelles was utilized to vary the porosity of the film.
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PMID:Photo-cross-linkable polymer micelles in hydrogen-bonding-built layer-by-layer films. 1954 31

We describe the preparation and characterisation of inorganic-organic hybrid block copolymer silver nanoparticles via the preparation of spherical multi-responsive polymeric micelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP(38)-b-PEO(211) and poly(acrylic acid)-block-poly(isopropyl acrylamide), PAA(55)-b-PNIPAAm(88) in the presence of AgNO(3). Hence, the P2MVP and PAA segments were employed to fix Ag(+) ions within the micellar core (25 degrees C) or shell (60 degrees C), while the PEO segments ensured spontaneous reduction of Ag(+) ions into metallic Ag, as well as colloidal stabilisation. Spherical and elongated composite core-shell(-corona) nanoparticles (CNPs) were formed containing several small, spherical silver nanoparticles within the micellar core or shell. As the co-assembly of the oppositely charged copolymers into micelles is electrostatically driven, the CNPs can be destabilised by, for example, addition of simple salts, i.e., the CNPs are stimuli responsive. CNP size and morphology control can be achieved via the preparation protocol. For example, heating to 60 degrees C, i.e., above the PNIPAAm LCST, results in core-shell-corona CNPs with the Ag-NPs situated in the aggregate shell.
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PMID:Environment-sensitive stabilisation of silver nanoparticles in aqueous solutions. 1971 64

Pluronic based core-shell nanostructures encapsulating gentamicin were designed in this study. Block copolymers of (PAA(+/-)Na-b-(PEO-b-PPO-b-PEO)-b-PAA(+/-)Na) were blended with PAA(-) Na(+) and complexed with the polycationic antibiotic gentamicin to form nanostructures. Synthesized nanostructures had a hydrodynamic diameter of 210 nm, zeta potentials of -0.7 (+/-0.2), and incorporated approximately 20% by weight of gentamicin. Nanostructures upon co-incubation with J774A.1 macrophage cells showed no adverse toxicity in vitro. Nanostructures administered in vivo either at multiple dosage of 5 microg g(-1) or single dosage of 15 microg g(-1) in AJ-646 mice infected with Salmonella resulted in significant reduction of viable bacteria in the liver and spleen. Histopathological evaluation for concentration-dependent toxicity at a dosage of 15 microg g(-1) revealed mineralized deposits in 50% kidney tissues of free gentamicin-treated mice which in contrast was absent in nanostructure-treated mice. Thus, encapsulation of gentamicin in nanostructures may reduce toxicity and improve in vivo bacterial clearance.
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PMID:Antibacterial efficacy of core-shell nanostructures encapsulating gentamicin against an in vivo intracellular Salmonella model. 2005 33

The enzymatic activity of Hl-lipase embedded in complexes of poly-2-methylvinylpyridinium-co-poly(ethylene oxide) (P2MVP(41)-PEO(205)) and poly(acrylic acid)(PAA(139)) is studied as a function of the PAA(139) + P2MVP(41)-PEO(205) complex composition. The measurements revealed that there are several factors that influence the enzymatic activity. When incorporated in micelles, the activity of lipase is increased, which suggests that the micelles favor the active state. The activity may further increase because the substrate tends to accumulate to the micelles. It is found that the presence of PAA(139) alone also increases the enzymatic activity somewhat. Increasing of the ionic strength decreases the enzymatic activity in all systems. However, at ionic strengths where the micelles are disintegrated (>0.5 M), the activity of lipase in the presence of both polyelectrolytes is still higher than the activity of free lipase. At 0.7 M NaCl it was found that lipase in the presence of (just) P2MVP(41)-PEO(205) is more active than lipase without this additive.
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PMID:Effects of polyelectrolyte complex micelles and their components on the enzymatic activity of lipase. 2038 19

The novel water-dispersible nanoparticles from the double hydrophilic poly(acrylic acid)-b-poly(ethylene oxide)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) triblock copolymer and oppositely charged surfactant dodecyltrimethyl ammonium bromide (DTAB) were prepared by mixing the individual aqueous solutions. The structure of the nanoparticles was investigated as a function of the degree of neutralization (DN) by turbidimetry, dynamic light scattering (DSL), zeta-potential measurement, and atomic force microscope (AFM). The neutralization of the anionic PAA blocks with cationic DTAB accompanied with the hydrophobic interaction of alkyl tails of DTAB led to formation of core-shell nanoparticles with the core of the DTAB neutralized PAA blocks and the shell of the looped PEO blocks. The water-dispersible nanoparticles with negative zeta-potential were obtained over the DN range from 0.4 to 2.0 and their sizes depended on the DN. The looped PEO blocks hindered the further neutralization of the PAA blocks with cationic DTAB, resulting in existence of some negative charged PAA-b-PEO-b-PAA backbones even when DN > 1.0. The spherical and ellipsoidal nature of these nanoparticles was observed with AFM.
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PMID:Nanoparticles of Block Ionomer Complexes from Double Hydrophilic Poly(acrylic acid)-b-poly(ethylene oxide)-b-poly(acrylic acid) Triblock Copolymer and Oppositely Charged Surfactant. 2065 26


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