Interaction of uranium(VI) with lipopolysaccharide

Bacteria have a great influence on the migration behaviour of heavy metals in the environment. Lipopolysaccharides form the main part of the outer membrane of Gram-negative bacteria. We investigated the interaction of the uranyl cation (UO2(2+)) with lipopolysaccharide (LPS) from Pseudomonas aeruginosa by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH and concentration range. Generally, LPS consists of a high density of different functionalities for metal binding such as carboxyl, phosphoryl, amino and hydroxyl groups. The dissociation constants and corresponding site densities of these functional groups were determined using potentiometric titration. The combination of both methods, potentiometry and TRLFS, show that at an excess of LPS uranyl phosphoryl coordination dominates, whereas at a slight deficit on LPS compared to uranyl, carboxyl groups also become important for uranyl coordination. The stability constants of one uranyl carboxyl complex and three different uranyl phosphoryl complexes and the luminescence properties of the phosphoryl complexes are reported.     

Polystyrene latex particles coated with crosslinked poly(N-isopropylacrylamide)

Thermoresponsive colloidal particles were prepared by seeded precipitation polymerization of N-isopropylacrylamide (NIPAM) in the presence of a crosslinking monomer, N,N-methylenebisacrylamide (MBA), using polystyrene latex particles (ca. 50 nm in diameter) as seeds in aqueous dispersion. Phase transitions of the prepared poly(N-isopropylacrylamide), PNIPAM, shells on polystyrene cores were studied in comparison to colloidal PNIPAM microgel particles, in H₂O and/or in D₂O by dynamic light scattering, microcalorimetry and by ¹H NMR spectroscopy including the measurements of spin–lattice (T1) and spin–spin (T2) relaxation times for the protons of PNIPAM. As expected, the seed particles grew in hydrodynamic size during the crosslinking polymerization of NIPAM, and a larger NIPAM to seed mass ratio in the polymerization batch led to a larger increase of particle size indicating a product coated with a thicker PNIPAM shell. Broader microcalorimetric endotherms of dehydration were observed for crosslinked PNIPAM on the solid cores compared to the PNIPAM microgels and also an increase of the transition temperature was observed. The calorimetric results were complemented by the NMR spectroscopy data of the ¹H-signal intensities upon heating in D₂O, showing that the phase transition of crosslinked PNIPAM on polystyrene core shifts towards higher temperatures when compared to the microgels, and also that the temperature range of the transition is broader.     

Colloidal stability of chitosan-modified poly(methyl methacrylate) latex particles

Experiments of coagulation kinetics were used to study the influence of the electrolyte concentration on the colloidal stability of cationic poly(methyl methacrylate) latex particles with various degrees of chitosan modification. For the chitosan-free latex products prepared by various levels of 2,2′ azobis(2-amidinopropane) dihydrochloride (V-50) at constant pH, the critical coagulation concentration (ccc) increases with increasing V-50 concentration, due to the enhanced particle surface charge density. On the other hand, the chitosan-modified latex products at constant pH do not exhibit very different values of ccc. This result is attributed to the counterbalance between two opposite effects related to the grafted chitosan, that is, the increased particle surface charge density and the enhanced shift of the particle's shear plane toward the aqueous phase with the chitosan content. The ccc of the latex products with various degrees of chitosan modification decreases significantly when the pH increases from 3 to 7. This is because the degree of ionization of the surface amino groups (the particle surface charge density) decreases with increasing pH. As a result, the stability of the colloidal system decreases significantly with increasing pH. The apparent Hamaker constant and diffuse potential were obtained from the coagulation kinetics data. These two parameters along with the zeta potential and particle size data for the latex samples taken immediately after the end of the coagulation experiments were also used to study the effect of ionic strength on the colloidal stability of the latex particles. Received: 10 October 1998 Accepted in revised form: 16 December 1998     

Poly(methyl methacrylate-co-ethyl acrylate) latex particles with poly(ethylene glycol) grafts: structure and film formation

Water-based copolymer dispersions were prepared using methyl methacrylate (MMA), ethyl acrylate (EA) (MMA/EA = 1:2), and a series of nonionic polymerizable surfactants, i.e., "surfmers" based on poly(ethylene glycol)-(meth)acrylates. The latexes were compared with the behavior of a conventionally stabilized (nonionic nonylphenol ethoxylate, NP100 with 84 ethylene oxide units) dispersion with the same MMA-EA composition (PMMAEA). A number of techniques were employed in order to characterize structure, dynamics, and film formation properties: solution/solid-state NMR, dynamic/static light scattering (DLS/SLS), differential scanning calorimetry (DSC), tensile/shear mode dynamic mechanical thermal analysis (DMTA), and atomic force microscopy (AFM). The surfmers were found to be miscible with the MMA-EA copolymer at room temperature, with 46-85 mol % of the reacted surfmer detected at the particle surfaces, and the remaining part buried in the particle bulk. In contrast, the NP100 surfactant formed a separate interphase between the copolymer particles with no mixing detected at room temperature or at 90 degrees C. For a 4.0% dry weight concentration, NP100 phase separated and further crystallized at room temperature over a period of several months. Composition fluctuations related to a limited blockiness on a length scale above approximately 2 nm were detected for PMMAEA particles, whereas the surfmer particles were found to be homogeneous also below this limit. On a particle-particle level, the dispersions tended to form colloidal crystals unless hindered by a broadened particle size distribution or, in the case of PMMAEA, by the action of NP100. Finally, a surface roughness (Rq) master plot was constructed for data above the glass transition temperature (Tg) from Tg + 11 degrees C to Tg + 57 degrees C and compared with the complex shear modulus over 11 frequency decades. Shift factors from the 2 methods obeyed the same Williams-Landel-Ferry (WLF) temperature dependence, thus connecting the long-time surface flattening process to the rheological behavior of the copolymer.     

Morphology control of soap-free seeded P(St-EA-AA) latex particles

Soap-free poly(styrene-ethyl acrylate-acrylic acid) latex particles with narrow size distribution and with surface carboxyl groups were synthesized by semicontinuous emulsion polymerization, and the particles with homogeneous multihollow structure were obtained after alkali posttreatment. Effects of treatment conditions and crosslinking agents on particle morphology were investigated. Results showed that the multihollow structure can be formed inside the uncrosslinked particles only when the treatment temperature exceeded 50 °C, the pH was higher than 10.0, the amount of 2-butanone was more than 3.0 ml and the treatment time was longer than 30 min. Furthermore, the volume expansion of the particles increased with the temperature increased to 90 °C, the pH to 12.5 or the amount of 2-butanone to 7.0 ml, and this value increased first and then decreased with the treatment time prolonged. Fine pores can be generated in the shell of particles crosslinked by 0.2 g of ethyl glycol dimethylacrylate (EGDMA), while no hollow structure formed inside particles when 0.4 g of EGDMA or 0.2 g of divinyl benzene was used.     

Dextran stabilized poly(methyl methacrylate) latex particles and their potential application for affinity purification of lectins

 Stable poly(methyl methacrylate) latex particles (220–360 nm in diameter) using dextran as the protective colloid were prepared and characterized in this study. Such an emulsion polymerization system follows Smith–Ewart Case III kinetics (i.e., the average number of free radicals per particle is greater than 0.5) due to the relatively large latex particle size. The carbohydrate content of these dextran modified emulsion polymers shows a maximum around 5% dextran based on total monomer weight. The latex stability during polymerization is closely related to the carbohydrate content of these latex particles, and it is controlled by the ratio of the thickness of the dextran adsorption layer to that of the electric double layer of the latex particles. The critical flocculation concentration (CFC) of the latex products correlates well with the latex stability during polymerization. The greater the total scrap produced during polymerization (i.e., the stronger the bridging flocculation), the lower is the CFC of the latex products. The affinity precipitation of concanavalin A (a model lectin used in this study) by the dextran modified PMMA latex particles is also illustrated in this study. The specifically adsorbed concanavalin A increases with the carbohydrate content of the dextran modified latex particles. Received: 9 December 1996 Accepted: 8 April 1997     

Formation of highly monodispersed emulsifier-free cationic poly(methylstyrene) latex particles

Highly monodispersed emulsifier-free poly(methylstyrene) (PMS) latex particles were prepared via an emulsifier-free emulsion polymerization in the presence of 2,2′-azobis-(2-amidineopropane) dihydrochloride (V-50) as an initiator. A combination of kinetics and molecular weight distribution studies revealed that the polymerization followed the micellization nucleation mechanism. Results showed that an appropriate initiator concentration was necessary to obtain monodisperse and stable latex particles. Conversion of methylstyrene was found to increase significantly with increasing initiator concentrations. However, the size of PMS latex particles decreased with both the increase of initiator concentration and the reaction temperature at a constant ionic strength. The particle size was increased as the ionic strength of the aqueous phase increased, yet the variation of ionic strength had little effect on the particle size distribution. SEM micrographs showed that an agitation rate of 350 rpm or higher was required in order to produce highly monodispersed poly(methylstyrene) latex particles. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2069–2074, 1999     

Synthesis of latex particles with surface amino groups

Monodisperse latex particles with surface amino groups were prepared by a two‐step emulsion polymerization. In the first step, the seeds were synthesized by batch emulsion polymerization of styrene; and in the second step, two different amino‐functionalized monomers [aminoethylmethacrylate hydrochloride (AEMH) and vinylbenzylamine hydrochloride (VBAH)], two different initiator systems (K₂S₂O₈ and K₂S₂O₈/Na₂S₂O₅) and mixtures of emulsifiers sodium dodecylsulfate (SDS) and Tween 21 were used to synthesize the final latexes. To characterize the final latexes, conversions were obtained gravimetrically and particle size distributions and average particle diameters were determined by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). The amount of amino groups was determined by the SPDP (N‐succinimidyl 3‐(2‐pyridyldithio)propionate) method. The influence of the different conditions used to synthesize the latexes on the colloidal stability of the particles was evaluated by measuring the diameters of the final latexes dispersed in solutions at different pHs and ionic strengths. The most stable latexes were obtained using the smallest seed, VBAH monomer, and the K₂S₂O₈/Na₂S₂O₅ initiator system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4230–4237, 2000     

Synthesis of composite latex particles filled with silica

Encapsulation of silica nanoparticles was performed by dispersion polymerization of styrene, butyl acrylate and butyl methacrylate in aqueous alcoholic media. Following previous works^1‐3), the silica beads were first modified by reacting on their surface the 3‐trimethoxysilyl propyl methacrylate coupling agent (MPS). In every case, the silica beads are all surrounded by polymer giving composite latex particles filled with silica. Each composite particle contains from one to a great number of silica beads. Changing the size or the concentration of the silica beads, and the experimental conditions for the synthesis of the polymer particles enables to control this number. One can take benefit of this to synthesize model composite particles with controlled compositions.     

Surface functionalization of polymer latex particles. I. Catalytic oxidation of poly(methylstyrene) latex particles in the presence of an anionic surfactant

A facile synthesis of functionalized poly[3(4)-methylstyrene] (PMS) latex particles containing aldehyde and carboxylic acid groups was achieved via an emulsion polymerization of 3(4)-methylstyrene in the presence of sodium dodecyl sulfonate, followed by an in-situ oxidation catalyzed by copper(II) chloride and t-butyl hydroperoxide (t-BuOOH) in the presence of t-butyl alcohol (t-BuOH). The structure of the anionic surfactant, metal catalyst, organic solvent, oxidant, and their concentrations strongly affected the rate of oxidation and the stability of the emulsion. The average size of the polymer latex particles was found to increase after oxidation, and the polymer was slightly crosslinked. A free-radical mechanism is proposed involving metal-catalyzed decomposition of t-BuOOH and benzylic oxidation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1863–1872, 1997     

Interactions of hairy latex particles with cationic copolymers

Interactions between polycations and core-corona particles are governed by ion-exchange reactions, entropically favored by the release of counterions. This complexation process allows the chains to penetrate into the shell, leading to adsorbed amounts greater than 1 mg m(-2). The destabilization occurs quickly, the domain of flocculation becomes larger when the concentration of monovalent salts is increased, and aggregates are composed of small and very compact clusters in a more or less self-similar structure at large scale. The adsorption of copolymers of low cationicity is characterized by still larger adsorbed amounts and layers thicker than the radius of gyration of the macromolecules. Depending on the charge content, the enhancement of the ionic strength can either promote the destabilization of the suspension or conversely induce the desorption of the chain. In pure water the structure of the flocs is long-range ordered and it becomes more heterogeneous in ionic media.     

Film formation stages for poly(vinyl acetate) latex particles: a photon transmission study

Photon transmission technique was used to monitor the evolution of transparency during film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (T _g) of PVAc. These films were annealed at elevated temperatures in various time intervals above the T _g of PVAc. It is observed that transmitted photon intensity (I _tr) from these films increased as the annealing temperature is increased. It is seen from I _tr curves that there are two film formation stages. These successive stages are named void closure (viscous flow) and interdiffusion. The activation energies for viscous flow (ΔH) and backbone motion (ΔE _b) were obtained by using well-defined models. The averaged values of the backbone (ΔE _b) and the viscous flow activation energies (ΔH) were found to be 188.6 and 5.6 kcal/mol, respectively. The minimum film formation (τ _M,T _M) and healing points (τ _H,T _H) were determined. Minimum film formation (ΔE _M) and healing activation energies (ΔE _H) were measured using these time–temperature pairs. ΔE _M and ΔE _H were found to be 32.5 and 28.3 kcal/mol, respectively.     

Morphology control in polystyrene/poly(methyl methacrylate) composite latex particles

The effect of the presence of different amounts of block copolymers [polystyrene-block-poly(methyl methacrylate)] on the morphology of polystyrene/poly (methyl methacrylate) composite latex particles was investigated. The block copolymers were produced in situ by controlled radical polymerization (CRP) through the addition of the second monomer to a seed prepared by miniemulsion polymerization with a certain amount of a CRP agent. With an increase in the amounts of the block copolymers, the particle morphology changed from a hemisphere morphology (for a latex without block copolymers, i.e., without the use of a CRP agent during the polymerization) to clear core–shell morphologies as a result of decreasing polymer–polymer interfacial tension © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2484–2493, 2007     

Interactions between dextran-modified poly(methyl methacrylate) latex particles and concanavalin A

The electrostatic and affinity interactions between concanavalin A (Con A) and dextran-modified latex particles were investigated. The ratio of the initial number of dextran active sites to that of Con A molecules plays an important role in determining the structure of flocs formed during adsorption and, thereby, has an influence on the amount of adsorbed Con A and the subsequent elution yield. NaCl and d-glucose, used successively in the two-step desorption of Con A, were employed to study the relative importance of electrostatic and affinity interactions involved in the Con A adsorption process. A significant fraction of adsorbed Con A is attributed to the electrostatic interaction mechanism. The feasibility of using the dextran-modified latex products to purify Con A from Jack bean meal was demonstrated. Received: 22 February 2000 Accepted: 19 September 2000     

The properties of covalently immobilized trypsin on soap-free P(MMA-EA-AA) latex particles

The covalent immobilization of trypsin onto poly[(methyl methacrylate)-co-(ethyl acrylate)-co-(acrylic acid)] latex particles, produced by a soap-free emulsion polymerization technique, was carried out using the carbodiimide method. The catalytic properties and kinetic parameters, as well as the stability of the immobilized enzyme were compared to those of the free enzyme. Results showed that the optimum temperature and pH for the immobilized trypsin in the hydrolysis of casein were 55 degrees C and 8.5, both of which were higher than that of the free form. It was found that K(m) (Michaelis constant) was 45.7 mg . ml(-1) and V(max) (maximal reaction rate) was 793.0 microg . min(-1) for immobilized trypsin, compared to a K(m) of 30.0 mg . ml(-1) and a V(max) of 5 467.5 microg . min(-1) for free trypsin. The immobilized trypsin exhibited much better thermal and chemical stabilities than its free counterpart and maintained over 63% of its initial activity after reusing ten times.     

Seeded polymerization of vinyl acetate using monodisperse poly(vinyl acetate) latex particles

The seeded polymerizations of vinyl acetate, using monodisperse poly(vinyl acetate) latex particles prepared in the absence of emulsifiers with potassium persulfate, have been investigated at 70°C with potassium persulfate as an initiator. New small particles were formed in the system containing a small amount of seed particles, but were not observed in the system containing a large amount of seed particles. The size of the secondary particles increased, and their number decreased, with an increase in the seed particle number. The minimum diameter of PVAc particles, which are stabilized by the sulfate ion groups bound at the end of polymer chains during polymerization, was determined to be 0.12 μm diameter from the limiting total surface area of seed particles which prevented further secondary nucleation. The minimum diameter of the particles increased as the speed of the stirrer increased. The new small particle number calculated using this value agreed well with that formed in the seeded polymerization.     

Interaction of cetyl-trimethylammonium bromide with swollen and collapsed poly(N-isopropylacrylamide) nanogel particles

The interaction of cetyl-trimethylammonium bromide (CTAB) with swollen and collapsed poly(N-isopropylacrylamide) (pNIPAM) monodisperse nanogel particles was investigated by electrophoretic mobility, dynamic light scattering, and potentiometric surfactant activity measurements. The surfactant binds to the nanogel particles as monomers in the whole CTAB concentration range and binds in the form of surfactant aggregates as well above a critical concentration (cac) in both the swollen and collapsed state of the pNIPAM. The swollen particle system is a thermodynamically stable solution. The collapsed nanogel particle system is an electrically stabilized colloid dispersion, which coagulates when the particles are near the electrically neutral state. An analytically undetectably small amount of surfactant binding (5 × 10(-7) mol/g of pNIPAM) leads to a dramatic effect on the stability of the pNIPAM nanogel system. The electrokinetic potential versus surfactant concentration functions unexpectedly strongly depend upon the temperature around the lower critical solution temperature (LCST) of the polymer, which was interpreted by the change of the polymer segment density in the surface layer of the collapsing nanogel particles.     

Interaction between poly(styrene-acrylic acid) latex nanoparticles and zinc oxide surfaces

Latex particles with an average diameter of 70 nm, functionalized at the surface with carboxylic groups, are chemically coated by layer-by-layer deposition onto a spherical probe attached on an atomic force microscope cantilever. The forces between poly(styrene-acrylic acid) latex nanoparticles and differently terminated zinc oxide surfaces are studied by a homemade atomic force microscope based apparatus. The results confirmed a preferred adhesion of the latex particles to zinc-terminated ZnO faces, 0001, compared to oxygen-terminated and apolar faces. The method proposed allows the measurement of the interaction between nanometric particles and planar surfaces, which may be of interest for different applications in surface and colloid sciences.