Probing the surfaces of core-shell and hollow nanoparticles by solvent relaxation NMR.

Measurement of the spin-spin NMR relaxation time (or its inverse, the rate) of water molecules in aqueous nanoparticle dispersions has become a popular approach to probe of the nature and structure of the particle surface and any adsorbed species. Here, we report on the characterisation of aqueous dispersions of hollow amorphous nanoparticles that have two liquid accessible surfaces (inner cavity surface and outer shell surface) plus the solid (silica) and core-shell (titania-silica) nanoparticle precursors from which the hollow particles have been prepared. In all cases, the observed water relaxation rates scale linearly with particle surface area, with the effect being more pronounced with increasing levels of titania present at the particle surface. Two distinct behaviours were observed for the hollow nanoparticles at very low volume fractions, which appear to merge with increasing surface area (particle concentration). Herewith, we further show the versatility of solvent NMR spectroscopy as a probe of surface character.

Investigation of gammaE-crystallin target protein binding to bovine lens alpha-crystallin by small-angle neutron scattering.

alpha-Crystallin, one of the main constituent proteins in the crystalline lens, is an important molecular chaperone both within and outside the lens. Presently, the structural relationship between alpha-crystallin and its target proteins during chaperone action is poorly understood. It has been hypothesised that target proteins bind within a central cavity. Small-angle neutron-scattering (SANS) experiments in conjunction with isotopic substitution were undertaken to investigate the interaction of a target lens protein (gammaE-crystallin) with alpha-crystallin (alpha(H)) and to measure the radius of gyration (Rg) of the proteins and their binary complexes in solution under thermal stress. The size of the alpha(H) in D(2)O incubated at 65 degrees C increased from 69+/-3 to 81+/-5 A over 40 min, in good agreement with previously published small-angle X-ray scattering (SAXS) and SANS measurements. Deuterated gammaE-crystallin in H(2)O buffer (gammaE(D)/H(2)O) and hydrogenous gammaE-crystallin in D(2)O buffer (gammaE(H)/D(2)O) free in solution were of insufficient size and/or too dilute to provide any measurable scattering over the angular range used, which was selected primarily to investigate gammaE:alpha(H) complexes. The evolution of the aggregation size/shape as an indicator of alpha(H) chaperone action was monitored by recording the neutron scattering in different H:D solvent contrasts under thermally stressed conditions (65 degrees C) for binary mixtures of alpha(H), gammaE(H), and gammaE(D). It was found that Rg(alpha(H):gammaE(D)/D(2)O)>Rg(alpha(H):gammaE(H)/D(2)O)>Rg(alpha(H)/D(2)O) and that Rg(alpha(H):gammaE(H)/D(2)O) approximately Rg(alpha(H)/D(2)O). The relative sizes observed for the complexes weighted by the respective scattering powers of the various components imply that gammaE-crystallin binds in a central cavity of the alpha-crystallin oligomer, during chaperone action.

Polymorphisms of the prion protein gene coding region in born-after-the-reinforced-ban (BARB) bovine spongiform encephalopathy cattle in Great Britain.

Polymorphisms of the prion protein gene are associated with differing susceptibilities to transmissible spongiform encephalopathy diseases, as shown for variant Creutzfeldt-Jakob disease in humans and scrapie in sheep, but not yet in cattle. Imposition of control measures in the UK, including a reinforced ruminant feed ban in 1996, has led to a reduction in the incidence of bovine spongiform encephalopathy (BSE). BSE-affected cattle born after 1996 in Great Britain have been termed born-after-the-reinforced-ban (BARB) cases. In this study, the PrP gene coding region from 100 BARB BSE cases and 66 matched healthy-control cattle was sequenced to investigate whether this would reveal a genetic basis to their origin. Polymorphisms identified were not found to be associated with increased susceptibility to BSE in the BARB cases. Analysis of BARB cases grouped either by clinical status or by whether they formed an isolated or clustered case was also undertaken, but differences were not found to be significant.

Metallosurfactants: interfaces and micelles.

Incorporating a metal cation as an integral component of the headgroup of a surfactant--a metallosurfactant--offers a route to concentrate these ions and their associated functionality at interfaces. To reduce the lability of the metal, various chelating or macrocyclic ligands may be employed leading to a family of homologous series of related metallosurfactants with a structural diversity that is arguably broader than is inherently possible with conventional surfactants. This review discusses the small number of key papers that are quantifying the physico-chemical properties of metallosurfactants and highlights their "classical" as well as "non-classical" surfactant behaviour, providing an insight into the structure of micelles and films formed from these novel materials.

An investigation into the role of Chlamydophila spp. in bovine upper respiratory tract disease.

An outbreak of upper respiratory tract disease was investigated in a group of 17 housed home-bred calves on a mixed dairy, beef and sheep farm in Devon. Conjunctival swabs were collected and tested for Chlamydophila spp. DNA using a PCR test that detects Chlamydophila abortus and Chlamydophila psittaci. Six of the calves tested gave a positive result. Further epidemiological observations and laboratory testing indicated that the adult dairy cows, from which the affected calves originated, were the most likely source of infection.

Which are the polyphosphate accumulating organisms in full-scale activated sludge enhanced biological phosphate removal systems in Australia?

AIMS: To see if the compositions of the microbial communities in full scale enhanced biological phosphorus removal activated sludge systems were the same as those from laboratory scale sequencing batch reactors fed a synthetic sewage. METHODS: Biomass samples taken from nine full scale enhanced biological phosphate removal (EBPR) activated sludge plants in the eastern states of Australia were analysed for their populations of polyphosphate (polyP)-accumulating organisms (PAO) using semi-quantitative fluorescence in situ hybridization (FISH) in combination with DAPI (4'-6-diamidino-2-phenylindole) staining for polyP. RESULTS: Very few betaproteobacterial Rhodocyclus related organisms could be detected by FISH in most of the plants examined, and even where present, not all these cells even within a single cluster, stained positively for polyP with DAPI. In some plants in samples from aerobic reactors the Actinobacteria dominated populations containing polyP. CONCLUSIONS: The PAO populations in full-scale EBPR systems often differ to those seen in laboratory scale reactors fed artificial sewage, and Rhodocyclus related organisms, dominating these latter communities may not be as important in full-scale systems. Instead Actinobacteria may be the major PAO. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings illustrate how little is still known about the microbial ecology of EBPR processes and that more emphasis should now be placed on analysis of full-scale plants if microbiological methods are to be applied to monitoring their performances.

Electrophoretic NMR studies of polymer and surfactant systems.

The aim of this tutorial review is to introduce to a broader readership the emerging technique of electrophoretic NMR (eNMR). The "electrophoretic" element of the technique refers to the fact that charged particles are induced to flow by the application of an electric field. This flow is measured using pulsed-gradient spin-echo NMR (PGSE-NMR). The great potential of this experimental approach is the fact that NMR is chemically selective and non-invasive. eNMR, especially when combined with the more established PGSE-NMR experiment, may therefore be used to quantify the structure of multi-component systems via the dynamics and charge of each species within a complex mixture. Accordingly, eNMR is likely to be of great significance for colloid scientists, biologists, technologists and formulation scientists.

Gelation of fluorinated liquids by non-fluorinated low-molecular-mass molecules.

A family of tetrahydroxy diesters has been synthesised and observed to gel a range of fluorinated solvents and their mixtures; the phase behaviour and gel microstructure are reported for a homologous family of these diesters in blends of 1H,1H-heptafluorobutanol (HFB) and 2H,3H-perfluoropentane (HPFP).

Nuclear magnetic resonance and small-angle neutron scattering studies of anionic surfactants with macrocounterions: tetramethylammonium dodecyl sulfate.

Micellar solutions of tetramethylammonium dodecyl sulfate have been studied to determine the degree of counterion binding. Tetramethylammonium chloride was added over a wide range of surfactant concentrations such that the total concentration of tetramethylammonium ions in solution remained constant. Small angle neutron scattering experiments showed a constancy in aggregation number across this series, consistent with the constant C(aq) concept of Bales et al. (J. Phys. Chem. B 2001, 105, 6798). Pulsed-field gradient and electrophoretic NMR experiments were used to determine the degree of counterion dissociation, alpha, which was found to be 0.33. This value is in contrast to the value from conductivity measurements (alpha = 0.2), but supports the concept of an aggregation number based definition of alpha.

Variegated micelle surfaces: correlating the microstructure of mixed surfactant micelles with bulk solution properties.

Electron paramagnetic resonance, viscosity, and small-angle neutron scattering (SANS) measurements have been used to study the interaction of mixed anionic/nonionic surfactant micelles with the polyampholytic protein gelatin. Sodium dodecyl sulfate (SDS) and the nonionic surfactant dodecylmalono-bis-N-methylglucamide (C12BNMG) were chosen as "interacting" and "noninteracting" surfactants, respectively; SDS micelles bind strongly to gelatin but C12BNMG micelles do not. Further, the two surfactants interact synergistically in the absence of the gelatin. The effects of total surfactant concentration and surfactant mole fraction have been investigated. Previous work (Griffiths et al. Langmuir 2000, 16 (26), 9983-9990) has shown that above a critical solution mole fraction, mixed micelles bind to gelatin. This critical mole fraction corresponds to a micelle surface that has no displaceable water (Griffiths et al. J. Phys. Chem. B 2001, 105 (31), 7465). On binding of the mixed micelle, the bulk solution viscosity increases, with the viscosity-surfactant concentration behavior being strongly dependent on the solution surfactant mole fraction. The viscosity at a stoichiometry of approximately one micelle per gelatin molecule observed in SDS-rich mixtures scales with the surface area of the micelle occupied by the interacting surfactant, SDS. Below the critical solution mole fraction, there is no significant increase in viscosity with increasing surfactant concentration. Further, the SANS behavior of the gelatin/mixed surfactant systems below the critical micelle mole fraction can be described as a simple summation of those arising from the separate gelatin and binary mixed surfactant micelles. By contrast, for systems above the critical micelle mole fraction, the SANS data cannot be described by such a simple approach. No signature from any unperturbed gelatin could be detected in the gelatin/mixed surfactant system. The gelatin scattering is very similar in form to the surfactant scattering, confirming the widely accepted picture that the polymer "wraps" around the micelle surface. The gelatin scattering in the presence of deuterated surfactants is insensitive to the micelle composition provided the composition is above the critical value, suggesting that the viscosity enhancement observed arises from the number and strength of the micelle-polymer contact points rather than the gelatin conformation per se.

Effect of ethanol on the interaction between poly(vinylpyrrolidone) and sodium dodecyl sulfate.

The effect of ethanol on the interaction between the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic polymer poly(vinylpyrrolidone) (PVP) has been investigated using a range of techniques including surface tension, fluorescence, electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS), and viscosity. Surface tension and fluorescence studies show that the critical micelle concentration (cmc) of the surfactant decreases to a minimum value around 15 wt % ethanol; that is, it follows the cosurfactant effect. However, in the presence of PVP, the onset of the interaction, denoted cmc(1), between the surfactant and the polymer is considerably less dependent on ethanol concentration. The saturation point, cmc(2), however, reflects the behavior of the cmc in that it decreases upon addition of ethanol. This results in a decrease in the amount of surfactant bound to the polymer [C(bound) = cmc(2) - cmc] at saturation. The viscosity of simple PVP solutions depends on ethanol concentration, but since SANS studies show that ethanol has no effect on the polymer conformation, the changes observed in the viscosity reflect the viscosity of the background solvent. There are significant increases in bulk viscosity when the surfactant is added, and these have been correlated with the polymer conformation extracted from an analysis of the SANS data and with the amount of polymer adsorbed at the micelle surface. Competition between ethanol and PVP to occupy the surfactant headgroup region exists; at low ethanol concentration, the PVP displaces the ethanol and the PVP/SDS complex resembles that formed in the absence of the ethanol. At higher ethanol contents, the polymer does not bind to the ethanol-rich micelle surface.

Understanding the mechanism of action of poly(amidoamine)s as endosomolytic polymers: correlation of physicochemical and biological properties.

Bioresponsive poly(amidoamine)s (PAA)s are currently under development as endosomolytic polymers for intracellular delivery of proteins and genes. Here for the first time, small-angle neutron scattering (SANS) is used to systematically investigate the pH-dependent conformational change of an endosomolytic polymer, the PAA ISA 23. The radius of gyration of the ISA23 was determined as a function of pH and counterion, the aim being to correlate changes in polymer conformation with membrane activity assessed using a rat red blood cell haemolysis assay. With decreasing pH, the ISA23 radius of gyration increased to a maximum (R(g) approximately 80 A) around pH = 3, before subsequently decreasing once more. At high pH and therefore high ionic strengths, the polymer is negatively charged and adopts a rather compact structure (R(g) approximately 20 A), presumably with the dissociated carboxylic groups on the exterior of the polymer coil. At low pH, the coil again collapses (R(g) < 20 A), presumably due to the effects of the high ionic strength. It is concluded that the nature of the salt form has no direct bearing on the size of the polymer coil, but it does indirectly determine the prevailing pH and, hence, polymer conformation. Pulsed-gradient spin-echo NMR measurements were in good agreement with the SANS estimates of the radius of gyration, although ISA23 polydispersity does complicate the data interpretation/comparison. These results support the proposed mode of action of PAAs, namely a coil expansion on passing from a neutral pH (extracellular) to an acidic pH (endosomal and lysosomal) environments. The results do, however, suggest that the charge on the polymer shows a closer correlation with the haemolysis activity rather than the polymer conformation.

The structure of metallomicelles.

The morphology of micelles formed by two novel metallosurfactants has been studied by small-angle neutron scattering (SANS) and small-angle-X-ray scattering (SAXS). The two surfactants both contain a dodecyl chain as the hydrophobic moiety, but differ in the structure of the head group. The surfactants are Cu(II) complexes of monopendant alcohol derivatives of a) the face-capping macrocycle 1,4,7-triazacyclanonane (tacn), and b) an analogue based upon the tetraazamacrocycle 1,4,7,10-tetraazacyclododecane. Here, neutron scattering has been used to study the overall size and shape of the surfactant micelles, in conjunction with X-ray scattering to locate the metal ions. For the 1,4,7,10-tetraazacyclododecane-based surfactant, oblate micelles are observed, which are smaller to the prolate micelles formed by the 1,4,7-triazacyclononane analogue. The X-ray scattering analysis shows that the metal ions are distributed throughout the polar head-group region, rather than at a well-defined radius; this is in good agreement with the SANS-derived dimensions of the micelle. Indeed, the same model for micelle morphology can be used to fit both the SANS and SAXS data.

Rheology of aqueous carbon black dispersions.

The interaction of carbon black with an acrylic resin has been investigated by rheology. Two carbon blacks, with similar particle size and surface characteristics but quite different particle morphologies, have been examined. These are somewhat arbitrarily denoted as "spherical" and "fractal" as shown by small-angle neutron scattering (SANS) and ultrasonic spectroscopy studies. In the absence of polymer, stable aqueous dispersions could not be obtained. Stable dispersions could be obtained, however, upon addition of polymer to a level corresponding to a ratio of 50 mg of polymer per 13 m2 (+/- m2) of surface area (i.e., 15 wt% particles). These stable dispersions exhibit flow typical of concentrated dispersions-Newtonian behavior up to some apparent "yield" or critical value, above which pronounced shear thinning is observed. The critical stress increases with increasing polymer concentration. When a significant amount of nonadsorbed polymer is also present, a second Newtonian plateau is superimposed on the shear-thinning behavior. This feature is observed for both particle types but is more pronounced for the fractal particle. When there is little or no nonadsorbed polymer, the viscosity of the fractal particle dispersions is greater than the viscosity of the spherical particle dispersions. At low polymer concentrations, the dispersions are predominantly viscous at low shear stresses. The phase angle decreases significantly over a narrow shear stress range and the rheology tends to more elastic behavior. At higher shear stresses, the dependence on particle morphology is weak.

Interaction between a partially fluorinated alkyl sulfate and gelatin in aqueous solution.

The interaction of a partially fluorinated alkyl sulfate, sodium 1H,1H,2H,2H-perfluorooctyl sulfate (C6F13CH2CH2OSO3Na), with the polyampholyte gelatin has been examined in aqueous solution using surface tension and small-angle neutron scattering (SANS). The 19F chemical shift of each fluorine environment in the surfactant is unaltered by the addition of gelatin, indicating that there is no contact between the gelatin and the fluorocarbon core of the micelle. The chemical shift of the two methylene groups closest to the headgroup is altered when gelatin is present, disclosing the location of the polymer. The critical micelle concentration (cmc) of the surfactant, cmc = 17+/-1 mM, corresponds to an effective alkyl chain (CnH2n+1) length of n = 11. In the presence of gelatin, the cmc is substantially reduced as expected, cmc(1) = 4+/-1 mM, which is also consistent with an effective alkyl chain length of n = 11. In the presence of the fluorosurfactant, the monotonic decay of the SANS from the gelatin-only system is replaced by a substantial peak at an intermediate Q value mirroring the micellar interaction. At low ionic strengths, the gelatin/micelle complex can be described by an ellipsoid. At higher ionic strengths, the electrostatic interaction between the micelles is screened and the peak in the gelatin scattering disappears. The correlation length describing the network structure decreases with increasing SDS concentration as the bound micelles promote a collapse of the network.

Environmental factors contributing to the "G bacteria" population in full-scale EBPR plants.

A survey of several enhanced biological phosphorus removal (EBPR) plants within Australia has demonstrated that a group of bacteria known as the "G" bacteria are able to proliferate under a broad range of plant configurations. The diverse designs and operational parameters of these plants did not permit definitive determination of the factor(s) contributing to the proliferation of G bacteria. Two plants were monitored over time to assess the G bacteria and phosphorus accumulating organisms (PAO) populations in relation to key operational parameters. The mixed liquor biomass and operational parameters were compared to other plants successfully and unsuccessfully reducing phosphorus from the wastewater. Two critical factors recognised in this study were the dissolved oxygen concentration in the aerobic zone and the type and amount of carbon source in the anaerobic zone.

Cell surface hydrophobicity and mycolic acid composition of Rhodococcus strains isolated from activated sludge foam.

The bacteria causing foaming in activated sludge plants are considered to be hydrophobic, and their hydrophobicity is assumed to be a crucial factor in their foam-forming ability. This study showed no consistent relationship between cell surface hydrophobicity (CSH), as determined by microbial adherence to hydrocarbons, of three Rhodococcus spp. isolated from activated sludge foam and their ability to produce a stable foam. There also appeared to be no correlation between the mycolic acid composition of these strains, in terms of chain length or degree of unsaturation, and either CSH or foaming ability. Zeolite and bentonite successfully prevented foaming by a Rhodococcus sp. in pure culture, which suggests that cell surface charge may also play a role in foam stabilisation.