Publications - 2009
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Pluronic triblock copolymer systems and their interactions with ibuprofen
Beth Foster, Terence Cosgrove and Boualem Hammouda
Langmuir (2009) 25, 6760-6766
DOI: 10.1021/la900298m
Abstract
Small-angle neutron scattering and pulsed-field gradient stimulated-echo nuclear magnetic resonance (NMR) have been used to study the structural characteristics of aqueous Pluronic solutions. In particular, changes in the micellar structure upon addition of ibuprofen to the solutions and altering the temperature have been investigated. Increases in temperature and ibuprofen concentration both appear to favor micellization, with increases observed in the aggregation number, fraction of polymer micellized, and core radius of the micelle, along with a decrease in the volume fraction of the solvent in the core. At high drug concentrations and/or temperatures, micelles of the more hydrophobic Pluronics scatter neutrons strongly at low Q, indicating attractive interactions between micelles or a change in the shape of the aggregates. The addition of ibuprofen to Pluronic P104 has also been found to reduce the critical micellization temperature from approximately 20 °C to below 13 °C. The hydrophobicity of the Pluronic, quantity of ibuprofen present, and temperature of the solution all seem to have a strong influence on the extent and nature of aggregation observed.
PFGSE-NMR study of pH-triggered behavior in pluronic-ibuprofen solutions
Beth Foster, Terence Cosgrove and Youssef Espidel
Langmuir (2009) 25, 6767-6771
DOI: 10.1021/la900299v
Abstract
The effect of drug addition and pH variation on Pluronic copolymer solutions has been investigated using pulsed-field gradient (PFG) NMR. Addition of ibuprofen to Pluronic P104 in solution reduced the overall pH from 7.5 to 4.5, as well as promoting micellization; a substantial increase in the hydrodynamic radius of the micelles, from 57.7 to 102.3 Å was observed, along with an increase in the fraction of polymer micellized. The aggregation behavior was attributed primarily to the presence of ibuprofen, rather than the reduction in pH observed, since the micellization of P104 alone was not found to be significantly altered by pH changes in the region of interest. Conversely, for the P104 solutions containing ibuprofen, a strong pH-dependence was observed when raising the pH above the pKa of ibuprofen. The data obtained showed that, above pH 4.5, ibuprofen is gradually released from the micelles as a result of its improved solubility, leading to a reduction in the polymer aggregation toward that observed before the addition of ibuprofen.
Locus-specific microemulsion catalysts for sulfur mustard (hd) chemical warfare agent decontamination.
Ian A. Fallis, Peter C. Griffiths, Terence Cosgrove, Cecile A. Dreiss, Norman Govan, Richard K. Heenan, Ian Holden, Robert L. Jenkins, Stephen J. Mitchell, Stuart Notman, Jamie A. Platts, James Riches, and Thomas Tatchell
J. Am. Chem. Soc. (2009) 131, 9746-9755
DOI: 10.1021/ja901872y
Abstract
The rates of catalytic oxidative decontamination of the chemical warfare agent (CWA) sulfur mustard (HD, bis(2-chlororethyl) sulfide) and a range (chloroethyl) sulfide simulants of variable lipophilicity have been examined using a hydrogen peroxide-based microemulsion system. SANS (small-angle neutron scattering), SAXS (small-angle X-ray scattering), PGSE-NMR (pulsed-gradient spin?echo NMR), fluorescence quenching, and electrospray mass spectroscopy (ESI-MS) were implemented to examine the distribution of HD, its simulants, and their oxidation/hydrolysis products in a model oil-in-water microemulsion. These measurements not only present a means of interpreting decontamination rates but also a rationale for the design of oxidation catalysts for these toxic materials. Here we show that by localizing manganese?Schiff base catalysts at the oil droplet?water interface or within the droplet core, a range of (chloroethyl) sulfides, including HD, spanning some 7 orders of octanol?water partition coefficient (Kow), may be oxidized with equal efficacy using dilute (5 wt. % of aqueous phase) hydrogen peroxide as a noncorrosive, environmentally benign oxidant (e.g., t1/2 (HD) 18 s, (2-chloroethyl phenyl sulfide, C6H5SCH2CH2Cl) 15 s, (thiodiglycol, S(CH2CH2OH)2) 19 s {20 °C}). Our observations demonstrate that by programming catalyst lipophilicity to colocalize catalyst and substrate, the inherent compartmentalization of the microemulsion can be exploited to achieve enhanced rates of reaction or to exert control over product selectivity. A combination of SANS, ESI-MS and fluorescence quenching measurements indicate that the enhanced catalytic activity is due to the locus of the catalyst and not a result of partial hydrolysis of the substrate.
Poly(ethylene oxide) adsorption on polystyrene latex particles in the presence of poly(styrenesulfonate sodium).
Dong Qiu, Terence Cosgrove, Patricia Revell, and Ian Howell
Macromolecules (2009) 42, 547-552
DOI: 10.1021/ma802237p
Abstract
The effect of a polyelectrolyte, poly(styrenesulfonate sodium) (PSS), on poly(ethylene oxide) (PEO) adsorption on the polystyrene latex (PSL) particle/water interface at different sodium chloride (NaCl) concentrations has been investigated by small-angle neutron scattering (SANS). Our study shows that in the absence of NaCl or with a low NaCl concentration, PSS forms a complex with PEO in the bulk solution and therefore strips PEO off from the latex particle surface because of the electrostatic repulsion between the latex particles and the PEO/PSS complexes. With increasing NaCl concentration, the electrostatic repulsions between the PEO/PSS complexes and PSL particles are reduced, and at the same time, PEO/PSS complexes break down and PEO adsorption is enhanced. With a further increase in NaCl concentration, PSS itself starts to adsorb on the PSL particles and competes with the PEO adsorption, which is then reduced.
A small-angle neutron scattering and rheology study of the composite of chitosan and gelatin.
Yuan Wang, Dong Qiu, Terence Cosgrove, and Mark L. Denbow.
Colloids Surf. B (2009) 70, 254-258
DOI: 10.1016/j.colsurfb.2008.12.034
Abstract
The composite chitosan/gelatin solutions and films formed from these solutions were studied by rheological measurements, SANS and tensile tests. The relationship between the inter-molecule interactions with microstructure, rheological behaviour of a solution and eventually the mechanical performance of formed films was established. It was found that the complex formed between chitosan and gelatin was mainly through hydrogen bond but the size of the structure was also affected by electrostatic repulsions. The local structure (correlation length) and the global structure (large inhomogeneous structure size) in the composite solutions were found to be highly correlated to each other. It was also found that the interactions between these two polymers in solution were closely related to the mechanical properties of the formed films. This work will enable one to design films with desired mechanical properties through the combination of different polymers at optimum weight ratios.
Not all anionic polyelectrolytes complex with DTAB
Yuguo Cui, Robert Pelton, Terence Cosgrove, Robert Richardson, Sheng Dai, Stuart Prescott, Isabelle Grillo, Howard Ketelson, and David Meadows.
Langmuir (2009) 25, 13712-13717
DOI: 10.1021/la900563y
Abstract
The influence of hydroxypropyl guar (HPG), with and without boric acid, on dodecyltrimethyl ammonium bromide (DTAB) micellization was characterized by surface tension measurements, isothermal titration calorimetry, and small-angle neutron scattering. Although HPG is a nonionic water-soluble polymer, borate ions form weak bonds with HPG, transforming it into an anionic polyelectrolyte, HPG?borate. Surprisingly, the three independent measurements showed that HPG?borate does not promote DTAB micellization or phase separation normally seen when mixing oppositely charged polyelectrolytes and surfactants. However, the neutron scattering results suggested that HPG?borate binds to and flocculates existing DTAB micelles. The unusual behavior of HPG?borate with DTAB was underscored by showing that carboxymethyl guar (CMG) formed precipitates with DTAB.
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