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Alison Paul

Publications and source records attributed to Alison Paul.

9 recordsLinked to original sources
PubMed2006

Fluorosurfactants at structural extremes: adsorption and aggregation.

Fluorosurfactants with several structural modifications have been synthesized, and the air/water interface and bulk aggregation properties investigated. The compounds were fluorinated ethylene oxide (EO) nonionics where the number and position of the hydrophilic group(s) has been radically altered to generate linear, bolaform, and Y-shaped analogues. A noticeable structure-interfacial packing relationship was observed via both tensiometric measurements and neutron reflection studies: the limiting molecular areas, a(cmc), and surface excesses, gamma(cmc), are strongly dependent on the number and position of the EO headgroups. Differing bulk aqueous properties were also observed. Small-angle neutron scattering shows an evolution of micelle structure from cylindrical to disk-like aggregates on changing from Y-shaped to bolaform molecular structure.

Journal Article↗
PubMed2006

Sir William Dunn (1833-1912): the man, his trust and his legacy to science and medicine.

William Dunn had no direct connections with medicine. He belonged to that Victorian generation of Scottish pioneers who went overseas to make their fortunes and, yet, devoted their money to numerous charitable purposes, mainly at home in the UK. His family origins were modest; born in Paisley, near Glasgow on 1 September 1833, he died in 1912 with an estate valued at 1.3 million pounds sterling. His fortune was made from a large worldwide trading empire with roots in South Africa, where he emigrated as a young man of 19--but later controlled from London. In his will, dated 4 November 1908, the key clause was 'to advance the cause of Christianity, to benefit children and young people, to support hospitals and alleviate human suffering, to encourage education and promote emigration'. After making provision for about half the total, he left the remainder in the hands of trustees. They allotted about 120 small sums to hospitals, nursing homes, orphanages and like institutions, but then decided that larger projects would be more likely to be permanent memorials to Sir William. After consulting the President of the Royal Society, Sir William Hardy, and the Secretary of the Medical Research Committee, Sir Walter Fletcher, the trustees gave 210,000 pounds sterling in 1920 to Sir Frederick Gowland Hopkins in biochemistry in Cambridge and 100,000 pounds sterling in 1922 to Professor Georges Dreyer in pathology in Oxford. Between them, these two laboratories have 'spawned' nine Nobel Prize winners. The 'alleviation of human suffering' achieved would surely have pleased Sir William and his trustees.

Biomedical Research↗
PubMed2005

What is so special about aerosol-OT? Part IV. Phenyl-tipped surfactants.

Properties are reported for new phenyl-tipped anionic surfactants, which are aromatic chain relatives of the normal aliphatic aerosol-OT (AOT, sodium bis(2-ethyl-1-hexyl)sulfosuccinate). Variations in chain length and branching with these aromatic surfactants have important effects on aqueous and water-in-oil (w/o) microemulsion phase properties. In dilute aqueous systems, chain structure affects the cmc and surface tension behavior: compared to linear chain analogues, the branched-chain surfactants display lower surface tensions but also reduced packing as measured by molecular area at the cmc a(cmc). Owing to the phenyl-tipped structure, water-in-oil microemulsions were stabilized with aromatic toluene as an oil but not with aliphatic heptane; the latter is commonly used with normal AOT. Contrast variation small-angle neutron scattering (SANS) was used to characterize the microemulsion aggregates and adsorbed films. These SANS data show that water-in-toluene microemulsions stabilized by aromatic-AOTs contain mildly polydisperse spherical nanodroplets of similar structure to those found in systems containing normal AOT. Molecular areas at the air-water and toluene-water interfaces are found to be of similar magnitude and follow a trend that correlates with variations in surfactant chain structure. The new results with aromatic surfactants build on extensive studies of aliphatic AOT analogues (Nave, S.; Eastoe, J.; Penfold, J. Langmuir 2000, 16, 8733. Nave, S.; Eastoe, J.; Heenan, R. K.; Steytler, D.; Grillo, I. Langmuir 2002, 16, 8741. Nave, S.; Eastoe, J.; Heenan, R. K.; Steytler, D.; Grillo, I. 2002, 18, 1505), suggesting that the versatility of normal AOT originates from an optimized head and chain spacer group rather than from any specific effects of the 2-ethyhexyl chain structure.

Journal Article↗
PubMed2005

Ionic liquid-in-oil microemulsions.

Phase stability and small-angle neutron scattering (SANS) data show that surfactant-stabilized nanodomains of a typical ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4]) may be dispersed by the nonionic surfactant Triton-X100 in cyclohexane. Analyses of these SANS data are consistent with the formation of ionic liquid-in-oil microemulsion droplets.

Journal Article↗
PubMed2005

Photo-stabilised microemulsions.

Light-induced stabilisation of water-in-heptane microemulsions has been achieved with a UV-sensitive gemini photo-surfactant.

Journal Article↗
PubMed2005

Explaining the phase behaviour of the pharmaceutically relevant polymers poly(ethylene glycol) and poly(vinyl pyrrolidone) in semi-fluorinated liquids.

Phase behaviour studies of low molecular weight poly(ethylene glycol) (denoted PEG 600 and PEG 1000, corresponding to molecular weights of 600 and 1000 g mol(-1), respectively) have been carried out in 2H,3H-perfluoropentane (HPFP) with and without added poly(vinyl pyrrolidone). The concentration and temperature dependencies of their phase behaviour and the effect of moisture on these systems have been established. Furthermore, the solubility of PEG 600 in binary mixtures of HPFP and perfluoropentane (PFP), as well as HPFP and perfluorodecalin (PFD) have been considered at high HPFP contents. A phase separation phenomenon in fluorinated non-aqueous media is reported for the first time: PEG 600 and PEG 1000 both show a lower critical solution temperature type phase separation boundary. The size of the PEGs was obtained from small-angle neutron scattering (radius of gyration) and pulsed-gradient spin-echo NMR (hydrodynamic radius) measurements. It is shown that polymer conformation follows a regular trend with solution concentration; the size increases from <10 A at 3 wt% in HPFP to 45 +/- 2 A at 20 wt% PEG. On changing the solvent composition by substitution of HPFP by PFP or PFD, the size decreases, consistent with a decrease in the hydrogen-bonding capacity of the solvent mixture. Computer modelling indicates an interaction between the PEG oxygen and the hydrogen of HPFP, an interaction that is absent for the fully fluorinated solvents. This indicates that hydrogen bonding is the driving force for polymer solubility in these solvents.

Chemistry, Pharmaceutical↗
PubMed2005

Towards an understanding of adsorption behaviour in non-aqueous systems: adsorption of poly(vinyl pyrrolidone) and poly(ethylene glycol) onto silica from 2H, 3H-perfluoropentane.

The adsorption behaviour of low molecular weight poly(ethylene glycol) (PEG 600) and poly(vinyl pyrrolidone) (PVP K25) to silica particles has been investigated at room temperature (21 degrees C) in the partially fluorinated solvent 2H,3H-perfluoropentane (HPFP). PVP (absorbed amount, Gamma = 12 mg g(-1)) was found to adsorb more strongly than PEG (Gamma = 4 mg g(-1)). Both of these values were higher than observed in water. In a further distinction to the aqueous case, where PVP displaces PEG from the interface, no competitive adsorption effects were observed between these two polymers in HPFP, with the adsorbed amounts of each polymer being unchanged by the presence of the other. The stability of silica suspensions in HPFP was primarily dependent on the presence of PVP; PEG/silica systems were unstable, but PVP/silica and PEG/PVP/silica systems formed stable suspensions. All suspensions were destabilized by the addition of small (0.15 wt%) amounts of water. The observations made in this work would point to a flocculation phenomenon due to the addition of water, and not Ostwald ripening. The mechanism of this destabilization is likely to be water acting as a flocculation bridge between particles.

Adsorption↗
PubMedDate not supplied

Poly(amidoamine) salt form: effect on pH-dependent membrane activity and polymer conformation in solution.

On exposure to an acidic pH, linear poly(amidoamine)s (PAAs) cause membrane perturbation and consequently have potential as endosomolytic polymers for the intracellular delivery of genes and toxins. Previous studies used PAAs in the hydrochloride form only. The aim of this study was to investigate systematically the effect of the PAA counterion on pH-dependent membrane activity, general cytotoxicity, and PAA solution properties to help guide optimization of PAA structure for further development of PAA-protein conjugates. PAAs (ISA 1, 4, 22, and 23; M(w) 10000-50000 g/mol) were synthesized to provide a library of PAAs having different counterions including the acetate, citrate, hydrochloride, lactate, phosphate, and sulfate salts. pH-Dependent membrane activity was assessed using a rat red blood cell haemolysis assay (conducted at a starting pH of 7.4, 6.5, or 5.5; 1 mg/mL; 1 h), and general cytotoxicity was investigated using a murine melanoma cell line (B16F10) and a human bladder endothelial-like cell line (ECV-304). Whereas poly(ethyleneimine) was haemolytic at the starting pH of 7.4 at 1 h [ approximately 50% haemoglobin (Hb) release], none of the PAA salts were haemolytic at a starting pH of 7.4 or 6.5. Although PAA acetate, citrate, and lactate were also non-haemolytic at the starting pH of 5.5, the sulfate and hydrochloride forms caused significant haemolysis (up to 80% Hb release) and ISA 22 and 23 phosphate were also markedly haemolytic ( approximately 70% Hb release). These counterion-specific differences were also clearly visible using scanning electron microscopy, which was used to visualize the red blood cell morphology. All PAAs were relatively nontoxic (IC(50) >or= 300-5000 microg/mL) compared to poly-l-lysine (IC(50) = 2-10 microg/mL), the PAA hydrochloride salts produced the greatest cytotoxicity, and the B16F10 cells were more sensitive than the ECV-304 cells. Small-angle neutron scattering suggested that ISA 23 hydrochloride had a larger hydrodynamic radius (5.1 +/- 0.2 nm) than the citrate salt (3.1 +/- 0.2 nm). These results provide indirect evidence for the salt- and pH-dependent changes in the conformation of the polymer coil. This study clearly demonstrates the importance of optimization of the counterion form when developing endosomolytic polymers designed to mediate pH-dependent membrane permeabilization.

Erythrocyte Membrane↗