Papers by Stephen Leharne
ABSTRACT Four synthetic surfactants, consisting of alkyi chains of either 16 or 18 carbon units, ... more ABSTRACT Four synthetic surfactants, consisting of alkyi chains of either 16 or 18 carbon units, with a polar head of either three or seven ethylene oxide units (termed C16(EO)3 C18(EO)3, C16(EO)7 and C18(EO)7) have been studied using thermal analysis in both their hydrated and non-hydrated states. The non-hydrated samples were investigated using differential thermal analysis (DTA), and dilute aqueous dispersions were studied using high-sensitivity differential scanning calorimetry (HSDSC). The non-hydrated (EO)3 surfactants exhibited a single melting transition, whilst the equivalent experiment for the (EO)7 systems revealed a pre-melting transition, which could be a change in crystal structure. Multiple transitions were observed with all of the hydrated samples following HSDSC investigation. These transitions are probably related to different levels of hydration of a non-homogeneous dispersion of the surfactant in the water. The following general conclusions were reached: the surfactants exhibit a phase transition at a temperature which is predominantly determined by the alkyl chain length, but the increasing chain length of the head group (polyoxyethylene) causes a decrease in transition temperature. It has proved possible to estimate the probable contribution to the enthalpy of transition that is associated with a methylene group and an ethylene oxide unit. This allows predictions to be made regarding the behaviour of similar surfactants. It was concluded that HSDSC is potentially of great value for studies of dilute solutions/dispersions of surfactants.
Drug Design, Development and Therapy, 2015
The aim of the work reported herein was to study the effect of glucosamine HCl (GlcN·HCl) on the ... more The aim of the work reported herein was to study the effect of glucosamine HCl (GlcN·HCl) on the bioactivity (BA) of insulin, administered via subcutaneous (SC) and oral routes, in adult male Sprague Dawley rats. The oral insulin delivery system (insulin-chitosan reverse micelle [IC-RM]) was prepared by solubilizing insulin-chitosan (13 kDa) polyelectrolyte complex in a RM system consisting of oleic acid, PEG-8 caprylic/capric glycerides, and polyglycerol-6-dioleate. The BA of insulin in vivo was evaluated by measuring blood glucose level using a blood glucose meter; the results revealed that the extent of hypoglycemic activity of SC insulin was GlcN·HCl dose dependent when they were administered simultaneously. A significant reduction in blood glucose levels (P<0.05) was found for the insulin:GlcN·HCl at mass ratios of 1:10 and 1:20, whereas lower ratios (eg, 1:1 and 1:4) showed no significant reduction. Furthermore, enhancement of the action of SC insulin was achieved by oral administration of GlcN·HCl for 5 consecutive days prior to insulin injection (P<0.05). For oral insulin administration via the IC-RM system, the presence of GlcN·HCl increased the hypoglycemic activity of insulin (P<0.05). The relative BA were 6.7% and 5.4% in the presence and absence of GlcN·HCl (ie, the increase in the relative BA was approximately 23% due to incorporating GlcN·HCl in the IC-RM system), respectively. The aforementioned findings offer an opportunity to incorporate GlcN·HCl in oral insulin delivery systems in order to enhance a reduction in blood glucose levels.
Geological Society, London, Engineering Geology Special Publications, 1998
Profiles of Drug Substances, Excipients and Related Methodology, 2011
Physical Chemistry Chemical Physics, 2009
The surface-enhanced Raman scattering (SERS) spectra of rhodanine adsorbed on silver nanoparticle... more The surface-enhanced Raman scattering (SERS) spectra of rhodanine adsorbed on silver nanoparticles have been examined using 514.5 and 632.8 nm excitation. There is evidence that, under the experimental conditions used, rhodanine undergoes a nanoparticle surface-induced reaction resulting in the formation of a dimeric species via the active methylene group in a process which is analogous to the Knoevenagel reaction. The experimental observations are supported by DFT calculations at the B3-LYP/cc-pVDZ level. Calculated energies for the interaction of the E and Z isomers of the dimers of rhodanine with silver nanoparticles support a model in which the (intra-molecular hydrogen bonded) E isomer dimer is of lower energy than the Z isomer. A strong band, at 1566 cm(-1), in the SERS spectrum of rhodanine is assigned to the nu(C double bond C) mode of the dimer species.
Langmuir, 1997
A high-sensitivity differential scanning calorimetry (HSDSC) study of aggregation transitions in ... more A high-sensitivity differential scanning calorimetry (HSDSC) study of aggregation transitions in dilute aqueous solutions of oxyethylene-oxypropylene-oxyethylene (EO-PO-EO) triblock copolymers (poloxamers) is reported. The data have been analyzed using a previously ...
Langmuir, 1999
... ethylene oxide composition. In this respect it must be anticipated that the order of decreasi... more ... ethylene oxide composition. In this respect it must be anticipated that the order of decreasing hydrophobicity is P103 > P105 > P108, which is the order of decreasingsolubilization enhancement effectiveness. We can therefore ...
Journal of Radioanalytical and Nuclear Chemistry, 2005
Page 1. Introduction Dialkyl phthalate esters are a group of contaminants commonly detected in se... more Page 1. Introduction Dialkyl phthalate esters are a group of contaminants commonly detected in sediment, soil and water. They have been linked with a variety of toxic effects in-cluding their ability to mimic oestrogen. They are ...
Journal of Pharmaceutical Sciences, 2009
When chitin is used in pharmaceutical formulations, processing of chitin with metal silicates is ... more When chitin is used in pharmaceutical formulations, processing of chitin with metal silicates is advantageous, from both an industrial and pharmaceutical perspective, compared to processing using silicon dioxide. Unlike the use of acidic and basic reagents for the industrial preparation of chitin-silica particles, coprecipitation of metal silicates is dependent upon a simple replacement reaction between sodium silicate and metal chlorides. When coprecipitated onto chitin particles, aluminum, magnesium, or calcium silicates result in nonhygroscopic, highly compactable/disintegrable compacts. Disintegration and hardness parameters for coprocessed chitin compacts were investigated and found to be independent of the particle size. Capillary action appears to be the major contributor to both water uptake and the driving force for disintegration of compacts. The good compaction and compression properties shown by the chitin-metal silicates were found to be strongly dependent upon the type of metal silicate coprecipitated onto chitin. In addition, the inherent binding and disintegration abilities of chitin-metal silicates are useful in pharmaceutical applications when poorly compressible and/or highly nonpolar drugs need to be formulated. ß
Journal of Chemical Education, 1997
High sensitivity differential scanning calorimetry ( HSDSC ) is a powerful and increasingly used ... more High sensitivity differential scanning calorimetry ( HSDSC ) is a powerful and increasingly used technique for the study of molecular energetics in relation to biopolymers (e.g. proteins and nucleic acids ) or biomacromolecular assemblies ( e.g. liposomes ). HSDSC is, for example, the only method which allows thermodynamic parameters to be obtained directly for protein unfolding. The thermodynamic basis for
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007
The purpose of this investigation was to examine the preparation and characterisation of hexane-i... more The purpose of this investigation was to examine the preparation and characterisation of hexane-in-water emulsions stabilised by clay particles. These emulsions, called Pickering emulsions, are characterised by the adsorption of solid particles at the oil/water (o/w) ...
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1996
A method is presented that may be used to calculate the concentration of surfactant (Croon) in th... more A method is presented that may be used to calculate the concentration of surfactant (Croon) in thermodynamic equilibrium with micellar aggregates using high sensitivity differential scanning calorimetry (HSDSC) output. The temperature dependence of this equilibrium process has been evaluated for a number of oxyethylene/oxypropylene/ oxyethylene triblock copolymers and the results are compared with previously published CMC data that were obtained using a dye solubilization technique. The polydispersity of the block copolymers preclude identifying Cmo n with the CMC. However, the Croon values obtained using the HSDSC technique are of the same order of magnitude and show the same functional relationship with temperature as the reported CMC data. It is therefore proposed that HSDSC provides a suitable method for the rapid evaluation of Cmon for the surfactants examined over a fairly wide range of temperatures. Analysis of the derived Croon data points to the importance of the oxypropylene block in determining Croon values. At any particular temperature the greater the size of the oxypropylene block the lower the Cmon value. On the other hand, increasing the oxyethylene block size increases the value of Cmon.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006
ABSTRACT A systematic investigation of surface tension, as a function of copolymer concentration,... more ABSTRACT A systematic investigation of surface tension, as a function of copolymer concentration, has been undertaken for a range of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers in aqueous solution. The copolymers examined form three distinct families, containing 20, 70, and 80% ethylene oxide. The focus of the study was the change in surface tension observed below the critical micelle concentration of the triblock copolymers. Thus, in general, the plots of surface tension as a function of copolymer concentration showed a low concentration break. In some cases a high concentration break—corresponding to the onset of micellisation—was also observed. Estimates of molecular area have been made for molecules adsorbed at the air–water interface either side of the low concentration break. Below the break the molecular area does not appears to show any straightforward relationship with molecular composition. However, multiple linear regression analysis of the experimentally determined molecular area data above the break indicates that there does appear to be a weak relationship (adjusted R2 = 0.64) between molecular area and molecular composition (based upon the manufacturers’ data sheets). Estimates were also made of pC20 values (the negative logarithm of the copolymer concentration that reduces the surface tension of pure water by 20 mN m−1). Multiple linear regression analysis of the pC20 data indicates that pC20 values are related to molecular composition (adjusted R2 = 0.78). In addition, multiple linear regression analysis shows that surface tension values at a variety of aqueous copolymer concentrations are strongly correlated with molecular composition.
Chemosphere, 2000
Adsorption at the air±water interface and soil sorption from aqueous solution have been investiga... more Adsorption at the air±water interface and soil sorption from aqueous solution have been investigated for a group of ethylene oxide (EO)±propylene oxide (PO) block copolymeric surfactants. The group which have a common structural formula of EO m PO n EO m is distinguished by the fact that they have large critical micelle concentration (CMC) values and therefore do not readily form micelles at common environmental concentrations and temperatures. Adsorption at the air±water interface is readily shown to be driven by the size of the hydrophobic PO block. The size of the reduction in surface tension produced by a common concentration of 10 À5 mol dm À3 linearly increases with the size of the PO block as does the eciency of adsorption at the air±water interface as measured by pC 20 ± the negative logarithm of the surfactant concentration that produces a reduction in surface tension of 20 mN m À1 . Soil sorption data have also been captured for these compounds and the data are readily ®tted to the Freundlich adsorption isotherm. However soil sorption is shown to be inversely related to the molecular mass of the molecules and appears to be related to the size of the hydrophilic EO blocks in the molecule. Ó
Chemosphere, 1999
Soil water/distribution coefficients (Kd) have been measured for the partitioning of naphthalene,... more Soil water/distribution coefficients (Kd) have been measured for the partitioning of naphthalene, phenanthrene and pyrene between aqueous surfactant solutions and a clean soil. The surfactants used are ABA block copolymers constructed from ethylene oxide (the monomer used to synthesise the hydrophilic A blocks) and propylene oxide (used for the manufacture of the hydrophobic B block). Three of these surfactants comprising
Lead release from several soil and road dust samples -- obtained from various locations in the Lo... more Lead release from several soil and road dust samples -- obtained from various locations in the London Borough of Greenwich -- has been investigated as a function of acid and chloride addition. The work shows that lead retention in dust samples is primarily dependent upon buffer capacity, which in turn appears to be related to carbonate content. The continuing addition
AAPS PharmSciTech, 2010
A co-processed excipient was prepared from commercially available crystalline mannitol and α-chit... more A co-processed excipient was prepared from commercially available crystalline mannitol and α-chitin using direct compression as well as spray, wet, and dry granulation. The effect of the ratio of the two components, percentage of lubricant and particle size, on the properties of the prepared co-processed excipient has been investigated. α-Chitin forms non-hygroscopic, highly compactable, disintegrable compacts when co-processed with crystalline mannitol. The compaction properties of the co-processed mannitol-chitin mixture were found to be dependent upon the quantity of mannitol added to chitin, in addition to the granulation procedure used. Optimal physicochemical properties of the excipient, from a manufacturing perspective, were obtained using a co-processed mannitol-chitin (2:8, w/w) mixture prepared by wet granulation (Cop-MC). Disintegration time, crushing strength, and friability of tablets, produced from Cop-MC using magnesium stearate as a lubricant, were found to be independent of the particle size of the prepared granules. The inherent binding and disintegration properties of the compressed Cop-MC are useful for the formulation of poorly compressible, high-strength, and low-strength active pharmaceutical ingredients. The ability to co-process α-chitin with crystalline mannitol allows chitin to be used as a valuable industrial pharmaceutical excipient.
Journal of Contaminant Hydrology, 1999
Ž . The adsorption of 5 surfactants P103, P105, F108, F127 and L92 to a sandy soil has been inves... more Ž . The adsorption of 5 surfactants P103, P105, F108, F127 and L92 to a sandy soil has been investigated. The surfactants are ABA block copolymers in which the A blocks are synthesised from ethylene oxide and the B block from propylene oxide. CMC values, for the block copolymers, as well as surfactant sorption to soil were measured by surface tension techniques. The adsorption of all five compounds can be described by the Freundlich adsorption isotherm. Adsorption, in each case, is related to the critical micelle concentration of the surfactant and the extent of adsorption appears to be linked also to the fraction of soil organic matter. q 0169-7722r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
Process Safety and Environmental Protection, 1999
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Papers by Stephen Leharne