Dehydration at the lens surface:surface energy and surfactant persistence

Purpose: Most published surface wettability data are based on hydrated materials and are dominated by the air-water interface. Water soluble species with hydrophobic domains (such as surfactants) interact directly with the hydrophobic domains in the lens polymer. Characterisation of relative polar and non-polar fractions of the dehydrated material provides an additional approach to surface analysis. Method: Probe liquids (water and diiodomethane) were used to characterise polar and dispersive components of surface energies of dehydrated lenses using the method of Owens and Wendt. A range of conventional and silicone hydrogel soft lenses was studied. The polar fraction (i.e. polar/total) of surface energy was used as a basis for the study of the structural effects that influence surfactant persistence on the lens surface. Results: When plotted against water content of the hydrated lens, polar fraction of surface energy (PFSE) values of the dehydrated lenses fell into two rectilinear bands. One of these bands covered PFSE values ranging from 0.4 to 0.8 and contained only conventional hydrogels, with two notable additions: the plasma coated silicone hydrogels lotrafilcon A and B. The second band covered PFSE values ranging from 0.04 to 0.28 and contained only silicone hydrogels. Significantly, the silicone hydrogel lenses with lowest PFSE values (p<0.15) are found to be prone to lipid deposition duringwear. Additionally, more hydrophobic surfactants were found to be more persistent on lenses with lower PFSE values. Conclusions: Measurement of polar fraction of surface energy provides an importantmechanistic insight into surface interactions of silicone hydrogels.

Ruthenium complexes as potential aqueous romp catalysts

The research described herein relates to studies into the Aqueous Ring-Opening Metathesis Polymerisation (ROMP) of bicyclic monomers using ruthenium complex catalysts. Two monomers were synthesised for the purpose of these studies, namely exo, exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid (7-oxanorbornenedicarboxylic acid) and exo, exo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid (norbornene dicarboxylic acid). A number of ruthenium complexes were synthesised, amongst them a novel complex containing the water soluble phosphine ligand trist(hydroxymethyl)phosphine P(CH2OH)3. Its synthesis and characterisation are described and its physical properties compared and contrasted to analogous compounds of platinum and palladium. Its peculiar properties are ascribed to a trans-placement of the phosphine ligands. Dilatometry was investigated as a technique for the acquisition of kinetic data from aqueous metathesis reactions. For the attempted polymerisation of 7-oxanorbonenedicarboxylic acid the results are explained in terms of a reverse Diels-Alder reaction of the monomer. The reaction between Ru(CO)Cl2(H2O) and 7-oxanorbonenedicarboxylic acid was monitored using UV/Vis spectrometry and kinetic data retrieved. The data are explained in terms of a two stage reaction consisting of consecutive first order processes.The reaction between 7-oxanorbornenedicarboxylic acid and Ru(CO)Cl2(H2O) or Ru(P(CH2OH)3)3Cl2 was found to produce fumaric acid as one of the major products. This reaction is previously unreported in the literature and a mechanism is proposed.

An Investigation of the destruction of ion exchange resins

Ion exchange resins are used for many purposes in various areas of science and commerce. One example is the use of cation exchange resins in the nuclear industry for the clean up of radioactively contaminated water (for example the removal of 137Cs). However, during removal of radionuclides, the resin itself becomes radioactively contaminated, and must be treated as Intermediate Level Waste. This radioactive contamination of the resin creates a disposal problem. Conventionally, there are two main avenues of disposal for industrial wastes, landfill burial or incineration. However, these are regarded as inappropriate for the disposal of the cation exchange resin involved in this project. Thus, a method involving the use of Fenton's Reagent (Hydrogen Peroxide/soluble Iron catalyst) to destroy the resin by wet oxidation has been developed. This process converts 95% of the solid resin to gaseous CO2, thus greatly reducing the volume of radioactive waste that has to be disposed of. However, hydrogen peroxide is an expensive reagent, and is a major component of the cost of any potential plant for the destruction of ion exchange resin. The aim of my project has been to discover a way of improving the efficiency of the destruction of the resin thus reducing the cost involved in the use of hydrogen peroxide. The work on this problem has been concentrated in two main areas:-1) Use of analytical techniques such as NMR and IR to follow the process of the hydrogen peroxide destruction of both resin beads and model systems such as water soluble calixarenes. 2) Use of various physical and chemical techniques in an attempt to improve the overall efficiency of hydrogen peroxide utilization. Examples of these techniques include UV irradiation, both with and without a photocatalyst, oxygen carrying molecules and various stirring regimes.

Solid dispersions: formulation, characterisation, permeability and genomic evaluation

Poor water solubility is characterised by low dissolution rate and consequently reduced bioavailability. Formulation of solid dispersion of the drug has attracted considerable interest as a means of improving dissolution process of a range of poorly water soluble drugs. This current study investigates the formulation of solid dispersion for a range of poorly water soluble drugs with varying physicochemical properties including paracetamol, sulphamethoxazole, phenacetin, indomethacin, chloramphenicol, phenylbutazone and succinylsulphathiazole. Solid dispersions were prepared using various drugs to polymer ratios. PEG 8000 was selected as a carrier in the solid dispersions. The study revealed that inclusion of drug within the polymeric matrix, ratio of drug to polymer and physicochemical properties of the drug molecules enhance the dissolution rate. Characterisations of the solid dispersions were performed using DSC, FTIR and SEM. These studies revealed that all seven drugs were present in the amorphous form within the solid dispersions and there was a lack of interaction between the PEG 8000 and drug. Stability studies for solid dispersions showed that all seven drugs studied were unstable at accelerated conditions (40°C±2°C/75%RH±5%RH) whereas, they were found to be stable for 12 months at room conditions. Permeability of indomethacin, phenacetin, phenylbutazone and paracetamol were higher for solid dispersions as compared to drug alone across Caco-2 cell monolayers. From the cell uptake studies it was shown that PEG 8000 enhanced rhodamine123 uptake which suggested that PEG 8000 may increase the permeability of these drugs in solid dispersions. Gene expression profiles analyzing the expression changes in the ABC and solute carrier transporter during permeability studies.ABCA10, ABCB4, ABCC12, SLC12A6, MCT13, SLC22A12 and SLC6A6 gene expression were increased by indomethacin alone whereas solid dispersion of indomethacin resulted in a slight increase in expression. ABCC12 and SAMC gene expression was increased in case of paracetamol alone but slightly increased when exposed to solid dispersion of paracetamol.

Iron in the substrates and sporophores of Agaricus bisporus (Lange) Pilat during growth and development

The changes of the concentration of iron in the growth substrates and the sporophores of Agaricus bisporus (Lange) Pilat that occurred during culture under standard commercial conditions, were observed using atomic absorption spectrophotometry and iron-59 radiotracing techniques. The routes of translocation and sites of iron accumulation within the sporophore were shovn to alter during development and by the use of novel, pelletised substrates the concentration of iron in the mycelium of the substrates and in developing sporophores was observed during culture. Findings indicated that the compost was the major source of iron and that the concentration of iron in the compost mycelium varied cyclically in relation to the periodic appearance of sporophores. In the casing layer the mycelium is organised into strands which are responsible for the movement of iron from the compost into developing sporophores. A photographic technique for estimating sporophore growth rates showed that the accumulation of iron was not concomitant with sporophore growth and this was attributable to a declining quantity of available iron in the compost mycelium during sporophore growth. Variations in the quantity of iron in sporophores resulted primarily from differences in the quantity of water soluble iron in the compost but, the productivity of the crop, the type of casing layer and differences in watering also influenced sporophore composition. Changes in the concentration of extractable iron in the compost and casing layer throughout culture were related to mycelial activity and to a lesser extent were influenced by watering and the bacterial populations of the casing layer. Thus, the findings of this study give some indication of the relative importance that different cultural conditions exert over sporophore composition together with demonstrations of the movement of a single material within the sporophores and substrates during the cultivation of Agaricus bisporus.

Cyclodextrin complexes of antimicrobial agents

Poorly water-soluble drugs show an increase in solubility in the presence of cyclodextrins (CyD) due to the formation of a water-soluble complex between the drug and dissolved CyD. This study investigated the interactions of -Cyd and hydroxypropyl--CyD (HP--CyD, M.S. = 0.6) with antimicrobial agents of limited solubility in an attempt to increase their microbiological efficacy. The agents studied were chlorhexidine dihydrochloride (CHX), p-hydroxybenzoic acid esters (methyl, ethyl, proply and butyl) and triclosan. The interactions between the antimicrobials and CyDs were studied in solution and solid phases. Phase solubility studied revealed an enhancement in the aqueous drug solubility in the presence of the CyD and also gave an indication of the complex stability constant (Ks). The temperature-dependence of the stability constant of the complex was modelled by the van't Hoff plot which yielded the thermodynamic parameters for complexation. Further confirmation of the inclusion of the antimicrobials within the cavity of the CyDs in aqueous solution was obtained from proton magnetic resonance and ultraviolet absorption spectroscopies. The former method indicated that the chlorophenyl moiety of the CHX was included within the -CyD cavity and the stoichiometry of the complex formed was 1:1. The solid-phase complexes were prepared by freeze-drying. The inclusion complex of triclosan with HP--CyD was obtained from aqueous solution with the addition of ammonia. Evidence to confirm complex formation was obtained from DSC, IR and X-ray powder diffraction studies. Dissolution studies of the solid inclusion complexes using the dispersed powder technique illustrated their superior solubilities as compared to the equimolar physical mix of the guest and CyD. It was shown that these solutions of the complex were supersaturated with respect to the free guest. This was further demonstrated by diffusion studies which showed the flux of free drug from donor solutions of the antimicrobial-CyD complex to be significantly greater than the flux from donor suspensions of drug alone.

Development of plasmid dna formulations for application as microspheric dna vaccines

The advent of DNA vaccines has heralded a new technology allowing the design and elicitation of immune responses more adequate for a wider range of pathogens. The formulation of these vaccines into the desired dosage forms extends their capability in terms of stability, routes of administration and efficacy. This thesis describes an investigation into the fabrication of plasmid DNA, the active principle of DNA vaccines, into microspheres, based on the tenet of an increased cellular uptake of microparticulate matter by phagocytic cells. The formulation of plasmid DNA into microspheres using two methods, is presented. Formulation of microspheric plasmid DNA using the double emulsion solvent evaporation method and a spray-drying method was explored. The former approach involves formation of a double emulsion, by homogenisation. This method produced microspheres of uniform size and smooth morphology, but had a detrimental effect on the formulated DNA. The spray-drying method resulted in microspheres with an improved preservation of DNA stability. The use of polyethylenimine (PEI) and stearylamine (SA) as agents in the microspheric formulation of plasmid DNA is a novel approach to DNA vaccine design. Using these molecules as model positively-charged agents, their influence on the characteristics of the microspheric formulations was investigated. PEI improved the entrapment efficiency of the plasmid DNA in microspheres, and has minimal effect on either the surface charge, morphology or size distribution of the formulations. Stearylamine effected an increase in the entrapment efficiency and stability of the plasmid DNA and its effect on the micropshere morphology was dependent on the method of preparation. The differences in the effects of the two molecules on microsphere formulations may be attributable to their dissimilar physico-chemical properties. PEI is water-soluble and highly-branched, while SA is hydrophobic and amphipathic. The positive charge of both molecules is imparted by amine functional groups. Preliminary data on the in vivo application of formulated DNA vaccine, using hepatitis B plasmid, showed superior humoral responses to the formulated antigen, compared with free (unformulated) antigen.

The application of monolayer studies in the understanding of liposomal formulations

The study of surfactant monolayers is certainly not a new technique, but the application of monolayer studies to elucidate controlling factors in liposome design remains an underutilised resource. Using a Langmuir-Blodgett trough, pure and mixed lipid monolayers can be investigated, both for their interactions within the monolayer, and for interfacial interactions with drugs in the aqueous sub-phase. Despite these monolayers effectively being only half a bilayer, with a flat rather than curved structure, information from these studies can be effectively translated into liposomal systems. Here we outline the background, general protocols and application of Langmuir studies with a focus on their application in liposomal systems. A range of case studies are discussed which show how the system can be used to support its application in the development of liposome drug delivery. Examples include investigations into the effect of cholesterol within the liposome bilayer, understanding effective lipid packaging within the bilayer to promote water soluble and poorly soluble drug retention, the effect of alkyl chain length on lipid packaging, and drug-monolayer electrostatic interactions that promote bilayer repackaging.

Some aspects of the analytical chemistry of malathion

A thorough investigation of the recommended colorimetric method for the determination of malathion (an organophosphorus pesticide) has led to the identification of the major cause of all the problems with which the method suffers. The method, which involves the extraction of the copper (II) complex or the hydrolysis product of malathion from aqueous solution into immiscible organic solvents, has many drawbacks. For example, the colour of the organic extract fades very quickly and a slight increase in the contact time of the hydrolysis product and the copper reagent within the aqueous solution, results in a decrease in the ab-solute absorbance. Also, the presence of any reducing agents can be a significant source of error. In the present work, it has been shown that the basic cause of all these problems is the ability of copper (II) ion to be reduced to copper (I) ion. It has further been shown that these problems can be resolved by re-placing copper (II) by bismuth (III). This has led to the development of a modified colorimetric method for the determination. of malathion, which has distinct advantages over all other existing methods in terms of reagents required, ease in application, avoidance of interferences and stability of colour for extended periods of time. The modified colorimetric method described above has been further improved by making use of a ligand exchange reaction involving dithizone. The resulting final organic extract in this case is bright orange in colour, the absorbance of which can be measured even with simple photometers. The usefulness of the modified colorimetric method has been demonstrated by determining malathion in technical products, and in aqueous solution containing the compound down to sub ppm levels. The scope and applicability of atomic absorption spectrophotometry has been extended by demonstrating for the first time that the technique can be used for the indirect determination of malathion. Almost all of the work described above has been accepted for publication by international journals and considerable interest in the work has been shown by chemists working in the field of pesticide analysis and research.

Free radicals as potential antitumour agents

The aim of this work was to use extremely low concentrations of free radical generating compounds as a 'catalyst' to trigger endogenous free radical chain reactions in the host and to selectively eliminate neoplastic cells in the host. To test the hypothesis, a number of free radical generating compounds were screened on several malignant cell lines in vitro to select model compounds that were used against tumour models in vivo. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and its derivatives were selected at the model compounds for in vivo experiments in view of their high cytotoxic potency against several malignant cell lines in vitro. The water soluble derivative, 2,2-diphenyl-1-(2', 4'-dinitro-6'-sulphophenyl) hydrazyl (DDSH) given by subcutaneous injections demonstrated significant antitumour activities against the MAC 16 murine colon adenocarcinoma implanted subcutaneously in male NMRI mice at nanomolar concentration range. 40-60% of long term survival of over 60 days was achieved (compared with control survival of 20 days) with total tumour elimination. This compound was also active against both P388 leukaemia in male BDF1 mice and TLX5 lymphoid tumour in male CBA/CA mice at a similar concentration range. However, some of these animals died suddenly after treatment with no evidence of disease present at post mortem. The cause of death was unknown but thought to be related to the treatment. There was significant increase in serum level of malondialdehyde (MDA) following treatment, but did not correlate to the antitumour activities of these compounds. Induction of supcroxide dismutase (SOD), and glutathione peroxidase (GPx) occurred around day 8 after the administration of DDSH. Histological sections of MAC16 tumours showed areas of extensive massive haemorrhagic necrosis and vascular collapse associated with perivascular cell death following the administration of nanomolar concentration of DDSH which was probably compatible with the effects of free radicals. It was concluded that the antitumour activities of these compounds may be related to free radical and cytokine production.

New hybrid system:poly (ethylene glycol) hydrogel with covalently bonded pegylated nanotubes

Hydrogels containing carbon nanotubes (CNTs) are expected to be promising conjugates because they might show a synergic combination of properties from both materials. Most of the hybrid materials containing CNTs only entrap them physically, and the covalent attachment has not been properly addressed yet. In this study, single-walled carbon nanotubes (SWNTs) were successfully incorporated into a poly(ethylene glycol) (PEG) hydrogel by covalent bonds to form a hybrid material. For this purpose, SWNTs were functionalized with poly(ethylene glycol) methacrylate (PEGMA) to obtain water-soluble pegylated SWNTs (SWNT–PEGMA). These functionalized SWNTs were covalently bonded through their PEG moieties to a PEG hydrogel. The hybrid network was obtained from the crosslinking reaction of poly(ethylene glycol) diacrylate prepolymer and the SWNT–PEGMA by dual photo-UV and thermal initiations. The mechanical and swelling properties of the new hybrid material were studied. In addition, the material and lixiviates were analyzed to elucidate any kind of SWNT release and to evaluate a possible in vitro cytotoxic effect. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Rosemary : a raw material for a new genre of bio-based antioxidants for sustainable applications

The potential replacement, partially or fully, of synthetic additives by bio-based alternatives derived from indigenous renewable non-food crop resources offers a market opportunity for a green supply of raw materials for different industrial and health products, with greater involvement of the farming community in crop production while addressing the ever more stringent environmental and pollution laws that now require the use of less potentially toxic/harmful ingredients, even if they are present in relatively small quantities. The work presented here relates to developing a new genre of environmentally-sustainable bio-based antioxidants (AO) for industrial uses that are obtained from extracts of UK-grown rosemary (Rosmarinus officinalis) plant. The performance of these AOs was tested, and their efficacy compared with some common and benchmark synthetic AOs from the same chemical class, in different products including polymers especially for packaging, as well as lubricants, cosmetics and health products. One of the main active ingredients in rosemary is Rosmarinic acid which is a water-soluble compound. This was chemically transformed into a number of ester derivatives, Rosmarinates, targeted for different applications. The parent and the modified antioxidants (the rosmarinates) were characterised and their antioxidancy were examined and tested in linear low-density polyethylene (LLDPE) and in polypropylene (PP) and compared with compounds of similar structure and with other well known synthetic antioxidants used commercially in polyolefins. The results show that antioxidants sourced from rosemary have the added benefit of being highly efficient and intrinsically more active than many synthetic and bio-based alternatives.

Chitosan-modified dry powder formulations for pulmonary gene delivery

Spray-drying is an effective process for preparing micron-dimensioned particles for pulmonary delivery. Previously, we have demonstrated enhanced dispersibility and fine particle fraction of spray-dried nonviral gene delivery formulations using amino acids or absorption enhancers as dispersibility-enhancing excipients. In this study, we investigate the use of the cationic polymer chitosan as a readily available and biocompatible dispersibility enhancer. Lactose-lipid:polycation:pDNA (LPD) powders were prepared by spray-drying and post-mixed with chitosan or spray-dried chitosan. In addition, the water-soluble chitosan derivative, trimethyl chitosan, was added to the lactose-LPD formulation before spray-drying. Spray-dried chitosan particles, displaying an irregular surface morphology and diameter of less than 2 mu m, readily adsorbed to lactose-LPD particles following mixing. In contrast with the smooth spherical surface of lactose-LPD particles, spray-dried trimethyl chitosan-lactose-LPD particles demonstrated increased surface roughness and a unimodal particle size distribution (mean diameter 3.4 mu m), compared with the multimodal distribution for unmodified lactose-LPD powders (mean diameter 23.7 mu m). The emitted dose and in vitro deposition of chitosan-modified powders was significantly greater than that of unmodified powders. Moreover, the inclusion of chitosan mediated an enhanced level of reporter gene expression. In summary, chitosan enhances the dispersibility and in vitro pulmonary deposition performance of spray-dried powders.

Noncovalent coatings for the separation of synthetic polypeptides by nonaqueous capillary electrophoresis

Recently, we demonstrated the possibility to extend the range of capillary electrophoresis (CE) applications to the separation of non-water-soluble synthetic polymers. This work focuses on the control of the electro-osmotic flow (EOF) and on the limitation of the solute adsorption in nonaqueous electrolytes. For these purposes, different strategies were investigated. For the initial, a viscous additive (ethylene glycol or glycerol) was used in the electrolyte in order to decrease the EOF magnitude and, possibly, to compete with solute adsorption. A second strategy was to modify, before separation, the fused-silica capillary wall by the adsorption of poly(ethylene oxide) (PEO) via hydrogen bonding. The influence of the molecular mass of the adsorbed PEO on the EOF magnitude and direction was studied in electrolytes based on methanol/acetonitrile mixtures containing ammonium ions. For PEO molecular masses above 1000 g/mol, reversed (anodic) EOF were reported in accordance with previous results obtained with PEO covalently bonded capillaries. The influence of the nature and the concentration of the background electrolyte cation on the EOF magnitude and direction were also investigated. A third strategy consisted in modifying the capillary wall by the adsorption of a cationic polyelectrolyte layer. Advantageously, this polyelectrolyte layer suppressed the adsorption of the polymer solutes onto the capillary wall. The results obtained in this work confirm the high potential and the versatility of CE for the characterization of ionizable organic polymers in nonaqueous media.

Physical and biological properties of a novel siloxane adhesive for soft tissue applications

The aim of this study was to investigate the adhesive properties of an in-house amino-propyltrimethoxysilane-methylenebisacrylamide (APTMS-MBA) siloxane system and compare them with a commercially available adhesive, n-butyl cyanoacrylate (nBCA). The ability of the material to perform as a soft tissue adhesive was established by measuring the physical (bond strength, curing time) and biological (cytotoxicity) properties of the adhesives on cartilage. Complementary physical techniques, X-ray photoelectron spectroscopy, Raman and infrared imaging, enabled the mode of action of the adhesive to the cartilage surface to be determined. Adhesion strength to cartilage was measured using a simple butt joint test after storage in phosphate-buffered saline solution at 37°C for periods up to 1 month. The adhesives were also characterised using two in vitro biological techniques. A live/dead stain assay enabled a measure of the viability of chondrocytes attached to the two adhesives to be made. A water-soluble tetrazolium assay was carried out using two different cell types, human dermal fibroblasts and ovine meniscal chondrocytes, in order to measure material cytotoxicity as a function of both supernatant concentration and time. IR imaging of the surface of cartilage treated with APTMS-MBA siloxane adhesive indicated that the adhesive penetrated the tissue surface marginally compared to nBCA which showed a greater depth of penetration. The curing time and adhesion strength values for APTMS-MBA siloxane and nBCA adhesives were measured to be 60 s/0.23 MPa and 38 min/0.62 MPa, respectively. These materials were found to be significantly stronger than either commercially available fibrin (0.02 MPa) or gelatin resorcinol formaldehyde (GRF) adhesives (0.1 MPa) (P <0.01). Cell culture experiments revealed that APTMS-MBA siloxane adhesive induced 2% cell death compared to 95% for the nBCA adhesive, which extended to a depth of approximately 100-150 μm into the cartilage surface. The WST-1 assay demonstrated that APTMS-MBA siloxane was significantly less cytotoxic than nBCA adhesive as an undiluted conditioned supernatant (P <0.001). These results suggest that the APTMS-MBA siloxane may be a useful adhesive for medical applications. © VSP 2005.