Hypercoiling and hydrophobically associating polymers : interfacial synthesis, surface properties and pharmaceutical applications

The objective of the work described was to identify and synthesize a range of biodegradable hypercoiling or hydrophobically associating polymers to mimic natural apoproteins, such as those found in lung surfactant or plasma apolipoproteins. Stirred interfacial polymerization was used to synthesize potentially biodegradable aromatic polyamides (Mw of 12,000-26,000) based on L-Iysine, L-Iysine ethyl ester, L-ornithine and DL-diaminopropionic acid, by reaction with isophthaloyl chloride. A similar technique was used to synthesize aliphatic polyamides based on L-Iysine ethyl ester and either adipoyl chloride or glutaryl chloride resulting in the synthesis of poly(lysine ethyl ester adipamide) [PLETESA] or poly(lysine ethyl ester glutaramide) (Mw of 126,000 and 26,000, respectively). PLETESA was found to be soluble in both polar and non-polar solvents and the hydrophobic/hydrophilic balance could be modified by partial saponification (66-75%) of the ethyl ester side chains. Surface or interfacial tension/pH profiles were used to assess the conformation of both the poly(isophthalamides) and partially saponified PLETESA in aqueous solution. The results demonstrated that a loss of charge from the polymer was accompanied by an initial fall in surface activity, followed by a rise in activity, and ultimately, by polymer precipitation. These observations were explained by a collapse of the polymer chains into non-surface active intramolecular coils, followed by a transition to an amphipathic conformation, and finally to a collapsed hydrophobe. 2-Dimensional NMR analysis of polymer conformation in polar and non-polar solvents revealed intramolecular associations between the hydrophobic groups within partially saponified PLETESA. Unsaponified PLETESA appeared to form a coiled structure in polar solvents where the ethyl ester side chains were contained within the polymer coil. The implications of the secondary structure of PLETESA and potential biomedical applications are discussed.

Mechanisms of heat and mass transfer to and from single drops freely-suspended in an air stream

A specially-designed vertical wind tunnel was used to freely suspend individual liquid drops of 5 mm initial diameter to investigate drop dynamics, terminal velocity and heat and mass transfer rates. Droplets of distilled, de-ionised water, n-propanol, iso-butanol, monoethanolamine and heptane were studied over a temperature range of 50oC to 82oC. The effects of substances that may provide drop surface rigidity (e.g. surface active agents, binders and polymers) on mass transfer rates were investigated by doping distilled de-ionised water drops with sodium di-octyl sulfo-succinate surfactant. Mass transfer rates decreased with reduced drop oscillation as a result of surfactant addition, confirming the importance of droplet surface instability. Rigid naphthalene spheres and drops which formed a skin were also studied; the results confirmed the reduced transfer rates in the absence of drop fluidity. Following consideration of fundamental drop dynamics in air and experimental results from this study, a novel dimensionless group, the Oteng-Attakora, (OT), number was included in the mass transfer equation to account for droplet surface behaviour and for prediction of heat and mass transfer rates from single drops which exhibit surface instability at Re>=500. The OT number and the modified mass transfer equation are respectively: OT=(ava2/d).de1.5(d/) Sh = 2 + 0.02OT0.15Re0.88Sc0.33 Under all conditions drop terminal velocity increased linearly with the square root of drop diameter and the drag coefficient was 1. The data were correlated with a modified equation by Finlay as follows: CD=0.237.((Re/P0.13)1.55(1/We.P0.13) The relevance of the new model to practical evaporative spray processes is discussed.

Steric stabilization and dissolution characteristics of aqueous suspensions of pharmaceutical interest

The adsorption of two qroups of nonionic surface active agents and a series of hiqh molecular weiqht hydrophilic polymer fractions onto a polystyrene latex and a drug substance diloxanide furoate B.P. has been investigated. The presence of pores within the drug surface has been demonstrated and this is shown to increase the adsorption of low molecular weight polymer species. Differences in the maximum amount of polymer adsorbed at both solid-solution interfaces have been ascribed to the different hydrophobicities of the surface as determined by contact angle measurements. Adsorbed layer thicknesses of polymer on polystyrene latex have been determined by three techniques: microelectrophoresis, intensity fluctuation spectroscopy and by viscometric means. These results, in combination with adsorption data, were used to interpret the configuration of the adsorbed polymer molecules at the interface. The type of druq suspension produced on adsorbing the different polymers in the absence of electrostatic stabilization was correlated with theoretical prediuctions of suspension characteristics deduced from potential energy diagrams, The agreement was good for the adsorption of short chain length surfactants, but for the polyvinylalcohols, discrepancies were found between experiment and theory. This was attributed to the inappropriate use of a mean segment density approximation within the adsorbed layer to calculate attractive potentials between particles. A maximum in the redispersibility values for suspensions coated with adsorbed nonylphenylethoxylates was attributed to "partial static stabilization" of the particles in conjunction with the attractive forces operating in the sediment between bare surface patches on neighbouring particles. No significant change in the dissolution of the drug was observed when nonylphenylethoxylates were adsorbed due to desorption upon contact with the dissolution medium. Pluronic F68 and all the polyvinylalcohol fractions caused a reduction in the dissolution rate which is explained by the decreased diffusion of drug' through the adsorbed polymer layer.

The effect of certain hydrophilic polymers on suspension stability

The adsorption of nonionic surface active agents of polyoxyethylene glycol monoethers of n hexadecanols on polystyrene latex and nonionic cellulose polymers of hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methylcellulose on polystyrene latex and ibuprofen drug particles have been studied. The adsorbed layer thicknesses were determined by means of microelectrophoretic and viscometric methods. The conformation of the adsorbed molecules at the solid-liquid interface was deduced from the molecular areas and the adsorbed layer thicknesses. Comparison of the adsorption results obtained from polystyrene latex and ibuprofen particles was made to explain the conformation difference between these two adsorbates. Sedimentation volumes and redispersibility values were the main criteria used to evaluate suspension stability. At low concentrations of surface active agents, hard caked suspensions were found, probably due to the attraction between the uncoated areas or, the mutual adsorption of the adsorbed molecules on the bare surface of the particles in the sediment. At high concentrations of hydroxypropyl cellulose and hydroxypropyl methylcellulose, heavily caked sediments were attributed to network structure formation by the adsorbed molecules. An attempt was made to relate the characteristics of the suspensions to the potential energy of interaction curves. Generally, the agreement between theory and experiment was good, but for hydroxyethyl cellulose-ibuprofen systems discrepancies were found. Experimental studies showed that hydroxyethyl cellulose flocculated polystyrene latex over a rather wide range of concentrations; similarly, hydroxyethyl cellulose-ibuprofen suspensions were also flocculated. Therefore, it ls suggested that a term to account for flocculation energy of the polymer should be added to the total energy of interaction. A rheometric method was employed to study the flocculation energy of the polymer.

Facile synthesis of hierarchical Cu2O nanocubes as visible light photocatalysts

Hierarchically structured Cu2O nanocubes have been synthesized by a facile and cost-effective one-pot, solution phase process. Self-assembly of 5 nm Cu2O nanocrystallites induced through reduction by glucose affords a mesoporous 375 nm cubic architecture with superior visible light photocatalytic performance in both methylene blue dye degradation and hydrogen production from water than conventional non-porous analogues. Hierarchical nanocubes offer improved accessible surface active sites and optical/electronic properties, which act in concert to confer 200–300% rate-enhancements for the photocatalytic decomposition of organic pollutants and solar fuels.

Analysis of tissue transglutaminase function in the migration of Swiss 3T3 fibroblasts:the active-state conformation of the enzyme does not affect cell motility but is important for its secretion

Increasing evidence suggests that tissue transglutaminase (tTGase; type II) is externalized from cells, where it may play a key role in cell attachment and spreading and in the stabilization of the extracellular matrix (ECM) through protein cross-linking. However, the relationship between these different functions and the enzyme's mechanism of secretion is not fully understood. We have investigated the role of tTGase in cell migration using two stably transfected fibroblast cell lines in which expression of tTGase in its active and inactive (C277S mutant) states is inducible through the tetracycline-regulated system. Cells overexpressing both forms of tTGase showed increased cell attachment and decreased cell migration on fibronectin. Both forms of the enzyme could be detected on the cell surface, but only the clone overexpressing catalytically active tTGase deposited the enzyme into the ECM and cell growth medium. Cells overexpressing the inactive form of tTGase did not deposit the enzyme into the ECM or secrete it into the cell culture medium. Similar results were obtained when cells were transfected with tTGase mutated at Tyr(274) (Y274A), the proposed site for the cis,trans peptide bond, suggesting that tTGase activity and/or its tertiary conformation dependent on this bond may be essential for its externalization mechanism. These results indicate that tTGase regulates cell motility as a novel cell-surface adhesion protein rather than as a matrix-cross-linking enzyme. They also provide further important insights into the mechanism of externalization of the enzyme into the extracellular matrix.

Phakometric measurement of ocular surface radii of curvature, axial separations and alignment in relaxed and accommodated human eyes

Measurements (autokeratometry, A-scan ultrasonography and video ophthalmophakometry) of ocular surface radii, axial separations and alignment were made in the horizontal meridian of nine emmetropes (aged 20-38 years) with relaxed (cycloplegia) and active accommodation (mean ± 95% confidence interval: 3.7 ± 1.1 D). The anterior chamber depth (-1.5 ± 0.3 D) and both crystalline lens surfaces (front 3.1 ± 0.8 D; rear 2.1 ± 0.6 D) contributed to dioptric vergence changes that accompany accommodation. Accommodation did not alter ocular surface alignment. Ocular misalignment in relaxed eyes is mainly because of eye rotation (5.7 ± 1.6° temporally) with small amounts of lens tilt (0.2 ± 0.8° temporally) and decentration (0.1 ± 0.1 mm nasally) but these results must be viewed with caution as we did not account for corneal asymmetry. Comparison of calculated and empirically derived coefficients (upon which ocular surface alignment calculations depend) revealed that negligible inherent errors arose from neglect of ocular surface asphericity, lens gradient refractive index properties, surface astigmatism, effects of pupil size and centration, assumed eye rotation axis position and use of linear equations for analysing Purkinje image shifts. © 2004 The College of Optometrists.

On the active site in H3PW12O40/SiO2 catalysts for fine chemical synthesis

The surface environment and structural evolution of silica supported phosphotungstic acid (H3PW12O40) catalysts have been investigated as a function of acid loading. H3PW12O40 clusters are deposited intact upon the silica surface, adopting a Stranksi-Krastanov growth mode forming a two-dimensional adlayer which saturates at 45wt% acid. Intimate contact with the silica support perturbs the local chemical environment of three tungstate centres, which become inequivalent with those in the remaining cluster, suggesting an adsorption mode involving three terminal W==O groups. Above the monolayer, H3PW12O40 clusters form three-dimensional crystallites with physico-chemical properties indistinguishable from those in the bulk heteropoly acid. These H3PW12O40/SiO2 materials are efficient for the solventless isomerisation of α-pinene under mild reaction conditions. Activity scales directly with the number of accessible perturbed tungstate sites at the silica interface; these are the active species.

Comparison of hydrophilic and hydrophobic active molecules release from polymer-phospholipid complexes

Hypercoiling polymers can be suited for application to living systems because they are similar in structure to the protein-based lipid assemblies found at fluid interfaces within the body. This leads to a range of exciting possibilities, not only in membrane transport applications but also in biosensors, drug delivery and mechanistic studies of biological membrane function. This study is focused in the study of the stability and suitability of nanostructures made of a hypercoiling polymer for drug delivery applications. The polymer poly (styrene-maleic acid) (PSMA) was combined with the phospholipid dimyristoylphosphatidylcholine (DMPC) to form amphiphilic nanostructures. The stability and suitability of these polymer-phospholipid nanocarriers for hydrophobic and hydrophilic molecules load and release was analyzed by several techniques. It was found that several of the studied molecules had a substantial effect on the surface charge and stability of the nanocarrier. It was also demonstrated that two types of nanocarriers, chemically modified and unmodified, were able to control the release of the molecules, especially in the case of hydrophobic compounds. In addition, as the hydrophobicity increased the release slowed down. These clear nanocarriers have the potential to behave very favorably at interfaces such as the tear lipid film were transparency is a requirement, giving a new way of controlled drug release in the eye.

Reaction-driven surface restructuring and selectivity control in allylic alcohol catalytic aerobic oxidation over Pd

Synchronous, time-resolved DRIFTS/MS/XAS cycling studies of the vapor-phase selective aerobic oxidation of crotyl alcohol over nanoparticulate Pd have revealed surface oxide as the desired catalytically active phase, with dynamic, reaction-induced Pd redox processes controlling selective versus combustion pathways.

Evidence for the surface-catalyzed suzuki-miyaura reaction over palladium nanoparticles:an operando XAS study

No need to get away: X-ray absorption spectroscopy of catalytically active palladium nanopartlcles during a SuzukiMlyaura cross-coupling reaction revealed that the nanopartlcles were stable under the reaction conditions, and that cross-coupling Involved the direct participation of surface palladium defect sites In the catalytic cycle (see picture). Selective chemical and structural poisons provided further evidence for a heterogeneous active site. © 2010 Wiley-VCH Verlag GmbH & Co. KCaA.

Bulk and surface switching in Mn-Fe-based Prussian blue analogues

Many Prussian Blue Analogues are known to show a thermally induced phase transition close to room temperature and a reversible, photo-induced phase transition at low temperatures. This work reports on magnetic measurements, X-ray photoemission and Raman spectroscopy on a particular class of these molecular heterobimetallic systems, specifically on Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition phenomena both in the bulk of the material and at the sample surface. Results indicate a high degree of charge transfer in the bulk, while a substantially reduced conversion is found at the sample surface, even in case of a near perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of the charge transfer transition in these materials is found to be primarily due to surface reconstruction. Substitution of a large fraction of charge transfer active Mn ions by charge transfer inactive Cu ions leads to a proportional conversion reduction with respect to the maximum conversion that is still stoichiometrically possible and shows the charge transfer capability of metal centers to be quite robust upon inclusion of a neighboring impurity. Additionally, a 532 nm photo-induced metastable state, reminiscent of the high temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The efficiency of photo-excitation to the metastable state is found to be maximized around 90 K. The photo-induced state is observed to relax to the low temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.

Effect of preparation conditions on the formation of the active phase of carbon fiber catalytic systems for the low-temperature oxidation of carbon monoxide

We studied the effects of the composition of impregnating solution and heat treatment conditions on the activity of catalytic systems for the low-temperature oxidation of CO obtained by the impregnation of Busofit carbon-fiber cloth with aqueous solutions of palladium, copper, and iron salts. The formation of an active phase in the synthesized catalysts at different stages of their preparation was examined with the use of differential thermal and thermogravimetric analyses, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and elemental spectral analysis. The catalytic system prepared by the impregnation of electrochemically treated Busofit with the solutions of PdCl, FeCl, CuBr, and Cu(NO ) and activated under optimum conditions ensured 100% CO conversion under a respiratory regime at both low (0.03%) and high (0.5%) carbon monoxide contents of air. It was found that the activation of a catalytic system at elevated temperatures (170-180°C) leads to the conversion of Pd(II) into Pd(I), which was predominantly localized in a near-surface layer. The promoting action of copper nitrate consists in the formation of a crystalline phase of the rhombic atacamite CuCl(OH). The catalyst surface is finally formed under the conditions of a catalytic reaction, when a joint Pd(I)-Cu(I) active site is formed. © 2014 Pleiades Publishing, Ltd.

High stability multiplexed fiber interferometer and its application on absolute displacement measurement and on-line surface metrology

We propose a self-reference multiplexed fibre interferometer (MFI) by using a tunable laser and fibre Bragg grating (FBG). The optical measurement system multiplexes two Michelson fibre interferometers with shared optical path in the main part of optical system. One fibre optic interferometer is used as a reference interferometer to monitor and control the high accuracy of the measurement system under environmental perturbations. The other is used as a measurement interferometer to obtain information from the target. An active phase tracking homodyne (APTH) technique is applied for signal processing to achieve high resolution. MFI can be utilised for high precision absolute displacement measurement with different combination of wavelengths from the tuneable laser. By means of Wavelength-Division-Multiplexing (WDM) technique, MFI is also capable of realising on-line surface measurement, in which traditional stylus scanning is replaced by spatial light-wave scanning so as to greatly improve the measurement speed and robustness.