Dipak K. Sarker

Engineering of nanoemulsions for drug delivery.

Nanoemulsions, usually spherical, are a group of dispersed particles used for pharmaceutical and biomedical aids and vehicles that show great promise for the future of cosmetics, diagnostics, drug therapies and biotechnologies. They exist in a wide variety of forms that are dictated by the particle components. Nanoemulsions are generally considered to be in the size range of less than and around 100 nm in diameter. The particles can exist as water-in-oil and oil-in-water forms, where the core of the particle is either water or oil, respectively. More complex variations also exist but these are often larger. The longer-term properties of the particle are dependent on the composition of the adsorbed material lying at the dispersed droplet interface with the dispersion medium. This has an impact on the partitioning and extraction of droplet contents. Thermodynamically stable particles are characterized by having a very low surface tension and this produces a very large surface area. Nanoemulsions can also include small meta-stable very small-scale emulsions; here the surface properties and chemistry can strongly influence behaviour. Processing, storage and formulation composition can also have an impact on the longevity of a pharmaceutical preparation. Some revolutionary new nanoemulsion droplets based on fluorinated compounds are finding a number of widespread biomedical roles and applications. Developments in nanoemulsion technology are likely to lead to a much greater use of this medium in future pharmaceuticals.

Developments in microarray technologies

The focus of high-throughput drug discovery has progressed through the genome and the transcriptome and is now moving towards more difficult problems in assessing the proteome, glycome and metabolome. Microarrays are currently the major tool in the assessment of gene expression via cDNA or RNA analysis; however, they are also used to screen libraries of proteins and small molecules. Microarrays have helped to extract more information from smaller sample volumes and enabled the incorporation of low-cost high-throughput assays in the drug discovery process. The technology continues to develop and is being rapidly transferred into more challenging areas, with the potential to further aid and enhance the drug discovery process through the development of, for example, proteomic, glycomic and tissue arrays.

Dynamic surface tension and adsorption properties of β-casein and β-lactoglobulin

The adsorption kinetic behaviour of β-lactoglobulin and β-casein solutions studied by dynamic surface tension measurements was interpreted by diffusion-controlled models. Approximate solutions of the model led to diffusion coefficients for short and long adsorption times. The coefficients associated with the short time region were found to be unexpectedly high. From the long time approximation, the coefficients reflect a slower process in the adsorption layer which is possibly superimposed by rearrangement processes.

Enhancement of Protein Foam Stability by Formation of Wheat Arabinoxylan-Protein Crosslinks

ABSTRACT The foam stability properties of a defined mixed solution of Tween 20 and bovine serum albumin was evaluated as a function of arabinoxylan concentration. A marked increase in the foam stability was observed with low concentrations of arabinoxylan. Maximum improvement in the foam stability was obtained with 0.2–0.3 mg/mL of arabinoxylan. Enhancement of foam stability due to a combination of bulk viscosity changes and surface effects was identified. The relative contribution of arabinoxylan to bulk viscosity and adsorbed layer structure was studied by examination of the properties of thin liquid films and the macroscopic air-water interface. Arabinoxylan reduced the rate of thin film drainage, increased the equilibrium thickness of the films, slowed the lateral diffusion of a fluorescent probe molecule located in the adsorbed layer, and increased the surface elasticity. These data are congruent with arabinoxylan-mediated crosslinking of adsorbed protein. These observations may be of significance in...

RESTORATION OF PROTEIN FOAM STABILITY THROUGH ELECTROSTATIC PROPYLENE GLYCOL ALGINATE-MEDIATED PROTEIN-PROTEIN INTERACTIONS

The action of propylene glycol alginate in the enhancement of foam stability of a destabilised Tween 20/bovine serum albumin mixed system was evaluated. A significant increase in the foam stability was observed in the presence of low concentrations of propylene glycol alginate. A pseudo-plateau level of foam stability was obtained in the presence of approximately 0.8 μg/ml propylene glycol alginate in the solution used to form the foam. Foam stability enhancement due to bulk viscosity changes and surface effects were elucidated. The increase in foam stability was investigated by reference to the properties of thin liquid films and the macroscopic interface of test solutions. Propylene glycol alginate was found to slow the rate of thin film drainage, increase the equilibrium thickness of the films, slow the lateral diffusion of a fluorescent probe molecule located in the adsorbed layer and increase the elasticity of the interface. Data are consistent with propylene glycol alginate-induced crosslinking of protein in the adsorbed layer. This polysaccharide presents a means for controlling protein foam stability.

Competitive adsorption of l-α-lysophosphatidylcholine/β-lactoglobulin mixtures at the interfaces of foams and foam lamellae

The stability of foams formed with the protein β-lactoglobulin as a function of increasing concentration of the lipid analogue l-α-lysophosphatidylcholine were investigated using a microconductivity technique. The drainage, surface diffusion and thickness properties of thin liquid films (foam lamallae) were also studied using optical microscopy including epi-illumination, fluorescence recovery after photobleaching and film interferometry techniques. In addition, the surfactant binding properties of the protein were examined. The addition of small quantities of l-α-lysophosphatidylcholine to β-lactoglobulin (molar ratio, R < 7:1) increased the foam stability, whereas a slightly higher concentration of surfactant in the mixture (R = 10) caused foam destabilisation. The explanation of these observations is based on changes in the composition and structure of the adsorbed interfacial layers of the thin films caused by competitive displacement of the protein by the surfactant.

Enhancement of the stability of protein-based food foams using trivalent cations

The potential for cations to cross-link protein molecules through electrostatic interaction and thereby enhance foaming properties was investigated using aluminium chloride, β-lactoglobulin and Tween 20 as a model system. The addition of the trivalent cations resulted in a noticable improvement in the foamability and foam stability. Optimal behaviour, specific to the protein and emulsifier concentrations used, was observed at 4–5 μM added aluminium ions. The mode of action of the cations was investigated further using isolated foam lamellae (thin liquid films). The appearance of aggregates in the thin liquid films, non-uniformity of the film, and an increase in the dilational viscosity/elastic modulus of the surface associated with the addition of aluminium cations have contributed to the development of a phenomenological model which explains the observed increase in foam stability.

Ozone decomposition on Ag/SiO2 and Ag/clinoptilolite catalysts at ambient temperature

Silver modified zeolite (Bulgarian natural clinoptilolite) and Ag/silica catalysts were synthesized by ion exchange and incipient wet impregnation method respectively and characterized by different techniques. DC arc-AES was used for Ag detection. XRD spectra show that Ag is loaded over the surface of the SiO(2) sample and that after the ion-exchange process the HEU type structure of clinoptilolite is retained. UV-VIS (specific reflection at 310 nm) and IR (band at 695 cm(-1)) spectroscopy analysis proved that silver is loaded as a T-atom into zeolite channels as Ag(+), instead of Na(+), Ca(2+), or K(+) ions, existing in the natural clinoptilolite form. The samples Ag/SiO(2) and Ag-clinoptilolite were tested as catalysts for decomposition of gas phase ozone. Very high catalytic activity (up to 99%) was observed and at the same time the catalysts remained active over time at room temperature.

Methylcellulose-induced stability changes in protein-based emulsions

The emulsifying and oil-in-water stabilizing properties of methylcellulose (MeC) were investigated in bovine serum albumin (BSA)-based emulsions. The creaming stability, flocculation, surface concentration of BSA and MeC and droplet size were determined. Results obtained showed modifications of creaming rates that were related to MeC concentrations in the continuous and dispersed phases. Viscosity effects on creaming and changes in average droplet size (d43) relating to droplet coverage were identified and delineated. Studies performed on macroscopic oil–water and air–water interfaces were used to identify interfacial structuring and composition. A good agreement was found between droplet surface composition and the resistance to coalescence of emulsion droplets. Emulsions that demonstrated a more rigid-like adsorbed interfacial layer were more stable with respect to coalescence. This study involving model emulsion systems provides a new insight into the stability of industrial preparations containing mixtures of proteins and polysaccharides.

Synthesis and applications of copillar[5]arene dithiols

Abstract A novel copillar[4+1]arene incorporating alkylthiol substituents was synthesised in three steps and structurally characterised as the first example of a pillar[n]arene to incorporate two terminal thiols on the same aromatic ring. The macrocycle was attached to gold electrodes through a standard dipping technique. Cyclic voltammetry demonstrated selectivity for Li+ over other alkali metal cations. The copillar[4+1]arene was also used as a capping agent in the preparation of 3 nm gold nanoparticles.