From Beads on a String to the Pearls of Regulation: the Structure and Dynamics of Chromatin

The assembly of eukaryotic chromatin, and the bearing of its structural organization on the regulation of gene expression, were the central topics of a recent conference organized jointly by the Biochemical Society and Wellcome Trust. A range of talks and poster presentations covered topical aspects of this research field and illuminated recent advances in our understanding of the structure and function of chromatin. The two-day meeting had stimulating presentations complemented with lively discourse and interactions of participants. In the present paper, we summarize the topics presented at the meeting, in particular highlighting subjects that are reviewed in more detail within this issue of Biochemical Society Transactions. The reports bring to life the truly fascinating molecular and structural biology of chromatin

Physical Characterization of Halofantrine-Encapsulated Fat Nanoemulsions

We report the colloidal characterisation of halofantrine (Hf) laden soybean oil (SBO) fat emulsions. Hf increased the zeta potential, at all pH values, of the fat emulsions. Concomitant with this, the isoelectric point (i.e.p.) of the emulsion increased to higher pH values. The emulsion was destabilised by a small amount of Hf; interestingly, however, this was ameliorated by increasing the amount of Hf. The particle size and polydispersity of the fat emulsion reflected this with a small Hf concentration resulting in a significant increase in both particle size and polydispersity, but less so as the Hf concentration was increased. Emulsions lost stability as the pH approached the i.e.p. and this effect was greatest for the small Hf concentration emulsions. Cryogenic transmission electron microscopy showed the presence of beading or string like behaviour leading to gross distortions of the spherical shape for highly unstable emulsions. We conclude that to maintain good stability for Hf laden SBO emulsions, the pH of the emulsion should be kept away from its isoelectric point, and also that the drug concentration should be maintained at a relatively high value

Physical characterisation of drug encapsulated soybean oil nano-emulsions

Lecithin based soybean oil emulsions, similar to Intralipid®, were used to successfully encapsulate drugs having a range of hydrophobicity and acid-base characteristics. The drugs studied were phenanthrene, diazepam, histamine and chloroquine and these were compared with previous studies involving halofantrine. The drug encapsulated emulsions were tested for pH, stability, particle size, zeta potential and morphology (cryo electron microscopy). Encapsulation of any drug was found to decrease the stability of the emulsion, increase the particle size, decrease the (negative) zeta potential and in some cases, resulted in distortions to the particles. Specifically, close to the isoelectric point, gross distortions were observed involving large, elongated, worm like structures for the drugs halofantrine and histamine. The short term stability of all drug encapsulated emulsions were good, however all showed some signs of instability with time, probably due to a concomitant pH drift to low pH values, resulting in a decreased zeta potential and loss of stability. Neither hydrophobicity nor the acid-base nature of the encapsulated drug was found to have a strong influence on the stability, particle size or zeta potential profile of the emulsion

Biodegradability of a selected range of polymers and polymer blends and standard methods for assessment of biodegradation

Synthetic polymers are important to the packaging industry but their use raises aesthetic and environmental concerns, particularly with regard to solid waste accumulation problems and the threat to wildlife. Some concerns are addressed by attention to problems associated with source reduction, incineration, recycling and landfill. Others are addressed by the development of new biodegradable polymers either alone or in blends. Materials used for biodegradable polymers include various forms of starch and products derived from it, biopolyesters and some synthetic polymers. Starch is rapidly metabolised and is an excellent base material for polymer blends or for infill of more environmentally inert polymers where it is metabolised to leave less residual polymer on biodegradation. This should help to improve the environmental impact of waste disposal. A number of standard methods have been developed to estimate the extent of biodegradability of polymers under various conditions and with a variety of organisms. They tend to be used mainly in the countries where they were developed but there is much overlap between the standards of different countries and wide scope for development of consistent and international standards

Physical Characterization of Halofantrine-Encapsulated Fat Nanoemulsions

We report the colloidal characterisation of halofantrine (Hf) laden soybean oil (SBO) fat emulsions. Hf increased the zeta potential, at all pH values, of the fat emulsions. Concomitant with this, the isoelectric point (i.e.p.) of the emulsion increased to higher pH values. The emulsion was destabilised by a small amount of Hf; interestingly, however, this was ameliorated by increasing the amount of Hf. The particle size and polydispersity of the fat emulsion reflected this with a small Hf concentration resulting in a significant increase in both particle size and polydispersity, but less so as the Hf concentration was increased. Emulsions lost stability as the pH approached the i.e.p. and this effect was greatest for the small Hf concentration emulsions. Cryogenic transmission electron microscopy showed the presence of beading or string like behaviour leading to gross distortions of the spherical shape for highly unstable emulsions. We conclude that to maintain good stability for Hf laden SBO emulsions, the pH of the emulsion should be kept away from its isoelectric point, and also that the drug concentration should be maintained at a relatively high value

Preparation, surface modification and characterisation of solution cast starch PVA blended films

Several blends have been prepared of polyvinyl alcohol, starch and glycerol. The blend containing 20% polyvinyl alcohol has been modified by application of chitosan to the surface. The blend, and its modified form have been characterised by atomic force microscopy, x-ray diffraction, Fourier transform infra-red spectroscopy, contact angle measurements, 13C-NMR spectroscopy and scanning electron microscopy. The blended films were flexible and homogeneous on a macroscopic scale but on a microscopic scale there seemed to be small patches of individual components. Surface modification altered some of the characteristics of the film. The blends had surface roughness intermediate between that of the pure components. The addition of chitosan made the film more hydrophobic than the unmodified film but slightly less than the starch film. There was no evidence of new bond formation among the individual components. Solution casting reduced the overall crystallinity in the blended films

Biodegradation by composting of surface modified starch and PVA blended films

Several starch/PVA/glycerol polymer blends were prepared by a solution casting technique and examined for biodegradation by composting over 45 days. Within this time frame, the starch and glycerol components were fully degraded, leaving the PVA component essentially intact. The lowest PVA content film (20%) was selected as a polymer with enough PVA to impart important physical characteristics, but also enough starch to be considered biodegradable. The film characteristics were further improved by surface modification with chitosan. This modification did not interfere with the biodegradation of the starch component. Furthermore, there was slight evidence that PVA biodegradation had been initiated in composted, surface modified starch/PVA blends