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A C Neville

Publications and source records attributed to A C Neville.

10 recordsLinked to original sources
PubMed1998

The role of pH, temperature and nucleation in the formation of cholesteric liquid crystal spherulites from chitin and chitosan.

The alpha chitin and chitosan used in the experiments came from crab shell waste (Sigma). This was treated to form a colloidal suspension of chitin or chitosan crystallites. The electrostatic 'charge coat' surrounding the chitin was then manipulated. This was achieved by alteration of the pH of the chitin or chitosan colloid (Chitin pKa = 6.1). This allowed the charge density on the crystalline rod of chitin or chitosan to be altered. The effect of this treatment was ascertained by measuring the diameter of spherulites formed in vitro. The results were analysed to see if the experimental optimal pH agreed with theoretical approximations. Further investigations were carried out on the initiation of the spherulites and the effect of temperature on spherulite formation. The spherulites form via self assembly through a liquid crystalline cholesteric phase. Manipulation of the electrostatic coat of the chitin could be a method of cellular remote control for formation of the helicoid in arthropod cuticle. This would allow the arthropods to set up conditions that aid the self assembly process.

Chitin↗
PubMed1997

The role of the electrostatic coat in the formation of cholesteric liquid crystal spherulites from alpha-chitin.

The alpha-chitin used in the experiments came from crab shell waste. This was boiled in 3M HC1 to form a colloidal suspension of chitin crystallites. The electrostatic 'cost' surrounding the chitin was then manipulated in two ways. The first was the alteration of the pH of the chitin colloid (Chitin pKa = 6.1). This allowed the charge density on the crystalline rod of chitin to be altered. The second way was to alter the background charge in the environment by adding salt solutions to the colloid. The effect of the treatments was ascertained by measuring the diameter of the spherulites formed in vitro. These spherulites formed via self assembly through a liquid crystalline cholesteric phase. Raising the pH (within limits), resulted in larger spherulites. Raising the background charge also gave larger spherulites (within limits). As such both background charge and charge on the rod can be used to control the self assembly of the cholesteric spherulites. Manipulation of the electrostatic coat of the chitin could be a method of cellular remote control for formation of the helicoid in arthropod cuticle. This would allow the arthropods to set up conditions that aid the self assembly process.

Animals↗
PubMed1981

Helicoidal architecture of fish eggshell.

Previous publications show arced patterns in electron micrographs of either microfibrils or canals in sectioned fish eggshells, but these have been misinterpreted. We show here that such patterns in the inner layer of cod (Gadus morrhua), plaice (Pleuronectes platessa) and trout (Salmo gairdneri) eggs arise from a helicoidal structure. This consists of a laminate of protein microfibrils, with the direction of ply processing like the steps of a spiral staircase and with the same sense as a left-handed corkscrew. Mechanically, this is an ideal way to strengthen a spherical shell, to resist deforming forces equally from any direction. Radial canals which traverse this layer are forced into flattened and twisted ribbons. Both the helicoidal microfibrillar structure and the canal shape in fish eggshells show remarkable convergent evolution with similar structures in insect cuticles. Trout eggs were resistant to deforming forces as high as 380,000 N/m2. Fish eggshells, like those of many other organisms, are mechanically well designed.

Animals↗
PubMed1976

The chitin crystallite in arthropod cuticle.

Electron microscopy has revealed that chitin from a representative selection of insect orders (plus one crustacean and one arachnid) is localized in crystallites about 2.8 nm across. Furthermore, these crystallites are arranged on an hexagonal or pseudo-hexagonal lattice, the lateral order of which varies considerably. The lattice becomes secondarily reoriented during cuticle expansion following an ecdysis. The size of the 'unit cell' has been measured both by optical diffraction and direct measurements of the micrographs, permitting an estimate of the chitin and resilin content for locust rubberlike cuticle. The number of poly-N-acetyl-glucosamine chains per sheet and sheets per crystallite can be estimated from the physical dimensions of the crystallite. Each crystallite is unlikely to comprise more than 3 sheets and 6 chains per sheet. The calculated and measured density of alpha-chitin can be shown to be in close agreement.

Animals↗