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 HCl to form a colloidal suspension of chitin crystallites. The electrostatic 'coat' 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. (C) 1997 Elsevier Science B.V.