Crystal formation of purine salts to investigate seeding processes

Abstract

Purines and punne salts are known to be the most widely distributed nitrogen containing compounds found in nature, and have a very important role in metabolism. Most purines form crystals when they precipitate out of solution, some of which deposit in various parts of the body, especially in the joints. The latter is responsible for the medical condition known as gout, which is characterised by inflammation. With this in mind, experiments were designed to explore whether the shape of these crystal that form in the body can be altered. In this study, aqueous solutions of purines and salts of purines were prepared. Crystals that precipitated out of these solutions under different conditions were isolated and observed under the polarised light-microscope. On the whole, theobromine formed small columnar prisms, while xanthine formed small and medium-sized crystals, which appear circular with a Maltese cross pattern at the centre. Caffeine was, by far, the easiest purine to crystallise, owing to its high solubility in an aqueous solution. In general, acicular or needle-like crystals of caffeine were formed, but at very low temperatures, plate-like caffeine crystals were obtained. Guanine and uric acid formed very few crystals owing to them being practically insoluble in water. Crystals of adenine were generally needle-like, comparable to those fonned by caffeine. Additionally, they formed bundles or clusters, with the needles pointing outwards from the clusters. Diversity of crystals involving theobromine increased when adding dicarboxylic acids in the solution. Long and slender plate-like crystals were observed. The introduction of sacchann m solution enabled the crystal morphologies to change drastically. Interesting dendritic crystals were formed from a saccharin-theobromine solution. Change in size and shape of theobromine was also observed on introducing alcohol in the aqueous environment. Caffeine crystals were overall unchanged on the introduction of dicarboxylic acids, saccharin or alcohols.