Doping Uric Acid Crystals. 1. Uric Acid Dihydrate

Abstract

The crystallization of uric acid dihydrate (UAD) from model supersaturated aqueous solutions containing 21 different molecular dye probes and 11 inorganic salts was investigated. UAD crystals grown at room temperature were found to include low concentrations (0.01-0.42%) of cationic and neutral dyes but not anionic dyes. From dilute dye solutions, a preference for inclusion in either {011} or {102} growth sectors was exhibited for some dyes while others showed little specificity. At higher dye concentrations, inclusion generally increased but specificity tended to diminish. Crysoidine G was exceptional in that over a broad range of solution concentrations, it was consistently and exclusively included on growth hillocks located in {011} sectors. Most dye-doped UAD crystals also exhibited morphological changes, namely the development of {210} faces, which are typically absent in pure UAD crystals. UAD grown from salt solutions showed inclusion of Na þ , K þ , and Mg 2þ ions in concentrations similar to dyes; however, none affected the macroscopic morphology. While the literature has numerous examples showing that anionic and polyanionic species can assert dramatic effects on the mineralization of inorganic phases, this study suggests that cationic species may play a more pronounced role in the crystallization of other types of biomaterials.

Urochrome Pigment in Uric Acid Crystals

“…The first studies on uric acid crystallization in the presence of colorants began in the 1930s, when Gaubert examined crystals grown in the presence of various synthetic dyes. Kleeberg added to this body of work with additional dye studies in the 1970s. , More recent work in our lab has shown that low concentrations of a wide variety of neutral and cationic dyes can be included in UA and UAD , often with high specificity. ,− When a cationic dye is included, charge-balance can be achieved by the parallel inclusion of a urate ion. For example, methylene blue (and several other dyes) is selectively included in {001} and {201} growth sectors of UA .…”

Hydrate Transformation via Anhydrate Pairs

“…On the basis of available X-ray and Raman data, it seemed more likely that the emergent UA crystal pairs were due to related defects introduced by the presence of 24-DAP in the growth solution. We know from previous work that when UAD is grown from solutions containing assorted dye additives, low concentrations of the dye in solution (<0.1%) can become trapped in the resultant crystal . Similarly, direct-injection mass spectrometry confirmed that trace amounts of 24-DAP were present in the UAD prisms (Figure S5).…”

Photonic Crystal Characterization of the Cuticles of Chrysina chrysargyrea and Chrysina optima Jewel Scarab Beetles

“…A key point of this discussion is the birefringence nature of the compound associated with the metallic-like structural color of these beetles [30,31,32,33,34,35], which should be deposited within the chitin structure. There are many reports of doping or functionalized uric acid [48,49,50,51,52], but not all of them present a birefringence [48]. The chemical extraction of the PCOC sample was attempted by using the method suggested by Caveney [38].…”