Uric Acid Dihydrate: Crystallography and Identification

Abstract

Unit-cell dimensions and optical data for uric acid and uric acid dihydrate show that there are structural resemblances, but that either can be readily distinguished by x-ray methods or by optical techniques. Density separation may be unsatisfactory because the dihydrate can lose water rather easily. Powder diffraction data are given.

Solid-State Dehydration of Uric Acid Dihydrate

“…This helps to unambiguously differentiate UAD from UA, which is biaxial positive with a 45.6°tilt in its optical plane through its largest plate face. 4,5 All UAD crystals were either used immediately after sieving or stored for short periods of time in chambers with 55% relative humidity to minimize unintended dehydration.…”

“…The spontaneous dehydration of UAD in air at room temperature has been suggested in several previous reports, including the earliest initial structural studies of this material. [4][5][6] However, the real-time kinetic and detailed structural aspects of UAD dehydration in air have not been previously studied in detail. The dehydration kinetics and phase transformations among different phases may have clinical consequences, both during the initial crystallization and aggregation stages of renal sediment formation as well as in their ex situ analysis.…”

Uric Acid Dihydrate Revisited

“…Uric acid [7,9-dihydro-1H-purine-2,6,8(3H)-trione dihydrate, UA], a major constituent of some mammalian calculi, crystallizes in two known forms, a stable anhydrous monoclinic form (AUA) and a poorly characterized form consistently described as orthorhombic (Ringertz, 1965(Ringertz, , 1966Lonsdale & Mason, 1966;Shirley, 1966;Sutor & Scheidt, 1968;Rinaudo & Boistelle, 1980). The crystal structure of AUA was published over 30 years ago by Ringertz (1966), but further single crystal work on the dihydrate (UAD) has only recently appeared (Artioli et al, 1997, hereafter AMG).…”

The Elusive Crystal Structure of Uric Acid Dihydrate: Implication for Epitaxial Growth During Biomineralization

“…As an insoluble component together with the anhydrous form of uric acid it is also the common means of nitrogen expulsion from birds and reptiles and it is found as an organic mineral residue in surface deposits (Bridge, 1974;Artioli, Galli & Ferrari, 1993). A number of studies have been performed in the past concerning the identification of uric acid dihydrate as a phase in urinary calculi (Shirley, 1966;Sutor, 1968;Sutor & Scheidt, 1968) and the definition of its crystal morphology and optical properties (Ringertz, 1965). From the cell parameters and knowledge of the commonly developed morphological faces, Lonsdale (1968) postulated that epitaxial growth plays an important role in controlling the nucleation and crystal growth of the phases commonly associated in human stones.…”