Solid-State Dehydration of Uric Acid Dihydrate

Abstract

Uric acid dihydrate (UAD) is a crystalline constituent present in a significant fraction of human renal precipitates. Using a combination of techniques including powder X-ray diffraction, hot-stage light microscopy, differential scanning calorimetry, and thermogravimetric analysis, the mechanism and kinetics of its irreversible dehydration to polycrystalline anhydrous uric acid (UA) is analyzed as a function of intrinsic sample parameters (e.g., crystal size, shape, structure) and environmental conditions (e.g., temperature and humidity). The highly anisotropic dehydration of UAD to UA is rationalized on the basis of its crystal structure and morphology, and appears to involve no other crystalline intermediate phases.Mechanistic models derived from both isothermal and nonisothermal kinetic data support a one-dimensional-phase boundary mechanism. Increasing relative humidity conditions were found to decrease the dehydration kinetics up to a point, after which a dissolution-recrystallization mechanism is enabled, and the conversion of UAD to UA is significantly accelerated.

Uric Acid Spherulites in the Reflector Layer of Firefly Light Organ

“…S1B) of monosodium urate monohydrate (MSUM) and plate-formed crystals (Fig. S1C) of uric acid dihydrate (UAD) were prepared as previous reports [6], [30]. The diffraction peak pattern of light organ is almost identical to the strongest peak of MSUM but has a little shift to lower angle compared to MSUM (Fig.…”

“…Uric acid or urate salt is a flat molecule [2], [6]. Thus, the single-peak diffraction signal detected in the light organ might come from a short face-face stacking axis formed by uric acid molecules.…”

“…Thus, the single-peak diffraction signal detected in the light organ might come from a short face-face stacking axis formed by uric acid molecules. The types of face-face interaction are found in all known structures of uric acid and urate salt [6], [33], but it doesn't mean that the material in the light organ corresponds to any of the known structures. We demonstrated both the light organ and the needle-formed monosodium urate monohydrate (MSUM) exhibited a highly similar single peak diffraction pattern (Fig.…”

“…Gout is a type of arthritis caused by the accumulation of needle-like crystals of urate salt–monosodium urate monohydrate–in the joints [5]. Various artificial uric acid or urate crystals have been extensively studied [6]–[9]. However, the physical property and formation of uric acid or urate crystals in the biological system, except monosodium urate monohydrate [10]–[12], are still poorly understood.…”

Polymorphism and Solvatomorphism 2010

“…160 The 2010 literature also contained a number of additional reports regarding the phase transformations among polymorphs and solvatomorphs of other organic compounds. Although some of these substances may have only limited pharmaceutical significance, the references summarized in Table 3, [161][162][163][164][165][166][167][168][169][170][171][172][173][174][175][176][177] are collected to pique the interests of appropriately directed investigators.…”