The growth of anhydrous uric acid (UA) and uric acid dihydrate (UAD) crystals from supersaturated aqueous solutions containing methylene blue, a cationic organic dye, has been investigated. Low concentrations of dye molecules were found to be included in both types of crystal matrixes during the growth process. Incorporation of dye into UA crystals occurs with high specificity, affecting primarily [001] and [201] growth sectors, while UAD crystals grown from solutions of similar dye concentration show inclusion but little specificity. The orientation of the UA-trapped species was determined from polarization data obtained from visible light microspectrometry. To achieve charge neutrality, a second anionic species must also be included with the methylene blue into UA and UAD crystal matrices. Under high pH conditions, crystallization of 1:1 stoichiometric mixtures of methylene blue and urate yields methylene blue hexahydrate (MBU.6(H2O). The crystal structure of MBU.6(H2O) reveals continuous pi-pi stacks of planes of dye cations and urate anions mediated by water molecules. This structure provides an optimal geometry for methylene blue-urate pairs and additional support for the incorporation of these dimers in uric acid single-crystal matrices. The strikingly different inclusion patterns in UA and UAD demonstrate that subtle changes in the crystal surfaces and/or growth dynamics can greatly affect recognition events.

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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.

In a real-world clinical practice setting, the 1-h PG ≥ 155 mg/dl (8.6 mmol/l) is superior for detecting high-risk individuals compared with HbA1c. Furthermore, HbA1c is a less precise correlate of insulin sensitivity and β-cell function than the 1-h PG and correlates poorly with the 2-h PG during the OGTT.