Modulated Uric Acid Crystal Growth in the Presence of Acridine Dyes

Abstract

Single crystals of anhydrous uric acid (UA) and uric acid dihydrate (UAD) were grown from supersaturated aqueous solutions containing the fluorescent dye acriflavine neutral (AN), a two-component commercial mixture of proflavine (P), and its 10-methylated analogue acriflavine (A). During UA crystal growth at 37 °C, small quantities of AN, P, and A dye probes are found to be selectively included in {001} and {201} growth sectors. Increasing concentrations of dye in solution show a general retardation in the growth of (121) faces, resulting in an overall change from a rectangular to a prismatic habit. For UAD growth at 25 °C, AN, P, and A inclusion does not appear to favor any particular growth sector, and no discernible habit changes are observed under even the most concentrated dye solutions examined. The average orientation of dye molecules trapped in the UA and UAD matrixes was determined from polarization data obtained from a home-built microspectrometer. Dye-surface recognition events can be discerned on the basis of the calculated dye orientation. The difference in the interlayer distance between uric acid layers in UA and UAD and the resultant surface perturbations caused by dye recognition and inclusion can be used to rationalize the observed habit modification in the anhydrous form.