Sheaves of wheat

Sulfadiazine, like other sulfas, has a low urinary solubility, particularly in acid urine. When the urine is alkalinized and pH rises above 7.15, the drug ionizes and forms a soluble salt that is excreted avoiding crystallization. It has been estimated that at a pH of 5.5 about 16 liters of urine will be needed to insure that the sulfadiazine is soluble when excreted following a dose of 4 g per day [5]. Indeed, the urinary solubility of sulfadiazine and its major metabolite, acetylsulfadiazine, are many times higher at a pH of 7.5 than at a pH of 6.5 (sulfadiazine 200 and 28 mg/dl, acetylsulfadiazine 512 and 75 mg/dl, respectively) [30]. The crystals of sulfadiazine and acetylsulfadiazine can be recognized by examining the urine sediment, where they resemble characteristic "sheaves of wheat" [3]. As the crystals transit... 

This has been performed for quaterthienyl (QT). QT crystallizes in microscopic needles (less than 25 im thick), which aggregate like sheaves of wheat. QT is nionoclinic, space group P2i/n, with refined unit cell parameters a =5.02(2) A, b = 30.63 (8) A, c = 4.85 (2) A,... 

If the concentration of nucleation events is extremely dense, there will be insufficient room for the spherulites to mature. Under such circumstances a multitude of lamellar bundles, termed sheaves, are produced. Toward either end of the bundle the lamellae splay out from each other to form a waisted structure. Sheaves are so named because of their outward similarity to wheat sheaves (albeit on a very different scale). Each sheaf is equivalent to the core of a spherulite. The middle of each sheaf consists of a small bundle of parallel lamellae. 

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