Di-L-phenylalanine sulfate monohydrate

Crystallizatioii of Di-L-phenylalanine Sulfate Monohydrate from Fermentation Broth... 

The characteristics of di-L-phenylalanine sulfate monohydrate crystals were investigated. Crystals of this compound were found to adopt two morphologies, i.e. needle form and thin plate form in the industrial plant. The former were metastable crystals and the latter were stable crystals which belonged to the same crystal system( monoclinic) as the pillar form crystals observed by powdered X-ray diffraction and solubility analyses. The needle form appeared at concentrations of L-phenylalanine higher than30g/dlat pH 1.7 to 2.0. On the other hand, the thin plate form appeared when the pH was below 1.0, or excess impurities (peak-A) derived from the mother liquid were accumulated in the crystallization liquid. 

Di-L-phenylalanine sulfate monohydrate crystals(C jjN02)2H2S04H20, Formula... 

Materials Di-L-phenylalanine sulfate monohydrate in the pillar form To 28 g/dl slurry of L-phenylalanine, 1.1 equivalents by volume of sulfuric acid were added with stirring at 60 C, and then cooled to room temperature with stirring. The pillar form crystals came out, the crystals were filtered then washed with water and dried in a vacuum desiccatorwith sulfuric acid. 

On the other hand the chart of the needle form crystals showed a different peak from the pillar form crystals. The solubility data of di-L-phenylalanine sulfate monohydrate and sodium sulfate are shown in Figure 3.These experimental results show that the needle form crystals is more soluble than the pillar form crystals. 

Effects of amino acids The effects of 18 kinds of amino acids on crystal appearance are summarized in table 4. Among these amino acids tested, only leucine and tryptophan affected the change in crystal form from pillars to thin plates at concentrations relative to Lmore than 3%. These two amino acids are hydrophobic, so they might interact with the Lrphenylalanine skeleton in the crystal structure of di-L-phenylalanine sulfate monohydrate and are supposed to suppress growth in the a-axis direction. Isoleucine, valine and tyrosine which are analogous... 

Two morphologically, different forms of di-L-phenylalanine sulfate monohydrate crystals were obtained in the industrial plant i.e. needle form and thin plate form. The former was metastable and the latter was stable. The needle form crystals appeared at concentrations of L-phenylalanine higher than 30 g/dl within the pH range of 1.7 to... 

Measurement of solubility of the needle form and the pillar form crystals For measurement, 30 ml of saturated sodium sulfate solution and 20 g of di-I phenylalanine sulfate monohydrate either in the needle form or pillar form were added at 10 to 60 0, into 50 ml glass tubes with a spiral stirrer. Then, the contents were set in a water bath regulated with an accuracy of 0.5 C for each experimental temperature. After stirring for about 24 hours, an aliquot was taken with a cotton-stopped pipette, and the concentration of L-phenylalaninein the filtrate was determined by HPLC (Type 638-50 Hitachi Co., Inc. Japan). 

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