Three polymorphic forms of dipotassium O-phospho-L-serinate hydrates

Abstract

Abstract Three polymorphic forms of dipotassium salt of O-phospho-L-serine were obtained from water solutions at different pH. Two forms (α and β) crystallize in the monoclinic space group P2, while the third (γ) crystallizes in the orthorhombic space group P212121. All crystals are composed of O-phospho-L-serine ions, potassium cations and water molecules of hydration. In all salts, the O-phospho-L-serine moiety exists as a dianion with two negatively charged phosphate groups, one negatively charged carboxyl group and one positively charged ammonium group. The molecular geometry of O-phospho-L-serine (PSer) dianions resembles that found for the zwitterions in crystalline L- and DL-forms of O-phosphoserine. The orientation of the phosphate group relative to the serine backbone is almost trans (–ap) in all three forms. In all forms, there are no significant differences in the values of the bond lengths in the O-phospho-L-serine moiety. The crystal packings are dominated by K…O interactions and intermolecular hydrogen bonds. The polyhedrons around the K+ cations are rather irregular. However, a specific spatial arrangement of potassium cations is similar in all three crystals.