CONFORMATION OF a-D-GLUCOPYRANOSE-1-PHOSPHATE ANION vs POLYMORPHISM OF DIRUBIDIUM GLUCOSE-1-PHOSPHATE DIHYDRATE CRYSTALS
Krystyna Stepniak, Tadeusz Lis*, Bozena Klimek, Anna E. Koziol
Faculty of Chemistry, Maria
Curie-Sk3odowska University, 20-031 Lublin, Poland;
E-mail: akoziol@hermes.umcs.lublin.pl
* Faculty of
Chemistry, University of Wroc3aw, 50-383 Wroc3aw, Poland
Keywords: a-D-glucopyranose-1-phosphate,
dirubidium glucose-1-phosphate dihydrate, polymorphism
The pyranose ring, a central part of the a-D-glucopyranose-1-phosphate anion
(G1P), adopts the 1C conformation with equatorial
substituents at C2, C3, C4 and C5 [1-3]. The conformational
changes of the molecule are limited to the rotations of the
phosphate and hydroxymethylene groups around the C1-O1 and C5-C6
bonds, respectively. The O5-C1-O1-P torsion angle is in the range
64-90, while two observed solid state orientations of the
hydroxyl O6 atom with respect to the pyranose are:
I (+sc, -sc) or E - in G1PHK [1] and G1P 2Na 3.5 H2O [2] crystals, and
II (+ap, +sc) or Z - in G1P 2K 2H2O salt [3].
The crystallization of G1P 2Rb from the H2O / iPrOH / EtOH solvent mixture at 10C gives several forms of crystals, all of them are dihydrates.
form I form II
Fig.1.
Crystal structure of polymorphs depends on the time of crystallization and pH. At the beginning, an unstable phase is formed, which is the orthorhombic form I (the space group P21212). Three modifications of this form have been isolated: Ia, Ib and Ic. Each of them contains partially disordered Rb+ cations with different occupancy factors, and additionally, disordered water molecule is present in Ic. The second stable orthorhombic form II (with the space group P212121) is a product of a long-time crystallization process.
The monotropic phase transition I ---> II is composed of two transformations:
(a) the reorientation of the O6 atom in the G1P anion (Fig.1), corresponding to the E ---> Z conformation change;
(b) disorder --- > order transformation of the Rb+ cation positions with resulting g differences in cation-anion, cation-water and cation-cation interactions (Fig. 2).
 |
Rb1: s.o.f. = 1; CN = 7 Rb2: s.o.f. = 0.5; CN = 6 Rb3a: s.o.f. = 0.05 ; CN = 4 Rb3b: s.o.f. = 0.175; CN = 6 Rb3c: s.o.f. = 0.175; CN = 5 Rb3d: s.o.f. = 0.1; CN = 5 |
 Fig. 2. |
Rb1:
s.o.f. = 1; CN = 8 Rb2: s.o.f. = 1; CN = 7 |