Filtern
Dokumenttyp
Sprache
- Englisch (2)
Referierte Publikation
- ja (2)
Schlagworte
- Crystal structures (2) (entfernen)
1,2,5,6,9,10-Hexabromocyclododecane (HBCD) is a widely used flame retardant, which tends to persist in the environment and accumulates in biota. The six stereoisomers (three racemates named α-, β-, and γ-HBCD) of the technical mixture were isolated with high-performance liquid chromatography (HPLC). Direct separations were performed on a chiral stationary phase containing permethylated -cyclodextrin (NUCLEODEX -PM column) and the pure enantiomers of α-, β-, and γ-HBCD were physically characterized for the first time. The absolute configurations of all six isomers were determined by anomalous dispersion using single crystal X-ray crystallography. Optical rotations αD in tetrahydrofuran were +4.2/-4.0 (α-HBCD), +26.1/-27.5 (β-HBCD), and +68.0/-66.3 (γ-HBCD). The sense of rotation could be correlated with the absolute configurations of α-, β-, and γ-HBCD enantiomers and their order of elution on a chiral permethylated β-cyclodextrin-bonded stationary phase. The diastereomers α-, β-, and γ-HBCD displayed distinctly different melting points as well as 1H-, 13C NMR, and IR spectra.
ß-Cyclodextrin (ßCD)-formic acid (1) and ß-CDacetic acid (2) inclusion complexes crystallizeas ß-CD...0.3HCOOH...7.7H2O and ß-CD...0.4CH3COOH...7.7H2O in themonoclinic space group P21 with comparable unit cell constants. Anisotropic refinement of atomic parameters against X-ray diffractiondata with Fo 2 > 2 (Fo 2) (986/8563 and 991/8358) converged at R-factors of 0.051 and 0.054 for 1 and 2,respectively. In both complexes, the ß-CD molecularconformation, hydration pattern and crystal packing are similar,but the inclusion geometries of the guest molecules are different.The ß-CD macrocycles adopt a ``round'' conformationstabilized by intramolecular, interglucose O3(n)...O2(n + 1)hydrogen bonds and their O6H groups are systematically hydratedby water molecules. In the asymmetric unit, each complex contains one ß-CD, 0.3 formic acid (or 0.4 acetic acid), and 7.7 water moleculesthat are distributed over 9 positions. Water sites located in the ß-CD cavity hydrogen bond to the guest molecule. In thecrystal lattice, ß-CD molecules are packed in a typical ``herringbone'' fashion. In 1, the formic acid (occupancy 0.3) is entirely included in the ß-CD cavity such that its C atom is shifted from the O4-plane center to the ß-CD O6-side by 2.90 Å and C=O, C-O bonds point to this side. In 2, the acetic acid (occupancy 0.4) is completely embedded in the ß-CD cavity, in which the carboxylic C atom is displaced from the O4-plane centerto the ß-CD O6-side by 0.87 Å; the C=O bond directsto the ß-CD O6-side and makes an angle of 15°to the ß-CD molecular axis. Furthermore, bothdimethyl-ß-CD-acetic acid and ß-CD-acetic acidcomplexes form a cage structure, showing that the small guestsenclosed entirely in the cavity either in ß-CD or indimethyl--CD do not affect the packing of the host macrocycles.