Crystal structure of beta-cyclodextrin-benzoic acid inclusion complex.
The inclusion complex of beta-cyclodextrin (beta-CD) with benzoic acid (BA) has been characterized crystallographically. Two beta-CDs cocrystallize with two BAs, 0.7 ethanol and 20.65 water molecules [2(C(6)H(10)O(5))(7).2(C(7)H(6)O(2)).0.7(C(2)H(6)O).20.65H(2)O] in the triclinic space group P1 with unit cell constants: a=15.210(1), b=15.678(1), c=15.687(1) A, alpha=89.13(1), beta=74.64(1), gamma=76.40(1) degrees. The anisotropic refinement of 1840 atomic parameters against 16,201 X-ray diffraction data converged at R=0.078. In the crystal lattice, beta-CD forms dimers stabilized by direct O-2(m)_1/O-3(m)_1...O-2(n)_2/O-3(n)_2 hydrogen bonds (intradimer) and by indirect O-6(m)_1...,O-6(n)_2 hydrogen bonds with one or two bridging water molecules joined in between (interdimer). These dimers are stacked like coins in a roll constructing endless channels where the guest molecules are included. The BA molecules protrude with their COOH groups at the beta-CD O-6-sides and are maintained in positions by hydrogen bonding to the surrounding O-6-H groups and water molecules. Water molecules (20.65) are distributed over 30 positions in the interstices between beta-CD molecules, except the water sites W-1, W-2 that are located in the channel of the beta-CD dimer. Water site W-2 is hydrogen bonded to the disordered ethanol molecule (occupancy 0.7).
Aree
Thammarat
T
Department of Chemistry, Faculty of Science, Chulalongkorn University, Phyathai Road, Pathumwan, 10330, Bangkok, Thailand. mam@atc.atccu.chula.ac.th
Chaichit
Narongsak
N
D019817:Benzoic Acid / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003505:Cyclodextrins / Q000737:chemistry*; D006860:Hydrogen Bonding; D047392:beta-Cyclodextrins
D003505:Cyclodextrins; D047392:beta-Cyclodextrins; D019817:Benzoic Acid; C031215:betadex