Structure of the inclusion complex of beta-cyclodextrin with 1,12-dodecanedioic acid using synchrotron radiation data; a detailed dimeric beta-cyclodextrin structure

A detailed crystal structure study of the dimeric inclusion complex of beta -cyclodextrin (beta CD) with 1,12-dodecanedioic acid is presented [IUPAC na me: beta-cyclodextrin-1,12-dodecanedioic acid (2/1)]. The structure was sol ved with synchrotron high-resolution data (0.65 Angstrom) at 100 K [crystal data: P1, Z = 1, a = 18.153 (7), b = 15.456 (8), c = 15.251 (4) Angstrom, alpha = 102.81 (2), beta = 113.13 (2), gamma = 99.90 (3)degrees, V = 3673 ( 3) Angstrom(3), R = 0.0474 for 25 134 unique reflections with I > 2 sigma(I )]. Moreover, the room-temperature structure is used for comparison [crysta l data: P1, Z = 1, a = 18.220 (3), b = 15.488(3), c = 15.409(3) Angstrom, a lpha = 102.903(6), beta = 113.122(5), gamma = 99.708(5)degrees, V = 3735.2 (12) Angstrom(3), R = 0.0828 for 8235 unique reflections with l > 2 sigma(I )]. Combining the high-resolution data and the low-temperature made possibl e the location of the disordered guest molecule, 1,12-dodecanedioic acid, i nside the wide cavity of the macrocycle formed by two beta CD monomers. Mor eover, almost all the H atoms of the beta CD macrocycle and many of the wat er molecules have been located in the low-temperature structure. Thus, for the first time, it has been possible to show in detail. up to now only give n by neutron diffraction data, that two beta CD monomers self-assemble thro ugh O3 ... O3 intermolecular hydrogen bonds to form the beta CD dimer, as w ell as describe the hydrogen-bonding scheme between the dimer's hydroxyl gr oups among themselves and with water molecules in the lattice. The long gue st threads through two host molecules forming a [3]pseudo-rotaxane. Its pol ar carboxyl groups, fully hydrated at the primary faces of the beta CD dime rs, influence their packing so that those faces are exposed to the solvent. This is in contrast to the packing of the B-cyclodextrin complexes of the corresponding aliphatic monoacids, where the dimeric complexes form channel s in order to isolate the terminal methyl group from the water environment of the lattice.