The crystal structures of 4-chlorophenoxyacetic acid (4CPA) included in beta-cyclodextrin (beta-CD) and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMbetaCD) have been studied by X-ray diffraction. The 4CPA/beta-CD complex crystallizes as a head-to-head dimer in the space group C2 in the Tetrad packing mode. The packing modes of some beta-CD dimeric complexes, having unique stackings, are also discussed. The 4CPA/TMbetaCD inclusion complex crystallizes in the space group P2(1) and its asymmetric unit contains two crystallographically independent complexes, complex A and complex B, exhibiting different conformations. The host molecule of complex A is significantly distorted, as a glucosidic residue rotated about the O4'-C1 and C4-O4 bonds forms an aperture where the guest molecule is accommodated. The phenyl moiety of the guest molecule of complex B is nearly perpendicular to the mean plane of the O4n atoms. The conformations of the guest molecules of the two complexes are similar. The crystal packing consists of antiparallel columns as in the majority of the TMbetaCD complexes published so far.
The crystal structures of the inclusion compounds of thymol, carvacrol and eugenol, (components of essential oils of vegetable origin) in -cyclodextrin have been determined. Thymol/-CD crystallizes in the space group P1 containing two host molecules in its asymmetric unit whereas both carvacrol/-CD and eugenol/-CD complexes crystallize in the space group C2. In all three complexes two host molecules form head-to-head dimers their guest/host stoichiometry being: 1/2 (carvacrol/-CD), 2/2 (thymol/-CD) and 3/2 (eugenol/-CD). In the cases of the thymol/-CD and the carvacrol/-CD complexes the -CD dimers are arranged according to the channel packing mode. The accommodation of the geometrical isomer guests is performed solely by their hydrophobic groups revealing the leading role of the hydrophobic driving forces in the complexation process whereas the position of their hydroxyl group affects the stoichiometry of the formed dimeric complexes. In the case of the eugenol/-CD dimeric complex one guest molecule is found lying between the -CD groups in a sandwich fashion whereas the other two symmetry related guests protrude outwards the narrower rim of the hosts with only their hydrophobic allylchain located inside the hosts' cavities. This arrangement prohibits the formation of a channel and the observed crystal packing is that of a Tetrad mode.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.