Structure of cycloheptaamylose inclusion-complexes: crystal structure of substituted benzoic acid and phenol derivatives

Cyclodextrins: Structural, Chemical, and Physical Properties, and Applications

Due to their unique structural, physical and chemical properties, cyclodextrins and their derivatives have been of great interest to scientists and researchers in both academia and industry for over a century. Many of the industrial applications of cyclodextrins have arisen from their ability to encapsulate, either partially or fully, other molecules, especially organic compounds. Cyclodextrins are non-toxic oligopolymers of glucose that help to increase the solubility of organic compounds with poor aqueous solubility, can mask odors from foul-smelling compounds, and have been widely studied in the area of drug delivery. In this review, we explore the structural and chemical properties of cyclodextrins that give rise to this encapsulation (i.e., the formation of inclusion complexes) ability. This review is unique from others written on this subject because it provides powerful insights into factors that affect cyclodextrin encapsulation. It also examines these insights in great detail. Later, we provide an overview of some industrial applications of cyclodextrins, while emphasizing the role of encapsulation in these applications. We strongly believe that cyclodextrins will continue to garner interest from scientists for many years to come, and that novel applications of cyclodextrins have yet to be discovered.

Novel Behavior of O-Methylated β-Cyclodextrins in Inclusion of meso-Tetraarylporphyrins

[structure: see text] The mechanism for formation of extremely stable 1:2 inclusion complexes of water-soluble meso-tetraarylporphyrins with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMe-beta-CD) in aqueous solutions has been studied by means of NMR spectroscopy and isothermal titration calorimetry. To simplify the system, 5,10,15-tris(3,5-dicarboxylatophenyl)-20-phenylporphyrin (1) was used as a guest porphyrin, because 1 forms only a 1:1 inclusion complex with cyclodextrin (CD). As host compounds, native beta-CD and the O-methylated-beta-CDs such as heptakis(2,3-di-O-methyl)- (2,3-DMe-beta-CD), heptakis(2,6-di-O-methyl)- (2,6-DMe-beta-CD), and TMe-beta-CDs were used. The thermodynamic parameters for complexation such as binding constants (K) and enthalpy (DeltaH degrees ) and entoropy changes (DeltaS degrees ) were determined by means of isothermal titration calorimetry. The K value for complexation of 1 with CD increases in the order beta-CD (K = (1.2 +/- 0.1) x 10(3) M(-)(1)) < 2,6-DMe-beta-CD ((1.2 +/- 0.1) x 10(4) M(-)(1)) << TMe-beta-CD ((6.9 +/- 0.4) x 10(6) M(-)(1)) < 2,3-DMe-beta-CD ((8.5 +/- 0.5) x 10(6) M(-)(1)), indicating participation of the secondary OCH(3) groups in extremely strong complexation of 1 with CD. Complex formation of 1 with beta-CD and 2,6-DMe-beta-CD is an enthalpically and entropically favorable process, while that with TMe-beta-CD and 2,3-DMe-beta-CD is an enthalpically much more favorable but an entropically less favorable process. The thermodynamic parameters suggest that inclusion of 1 into the cavities of TMe-beta-CD and 2,3-DMe-beta-CD is promoted by van der Waals interactions, which are stronger than those in the cases of beta-CD and 2,6-DMe-beta-CD. (13)C NMR spectra show that the conformations of both TMe-beta-CD and 2,3-DMe-beta-CD are altered upon inclusion of 1, while those of beta-CD and 2,6-DMe-beta-CD are mostly retained. On the basis of these results, it can be concluded that induced-fit type complexation of 1 with TMe-beta-CD and 2,3-DMe-beta-CD causes extremely strong binding of the host to the guest.

Analysis and modelling of the structures of beta-cyclodextrin complexes

A systematic computer graphics study of all available beta-cyclodextrin crystal structures has been carried out specifically to aid in the modelling and design of beta-cyclodextrin-drug complexes. The analyses show that the basic conformation of the molecule remains constant among natural, mono-substituted and partially permethylated beta-cyclodextrins, with major changes observed only in the case of full permethylation. In all the structures, however, there are no significant perturbations caused by guest molecule inclusion. On the basis of these observations models are proposed for the structures of beta-cyclodextrin-indomethacin complexes, the principal features of which are shown to be consistent with the data obtained in 1H-NMR studies.

Structure of inclusion complexes of cyclomaltoheptaose (cycloheptaamylose): crystal structure of the 1-adamantanemethanol adduct

Cyclomaltoheptaose (cycloheptaamylose) has been crystallized with 1-adamantanemethanol as the guest molecule. The complex crystallized in space group C222(1), with unit-cell dimensions a = 19.162 (13), b = 23.965 (17), and c = 32.597 (27) A. The structure was solved by rotation-translation search-methods. The cyclomaltoheptaose exists as a dimer in the crystal by means of extensive hydrogen-bonding across the secondary hydroxyl ends of two cyclomaltoheptaose molecules. The two halves of the dimer are related by a crystallographic two-fold axis. The primary hydroxyl ends of two adjacent cyclomaltoheptaose molecules are also related by a crystallographic two-fold axis, but do not directly hydrogen bond to one another. Instead, they are held in place by a strong hydrogen bond from the hydroxyl group of the 1-adamantanemethanol to a primary hydroxyl group on an adjacent cyclomaltoheptaose molecule. Other stabilizing hydrogen bonds are formed via three water molecules which are situated at the primary hydroxyl interface, and others that form parallel columns stabilizing the crystal structure. A unique feature of this complex is the presence of trapped water in the cavity at the secondary hydroxyl interface. This water is distributed over 3 disordered sites. Its presence blocks one possible site for the 1-adamantanemethanol, which, instead, binds near the primary hydroxyl end, with its hydroxyl group and part of the adamantane moiety protruding from the cyclomaltoheptaose.