Molecular structures of the inclusion complexes β-cyclodextrin–1,2-bis(4-aminophenyl)ethane and β-cyclodextrin–4,4′-diaminobiphenyl; packing of dimeric β-cyclodextrin inclusion complexes (original) (raw)
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Cyclodextrin Inclusion Complexes: Host–Guest Interactions and Hydrogen-Bonding Networks
Acta Crystallographica Section A Foundations of Crystallography, 1998
An overview is given on the structural characteristics of- ,-and-cyclodextrins (CDs). These cyclic oligosaccharides consisting of six, seven and eight glucoses form inclusion complexes with guest molecules small enough to ®t into their central cavities and serve as good model systems for non-covalent bonding. Depending on the size and the ionic or molecular nature of the guests, the complexes crystallize in cage-or channel-type structures. X-ray and neutron diffraction have been used to study intermolecular interactions; they provide insight into OÐHÁ Á ÁO and CÐHÁ Á ÁO hydrogen bonds stabilizing the macrocyclic conformations and the inclusion of the guest molecules. Throughout the crystal lattices of the CD hydrates, which abound with OÐH groups, cooperative networks are formed by OÐHÁ Á ÁO hydrogen bonds; in the-CD macrocycle, dynamic disorder of the¯ip-¯op type is observed, OÐ (1 2 H)Á Á Á(1 2 H)ÐO, between O(2)ÐH and O(3)ÐH groups of adjacent glucoses.
Structure of guest-host complexes of β-cyclodextrin with arenes: a quantum-chemical study
Russian Chemical Bulletin, 1999
The structure of ]3-cyclodextrin (~-CD), as well as the structure and energetics of[3-CD-naphthalene, 13-CD--fluorene, l~-CD--phenanthrene, t3-CD--cyclohexane (I : 1), and !3-CD--naphthalene (2 : 2) inclusion complexes was studied by the semiempirical MNDO/PM3 method. Calculations ofa [3-CD--naphthalene--cyclohexane 11 : I : 1) complex were also performed. The minimum heat of formation was found for the symmetric 13-CD conformation with C7 symmetry axis. The structure is stabilized by the ring of interunit H-bonds formed by the protons of the 2-OH groups and the O atoms of the 3"-OH groups of the glucose units. Preferableness of this orientation of interunit H-bonds was confirmed by ab initio calculations of the molecule of c~-(I-4)-glucobiose (maltose) in the M P2/6-31G(d,p)//6-31G(d.p) approximation. The formation of any inclusion compounds of [3-CD with arenes is energetically favorable: the complexation energy varies in the range -9 to -12 kcal tool -I. Among complexes with naphthalene, that of composition 2 : 2 is the most energetically lhvorable, which is in agreement with experimental data. In this complex. 13-CD exists as a dimer of the "head-to-head" type. in which both partners are linked by a system of H-bonds. The structure of the "head-to-head" dimer of 13-CD was simulated by ab initio calculations of the H-borlded dimer of a-o-glucose in the RHF/6-31G(d,p) approximation, in the dimer, both components are linked by a pair of H-bonds formed by the protons of the 3-OH groups and the O atoms of the 2-OH grou0s. The dimerization enemies obtained from ab initio and semiempirical MNDO/PM3 and AMI calculations differ by about 2.5 times (8.6 vs. 3.2 and 3.8 kcal tool -t, respectively). naphthalene--cyclohexane complex, H-bonds in 13-cyclodextrin molecule, ab initio quantum-chemical calculations of maltose molecule and glucose dimer, semiempirical M N DO/PM3 method.
Journal of Inclusion Phenomena, 2002
β-Cyclodextrin (β-CD) and p-hydroxybenzaldehyde (p-HB) were studied by 1 H-NMR in deuterated aqueous solution and the stoichiometry of the resulting complex (1:1) was determined by the continuous variation method. Inclusion of p-HB in β-CD was confirmed by the observation of NMR shifts for the inside H5 protons of the β-CD cavity. In the solid state X-ray analysis was carried out and revealed the detailed structure of the inclusion complex. Two β-CDs cocrystallize with four p-HB and 9.45 water molecules [2(C 6 H 10 O 5) 7 •4C 7 H 6 O 2 •9.45H 2 O] in the triclinic space group P 1 with unit cell parameters: a = 15.262(2), b = 15.728(1), c = 16.350(1) Å, α = 92.67(1) • , β = 96.97(1) • , γ = 103.31(1) •. The anisotropic refinement of 1973 atomic parameters converged at an R-factor = 0.066 for 10157 data with F 2 o > 2σ (F 2 o). The 2:4 stoichiometry for the β-CD inclusion complex with p-HB in the crystalline state is different from that obtained in solution. β-CD forms dimers stabilized by direct O2(m)_1/O3(m)_1• • •O2(n)_2/O3(n)_2 hydrogen bonds (intradimer) and by indirect O6(m)_1• • •O6(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 infinite channels where the p-HB molecules are included. The p-HB molecules direct their polar CHO and OH groups into the nonpolar β-CD cavities and are hydrogen bonded to each other, yielding infinite, antiparallel chains. In addition, crystals of the complex were also investigated with thermogravimetry, vibrational spectroscopy (FTIR), and 13 C CP-MAS NMR spectroscopy. The results obtained enabled us to structurally characterize the β-CD inclusion complex with p-HB. * Supplementary data relating to this article are deposited with the British Library as Supplementary Publication No. 82299 (7 pages).
Conformational and circular dichroism studies on cyclodextrin inclusion complexes
Pure and Applied Chemistry, 1997
A &mework aimed at elucidating the structure of inclusion complexes between cyclodextrins (CDx) and several chromophores of photochemical interest is presented. The scheme is composed by a set of Molecular Mechanics calculations, Monte Car10 simulations including solvent effects and reproduction of the Induced Circular Dichroism (ICD) using quantum mechanically calculated properties combined to the Kirkwood-Tinoco expressions for the induced rotational strength. Examples of molecular recognition between a,P and y-CDx and a variety of chromophores of fundamental as well as of applicative interest , such as phenols, dimethoxybenzenes and buclaninstedlerene are examined. The method proposed proves to be a suitable instrument to elucidate different geomdcal configurations and to be able to gain insight into the relationship between structural and dynamic properties of the complexes studied. &&j&&g Supramolecular self-assembly has received recently a great deal of interest in several fields of Chemistry and Biology7 as it provides the physical basis for molecular recognition , formation of enzyme-complexes with substrates and is also related to protein folding. A remarkable model for this phenomenon is represented by the inclusion of a variety of organic compounds of molecules of suitable size in cyclodextrins (CDx), cyclic oligosaccharides consisting of sii (a-CDx) , seven (p-CDx) or eight ('y-CDx) D(+) glucopyranose units linked by u-(1,4) bonds and containing a central, hydrophobic cavity with a diameter of 5-8 A (1). The stability of the inclusion is determined by the fit of the molecular shape of the guest to the surface of the cavity, with intervention of van der W a a l s forces, hydrogen bonding, decrease of strain energy and release of high energy water molecules &om the cavity.The high solubility in water of the inclusion complexes of hydrophobic molecules in CDx has been exploited for a number of applications in pharmaceutical chemistry , food technology and plant protection industries. Moreover, due to their capability in binding substrates quickly, selectively and reversibly and to behave as catalysts in many chemical reactions, CDx can be considered good model enzymes. It is , therefore, of fundamental importance to understand the physics of complexation, i.e. the driving forces which govern the
Structure of the γ-cyclodextrin–1-propanol–17H2O inclusion complex
Acta Crystallographica Section B Structural Science, 1991
The crystal structure of the hydrated 1-propanol inclusion complex of y-cyclodextrin (y-CD), C48Hs0040.C3HsO.17"0H20, was determined from two sets of X-ray diffraction data collected from two crystals grown in different batches; the results are practically identical except for a few occupancy factors of water molecules and hydrogen-bonding interactions involving 0(6) and water molecules. Both crystals have tetragonal space group P42~2 with cell dimensions: a = b = 23-840 (5), c = 23.227 (5) ,~, and a = b-23.8093 (5), c-23.2069 (6) ,A,, respectively, Z = 6. The structures were refined by the blocked full-matrix least-squares method to R factors of 0.067 for 5029 unique observed reflections [I_ 3o-(/)] and 0.082 for 4303 unique observed reflections, respectively. The y-CD molecules are stacked on top of each other, their axes coinciding with the crystal fourfold rotation axis. Within the same stack, three independent ,/,-CO molecules are in tail-to-tail, head-to-head and head-to-tail arrangements, and hydrogen bonds are formed between the adjacent y-CD molecules with the O(2), 0(3) and 0(6) hydroxyls. The cavities of the y-CD molecules form endless 'major' channels. They accommodate 3.1 water molecules distributed over eight sites and the 1-propanol molecules which, however, could not be traced unambiguously owing to crystallographic disorder around the fourfold axis. The 'minor' interstitial channels between the stacks of y-CD molecules are filled with 9.7 water molecules distributed over 12 sites which are involved in a complicated hydrogenbonding network to primary and secondary hydroxyls of y-CD molecules. There are 12.8 H20 in the asymmetric unit, or 12.8 x 8/6 = 17.0 H20 per y-CD molecule, as given in the title. All glucose residues are in the usual 4C~ chair conformation with minor distortion. In the series a-, fly y-CD, the C(4)-O(4)-C(1)' interglucose bond angles reduce from 119.0 to 117.7 to 116.8 °. The average 0(2).-.0(3)' intramolecular hydrogen-bonding distances between adjacent glucoses for y-CD is 2.83 ,~,, much shorter than for a-CD (about 3-00 A), but * Part XXVI of the series Topography of Cyclodextrin Inclusion Complexes. Part XXV: Steiner, Mason & Saenger (1990). i" Author to whom correspondence should be addressed. 0108-7681/91/050731-08503.00 nearly the same as for Fl-CD, indicating a tighter ring of hydrogen bonds around the 0(2), 0(3) rims in fl-and y-CD than in a-CD. The 0(6) hydroxyl groups of glucoses 1 to 5 are twofold disordered with the major occupation sites pointing 'away' from the molecular cavity, while the minor occupation sites point 'inward'.
Carbohydrate Research, 2004
The crystal structure of the host-guest noncovalent complex of cyclomaltoheptaose (b-cyclodextrin, bCD) with the Odiglycosyl flavonoid neohesperidin dihydrochalcone [(3,5-dihydroxy-4-(3-hydroxy-4-methoxyhydrocinnamoyl)phenyl-2-O-(a-L Lrhamnopyranosyl)-b-D D -glucopyranoside, NDC] has been determined from single-crystal X-ray diffraction data collected at low temperature (130 K), using synchrotron radiation. The crystal data are as follows: A, orthorhombic, space group C222 1 . The structure contains 19 molecules of water, of which 11 appeared well positioned, whereas 9 are disordered over 23-positions. The bCD-NDC complex is characterized by one aromatic part of NDC deeply inserted into the hydrophobic cavity of the bCD through the primary OH rim, and it is present in the crystal as a dimer. The dimeric units, formed by head-to-head assemblies of CD molecules, each with its guest, are self-assembled in columns. The stability of the columns is provided by host-guest and guest-guest attractive interactions, thus showing a key role of the guest molecules in the crystal architecture. The guest conformation in the complex is different from that reported in the literature for uncomplexed NDC. The host-induced conformational changes on NDC provide the optimum geometry requirements for the assembly of the dimeric units.
Preparation and solid state properties of cyclodextrin complexes of selected drug molecules
1999
A large number of pharmaceutically important drugs are poorly soluble in water. This study focuses on the 'smart' molecule that can enhance the solubility and hence increase the bioavailability of these drugs. This molecule is a cyclodextrin and is known to form inclusion compounds with various drug molecules. The preparation of P-cyclodextrin CP-CD), y-cyclodextrin (y-CD), heptakis(2,6-di-O-J, methyl)-p-cyclodextrin (Dimeb) and heptakis(:J>•tri-0-methyl)-P-cyclodextrin (Trimeb) 3, complexes with clofibric acid as well as the heptakis(2j•tri-O-methyl)-p-cyclodextrin (Trimeb) complex with clofibrate is reported. The complexes were characterised by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), ultraviolet spectrophotometry (UV), infrared spectroscopy (IR), X-ray powder diffraction (XRD) and single crystal X-ray analysis. Infrared spectroscopy for the four inclusion complexes of clofibric acid showed a significant shift of the C=O stretching frequency in the complexed drug relative to the uncomplexed drug. The crystal structures of the complexes, except that of the Dimeb complex with clofibric acid, were solved. The guest molecules in the P-and y-CD complexes were found to be disordered, preventing detailed interpretation of the mode of inclusion. The guest molecules in the two Trimeb complexes were resolved and the modes of inclusion were revealed. The aliphatic chains of the guests were found to be inserted in the cavity, while the chlorophenyl rings protrude from the secondary side of the Trimeb molecule. Kinetics of dehydration studies for P-and y-CD complexes of clofibric acid, as well as for their
2013
Cyclodextrins (CD) are cyclic oligosaccharides composed of six to more than sixty glucose units. α-CD, β-CD and γ-CD are well known CD consisting of 6, 7 and 8 glycopyranose units, respectively, that are torus-like rings built up from glycopyranose units. The secondary hydroxyl groups are situated on one of the two edges of the ring, whereas all the primary ones are placed on the other edge. The ring is a conical cylinder, which is frequently characterized as a doughnut or wreath shaped truncated cone. The cavity is lined with hydrogen atoms and glycosidic oxygen bridges, respectively. The primary and secondary hydroxyls on the outside of the cyclodextrins make cyclodextrins water-soluble. The cavity of the cyclodextrin consists of a ring of C-H groups, a ring of glycosidic oxygen atoms and again a ring of C-H groups. This renders the interior of the cyclodextrin rings less polar. As a consequence, the hydrophilic sites which are outside of the torus enable CD to be soluble in water, whereas the apolar cavity site which provides a hydrophobic matrix, enables CD to form inclusion complex with a variety of hydrophobic guest molecules. In addition, CD contains repeating units of-OCCO-binding motif on both their primary and secondary faces. This makes CD able to form extended structures with metal cations of Group IA and IIA (MOFs). The main goal of this thesis was to design, prepare and characterize new crystal systems based on cyclodextrins properties in combination with: 1. Para aminobenzoic acid (pABA) as a drug model to study the effect of complexation phenomena on the solubility of drugs. Their structure and mode of interaction were characterized by combination a theoretical and experimental approaches. 2. Potassium hydroxide to prepare cyclodextrin Metal-Organic Frameworks (CD-MOFs) formed by coordinating the cyclodextrins to potassium cation. Consequently, taking the advantages of this interaction between cyclodextrin and alkali metal cation, formation of inclusion complexes as CD-MOFs drug carrier was favored. 3. Aegelinol, a natural product, for analytical purposes to determine the absolute configuration of this compound by formation of an inclusion complex with a host of known chirality (cyclodextrins consists of several optically active D-glucose units). This should allow direct determination of the absolute configuration of the guest (aegelinol).