Inhibitory Effect of Cyclodextrins on the Discoloration Reaction of an Anthocyanidin, Pelargonidin Chloride, in Acidic Media

An anthocyanidin, pelargonidin (PG), loses its color with time in acidic media. The rate determining step of the discoloration reaction at pH 1–4 is the nucleophilic attack of the OH^- ion on PG to give a hemiacetal, which readily isomerizes to the corresponding -diketone. Native, branched, and methylated cyclodextrins (CDs) form inclusion complexes with PG to retard the discoloration. The inhibitory effect (copigmentation) of CDs on the PG discoloration is slight in -CD, significant in - and -CDs, and the largest in heptakis(2,6-dimethyl)--CD (DM--CD). The -CD and DM--CD include the phenyl moiety of PG, whereas -CD includes the benzopyrylium moiety of PG. The CD cavities protect the reaction site of included PG from the attack of the OH^- ion.     

Solubility Study of Nimodipine Inclusion Complexation with α- and β-Cyclodextrin and some Substituted Cyclodextrins

The solubility of nimodipine was measured in aqueous solutions of the following cyclodextrins: -cyclodextrin (-CD), hydroxypropyl--CD (HP--CD), -cyclodextrin (-CD), random substituted methyl--CD (M--CD), three hydroxypropyl--CDs (HP--CD) with mutually different average degree of substitution, and hydroxypropyl--cyclodextrin (HP--CD). From the determined linear solubility diagrams the values of the binding constant K₁₁ of the inclusion complexes of nimodipine with the respective CDs were evaluated. The -CDs efficiently solubilized sparingly soluble nimodipine, the highest value of K₁₁ was found for M--CD (1680 M^-1), followed by -CD (550 M^-1) and HP--CDs, where the higher degree of substitution lowered K₁₁. Only slight solubilization of nimodipine was observed in the solutions of the -CDs and HP--CD.     

Energetics of Water/Cyclodextrins Interactions

The heat capacities of solid -CD, 8.1 H₂O and -CD, 6.0 H₂O have been measured between 10 and 300 K by adiabatic calorimetry. Using earlier results obtained in similar experiments with anhydrous cyclodextrins and with -CD, 9.7 H₂O, a comparative analysis has been developed. The energetic behaviours of anhydrous and hydrated cyclodextrins (CDs) have been compared in order to investigate the role of water molecules in the stabilization of the cyclodextrin's rings and on their reactivities. Calculations, based on the additivity of thermodynamic properties, provide the energetic and entropic average contributions of water molecules in each cyclodextrin. From these results, we assumed that the water–water and water–CD interactions are rather different according to the cyclodextrin. In the (-CD, 9.7 H₂O) structure, the water molecules seem to be better organised in a relatively independent network. Concerning hydrated -CD and -CD, stronger water–CD interactions probably prevent an optimal organisation of the water–water bonds network. Differential scanning calorimetry was also used to follow the evolution of the thermal behaviour of -CD, nH₂O versus hydration ratio between 170 and 300 K. Our results indicate that the -CD ring needs at least 1.6 water molecules to be stabilized in the solid state.     

Photometric detection of cyclodextrins in liquid chromatography by using iodine generated electrochemically in-situ

A method has been developed for photometric detection of cyclodextrins (CD) in liquid chromatography using iodine (I₂) generated electrochemically in-situ. Iodide ion in the mobile phase was electrochemically oxidized to I₂ which was subsequently reacted with I^–, in an electrochemical flow cell, forming I₃^–. The absorbance of I₃^– was found to be greatly enhanced when CD were present in the mobile phase. The absorbance enhancement was caused by the change in the mole fraction of I₃^–, because of the inclusion reaction of I₃^– with CD. On the basis of this phenomenon, CD were detected by means of a photodiode-array UV–visible detector positioned downstream of the electrochemical flow cell. The signals were found to be linearly dependent on CD concentration. Because the formation constants of I₃^– with CD decrease in the order -CD>-CD>-CD, -CD was most detectable by the method. Detection limits were 1.0 mol L^–1 for -CD, 65 mol L^–1 for monoG1--CD, 100 mol L^–1 for -CD, and 200 mol L^–1 for -CD.     

Darstellung,Thermisches Verhalten und Gitterparameter von Erbiumfluorooxalattetrahydrat ErFC2O4 · 4H2O

Zusammenfassung Erbiumfluorhydrat ErF₃ · 1.1 H₂O bildet in Oxalsäurelösungen Erbiumfluorooxalattetrahydrat ErFC₂O₄ · 4 H₂O. Das ErFC₂O₄ · 4 H₂O ist grobkristallin, unlöslich in verdünnten Säuren und Laugen und löslich in konzentrierter Schwefelsäure. Beim thermogravimetrischen Abbau bildet es die Verbindungen ErFC₂O₄ · 2 H₂O, ErFC₂O₄ · · H₂O, ErFC₂O₄, ErOF und ErO_1.5. Die Kristallstruktur des ErFC₂O₄ · 4 H₂O ist orthorhombisch mit den Gitterkonstantena=11.217±0.007 Å,b-13.046±0.008 Å,c=9.191±0.005 Å undZ=6.

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Erbium fluoride hydrate ErF₃ · 1.1 H₂O forms in solutions of oxalic acid erbium fluorooxalate tetrahydrate ErFC₂O₄ · 4 H₂O. The ErFC₂O₄ · 4 H₂O is coarse-crystalline, insoluble in diluted acids and bases and soluble in concentrated sulphuric acid. During thermal decomposition ErFC₂O₄ · 2 H₂O, ErFC₂O₄ · H₂O, ErFC₂O₄, ErOF and ErO_1.5 are formed. The crystal structure of ErFC₂O₄ · 4H₂O is orthorhombic, with lattice constantsa=11.217±0.007 Å,b=13.046±0.008, Å c=9.191±±0.005Å andZ=6.

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Résumé Le fluorure d'erbium hydraté (ErF₃ · 1.1 H₂O) forme dans l'acide oxalique fluorooxalate d'erbium tétrahydraté (ErFC₂O₄ · 4 H₂O), un précipité consistant à gros cristaux insoluble dans les acides et bases dilués, mais soluble dans l'acide sulfurique concentré. Au cours de sa décomposition thermique on obtient ErFC₂O₄ · 2 H₂O; ErFC₂O₄ · H₂O; ErFC₂O₄, ErOF et ErO_1.5. ErFC₂O₄ · 4 H₂O a une structure cristalline ortorhombique avec les paramètres suivants:a=11.217±0.007 Å,b=13.046±0.008 Å,c-9.191 ±0.005 Å,Z=6.

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ErF₃ · 1.1 H₂O, ErFC₂O₄ · 4H₂O. ErFC₂O₄ · 4H₂O, - , , . : ErFC₂O₄ · 2H₂O. ErFC₂O₄ · H₂O, ErFC₂O₄, ErOF ErO_1·5. ErFC₂O₄ · 4 H₂O a=11,217±0,007 Å,b=13,046±0,008 Å,c=9,191± 0,005 Å Z=6.

     

Inclusion of Ring A of Cholesterol Inside the β-Cyclodextrin Cavity: Evidence from Oxidation Reactions and Structural Studies

The disposition of cholesterol inside the -cyclodextrin cavity(-CD) was deduced from oxidation of cholesterol secondary alcoholgroups by Ca(OCl)₂ and H₂O₂ in thepyridine–acetic acid system. The amount of cholest-4-ene-3-one formedwas found to be proportional to the concentration of -cyclodextrin,resulting in 56.1% of ketone. The oxidation rate was enhanced by-cyclodextrin and its methyl, polymer and 1 : 1copper(II)–-cyclodextrin derivatives. Detailed investigationsinvolving UV-visible, ¹³C- and ¹H-NMR(T₁, 1D NOE and ROESY) spectroscopic studies were carried out.A binding constant value of 15,385 ± 1500 M^-2 wasobtained for the 2 : 1heptakis-2,6-di-O-methyl--cyclodextrin(DM-CD) : cholesterolcomplex in chloroform from UV studies. Proton and solid state¹³C-CP MAS spectra of the -CD–cholesterol mixtureshowed large magnitude shifts for the protons from the wider end of the-CD cavity as well as those of ring A and ring B of cholesterol. Both1D NOE and ROESY measurements indicated the proximity between ring A andring B protons of cholesterol and the wider end protons of -CD andDM-CD. Besides, analysis of _c,_i and tau;_m from T₁measurements showed not only a lowering of rotational motions but a value of 0.016–0.048 for some of the cholesterol protons, typical of aweak complex. Based on these studies, a probable structure for the 2 : 1complex involving two molecules of -CD/DM-CD was proposed withportions of ring A and ring B being present inside the wider end of the-CD/DM-CD cavity and ring D and the side chain attached atposition 17, projecting into the wider end of the secondCD/DM-CD molecule.     

Order and disorder in mixed metal linear chains: The homo and heterobimetallic EDTA (M(H2O)4OIOII)[M′(EDTA)] · 6H2O complexes (M = Mg,Mn, Co,Zn and Ni; M′ = Co,Ni, Cu and Zn)

Summary Polymetallic solid solutions of the ethylenediaminetetracetic acid (EDTA) and six divalent metal ions exist in the range: MgMnCoZnNiCu(EDTA) · 6H₂O where + + + + + =2, 01, 0,,2, 0, 1.This type of structure is characterized by the presence of two different octahedral carboxylate-bridged coordination sites forming infinite zig-zag chains. Visible and i.r. spectra and t.g.a. analysis show that there is occupational preference for the two coordination sites in the crystalline structure.Due to this preference, and also to the structural features, the heterobimetallic MM(EDTA) · 6H₂O compounds constitute a structurally new class of materials which can be described as ordered alternating-heterobimetallic polymeric coordination complexes.     

Inclusion Complexes of Cyclodextrins with 4-Amino-1,8-Naphthalimides

The formation of inclusion complexes between 4-amino-1,8-naphthalimides and cyclodextrins (CDs) was investigated. The naphthalimides used in the study were 4-amino-1,8-naphthalimide (I) and4-(2-phosphonoethylamino)-N-(2-phosphonoethyl)-1,8-naphthalimide,tetraethylester (II). The CDs employed were -CD, -CD, -CD, HP--CD, HP--CD andHP--CD (HP = hydroxypropyl). Evidence for complex formation was obtained from the changes in the fluorescence spectra of the dyes in the presence of increasing amounts of the CDs. The most striking changes were observed with HP--CD and HP--CD. Treatment of the data using Benesi–Hildebrand plotswas consistent with a 1:1 inclusion model. The determined stabilityconstants were (K_eq, M^-1): 106 (I:HP--CD, pH = 2.0), 193 (I:HP--CD, pH = 7.0), 113 (I:HP--CD, pH = 7.0), 155(II:HP--CD, pH = 2.0), 121 (II:HP--CD,pH = 7.0), 301 (II:HP--CD, pH = 7.0). It can beconcluded that compound I forms a more stable complex with HP--CD than with HP--CD. Compound II, on the other hand, forms a more stable complex with HP--CD than with HP--CD.     

The supramolecular structures and reactivities of some complexes of chiral crown ethers with borane ammonia

Whereas 1 1 crystalline complexes have been isolated between borane ammonia and methyl 4,6-O-benzylidene-2,3-dideoxy--d-galactopyranosido [2,3-b]-1,4,7,10,13,16-hexaoxacyclo-octadecane (1), methyl 4,6-O-benzylidene-2,3-dideoxy--d-mannopyranosido [2,3-b] (methyl 4,6-O-benzylidene-2,3-dideoxy--d-mannopyranosido [2,3-k]-1,4,7,10,13,16-hexaoxacyclo-octadecane (3), and (1R,2R,7R,24R)-3,5,8,11,14,17,20,23,26,28-decaoxatricyclo-[21.4.0.0^2,7]octacosane (4), the hosts, methyl, 4,6-O-benzylidene-2,3-dideoxy--d-mannopyranosido[2,3-b] 1,4,7,10,13,16-hexaoxacyclo-octadecane (2) and 1,4 1,4 3,6 3,6-tetra-anhydro-2,2 5,5-bis-O-oxydiethylenedi-d-mannitol (5) have yielded 2 1 (guest:host) crystalline complexes with borane ammonia as guest. X-ray analyses of the supramolecular structures of BH₃NH₃ ·1, (BH₃NH₃)₂ ·2, BH₃NH₃ ·3, BH₃NH₃ ·4, and (BH₃NH₃)₂ ·5 have been carried out and BH₃NH₃ ·1, BH₃NH₃ ·2, and (BH₃NH₃)₂ ·5 have been shown to reduce acetophenone with enantiomeric excesses of 5, 13, and 10% respectively. Supplementary Data relating to this article (atomic coordinates of the hydrogen atoms and thermal parameters) are deposited with the British Library as Supplementary Publication No. SUP 82017 (74 pages).Dedicated to Professor H. M. Powell.     

Ultrasonic study of the molecular encapsulation and the micellization processes of dodecylethyldimethylammonium bromide-water solutions in the presence of β-cyclodextrin or 2,6-di-o-methyl-β-cyclodextrin

Aqueous solutions of -cyclodextrin (-CD) or 2,6-di-o-methyl--cyclodextrin (DM--CD) and dodecylethyldimethylammonium bromide (D₁₂EDMAB) have been studied from speed of sound (u) data at 298.15 K, using a pulse-echo-overlap technique. The molecular encapsulation process of the surfactant monomer into the cyclodextrin cavity and its effect in the micellization process of the surfactant have been analyzed from theu measurements: I) as a function of [D₁₂EDMAB] in the presence of several initial cyclodextrin concentrations (-CD or.DM--CD); II) as a function of [cyclodextrin] (-CD or DM--CD), for an initial micellar solution of D₁₂EDMAB and; III) as a function of the [cyclodextrin]/[surfactant] stoichiometric concentrations. Both inclusion complexes formed (-CDD₁₂EDMAB) and (DM--CDD₁₂EDMAB) have stoichiometries of 11, and their association constantK have been determined using a model proposed in this work, based on the additivity of the different contributions of the involved species to the speed of sound. The apparent critical micellar concentration, cmc^*, of D₁₂EDMAB is found to increase linearly upon the addition of cyclodextrin (-CD or DM--CD). The free surfactant concentration in the micellar region, [D₁₂EDMAB]_f, decreases in the presence of -CD and slightly increases in the presence of DM--CD. The influence of the parcial methylation of the -cyclodextrin (-CDDM--CD) and of the polar head of the surfactant (D₁₂TAB D₁₂EDMAB) on the complextion and micellar parameters are also discussed.Supplementary material available: Tables of speed of sound (14 pages) are available from the authors.     

FT-Raman Spectra of 2-, 3-, and 4-Chlorostyrene Molecules Included in Cyclodextrins

FT-Raman spectra of 2-, 3-, and 4-chlorostyrene included in-cyclodextrin (CD),glycerol ether -CD, -CD,sulfated -CD, andglycerol ether -CD were recorded.In the inclusion complexes, the area of the vinyl(C=C) band decreased remarkably, whereasthe area of the phenyl (C=C) band increasedcompared to those of liquid 2-, 3-, and 4-chlorostyrene,respectively. From the results, the inclusion structures of2-, 3-, and 4-chlorostyrene were discussed.     

FT-IR and raman spectra of a series of metallo-β-cyclodextrin complexes

A series of metallo--CD complexes were prepared and formulated as [M₂(OH)₂ -CD·2 H₂O] ^n– . Changes in the FT-IR and Raman Spectra of-CD on coordination may be taken as evidence for complexation and support for a hydroxy bridged binuclear structure. Further support was obtained from uv/visible and magnetic moment measurements.     

Effects of Modified β-Cyclodextrins on the Hydrolysis Reaction of p-Nitrophenyl α-Methoxyphenylacetate

Effects of -cyclodextrin (-CD) 1and its derivatives 2–7 on the deacylationreaction of p-nitrophenyl (R or S)--methoxyphenylacetatewere studied. The-CD derivatives used were6--D-glucosyl--CD 2, sulfated-CD (7–11 sulfate groups/CD ring) 3,dimethylated -CD 4, carboxymethylated-CD (3.5 carboxymethyl groups/CD ring) 5,2-tri(2-hydroxypropyl)--CD 6, and-CD appended on poly(allylamine) 7. Therate constant (k ^CD) of thesubstrate/-CD complexes and the formationconstants (K) of the complexes were determinedfrom the dependence of the pseudo-first order rateconstants of the deacylation reaction on theconcentration of -CDs. The order ofk ^CD for the R-enantiomer at pH8.0 is 45H₂O3 6 1 2 7, whilethat for the S-enantiomer is 4 5 6H₂O 1 2 3 7: H₂O denotes the rate in theabsence of -CDs. The order of K values is3 7 6 2 1 4 5. This work indicates that, though thesecondary hydroxyl groups of -CD play criticalroles in the deacylation reactions of the esterscomplexed with -CDs, the reactivity of theester/-CD complexes depends highly on thenature of the substituents at the secondary face of-CD. It also suggests that the substratesinserted from the secondary side as well as theprimary side of -CD of poly(allylamine)-bound-CD undergo the reaction by attack of aminogroups on the polymer chain.     

Synthesis and thermal study of some adducts of morpholine with nickel(II) nitrite,sulphate and perchlorate

The preparations of the nickel-morpholine (Morph) complexes Ni(NO₂)₂·3Morph and Ni(ClO₄)₂·4Morph·2H₂O are described. The thermal treatment of this perchlorate and of NiSO₄·2Morph led to the isolation of Ni(ClO₄)₂·2Morph·2H₂O and NiSO₄·Morph. The magnetic moments, diffuse reflectance spectra and infrared spectra of these compounds are all compatible with a pseudo-octahedral environment around the nickel atom.

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Zusammenfassung Die Darstellung der Nickel-Morpholin(Morph)-Komplexe Ni(NO₂)₂·3Morph und Ni(ClO₄)₂·4Morph·2H₂O wird beschrieben. Die thermische Behandlung dieses Perchlorates und von NiSO₄·2Morph ergibt Ni(ClO₄)₂·2Morph·2H₂O und NiSO₄Morph. Magnetisches Moment sowie diffuse Reflektionsspektren und Infrarotspektren dieser Verbindungen sind kompatibel mit einer pseudooktaedrischen Koordination des Nickelatoms.

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, () : Ni(NO₂)₂·, NiSO₄·2 Ni(ClO₄)₂·4·2H₂O. NiSO₄· Ni(ClO₄)₂·2·2H₂O. , , .

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The authors are indebted to Consejeria de Cultura y Educación de la Comunidad Autónoma de Murcia for financial support.     

The structures of macrocyclic heterocyclophane inclusion complexes

Crystal and molecular structures of (1:1) molecular complexes of N,N,N,N-tetramethyl-2, 11, 20, 29-tetraaza [3.3.3.3] paracyclophane (1) with CHCl₃, CH₂Cl₂, CH₃CN and CO₂ are reported. The macrocycle has square-box structure, giving hydrophobic cavity surrounded by four benzene rings. The guest molecules are included in the cavity. The uncomplexed1 was found to have a rectangular form, indicating large conformational flexibility of1. In solution,1 is achiral because rapid RS interconversion, but in solid, the macrocyclic conformation is frozen as R-conformer or S-conformer. The macrocycles with the same chirality are stacked alongb-axis to form chiral molecular columns, R-colums or S-columns. Complexes of1 crystallize differently depending on the guest molecules. R-columns (S-columns) packed alonga-axis produce R-layers (S-layers), which are further packed alongc-axis using R-layer to R-layer contact (RR) or SS and RS or SR. The crystals of1·CHCl₃ are formulated as--RRR--=[R]_n (Type I, chiral) and those of1·CH₃CN or1·CO₂ and1·CH₂Cl₂ are represented by [RS]_n (Type IIA, racemic) and [RRSS]_n (Type IIB, racemic), respectively.     

β-Cyclodextrin Mediated Synthesis of Syndiotactic-rich Polystyrene

Stereoregular polystyrene (PS) was prepared using various molarequivalents of -cyclodextrin (-CD) by polymerisingstyrene in the presence of -CD. Stereoregular (isotactic,atactic and syndiotactic) distributions of the preparedpolystyrene polymers were determined from terminal modelBernoullian statistics using ¹³C NMR data. Inclusioncomplexation of styrene by -cyclodextrin was detected byUV-Visible spectroscopy, which gave a binding constant value of31606 ± 3350 M^-1 for the 1 : 1 complex. With anincrease in the styrene : -CD ratios, the proportionof syndiotactic polymers increased. The glass transitiontemperature (T_g) of the polymer also increased along withmelting temperature (T_m) at higher styrene : -CDratios. In addition, the molecular weight of the polymers prepareddecreased with increase in the -CD concentration.     

Comparison of the Complexation of Cosmetical and Pharmaceutical Compounds with γ-Cyclodextrin, 2-Hydroxypropyl-β-cyclodextrin and Water-Soluble β-Cyclodextrin-co-epichlorhydrin Polymers

The ability of different cyclodextrins (CDs): CD, 2-hydroxypropyl CD to complex drugs like 3--hydroxy-11-oxoolean- 12-en-30-oic acid, 2-ethylhexyl-3-(4-methoxyphenyl)-2-propanoate and menthol was compared to that of water-soluble polymers: CD-co-epichlorhydrin polymer (pCD/EP) and CD-co-epichlorhydrin polymer partially modified with trimethylammonium groups (pCD/EPN⁺). 3--Hydroxy-11-oxoolean-12-en-30-oic acid was poorly solubilized by CD compared with other CD derivatives, however the determination of the complexation constants was possible for pCD/EP, K₁₁ = 740, K₁₂ = 4, for pCD/EPN⁺, K₁₁ = 681, for CD, K₁₁ = 16 and for hydroxypropyl CD, K₁₁ = 114, K₁₂ = 3.4. A significant increase of the solubility was observed for 2-ethylhexyl-3-(4-methoxyphenyl)-2-propanoate with all host molecules, it was 916 times its solubility in pure water with pCD/EPN⁺, 1116 and 1300 times with 2-hydroxypropyl CD and pCD/EP respectively. The association constants are K₁₁ = 7970, K₁₁ = 4700, K₁₁ = 1470, K₁₁ = 230 and K₁₂ = 200 with pCD/EP, pCD/EPN⁺, CD, 2-hydroxypropyl CD respectively. An increase of the solubility of menthol was observed with all CD derivatives, up to 36–37 times, except for CD. The complexation constants are similar equal to about 200.     

Inclusion Complexes of Cyclodextrins with Tetrakis(4-carboxyphenyl)porphyrin and Tetrakis(4-sulfonatophenyl)porphyrin in Aqueous Solutions

In neutral and alkaline solutions, tetrakis(4-carboxyphenyl)porphyrin (TCPP) and tetrakis(4-sulfonatophenyl)porphyrin (TSPP) form 1:1 and 2:1 host–guest inclusion complexes with -cyclodextrin (-CD), -cyclodextrin (-CD), and 6-deoxy-6-diethylamino--CD (DEA--CD), except for DEA--CD in alkaline solution. On the other hand, TCPP and TSPP form only 1:1 inclusion complexes with 6-deoxy-6-dihexylamino--CD (DHA--CD). The limited solubilities of DEA--CD in alkaline solution and DHA--CD are likely responsible for no observation of the 2:1 inclusion complex containing DEA--CD in alkaline solution and that containing DHA--CD. The equilibrium constants (Ks) of TCPP and TSPP for the formation of the inclusion complexes have been estimated from the absorption and/or fluorescence intensity changes in neutral and alkaline solutions. The K₂ values, which are the equilibrium constants for the formation of the 2:1 host–guest inclusion complex from the 1:1 inclusion complex, are about one tenth the corresponding K₁ values, except for the -CD–TSPP system in alkaline solution. In neutral solution, where DEA--CD and DHA--CD are in protonated forms, the electrostatic force operates between DEA--CD (DHA--CD) and TCPP (TSPP), leading to the greater K values than those in alkaline solution, where DEA--CD and DHA--CD exist as neutral species.     

Structure of the β-Cyclodextrin·p-Hydroxybenzaldehyde Inclusion Complex in Aqueous Solution and in the Crystalline State

-Cyclodextrin (-CD) and p-hydroxybenzaldehyde (p-HB) were studied by ¹H-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 -CD was confirmed by the observation of NMR shifts for the inside H5 protons of the -CD cavity. In the solid state X-ray analysis was carried out and revealed the detailed structure of the inclusion complex. Two -CDs cocrystallize with four p-HB and 9.45 water molecules[2(C₆H₁₀O₅)^7·4C₇H₆O_2·9.45H₂O] in the triclinic space group P1 with unit cell parameters: a = 15.262(2), b = 15.728(1), c = 16.350(1) Å, = 92.67(1)°, = 96.97(1)°, = 103.31(1)°. The anisotropic refinement of 1973 atomic parameters converged at an R-factor = 0.066 for 10157 data with F_o ² > 2 (F_o ²). The 2:4 stoichiometry for the -CD inclusion complex with p-HB in the crystalline state is different from that obtained in solution. -CD forms dimers stabilized by direct O2(m)₁O3(m)₁·O2(n)₂O3(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 -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 ¹³C CP-MAS NMR spectroscopy. The results obtained enabled us to structurally characterize the -CD inclusion complex with p-HB.     

Association Constant Prediction for the Inclusion of α-Cyclodextrin with Benzene Derivatives by an Artificial Neural Network

The association constants (K_a) for the inclusion complexation of -cyclodextrin (-CD) with 72 mono- and 1,4-disubstituted benzenes were predicted successfully by an artificial neural network (ANN) with molar refraction (R_m) and hydrophobic constant () as input parameters, which reflect the volume and hydrophobicity of the substituents respectively. The predictions strongly suggested that the inclusion complexation of -CD with guest molecules was mainly driven by van der Waals forces and hydrophobic interactions