Effects of water and alcohol on the formation of inclusion complexes of d-limonene and cyclodextrins

Abstract

Systematic studies have been carried out on the role of water and alcohol in the formation of inclusion complexes between d-limonene and α-, β- and γ-cyclodextrin (CD) by a micro-aqueous method. The inclusion complex was barely formed at zero water content for all CDs. Above the specific water content for each CD, formation of the inclusion complex correlated well with an equation which was derived on the autocatalytic assumption for the inclusion phenomenon. The inclusion complex correlated well with an equation which was derived on the autocatalytic assumption for the inclusion phrnomenon. The minimum water content, which was defined as 1% of the maximum concentration of the inclusion complex formed, coincided with the number of water molecules inside the cavity of the CD. In the presence of ethanol, a significant amount of the inclusion complex was formed for β- and γ-CD/limonene systems, particularly at lower moisture content. However, for α-CD the inclusion fraction decreased significantly in the presence of ethanol. This means that ethanol inhibits the formation of the inclusion complex between x-CD and d-limonene. For other linear alcohols, the formation of the inclusion complex between d-limonene and β-CD increased with decreasing alkyl chain length. This suggests that the more hydrophilic and the smaller (in molecular size) the alcohol is, the more enhanced is the inclusion of d-limonene to β-CD.     

Bis(2-Amino-5-bromopyrimidinium) Tetrahalometallates: Crystal structures of (2-amino-5-bromopyrimidinium)2 MCl4 (M = Co,Zn)

The reactions of metal(II) chlorides and bromides with 2-amino-5-bromopyrimidine (2-abpm) in neutral and acidic solution were investigated. The reaction with ZnCl₂, ZnBr₂, CoCl₂, CoBr₂ and MnCl₂ in acidic nitromethane solution gave complexes of the formula (2-abpmH)₂MX₄ (1, M?=?Zn, X?=?Cl; 2, M?=?Zn, X?=?Br; 3, M?=?Co, X?=?Cl; 4, M?=?Co, X?=?Br; 5, M?=?Mn, X?=?Cl). Crystals of 1 and 3 suitable for single crystal X-ray diffraction were obtained. Crystal data: For (1): triclinic, P-1, a?=?6.2485(13), b?=?9.0520(14), c?=?15.334(4)?Å, α?=?94.81(2), β?=?95.224(17), γ?=?98.027(17)°, V?=?851.1(3)?ų, Z?=?2, R?=?0.0596 for [|I|?≥?2σ(I)]. For (3): triclinic, P-1, a?=?6.2438(13), b?=?9.0597(15), c?=?15.318(3)?Å, α?=?94.749(18), β?=?95.343(15), γ?=?98.021(17)°, V?=?850.2(3)?ų, Z?=?2, R?=?0.0452 for [|I|?≥?2σ(I) ]. Variable temperature magnetic susceptibility data indicates weak antiferromagnetic interactions in the cobalt and manganese complexes.     

Competitive formation of M+˙ and [M + H]+ ions under fast atom bombardment conditions

The competitive formation of molecular ions M^+˙ and protonated molecules [M + H]⁺ under fast atom bombardment (FAB) conditions was examined using various kinds of organic compounds. The use of protic/hydrophilic matrices such as thioglycerol and glycerol resulted in relatively large values of the peak intensity ratio I([M + H]⁺)/I(M^+˙) compared with the use of relatively aprotic/hydrophobic matrices such as m-nitrobenzyl alcohol and o-nitrophenyl octyl ether. The change of matrix from thiol-containing such as thioglycerol and dithiothreitol to alcoholic such as glycerol and pentamethylene glycol increased the I([M + H]⁺)/I(M^+˙) ratio. Furthermore, the change of matrix increased the peak intensity ratio of the doubly charged ion [M + 2H]²⁺ to [M + H]⁺ in the FAB mass spectra of angiotensin I and gramicidin S. The addition of acids to the matrix solution increased the I([M + H]⁺)/I(M^+˙) ratio, although such an effect did not always occur. The acetylation of simple aniline compounds markedly increased the I([M + H]⁺)/I(M^+˙) ratio. It was concluded from these results that the hydrogen bonding interaction between hydroxyl groups(s) of the matrix and basic site(s) of analyte molecules in solution acts advantageously as a quasi-preformed state for [M + H]⁺ formation, and that the presence of significant proton acceptor(s) such as carbonyl group in analytes hinder the M^+˙ formation which may generally occur under FAB conditions. The formation of M^+˙ and [M + H]⁺ ions seemed to occur competitively, reflecting or according to the interaction or solvation states between the analyte and matrix molecules in solution and the structural characteristics of the analytes.     

Formation of crystalline inclusion compounds of poly (vinyl chloride) of different stereoregularity with γ-cyclodextrin

This work reports the formation and detailed characterization of the γ-cyclodextrin (γ-CD) inclusion compounds (ICs) formed with two poly (vinyl chloride) samples with different isotactic content. The ICs were characterized by X-ray diffraction, solid state ¹³C-NMR, solution ¹H-NMR, FT-infrared, differential scanning calorimetry, and thermogravimetric analysis. Experimental evidence of the inclusion of the guest polymer chains into the narrow channels created by the γ-CD crystalline host lattice has been obtained. Examination of coalesced poly (vinyl chlorides) (PVCs) obtained after the host γ-CD is removed reveals different characteristics specifically for the coalesced PVC sample with higher isotactic content. An increase in T_g was observed by DSC for this PVC. To the contrary, the T_g of the coalesced PVC sample with lower isotactic content is almost the same as that of the as-synthesized sample. Thermogravimetric analysis indicated that coalesced PVC with higher isotactic content acquires a degree of stabilization after modification by threading into and being extracted from its γ-CD IC. The results suggest that an irreversible conformational change takes place when PVC forms ICs with a solid host lattice like γ-CD. The PVC molecules extend and reorganize into a more stable conformation in the IC, consequently improving the properties of the coalesced sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2503–2513, 2007     

Direct evidence for symmetry control in cyclodextrin-water interactions

Abstract

The cyclodextrins, cyclic oligosaccharides possessing generally 6, 7, or 8 α, 1 –4 linked glucopyranose units, are widely used for the solubilisation and transport of organic molecules in aqueous media.³ Their solubilities 145 gL^?1, α-Cd; 20 gL^?1, β-CD; 220 gL^?1, γ-CD, are considerably lower than those of simple saccharides and in particular that of β-CD, the most widely available compound, is anomalously low. We have previously shown that the solubilities arise from symmetry determined interactions of the CDs with the dynamic hexagonal structure of water. In the case of the unmodified cyclodextrins all three compounds exist in solution as large aggregates, thus the solubility of these systems is controlled by the interactions between these hydrogen bonded aggregates and the hydrogen bonding networks present in water. In the case of α- or γ-CD there are favorable overlaps with the hexagonal water structure, however for the seven-fold symmetry of β-CD no such favorable interactions can occur between the odd symmetry element and the even symmetry elements of water. Hence the observed solubilities of α- and γ-CD are higher than that of β-CD.     

Investigation of the inclusion of the herbicide cycluron in native cyclodextrins by X-ray diffraction,nuclear magnetic resonance spectroscopy and isothermal titration calorimetry

The formation of inclusion complexes between the native cyclodextrins (CDs) and the urea herbicide cycluron has been investigated both in solution and in the solid state. Single-crystal X-ray structures of both the uncomplexed guest and the β-CD·cycluron complex were determined while powder X-ray diffraction was used to confirm complexation between γ-CD and cycluron in the solid state. Solution-state complexation between the herbicide and α-, β- and γ-CD was established using ¹H NMR spectroscopy and isothermal titration calorimetry (ITC). From the ¹H NMR spectroscopic studies 1:1 complex stoichiometry was indicated in all cases and association constant values (K) were determined as 228, 3254 and 155 for the complexes α-CD·cycluron, β-CD·cycluron and γ-CD·cycluron, respectively. Assigning a 1:1 host–guest ratio, the ITC technique produced K values of the same order as those determined using the spectroscopic method. The thermodynamic parameters ΔH, ΔS and ΔG obtained using ITC provide insights into the driving forces involved during complex formation.     

Complexes of α-, β-, and γ-cyclodextrins with nitrophenols: A theoretical study of the structure and energy

Detailed quantum mechanical calculations of the interaction of cyclodextrin (α-, β-, and γ-CD) with 4-nitrophenol (I), 4-nitro-2,6-dimethylphenol (II), 4-nitro-3,5-dimethylphenol (III), and their anions (IVVI) with the formation of intercalation complexes are carried out for the first time. The calculations of the compounds are performed within the density functional theory by the hybrid Becke–Lee–Yang–Parr (B3LYP) method with LanL2DZ basis sets. For the α-CD+III and α-CD+VI complexes it is shown that a nitrophenol molecule of III and a nitrophenolate anion of VI are not contained in the α-CD torus, which agrees with the experimental equilibrium constants. It is found that the calculated equilibrium constants of the formation of guest–host complexes with phenolate anions are much larger than those of neutral molecules. The most stable CD complexes with nitrophenols and their anions should be expected for γ-CD. The β-CD complexes when the guest enters into the host cavity are formed only with compounds I, V, and VI.     

Noncovalent interactions of pentafluorobenzoate in the Zn(II) and Cd(II) complexes

[Zn(Phen)2(Pfbz)(H2O)](Pfbz)(H2O)2 (I) and 2[Cd(Phen)2(Pfbz)(ONO2)][Cd(Phen)2(ONO2)2] (II) (Phen-1,10-phtnanthroline) containing the fluorine type ligand, pentafluorobenzoate (Pfbz) have been synthesized. Elemental analysis, IR spectra, and X-ray crystal structure analysis were carried out to determine the compositions and crystal structures of the two compounds. The crystal packing exhibits intricate intermolecular π-π stacking interactions and various hydrogen bonds. The C-H···F-C interactions and weak F···F interactions play important roles in the formation of the supramolecular network. Emission properties of I and II are also investigated. The text was submitted by the authors in English.     

Structural features and N-H…O and O-H…O hydrogen-bonded supramolecular frameworks in 2-methylanilinium hydrogen DL-malate hydrate, 4-methoxyanilinium and 4-methylanilinium hydrogen DL-malate salts

In the crystal structure of 2-methylanilinium hydrogen DL-malate hydrate (I), an additional water molecule is present in asymmetric unit. In the crystal structures of 4-methoxyanilinium hydrogen DL-malate (II) and 4-methylanilinium hydrogen DL-malate (III), the hydrogen malate anions exhibit configurational disorder with major component occupy S-configuration and minor component occupy R-configuration provided both (II) and (III) are prepared from a racemic mixture of DL-malic acid. In crystal structures of compounds (I)–(III), the hydrogen malate anions and anilinium cations from O-H…O and N-H…O hydrogen bonds which exhibit interesting supramolecular frameworks. In compound (I), the N-H…O and O-H…O hydrogen-bonded anionic-cationic framework form two-dimensional hydrophilic and hydrophobic layers in which the lattice water molecules are embedded in hydrophilic layers. However, in crystal structures of (II) and (III), the hydrogen DL-malate anions form two-dimensional anionic substructure through O-H…O hydrogen bond, in which the anilinium cations are anchored through N-H…O hydrogen bonds.

     

Spectroscopic properties,structure, and photoinduced motion of 4-(2-naphthyl)pyridine in cyclodextrin cavities

Spontaneous and photoinduced protonation of 4-(2-naphthyl)pyridine (1) in solutions and in complexes with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was studied using the absorption and fluorescence spectroscopies. The structures and stabilities of complexes of compound 1 and its quaternized derivative, 1-methyl-4-(2-naphthyl)pyridinium perchlorate (3), with β-CD and HP-β-CD were examined by ¹H NMR titration (logK = 1.5–2.3). The molecule of naphthylpyridine 1 is always in the cyclodextrin cavity, regardless of the pH value of the solution. 2-Hydroxypropyl-β-cyclodextrin binds better the neutral form of compound 1 than does β-CD, while naphthylpyridinium salts exhibit nearly equal affinities to both cavitands. According to spectroscopic data, pK _a (1) is 5.12 in water, which favors protonation of the N atom both in the ground and excited states; as a result, the fluorescence spectrum exhibits only the band of the protonated form with a lifetime of 15 ns. The addition of HP-β-CD to a solution of naphthylpyridine 1 results in the formation of inclusion complex 1@HP-β-CD, lowers pK _a to 4.62, and gives rise to a fluorescence band of the nonprotonated form of compound 1 with a lifetime of 1.25 ns. Therefore, the presence of compound 1 in the HP-β-CD cavity precludes its protonation in the excited state. The initial portions of the fluorescence curves for compound 1 in solution and in its complex with HP-β-CD obtained upon pulsed excitation were compared to propose the initiation mechanism of short-lived fluorescence of the nonprotonated form of naphthylpyridine 1. Quantum chemical modeling of the protonation and complexation of compound 1 in the presence of water was performed. Based on the results obtained, a reversible photoinduced mechanical motion of naphthylpyridine 1 in the HP-β-CD cavity was suggested.     

The modes of complexation of benzimidazole with aqueous β-cyclodextrin explored by phase solubility, potentiometric titration, 1H-NMR and molecular modeling studies

The results of rigorous modeling of phase solubility diagrams, pH solubility profiles and potentiometric titrations revealed the following for benzimidazole (BZ) and BZ/β-CD complexation in aqueous solution: (a) the pK _a value of BZ estimated at 5.66 ± 0.08 was reduced to 5.33 ± 0.06 in the presence of 15 mM β-CD at 25 °C, thus indicating inclusion complex formation; (b) BZ forms soluble 1:1 and 2:1 BZ/β-CD complexes with complex formation constants K ₁₁ = 104 ± 8 M⁻¹ and K ₂₁ = 16 ± 6 M⁻¹; (c) protonated BZ forms only 1:1 complex with K ₁₁ = 42 ± 12 M⁻¹; (d) ¹H-NMR studies in D₂O showed significant upfield chemical shift displacements for inner cavity β-CD protons indicating inclusion complex formation, while (e) Molecular modeling of BZ-β-CD interactions in water clearly indicated complete inclusion of one BZ molecule into the β-CD cavity.     

Synthesis and structure of tin tetrachloride adducts with crown ether: Crystal structure of [Sn(H2O)2Cl4] · 18C6 and [Sn(H2O)2Cl4] · 18C6 · 2H2O

Tin coordination compounds [Sn(H₂O)₂Cl₄] · 18C6 (I) and [Sn(H₂O)₂Cl₄] · 18C6 · 2H₂O (II) were synthesized and identified by IR spectroscopy, CH analysis, and X-ray powder diffraction. The crystal structures of compounds I and II were determined. The crystals of I and II are orthorhombic; a = 16.871(1) ?, b = 7.7305(7) ?, c = 16.939(1) ?, Z = 4, space group Cmca for I; a = 14.206(2) ?, b = 20.376(3) ?, c = 8.319(1) A, Z = 4, space group Pna21 for II. The structural units of I and II are [Sn(H₂O)₂Cl₄] · 18C6 complex molecules (in II, also water molecules of crystallization). The coordinated water molecules in I are trans and those in II are cis to each other. The structural units in the crystals of I and II are combined only by hydrogen bonds between water molecules and the crown-ether oxygen atoms with the formation of the chain structure. Complex I was tested as the precursor of tin dioxide in a chemical vapor deposition (CVD) process. The morphology of the obtained film was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the composition was studied by laser mass spectrometry for elemental analysis.     

A copper(II) complex of benzimidazole-based ligand: synthesis,structure, redox aspects and fluorescence properties

Employing 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1H-benzimidazole (bpb) as a monodentate ligand, a new greenish-blue copper(II) complex, [Cu(bpb)₂(NO₃)₂] (1a), has been synthesized. 1a has been characterized analytically and spectroscopically. The X-ray crystal structure of 1a reveals that it adopts a cis disposition with respect to the ligands. The solid state structure of 1a is stabilized by intramolecular offset face-to-face π–π stacking. Non-covalent supramolecular edge-to-face C–H?π interactions with neighboring molecules give 1-D supramolecular chains that further lead to the formation of an assembled 3-D supramolecular metal-organic framework via hydrogen bonding interactions. 1a shows blue fluorescence most likely due to intramolecular offset face-to-face π–π stacking. At room temperature, 1a is one-electron paramagnetic. It shows a rhombic EPR spectrum with g₁ = 2.12, g₂ = 2.42, and g₃ = 2.52 in the solid state at liquid nitrogen temperature. In cyclic voltammetry, 1a displays a one-electron oxidative Cu(II)/Cu(III) couple. Our DFT calculations, corroborate the observed experimental results of 1a.     

High-Speed Separation of Oleanolic acid and Ursolic acid from the Fruit of Ligustrum Lucidum ait and Crataegus by Cyclodextrin-Modified Micellar Electrokinetic Chromatography

ABSTRACT

A cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) technique for determining oleanolic acid and ursolic acid in the fruit of Ligustrum lucidum Ait and Crataegus was developed. The two bio-active components were successfully separated within 4 minutes using a pH 8.5 sodium borate buffer containing 60mM SDS and 2mM γ-CD. The correlation coefficients of the linear calibration graphs for the analyses exceeded 0.9980. The effects of pH, SDS, γ-CD, sodium borate and temperature on separation were also investigated.     

DIRECT SYNTHESIS AND CRYSTAL STRUCTURE OF DIIODOETHYLENDIAMINELEAD(II) DIMETHYLSULFOXIDE

Abstract

A direct method of obtaining PbEnI₂.DMSO is reported. The crystal structure of the compound was determined by X-ray techniques. PbEnI₂.DMSO is triclinic, space group P 1, C₄H₁₄I₂N₂PbS, a=10.225(3), b=10.132(3), c=6.900(2) Å; α=90.83(2), β=88.30(2), γ=106.35(4)°; V=685.6(4) ų; z=2, calculated density 2.92 gcm^?3. Neutral PbEnI₂ complexes are associated with DMSO molecules via H-bonds. The lead(II) ion is covalently linked with a chelated En molecule (Pb-N 2.46–2.48 Å) and I^? anions (Pb-I 3.087–3.343 Å). Covalently bonded atoms form an umbrella-like coordination Pb(II) polyhedron. The side containing the lone electron pair of the lead(II) ion has coordination completed by two I^? anions of neighbouring molecules with the Pb-I 3.621–3.627 Å.     

Single-crystal-to-single-crystal Transformation of the Dichloromethane Solvate of the Shiff Base Manganese(III) Complex to a Solvent Free Material

The chloride complex of Mn(III)with an optically active Schiff base derived from3,5-tert-butyl-salicyl aldehyde and(1R,3S)-1,2,2,-trimethylcyclopentane-1,3-diaminecrystallizes as a 1 : 1 solvate (I) withCH₂Cl₂ and transforms at room temperature toa solvent-free compound (II) without destructionof the crystals. Two X-ray diffraction experimentscarried out on the same crystal at 120 K revealed thatthe guest CH₂Cl₂ molecules are completelyenclosed in the host matrix and that drasticconformational changes of the complex molecules occurduring removal of solvent. A possible mechanism of thecrystal transformation is disscused. The spectralevidence on association of the metal complex withdichloromethane in solution are demonstrated.     

Syntheses,crystal structures,and thermal stabilities of the first Hofmann-DMF-type complexes Zn(DMF)2M(CN)4 (M = Ni,Pd, Pt)

The first Hofmann-DMF-type complexes Zn(DMF)₂M(CN)₄ (M = Ni (1), Pd (2), Pt (3)) have been synthesized by solution diffusion and characterized structurally by single-crystal X-ray diffraction. The structure consists of 2-D corrugated sheets stacking along the a-axis in an ABAB packing mode without interpenetration. The octahedral Zn ions and square-planar M ions occupy special positions of 2/m site symmetry. The DMF, except for six methyl H atoms, lies on a crystallographic mirror plane; the DMF molecules coordinate to axial sites of Zn on both sides of the sheet. The framework of 1 begins to collapse with loss of coordinated DMF.     

A Photochemical/Thermal Switch Based on 4,4′-Bis(benzimidazolio)stilbene: Synthesis and Supramolecular Properties.

Stilbene derivatives are well-recognised substructures of molecular switches based on photochemically and/or thermally induced (E)/(Z) isomerisation. We combined a stilbene motif with two benzimidazolium arms to prepare new sorts of supramolecular building blocks and examined their binding properties towards cucurbit[n]urils (n=7, 8) and cyclodextrins (β-CD, γ-CD) in water. Based on the ¹H NMR data and molecular dynamics simulations, we found that two distinct complexes with different stoichiometry, i. e., guest@β-CD and guest@β-CD₂, coexist in equilibrium in a water solution of the (Z)-stilbene-based guests. We also demonstrated that the bis(benzimidazolio)stilbene guests can be transformed from the (E) into the (Z) form via UV irradiation and back via thermal treatment in DMSO.     

Crystal structures of ethylenediaminecadmium(II) tetracyanocadmate(II)-benzene(1/2) and ethylenediaminecadmium(II) tetracyanocadmate(II)

The crystal structure of ethylenediaminecadmium(II) tetracyanocadmate(II)-benzene(1/2),I, has been redetermined based on 1632 reflections collected anew for the crystal coated with epoxy resin, with a final conventionalR=0.038;I crystallizes in space groupP4₂22, witha=b=8.265(1) andc=15.512(3) Å, andZ=2. Ethylenediaminecadmium(II) tetracyanocadmate(II),II, is concluded to be identical with the residual metal complex host ofI, remaining after the liberation of the guest benzene molecules;II crystallizes from an aqueous solution containing bis- or tris-ethylenediaminecadmium(II) tetracyanocadmate(II) in space groupI4₁/acd, witha=b=14.366(1) andc=23.771(4) Å, andZ=16; refinement led to a conventionalR=0.043 for 1181 reflections. The bridging ethylenediamine ligand inI turns to a chelating one inII; dissociation and recombination should occur in the coordination sphere of the six-coordinate cadmium atom, whenII is derived fromI by the liberation of the guest molecules. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82018 (30 pages).Dedicated to Professor H. M. Powell.     

Synthesis and crystal structure of a novel coordination polymer: {[Zn<Subscript>2</Subscript>(6-Pydc)<Subscript>2</Subscript>(Bpp)<Subscript>2</Subscript>] · 4H<Subscript>2</Subscript>O}<Emphasis Type="Italic">n</Emphasis>

A 1D zigzag coordination polymer {[Zn₂(2,6-Pydc)₂(Bpp)₂] · 4H₂O} _n (I) [2,6-H₂Pydc = 2,6-pyridinedicarboxylic acid, Bpp = 1,3-bis(4-pyridyl)propane] has been synthesized via the hydrothermal method. Single crystal structural analysis exhibits that a novel 2D complicated framework comprised of two kinds of infinite 1D zigzag chains was stabilized by chains through hydrogen bonding, and π-π stacking interaction, which aggregate together to give birth to the 3D network structure via the C-H…O interaction.