Synthesis and structural aspects of urea/dialkylamine inclusion compounds

The synthesis and structural aspects of urea host-guest inclusion compounds containing linear secondary alkylamines (dibutyl-,dipentyl-, dihexyl-, dioctyl-) at 25°C are reported. Elemental analysis,¹³C CP-MAS NMR and¹H-NMR Spectroscopy, and Powder X-ray Diffraction Analysis confirm the inclusion process. The basic host structure of the products is similar to that of urea-hydrocarbon systems.¹³C MAS-NMR experiments show chemical shift differences for the confined guest molecule with respect to the liquid phase. Stoichiometry and |c _g| values for the inclusion compounds with dipentyl-and dihexylamine suggest a commensurate structure.     

Reaction of isosteviol diterpenoid with selenium dioxide

Diterpenoid isosteviol was oxidized by selenium dioxide in acetic anhydride or in a mixture of acetic anhydride with dioxane to 15-oxo-derivative, whereas reaction with SeO₂ in boiling ethanol led to a mixture of mono- and diselenides. Molecular structure of the monoselenide is established by the X-ray structural analysis.     

Potentiometric characterisation of cyclodextrin inclusion complexes of local anaesthetics

The complexation of several local anaesthetics by β and γ-cyclodextrins was studied by potentiometry with glass electrode. Tetracaine and dibucaine complexation constants were determined at 25°C in the presence of 0.1 M of NaCl. It was found that prilocaine and lidocaine complexes cannot be detected.     

Inclusion complexes of the natural product gossypol. Clathrate type inclusion complexes of gossypol with carbonyl group containing guests

The crystal structures of 2:1 inclusion complexes of gossypol with methyl propionate (GPMEP) and ethyl acetoacetate (GPEAA) have been determined by X-ray structure analysis. The crystals of GPMEP, C₃₀H₃₀O₈l/2 C₄H₈O₂, are monoclinic, space groupC2/c,a=11.079(3),b = 30.724(7), c = 16.515(5) Å, = 90.46(2)°,V = 5621(3) Å,Z = 8,D _x = 1.33 g cm^–3. The structure has been refined to the finalR value of 0.059 for 1899 observed reflections. The crystals of GPEAA, C₃₀H₃₀O₈l/2 C₆H₁₀O₃, are monoclinic, space groupC2/c,a=11.095(2),b=30.604(9),c = 16.955(5) Å, = 88.27(2)°,V = 5754(3) Å,Z = 8,D _x = 1.35 g cm^–3. The structure has been refined to the finalR value of 0.056 for 2502 observed reflections.In contrast to previously investigated inclusion complexes of gossypol the host molecules do not form centrosymmetric dimersvia hydrogen bonds. In the crystal structures the racemic gossypol is separated into enantiomers forming alternating bimolecular layers. Nearly perpendicular to these chiral bilayers run elongated cavities enclosed on each side by layers of opposite chirality. The surface of these layers is hydrophobic, the polar groups are hidden inside the layer. Guest molecules which are hydrogen bonded to the host are included in cylindrically shaped cavities. Possible hydrogen bonds between host and guest are analysed for this isostructural class of complexes.     

Stabilization of dyes against hydrolytic decomposition by the formation of inclusion compounds

The decomposition reactions of the dyes phenol blue and murexide were measured spectroscopically in acidic solution at different temperatures. From these reaction rates and their temperature dependence in the absence and presence of various hosts, the stability constants and the reaction enthalpies of the dye complexes with noncyclic dextrins, cyclodextrins and cucurbituril were calculated.-Cyclodextrin enhances the stability of phenol blue in acidic solution. This effect is even more pronounced with cucurbituril. Due to the molecular structure of murexide this dye cannot form inclusion complexes with hosts containing hydrophobic cavities.     

Structure-retention studies on the inclusion complex formation of some polycyclic aromatic hydrocarbons with β-cyclodextrin

Summary The retention behaviour of a group of polycyclic aromatic hydrocarbons having nearly equal ionization potentials but different molecular polarizability values was investigated using reversed-phase HPLC. Methanol-water binary systems containing -cyclodextrin were applied as the mobile phase. The relationships between the capacity factors, molecular polarizabilities and the shape parameter of solute molecules are discussed.     

Crystal structure of the 1:3 thiourea-hexachloroethane inclusion compound at 295 K

The crystal structure of the 1:3 thiourea-hexachloroethane inclusion compound at 295 K has been determined. The parameters of the rhombohedral Bravais cell (space group R3ˉc) are a = 16.097(2) Å, c = 12.450(3) Å, V = 2793.6(8) ų, d _calc = 1.659 g/cm³, d _exp = 1.661±0.005 g/cm³, Z = 6 for C₅H₁₂Cl₆N₆S₃. The disordered guest molecules lie in the channels (parallel to the c axis) of the clathrate framework constructed from thiourea molecules linked by N-H...S hydrogen bonds. The mutual arrangement of the carbon and chlorine atoms is such that they define four orientations of the C-C bond relative to the channel of the host framework with nearly eclipsed conformations of hexachloroethane: one orientation along the triple bond axis (channel axis) and three equiprobable orientations at an angle of 74(2)° to the axis; for the coaxial orientation, there are two different configurations of the guest with slightly different geometries. The relative contributions of each of the five orientations were determined from the site occupancies of the guest atoms: 26.18 (coaxial orientations) and 3×19%. The resulting structure model is compared with the literature data about guest disordering in the structure of an adduct of the same composition determined at 233 K and with other similar structures. Original Russian Text Copyright ? 2007 by S. F. Solodovnikov, G. N. Chekhova, G. V. Romanenko, N. V. Podberezskaya, Z. A. Solodovnikova, D. V. Pinakov, and A. R. Semenov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 2, pp. 348–357, March–April, 2007.     

Cyclodextrin inclusion complexes as novel MOCVD precursors for potential cobalt oxide deposition

The potential use of the inclusion complexes of β‐cyclodextrins with metal halides as novel precursors in MOCVD applications was examined in terms of microstructure, thermal stability and chemical modifications during heating. The investigation was especially focused on the inclusion complex of β‐cyclodextrin with cobalt iodide for cobalt oxide thin film deposition. The general composition assigned to the dextrin's inclusion complex was: (β‐CD)₂^?CoI₇^?11H₂O. It was found that the inclusion complex of β‐cyclodextrin with CoI₂ may prove a promising alternative to traditional metalorganic or organometallic Co‐precursors for precise CVD applications. The sublimation temperature must be preferably in the range 70–125 °C, and the decomposition temperature (substrate temperature) in the range of 350–400 °C. Three distinct regions can be recognized by heating: transformation of tightly bound water molecules into easily movable ones, sublimation of iodine ions and Co atoms oscillation and thermal decomposition of the glycositic ring into volatile by‐products. Copyright © 2009 John Wiley & Sons, Ltd.     

The influence of thermal treatment on the nitrate band intensities in infra-red spectra of nitrate inclusion complexes of the zeolite 4A

The changes occurring in the included component in the course of thermal treatment of inclusion complexes of zeolite 4A with alkali nitrates were followed by IR spectroscopy and the results obtained were correlated with the data of TG analysis. An increase in temperature caused changes in the breadth and intensity of the nitrate bands (at about 1450 and 1380 cm^–1) and the appearance of a new band at about 1350 cm^–1. All the mentioned effects relate to the temperature interval starting from room temperature up to 670 K and are attributed to the increase in the thermal motion of included species in zeolite cages. The activation energy of the coordination change of the nitrate groups in the cage was calculated from the ratio of intensities of the nitrate bands at 1450 and 1350 cm^–1 and the intensity of the zeolite band at 460 cm^–1, originating from aT–O bending vibration as a function of temperature. At temperatures exceeding 720 K decomposition of included nitrate was noticed. Having this in mind, it was concluded that the changes of the band intensities were closely connected with this process.     

Crystalline inclusion complexes formed between the drug diflunisal and block copolymers

The solid form of drugs plays a central role in optimizing the physicochemical properties of drugs, and new solid forms will provide more options to achieve the desirable pharmaceutical profiles of drugs. Recently, certain drugs have been found to form crystalline inclusion complexes (ICs) with multiple types of linear polymers, representing a new subcategory of pharmaceutical solids. In this study, we used diflunisal (DIF) as the model drug host and extended the guest of drug/polymer ICs from homopolymers to block copolymers of poly(ethylene glycol) (PEG) and poly(ε-caprolactone) (PCL). The block length in the guest copolymers showed a significant influence on the formation, thermal stability and dissolution behavior of the DIF ICs. Though the PEG block could hardly be included alone, it could indeed be included in the DIF ICs when the PCL block was long enough. The increase of the PCL block length produced IC crystals with improved thermal stability. The dissolution profiles of DIF/block copolymer ICs exhibited gradually decreased aqueous solubility and dissolution rate with the increasing PCL block length. These results demonstrate the possibility of using drug/polymer ICs to modulate the desired pharmaceutical profiles of drugs in a predictable and controllable manner.     

The effects of increasing NaCl concentration on the stability of inclusion complexes in aqueous solution

Equilibrium constants and standard molar enthalpies of reaction were determined by titration calorimetry for the reaction of 1-butanol with 2-hydroxypropyl-b-cyclodextrin (HP-b-CD) in aqueous solution at different concentrations of NaCl (0-1.9 M). The standard molar free energy and entropy changes associated to the complexation were calculated from the corresponding equilibrium constants, K, and standard enthalpies determined experimentally. In NaCl solutions the inclusion complexes ButOH/HP-b-CD are more stable than in water and their stability increases at increasing NaCl concentration; otherwise, the standard molar enthalpy associated to the formation of the complexes does not change with the increasing of salt concentration. The dependence of K on NaCl concentration were used to evaluate the number of water molecules displaced from the hydration shells of HP-b-CD and ButOH in forming complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and characterization of the crystalline inclusion complexes between cyclodextrins and poly(1,3-dioxolane)

The preparation and characterization of the crystalline inclusion complexes between a polymeric guest, poly(1,3-dioxolane) (PDXL), and small-molecular hosts, cyclodextrins (CDs) are reported. It is observed that the polymer guest can form crystalline inclusion complexes with three kinds of cyclodextrins, which may be attributed to the high oxygen atom density in PDXL chain. The crystalline inclusion complexes were characterized with FTIR , TGA, X-ray diffraction, SEM, 1H NMR and 13C CP/MAS NMR spectroscopes. It was found that the crystalline inclusion complexes have higher temperature stability than the pure CDs. The X-ray powder diffraction patterns of the crystalline inclusion complexes proved that they have columnar structures. 13C CP/MAS NMR spectra of the crystalline inclusion complexes indicate that CDs adopt a more symmetrical conformation in the complexes, while pure CDs assume a less symmetrical conformation in the crystal without a guest inside their cavities. The morphology of the crystal was     

Inclusion complexes of the natural product gossypol. Strong influence of the guest on the host structure in channel-type isostructural inclusion complexes of gossypol

The crystal structures of 1 : 1 inclusion complexes of gossypol with tetrahydrofuran (GPTHF), cyclohexanone (GPCHN) and butanal (GPBTA) have been determined by X-ray structure analysis. The crystals of GPTHF are triclinic, space group P,a = 10.788(2),b = 10.979(3),c = 13,880(2) Å, = 80. 11(2), = 103.87(1), = 77.96(2)°,V = 1517.8(6) ų,Z = 2,R = 0.052 for 2701 observed reflections. The crystals of GPCHN are triclinic, space groups P,a = 10.803(4),b = 11.157(5),c = 15.428(6) Å, = 108.75(3), = 106.93(3), = 103.34(3)°,V = 1573(1) ų,Z = 2,R = 0.071 for 1879 observed reflections. The crystals of GPBTA are triclinic, space group P,a = 10.190(2),b = 11.335(1),c = 14.665(2) Å, = 73.04(1), = 103.74(1), = 81.07(1)°,V = 1529.9(5) ų,Z = 2,R = 0.068 for 2964 observed reflections. Crystal data for another 13 isostructural inclusion complexes are given.[/p]In this isostructural group of complexes guest molecules are accommodated in channels and are hydrogen bonded to the host molecules via an 0(1)-H....O(1) hydrogen bond. The molecular association changes significantly with the shape and size of the guest component. In GPTHF centrosymmetric dimers of gossypol formedvia O(5)-H...O(3) hydrogen bonds are associated in columns via a weak O(4)-H...O(8) hydrogen bond. In GPCHN the latter bond disappears as the distance O(4)-O(8) is increased to 3.73 Å. In GPBTA the O(5)-H...O(3) bond is replaced by three centre hydrogen bonds O(5)-H...O(2) and O(3)-H...O(5), and a centrosymmetric dimer of a new type is formed. These dimers are further connected by two weak hydrogen bonds to form columns. The butanal molecule interacts with the host structure via two hydrogen bonds. This indicates that a guest component can activate or deactivate different functional groups of the host in channel inclusion complexes of gossypol for hydrogen bond formation.     

Site-selective formation of optically active inclusion complexes of alkoxo-subphthalocyanines with beta-cyclodextrin at the toluene/water interface

Several subphthalocyanine derivatives that contain an alkoxo substituent as an axial ligand (RO-Subpc, R = 9-anthracenemethyl, benzyl, phenyl, 3,5-dimethylbenzyl, 3,5-dimethylphenyl, 4-methylbenzyl, and 4-methylphenyl) were synthesized. The formation of inclusion complexes of RO-Subpc with beta-CD in DMSO and at the toluene/water interface was investigated by UV/Vis absorption spectroscopy, induced circular dichroism (ICD), and nuclear magnetic resonance (NMR) measurements. Interfacial tension measurements suggested that beta-CD adsorbed as a monolayer at the toluene/water interface and probably orientated towards the toluene phase with its primary face. The 1:1 composition of beta-CD.RO-Subpc inclusion complexes was confirmed in DMSO and at the toluene/water interface for BzO-Subpc, PhO-Subpc, MeBzO-Subpc, and MePhO-Subpc. A 2:1 inclusion complex of AnO-Subpc formed in DMSO. The observed ICD spectra of beta-CDRO-Subpc inclusion complexes are discussed with respect to molecular modeling and the simulation based on Tinoco-Kirkwood theory. Interestingly, the ICD spectra of beta-CD.BzO-Subpc and beta-CD.MeBzO-Subpc inclusion complexes exhibited a negative sign in DMSO and a positive sign at the toluene/water interface. This reversal of the ICD sign strongly suggests a difference in the structure of the inclusion complexes: beta-CD at the interface formed the inclusion complex with its primary face, whereas the secondary face of beta-CD bound favorably to RO-Subpc in DMSO.     

Catalytic hydrogenation of aromatic nitro compounds by non-noble metal complexes of chitosan

Silica-supported mono-metal (such as Ni, Cu) complexes and mixed metal (such as Cu/Zn, Cu/Cr) complexes of chitosan have been prepared. It is found that these non-noble metal complexes could be used as efficient catalysts for the hydrogenation of aromatic nitro compounds. The effects of type of metal, reaction temperature and pressure, solvent, nitrogen/metal molar ratio in the complex catalysts on the yields from nitrobenzene to aniline have been examined. It was also found that catalysts are active for the catalytic hydrogenation of other aromatic nitro compounds such as 2-nitroanisole, 2-nitroaniline, 2-nitrotoluene and 1-chloro-4-nitrobenzene.     

Formation of poly(ethylene glycol) inclusion complexes in aqueous solutions of mixed cyclodextrins

Even though the addition of modified cyclodextrins (modified CDs) accelerates the precipitation in aqueous solutions of poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) the final amount of formed solid complex remains unchanged, with no significant presence of modified CDs detected by MALDI-TOF mass spectrometry. Thus unsuitability of kinetic turbidity measurements for determination of binding parameters was confirmed. On the other hand, theoretical calculations based on a model of a chain of freely accessible binding sites demonstrated that the results do not necessarily contradict the finding that individual modified CD molecules can thread onto PEG chains with the efficiency comparable to that of natural (unmodified) α-CD.     

Effect of the size of calixarene macrocycle on the thermodynamic parameters of formation of inclusion compounds in guest vapor—solid host systems

The influence of the calixarene macrocycle size on the thermodynamic parameters of inclusion formation in organic guest vapor—solid host systems was studied in the series of tert-butylcalix[4]arene (1), tert-butylcalix[6]arene (2), and tert-butylcalix[8]arene (3). For this purpose, sorption isotherms of a guest vapor by a solid host were determined using the static method of headspace GC analysis for the systems involving calixarenes 2 and 3 in addition to the earlier obtained data for calixarene 1. Besides, the stoichiometry and decomposition temperatures of saturated clathrates formed in these systems were determined using thermogravimetry. The compositions of some of these clathrates differ substantially from those of clathrates crystallized from a host solution in a liquid guest. For the most guests studied with the thermodynamic activity below 0.6, their uptake by calixarenes 1—3 changes in the series 2 < 1 < 3. As a whole, the trend for each particular parameter of clathrates of hosts 1—3 (stoichiometry, guest activity at 50% saturation of the host) with increasing the size of the calixarene macrocycle is specific for each guest studied. The results obtained are useful for the estimation of receptor properties of calixarenes in quartz microbalance sensors.     

Hydrate inclusion compounds

There are three general classes of hydrate inclusion compounds: the gas hydrates, the per-alkyl onium salt hydrates, and the alkylamine hydrates. The first are clathrates, the second are ionic inclusion compounds, the third are semi-clathrates. Crystallization occurs because the H₂O molecules, like SiO₂, can form three-dimensional four-connected nets. With water alone, these are the ices. In the inclusion hydrates, nets with larger voids are stabilized by including other guest molecules. Anions and hydrogen-bonding functional groups can replace water molecules in these nets, in which case the guest species are cations or hydrophobic moieties of organic molecules. The guest must satisfy two criteria. One is dimensional, to ensure a comfortable fit within the voids. The other is functional. The guest molecules cannot have either a single strong hydrogen-bonding group, such as an amide or a carboxylate, or a number of moderately strong hydrogen-bonding groups, as in a polyol or a carbohydrate.The common topological feature of these nets is the pentagonal dodecahedra: i.e., 5¹²-hedron. These are combined with 5¹²6²-hedra, 5¹²6³-hedra, 5¹²6⁴-hedra and combinations of these polyhedra, to from five known nets. Two of these are the well-known 12 and 17 Å cubic gas hydrate structures,Pm3n, Fd3m; one is tetragonal,P4 ₂/mnm, and two are hexagonal,P6 ₃/mmc andP6/mmm. The clathrate hydrates provide examples of the two cubic and the tetragonal structures. The alkyl onium salt hydrates have distorted versions of thePm3n cubic, the tetragonal, and one of the hexagonal structures. The alkylamine hydrate structures hitherto determined provide examples of distorted versions of the two hexagonal structures.There are also three hydrate inclusion structures, represented by single examples, which do not involve the 5¹²-hedra. These are 4(CH₃)₃CHNH₂·39H₂O which is a clathrate; HPF₆·6H₂O and (CH₃)₄NOH·5H₂O which are ionic-water inclusion hydrates. In the monoclinic 6(CH₃CH₂CH₂NH₂)·105H₂O and the orthorhombic 3(CH₂CH₂)₂NH·26H₂O, the water structure is more complex. The idealization of these nets in terms of the close-packing of semi-regular polyhedra becomes difficult and artificial. There is an approach towards the complexity of the water salt structures found in the crystals of proteins.     

Phase diagrams of urea inclusion compounds

The stearic acid-urea binary system exhibits an unusual phase diagram, which, on the one hand, indicates an incongruently melting inclusion compound and on the other hand a miscibility gap in the liquid phases. The peritectic point lies near the melting point of urea and the unstable congruent melting point of the inclusion compound coincides with the melting point of urea. In addition to the processing of the phase diagram, the pure inclusion compound was prepared and its DSC curve, FTIR spectrum and X-ray diffractogram were recorded.     

Molecular mixing of incompatible polymers through formation of and coalescence from their common crystalline cyclodextrin inclusion compounds

We describe the successful mixing of polymer pairs and triplets that are normally incompatible to form blends that possess molecular‐level homogeneity. This is achieved by the simultaneous formation of crystalline inclusion compounds (ICs) between host cyclodextrins (CDs) and two or more guest polymers, followed by coalescing the included guest polymers from their common CD–ICs to form blends. Several such CD–IC fabricated blends, including both polymer1/polymer2 binary and polymer1/ polymer2/polymer3 ternary blends, are described and examined by means of X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and solid‐state NMR to probe their levels of mixing. It is generally observed that homogeneous blends with a molecular‐level mixing of blend components is achieved, even when the blend components are normally immiscible by the usual solution and melt blending techniques. In addition, when block copolymers composed of inherently immiscible blocks are coalesced from their CD–ICs, significant suppression of their normal phase‐segregated morphologies generally occurs. Preliminary observations of the thermal and temporal stabilities of the CD–IC coalesced blends and block copolymers are reported, and CD–IC fabrication of polymer blends and reorganization of block copolymers are suggested as a potentially novel means to achieve a significant expansion of the range of useful polymer materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4207–4224, 2004