Formation Of Inclusion Compounds Research Articles

Investigation of buffer-cyclodextrin systems

Equilibrium constants for the formation of inclusion compounds of 3-hydroxy-2-naphthoic acid with β-cyclodextrin were determined in aqueous solutions, in the absence and presence of buffers, by the steady-state fluorescence Benesi–Hildebrand method. Almost all the buffers that are usually used have been tested and they are found to have an influence on the formation constants. We suggest that buffers should not be used in aqueous solutions of cyclodextrins unless the experimental error is unacceptable. Furthermore, we obtained the inclusion compound formation constants (Ksalt) of β-CD with some buffer components by using a fluorescence competitive inhibition technique. NaClO4, KClO4, KCl, KHC8H4O4, KH2C6H5O7 and NaHC4H4O6 can form 1:1 inclusion complexes with β-cyclodextrin (Ksalt>0) while KF, K2SO4, NaH2PO4, NaAc, Na2HPO4 and NaHCO3 cannot (Ksalt<0).

Complexation with diol host compounds. Part 32.† Separation of lutidine isomers by 1,1,6,6-tetraphenylhexa-2,4-diyne-1,6-diol

The title host compound forms inclusion compounds with 2,4-, 3,5- and 2,6-lutidine. In each case the host∶guest ratio is 1∶2 and the structures are stabilised by (Host)O–H· · ·N(Guest) hydrogen bonds. Competition experiments show that the host selects the guests in order of preference of 3,5-lutidine > 2,6-lutidine > 2,4-lutidine. These results are in general agreement with the lattice energy calculations.

Selective Inclusion Phenomena in Lithocholamide Crystal Lattices; Design of Bilayered Assemblies through Ladder-type Hydrogen Bonding Network

Abstract The substitution of lithocholic acid (1) to lithocholamide (4) led to the finding of the formation of channel-type inclusion compounds with a limited range of organic substances, such as alcohols, ketones and so on. The inclusion behavior of 4 is greatly different from those of the known hosts of bile acids and their derivatives.

Vibrational spectroscopic studies of host-guest compounds

This paper reviews the results obtained from vibrational studies (infrared and Raman) of host-guest compounds. These techniques can give information such as: confirmation of inclusion compound formation; host-guest interactions; the state of aggregation and configuration of the guest molecules; the translational and rotational motions of the guest; the spectra of hosts and guests in unusual configurations.

Study of the inclusion compounds formed between α-cyclodextrin and high molecular weight poly(ethylene oxide) and poly(ϵ-caprolactone)

We report the formation of high molecular weight polymer inclusion compounds (ICs) between α-cyclodextrin and poly(ethylene oxide) (PEO) ( M n = 100 kg mol −1), and poly(ϵ-caprolactone) (PCL) ( M n = 40 kg mol −1). Both high molecular weight polymer ICs were successfully made by ultrasonic and heating techniques. Dsc, tga, X-ray diffraction, FT i.r. and solid state 13C n.m.r. were utilized to observe the PCL and PEO polymer chains included inside the channels formed by α-cyclodextrin. Dsc and tga scans showed that the high temperature stable polymer-CD-IC samples contain no free crystalline polymer. The much higher decomposition temperatures observed for these polymer-CD-ICs may imply that polymer chains included inside the polymer CD-IC channels can greatly improve cyclodextrin's stability. The polymer-CD-IC's X-ray diffraction patterns were very similar to that of valeric acid-CD-IC, which is confirmed to be a channel crystal structure, and the strong peak for both polymer-CD-ICs at approximately 20.0° (2θ) may confirm their IC formation. New bands appeared at 1729 cm −1 for PEO-CD-IC and at 1739 cm −1 for PCL-CD-IC in their FTi.r. spectra. Both bands were absent from the α-cyclodextrin spectrum. In CP/MAS/DD 13C n.m.r. spectra, single resonances for PEO-CD-IC, which compared with the multiple resonances observed for each carbon type in α-cyclodextrin, may indicate that α-cyclodextrin adopts a more symmetrical cyclic conformation in the PEO-CD-IC sample, while pure α-cyclodextrin assumes a less symmetrical conformation in the crystal when it does not include a guest polymer PEO inside its cavity. A one-pulse 13C n.m.r. spectrum was observed to identify the resonance peak for PEO inside the PEO-CD-IC.

Functionalization of Inclusion Cavities of Bile Acid Hosts. Channel-Type Inclusion Compounds of Cholamide

Abstract Clathrate formation and crystal structures of 3α, 7α, 12α-trihydroxy-5β-cholan-24-amide (cholamide) have been investigated. Cholamide forms inclusion compounds with various organic compounds having hydrogen-bond (H-bond) donors. X-Ray crystallographic studies showed that cholamide has bilayer structures with molecular channels. The crystal structures are quite similar to those of channel-type inclusion crystals of cholic acid. Steric dimensions of the host cavities are identical, but cholamide has an H-bond ‘hook’ on the wall of the channels, while cholic acid does not. This difference is correlated with not only the inclusion abilities but also the molecular structures. Two H-bond donors of the amide group yield a hydrophilic inclusion cavity that includes H-bond acceptors, and one H-bond donor of the carboxylic acid gives a lipophilic inclusion cavity that includes non-polar or less polar compounds.

Effect of Guest Species on Inclusion Compound Formation of Deoxycholic Acid by Co-Grinding

Abstract Deoxycholic acid (DCA) was ground with a guest compound by using a vibrational mill. Powder X-ray diffraction, differential scanning calorimetry, and fluorescence spectroscopic data indicated the formation of the inclusion complex in the ground mixture of DCA–phenanthrene and DCA–naphthalene systems. The DCA–naphthalene ground mixture was found to have higher crystallinity than the DCA–phenanthrene ground mixture, and this was assumed to relate to the difference in the crystallization temperature of the inclusion complex. When low-temperature grinding was performed for DCA and other aromatic hydrocarbons along with naphthalene and phenanthrene, all the ground mixtures were obtained in amorphous state. Crystallization of inclusion compounds from the amorphous ground mixtures was observed to occur at a higher temperature as the stoichiometric ratio (DCA/guest) of the compound increased. With regard to the formation of crystalline complex between DCA and a guest, such as naphthalene, by grinding at room temperature, a two-step mechanism was proposed: i.e., (i) amorphization of both DCA and guest crystals, and (ii) crystallization of the inclusion complex induced above a certain temperature.

1,1,2-Triphenyl-1,2-ethanediol: A Host for Carboxylic Acids and Amides in Coordinatoclathrates⋆

The chiral diols (R)- and (S)-1 are found to form inclusion compounds with carboxylic acids and amides, as indicated by the relevant IR spectra. Two clathrates, (R)-1 · CH3CO2H and (S)-1 · CH3NHCHO have been characterized by their crystal structures. The interaction between the diol 1, which functions as the host compound, and the guest compounds, is based on hydrogen bonds. Enantiomerically pure 1 can serve as chiral solvating agent in NMR spectroscopy.

Combinatorial Chemistry of Inclusion Compounds by using Steroids

Steroidal acids and their derivatives form inclusion compounds with a variety of organic substances. Over one thousand derivatives are candidates for hosts of the compounds. The study on steroidal inclusion compounds provides systematic data for considering relationships between molecular structures and molecular assemblies, indicating that combinatorial chemistry can be applied to inclusion chemistry.

2,4-D-α-Cyclodextrin Complexes

The aqueous solubility of the pesticide 2,4-D was improved by inclusion complexation with α-CD. The formation of such inclusion compounds was studied via the phase-solubility diagram (solution state) and by DSC and HSM (solid state). 2,4-D presented a typical Bs Higuchi solubility curve, coprecipitating a 1:2 pesticide-α-CD complex. In order to obtain solid complexes, three processing methods were checked: kneading, coprecipitation and spray-drying. DSC and HSM showed that only the last two of these yielded true inclusion compounds. Chemical analysis also revealed that the stoichiometry of such solid complexes corresponds to a 2,4-D-α-CD ratio of 1:2.

Crystal structure and thermochromic behavior of the inclusion compounds of 4,5-diphenyl-2-(4-nitrophenyl)-1H-imidazole and of 4,5-diphenyl-2-(2-hydroxy-5-nitrophenyl)-1H-imidazole

4,5-Diphenyl-2-(4-nitrophenyl)-1H-imidazole 2 and 4,5-diphenyl-2-(2-hydroxy-5-nitrophenyl)-1H-imidazole 3 form inclusion compounds with various guest molecules that possess hydrogen donor or hydrogen acceptor groups. The guest molecules play a crucial role in building up the three-dimensional structure. The guest molecules link host molecules through hydrogen bonds. The colors of the solid compounds vary from light yellow to dark red. The thermochromic properties have been determined by the removal of the guest molecules. The crystal structure and the thermal behavior are described and discussed.

First Columnar Monolayer Structure of Bile Acids Inclusion Crystal. Inclusion Compounds of 23-Nordeoxycholic Acid

Abstract A new host, 23-nordeoxycholic acid, which forms inclusion compounds with many organic compounds, have a novel monolayer columnar structure in spite of a facially amphiphilic molecular structure.

CLATHRATE AND INCLUSION COMPOUNDS. PART 13 1. VIBRATIONAL AND NMR SPECTROSCOPIC STUDIES OF CARBOXYLIC ACID GUESTS IN UREA

Infrared, Raman and solid state13C NMR spectra have been recorded for arange of inclusion compounds of urea containingstraight chain aliphatic carboxylic acids(butyric – decanoic) as guests. Inclusioncompounds are not formed with formic, acetic andpropionic acids. Thiourea does not forminclusion compounds with any of the C1 to C10acids. The vibrational and NMR data support theconclusion that the acids are present ashydrogen bonded dimers in the channels of thehost. The alkyl chain 13C chemical shiftvalues are very different from those of acidguests in the cavities formed in Dianin'scompound. These suggest that the alkyl chainsare present in the all-trans conformation,although weak bands observed in the spectrum ofthe decanoic acid inclusion compound lend somesupport to suggestions based on MM calculationsthat other conformations might be present.

CLATHRATE-FORMING ION EXCHANGERS

ABSTRACT This paper summarises the results obtained by studying a new phenomenon in the area of ion exchange and ion exchangers, namely, the formation of clathrate-like crystalline polyhydrates in the ion-exchanger phase. Interaction of swelling water molecules in ion exchangers of certain types (e.g., polyacrylic) has been shown to cause the formation of a clathrate (cellular) structures at temperatures above 273K which in turn leads to the formation of inclusion compounds. The polyhydrate structure can be described as a framework of water molecules arising through the combination of single or joined polyhedra (“host”) containing the matrix of the ion exchanger along with fixed- and counter-ions ( “guest”) in their cavities. The melting (decomposition) temperature of solid clathrate polyhydrate depends on the nature of “guest” components and, for the ion exchanger of a given type, also on the nature of the counter-ion. The paper reports the results obtained by studying clathrate formation, composition and structure of ion-exchanger hydrates by using DTA; DTA under pressure; NMR; electric conductivity techniques, and by absorption of “help gases”. The purposeful synthesis of clathrate-forming ion exchangers and their application for determination of swelling pressure in resin beads; for separation and purification of ionic and gaseous substances, and for solution of some other theoretical and practical problems of ion exchange are also described. An interpretation of Pauling theory of clathrate anaesthesia is discussed within the frame of the results obtained.

Solubility study of tolbutamide in monocomponent and dicomponent solutions of water

Solubility of tolbutamide was studied in different monocomponent (aqueous solutions of surfactant or β-cyclodextrin) and dicomponent solutions (aqueous solutions of surfactant with β-cyclodextrin). Surfactants used were Tween 20 (Polysorbate 20), Brij 35 (Poloxyl 23 lauryl ether) and sodium lauryl sulphate. In dicomponent solutions, surfactant/ β-cyclodextrin ratios were 1:1, 1:2, 1:3 mol/mol. Results of drug solubility from demineralised water and monocomponent solutions containing different surfactants in various concentrations were almost the same, even though most of the used concentrations were above the critical micelle concentrations of some of the surface active agents. Although tolbutamide/ β-cyclodextrin inclusion compound was formed in the monocomponent solutions of β-cyclodextrin, however, the formation of an inclusion compound was impeded in the Brij 35/ β-cyclodextrin and sodium lauryl sulphate/ β-cyclodextrin dicomponent solutions. Data indicate that surfactants compete with drug molecules to form inclusion compounds with β-cyclodextrin and eventually modify the drug solubility. Results also demonstrate that the resultant competitive binding depends on the chemistry of surface active agents.

Theoretical and technological principles for fabrication of high-quality viscose from celluloses of different origin

Problems of stoichiometry and the depth of the phase transition in mercerization with NaOH solutions of different concentration are examined with respect to formation of inclusion compounds of sodium hydroxide with cellulose. The conclusions concerning the existence of optimum concentrations at the end of the phase transition region were confirmed by the data on the structure of the cellulose xanthate and the filterability of the viscoses. Mercerization with solutions of NaOH whose concentrations are contiguous to the region of optimum concentrations makes it possible to obtain spinning solutions with good filterability with a reduction in the consumption of carbon disulfide.

Polymer Inclusion Compounds: Model Systems for Ordered Bulk Polymer Phases and Starting Materials for Fabricating Polymer-Polymer Molecular Composites

Several small molecules can be cocrystallized with polymers to form inclusion compounds (ICs). Urea, perhydrotriphenylene and the cyclodextrins are examples, and serve to form the host crystalline lattice containing the guest polymer chains in their ICs. The guest polymer chains are confined to narrow, cylindrical channels created by the host, small-molecule lattice, where the polymers are highly extended as a consequence of being squeezed, and are separated from neighbouring polymer chains by the IC channel walls composed exclusively of the small-molecule lattice. The net result is a unique solid-state environment for polymers residing in IC channels, which can be utilized as model systems for ordered, bulk polymer phases. Comparison of the behaviour of polymer chains isolated and extended in IC crystals with the behaviour observed for ordered, bulk phases of polymers is beginning to permit an assessment of contributions made by the inherent, single chain and the cooperative, interchain interactions to the properties of ordered, bulk polymers. It is also possible to release and coalesce polymers from their IC crystals in a manner which leads to their consolidation with a chain-extended morphology. Embedding polymer IC crystals into a carrier polymer, followed by in situ release and coalescence of the included polymers from their IC crystals, offers a means to obtain polymer-polymer composites with unique morphologies. Several such polymer IC-generated composites are described and it is suggested that their unique morphologies might translate into useful, tailorable properties, as well as providing a means for addressing several questions that are fundamental to the behaviour of both phase-separated and homogeneous polymer solids.

Cholic Acid Inclusion Compounds with Aromatic Ketone Guests: Structure and Reaction Kinetics

The crystal structure of the inclusion compound formed with host cholic acid and guest propiophenone indicates different packing from that seen in other CA·aromatic guest compounds. Space group P21, a = 16.790(1), b = 7.928(5), c = 12.262(3) Å, β = 114.25(2)°, Z = 2, Dc = 1.211 g.cm−3, R = 0.0515 for 2145 independent reflections. The kinetics of decomposition of the inclusion compounds of the inclusion compounds of CA with acetophenone and propiophenone are presented and mechanism and rate of decomposition compared and contrasted. The steroidal bile acid (3α, 7α, 12α-trihydroxy-5β-cholan-24-oic acid), commonly known as cholic acid (CA), forms inclusion compounds with a wide range of guest molecules. The crystal structures of the inclusion compounds with water1,2,3 and alcohol guests4,5,6 exhibit extensive host-host and host-guest hydrogen bonding. The inclusion compound of CA with acetone and three water molecules is comprised of hydrogen bonded bilayers of host and guest which pack together resulting in a close packed structure7. All water molecules and host and guest hydroxyl and carbonyl groups are involved in intermolecular hydrogen bonds of which there are ten per asymmetric unit. Apart from the above examples and an interesting structure of CA with m-fluoro-aniline, which exhibits an unusual 1:2 host:guest ratio and peculiar packing arrangement8, most CA inclusion compounds form tubulate clathrate type structures. Puckered host steroid bilayers pack together such that channels are formed in which the guest molecules are trapped without benefit of short range host-guest interactions. Bilayers result from the head to tail and α-face to α-face hydrogen bonding of the host while adjacent bilayers are bound by van der Waals forces. Guest molecules included in such fashion encompass lactones,9,10 benzene11 and benzene derivatives,12,13 aliphatic ketones14 and esters15. We have in the past considered the phases occurring during thermal decomposition of various CA inclusion compounds7 and the different packing modes and subtle guest responsive changes in host conformation and packing occurring15. More recently we have undertaken study of the rates and mechanisms of decomposition of CA tubulate clathrates with substituted aromatic guests16 as well as investigated the solid state reactivity of CA and its O(28) methyl ester, methyl cholate (MC)17. We now present the crystal structure of the 1:1 inclusion compound formed by CA with propiophenone (CAPR) and consider the complex thermal decomposition modes of this compound and that formed by CA with acetophenone13 (CAACET) both with respec to rate and mechanism of reaction. Kinetic parameters are derived and presented for comparison.

Formation, Characterization, and Segmental Mobilities of Block Copolymers in Their Urea Inclusion Compound Crystals

We report the formation of crystalline inclusion compounds (ICs) between the small-molecule host urea (U) and two block copolymer guests: (i) poly(e-caprolactone)−polybutadiene (PCL−PBD) and (ii) ...

Cholic Acid Inclusion Compounds with Aromatic Guests: Structures and Decomposition Kinetics

Cholic acid forms 1:1 (host:guest) inclusion compounds with a variety of aromatic guest molecules. The crystal structures of the inclusion compounds with benzonitrile and p-nitro toluene have been elucidated. CA·benzonitrile: space group p21, a = 13.642(3), b = 8.133(2), c = 14.055(3) Å, β = 114.12(2)°, Z = 2, Dc = 1.194 g.cm−3, final R factor = 0.0781 for 1853 independent reflections. CA·p-nitro toluene: space group P21, a = 13.495(1), b = 8.266(4), c = 14.398(2) Å, β = 114.61(1)°, Z = 2, Dc = 1.249 g.cm−3, final R factor = 0.0608 for 2783 independent reflections. The kinetics of decomposition of these and related compounds are investigated and kinetic parametesrs Ea and In A so derived compared and contrasted. 3α, 7α, 12α-trihydroxy-5β-cholan-24-oic acid or Cholic acid (CA) has been shown to form inclusion compounds with a variety of guest molecules. The 1:1 inclusion compounds with methanol, ethanol and n-propanol1,2,3 exhibit extensive host-host and hostguest hydrogen bonding and the guest molecules are accommodated in cavities. The structures of the hydrate4 and hemihydrate5,6 are composed of hydrogenbonded bilayers and helical columns respectively while the inclusion compound with acetone and three water molecules7 is composed of bilayers of host and guest hydrogen bonded together in a system containing ten unique hydrogen bonds. The bulk of CA inclusion compounds crystallise as tubulate clathrates in which host molecules are hydrogen bonded together in a head to tail fashion to form puckered bilayers with the hydrophobic β faces exposed on the bilayer surfaces. These bilayers are in turn packed such that channels remain between them in which guest molecules are stacked in columns parallel to the b crystallographic direction. Guest molecules such as aliphatic ketones8, lactones9, aliphatic10 and vinyl esters as well as the aromatic guests nitrobenzene, aniline11, acetophenone12 and benzene13 are included in this manner. Given the similarities in the structures of these compounds we decided to investigate the kinetics of decomposition with the aim of relating reactivity to structure at a molecular level. The kinetics of decomposition of a variety of inorganic salts and hydrates have been extensively studied14,15,16 and the effects of changes in reaction conditions, particle size and sample pretreatment investigated.17,18,19 The decomposition kinetics of solid organic clathrates has not been considered in spite of the potential insights into stability and host-guest interactions to be gained therefrom. We present the decomposition kinetics of a group of CA inclusion compounds with the aromatic guest molecules benzonitrile (CABN), aniline (CAAN), nitrobenzene (CANI), p-nitro-toluene (CAPNOT) and p-toluidine (CAPTOL). Possible mechanisms for the decomposition reaction are advanced and the crystal structures of CA with benzonitrile and p-nitro-toluene guests are presented while those of the other inclusion compounds included in this study have been published elsewhere.11,20