HPLC study of the host–guest complexation between fluorescent glutathione derivatives and β-cyclodextrin

RP-HPLC and the van’t Hoff law were used to study the association in which β-cyclodextrin forms inclusion complexes with aminothiol–phthaldialdehyde derivatives prepared from either glutathione (GSH) or γ-glutamylcysteine (γ-glucys) and either naphthalene-2,3-dicarboxaldehyde (NDA) or o-phthaldialdehyde (OPA). Elution was carried out at pH 8.5, the derivatization pH which gave the highest fluorescence signal during batch experiments. The variation of the retention factor (k) was monitored as a function of column temperature (10–35 °C) and β-cyclodextrin concentration (0–5 mM) in the mobile phase. Apparent binding constants, enthalpy and entropy were calculated from van’t Hoff plots for the complexation reaction. These data lay the groundwork for the improvement of high throughput GSH quantification methods using fluorimetry in biological and vegetal samples.     

The formation of host–guest complexes between surfactants and cyclodextrins

Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host–guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host–guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD–surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature.     

Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium

In this work, the host–guest interaction between calixpyridinium and the anionic anticancer drug methotrexate disodium was explored in water. Unexpectedly, an interesting anisotropic needle-like rather than an ordinary isotropic spherical supramolecular amphiphilic assembly was fabricated by the complexation of calixpyridinium with methotrexate disodium. It is the second anionic guest to be discovered to form the non-spherical supramolecular assembly upon complexation with calixpyridinium. This discovery implies the possibility to construct various topological nanostructures based on the host–guest interactions between calixpyridinium and the anionic drugs in the future. The resulting calixpyridinium–drug assemblies with different morphologies may have the diverse potentials to adjust the efficacies of anionic drugs.     

Comparing of the host–guest interaction in the Hofmann-1,10-diaminodecane and Hofmann-1,12-diaminododecane-type clathrates

M(1,12-diaminododecane)Ni(CN)4.G (M = Co, Ni or Cd; G = chlorobenzene; 1,2-; 1,3- or 1,4- dichlorobenzene) clathrates were prepared in powder form for the first time and their infrared spectra were reported and then compared with M(1,10-diaminodecane)Ni(CN)₄.1,5G (M = Co, Ni or Cd; G = chlorobenzene; 1,2-; 1,3- or 1,4-dichlorobenzene) clathrates. The spectral results suggest that the characteristic ν(CN) and δ(NiCN) frequencies are found to be similar to those known for the Hofmann type compounds, in that prepared compounds are similar in structure to this type compounds and their structures consist of polymeric layers [M–Ni(CN)₄]_∞ with the 1,12-diaminododecane molecule bound to the metal atom (M). Also, the results suggest that the ligand molecule with 10 to 12 of chain length have no effect on vibrational bands of the guest molecules in the similar Hofmann-diam-type clathrates. The normal mode frequencies and corresponding vibrational assignments of chlorobenzene and 1,2-; 1,3- or 1,4-dichlorobenzene in the ground state were calculated by DFT/B3LYP level of theory using the 6-311G(d, p) basis set in Gauss-view. In addition, these theoretical results were compared to the experimental results for the vibrational modes of host molecules.     

Hydrogen bonding between carboxylic acids and amide-based macrocycles in their host–guest complexes

For 12- and 13-membered macrocycles in which two amide linkages are integrated in the macrocyclic ring systems, the formation of 1:1 host–guest complexes with acetic and benzoic acids has been confirmed by NMR titrations. The complex formation occurs with the formation constants of 8–27 M^? 1, under competition with the dimerisation of acid molecules. Benzoic acid tends to form more stable complexes than acetic acid. The binding force is due to a pair of hydrogen bonds, O_carboxyl–H…O = C_amide and C = O_carboxyl…H–N_amide, between the carboxyl group of a guest molecule and the amide group of a host molecule. The former bond is stronger than the latter, and defines the stability of the complexes. The formation of the pair of hydrogen bonds is accompanied by the conformational conversion of the amide group from the trans-form to the cis-form. The influence of such a conversion on the internal molecular motion is observed as a slight broadening of signal width.

For 12- and 13-membered macrocycles in which two amide linkages are integrated in the macrocyclic ring systems, the formation of 1:1 host–guest complexes with acetic and benzoic acids has been confirmed by NMR titrations. The binding force for the complex formation is due to a pair of hydrogen bonds, O_carboxyl–H…O = C_amide and C = O_carboxyl…H–N_amide. The former bond is stronger than the latter and dominates the hydrogen-bond formation. The formation of the pair of hydrogen bonds is accompanied by the conformational conversion of the amide group from the stable trans-form to the less stable cis-form.     

Host–guest system of Vitamin B10 in β-cyclodextrin: characterization of the interaction in solution and in solid state

Conventional drugs are usually formulated for the immediate release of the medicinal substances and for obtaining the desired therapeutic effect. The aim of this paper was to investigate the possible interactions between Vitamin B10 and β-cyclodextrin (β-CD), to determine the physical-chemical characteristics and the interactions present in the corresponding inclusion compound. The so-obtained compounds were characterized by X-ray diffraction, DSC and FTIR spectroscopy. ¹H NMR and UV–vis spectroscopic methods were employed to study the inclusion process in aqueous solution. The X-ray powder diffraction patterns demonstrate the inclusion compound formation, especially for the lyophilized product where the amorphous phase dominates. The existence of the inclusion compounds obtained by different methods was confirmed by comparing with DSC and FTIR data of the pure compounds and the (1:1) Vitamin B10:β-CD physical mixture (pm). ¹H NMR measurements on aqueous solutions of Vitamin B10 and β-CD in D₂O allowed us to establish the corresponding Vitamin B10’s and cyclodextrin’s protons implied in the complexation process. 2D NMR spectroscopy established the geometry of the inclusion complex. ¹H NMR, UV–Vis and fluorescence data were used to obtain the stoichiometry and the stability constant of the complex.     

Study of asymmetric aldol and Mannich reactions catalyzed by proline–thiourea host–guest complexes in nonpolar solvents

A proline–thiourea host–guest complex has been described as a good catalyst for asymmetric reactions such as aldol and Mannich reactions. High stereoselectivities were obtained under optimal conditions. Thiourea was observed to have an important effect on the reactivity and selectivity, even in an unconventional nonpolar reaction medium and without the need to utilize low temperatures. This proline–thiourea host–guest system has the ability to participate in a hydrogen bonding network.     

Host–guest inclusion complex of β-cyclodextrin and benzoic acid in water–ethanol solvents: spectroscopic and thermodynamic characterization of complex formation

Journal of Thermal Analysis and Calorimetry - In this study, an inclusion complex of benzoic acid with β-cyclodextrin (BA-βCD) was obtained from water–ethanol solvents. The yield of...     

Study of complex formation between ��-cyclodextrin and benzene

In this work study of complex formation of ??-cyclodextrin with benzene was performed both experimentally and theoretically. Interaction of benzene with ??-cyclodextrin in aqueous solutions was investigated by means of UV spectroscopy at temperatures in the range 291?C303 K. The stoichiometric composition, stability constant, and thermodynamic parameters of ????-cyclodextrin-benzene?? supramolecular structures formation were calculated from spectroscopic data. It was proved that 1:1 inclusion complex is mainly formed in aqueous solutions. The calculations of a spatial structure, formation energy, and vibration spectra in IR range for the complex of ??-cyclodextrin with benzene were performed by Hartree?CFock?CRoothaan method within PM3 semiempirical approximation with quantum chemistry package GAMESS (version 6.4). The calculated energy parameters for ????-cyclodextrin-benzene?? inclusion complex are in agreement with experimental data.     

Redox induced translocation of a guest molecule between viologen-resorcinarene and β-cyclodextrin

Here we report the design of a three-component supramolecular system in which a guest molecule reversibly translocates between two macrocyclic hosts.     

Crystalline γ-cyclodextrin metal organic framework nano-containers for encapsulation of benzaldehyde and their host–guest interactions

Journal of Inclusion Phenomena and Macrocyclic Chemistry - The nano-porous crystals of γ-cyclodextrin MOF (CDMOF) were synthesized and encapsulated with benzaldehyde. The host–guest...     

Solid-state NMR studies of host–guest chemistry in metal-organic frameworks

Metal-organic frameworks (MOFs) are an emerging class of porous materials with potential applications in a wide variety of fields. The knowledge about the detailed interactions between MOFs and guest molecules is critical for the understanding of their structure-property relationships at working conditions. In this review, recent advances for solid-state NMR studies of host–guest chemistry of MOFs in the application fields of gaseous adsorption, chemical separation, drug delivery, chemical sensor, and heterogeneous catalysis were briefly introduced. The adsorption property and dynamic behavior of adsorbed gases confined inside the MOFs channels were elucidated from variable-temperature (VT) solid-state NMR. Moreover, the detailed mechanism of gas-phase and liquid-phase adsorptive separations on MOFs adsorbents was uncovered on the basis of solid-state NMR measurements. Multi-nuclear ¹H, ¹³C, ¹⁵N, and ³¹P MAS NMR was utilized to explore the interactions between drug molecules and MOFs at the atomic scale to monitor the controlled release process of drugs. Furthermore, the investigation of the interactions between guest molecules and MOFs in the application areas of chemical sensor, toxic chemicals removal, and catalysis using solid-state NMR was briefly discussed as well.     

Complex formation between α-cyclodextrin and amines in water and DMF solvents

Complexation between -cyclodextrin (-CD) and aliphatic amines in water and DMF solvents was studied by calorimetry. Amines form complexes with -CD in both solvents but the nature of the complexes is quite different. In DMF the amines donate a hydrogen from the amine N–H group to the cyclodextrin forming a normal hydrogen bonded complex. In DMF solutions with large amine concentrations, complexes other than 11 are observed. In contrast, in aqueous environment the amines form inclusion complexes in which the amine alkyl group penetrates the -CD cavity and is stabilized by van der Waals interactions. The equilibrium constants for the complexes formed in water solvent increase with increasing alkyl chain length due to an entropy effect.     

Supramolecular end-group separation of linear polymers with different terminals through host–guest interaction

By increasing the hydrophobicity of end group, the complexation rate between α-cyclodextrin (α-CD) and poly(ethylene glycol) (PEG) derivative speeds up greatly. Based on such a huge difference of complexation kinetics, the PEG derivative with palmityloxy terminal (PEG-C16) can be successfully separated from a carboxylic acid end-functionalized analogue (PEG-COOH) by once supramolecular purification. Adding α-CD into the aqueous solution of PEG-C16/PEG-COOH mixture, PEG-C16 is encapsulated into α-CD cavity to form the crystalline inclusion complex in a very short time, while almost all of PEG-COOH molecules are still reserved in the aqueous solution. After dichloromethane extraction, the pure PEG-C16 is obtained. Moreover, the host CD can be recycled. Thus, it is an efficient green way to separate and purify the linear polymers with different terminal functionality.     

Interconversion of host–guest components in supramolecular assemblies of polycarboxylic acids and reduced Schiff bases

Eight supramolecular assemblies of benzene-1,3,5-tricarboxylic acid (H₃BTC) and benzene-1,2,4,5-tetracarboxylic acid (H₄BTtC) with reduced Schiff base of flexible backbone having phenolic and pyridyl groups, i.e., 1,2-bis(2-hydroxybenzylamino)ethane, 1,3-bis(2-hydroxybenzylamino)propane, 1,4-bis(2-hydroxybenzylamino)butane and 1,4-bis(4-pyridinylmethylamino)butane have been constructed by proton transfer reaction. H₃BTC forms host–guest type assemblies with amines having phenolic functionality, while a layered structure was obtained with pyridyl functionalized amine. H₄BTtC also formed host–guest assemblies with the diamines where reduced Schiff base acts as host and acid moiety acts as the guest. Different conformations of the diamines were observed in these assemblies. Theoretical studies were performed to analyze the effect of varied chain lengths of diamines on hydrogen bond interaction energy of the adducts.     

Solvent effects in competition between guest molecules forβ-cyclodextrin

The effect was investigated of increasing concentrations of co-solvents ethanol, isopropanol, tetrahydrofuran (THF), dimethylformamide (DMF), formamide and ethylene glycol on the selectivity of inclusion for binary mixtures of the following guest molecules: pinene, eugenol, cineole, limonene and camphor, and of isopropanol for the ternary mixtures eugenol/cineole/pinene; and limonene/cineole/pinene. In contrast to the strong solvent dependent effects on-cyclodextrin solubility, the changes in selectivity are similar for each system, show little variation from solvent to solvent and are guest dependent. Similar guest induced effects are observed for ternary mixtures. They appear to be additive.     

Enthalpic interaction coefficients of NaI–alkanediol pairs in methanol and in water

The dissolution enthalpies of NaI in the mixtures of methanol with 1,2-alkanediols (1,2-propanediol, 1,2-butanediol, 1,2-pentanediol) and with ??,??-alkanediols (1,3-propanediol, 1,4-butanediol, 1,5-pentanediol), as well NaI in the mixtures of water with 1,3-propanediol and 1,2-pentanediol, were determined at 298.15?K. The energetic effect of interactions between the investigated alkanediols and NaI in methanol and in water was calculated using the enthalpic pair interaction coefficients (h _xy ) model. These results along with the other data concerning the NaI?Cnon-electrolyte pairs taken from our earlier reports and from the literature were analyzed with respect to the effect of the non-electrolyte properties on the variations of the h _xy values. The group contributions illustrating the interactions of NaI with selected functional groups in non-electrolyte (alkanediol and alkanol) molecules, namely: CH₂ and OH groups were calculated and discussed.     

The effect of heavy metals on the anthracene–Me-β-cyclodextrin host–guest inclusion complexes

Anthracene was used to form an inclusion complex with methylated-β-cyclodextrin (Me-β-CD) in water. In aqueous Me-β-CD solution, typical fluorescence emission of anthracene was observed. Benesi–Hildebrand's method was used to obtain the stoichiometry of the anthracene–Me-β-CD complex. The Stern–Volmer quenching constants, K_sv, and fluorescence quantum yields were calculated according to changes in the fluorescence emission intensity of anthracene–Me-β-CD inclusion complexes by adding various amounts of Pb²⁺ and Cd²⁺ salts in water. The K_sv values and fluorescence quantum yields indicate that Pb²⁺ salts quench the anthracene–Me-β-CD inclusion complexes more efficiently than Cd²⁺ salts.     

Synthesis of a hexacationic cyclophane and formation of EDA-type host–guest complexes

A polycationic cyclophane with six cationic sites (three 4,4′-bipyridinium cation units) supported by a rigid cyclic skeleton was synthesized. It formed electron donor–acceptor complexes with electron-rich compounds, and their inclusion properties with pyrene and calixresorcin[4]arene were studied.     

Adsorption interaction between Al–5% Pb alloy and water

The adsorption and structural features of Al–5% Pb alloy powder before and after reacting with water are analyzed. Results from studying the morphology and phase composition of the oxidation products are presented, and the specific surface area and porosity of the powders are calculated. It is shown experimentally that water treatment of Al–5% Pb alloy powder even at room temperature leads to the formation of new phases and affects the powder’s morphology. It is established that a major role in the properties of the watertreated powders is played by nanopores that form between crystallites on a particle’s surface during waterinduced oxidation and subsequent thermal dehydration.