Spectroscopic studies on the inclusion behavior between caffenic acid and ��-cyclodextrin

To investigate the inclusion ability of ??-cyclodextrin (??-CD) for caffenic acid (CA). The conditions for the formation of inclusion complex and the binding constant between ??-CD and CA were determined by fluorescent and ultraviolet spectroscopic methods. The behavior of CA as a free radical scavenger before and after its inclusion was investigated. In addition, solid samples of the inclusion complex, prepared through the co-precipitation and grinding methods, were characterized via IR spectroscopy and differential scanning calorimetry. The inclusion complex was further characterized with ¹H NMR spectroscopy. By using fluorescent and ultraviolet spectroscopy, the conditions for the formation of inclusion complex between ??-CD and CA were optimized and the binding constant determined. It was observed that the guest molecule behaves as a better anti-oxidant after its inclusion into ??-CD.     

Spectroscopic studies of inclusion complex of β-cyclodextrin and benzidine diammonium dipicrate

Formation of inclusion complex between benzidine diammonium dipicrate and β-cyclodextrin with stoichiometry 1:2 (guest–host) has been established by UV, ¹H NMR, ¹³C NMR, IR spectra and powder X-ray diffractometry. ¹H NMR studies are used to confirm the inclusion and to provide information on the geometry of dipicrate inside the cavity of β-cyclodextrin.     

Thermodynamic studies of inclusion complex formation between alkylpyridinium chlorides and β-cyclodextrin using conductometric method

Thermodynamics on inclusion complexation of β-cyclodextrin (β-CD) with n-alkylpyridinium chlorides (C _n PC, n = 12, 14, 16) were measured by conductivity technique to evaluate the effects of chain length of C _n PC and temperature. The data obtained indicate that inclusion complexes S(CD) and S(CD)₂ had formed between surfactant and β-CD in aqueous solution. Investigation showed that the K ₁ (first equilibrium constant) for S(CD) formation is greater than K ₂ (second equilibrium constant) for S(CD)₂ formation. It has been found that C₁₂PC forms only the 1:1 complex, while C₁₄PC and C₁₆PC form 1:1 and 1:2 complexes. Thermodynamic parameters of the complexation, i.e. ΔG°, ΔH° and ΔS° have been also calculated. The large values of ΔG° indicate that complexation between surfactant and β-CD is very favorable.     

Mass spectrometry and molecular modeling studies on the inclusion complexes between alendronate and β-cyclodextrin

Complexation of alendronate sodium (AlnNa) with β-cyclodextrin (β-CD) was studied by means of ESI-mass spectrometry. The experimental results show that stable 1:1 inclusion complexes between selected bisphosphonates and β-CD were formed. In addition, complexes with different stoichiometry were observed. DFT/B3LYP calculations were performed to elucidate the different inclusion behavior between alendronate and β-CD. Molecular modeling showed that the inclusion complex of Aln-β-CD where the two phosphonate groups bound to the central carbon atom of bisphosphonate were inserted into the cavity of β-CD from its “top” side was thermodynamically more favorable than when they were inserted from its “bottom” side; the complexation energy was ?74.05 versus ?60.85 kcal/mol. The calculations indicated that the formation of conventional hydrogen bonds was the main factor for non-covalent β-CD:Aln complex formation and stabilization in the gas phase.     

Spectroscopic (fluorescence, 1D-ROESY) and theoretical studies of the thiabendazole and β-cyclodextrin inclusion complex

The inclusion complex between the anti-helminthic drug thiabendazole (TBZ) and the β-cyclodextrin (βCD) was characterized in solution using fluorescence and ¹H-Nuclear Magnetic Resonance spectroscopy and studied theoretically by semi empirical PM3 and density functional theory (DFT) quantum mechanical calculations. Thermodynamic stability associated with the formation of the TBZ:βCD inclusion complex in aqueous solution was determined treating the drug’s fluorescence enhancement in the presence of cyclodextrin by a non-linear model, which indicated a moderate host–guest affinity at equilibrium (K 150 ± 31 at 25 °C). Its supramolecular structure in solution was studied through the 1D-ROESY NMR experiment, which produced evidence that the guest molecular encapsulation occurs preferably via the drug’s benzimidazole group. Theoretical study employing molecular optimization with the semi empirical PM3 method provided two energetic-equivalent complex structures that are in accordance with the NMR experimental evidences. Single point energy calculations with DFT at the B3LYP/6-31G (d,p) level suggest the most stable structure of the inclusion complex and further comprehension on the interactions and conformational strains involved in its formation.     

Phase solubility and thermoanalytical studies of the inclusion complex formation between curcumin and hydroxypropyl-β-cyclodextrin in hydroalcoholic solutions

Journal of Thermal Analysis and Calorimetry - Curcumin (CURC) is endowed with many pharmacological properties, among these anti-inflammatory, antioxidant, antimicrobial, and anticancer activity....     

Effect of solution pH on complex formation between epi-type catechin and β-cyclodextrin

Journal of Thermal Analysis and Calorimetry - The effect of solution pH on the formation of an inclusion complex between (?)-epigallocatechin gallate (EGCg: pKa?=?7.5) and...     

Theoretical investigation to characterize the inclusion complex of α-lipoic acid and β-cyclodextrin

We simulated the docking of α-lipoic acid (α-LA) in β-cyclodextrin (β-CD) using two models. We considered in this study complexes formed by 1:1 host–guest stoichiometry in vacuo and in aqueous phase, using PM6, DFT and ONIOM2 hybrid calculations. The results obtained with PM6 method clearly indicate that the complexes formed are energetically favored with or without solvent, model 2 (α-LA entering the cavity of β-CD from its wide side by COOH group) is found more favored than model 1 (α-LA entering into the cavity of β-CD from its wide side by cyclic group), the preference being greater in the case of ONIOM2 calculations. In addition, NBO analysis gives that mutual interactions between the donor and acceptor orbitals of α-lipoic acid and β-CD plays an important role to the stabilization of such a complex. Finally, ¹H nuclear magnetic resonance (NMR) chemical shifts of free and complexed α-LA were calculated by the Gauge-Including Atomic Orbital (GIAO) method and compared with available experimental data. The results of GIAO calculations were analyzed and discussed.     

Difference in formation mechanism of inclusion complex between configuration isomers of gallate-type catechin and β-cyclodextrin

Journal of Thermal Analysis and Calorimetry - The formation mechanism of inclusion complex between (-)-epigallocatechin gallate (EGCg), which is the main catechin in tea leaves, or...     

Kinetic studies on the thermal dissociation of the inclusion complex of β-cyclodextrin with cinnamic aldehyde

The stability of the inclusion complex of -CD with cinnamic aldehyde was investigated by means of TG and DSC. The mass loss takes place in three stages: dehydration occurs at 50–120°C; dissociation of -CD·C₉H₈O proceeds in the range 200–260°C; and decomposition of -CD begins at 280°C. The kinetics of the dissociation of -CD·C₉H₈O was studied by means of thermogravimetry both at constant temperature and with linearly increasing temperature. The results demonstrate that the dissociation of -CD·C₉H₈O is dominated by a one-dimensional diffusion process. The activation energyE is 160 kJ mol^–1, and the pre-exponential factorA is 5.8×10¹⁴ min^–1. Scanning electron microscope observations and the results of crystal structure analysis are in good agreement with those of thermogravimetry.     

Electrochemical signal modulation in homogeneous solutions using the formation of an inclusion complex between ferrocene and β-cyclodextrin on a DNA scaffold

Two DNA conjugates modified with ferrocene and β-cyclodextrin were prepared as a pair of probes that work cooperatively for DNA sensing, in which the electrochemical signal of ferrocene on one probe was significantly "quenched" by the formation of an inclusion complex with β-cyclodextrin of the other probe on the DNA templates.     

Host-guest inclusion complex between β-cyclodextrin and paeonol: A theoretical approach

Host-guest interactions of β-cyclodextrin (β-CD) with paeonol (PAE) were simulated using semi-empirical PM3 and both ONIOM2 [(B3LYP/6-31G*:PM3), (HF/6-31G*:PM3)] methods. The results obtained with PM3 method clearly indicate that the complexes formed are energetically favored with or without solvent, the model 1 (PAE entering into the cavity of β-CD from its wide side by OCH3 group) is found more favored than the model 2 (PAE entering into the cavity of β-CD from its wide side by COCH3 group). Finally, natural bonding orbital (NBO) analysis was performed based on ONIOM2 optimized complexes to quantify the donor–acceptor interactions between PAE and β-CD.     

The structural analysis of the inclusion complex of β-cyclodextrin with m-nitrophenoxyacetic acid

The inclusion complex of β-cyclodextrin with m-nitrophenoxyacetic acid was studied by single crystal X-ray diffraction,2D NMR spectroscopy and semi-empirical methods AMI.The crystallographic study shows that two β-cyclodextrins are held together by hydrogen bonds to form head-to-head dimers.The disordered guest molecule adjusts itself to attain the most stable accommodation into the cavity in which the nitro group is located at the dimer interface while the carboxyl group is buried in the primary hydroxyl groups of β-cyclodextrin.The guest inside the cavity is disordered over two sites and exhibits mobility.Moreover,2D NMR spectroscopy and theoretical study show the same inclusion behavior.In comparison to the inclusion complex of β-cyclodextrin with p-nitrophenoxyacetic acid,the host-guest stoichiometries are different,i.e.,2:1 for m-nitrophenoxyacetic acid and 1:1 for p-nitrophenoxyacetic acid,while the inclusion orientation and the packing pattern of the host are similar in both complexes.     

Volumetric study on the inclusion complex formation of α- and β-cyclodextrin with 1-alkanols at different temperatures

The partial molar volumes (V_a) of 1-alkanols (carbon number, m=5, 6, 7) in - and -cyclodextrin (CD) solutions at 5.00 mmol kg^–1 have been determined as a function of alkanol concentration (C_a) between 293.2 and 308.2 K by using a dilatometer. It has been observed that with an increase in C_a, V_a increased in -CD solution but decreased in -CD solution, asymptotically to a value of V_a in CD-free water. The dependence of V_a on C_a provided the binding constant (K) of 1:1 complex, the volume change in complex formation, and the partial molar volume of complex itself. The complex formation mechanism has been discussed on the basis of these values and their carbon number dependences in the respect of geometric behavior, hydrophobic interaction, and van der Waals interaction. It is concluded that the CD cavity in water is not rigid but flexible for fitting in nicely with guest molecule.     

Investigation of the inclusion complex of tolfenamic acid with β-cyclodextrin: Geometry and NBO analysis

Quantum chemical calculations were carried out to investigate geometry and driving forces for inclusion complexes of tolfenamic acid (TA) into β-CD (at 1:1 stoichiometry). Two possible orientations of TA in the β-CD cavity were considered. Both PM3MM and ONIOM2 method evidence that TA is encapsulated in the β-CD cavity for A and B orientation. Finally, charge transfer between the donor and acceptor orbitals of each TA and β-CD play an important role to stabilize the inclusion complex.     

Comparison between 2-hydroxypropyl-��-cyclodextrin and 2-hydroxypropyl-��-cyclodextrin for inclusion complex formation with danazol

Complexation in solution between danazol and two different cyclodextrins [2-hydroxypropyl-??-cyclodextrin (HP-??-CD) and 2-hydroxypropyl-??-cyclodextrin (HP-??-CD)] was studied using phase solubility analysis, and one- and two-dimensional ¹H-NMR. The increase of danazol solubility in the aqueous cyclodextrin solutions showed a linear relationship (A_L profile). The apparent stability constant, K _1:1, of each complex was calculated and found to be 51.7 × 10³ and 7.3 × 10³ M^?1 for danazol?CHP-??-CD and danazol?CHP-??-CD, respectively. ¹H-NMR spectroscopic analysis of varying ratios of danazol and the different cyclodextrins in a mixture of EtOD?CD₂O confirmed the 1:1 stoichiometry. Cross-peaks, from 2D ROESY ¹H-NMR spectra, between protons of danazol and H3?? and H5??of cyclodextrins, which stay inside the cyclodextrin cavity, proved the formation of an inclusion complex between danazol and the cyclodextrins. For HP-??-CD, the inclusion complex is formed by entrance of the isooxazole and the A rings of danazol in the cyclodextrin cavity. For HP-??-CD, two different inclusion structures may exist simultaneously in solution: one with the isooxazole and A ring in the cavity and the other with the C and D ring inside the cavity. DLS showed that self-aggregation of the CD??s was absent in the danazol HP-??-CD system up to a CD concentration of 10% and in the danazol HP-??-CD system up to a CD concentration of 5%.     

Phase solubility and FTIR-ATR studies of idebenone/sulfobutyl ether β-cyclodextrin inclusion complex

The favourable accessibility offered by sulfobutyl ether β-cyclodextrin (SBE-β-CD) for the complexation with idebenone (IDE) has been probed, as a function of temperature, in liquid state, by phase solubility study, and, in solid state, by FTIR-ATR technique. The phase solubility results indicated the formation of a IDE/SBE-β-CD inclusion complex with 1:1 molar ratio (A_L type diagram), whose apparent stability constants at T = 300, 310, and 320 K have been estimated according to the Higuchi–Connors method. The formation of the inclusion complex has been confirmed on a freeze-dried and a co-precipitated product by FTIR-ATR spectroscopy, monitoring the changes induced by complexation on some characteristic vibrational bands of IDE. Quantitative studies, performed in a wide T range, from T = 250 K to T = 340 K, allowed us to extract information on the effect of temperature on the different hydrogen-bonded environments involving host, guest, and crystallization water molecules. Again, complexation is proved to enhance the stability of the guest, at least in the explored T range.     

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.     

Study on preparation and inclusion behavior of inclusion complexes between β-cyclodextrin derivatives with benzophenone

In the paper, the two chemically modified β-cyclodextrin derivatives of 4,4´-diaminodiphenyl ether-bridged-bis-β-cyclodextrins (ODA-bis-β-CD) and p-aminobenzenesulfonic acid-β-cyclodextrin (ABS-β-CD) were synthesized, and then these two β-cyclodextrin derivatives were respectively formed into inclusion complexes with benzophenone (BP) by co-precipitation method. The structure of the inclusion complexes were characterized by UV/vis spectroscopy, FT-IR spectroscopy, elemental analysis, ¹H NMR spectroscopy and XRD. Spectral titration was performed to study the inclusion behavior of the inclusion complexes. These experiments indicated that two inclusion complexes were formed at a stoichiometric ratio of 1:1 and the inclusion stability constants at different temperatures were calculated using the Benesi–Hildebrand (B–H) equation. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were obtained. As a result, it was found that the two chemically modified β-cyclodextrins containing BP were exothermic and spontaneous process (ΔG°?<?0), and the processes of inclusion complexation were mainly enthalpy driven with negative or minor negative entropic contribution.