Qing-Xiang Guo

The Driving Forces in the Inclusion Complexation of Cyclodextrins

The driving forces leading to the inclusion complexation of cyclodextrins were reviewed, which included the electrostatic interaction, van der Waalsinteraction, hydrophobic interaction, hydrogen bonding, release of conformational strain,exclusion of cavity-bound high-energy water, and charge–transferinteraction. It was shown that except for the release of conformation strain and exclusion of cavity-bound water, the otherinteractions were indeed contributive to the complex formation. However, it was concludedthat the enthalpy and entropy changes of the complexation were not good criteria to be used injudging whether a particular driving force was present or important, mainly because of theoccurrence of enthalpy-entropy compensation. On the other hand, the multivariate quantitativestructure-activity relationship analyses usually could illustrate which driving forces wereimportant in certain inclusion complexation systems.

Use of Quantum Chemical Methods to Study Cyclodextrin Chemistry

Studies of cyclodextrin chemistry by quantum chemical methods are briefly surveyed. Emphases are put on what types of quantum chemical methods can be used for cyclodextrin chemistry, how to use quantum chemical methods to find the global minimum, to study the structures, binding energies, driving forces for cyclodextrin complexes, as well as chemical reactions occurring inside cyclodextrin cavities. Problems associated with the application of quantum chemical methods in cyclodextrin chemistry are also discussed.

Substituent Effects on the Driving Force for Inclusion Complexation of α- and β-Cyclodextrin with Monosubstituted Benzene Derivatives

The association constant values, Ka, for the inclusion of α- and β-CD with monosubstituted benzene derivatives were determined by means of UV-vis and fluorescence spectroscopy. The stability of the complexes is influenced by the properties of the substituents of the guest compounds. Regression analysis was used to create a set of inclusion models with the experimental association constant ln Ka and the corresponding substituent molar refraction Rm, hydrophobic constant π and Hammett σ constant of the benzene derivatives. The ln Ka value mainly correlated with Rm for α-CD and with both Rm and π for β-CD complexes. The association constants predicted by the models are in good agreement with the experimentally determined data. This suggests that the inclusion complexation of benzene derivatives with α-CD is predominantly driven by van der Waals force and with β-CD mainly by van der Waals force and hydrophobic interactions.

Study of the inclusion processes of styrene and α-methyl-styrene in β-cyclodextrin

Abstract The inclusion complexes of styrene and α-methyl-styrene with β-cyclodextrin (β-CD) were investigated by using [ 1 H ] NMR titration in solution and X-ray diffraction (XRD) analysis, thermo-gravimetric analysis (TGA), elemental analysis (EA) in the solid state. The inclusion process has been studied by using PM3 quantum-mechanical semi-empirical method. The calculated results are in agreed with the experimental data. All results show that α-methyl-styrene has stronger interaction with β-cyclodextrin than styrene does, so the complex of β-CD–α-methyl-styrene is more stable.

Association constant prediction for the inclusion of alpha-cyclodextrin with benzene derivatives by an artificial neural network

The association constants (Ka) for the inclusion complexation of α-cyclodextrin (α-CD) with 72 mono- and 1,4-disubstituted benzenes were predicted successfully by an artificial neural network (ANN) with molar refraction (Rm) and hydrophobic constant (π) as input parameters, which reflect the volume and hydrophobicity of the substituents respectively. The predictions strongly suggested that the inclusion complexation of α-CD with guest molecules was mainly driven by van der Waals forces and hydrophobic interactions

Theoretical Study of the Inclusion Processes of Ibuprofen Enantiomers with Native and Modified β-CDs

PM3 calculations in vacuum were performedon the inclusion complexation ofβ-cyclodextrin (β-CD),heptakis-(2-O-methyl)-β-cyclodextrin(2-Me-β-CD) and heptakis-(6-O-methyl)-β-cyclodextrin(6-Me-β-CD) withibuprofen (IB) enantiomers. Inclusion processpathways are described and the most probablestructure of the 1:1 complex are sought througha potential energy scan. The energy differencesbetween the inclusion complexes and the hosts(native and modified CDs) by calculation show thatmodified CDs have much more interaction sites withIB and enhance van der Waals interaction andhydrophobic interaction between them, form morestable complexes than native CD does.Stabilization energies of S-IB complexes arehigher than that of R-IB complexes both for nativeand modified CDs.

Substituent effect and enthalpy-entropy compensation on the inclusion of beta-cyclodextrin with 1-substituted naphthalenes

The inclusion complexation ofβ-CD with 1-substituted naphthalenes has been investigated by fluorescence spectroscopy. It was observed that the association constants were influenced by the molar refraction (Rm), hydrophobic constant (πx), and Hammett constant (σx) of substituents in the guest compounds. The thermodynamic parameters ΔG0, ΔH0, and ΔS0 determined by measuring the temperature-dependentKa values shows that inclusion complex formation is enthalpy driven. The results are discussed in terms of enthalpy-entropy compensation.

Experimental and Theoretical Studies on the Inclusion Complexation of β-Cyclodextrin with Phenothiazine Derivatives

Inclusion complexation of β-cyclodextrin (β-CD) with N-phenylphenothiazine ( 1), N-benzylphenothiazine ( 2) and N-phenethylphenothiazine ( 3) has been studied by means of UV-vis spectroscopy and molecular dynamics simulations. The association constants (Ka) were determined to be 126, 312 and 211 dm3/mol for inclusion of β-CD with 1, 2 and 3, respectively. It shows that the Ka values are affected by the substituents of the guest compounds. The structures of the complexes and the conformation of the guest compounds bound by β-CD in the complex have been discussed.