Quantum chemical investigations on hydrogen bonding interactions established in the inclusion complex β-cyclodextrin/benzocaine through the DFT, AIM and NBO approaches

Theoretical study of the formation of inclusion complexes with some terpenes using different solvating models

CONTEXT

Essential oil molecules have various nutritional and medical uses. However, their applications are limited by their low polarity and high volatility. Inclusion complexes provide a way to overcome these limitations. Cyclodextrins are cyclic oligosaccharides composed of macrocyclic rings of glucose units linked by α-1,4 glycosidic bonds, which are used to prepare inclusion complexes with essential oils. Experiments on the formation of inclusion complexes show that essential oil molecules can bind to cyclodextrins in various ways. Electronic structure calculations help to understand why some essential oil molecules bind more effectively than others in the formation of inclusion complexes with cyclodextrins.

METHODS

Our study employed theoretical calculations to investigate the interaction between beta-cyclodextrin and six essential oil molecules. The selected essential oil molecules were carvacrol, carvone, eugenol, limonene, p-cymene, and thymol. Molecular docking between the essential oil molecules and cyclodextrin resulted in both complexed structures and non-complexed structures, with some molecules positioned outside the cyclodextrin cavity. The interaction energies, calculated using the AutoDock Vina program, indicated that the complexed essential oil molecules exhibit the lowest energy. Electronic structure calculations were performed using the Gaussian16 program to analyze the structures obtained from the docking process. DFT calculations employing the ωB97XD functional to describe the inclusion complex and PM7 to describe the solvent model in the ONIOM approach revealed that molecules containing hydroxyl groups form hydrogen bonds with cyclodextrin, resulting in more stable structures compared to those lacking this functional group. Additionally, the use of explicit solvent facilitates the inclusion of essential oil molecules by altering the deformation energies of cyclodextrin. These theoretical results explain the advantage of using solvents in the preparation of experimental inclusion complexes.

Current Status of Quantum Chemical Studies of Cyclodextrin Host-Guest Complexes

This article aims to review the application of various quantum chemical methods (semi-empirical, density functional theory (DFT), second order Møller-Plesset perturbation theory (MP2)) in the studies of cyclodextrin host-guest complexes. The details of applied approaches such as functionals, basis sets, dispersion corrections or solvent treatment methods are analyzed, pointing to the best possible options for such theoretical studies. Apart from reviewing the ways that the computations are usually performed, the reasons for such studies are presented and discussed. The successful applications of theoretical calculations are not limited to the determination of stable conformations but also include the prediction of thermodynamic properties as well as UV-Vis, IR, and NMR spectra. It has been shown that quantum chemical calculations, when applied to the studies of CD complexes, can provide results unobtainable by any other methods, both experimental and computational.

Highly sensitive determination of anesthetic drug benzocaine based on hydroxypropyl-β-cyclodextrin-carbon black nanohybrids

Benzocaine (BZC) is a local anaesthetic drug coupled with numerous adverse effects, and thus poses a great challenge for its simple and highly sensitive detection. For resolving this issue, hydroxypropyl-β-cyclodextrin-carbon black (HP-β-CD-CB) nanohybrid that possesses the collaborative advantages of CB (e.g., excellent electrical properties, large surface area) and HP-β-CD (e.g., high molecule recognition and preconcentration capability) was synthesized in this study via a simple process and then utilized as a novel electrode material to electrochemically detect BZC. With the optimized experimental conditions, the HP-β-CD-CB nanohybrid-modified electrode shows wide linearity from 0.05 to 7.0 μM and very low detection limit (0.015 μM) for BZC detection. In addition, the repeatability, stability, and selectivity as well as practical-sample analysis of the HP-β-CD-CB electrode were investigated, and the observed results are desirable. The superior sensing performances coupled with its advantages including low-cost, simple and highly sensitive detection suggest that HP-β-CD-CB has important potential application for BZC analysis in practical samples.

Relative Position and Relative Rotation in Supramolecular Systems through the Analysis of the Principal Axes of Inertia: Ferrocene/Cucurbit[7]uril and Ferrocenyl Azide/β-Cyclodextrin Case Studies

Parameters comprising the relative position and relative rotation of molecules can be evaluated when the principal axes of inertia of the entities in a supramolecular association are employed as reference. Such information applies to the characterization and identification of experimental and theoretical nonbonded systems. The parameters are relevant to geometric comparison (for theory and experiment) and, for instance, to monitoring structures by theoretical simulations. This work introduces a software developed to obtain such parameters through the discussion of some intriguing host-guest systems, the ferrocene/cucurbit[7]uril and ferrocenyl azide/β-cyclodextrin. The ideas within this contribution naturally apply to the study of other nonbonded associations beyond host-guest chemistry. A modified version of the software discussed herein serves to obtain user-defined spatial arrangements for two nonbonded entities. Therefore, with a given geometry, for instance, from X-ray data, the parameters can be derived, and with the parameters, from a theoretical perspective, a spatial arrangement can be obtained.

Preparation, characterization and molecular modeling studies of the beta-cyclodextrin inclusion complex with benzoguanamine and its analytical application as chemosensor for the selective sensing of Ce4

The inclusion complex of β-cyclodextrin (β-CD) with benzoguanamine (BGA) has been investigated in three states. UV-Visible and fluorescence spectral techniques are used in liquid state. FTIR, NMR and MASS techniques are used in solid state and virtual state studies are done by molecular simulation work. The binding constants for the formation of 1:1 BGA:β-CD inclusion complex is estimated by UV-Visible and fluorescence spectral techniques. The chemosensory ability of BGA:β-CD complex was investigated thoroughly for various metal cations and we found the emission of complex showed a linear increase in the intensity for Ce⁴⁺ with the linearity range of 1000 μM-2000 μM. Sensitivity analysis shows good sensing for Ce⁴⁺ with the LOD of 671 μM and LOQ of 2034 μM. Our result suggests that the BGA:β-CD inclusion complex would be promising material for developing solid state sensory device for sensing Ce⁴⁺.

The solvent effects on dimethyl phthalate investigated by FTIR characterization, solvent parameter correlation and DFT computation

This study set out with the aim of investigating the solvent effects on dimethyl phthalate (DMP) using FTIR characterization, solvent parameter correlation and DFT calculation. DMP exposed to 17 organic solvents manifested varying shift in the carbonyl stretching vibration frequency (ν_CO). Non-alkanols induced Band I and alkanols produced Band I and Band II. Through correlating the ν_CO with the empirical solvent scales including acceptor parameter (AN), Schleyer's linear free energy parameter (G), and linear free salvation energy relationships (LSER), Band I was mainly ascribed to non-specific effects from either non-alkanols or alkanol polymers ((alkanol)_n). ν_CO of the latter indicated minor red shift and less variability compared to the former. An assumption was made and validated about the sequestering of hydroxyl group by the bulky hydrophobic chain in (alkanol)_n, creating what we refer to as "screening effects". Ab initio calculation, on the other hand, provided insights for possible hydrogen binding between DMP and (ethanol)_n or between ethanol monomers. The two components of Band I observed in inert solvents were assigned to the two CO groups adopting differentiated conformations. This in turn prompted our consideration that hydrogen binding was highly selective in favor of lowly associated (alkanol)_n and the particular CO group having relatively less steric hindrance and stronger electron-donating capacity. Band II was therefore believed to derive from hydrogen-bond interactions mainly in manner of 1:1 and 1:2 DMP-(alkanol)_n complexes.