Quantitative conformational stability host-guest complex of Carvacrol and Thymol with β-cyclodextrin: a theoretical investigation

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.

The supramolecularly complexes of calix[4]arene derivatives toward favipiravir antiviral drug (used to treatment of COVID-19): a DFT study on the geometry optimization, electronic structure and infrared spectroscopy of adsorption and sensing

While the world is in search of a vaccine that can cure COVID-19 disease, favipiravir is the most commonly used antiviral drug in the treatment of patients during the pandemic process. In this study, we investigated the host-guest interaction between the popular supramolecule calix[4]arene derivatives and the favipiravir drug by using the DFT (Density Functional Theory) method. The B3LYP hybrid method and 6-31G (d,p) basis set were utilized to determine the optimized structures of the host and guest molecules and their complexes. The negative adsorption energy (∆E) and adsorption enthalpy (∆H) calculated for the complexes formed between calix[4]arene compounds and favipiravir drug molecule mentioned that adsorption of favipiravir molecule was an exothermic process on calix[4]arene structures. On the other hand, among the calixarene derivatives in the study, Gibbs free energy change (∆G) value for the adsorption was only negative on calix[4]arene4 molecule. The infrared spectroscopy (IR) calculations were performed by examining the C=O, O-H and NH2 vibrational frequencies to see the adsorption behavior in the favipiravir-calix[4]arene complex. After adsorption of the favipiravir molecule, HOMO-LUMO gap values decreased significantly for the structures and therefore electrical conductivity increased proportionally. In addition, sensor response factors, Fermi energy levels and workfunction changes of calix[4]arene derivatives were calculated and examined. Charge transfer between the four calix[4]arene compounds and the favipiravir molecule has occurred after adsorption. This attributes that calix[4]arene derivatives can be used as a well-suited favipiravir sensor (electronic and workfunction) and adsorbent at room temperature. Based on the calculations made to see the solvent effect on the adsorption of favipiravir it was determined that it did not affect the interaction between the drug molecule and the calix[4]arene compound too much and the adsorption energy turned into a slightly less negative value.

A quantum chemical study of encapsulation and stabilization of gallic acid in β-cyclodextrin as a drug delivery system

This research paper describes the study of the inclusion complex formation of a 1:1 stoichiometry ratio of host–guest inclusion complex (X-β-CD) between gallic acid (GA), which is reported to have anti-cancer effects, and β-cyclodextrin (β-CD). The use of β-CD for the encapsulation of bioactive compounds can protect the drugs against conjugation and metabolic inactivation and improve the aqueous solubility for increasing their capacity to functionalize the products. The objective of this study is to give insight on the mechanism of complexation and the capability of β-CD to encapsulate GA compound (X) in gas and solution phases. We examine and compare the performances of different quantum mechanical methods, namely HF/6-31G* and density functional theory (DFT; B97D3/6-31G* functional including dispersion correction), to study the importance of the contribution of the dispersion forces and the hydrogen bonding in the mechanism of interaction. The stability of the optimized geometries of the complex was evaluated with the supermolecule method. Two modes of complexation are taken into consideration. Moreover, the inclusion complex can be confirmed using the frontier molecular orbital (FMO) theory, the global indices of reactivity, the electronic populations condensed natural bond orbital (NBO) analysis, and the molecular docking, which examine the quality and the nature of the hydrophobic interactions during the complexation process.