Host-guest complex of nabumetone: β-cyclodextrin: quantum chemical study and QTAIM analysis

Deciphering the Underlying Mechanism of Anion Binding by Asymmetrical Squaramide-Based Dipeptides

Anions are involved in many important processes, which has led to growing interest in designing new molecules to bind them effectively. Squaramides have gained considerable attention as effective anion receptors due to their dual hydrogen bond donor capability. Combining squaramide with biomolecules is a promising approach for designing and developing biomimetic receptors for anions with enhanced H-bonding abilities, particularly due to their functional versatility. The present study explores the mechanism of interaction of H2PO4- and HSO4- anions with three asymmetrical squaramide-based dipeptide receptors, emphasizing the role of noncovalent interactions. The conformational states of the receptors and the amino acids of the dipeptide with varying side chain lengths are the two major factors that influence these interactions. The conformational analysis of the receptors and their anion complexes performed using conformer-rotamer ensemble sampling tool (CREST) and molecular dynamics (MD) simulations, shows that the anti/anti conformations are the most abundant. Following the MD simulations, density functional theory (DFT) was used to perform electronic structure calculations on the 1:1 receptor-anion complexes. Our findings indicate that the N-H···O and O-H···O═C interactions primarily drive the formation of the receptor-anion complexes. Energy decomposition analysis based on absolutely localized molecular orbitals (ALMO-EDA) highlighted the role of the electrostatic energy (ΔEelst) in stabilizing the receptor-anion complexes. Further confirmation of the intermolecular N-H···O and O-H···O═C interactions in the complexes was attained through several analytic tools. This outcome lays a foundation for designing and developing more efficient and selective dipeptide-based anion receptors.

Biopharmaceutical Characterization and Stability of Nabumetone-Cyclodextrins Complexes Prepared by Grinding

Background: Nabumetone (NAB) is a poorly soluble nonsteroidal anti-inflammatory prodrug (BCS class II drug) whose solubility is significantly improved by complexation with cyclodextrins (CDs). Methods: The solid complexes, in a 1:1 molar ratio, were prepared by mechanochemical activation by grinding, using β-cyclodextrin (β-CD) and its derivatives, hydroxypropyl- and sulfobutylether-β-cyclodextrin (HP-β-CD and SBE-β-CD). The complexation was confirmed by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and attenuated total reflectance Fourier-transformed infrared spectroscopy (ATR-FTIR). Obtained products were further characterized regarding their solubility, in vitro dissolution, permeability and chemical stability. Results: Co-grinding with HP-β-CD and SBE-β-CD yielded products that showed in vitro dissolution profiles in hydrochloric acid medium (pH 1.2) that were substantially different from that of pure NAB, yielding dissolution efficiency enhancements of 34.86 ± 1.64 and 58.30 ± 0.28 times, respectively, for the optimized products. Their in vitro dissolution and gastrointestinal permeability were also studied in a low-volume environment at pH 6.8, corresponding to the intestinal environment. Both β-CD derivatives increased NAB dissolution rate and NAB mass transport across the biomimetic membrane. The effect of β-CD derivatives on NAB chemical stability was studied under the stress conditions by the developed and validated UHPLC-DAD-HRMS method. In acidic conditions, pure and complexed NAB was prone to hydrolytic degradation, yielding one degradation product-pharmacologically inactive NAB metabolite. However, under the oxidative conditions at elevated temperatures, 10 NAB degradation products were identified from co-ground samples. All systems were stable during photo- and long-term stability studies. Conclusions: NAB complexes with HP-β-CD and SBE-β-CD are promising candidates for pharmaceutical product development.

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.

Evaluation of the molecular inclusion process of β-hexachlorocyclohexane in cyclodextrins

The present work aimed to study the guest-host complexes of β-hexachlorocyclohexane (β-HCH), a pesticide with high environmental stability that can cause severe health problems, with the most common cyclodextrins (α-, β-, and γ-CDs). The formation reactions of these molecular inclusion complexes were addressed in this research. The multiple minima hypersurface methodology, quantum calculations based on density functional theory and a topological exploration of the electron density based on the quantum theory of atoms in molecules approach were used to characterize the interaction spaces of the pollutant with the three CDs. Additionally, charge distribution, charge transfer and dual descriptor analyses were employed to elucidate the driving forces involved in the formation of these molecular inclusion complexes. Three types of fundamental interactions were observed: total occlusion, partial occlusion and external interaction (non-occlusion). Finally, experiments were performed to confirm the formation of the studied complexes. The most stable complexes were obtained when γ-CD was the host molecule. The interactions between the pesticide and CDs have fundamentally dispersive natures, as was confirmed experimentally by spectroscopic results. All the obtained results suggest the possibility of using CDs for the purification and treatment of water polluted with β-HCH.