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In the present work, the host–guest complexation between l-Metheonine/β-Cyclodextrin was investigated using the DFT/B97-D3/6-31G (d) level of the theory. The results obtained clearly indicate that the Orientation B (the carboxylic group of l-Metheonine points toward the primary hydroxyl of β-CD) is energetically favored than that one of the Orientation A (the carboxylic group of l-Metheonine points toward the secondary hydroxyl of β-CD). The energy decomposition analysis, thermodynamic parameters, HOMO, LUMO, the global reactivity descriptors and non covalent interactions-reduced density gradient analysis of the two complexes were calculated and interpreted. The QAIM theory has been used to examine the properties of the bond critical points. Finally, the 1H nuclear magnetic resonance (NMR) chemical shift of the complexes was studied using the Gauge-Including Atomic Orbital (GIAO) method and compared with experimental values. The structures of inclusion complexes of l-Metheonine@β-CD.

In the present work, a quantum chemical calculation of energies, geometric parameters, frontier molecular orbitals, thermodynamic parameters, for inclusion complex of host β-Cyclodextrin and guest 8-Anilinonaphthalene-1-sulfonate (1,8-ANS@β-CD) have been investigated using the following functionals, B3LYP, M06-2X and WB97X-D with the split valence double zeta 6-31G(d) basis set in both gas and aqueous phases. The results indicate that the orientation in which the guest molecule points toward the primary hydroxyls of the hydrophobic cavity of β-CD is energetically preferred and exhibited a good agreement with the experimental results. NBO and QTAIM analysis are carried out in order to understand various second-order interactions between the filled orbital of one subsystem and vacant orbital of another subsystem. The 1H nuclear magnetic resonance (NMR) chemical shift of the complexes was studied using the Gauge-Including Atomic Orbital (GIAO) method and compared with experimental values.

In this work, the thymoquinone (TQ)/hydroxypropyl-β-cyclodextrin (HPβ-CD) inclusion complex has been investigated employing quantum mechanical calculations in gas phase and in water. Complexation energies, geometries parameters and thermodynamic parameters ΔH°, ΔS° and ΔG° have been investigated and analyzed. The results obtained clearly indicate that the complexation process with Orientation B (TQ enters into the cavity of HPβ-CD from its wide side by C2H6 group) is energetically favored than that of Orientation A (TQ penetrates the HPβ-CD cavity from its wide side by methyl group). Time-dependent (TD)-DFT analysis performed in water using polarizable continuum model (PCM) calculations reveal that the main absorption bands of thymoquinone arise from the π→π* transition, after encapsulated by hydroxypropyl-β-cyclodextrin to form inclusion complexes. (HOMO- LUMO) energy and global reactivity descriptor values were evaluated. The results of electrophilicity based charge transfer (ECT) indicate that, the charge transfer occurs from the host to the guest. The Hirschfield surface is also investigated. From QTAIM analysis, ∇2ρ(r) > 0 and H(r) > 0 at critical points for all intermolecular interactions correspond to weak H-bonds and affirm dominance of electrostatic interactions. Also, the ratio –G(r)/V(r) > 1 confirms the presence of weak hydrogen bonding and van der Waals interactions stabilizing the complex. In addition, the reduced density gradient (RDG) and the independent gradient model (IGM) methods were used to reveal and distinguish between attractive interactions such hydrogen bonds, repulsive interactions and van der Waals interactions. At last, 1H NMR chemical shifts were computed with gage-including atomic orbital (GIAO) and compared with experimental results.

The interactions of the neurotransmitter dopamine (DA) with β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was characterized using UV–visible, 2D fluorescence, 3D fluorescence, FT–IR, PXRD and SEM techniques. PM3, PM7 and DFT methods were used to optimize the structures of the inclusion complexes in the gas phase. The absorbance and fluorescence intensities of DA increased in the presence of CDs in aqueous solution. The binding energy, HOMO–LUMO energy gap and Mulliken atomic charges were computed for the inclusion complexes. NBO analysis revealed a greater number of intermolecular hydrogen bonds in DA:HP-β-CD. Experimental and theoretical results suggested that the DA molecule is deeply embedded in the cavities of both CDs.

In this work, a theoretical study has been conducted using DFT and TD-DFT methods on 2,2’-Bpy and 2,2’-Bpy@β-CD inclusion complex (1:1) in different solvent. The properties of 2,2’-Bpy and 2,2’-Bpy@β-CD inclusion complex, including UV-Vis spectra, oscillator strength (f) , transition energy , gap energy (EHOMO-ELUMO) are calculated to give more insight about absorption and emission properties of the studied molecules. The TD-DFT/B3LYP/6-31 (d) investigation gives that the major transition on UV-visible spectra of free 2,2’-Bpy is occurred between π→π* and it is greatly affected by the polarity of the solvent. The presence of β-CD modify largely spectroscopic properties, in addition to π→π* transition the n→π* one is occurred and the micro environment of 2,2’-Bpy is largely changed. Finally, NBO, NCI and MEP analysis suggest that non covalent interactions such as hydrogen bonds and Van der Waals interactions influence greatly absorption and emission spectra of 2,2’-Byp upon 1 :1 complex formation into β-CD. .Keywords: 2,2’-Bpy, 2,2’-Bpy@β-CD, absorption, emission and TD-DFT.

This study presents a computational investigation of inclusion complex formation between thymol (Thym) and β-cyclodextrin in vacuum. Geometry optimizations were performed by HF/6-31G(d,p), B3LYP/6-31G(d,p), PBEPBE/6-31G and CAM-B3LYP/6-31G levels of theory. Time-dependent density functional theory (TD-DFT) was used to calculate the electronic transitions of formed complexes at B3LYP/6-31G(d,p) level using the ground state geometry from optimized complexes in A and B orientations. Ecomplexation, Edeformation, Einteraction have been calculated and compared for both orientation A and B. PBEPBE/6-31G and CAM-B3LYP/6-31G calculations shows that B orientation is more stable than A one, for each orientation Thym is totally encapsulated into β-CD cavity. Charge transfer between host and guest is the most important factor stabilizing the inclusion complex Thym/β-CD; this is confirmed by TD-DFT calculation and NBO analysis.

In the present work, a detailled computational study of vanillin@β-CD 1:1 inclusion complex was investigated. Firstly, the favor geometry of vanillin@β-CD inclusion complex was located by PM6-DH+ semi empirical calculation for A and B models. Then, the reactivity parameters calculated by B3LYP/6-311G(d, p), ωB97xD/6-311G(d, p) and M06-2×/6-311G(d, p) in both vacuum and water showed clearly that B model is more active than A one. For the two models, vanillin guest is totally embedded into β-CD cavity. Vertical electronic transitions obtained from UV–visible calculation show the presence of intra and intermolecular transitions between vanillin and β-CD. In addition, the investigation of intermolecular interactions established between vanillin and β-CD by: EDA, NBO, AIM,NCI and IGM suggest that H-bond and van Der waals interactions are the major contributions stabilizing the studied inclusion complex. Finally, a good agreement between experimental and calculated GIAO/1HNMR shifts was observed.

The interactions between carvacrol (CAR) and β-cyclodextrin (β-CD) have been analyzed employing PM3, ONIOM2 and DFT methods in vacuum and in water. Complexation, deformation, HOMO and LUMO energies were determined and discussed. Van der Waals interactions are mostly responsible for enthalpy driven complex formation of CAR with β-CD. Finally, TD-DFT of visible spectra and NBO calculations were analyzed and discussed. Theoretical studies propose that hydrophobic interaction and hydrogen bonding play significant role in determining the stability of the complexes.

This article describes the processes of the formation of 2-oxo-N-phenyl-3-oxazolidinesulfonamide@β-cyclodextrin (ONPOS@β-CD) complex with molecular dynamics and quantum mechanics with the aim of determining the most important driving forces of the complexation. According to the results obtained from molecular dynamics simulation, hydrophobic forces are the most significant driving forces; whereas quantum mechanics calculations give rather hydrogen bonding interactions the predominate one in the complexation process.

A theoretical study has been conducted on the complexes (1,8-ANS/CB[7]), which formed between the guest 8-Anilinonaphthalene-1-sulfonate (1,8-ANS) and the host Cucurbit[7]uril (CB[7]) to determine the geometries, binding energies and the driving forces which governed its formation. The possible structures were investigated using semi-empirical PM3 method and density functional theory (DFT) incorporating various hybrid exchange-correlation functionals: B3LYP/6-31G(d), M06–2X/6-31G(d) and ωB97X-D/6-31G(d) levels of theory in vacuum and in water. It has been concluded that there is an exclusion of the 1,8-ANS molecule from the CB[7] cavity. Furthermore, the donor-acceptor interactions between host and guest were performed using Natural Bond Orbitals (NBO) and Quantum Theory of Atom In Molecule (QTAIM) analysis. Finally, and based on the Gauge-Including Atomic Orbital (GIAO) method, the 1H Proton Nuclear Magnetic Resonance (1H NMR) study has been used to confirm and give more information about the geometry of formed complexes. The results will be discussed in details.

In this work, the host-guest inclusion complexes of pyroquilon (Pyn) with two cucurbit[n]urils (CB[7] and CB[8]) were investigated by the density functional theory including dispersion correction (DFT-D3) method using the following functional, B3LYP and M06-2X with the split valence double zeta 6-31G(d) basis set in both gas and aqueous phases. The geometries of these complexes were optimized and the results were analyzed and compared. To provide insights into the contributions of different components of interaction energy of studied complexes, we used the energy decomposition analysis (EDA) which provides quantitative interpretation of chemical bonds. HOMO and LUMO energies, the global chemical reactivity descriptors and Fukui function were computed. The absorption spectra of the complexes have been calculated using TD-DFT method. Molecular electrostatic potential was calculated to predict the reactive sites for electrophilic and nucleophilic attack. The study of the type of the interaction between the pyroquilon molecule and the two hosts is better explained using the non-covalent interaction-reduced density gradient (NCI-RDG). AIM analyses demonstrate the establishment of conventional H-bond interaction. The 1H nuclear magnetic resonance (1H NMR) chemical shift of the complexes was studied using the Gauge-Including Atomic Orbital (GIAO) method and compared with experimental data. It has been shown that hydrogen bond energies from the QTAIM theory correlate well with the 1H NMR chemical shifts calculated.

Density functional theory (DFT) calculations at the B97-D3/6-31G (d)level are performed to investigate the inclusion complex of l -Glutamine/β–Cyclodextrin. The results indicate, the orientation in which the guest molecule points toward the primary hydroxyls of the hydrophobic cavity of β–Cyclodextrin is energetically preferred and in consistency with experimental observation. Energy decomposition analysis, thermodynamic parameters, the electronic properties, such as the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the global indices of reactivity such as, electronegativity (χ), electronic potential (μ), hardness (η) global electrophilicity index (ω) and molecular electrostatic potential surface (MESP) mapping have been dealt and interpreted at same level of theory. Natural atomic charge and non-covalent interactions-reduced density gradient analysis properties of the two complexes were also calculated and interpreted. Natural bond orbital (NBO) analysis is carried out to analyze mutual interactions between donor and acceptor orbital of l -Glutamine and β-CD play an important role to the stabilization of such complex. Finally, the quantum theory of atoms in molecules (QAIM) theory has been also used to examine the properties of the bond critical points: their electron densities and Laplacians.

In the present work, we investigate theoretically, the structure and electronic properties of inclusion complex of cucurbit [7]uril(Q[7]) with Albendazole (ABZ) using DFT calculations. Two modes of complexation were taken into consideration and the effect of solvent is explicitly taken into account. The results obtained with B3LYP/6-31G (d) method clearly indicate that the complexes formed are energetically favored with or without solvent. C1 complex (Albendazole entering the cavity of Q[7] by propyl and aromatic groups) is found more favored than C2 complex (Albendazole entering the cavity of Q[7] by carbamate group). 1H nuclear magnetic resonance (NMR) was calculated by the Gauge-Including Atomic Orbital method and compared with available experimental data. Finally, TD-DFT calculations of visible spectra were analyzed and discussed. The theoretical calculation agrees well with that obtained from experimental data.

The binding of the carbendazim (CBZ) with cucurbit[7]uril (CB[7]) was investigated theoretically using HF/6-31G and B3LYP/6-31G methods. Two modes of complexation were considered for studying such complex. In A complex the benzimidazole group of the guest was introduced into CB[7] cavity, while in B complex the carbamate group was included in the CB[7] cavity. Energetic analysis indicates that the formed complexes are stable and both host and guest were little deformed after complexation. Electronic properties given by TD-DFT calculation clearly demonstrate that a charge transfer was occurred between CBZ and CB[7] molecules.

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.

The binding of the N-acetyl-4-aminophenol (NAPAP) with Me-β-CD was investigated using semi-empirical and ONIOM2 methods. Two modes of complexation were considered for studying such complex. In A complex the OH group of the guest was pointed toward smaller rim of Me-β-CD, while in B complex the OH group was directed to the wider rim. The semi-empirical results gives that B model is more preferred than A one. Also, the ONIOM2 calculations give preference to B model. The geometrical analysis of the inclusion complexes shows that both NAPAP and Me-β-CD were deformed to increase mutual interactions. Finally, natural bond orbital (NBO) analysis reveals that Van Der Waals interactions are the main driving force of formation of inclusion complex.

The structural aspects for the complexation of ortho-anisidine (O-AN)/β-cyclodextrin were explored by using PM6, density function theory B3LYP/6-31G*, M05-2X/6-31G*, B3PW91/6-31G*, MPW1PW91/6-31G*, HF/6-31G* methods and several combinations of ONIOM2 hybrid calculations. Calculations were performed upon the inclusion complexation of β-cyclodextrin (β-CD) with neutral (O-AN1) and cationic (O-AN2) species of ortho-anisidine. The obtained results with PM6 method clearly indicate that the formed complexes are energetically favored, the complex of O-AN2/β-CD in B orientation is significantly more favorable than the others energetically. The structures show the presence of several intermolecular hydrogen bond interactions that were studied on the basis of natural bonding orbital (NBO) analysis, employed to quantify the donor–acceptor interactions between ortho-anisidine and β-CD.

The inclusion complex of β-cyclodextrin (β-CD) and diphenylamine (DPA) was investigated by using PM3MM, DFT, HF and ONIOM2 methods. The most stable structure was obtained at the optimum position and angle. The results indicate that the inclusion complex formed by DPA entering into the cavity of β-CD from its wide side (the secondary hydroxyl group side) is more stable than that formed by DPA entering into the cavity of β-CD from its narrow side (the primary hydroxyl group side). The structures show the presence of several intermolecular hydrogen bond interactions that were studied on the basis of natural bonding orbital (NBO) analysis, employed to quantify the donor–acceptor interactions between diphenylamine and β-CD. A study of these complexes in solution was carried out using the CPCM model to examine the influence of solvation on the stability of the diphenylamine β-CD complex.

PM3 and ONIOM2 were carried out to investigate the structures and properties for the inclusion complexes of chloramphenicol tautomers into β-cyclodextrin (at 1:1 stoichiometry). Two possible orientations into host cavity were considered for both enol and keto chloramphenicol. The PM3 results gives that B orientation is more preferred for enol and keto form, the preference is of 0.63 and 1.67 kcal/mol respectively. This preference is greater in the case of ONIOM2 calculations. Finally, the chemical shifts (ppm) of free and complexed chloramphenicol were calculated at B3LYP/6-31G(d) by (GIAO method) and compared with experimental data taken from the literature.

The binding of the ethyl p-hydroxybenzoate with β-CD was investigated using PM3MM and ONIOM2 (MPW1PW91/6-31G: PM3MM) methods. Two modes of complexation were considered for studying such complex. In A complex the OH group of the guest was pointed toward secondary hydroxyls of β-CD, while in B complex the OH group was directed to primary hydroxyls. The lowest energy structure obtained with ONIOM2 for B complex (the preferred complex) showed that the aromatic ring is totally embedded in β-CD while alkyl chain remains outside the cavity. This preferred arrangement increases intermolecular and H-bond interactions between ethyl p-hydroxybenzoate and β-CD. This is confirmed by NBO analysis.

Two models namely A and B were considered to investigate the inclusion process of ethylparaben into β-CD cavity by means PM3, HF/6-31G (d) and B3LYP/6-31G (d). The obtained results with PM3 method clearly indicate that the formed complexes are energetically favored with or without solvent; the B complex is found more favored than A complex. The calculated deformations energies show that the geometry of β-CD is deformed in the complexation process on the other hand the ethylparaben do not undergo deformation. Finally, From NBO analysis, the donor and acceptor interactions between ethylparaben and β-CD were analyzed and discussed.

Geometry optimizations of para-nitrobenzoic acid (PNBA)/β-cyclodextrin complex were carried out using MM+, PM3 and density function theory B3LYP/6-31G*. Calculations were performed upon the inclusion complexation of β-cyclodextrin (CD) with neutral (PNBA1) and anionic (PNBA2) species of para-nitrobenzoic acid. The results obtained from both methods consistently indicate that the complex of PNBA2/β-CD (B) is significantly more favorable than the others energetically. The negative enthalpy changes calculated from the statistical thermodynamic calculation suggest that both the inclusion complexation is favored enthalpy-driven process. The geometry of the most stable complex shows that the aromatic ring is deeply self-included inside the hydrophobic cavity of β-CD and also intermolecular hydrogen bonds were established between host and guest molecules. This suggests that hydrophobic effect and hydrogen bond play an important role in the complexation process.

The inclusion process involving β-cyclodextrin (β-CD) and 3-amino-5-nitrobenzisothiazole (ANBT) has been investigated by using the MM+ force field, AM1, PM3, HF and B3LYP theories. In this study we took into account only the stochiometry1:1. The complexation and interaction energies for both orientations considered in this research are reported. All quantum computational methods gave the A orientation as the most favorable in which the guest molecule is totally embedded in the hydrophobic cavity of the cyclodextrin with the NO2 group located near the primary hydroxyls of the β-CD and the NH2 group near the secondary hydroxyls with no hydrogen bonding formation. The negative complexation and interaction energies calculated suggest that the inclusion complexes are stable. HOMO and LUMO orbital investigations confirm the better stability of the A orientation.