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The volume function was employed to predict crystal structures. Face-centered cubic and hexagonal close-packed structures were identified as minima on the function. The optimization of the function...

Supramolecular systems (macromolecules), such as calix[n]arenes (SCn), cyclodextrins (CDs), and cucurbiturils (CBs), are promising vehicles for anticancer drugs. In this work, guest–host complexes of carboplatin, a second-generation platinum-based anticancer drug, and p-4-sulfocalix[n]arenes (n = 4 and 6; PS4 and PS6, respectively) were prepared and studied using 1H NMR, UV, Job’s plot analysis, HPLC, and density-functional theory calculations. The experimental and the computational studies suggest the formation of 1:1 complexes between carboplatin and each of PS4 and PS6. The stability constants of the formed complexes were estimated to be 5.3 × 104 M–1 and 9.8 × 104 M–1, which correspond to free energy of complexation of −6.40 and −6.81 kcal mol–1, in the case of PS4 and PS6, respectively. The interaction free energy depends on the different inclusion modes of carboplatin in the host cavities. UV–vis findings and atoms in molecules analysis showed that hydrogen bond interactions stabilize the host–guest complexes without the full inclusion in the host cavity. The in vitro anticancer study revealed that both complexes exhibited stronger anticancer activities against breast adenocarcinoma cells (MCF-7) and lung cancer cells (A-549) compared to free carboplatin, preluding to their potential use in cancer therapy.

Herein, we report the synthesis of a series of bis(silanechalcogenones) [Ch = Te (2), S (3), or Se (4)] using an N-heterocyclic silylene-based SiCSi pincer ligand (1). 2 is the first example of a bis(silanetellurone) derivative. The bonding patterns of 2-4 were extensively studied by natural bond orbital, quantum theory of atoms in molecules, and noncovalent interaction index analyses, and these exhibit weak C-H···Ch interaction. The analogous reaction of 1 with trimethyl N-oxide produced a novel bis(cyclosiloxane) derivative (5). All of the complexes are duly characterized by single-crystal X-ray diffraction studies, multinuclear nuclear magnetic resonance (1H, 13C, and 29Si) spectroscopy, and high-resolution mass spectrometry.

We have scrutinized thirteen new derivatives of cyclic and acyclic silylenes and compared their structural and thermodynamic parameters, at M06-2X/6–311++G** level of theory. The cyclic three- and five-membered silylenes include (2-hydroxy)cyclopropasilylene-2-ene (1), (2,3-dihydroxy)cyclopropasilylene-2-ene (2), (2-hydroxy)cyclopentasilylene-2,4-diene (3), and (2,5-dihydroxy)cyclopentasilylene-2,4-diene (4). The acyclic isomers consist of hydroxypropa-2-silylene (1′), (1,3-dihydroxy)propa-2-silylene (2′), (2-hydroxy)penta-3-silylene (3′), (2-hydroxy)penta-3-silylene-1,4-diene (3″), (2,4-dihydroxy)penta-3-silylene (4′), and (2,4-dihydroxy)penta-3-silylene-1,4-diene (4″). In addition, keto forms of 3″ (3”K) and 4″ (4”K1 and 4”K2) along with protonated forms of silylenes (1H, 1’H, 2H, 2’H, 3H, 3’H, 3”H, 3”K-H, 4H, 4’H, 4”H, 4”K1-H, and 4”K2-H) are investigated for determining their proton affinities (PAs) and intramolecular hydrogen bondings (IHBs). The results show that 4′ shows the lowest singlet-triplet energy gap (ΔEs-t = −19.03 eV) and band gap (ΔEH-L = −2.01 eV) and the highest nucleophilicity (N = 4.02 eV), chemical potential (μ = −3.38 eV), and PA (382.85 kcal/mol) which correlates with its strongest IHB. Atoms in molecules (AIM) analysis represents the highest electron density (ρ(r) = 0.033) at bond critical point (BCP) of IHB in 4′. The natural bond orbital (NBO) analysis shows the highest value of second-order perturbation stabilization energy (E2 = 7.85 kcal/mol) for 4′ which is in consistent with the lowest bond length of IHB (1.84 A). Furthermore, the infrared (IR) spectroscopy indicates the lowest vibrational frequency of O-H bond νOH(νOH= 3542.87 cm−1) which verifies the strong IHB of 4′. The overall order of the IHB strength is 4′ > 4” > 4’H > 4”H > 2’ > 2’H.

X-ray, energetic photon, and electron irradiation can ionize and electronically excite target atoms and molecules. These excitations undergo complicated relaxation and energy-transfer processes that ultimately determine the manifold system responses to the deposited excess energy. In weakly bound gas- and solution-phase samples, intermolecular Coulomb decay (ICD) and electron-transfer-mediated decay (ETMD) can occur with neighboring atoms or molecules, leading to efficient transfer of the excess energy to the surroundings. In ionic solids such as metal oxides, intra- and interatomic Auger decay produces localized final states that lead to lattice damage and typically the removal of cations from the substrate. The relative importance of Auger-stimulated damage (ASD) versus ICD and ETMD in microsolvated nanoparticle interfaces is not known. Though ASD is generally expected, essentially no lattice damage resulting from the ionization and electronic excitation of microsolvated boehmite (AlOOH) nanoplatelets has been detected. Rather efficient energy transfer and soft ionization of interfacial water molecules has been observed. This is likely a general phenomenon at gas-oxyhydroxide nanoparticle interfaces where the density of states of the ionized chemisorbed species significantly overlaps with the core hole states of the solid.

Recent theory developments in ensemble density functional theory (EDFT) promise to bring decades of work for ground-states to the practical resolution of excited-states - provided newly-discovered "density-driven correlations" can be dealt with and adequate effective potentials can be found. This Letter introduces simple theories for both; and shows that EDFT using these theories outperforms ΔSCF DFT and time-dependent DFT for low-lying gaps in most of the small atoms and molecules tested, even when all use the same density functional approximations. It thus establishes EDFT as a promising tool for low-cost studies of excited states; and provides a clear route to practical EDFT implementation of arbitrary functional approximations.

In this study, we have investigated the interaction between Al12N12 nano-cluster and titanocene dichloride anticancer drug complex using B3P86 functional. Two interactions modes between Al12N12 nano-cluster and titanocene dichloride complex (TiCl2Cp2, Cp = η5-(C5H5)2) have been studied. The bonding interaction between the Al12N12 nano-cluster and anticancer drug has been examined through energy decomposition analysis (EDA). In addition, Shubin Liu’s energy decomposition analysis (EDA-SBL) has been used to study the source of energy different between various isomers of Al12N12···cp2TiCl2 complex. Charge transfer between fragments have been illustrated with electrophilicity-based charge transfer (ECT). The related molecular properties to the biological activity of these drug precursor molecules have been studied (octanol–water partition coefficient (log P), molecular volume (Vm)). The quantum theory of atoms in molecules (QTAIM) analysis has been applied to assess the Al–Cl bonds within the Al12N12···cp2TiCl2 complexes.

The formation of purine and pyrimidine base pairs (BPs), which contributes to shaping of the canonical and noncanonical 3D structures of nucleic acids, is one the most investigated phenomena in chemistry and life sciences. In this contribution, the anatomy of the bond energy (BDE) of the base-pairing interaction in 39 different arrangements found experimentally or predicted for DNA structures containing the four common nucleobases (A, C, G, T) in their neutral or protonated forms is described in light of the theory of interacting quantum atoms within the context of the quantum theory of atoms in molecules. The interplay of individual energy components involved in the three stages of the bond formation process (structural deformation, electron-density promotion, and intermolecular interaction) is studied. We recognized that for the neutral BPs, variations in the kinetic and electrostatic contributions to the BDE are rather negligible, leaving the exchange-correlation energy as the main stabilizing component. It is shown that the contribution of the exchange-correlation term can be recovered by including atoms that are formally assumed to be hydrogen bonded (primary interaction). In contrast, to recover the electrostatic component of interaction, one must consider both the primary and secondary (formally nonbonded atoms) interatomic interactions. The results of our study were employed to design new types of BPs with altered bonding anatomy. We demonstrate that improving the electrostatic characteristics of the BPs does not necessarily result in greater interaction energies if weak secondary hydrogen bonding is destroyed. However, the main tuning factor for systems with conserved interacting faces (primary interactions) is the electrostatic component of the interaction energy resulting from the secondary atom-atom electrostatics.

Despite the belief that noble gases (Ng) are completely inert and cannot form stable molecules, a variety of Ng compounds have been reported under laboratory conditions and others were recently detected in the interstellar media, raising interest in knowing and studying their bond nature and the physicochemical properties associated with their stability. In the present work, a systematic analysis of the thermodynamic stability of noble gas halide cations (NgX+ ) at the CCSD(T)/def2-QZVP level have been performed. In addition, chemical bond was characterized through Natural Bonding Theory (NBO), Quantum Theory of Atoms in Molecules (QTAIM) and Energy Decomposition Analysis (EDA) with relativistic corrections. All methods suggest that NgX+ compounds possess a strong covalent bond. However, results show that only compounds containing Ar-Rn atoms are thermodynamic stable with a highly energetic and endergonic dissociation process. For these reasons, it is possible to suggest that several compounds that have not yet been reported could be obtained at the laboratory level or observed in the interstellar medium.

The feasibility of detecting a Chlorofluoromethane (CFM) gas molecule on the outer surface of a pristine single‐walled boron nitride nanotube as well as Al‐, Ga‐, P‐, and As‐doped structures. A periodic boundary condition (PBC), within a density functional theory (DFT) method, using the Perdew, Burke, and Ernzerhof exchange‐correlation (PBE0) functional, together with a 6‐311G(d) basis set was used. Subsequently, the B3LYP, CAM−B3LYP, ωB97XD, and M06‐2X functionals were also employed to consider the single point energies. Natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) were implemented by using the PBE0/6‐311G(d). To explore the nature of the intermolecular interactions, density of state (DOS), Wiberg bond index (WBI), natural charge, natural electron configuration, donor–acceptor natural bond orbital interactions, the second‐order perturbation energies tests, and noncovalent interaction (NCI) analysis are performed. The sensitivity of the adsorption will be increased when the gas molecule interacts with decorated nanotubes; therefore, the change of electronic properties can be used to design suitable nanosensors.

The parameters of stimulated lasing in diffuse discharges formed in mixtures of helium and fluorine in a strongly inhomogeneous electric field are investigated. Lasing is obtained in the visible and VUV spectral regions on the transitions of fluorine atoms and molecules. It is shown that lasing in He – F2 mixtures at a wavelength of 157 nm continues for several half-periods of the discharge current. Due to the homogeneity of the diffuse discharge, the maximum lasing efficiency of the F2 laser is 0.15 %, which corresponds to the efficiency of this type of lasers pumped by pre-ionised transverse volume discharges.

N-Heterocyclic carbene and phosphine can be labeled as solid σ-donor ligands and can contribute to stable complexes. In addition, the constructed complex can accommodate a wide variety of applications, such as pharmaceutical products. In the light of this, a theoretical analysis was carried out on the existence of metal–drug interactions of group 11 metal ions in coordination with symmetrical unsaturated N-heterocyclic carbenes [NHC(R)(R′)] and monodentate phosphine (PR3). The R substitutes on N atoms in NHC and phosphines are identical, and R′ substitutes are located on two noncarbenic carbon atoms (C4 and C5) in the heterocycle complexes. All complexes are in general formula, [Tgt → ML] {where M = Cu(I), Ag(I), Au(I), Tgt = 2,3,4,6-tetra-O-acetyl-1-thio-β-d-glucopyranoside, L= [NHC(R)(R′)], and PR3; R = F, Cl, Br, H, CH3, C2H5, SiH3, 2,6-diisopropylphenyl; R′ = H and Ph} at the PBE-D3/def2-TZVP level of theory. Findings show greater tolerance for the release of drugs in the presence of Ag(I) metal ions than the other metal ions studied here. Applying natural bond orbital (NBO), atoms in molecules (AIMs), energy decomposition analysis (EDA), and extended transition-state natural orbital for chemical valence (ETS-NOCV) analysis have been researched in order to ascertain the nature of M ← S and M ← C (M ← P) bonds in the complexes. Results have shown that σ donation from S to M atoms in [Tgt → MPR3] complexes is better and the π acceptor is weaker than the corresponding [Tgt → MNHC(R)(R′)] complexes.

Following our quest for stable group 14 divalents, novel N-heterocyclic plumbylenes (NHPbs), composed of 2,4,6-cycloheptatriene-2,7-diazaplumbylene (1), benzannulated with one (2), two (3, 4), and three benzene rings (5), are compared and contrasted at the density functional theory level. Results indicate that in going from 1 to 5, the absolute values of singlet-triplet energy gap (ΔEs-t) and band gap (ΔEH-L) increase, while nucleophilicity (N), electrophilicity (ω), and chemical potential (μ) decrease. The most benzannulated structure, ([a,c,e]tribenzo)cyclohepta-2,7-diazaplumbylene (5), turns out as the most stable plumbylene for showing the most negative ΔEs-t of − 194.94 kcal/mol. Furthermore, 5 shows the highest ΔEH-L (− 2.75 eV), with the lowest N (1.31 eV), ω (8.20 eV), μ (− 7.15 eV), and charge of (+ 0.736) on Pb atom. Isodesmic reactions of 1-5 with common transition metal halides, MX2, give forty new metal complexes of 1M-X-5M-X, where M = Pt and Pd, while X = F, Cl, Br, and I. Their complexation energies (ΔECom) indicate that 1-5 are rather stronger ligands with Pt than Pd. Bader’s atoms in molecules (AIM) and NBO analyses show the partial covalent and partial electrostatic nature of Pb-M bonds.

In the present investigation, the feasibility of detecting the bromochlorodifluoromethane (BCF) gas molecule onto the outer surface of pristine single-wall silicon carbide nanotube (SiCNT), as well as its germanium-doped structures (SiCGeNT), was carefully evaluated. For achieving this goal, a density functional theory level of study using the Perdew, Burke, and Ernzerhof exchange-correlation (PBEPBE) functional together with a 6-311G(d) basis set has been used. Subsequently, the B3LYP, CAM-B3LYP, ωB97XD, and M06-2X functionals with a 6-311G(d) basis set were also employed to consider the single-point energies. Natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) were implemented by using the PBEPBE/6-311G(d) method, and the results were compatible with the electronic properties. In this regard, the total density of states (TDOSs), the Wiberg bond index (WBI), natural charge, natural electron configuration, donor-acceptor natural bond orbital interactions, and the second-order perturbation energies are performed to explore the nature of the intermolecular interactions. All of the energy calculations and population analyses denote that by adsorping of the gas molecule onto the surface of the considered nanostructures, the intermolecular interactions are of the type of strong physical adsorption. The doped nanotubes have a very high adsorption energy compared with pristine nanotube. Generally, it was revealed that the sensitivity of the adsorption will be increased when the gas molecule interacts with decorated nanotubes and decrease the HOMO-LUMO band gap; therefore, the change of electronic properties can be used to design suitable nanosensors to detect BCF gas.

The present contribution elucidates the non-covalent interactions present within the molecular frameworks of a miscellany of mono and dihalo-salicylic acid derivatives from the viewpoint of the “atoms-in-molecule” (AIM) formalism. The pivotal roles of hydrogen bonds (HBs) and other short-contact non-covalent interactions, such as H···H and O···O/O···X (X = F, Cl, Br), toward the conformational preferences of the studied aromatic systems have been depicted in detail. Moreover, the modulations of the π-aromaticity of the studied systems in the presence of the concerned non-covalent interactions have been ascertained employing the nucleus-independent chemical shift (NICS) descriptor.

Electrophilicity index (ω) is an important theoretical construct of atoms and molecules and is widely used to understand various chemical phenomena and determine physico-chemical properties. Accordingly, it becomes useful to find an accurate expression for it which is free from any inconsistencies. In view of this, a simple yet rigorous expression is proposed to compute Electrophilicity Index. Since our model is based on ionization potential and electron affinity, it provides a more reliable measure for any electronic changes taking place in a species. Our suggested definition is free from any operational and dimensional discrepancies. We have reported atomic electrophilicity indices for 74 elements of the periodic table invoking our proposed ansatz. The proposed model follows all the sine qua non of existing scale of electrophilicity index. Electrophilicity Equalization Principle is also validated through our computed values. In general, the new expression appears to be powerful and suitable for application in diverse realms.

The present study examines bonding patterns between copper Cun clusters (n = 3–20) and aromatic compounds (benzene, phenol, and benzaldehyde) using a density-functional theory (DFT) approach. Hirshfeld population, natural bond orbital (NBO), molecular orbitals, and quantum theory of atoms in molecules (QTAIM) analyses suggested the formation of two types of interactions Cu–arene and C–H···Cu, in the complexation of copper clusters by an aromatic compound.

Nanoporous membranes are widely used in various fields, such as gas separation, water purification, catalytic processes, and the use of batteries in electrodes. Nowadays, hollow carbon spheres or nanowires are attracting attention of researchers and experimenters due to high adjustability of their mechanical and chemical properties. This makes it possible, among other things, to more accurately adjust permeability of membranes created from this material for various atoms and molecules, which ensures a good degree of gas separation. The mathematical simulation of gas separation via nanocapsule and hollow nanowire porous membrane is performed. Research has shown that such membranes are able to separate He/$$\text{CH}_4$$ CH 4 /$$\text{H}_2$$ H 2 /$$\text{N}_2$$ N 2 gas mixtures.

In the current study, the molecular structures of the two new azomethine dyes such as AAFOH-1 and AAFOH-2 have been investigated with the use of density functional theory (DFT/B3LYP/6-311+G(d)) in a DMSO solvent for the first time. The electronic spectra of the new dyes in a DMSO solvent were carried out by temporally dependent density functional theory (TD-DFT) method. The computed absorption spectral data of the investigated molecules are in good agreement with the experimental data, thus allowing an assignment of the UV/Vis spectra. The equilibrium geometry, the HOMO and LUMO molecular orbitals, excitation energies, oscillator strengths and natural bond orbital (NBO) analysis for the molecules have also been calculated and presented. The electron location function (ELF), localized orbital locator (LOL), and quantum theory of atoms in molecules (QTAIM) analyses were also carried out. On the basis of polyvinyl alcohol (PVA) and the new synthesized azomethine dyes polarizing films were developed. The main optical parameters of polarizing PVA-films (transmittance, polarization efficiency, and dichroic ratio) have been measured and discussed. Anizotropy of thermal conductivity of the PVA-films have been studied.

A density functional study of dihydrogen adsorption and storage capacity of reported stable clusters MLi4+ (M = C, Si, Ge) has been performed at different levels. The cationic systems MLi4+ (M = C, Si, Ge) can adsorb up to 12, 12, and 14 hydrogen molecules respectively with respective H2 gravimetric uptake capacity of 37.82, 30.22, and 21.94 wt%. The interactions of MLi4+ (M = C, Si, Ge) with H2 molecules are analyzed by means of the bond critical points (bcp) in the quantum theory of atoms in molecules (QTAIM). The Gibbs free energy corrected adsorption energies indicate that the maximum adsorption of MLi4+ (M = C, Si, Ge) are energetically favorable at low temperature or high pressure. Atom-centered density matrix propagation (ADMP) molecular dynamics simulations are performed at different temperatures. It can be found that MLi4+ (M = C, Si, Ge) can bind 3, 6, and 4 hydrogen molecules with respective gravimetric densities of 13.20, 17.80, and 7.43 wt% at 200 K and 1atm. At room temperature, MLi4+ (M = C, Si, Ge) can adsorb 3, 5, and 3 hydrogen molecules with gravimetric densities of 13.20, 15.29, and 5.68 wt%.

The quantum theory of atoms in molecules (QTAIM) provides a theoretical foundation to determine the properties of functional groups through additive atomic contributions. Many studies have used QTAIM in their analyses with a variety of electronic structure methods, but it is unknown if the properties measured using one model chemistry, the combination of the electronic structure method and basis set, can be compared to those measured by another. Here, we evaluate the sensitivity of QTAIM functional group and bond critical point properties using six functionals and seven basis sets. High-level B2PLYPD3-BJ/aug-cc-pV5Z reference values are provided for 116 functional groups and the property sensitivity with respect to these values are evaluated based on absolute deviations and by assessing linear relationships. Functional group properties, including charges, dipoles, quadrupoles and volumes, were found to be mostly insensitive to choice of computational model chemistry. However, due to structural and topological inconsistencies, the 6-31G(d) basis set is not recommended for use. Bond critical point properties varied with choice of model chemistry, but models incorporating hybrid functionals and triple-ζ basis sets provided values suitable for use in regression studies.

The synthesis and X-ray structure determination of the [Mn(CO)4{(C6H5)2P-S-C(Br2)-P(C6H5)2}]Br complex (1) are described. The C—Br...Br dihalogen bond present in1has been characterized by means of topological studies of the electron density. Both the quantum theory of atoms in molecules and the electron localization function approaches have been applied to several theoretically calculated wavefunctions as well as to an X-ray constrained wavefunction. In addition, a number of theoretical techniques, such as the source function, the reduced density gradient method and the interacting quantum atoms approach, among others, have been used to analyse the dihalogen bond as well as several intramolecular interactions of the type C—H...Br—C which have also been detected in1. The results show clearly that while bonding in the latter interactions are dominated by electrostatic components, the former has a high degree of covalency.

Although several studies have attempted to deduce by theoretical calculations the reaction mechanism of carmustine with DNA, no study has presented data on the reaction sites and the behavior of the electrons of the participating molecules. Thus, the objective of this paper is to apply the NBO (Natural Bond Orbital) model from the donor-acceptor point of view and the QTAIM (Quantum Theory: Atoms in Molecules) theory from the Laplacian of electronic density and the energy partition formalism IQA (Interacting Quantum Atoms) to quantify the interactions present in the alkylation between carmustine and DNA. The results showed that the decomposition of carmustine forms the chloroethyl ion and the 2-chloroethyldiazene hydroxide molecule, which subsequently breaks down to form 2-chloroethanol and N2. The NBO, QTAIM, and IQA data demonstrated that the ionic carbon of the chloroethyl ion suffers a nucleophilic attack from the O6-guanine. In the alkylation between intermediate 1,O6-ethanoguanine and cytosine, the bond between the CO of the intermediate ring breaks with a subsequent nucleophilic attack of the N of the cytosine with the C of the ring of the molecule 1,O6-ethanoguanine, forming a bridge of ethane between the guanine and cytosine bases.

Quantum theory of atoms in molecules and the orbital-free density functional theory (DFT) are combined in this work to study the spatial distribution of electrostatic and quantum electronic forces acting in stable crystals. The electron distribution is determined by electrostatic electron mutual repulsion corrected for exchange and correlation, their attraction to nuclei and by electron kinetic energy. The latter defines the spread of permissible variations in the electron momentum resulting from the de Broglie relationship and uncertainty principle, as far as the limitations of Pauli principle and the presence of atomic nuclei and other electrons allow. All forces are expressed via kinetic and DFT potentials and then defined in terms of the experimental electron density and its derivatives; hence, this approach may be considered as orbital-free quantum crystallography. The net force acting on an electron in a crystal at equilibrium is zero everywhere, presenting a balance of the kinetic F kin( r ) and potential forces F ( r ). The critical points of both potentials are analyzed and they are recognized as the points at which forces F kin( r ) and F ( r ) individually are zero (the Lagrange points). The positions of these points in a crystal are described according to Wyckoff notations, while their types depend on the considered scalar field. It was found that F ( r ) force pushes electrons to the atomic nuclei, while the kinetic force F kin( r ) draws electrons from nuclei. This favors formation of electron concentration bridges between some of the nearest atoms. However, in a crystal at equilibrium, only kinetic potential v kin( r ) and corresponding force exhibit the electronic shells and atomic-like zero-flux basins around the nuclear attractors. The force-field approach and quantum topological theory of atoms in molecules are compared and their distinctions are clarified.

A series of hydrogen-bonded complexes between N-heterocyclic analogs of Indene and amino acid side-chain mimics have been analyzed employing second-order Moller-Plesset perturbation (MP2) theory and density functional theory with dispersion function (DFT-D) calculations with the aim of gaining greater insight in to the nature of intermolecular interactions in these systems. In this study, the hydrogen bonding ability of N-heterocyclic analogs of Indene towards amino acid side-chain mimics follows the sequence Azaindazole (AIND) > Indazole (IND) > Azaindole (AIN) > Indole (IN) whereas the hydrogen bonding ability of amino acid side-chain mimics towards N-heterocyclic analogs of Indene follows the sequence AcOH > MeNH2 > MeOH > MeSH. Bader’s theory of atoms in molecules (AIM) and natural bond orbitals (NBO) analyses are employed to elucidate the interaction characteristics in the complexes under study. The purpose of conducting these studies is to measure the relative strength of hydrogen bonding interactions such as N-H···O=C, N-H···O, N-H···S, N-H···N, and O-H···N in these complexes and their role in providing stability to the complexes. The AIM theory shows good correlation of the electron density and its Laplacian at the bond critical points (BCP) with the computed stabilization energy for all the complexes under study.

An increase in the water solubility of acenaphthene-1,2-dione (AD) with p-sulfonatocalix[4]arene (p-SC4) is studied by means of simple method using UV chamber and analysed quantitatively using LC. The host guest interaction of AD with p-SC4 is studied using UV–visible absorption and emission spectral studies. The electrochemical properties of AD in the presence of p-SC4 is investigated using cyclic voltammetry method. The mode of binding is investigated using 1H NMR and ROESY techniques. Computational modelling shows that there are various kinds of non-covalent interactions favour the stability of the complexes. The presence of bond critical points between phenyl rings of p-SC4 and AD molecules are confirmed through density functional theory (DFT) and atoms in molecules approaches. Our study clearly reveals that there is strong charge transfer process between p-SC4 (SO3 group) and AD (aryl C-H…O) molecule during the inclusion process. In addition to this, dispersion interaction plays a vital role in the AD absorption on p-SC4 moiety which is confirmed through BE calculations and bond critical points between aromatic clouds.

Fundamental materials properties are determined by electrons under the potential energy from the nuclei, the electron mass, and their mutual repulsion. The variable from material to material is the ion potential. The logical procedure of computing electronic properties is to go from the potential to the electron distribution. This enables practical computation of the material properties ranging from atoms and molecules to solids. This method has blossomed due to the effort of numerous people. The concept is analogous to changing prediction of human population distribution from the landscape of hills and dales to determination of the landscape from a population distribution. In atomic systems, quantum quirkiness allows this switch, but dictates that it is only one slice in the tomography of the quantum state. The author shares his experience in the development from this slice, but hews close to the powerful concept of switching the landscape with the population.

Reactions of photochemical hydrogen transfer are modeled by means of quantum chemistry. Nitromethane and nitrobenzene in the triplet state in combination with ammonia, methylamine, or dimethylamine as hydrogen donors are studied. The structures of reaction complexes of the original materials, the transitional states and reaction products, the activation energies of the reactions, and changes in the standard enthalpies of the reactions are determined. The profiles of the potential energy surfaces of certain reactions are modeled. It is established that all profiles are very smooth, and the activation energies are low. The distribution of electron density in complexes is studied using Bader’s theory of atoms in molecules. All complexes have a characteristic ring structure that can be considered a source of additional interaction during a reaction. It is suggested that such a structure is responsible for the low activation energies of the reaction.

The adsorption behavior of atenolol molecule over the pristine carbon nanotube and boron nitride nanotube as well as functionalized carbon nanotube was performed employing the B3LYP and CAM-B3LYP methods with 6-311G(d, p) basis set in two phases (gas and water solution). We used natural bond orbital, non-covalent interactions and the quantum theory of atoms in molecules to investigate the hydrogen bonds, interaction energies and charge transfers between the atenolol drug and nanosystems. In all cases, the process of intermolecular interaction between atenolol and nanosystems is exothermic showing that the optimized complexes are stable. The hydrogen-bonding interactions between drug and CNT–(COOH)3 play an important role for the different kinds of adsorption. In addition, data showed that there is a large charge donation and back-donation for atenolol adsorption on the surface of CNT–(COOH)3. Results indicated that although in the case of pristine carbon nanotube, the adsorption is weak, functionalization of carbon nanotube with –COOH groups can effectively modify the surface of nanotubes towards atenolol molecules adsorption and improve their solubility in water solution.

Laetrile (D-mandelonitrile-β-D-glucuronic acid, 1COOH) is being promoted, more and more, as an alternate cancer treatment, in many countries. Here we show how intramolecular long-range hydrogen bonding (ILRHB) affects proton affinity (PA) of 1COOH and turns it into a rather strong acid at M06/6–311 + + G(d,p) level of theory. The ILRHB between carboxylate and the –CN of 1COOH activates the cyanide and provides a form of neighboring group participation (anchimeric assistance) in which the rate of the cyanide release is increased. The released cyanide is reported to kill cancer cells more rigorously than the normal ones. Constituents (–CN, –ph and –OH) effects on 1COOH acidity are probed. The –OH groups show the highest impact on increasing the relative acidity in H2O, DMSO and gas phase. The 1COOH and its derivatives appear more acidic in DMSO than in water. Quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO) analysis and the polarized continuum mode (PCM) are used for calculation of the pKa values.

MP2/aug-cc-pVDZ calculations were employed to interpret the molecular interactions of iminophosphorane (IP) and HSX (X = F, Cl and Br). The halogen bond (X···N), hydrogen bond (H···N, H···X, H···S) and S···N interactions were found for complex formation between IP and HSX molecules. Among the predicted models, the S···N and H···N interactions have been recognized as important types of these interactions which were more stable than other types. Quantum theory of atoms in molecules and natural bond orbital methods were used in this study to dissect the nature of these interactions and charge distribution of IP and IP···HSX structures. To further explore the interactions, the interaction energies, the electron density (ρ), the Laplacian (∇2ρ), the bond ellipticity (ɛ), the second-order perturbation energies (E(2)) and the charge transfer qCT were analyzed. Reasonable coincidence of value has been found in these interactions.

In this work, the degradation of sulfamethazine (SMT), sulfadiazine (SMD), and sulfamethoxazole (SMX) by using UV light, UV/H2O2, and UV/S2O8-2 was analyzed. Direct photolysis was studied by varying the lamp power and the solution pH. DFT calculations were carried out to corroborate the efficiency of the degradation as a function of the solution pH. The variation of the apparent rate constant, kap, was determined in the indirect photolysis by employing an experimental Box-Behnken-type response surface design. The results evidenced that SMX can be efficiently degraded by applying UV radiation independent of the operating conditions. Nevertheless, the quantum yields for SMT and SMD were close to zero, indicating a low energy efficiency for their photochemical transformation. The effect of the solution pH showed that the photodegradation of sulfonamides depends both on the amount of radiation absorbed as the electronic density. Calculations based on density functional theory and supported by the quantum theory of atoms in molecules allowed to describe fragmentation patterns in the systems under study, proving the lability of S14-C2, N17-C18, and N22-O22 bonds, for SMT, SMD, and SMX, respectively. From response surface methodology, four statistically reliable equations were obtained to determine the kap value as a function of the system operating conditions. Finally, SO4•- radicals proved to have a higher reactivity to degrade SMT and SMD compared with HO• radicals regardless of the operating conditions of the system.

[Ni{2-H2NC(=O)C5H4N}2(H2O)2][Ni{2,6-(O2C)2C5H3N}2]·4.67H2O, a new complex salt containing a bis(2,6-dicarboxypyridine)nickel(II) anion and a bis(2-amidopyridine)diaquanickel(II) cation, was synthesized and characterized. The crystal is stabilized by an extensive network of hydrogen bonds. Alternate layers of anions and cations/water molecules parallel to (010) can be distinguished. Computational studies of the network packing of the title compound by high-level DFT-D/B3LYP calculations indicate stabilization of the networks with conventional and non-conventional intermolecular O—H...O, N—H...O and C—H...O hydrogen bonds along with π-stacking contacts. Due to the presence of water molecules and the importance of forming hydrogen bonds with the involvement of water clusters to the stability of the crystal packing, the importance and role of these water clusters, and the quantitative stability resulting from the formation of hydrogen bonds and possibly other noncovalent bonds such as π-stacking are examined. The binding energies obtained by DFT-D calculations for these contacts indicate that hydrogen bonds, especially O—H...O and N—H...O, control the construction of the crystalline packing. Additionally, the results of Bader's theory of AIM for these interactions agree reasonably well with the calculated energies.

In order to assess safety and efficacy of small molecule drugs as well as agrochemicals, it is key to understanding the nature of protein-ligand interaction on an atomistic level. Prothioconazole (PTZ), although commonly considered to be an azole-like inhibitor of sterol 14-α demethylase (CYP51), differs from classical azoles with respect to how it binds its target. The available evidence is only indirect, as crystallographic elucidation of CYP51 complexed with PTZ have not yet been successful. We derive a binding mode hypothesis for PTZ binding its target, compare to DPZ, a triazole-type metabolite of PTZ, and set our findings into context of its biochemistry and spectroscopy. Quantum Theory of Atoms in Molecules (QTAIM) analysis of computed DFT electron densities is used to qualitatively understand the topology of binding, revealing significant differences of how R- and S-enantiomers are binding and, in particular, how the thiozolinthione head of PTZ binds to heme compared to DPZ's triazole head. The difference of binding enthalpy is calculated at coupled cluster (DLPNO-CCSD(T)) level of theory, and we find that DPZ binds stronger to CYP51 than PTZ by more than ΔH ~ 11 kcal/mol.

The [n]cyclacene as a class of aromatic nanobelts can be considered for synthesizing new compounds. Here, the binary systems involving hydrogen and halogen bonded [12]cyclacenes are investigated at M06-2X/6-311++G(d,p) level of theory. The calculations are performed in gas phase and in water and acetone solvents. Because of their opportunities for the various applications in materials science, some electronic properties such as HOMO–LUMO gap, electronic chemical potential, first ionization energy, electron affinity, electrophilicity index, chemical hardness, and softness are examined. The role of hydrogen and halogen bonds on stability of dyads is also studied by atoms in molecules (AIM) theory.

A novel non-classical mereological concept (Molecule in Atoms-of) built up by blending the Metaphysics of Xavier Zubiri and the Quantum Theory of Atoms in Molecules (QTAIM) of R. F. W. Bader is proposed. It is argued that this philosophical concept is necessary to properly account for what happens in a chemical reaction. From the topology of the gradient of the laplacian of the electronic charge density, $$\nabla \nabla^{2} \rho ( \varvec{r} )$$ within the QTAIM framework, different “atomic graphs” (corresponding to different hybridizations) are found for each atom depending on the molecular context, reflecting how the whole molecule affects each atom. In this way, the whole molecular system imposes certain geometry onto each atom, and every atom exhibits different ontological modality. On the Metaphysical side, for X. Zubiri real things (denoted as “de Suyo”) are system of different notes (adventitious, constitutional and essential). The physical essence is the subsystem of essential notes (notes-of) with a coherence unity. Every note is grounded on the essence. The unity of the system is present somehow in every note-of beforehand, and every essential note-of turns towards the other (“respectivity”). The essence determines the position of each note within the system, and hence is the grounding for modality of the notes. By conflating both “theories” and taking the atoms as essential notes, we propose the concept of “Molecule in atoms-of” or “atoms-of in Molecules”. Within the course of a chemical reaction the atoms-of modified their “of” as required by the new molecular unity being formed, and eventually change their modality. The validity to the Zubiri’s statements, is attained by evaluating necessity (□) and possibility (◊) in a set-up of finite accessible “possible worlds”.

Aminopyrimidine, triaminopyrimidine, and cyanuric acid as artificial bases can be used to design and prepare multi-stranded DNA structures. In this manuscript, we theoretically investigate the stability of hydrogen-bonded hexagonal structures arising from the self-assembly of aminopyrimidine and cyanuric acid, as well as triaminopyrimidine and cyanuric acid in gas phase and in water. The influence of hydrogen bonds on the stability of hexagonal arrangements is examined by atoms in molecules and natural bond orbital analyses. Moreover, the mutual effects of hydrogen bonds on each other are also evaluated in the hexagonal structures using cooperative energy. Whereas the self-assembly of the hydrogen-bonded hexagonal arrangements may be considered to form new nanostructures, metal sensors, and ion channels, some electronic properties such as band gap, first ionization energy, electron affinity, electronegativity, electronic chemical potential, electrophilicity index, global chemical hardness, and chemical softness are theoretically estimated at M06-2X/6-311++G(d,p) level.

High harmonic generation (HHG) has important applications in attosecond science, such as generating attosecond pulses and probing the structure and the electron dynamics of atoms and molecules with attosecond resolution. Different from symmetric cases, because of symmetry breaking, asymmetric molecules can emit both odd-order and even-order harmonics in strong single-color laser fields. Ultrafast probing of polar molecules with HHG is a hot issue in recent years, as polar molecules are generally very active in chemical reactions. With dividing the HHG signal into odd and even parts, recent studies have shown that odd and even harmonics from asymmetric molecules have different properties in frequency domain. To explain this typical difference, a theoretical model has been developed to describe the generation mechanism of odd versus even HHG from asymmetric molecules. It is shown that during the process of tunneling, the gerade component of the asymmetric orbital plays a dominating role and the contributions of the ungerade component can be neglected. Thereafter, the recombination of the rescattering electron with the gerade (ungerade) component of the asymmetric orbital mainly contributes to the emission of odd (even) harmonics. As a result, odd and even harmonics carry different information of the asymmetric system. Recently, it has been shown that the contributions of the ungerade component of asymmetric orbital to ionization are strongly suppressed due to the destructive intramolecular interference. This suppressing effect is general for strong-field ionization of polar molecules, implying that the theoretical model of odd-even HHG holds for a wide parameter region. These results open a new perspective for probing polar molecules with odd-even HHG. Specifically, when it is relatively difficult to read the information of the molecular structure or the electron dynamics through the whole harmonic spectrum of asymmetric molecules, one can extract the characteristic information of odd or even harmonic separately, then this characteristic information can be integrated and inverted to get the information of the whole asymmetric system. These discussions suggest ultrafast probing of asymmetric molecules with odd-even high-harmonic spectroscopy (HHS), where odd and even harmonics are treated independently. This idea of odd-even HHS and the theoretical model of odd-even HHG mentioned above have been widely used in ultrafast probing of asymmetric molecules in theoretical studies. For example, it has been shown that odd-even HHS and this theoretical model can be used to reconstruct the asymmetric molecular orbital, probe the nuclear dynamics of polar molecules, calibrate the degree of orientation of asymmetric molecules, and probe the structure of multi-center molecules, etc. Experimentally, the idea of odd-even HHS has also been widely used in probing the structure and the electron dynamics of polar molecules. In particular, this theoretical model of odd-even HHG has also been used in probing the shape resonance and charge transport of asymmetric molecules in experiments. In addition, theoretical studies based on the first-principle calculations have also shown the applicability of this theoretical model of odd-even HHG, which provides the theoretical tool for the present odd-even HHS. The research and development of odd-even HHS plays an important role in promoting the application of HHG in attosecond science and chemical reactions.

Изучено распределение электронной плотности 14 циклических соединений и одного нециклического. Проведен анализ зарядов и объемов групп, найдены группы доноры и акцепторы электронной плотности. Рассмотрено изменение электронной плотности серосодержащих групп под влиянием окружения. The electron density distribution of 14 cyclic compounds and one non-cyclic compound was studied. The group charges and group volumes were analyzed, and the electron density donor and acceptor groups were found. Changes in the electronic density of sulfur-containing groups under the influence of the environment are considered.

This article reports predicted hydrogen sensing performance data for black phosphorene (BP) monolayer doped with group 10 elements (Ni, Pd, and Pt) at the HSE06/Def2-TZVP level of theory. Different among others, the H2 molecule adopted a parallel configuration over the Ni-BP surface in the armchair direction. The stabilization of hydrogen over the four BP sensors led to small adsorption energies (up to −0.27 kcal/mol). The BP modification led to an indirect bandgap and n-type doping behavior. The reported results confirmed that nickel doping could transform the pristine BP to a sensitive, reusable sensor (recovery time up to 1.6 ps) with reasonably high response of 28.2 at room temperature. In selectivity terms, however, the Ni-BP was found to be an efficient sensor for hydrogen purification. The Ni-BP material was the best work function sensor in this series as well. However, the Pt-BP sensor demonstrated a higher selectivity (4.56) in nitrogen. The results were also discussed in terms of the quantum theory of atoms in molecules (QTAIM), non-covalent interactions (NCI), formation energy, and surface diffusion. These data would be quite relevant to the rational design of novel sensors of hydrogen.

This work is dedicated to theoretically investigate the formation process of C2H5OH···nCO2 (n = 1-5) complexes and to shed light on the nature of interactions formed under the variation of CO2 concentration. It is found that CO2 molecules tend to locate around the polarized -OH group to interact with the lone pairs of the O atom. The interaction of ethanol with three CO2 molecules (C2H5OH···3CO2) induces the most stable structure in the sequence considered. The atoms in molecules (AIM), NCIplot, and natural bond orbital (NBO) analyses point out that the Oethanol···CCO2 tetrel bond overcomes hydrogen, chalcogen, and CO2···CO2 tetrel-bonded interactions and mainly contributes to the strength of C2H5OH···nCO2 (n = 1-5) complexes. All intermolecular interactions in the examined complexes are weakly noncovalent, and their positive cooperativity is evaluated to be slightly weaker than that of CO2 pure systems. SAPT2+ and molecular electrostatic potential (MEP) calculations indicate that the electrostatic force is the main factor underlying the attractive interplay in the complexes of C2H5OH and CO2.

By the transmetallation of ppyHgCl [ppy = 2-(2'-pyridyl)phenyl] (1) with SnCl4 and SbCl3, the synthesis of the monoorgano main group halides, [ppySnCl(3)(H2O)]center dot 2(0.5diox) (diox = 1,4-dioxane) [2(H2O)]center dot 2(0.5diox) and [ppySbCl(2)] (3) was achieved. The reaction of 1 with BiCl3 does not give the analogous monoorganobismuth dichloride. Instead, it results in the formation of [(ppy)(2)Bi](+)center dot[ppyBiCl(3)](-) (4). Reactions of (ppy)(2)Te and (ppyTe)(2) with SO2Cl2 and Br-2 result in the formation of ppyTeCl (5) and ppyTeBr (6) respectively. All the synthesized compounds were characterized by multi-nuclear NMR spectroscopy (H-1, C-13, Sn-119, and Te-125), FT-IR spectroscopy, ESI-MS, CHN analysis, and single-crystal X-ray diffraction studies. The molecular structures of 2-6 reveal strong intramolecular coordination of the N-atoms of the pendant arms with the main group element centers. DFT calculations; including Natural Bond Order (NBO), Electron Localization Function (ELF), Electrostatic Surface Potential (ESP) and Atoms in Molecules (AIM) infer that the stability of 2-6 relies on the sigma-hole participation of the element center with the N-lone pair of the pyridyl arm.

Herein, the potentiality of carbon-containing molecules (W–C–F3, where W is a withdrawing atom or group) to interact with Lewis bases (B), Lewis acids (A) and σ–hole-containing molecules (X2) with W–C···B/A/X2 angle of 180° was reported. −σ–hole and +σ–hole terminologies were implemented to describe the interactions of W–C–F3 with nucleophilic and electrophilic sites, respectively. To characterize such interactions, quantum mechanical calculations including geometrical optimization, ±σ–hole test, interaction energy calculation, quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) index calculation were performed at MP2/aug-cc-pVTZ(PP) level of theory. The results showed (1) the electrostatic potentiality of the W–C–F3 molecules to favorably interact with Lewis bases and acids, (2) the dependency of ±σ–hole interaction energies on the σ–hole size of the tetrel atom and (3) descending of interaction energies in the order W–C–F3···B > W–C–F3···X2 > W–C–F3···A. QTAIM, and NCI calculations revealed the noncovalent nature of the ±σ–hole interactions. Further, an investigation on F–C–X3 model was carried out to highlight the emerging role of X3 atoms in ±σ–hole interactions. Comprising of the findings, the most favorable interaction energies were denoted when the F–C–X3 interact with X2 molecules compared to those with B and A molecules.

In this article, we report on the results of experimental and theoretical (DFT calculation of an isolated molecule) investigation of electron density in a triphenylantimony disorbate complex (triphenylantimony bis(hexa-2,4-dienoate), Ph3Sb(O2CCH=CH–CH=CH–CH3)2 (1)). A topological analysis of the electron density was carried out in the framework of the quantum theory of atoms in molecules (QTAIM), which allows to study the nature of chemical bonds and the molecular graph in Ph3Sb(O2CCH=CH–CH=CH–CH3)2 complex. The molecular graph is an important tool for determining the interacting atoms. However, the molecular graph of the triphenylantimony disorbate complex did not show the presence of the “expected” intramolecular interactions between the antimony atom and the carbonyl oxygen one. Such a situation can be caused by electron density low curvature between these atoms. It is extremely difficult case, and sometimes it is not possible to find all the “expected” bond paths and critical points (3,−1). Thus, the molecular graph for this class of compounds does not provide a definitive picture of the chemical bonding and should be complemented with other descriptors, such as а source function (SF) and non-covalent interaction (NCI) index. It was found that in some cases using the SF on the NCI isosurface allows to interpret intramolecular interactions in the absence of a bond critical point more correctly. In this article, presence of intramolecular interaction in the absence of a bond critical point between the antimony atom and the carboxylate oxygen one was shown. The carboxylate fragment always acts as a source of the electron density for the Sb…O(carbonyl) interactions, whereas the antimony atom can be both a source and a sink for it.

High-level ab initio calculations show that the MCl3- anions comprising Group 2B M atoms Zn, Cd, and Hg form a stable complex with the CN- anion, despite the like charge of the two ions. The complexation occurs despite a negative π-hole region above the M atom of MCl3- . The dimerization distorts the planar geometry of MCl3- into a pyramidal shape which reduces the negative potential above the M atom, facilitating a close approach of the two anions, with R(M⋅⋅⋅C)∼2 A, and an overall attractive electrostatic attraction within the dimer. In the gas phase, this dimer is less stable than the pair of separated ions by some 30 kcal/mol. However, the dissociation must surmount an energy barrier of roughly 25 kcal/mol which occurs at an intermolecular distance of 4 A. In aqueous solution, the dimerization process is exothermic and barrier-free, with a binding energy in the 11-18 kcal/mol range.

In this investigation, the adsorption behavior of E2H2 and E2H4 (E = C, Si) gas molecules on B12N12 nano-cage was studied at M062X/6-311G(d,p) level of theory. The interactions between the E2H2 and E2H4 molecules and B12N12 nano-cage were illustrated with energy decomposition analysis (EDA). Variations in the frontier orbitals energies and structural parameters were studied. Charge transfer between fragments was illustrated with electrophilicity-based charge transfer (ECT) and extended charge decomposition analysis (ECDA). Thermochemical parameters of the E2H2 and E2H4 molecules adsorptions on nano-cage revealed that adsorptions proceed spontaneously and easily. In addition, Quantum theory of atoms in molecules (QTAIM) analysis was employed for illustration of the E-B and E-N bonds in the E2H2…B12N12 and E2H4…B12N12 molecules.