HOMO-LUMO Interaction Research Articles

TOPO-decanoic acid based DES – Structural insights using DFT, physico-chemical investigations and extraction efficiency of DES diluted with chloroform

Deep eutectic solvents (DESs) are recently regarded as evolving candidates in the field of separation science in order to achieve sustainability. In the present work, hydrophobic TOPO-Decanoic acid DES has been synthesized and scrutinized by FTIR and 1HNMR studies. The structures of TOPO (Tri-octyl phosphine oxide), decanoic acid, chloroform, DES and DES + chloroform have been optimized employing B3LYP functional using DFT-D3 of Grimme’s method. The HOMO-LUMO (Eg) energy gap, bond lengths, mulliken charges,dipole moment and interaction energy has been evaluated using DFT. The geometry optimization provides the bond parameters which explain about the existence of non-bonded interactions. DES and DES + chloroform show more reactiveness as compared to its constituents evident from the chemical potential value. Physico-chemical properties such as density, volumetric (V), dielectric constant (ε), refractive index (nD) and ultrasonic velocity (U) of the hydrophobic TOPO-Decanoic acid DES diluted with polar cosolvent chloroform have been determined over a wide range of mole fraction of DES at 298.15 K. The excess properties such as VE, εE, nDE and UE have been calculated to predict the type of inter-molecular interaction existing within the components of the DES diluted chloroform mixture. Different mixing rules have been used to estimate properties such as dielectric permittivity, refractive index and ultrasonic velocity. Various acoustic parameters such as Z, βs, and (Lf)mix of binary mixtures are evaluated to predict about the presence of inter molecular interactions within the mixture components. The prepared hydrophobic eutectic mixture in chloroform has been further used for extraction of Y (III) and Eu (III). The solvent extraction of Eu (III) showed better performance as compared to that of Y (III).

Antiferromagnetic Interactions through the Thirteen Å Metal–Metal Distances in Heterometallic One‐Dimensional Chains

AbstractA heterometallic and paramagnetic one‐dimensional aligned chain in −Rh(+2)−Rh(+2)− Pt(+2)−Ni(+2)−Pt(+2)− with direct metal−metal bonds was obtained via HOMO–LUMO interactions at the σ* (dz2) orbital between [Rh2(O2CCH3)4] and [Pt2Ni(piam)4(NH3)4] (piam=pivalamidate). The one‐dimensional chains had straight backbones attributed to face‐to‐face stacking of each complex, and the Ni atoms were separated by approximately 13 Å from four different metals. Each Ni atom had two unpaired electrons in the d‐orbitals, which strongly exchanged with J=−37.9 cm−1 through the diamagnetic −Pt−Rh−Rh−Pt− bonds.

Antiferromagnetic Interactions through the Thirteen Å Metal-Metal Distances in Heterometallic One-Dimensional Chains.

A heterometallic and paramagnetic one-dimensional aligned chain in -Rh(+2)-Rh(+2)- Pt(+2)-Ni(+2)-Pt(+2)- with direct metal-metal bonds was obtained via HOMO-LUMO interactions at the σ* (dz2) orbital between [Rh2(O2CCH3)4] and [Pt2Ni(piam)4(NH3)4] (piam=pivalamidate). The one-dimensional chains had straight backbones attributed to face-to-face stacking of each complex, and the Ni atoms were separated by approximately 13 Å from four different metals. Each Ni atom had two unpaired electrons in the d-orbitals, which strongly exchanged with J=-37.9 cm-1 through the diamagnetic -Pt-Rh-Rh-Pt- bonds.

Shapeshifting Nucleophiles HO-(NH3)n React with Methyl Chloride.

The microsolvated anions HO-(NH3)n were found to induce new nucleophile NH2-(H2O)(NH3)n-1 via intramolecular proton transfer. Hence, the ion-molecule nucleophilic substitution (SN2) reaction between CH3Cl and these shapeshifting nucleophiles lead to both the HO- path and NH2- path, meaning that the respective attacking nucleophile is HO- or NH2-. The CCSD(T) level of calculation was performed to characterize the potential energy surfaces. Calculations indicate that the HO- species are lower in energy than the NH2- species, and the SN2 reaction barriers are lower for the HO- path than the NH2--path. Incremental solvation increases the barrier for both paths. Comparison between HO-(NH3)n and HOO-(NH3)n confirmed the existence of an α-effect under microsolvated conditions. Comparison between HO-(NH3)n and HO-(H2O)n indicated that the more polarized H2O stabilizes the nucleophiles more than NH3, and thus, the hydrated systems have higher SN2 reaction barriers. The aforementioned barrier changes can be explained by the differential stabilization of the nucleophile and HOMO levels upon solvation, thus affecting the HOMO-LUMO interaction between the nucleophile and substrate. For the same kind of nucleophilic attacking atom, O or N, the reaction barrier has a good linear correlation with the HOMO level of the nucleophiles. Hence, the HOMO level or the binding energy of microsolvated nucleophiles is a good indicator to evaluate the order of barrier heights. This work expands our understanding of the microsolvation effect on prototype SN2 reactions beyond the water solvent.

Molecular Dynamic, Hirshfeld Surface, Computational Quantum and Spectroscopic analysis of 4-Hydroxy-1-Naphthaldehyde

aims: Computational Quantum and Spectroscopic analysis of 4-Hydroxy-1-Naphthaldehyde Background: Known also as 4-Hydroxynaphthalene-1-carbaldehyde, 4-hydroxy-1-naphthaldehyde (4H1NA) is a crucial precursor of many coordinating agents. A commercial compound called 4-hydroxy-1-naphthaldehyde (4H1NA) can be used to make a number of different sensors. In the development of many chemosensors, they operate effectively as a functionalized fluorescent backbone. Objectives: Molecular Dynamic, Hirshfeld Surface, Computational Quantum analysis of Naphthalde-hyde. Methods: The methods employed in the analysis of the compound involve the DFT calculations, using the DFT method and B3LYP/6-311++G (d, p) basis set with respect to its FTIR, NMR, and UV-Visible spectrum. The NMR chemical shifts of carbon and protons in CDCl3 were determined by the GIAO method. For the molecule of reference, HOMO-LUMO and Donor-Acceptor interactions were also taken into consideration. Investigations also looked into E.L.F., Fukui activity, and non-linear optical properties. Results: The investigation of compounds at their atomic level was analyzed using computational methods so that chemical, medicinal, and environmental research make use of them to make the molecule more in an improved form with distinguished properties. Strong interaction has been produced as a result of electron transfer from the oxygen atoms lone pair LP (2) to the anti-bonding orbital *(C3-C5) with a significant stabilization energy of 42.61kcal/mol. The attributes of the NLO molecule were calculated and found to be superior to those of the urea molecule, with linear and first-order hyperpolarizability situations. Our findings imply that the reference molecule can be a heavier contender for NLO as a surface material and could be considered a vital substance for medical purposes in the drug industry due to its maximum electrophilicity index. Conclusion: A commercial compound called 4-hydroxy-1-naphthaldehyde (4H1NA) can be used to make several different sensors. The compound has good structural and optical properties. They can be employed for a variety of optical limiting applications because of their unusual optical characteristic, which exhibits third-order non-linear behavior.

Discovery of oxazine-linked pyrimidine as an inhibitor of breast cancer growth and metastasis by abrogating NF-κB activation.

Nuclear factor kappa (NF-κB) plays a key role in cancer cell proliferation; thus, small molecule inhibitors of NF-κB activity can effectively inhibit breast cancer (BC) progression. We have previously reported oxazine and piperazine-linked pyrimidines as novel anti-cancer agents that can suppress NF-κB activation in BC cells. Moreover, the TRX-01 compound, an oxazine-linked pyrimidine, inhibited MCF-7 cells at a concentration of 9.17 µM in the Alamar Blue assay. This work involved the analysis of frontier molecular orbitals, HOMO-LUMO interactions, and molecular electrostatic potential for the TRX-01 structure. Additionally, the TRX-01 compound was studied for cytotoxicity, and migration as well as invasion assays were performed on BC cells. Finally, TRX-01 blocked the translocation of NF-κB from the cytoplasm to the nucleus in MCF-7 cells and reduced NF-κB and IκBα levels in a dose-dependent manner. It also suppressed migratory and invasive properties of BC cells. Overall, the data indicates that TRX-01 can function as a novel blocker of BC growth and metastasis by targeting NF-κB activation.

Understanding the Retro‐Cope Elimination Reaction of Linear Alkynes

AbstractThe bioorthogonal retro‐Cope elimination reaction of linear alkynes R3C−C≡C−X (R3 = combinations of H, MeO, F; X = H, F, Cl, Br, I) with N,N‐dimethylhydroxylamine was quantum chemically investigated using relativistic density functional theory at ZORA‐BP86/TZ2P. This novel reaction can be tuned through judicious substitution of the alkyne at both the terminal and propargylic position to render second‐order kinetics that rival and out‐compete strain‐promoted variants. Activation strain and quantitative molecular orbital analyses reveal that, both upon terminal or propargylic substitution of propyne, the main effect of substituting H for X is a lowering of the propyne LUMO which stabilizes the HOMO–LUMO interactions and thus the transition state. In the case of terminal substitution with larger halogens (X = Cl, Br, I), a secondary effect interferes: steric repulsion with these larger halogens is absorbed into a longer forming C⋯N bond leading to a more asynchronous reaction accompanied by less (not more) steric Pauli repulsion.

Theoretical insight into the unexpected initial (3 + 2) cycloaddition reaction of mesitonitrile oxide with 1, 4-diazepine derivatives: A computational study

1,4-Diazepine as an active drug component underlies the potency of most psychotic, anticancer, anticonvulsant, and antibacterial drugs in the market and is, therefore crucial in chemotherapeutic treatment in biomedicine. Proper functionalization of this moiety can afford even more potent drugs. As a result of their therapeutic significance, this study aims at precisely giving a comprehensive computational insight into the unexpected initial reactivity of 1,4-diazepine derivatives and mesitonitrile oxide. The initial reaction between mesitonitrile oxide and 1,4-diazepine derivatives proceeds via a (3 + 2) cycloaddition reaction which leads to the formation of a cycloadduct where the mesitonitrile oxide unexpectedly adds across the imine functionality at the expense of the potential olefinic carbon-carbon double bond. Calculations at the density functional theory (DFT) M06/6-311G (d, p) level of theory indicate that the initial (3 + 2) cycloaddition reaction of mesitonitrile oxide (1,3-dipole) and 1,4-diazepine derivatives (dipolarophile) in all cases proceeds to form the cycloadduct where the 1,3-dipole adds preferentially to the imine functionality at the expense of the potential olefinic carbon-carbon double bond. In light of the parent reaction, the most kinetically favored cycloadductP3A had a rate constant of 5.1 × 106 M−1s−1, which is about 12 manifolds faster than the next competing stereoisomer P1A with a rate constant of 4.1 × 105 M−1s−1 and about 1024 faster than the most favored cycloadduct P3B with a rate constant of 7.2 × 10−19 M−1s−1 in the unfavored pathway (Path B). Irrespective of the electronic and steric nature of the electron-donating (EDG) and electron-withdrawing (EWG) substituents placed on the dipolarophile, the selectivities of the reaction were maintained. Rationalization of the potential energy surface depicts that the 1,3-dipole adds across the dipolarophile via an asynchronous concerted mechanism. Rationalization of the HOMO-LUMO energies of the mesitonitrile oxide (1,3-dipole) and the 1,4-diazepine derivatives (dipolarophile) depict that the EDG-substituted dipolarophile react as nucleophiles, whereas the dipole reacts as an electrophile. Conversely, the HOMO-LUMO interaction between the EWG-substituted dipolarophile indicates that the EWG-substituted dipolarophile react as electrophiles, whereas the dipole reacts as a nucleophile. The electrophilic parr function at various reactive sites of the dipolarophile shows that the 1,3-dipole preferentially adds across the local centers with the largest electrophilic NBO or Mulliken spin densities which is consistent with the energetic trend observed. The reactivity of the 1,4-diazepine derivatives and the mesitonitrile oxide showed poor stereoselectivity.

Density functional analysis of molecular crystal: bis-l-Phenyl alanine mandelate

A novel organic nonlinear four component molecular crystal bis-l-phenylalanine mandelate (BLPAMA) has been synthesized and single crystal has been grown by slow evaporation method in an aqueous solution at ambient temperature. The characterization studies support the formation of the neutral novel organic molecular crystal containing 68 atoms in a molecule. The experimental and theoretical density functional analysis (DFT) have been compared for the vibrational changes, dipolar interactions, 1H and 13C NMR values, UV-Vis absorption pattern, HOMO-LUMO interactions, hyperconjugation effects, Natural Bond Orbital (NBO) and Natural Hybridisation Orbital (NHO) analysis. The molecular structure obtained from the solid state experimental data using ORTEP diagram has been compared with the gaseous state optimized stucture obtained from DFT data using Gaussian 98 software with MO6-31++(d,p) basis set. The DFT study of the title compound has confirmed the crystal formation through charge transfer mechanism, hydrogen bonding interactions and van der Waals forces of attraction. The stress and strain in the title compound leads to the low energy gap nonlinear molecular sheet formation. The title compound shows electrochemical activity due to the highly reactive and relatively unstable structure.

Structural, spectroscopic, electronic, Hirshfeld, QTAIM and biological predications of a hybrid 2,6-dichloropurine compound: A detailed density functional theoretical study

Extensive research into the optimized structure, spectroscopic and biological properties of 2,6-dichloropurine (6DCP) was conducted using IR/Raman and NMR techniques, as well as theoretically using the DFT approach with B3LYP, CAM-B3LYP, and PBEPBE function levels at 6-311++G(d, p) basis set. The computational results from DFT approaches such as geometrical, IR/Raman and NMR spectra were compared with the experimental results. All our theoretical calculations were in good agreement with observed data. The electronic HOMO-LUMO, H-bonding and strong conjugative interactions across different molecular entities are discussed to reveal the accompanying pharmaceutical intermediate. The molecular properties such as chemical reactivity descriptors, mapped ESP, dipole moment, mean polarizability, and first order hyperpolarizability of the title molecule were calculated by quantum mechanical calculations. The high value of the electronic dipole moment and polarizability estimate for the 6DCP molecule may improve its biological activity. The NBO study has enabled researchers to investigate hyper-conjugate interactions, intramolecular bonding, and strong H-bonding interactions. Strong H-bonding interaction energies of 120.47 kcal/mol have been performed at the DFT/PBEPBE level.

Intermolecular Covalent Interactions: Nature and Directionality.

Quantum chemical methods were employed to analyze the nature and the origin of the directionality of pnictogen (PnB), chalcogen (ChB), and halogen bonds (XB) in archetypal Fm Z⋅⋅⋅F- complexes (Z=Pn, Ch, X), using relativistic density functional theory (DFT) at ZORA-M06/QZ4P. Quantitative Kohn-Sham MO and energy decomposition analyses (EDA) show that all these intermolecular interactions have in common that covalence, that is, HOMO-LUMO interactions, provide a crucial contribution to the bond energy, besides electrostatic attraction. Strikingly, all these bonds are directional (i.e., F-Z⋅⋅⋅F- is approximately linear) despite, and not because of, the electrostatic interactions which, in fact, favor bending. This constitutes a breakdown of the σ-hole model. It was shown how the σ-hole model fails by neglecting both, the essential physics behind the electrostatic interaction and that behind the directionality of electron-rich intermolecular interactions. Our findings are general and extend to the neutral, weaker ClI⋅⋅⋅NH3 , HClTe⋅⋅⋅NH3 , and H2 ClSb⋅⋅⋅NH3 complexes.

Structural confirmation and spectroscopic signature of N-Allyl-2‑hydroxy-5-methyl-3-oxo-2, 3-dihydrobenzofuran-2-carboxamide and its monohydrate cluster

We performed optimization of a bio-relevant molecule N-Allyl-2‑hydroxy-5-methyl-3-oxo-2, 3-dihydrobenzofuran-2-carboxamide and its monohydrate cluster in the isolated form. Potential energy scanning for the target molecule was carried out. Consequently, three stable conformers were obtained. The effect of interfusion of a water molecule on energy and vibrational modes of the target molecule was also investigated in the most stable conformer. The electronic structures and vibrational spectra of all the three conformers were computed. The FTIR spectrum of the target molecule was recorded at the spectral width of 4000–400cm−1 which was compared with the theoretically computed spectrum of the most stable conformer. We have computed Raman spectra of all the conformers. All theoretical calculations performed in this investigation were done at DFT/B3LYP level of theory. The standard normal coordinate analysis (NCA) method was used to calculate the potential energy distributions of normal modes of the target molecule and its monohydrate cluster. Moreover, the NBO calculations for the target molecule and its monohydrate cluster were done to determine electronic structures, bond energies, occupancies, HOMO-LUMO and hyper-conjugative interaction energies of donor-acceptor interactions. The enthalpy of formation showed that the formation of the monohydrated cluster is of an exothermic nature.

Conformational stability, quantum computational, spectroscopic, molecular docking and molecular dynamic simulation study of 2-hydroxy-1-naphthaldehyde

Experimental FTIR, NMR and UV-visible spectrum analyses were used to describe the title compound 2-Hydroxy-1-Naphthaldehyde. The optimized molecular geometry and vibrational wave numbers were determined by using the DFT approach and B3LYP/6-311++G(d, p) basis set. VEDA was used to determine the vibrational assignments. The GIAO technique was used to compute carbon and proton NMR chemical shifts in CDCl3. The most reactive location of the 2H1NA molecule, according to MEP map analysis, is the site containing the oxygen atom. TD-DFT approach was used to produce the theoretical UV-visible spectrum in MeOH and gas phase. HOMO-LUMO and Donor-Acceptor (NBO) interactions were investigated for the title compound. In addition, nonlinear optical characteristics, ELF and Fukui activity were investigated. Temperature-dependent thermodynamic characteristics were also computed. The 3D intermolecular interactions of the crystal surface were characterised using Hirshfeld surface analysis, whereas the 2D interactions were explained using fingerprint plots. 2H1NA was stabilized by the development of H—H/H—C/H—O contacts. The bioactive probability of the title molecule was theoretically demonstrated by computing the electrophilicity index. In a biological study six different receptors, molecular docking was performed to evaluate the best ligand-protein interactions and likeness to the active substance. Biomolecular stability was investigated using a molecular dynamics simulation.

Ab Initio Study of Hydrostable Metal–Organic Frameworks for Postsynthetic Modification and Tuning toward Practical Applications

Metal–organic frameworks (MOFs), a subclass of nanoporous coordination polymers, have emerged as one of the most promising next-generation materials. The postsynthetic modification method, a strategy that provides tunability and control of these materials, plays an important role in enhancing its properties and functionalities. However, knowing adjustments which leads to a desired structure–function a priori remains a challenge. In this comprehensive study, the intermolecular interactions between 21 industrially important gases and a hydrostable STAM-17-OEt MOF were investigated using density functional theory. Substitutions on its 5-ethoxy isophthalate linker included two classes of chemical groups, electron-donating (−NH2, −OH, and −CH3) and electron-withdrawing (−CN, −COOH, and −F), as well as the effect of mono-, di-, and tri-substitutions. This resulted in 651 unique MOF–gas complexes. The adsorption energies at the ground state and room temperature, bond lengths, adsorption geometry, natural bond orbital analysis of the electric structure, HOMO–LUMO interactions, and the predicted zwitterionic properties are presented and discussed. This study provides a viable strategy for the functionalization, which leads to the strongest affinity for each gas, an insight into the role of different chemical groups in adsorbing various gas molecules, and identifies synthetic routes for moderating the gas adsorption capacity and reducing water adsorption. Recommendations for various applications are discussed. A custom Python script to assess and visualize the hypothetical separation of two equal gas mixtures of interest is provided. The methodology presented here provides new opportunities to expand the chemical space and physical properties of STAM-17-OEt and advances the development of other hydrostable MOFs.

Boosted Electronic, NLO and Absorption Characteristics for Quercetin and Taxifolin; Comparative Experimental and DFT Studies

In the present study, a considerable, reproducible, and eco-friendly biological synthesis of Ag nanoparticles using Mangifera indica leaf extract as a reductant is documented. The spectroscopic characteristics of synthesized Ag nanoparticles are described by both UV-Vis and FT-IR techniques. The bandgap offsets, reactivity, and NLO properties for two flavonoids, quercetin, and taxifolin, are examined using the DFT approach. Also, a detailed comparative analysis for HOMO-LUMO interactions among quercetin and taxifolin is discussed. Results show that quercetin and taxifolin possess dipole moment (DM=4.79, 3.99 Debye) and bandgap offset (2.59, 2.98 eV). Both molecules are promising candidates as window layers for solar cells and memory switch devices. In addition, hyperpolarizability calculations show that quercetin NLO response is higher than taxifolin, which sets a revolutionary recall for NLO manufacture upgrade. Moreover, NBO and UV-Vis absorption characteristics are reported as well.

Boosted Electronic, NLO and Absorption Characteristics for Quercetin and Taxifolin: Comparative Experimental and DFT Studies

In the present study, a considerable, reproducible, and eco-friendly biological synthesis of Ag nanoparticles using Mangifera indica leaf extract as a reductant is documented. The spectroscopic characteristics of synthesized Ag nanoparticles are described by both UV-Vis and FT-IR techniques. The bandgap offsets, reactivity, and NLO properties for two flavonoids, quercetin, and taxifolin, are examined using the DFT approach. Also, a detailed comparative analysis for HOMO-LUMO interactions among quercetin and taxifolin is discussed. Results show that quercetin and taxifolin possess dipole moment (DM=4.79, 3.99 Debye) and bandgap offset (2.59, 2.98 eV). Both molecules are promising candidates as window layers for solar cells and memory switch devices. In addition, hyperpolarizability calculations show that quercetin NLO response is higher than taxifolin, which sets a revolutionary recall for NLO manufacture upgrade. Moreover, NBO and UV-Vis absorption characteristics are reported as well.

A DFT and molecular dynamics simulation study of single-walled carbon nanotube as a drug delivery system for few model nitrogen mustard drugs

• Optimized geometries of the model nitrogen mustards substituted with heterocycles, SWCNT and the complexes between them were calculated using DFT technique. • Interaction energies were calculated from the optimized structures. • HOMO, LUMO, DOS, NBO and various quantum chemical descriptors were calculated for the optimized complexes. • NCI plots were calculated to show the interactions between drug and SWCNT • Molecular dynamics simulations were performed to investigate the effect of EtOH solvents on the stability of the complexes between drug and SWCNT Current study mainly describes the delivery of three model nitrogen mustard drugs with heterocyclic substituents by single-walled carbon nanotube (SWCNT) as a drug delivery system. The electronic properties and interaction energies were calculated using density functional theory (DFT). Results suggest that the model drugs bind exothermically with SWCNT. HOMO-LUMO, DOS plots and non-covalent interaction (NCI) plots indicate that the interaction between the drugs and SWCNT are weak. Further, calculations of quantum mechanical descriptors suggest that electron migration takes place from SWCNT to the drug. Finally, molecular dynamics simulation was performed to investigate the effect of EtOH co-solvent on the stability of the drug-SWCNT complex. The results suggest that the complexes are most stable in a water environment and the addition of EtOH co-solvent makes it unstable. In summary, all the results suggest that SWCNT may successfully deliver the investigated model nitrogen mustard drugs and these systems are most stable in a water solvent.

Spectroscopic Investigation of Electron-Releasing Functional Groups Substituted N-Iso-Butyl, S-2-Nitro-1-Phenylethyl Dithiocarbamate – A DFT Approach

Quantum chemical calculations have been carried out to explore structural and spectroscopic properties of some derivatives of N-iso-butyl, S-2-nitro-1-phenylethyl dithiocarbamate molecule in neutral and cationic forms. Electron-releasing groups (Me, OH and OMe) are considered to explore their effect on geometrical parameters, vibrational spectra and electronic properties of N-iso-butyl, S-2-nitro-1-phenylethyl dithiocarbamate. All the computations were performed at DFT/B3LYP level of Gaussian09 suite. The Raman spectra at different laser exciting frequencies are presented. The potential energy distributions of the considered derivatives were calculated by using the normal coordinate analysis method. The NBO calculations were performed to study the donor-acceptor interactions, HOMO-LUMO, electronic structure and hyper-conjugative interaction energies. The vibrational contribution of various thermodynamical parameters, viz, entropy, specific heat and free energy have also been presented and discussed in detail. Moreover, we have also explored the effect of temperature at specific heat and partition function of these molecules. Molecular docking studies have been performed to understand the nature of the interactions and the probable binding sites of NSD, NSD-Me, NSD-OH and NSD-OMe molecules in the active pockets of the 2KCE receptor.

An orbital picture extracted from correlated electronic wavefunctions and application to forbidden reactions: 70 years of the frontier orbital theory.

The one-electron picture in molecular electronic state theory, particularly the molecular orbital (MO) theory with the Hartree-Fock approximation, has set a foundation to develop chemical science. Frontier orbital theory, or the theory of HOMO (highest occupied MO)-LUMO (lowest unoccupied MO) interaction, and the conservation rule of orbital symmetry are among the brightest achievements in a molecular orbital picture. After 70 years from the birth of frontier orbital theory, however, electronic wavefunctions treated in current quantum chemistry are often highly correlated and consist of extensive scales of electronic configurations to be more accurate and to cope with far more complicated reactions than concerted reactions. Under such circumstances, the MO approximation itself readily loses its validity, let alone the utter dominance of the HOMO-LUMO interaction. Recently, we have proposed an invariant method to extract general orbitals from such correlated electronic wavefunctions, which we refer to as Energy Natural Orbitals (ENOs) [K. Takatsuka and Y. Arasaki, J. Chem. Phys. 154, 094103 (2021)]. The energies of ENOs are summed exactly to the total electronic energy. The topological (symmetry) properties of a total wavefunction are represented by the relative phases of ENOs along with the continuity and crossing (avoided and conical intersection) among them. Only a small number of ENOs often dominate and characterize chemical reactions. With these properties of ENO, we explore a couple of simple and typical symmetry forbidden reactions, illustrating the effects of electron correlation and degeneracy in relevant ENOs. We propose the notion of "internal conical intersection" among ENOs, which leads to Jahn-Teller effect, pseudo-Jahn-Teller effect, and so on. We dare to explain the primary origin of elementary conical intersections and multidimensional avoided crossing in chemical reactions with the use of the notion of orbital crossing between those of HOMO-HOMO and LUMO-LUMO interactions and so on.

Solid-state zwitterionic tautomerization of 2-((5-methyl-1H-pyrazol-3-yl)methyl)-1H-benzimidazole: Synthesis, characterization, DFT calculation and docking studies

The synthesis, characterization and single crystal X-Ray diffraction structure of 2-((5-methyl-1H-pyrazol-3-yl)methyl)-1H-benzimidazole are reported. The physicochemical characterization of the title compound was performed by spectroscopic techniques like FTIR, NMR analysis and single crystal X-ray diffraction. These data, together with the computed vibrational frequencies and NMR chemical shifts at the B3LYP/6–311++G(d,p) level of theory, are in agreement, and the confirmation of the coexistence of the two Zwitterionic tautomer's in the solid-state is proven using X-ray diffraction. The electronic and structural properties were investigated by DFT method at the geometry-optimized B3LYP/6–311++G(d,p) level. The HOMO-LUMO interactions were also studied. In order to explore the biological importance of the compound, molecular docking interactions have been studied to investigate the inhibition properties of the 2-((5-methyl-1H-pyrazol-3-yl)methyl)-1H-benzoimidazole molecule, indicative of the drug likeliness behavior of the synthesized molecule.