Unveiling the Unusual Mn(CO)3 Migration in a Manganese Cyclohexenyl Complex by DFT Computations.

Homogeneous catalysis involving a transition metal agostic interaction (TM…H…C) is an attractive strategy for C-H bond activation, in which the transition metal agostic intermediates serve as the critical component. To investigate the roles of manganese agostic intermediates in the unusual migration of the Mn(CO)3 fragment in the (exo-phenyl)(η3-cyclohexenyl)manganese tricarbonyl [(Ph)(η3-C6H8)Mn(CO)3] (complex 1) under the protonation of tetrafluoroboric acid-diethyl ether (HBF4.Et2O), a comprehensive density functional theory (DFT) theoretical study was performed. The computational results showed that formation of the [(cyclohex-3-enyl)-η6-benzene]manganese tricarbonyl complex [(C6H9)(η6-Ph)Mn(CO)3+][BF4] (complex 2) was achieved via a series of mono-agostic and di-agostic intermediates. The overall rate-limiting step for this unusual migration of the Mn(CO)3 fragment is the formation of the di-agostic (η2-phenyl)manganese complex 8 (4 → 5 → 8) with a Gibbs barrier of 15.4 kcal mol-1. The agostic intermediates with TM…H…C agostic interactions were well-characterized by geometry parameters, Atoms-In-Molecules (AIM) analyses, and the Natural Adaptive Orbitals (NAdOs). The located pathways in the current study successfully explained the experimental observations, and the findings on the TM…H…C agostic interaction provided a new aspect of the catalytic reaction with the manganese complex.

Comparison of Cu3, Cu5, and Cu7 clusters as potential antioxidants: A theoretical quest.

CONTEXT: Herein, we compare and contrast the dual roles of Cun clusters (n = 3, 5, and 7 atoms) in scavenging or generating RO• free radicals from ROH at the theoretical levels (where R = H, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, and phenyl). This investigation is performed in water media to mimic the actual environment in the biological system. In the presence of the Cun clusters, bond dissociation energy (BDE) of RO-H and R-OH is reduced. This is clear evidence for the increased possibility of both the RO-H and R-OH bonds breakage and scavenging of RO• radicals. The nature of anchoring bonds responsible for the interaction of Cun clusters with ROH and RO• are interpreted using the quantum theory of atoms in molecules (QTAIM) and the natural bond orbital (NBO) analysis. The DFT results indicate that the O•⋅⋅⋅•Cu bond is stronger and has more covalent character in RO•⋅⋅⋅•Cun radical complexes than in ROH⋅⋅⋅•Cun. Therefore, the interactions of Cun clusters with RO• radicals (antioxidant) are more pronounced than their interactions with ROH non-radicals (pro-oxidant). METHODS: The GAMESS software package was utilized in this paper. The B3LYP and M06 functions with the 6-311 + + G(d,p), and LANL2DZ/SDD basis sets was used to perform the important geometrical parameters of RO•⋅⋅⋅•Cun and ROH⋅⋅⋅•Cun, binding energy (Eb), and bond dissociation energy (BDE).

Pnictogen bond-driven control of the molecular interaction between organophosphorus and acetylcholinesterase enzyme.

This study addresses a comprehensive assessment of the interaction between chemical warfare agents (CWA) and acetylcholinesterase (AChE) systems, focus on the intriguing pnictogen-bond interaction (PnB). Utilizing the crystallographic data from the Protein Data Bank pertaining to the AChE-CWA complex involving Sarin (GB), Cyclosarin (GF), 2-[fluoro(methyl)phosphoryl]oxy-1,1-dimethylcyclopentane (GP) and venomous agent X (VX) agents, the CWA is systematically displaced by increments of 0.1 Å along the PO bond axis, extending its distance by 4 Å from the original position. The AIM analysis was carried out and consistently revealed the presence of a significant interaction along the PO bond. Investigating the intrinsic nature of the PnB, the NBO and the EDA analysis unearthed the contribution of orbital factors to the overall energy of the system. Strikingly, this observation challenges the conventional σ-hole explanation commonly associated with such interactions. This finding adds a layer of complexity to understanding of PnB, encouraging further exploration into the underlying mechanisms governing these intriguing chemical phenomena.

Insight into crystal structures and identification of potential styrylthieno[2,3-b]pyridine-2-carboxamidederivatives against COVID-19 Mpro through structure-guided modeling and simulation approach.

Anti-SARS-CoV-2 drugs are urgently needed to prevent the pandemic and for immunization. Their protease inhibitor treatment for COVID-19 has been used in clinical trials. In Calu-3 and THP1 cells, 3CL SARS-CoV-2 Mpro protease is required for viral expression, replication, and the activation of the cytokines IL-1, IL-6, and TNF-. The Mpro structure was chosen for this investigation because of its activity as a chymotrypsin-like enzyme and the presence of a cysteine-containing catalytic domain. Thienopyridine derivatives increase the release of nitric oxide from coronary endothelial cells, which is an important cell signaling molecule with antibacterial activity against bacteria, protozoa, and some viruses. Using DFT calculations, global descriptors are computed from HOMO-LUMO orbitals; the molecular reactivity sites are analyzed from an electrostatic potential map. NLO properties are calculated, and topological analysis is also part of the QTAIM studies. Both compounds 1 and 2 were designed from the precursor molecule pyrimidine and exhibited binding energies (-14.6708 kcal/mol and -16.4521 kcal/mol). The binding mechanisms of molecule 1 towards SARS-COV-2 3CL Mpro exhibited strong hydrogen bonding as well as Vdw interaction. In contrast, derivative 2 was bound to the active site protein's active studied that several residues and positions, including (His41, Cys44, Asp48, Met49, Pro52, Tyr54, Phe140, Leu141, Ser144, His163, Ser144, Cys145, His164, Met165, Glu166, Leu167, Asp187, Gln189, Thr190, and GLn192) are critical for the maintenance of inhibitors inside the active pocket. Molecular docking and 100 ns MD simulation analysis revealed that Both compounds 1 and 2 with higher binding affinity and stability toward the SARS-COV-2 3CL Mpro protein. Binding free energy calculations and other MD parameters support the finding.Communicated by Ramaswamy H. Sarma.

Cocrystals assembled from iodoperfluorobenzene and flexible NTPO via halogen and π-hole bonds.

Two binary cocrystals of 1,4-diiodotetrafluorobenzene (1,4-DITFB, C6F4I2) and 1,3,5-trifluoro-2,4,6-triiodobenzene (1,3,5-TITFB, C6F3I3) with the flexible 2-{[(naphthalen-2-yl)methyl]sulfanyl}pyridine 1-oxide (NTPO, C16H13NOS) molecule were successfully prepared and characterized by X-ray diffraction and quantum chemistry calculation methods. X-ray diffraction analysis reveals that the conformation of the flexible NTPO molecule has been changed significantly after introducing the 1,4-DITFB or 1,3,5-TITFB molecule into the NTPO lattice. Also the formation of the binary cocrystals is driven mainly by robust C-I...-O-N+ halogen bonds and π-hole...π-bond interactions, and they possess `sandwich' structural frameworks. Moreover, interaction energy analysis and AIM analysis were used to explore the contribution of different fragments to the structural stability and the corresponding electronic properties, which reveals that the robust halogen bonds with shorter bonding lengths [2.768 (4) and 2.789 (3) Å] are suggested to be covalent to a certain degree.

Bis(2-nitrophenyl) selenide, bis(2-aminophenyl) selenide and bis(2-aminophenyl) telluride: structural and theoretical analysis.

Three organoselenium and organotellurium compounds containing ortho substitutents, namely, bis(2-nitrophenyl) selenide, C12H8N2O4Se, 2, bis(2-aminophenyl) selenide, C12H12N2Se, 3, and bis(2-aminophenyl) telluride, C12H12N2Te, 7, have been investigated by both structural and theoretical methods. In the structures of all three compounds, there are intramolecular contacts between both Se and Te with the ortho substituents. In the case of 2, this is achieved by rotation of the nitro group from the arene plane. For 3, both amino groups exhibit pyramidal geometry and are involved in intramolecular N-H...Se interactions, with one also participating in intermolecular N-H...N hydrogen bonding. While 3 and 7 are structurally similar, there are some significant differences. In addition to both intramolecular N-H...Te interactions and intermolecular N-H...N hydrogen bonding, 7 also exhibits intramolecular N-H...N hydrogen bonding. In the packing of these molecules, for 2, there are weak intermolecular C-H...O contacts and these, along with the O...N interactions mentioned above, link the molecules into a three-dimensional array. For 3, in addition to the N-H...N and N-H...Se interactions, there are also weak intermolecular C-H...Se interactions, which also link the molecules into a three-dimensional array. On the other hand, 7 shows intermolecular N-H...N interactions linking the molecules into R22(16) centrosymmetric dimers. In the theoretical studies, for compound 2, AIM (atoms in molecules) analysis revealed critical points in the Se...O interactions with values of 0.017 and 0.026 a.u. These values are suggestive of weak interactions present between Se and O atoms. For 3 and 7, the molecular structures displayed intramolecular, as well as intermolecular, hydrogen-bond interactions of the N-H...N type. The strength of this hydrogen-bond interaction was calculated by AIM analysis. Here, the intermolecular (N-H...N) hydrogen bond is stronger than the intramolecular hydrogen bond. This was confirmed by the electron densities for 3 and 7 [ρ(r) = 0.015 and 0.011, respectively].

Synthesis, Crystal Structure, and Computational Methods of Vanadium and Copper Compounds as Potential Drugs for Cancer Treatment.

Transition metal-based compounds have shown promising uses as therapeutic agents. Among their unique characteristics, these compounds are suitable for interaction with specific biological targets, making them important potential drugs to treat various diseases. Copper compounds, of which Casiopeinas® are an excellent example, have shown promising results as alternatives to current cancer therapies, in part because of their intercalative properties with DNA. Vanadium compounds have been extensively studied for their pharmacological properties and application, mostly in diabetes, although recently, there is a growing interest in testing their activity as anti-cancer agents. In the present work, two compounds, [Cu(Metf)(bipy)Cl]Cl·2H2O and [Cu(Impy)(Gly)(H2O)]VO3, were obtained and characterized by visible and FTIR spectroscopies, single-crystal X-ray diffraction, and theoretical methods. The structural and electronic properties of the compounds were calculated through the density functional theory (DFT) using the Austin-Frisch-Petersson functional with dispersion APFD, and the 6-311 + G(2d,p) basis set. Non-covalent interactions were analyzed using Hirshfeld surface analysis (HSA) and atom in molecules analysis (AIM). Additionally, docking analysis to test DNA/RNA interactions with the Casiopeina-like complexes were carried out. The compounds provide metals that can interact with critical biological targets. In addition, they show interesting non-covalent interactions that are responsible for their supramolecular arrangements.

Conformational transitions of the quercetin molecule via the rotations of its rings: a comprehensive theoretical study.

Quercetin is an important flavonoid compound, usually extracted from plants, vegetables and fruits such as blueberries, apples, green tea, wine, onions and possessing broad range of pharmacological properties, in particular, powerful antioxidant, antitoxic, antiinflammation and antimicrobial effects due to its various reactive sites. The structure of this phenolic compound consists of three (A + C) and B rings, bearing five hydroxyl groups. Primarily, the chemical structure of quercetin determines its physico-chemical properties. Earlier, it was established that isolated quercetin molecule can acquire 48 stable conformations (24 planar and 24 non-planar) due to the mobility of its hydroxyl groups and (A + C) and B rings with relative Gibbs free energies in the range of 0.0-25.3 kcal·mol-1 under normal conditions (Brovarets' et al., 2019c). In this work by quantum-mechanical calculations at the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of theory and Bader's 'Quantum Theory of Atoms in Molecules', we have theoretically modeled the interconversions in the 24 pairs of the conformers of the quercetin molecule, occuring via the rotation of its non-deformable (A+С) and B rings around the С2-С1' bond through the quasi-orthogonal transition state with low values of the imaginary frequencies (28-33/29-36 cm-1) and Gibbs free energies of activation in the range of 2.17-5.68/1.86-4.90 kcal·mol-1 in the continuum with dielectric permittivity ε = 1/ε = 4 under normal conditions. Also, we studied the changes of the number of physico-chemical characteristics of all intramolecular-specific contacts - hydrogen bonds and attractive van der Waals contacts during these conformational rearrangements.Communicated by Ramaswamy H. Sarma.

Multicomponent supramolecular assemblies of 1(2H)-Phthalazinone and Tetrafluoroterephthalic acid: Understanding the role of hydrogen bonding on the structure and properties using experimental and computational analyses.

Two novel cocrystals were successfully constructed by 1(2H)-Phthalazinone (PHT) and Tetrafluoroterephthalic acid (TETA) based on O-H⋯O, N-H⋯O, C-H⋯O, C-H⋯F, N-H⋯N and C-H⋯N hydrogen bonding networks, and were well depicted by single crystal diffraction analysis. As predicted by electrostatic potential analysis, the stoichiometry of PHT to TETA is 2:1 and stabilized by O-H⋯O and N-H⋯O hydrogen bonds. The single crystal X-ray diffraction characterized that the two cocrystals were all made up by 2PHT-TETA motif in different ways. AIM analysis and Hirshfeld surfaces indicated the adjacent 2PHT-TETA units assemble through C-H⋯O, C-H⋯F and C-H⋯N hydrogen bonds, producing a 2D plane structure in cocrystal I. Meanwhile, the C-H⋯F, N-H⋯N and C-H⋯O hydrogen bonds between 2PHT-TETA units were the stabilizing factors in cocrystal II. Topological parameters such as ∇2ρ and H revealed the strength of hydrogen bonds were moderate in nature except O31⋯H32-O34 (1.704Å, -60.336kJmol-1) in compound I. The hydrogen bonding interactions, cocrystal stability and electron donor-acceptor interactions were investigated using natural bonding orbital analysis. It showed that electron transfer of n(O) σ*(O-H) and n(O) σ*(N-H) between PHT and TETA influence the packing characteristics significantly. Structural changes accompanying cocrystal process have been rationalized through the IR spectrum along with the quantum chemical calculations. The frequency downshifts of CO, N-H and O-H stretching after cocrystallization have been attributed to hydrogen bonding interactions.

A quantum chemical perspective on the potency of electron donors and acceptors in pnicogen bonds (AS...N, P...N, N...N).

A quantum chemical perspective of 31 structures contains electron acceptors: ASCl3 (arsenic trichloride), PCl3 (phosphorous trichloride) and NCl3 (nitrogen trichloride); forming non-covalent bond with various nitrogen-based electron donors that resulted in pnicogen bonds, AS...N, P...N and N...N were calculated at M062X/def2-QZVP level of theory. Besides the above method, MP2/def2-QZVP and CCSD(T)/def2-QZVP level of theories have also been analysed to have in depth knowledge about the bonds formed. The nature of the bonds was assumed from the electrostatic potential evaluated for all the monomers, where σ hole is positive for all the monomers. The strongest pnicogen bonds are ASCl3-NF2H, PCl3-NCH3CH3CH3 and NCl3-NCH3CH3CH3 having interaction energies as -4.15, -11.58 and -3.25 kcal/mol, respectively, at MP2/def2-QZVP level of theory. Further at CCSD(T)/def2-QZVP level of theory, ASCl3-NF2H and NCl3-NCH3CH3CH3 are found to be the most stable with interaction energies as -3.53 and -2.45 kcal/mol, respectively. The potential energy surface scan was performed for all the stable complexes in order to confirm the existences of energies are true minima. Moreover to confirm the halogen and pnicogen bonds, AIM analysis was carried out. The results from the above factors of pnicogen bond will help crystal growth, material science and engineering community to explore novel materials, which abide for modernization. Graphical abstract PCl3-NCH3CH3CH3 complex with 2.61 Å and pnicogen angle of 178.54° is strong, and interaction energy is -11.58 kcal/mol. Electron donors - ASCl3, PCl3 and NCl3 and electron acceptors -NCH3CH3CH3, NH3C2 and NHCO have strong electrostatic contribution. High and low values of (ρ) ∇2(ρ) reveal the strong and weak pnicogen bond. Schematic representation of acceptors surrounded by its donors and Electrostatic Potential map.

Unusual structure of a biphenyl fragment: the important role of weak interactions.

1,5-Bis([1,1'-biphenyl]-4-yl)-5-hydroxy-3-methylheptane-1,6-dione, C32H30O3, was investigated by X-ray analysis, quantum chemical calculations and AIM (atoms in molecules) analysis. It was shown that four intramolecular C-H...π forces are established between the two biphenyl fragments. C-H...π interactions lead to a bending of the biphenyl part. The energy of the intramolecular interactions was estimated and the exclusive role of the moment of force was established.

The many flavours of halogen bonds - message from experimental electron density and Raman spectroscopy.

Experimental electron-density studies based on high-resolution diffraction experiments allow halogen bonds between heavy halogens to be classified. The topological properties of the electron density in Cl...Cl contacts vary smoothly as a function of the interaction distance. The situation is less straightforward for halogen bonds between iodine and small electronegative nucleophiles, such as nitrogen or oxygen, where the electron density in the bond critical point does not simply increase for shorter distances. The number of successful charge-density studies involving iodine is small, but at least individual examples for three cases have been observed. (a) Very short halogen bonds between electron-rich nucleophiles and heavy halogen atoms resemble three-centre-four-electron bonds, with a rather symmetric heavy halogen and without an appreciable σ hole. (b) For a narrow intermediate range of halogen bonds, the asymmetric electronic situation for the heavy halogen with a pronounced σ hole leads to rather low electron density in the (3,-1) critical point of the halogen bond; the properties of this bond critical point cannot fully describe the nature of the associated interaction. (c) For longer and presumably weaker contacts, the electron density in the halogen bond critical point is only to a minor extent reduced by the presence of the σ hole and hence may be higher than in the aforementioned case. In addition to the electron density and its derived properties, the halogen-carbon bond distance opposite to the σ hole and the Raman frequency for the associated vibration emerge as alternative criteria to gauge the halogen-bond strength. We find exceptionally long C-I distances for tetrafluorodiiodobenzene molecules in cocrystals with short halogen bonds and a significant red shift for their Raman vibrations.

Tetrel Bonding Interactions in Perchlorinated Cyclopenta- and Cyclohexatetrelanes: A Combined DFT and CSD Study.

In this manuscript, we combined DFT calculations (PBE0-D3/def2-TZVP level of theory) and a Cambridge Structural Database (CSD) survey to evaluate the ability of perchlorinated cyclopenta- and cyclohexatetrelanes in establishing tetrel bonding interactions. For this purpose, we used Tr5Cl10 and Tr6Cl12 (Tr = Si and Ge) and HCN, HF, OH- and Cl- as electron donor entities. Furthermore, we performed an Atoms in Molecules (AIM) analysis to further describe and characterize the interactions studied herein. A survey of crystal structures in the CSD reveals that close contacts between Si and lone-pair-possessing atoms are quite common and oriented along the extension of the covalent bond formed by the silicon with the halogen atom.

Crystallographic and computational study of a network composed of [ZnCl4]2- anions and triply protonated 4'-functionalized terpyridine cations.

We report herein the synthesis, crystallographic analysis and a study of the noncovalent interactions observed in the new 4'-substituted terpyridine-based derivative bis[4'-(isoquinolin-2-ium-4-yl)-2,2':6',2''-terpyridine-1,1''-diium] tris[tetrachloridozincate(II)] monohydrate, (C24H19N4)2[ZnCl4]3·H2O or (ITPH3)2[ZnCl4]3·H2O, where (ITPH3)3+ is the triply protonated cation derived from 4'-(isoquinolin-4-yl)-2,2':6',2''-terpyridine (ITP) [Granifo et al. (2016). Acta Cryst. C72, 932-938]. The (ITPH3)3+ cation presents a number of interesting similarities and differences compared with its neutral ITP relative, mainly in the role fulfilled in the packing arrangement by the profuse set of D-H...A [D (donor) = C, N or O; A (acceptor) = O or Cl], π-π and anion...π noncovalent interactions present. We discuss these interactions in two different complementary ways, viz. using a point-to-point approach in the light of Bader's theory of Atoms In Molecules (AIM), analyzing the individual significance of each interaction, and in a more `global' analysis, making use of the Hirshfeld surfaces and the associated enrichment ratio (ER) approach, evaluating the surprisingly large co-operative effect of the superabundant weaker contacts.

Intermolecular hydrogen bonds between 1,4-benzoquinones and HF molecule: Synergetic effects, reduction potentials and electron affinities.

Some biological activities of quinones can be attributed to the H-bonding ability of acceptor oxygen atoms. According to the results obtained from the quantum mechanical calculations performed on a wide variety of complexes between the 1,4-benzoquinone (BQ) derivatives and HF molecules, the interplay between H-bonds and individual H-bond interaction energies (EHB) can be affected by the substituents placed on the six-membered ring of BQ. The total binding energies of complexes become more negative by the electron donating substituents (EDSs) while the changes are reversed by the electron withdrawing substituents (EWSs). The mutual interplay between the X-BQ⋯(HF)n (n=1-3) interactions has been investigated using the geometrical parameters, synergetic energies (SE) and the EHB values. Hydrogen bonding decreases the reduction potentials (E0red) and increases the electron affinities (EA) of X-BQ derivatives. Linear relationships have been observed between the E0red (and EA) values and the Hammett constants of substituents.

On the Importance of π-Hole Beryllium Bonds: Theoretical Study and Biological Implications.

In this study, the ability of beryllium compounds to establish π-hole bonding interactions has been evaluated at the RI-MP2/def2-TZVPD level of theory. A search of the Protein Data Bank revealed some X-ray crystal structures in which BeF3- moieties act as electron-acceptor entities. We have used [Mg(BeF3 )(HCOO)] (1) as a π-hole bond donor and CO, CH3 CN, NH3 , O(CH3 )2 , S(CH3 )2 , H3 PO, and glycine as electron-rich entities. In all cases, favorable binding energies were obtained, reflecting the attractive nature of the interaction involving the trivalent beryllium atom (-BeF3 moiety). In addition, we have used Bader's theory of "atoms in molecules" and noncovalent interaction (NCI) plot analysis to further investigate and characterize the π-hole complexes described herein. To the best of our knowledge, π-hole interactions involving beryllium have not hitherto been described in the literature.

Synthesis, Spectral Studies and Quantum-Chemical Investigations on the Powerful Fluorophores: Imidazo[4,5-a]acridines.

The new 3H-imidazo[4,5-a]acridine-11-carbonitriles were prepared from the reaction of 1-alkyl-5-nitro-1H-benzoimidazoles with 2-(4-methoxyphenyl)acetonitrile and benzyl cyanide by nucleophilic substitution of hydrogen in high yields. Physical spectral and analytical data have confirmed the structures of the synthesized dyes. The optical and solvatochromic properties of these compounds were investigated and the results showed that they show very interesting photophysical properties. Density functional theory (DFT) calculations of fluorescent dyes were performed to provide the optimized geometries and relevant frontier orbitals. Furthermore, intra- and intermolecular interactions in fluorescent imidazo[4,5-a]acridines were evaluated by AIM (Atoms in Molecules) analysis.

π-Stacking effects on the hydrogen bonding capacity of methyl 2-naphthoate.

π-stacking effects of fused two-ring system of methyl 2-naphthoate (MNP) with benzene derivatives on the CO group, as a hydrogen bond acceptor, has been investigated by the quantum mechanical calculations at the M06-2X/6-311++G(d,p) level of theory. All substituents enhance the stacking interactions relative to the unsubstituted case, where enhancement is higher for electron-withdrawing substituents (EWSs). The hydrogen bonding ability of lone pairs of O* atom of stacked MNP decreases in the presence of strong electron-withdrawing substituents (NO2, NO and CN). The hydrogen bond ability of CO group of MNP is related to the sum of local minima of electrostatic potentials (∑ESPs) observed between stacked rings. The charge transfer (CT) is lower in the presence of EWSs. The study also shows that the interaction energies (ΔE) are linearly dependent on the combination of the sum of electron densities calculated at the bond critical points (BCPs) between the rings (∑ρBCP) and the sum of electron charge densities calculated at the ring critical points (∑ρRCP). There are good relationships between the Hammett constant σmeta and the global minimum of electrostatic potential around the O* atom (Vmin), the sum of local minima of the electrostatic potentials obtained between stacked rings, and the results of natural population analysis (NPA). An excellent correlation was found between the ΔE values and a combination of the electrostatic (σmeta), resonance/induction (σpara) and dispersion/polarizibility (molar refractivity, MR) substituent constant terms.

Molecular structure and vibrational spectroscopic studies on 2-furanacetic acid monomer and dimer.

In this work, molecular geometries and fundamental vibrational frequencies of 2-furanacetic acid (2FAA) and its hydrogen bonded dimer were investigated using DFT/B3LYP method with 6-311++G(d,p) as basis set. The FT-infrared and FT-Raman spectra of the 2FAA compound were recorded in the region 4000-400 cm(-1). The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. Complete vibrational assignments and analysis of the fundamental modes of monomer and dimer structures were performed on the basis of the potential energy distribution (PED) calculations. A study on the electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. Molecular stability arising from hyperconjugative interactions and charge delocalization has been analyzed using Natural Bond Orbital (NBO) analysis. Topological parameters such an electron density and its Laplacian at bond critical points (BCP) of O-H and O⋯H contact bonds were analyzed in details with the help of the atoms in molecules (AIM) approach in order to study the intermolecular hydrogen bonding. The nonlinear optical properties of the title molecule have been investigated. Moreover, molecular electrostatic potential (MEP) surface was plotted for predicting sites and relative reactivities towards electrophilic and nucleophilic attack. The nonlinear optical properties were reported and compared with that of the urea. The thermodynamic properties like heat capacity, entropy, and enthalpy have been calculated for the molecule at different temperatures.

Investigation of the structure and interaction of cellulose triacetate I crystal using ab initio calculations.

The crystal structure of cellulose triacetate I (CTA I) was investigated using first-principles density functional theory (DFT) calculations. The results are in good agreement with the experimental structure obtained by Sikorski et al. when performing the calculation with inclusion of the dispersion correction. However, the cell parameters calculated with inclusion of the dispersion correction are slightly smaller than those experimentally obtained, especially along the a-axis. This smaller cell parameter could be reasonably explained by considering thermal expansion effects, since optimization with the density functional calculation gives the structure without inclusion of thermal effects. The atoms-in-molecules (AIM) theory is also employed to identify and characterize interatomic interactions in the CTA I crystal. CH/O interactions sites are shown to exist in the crystal structure of CTA I. Moreover, CH/O interactions are considered the main interactions in operation to maintain the crystal structure of CTA I.