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Advanced theoretical methodologies and photoelectron photoion coincidence spectroscopy were used to investigate the photoionization of ethanolamine in the 8–18 eV energy range. We identified the low-lying cation conformers and the excited cation electronic states after vertical excitation from the most stable neutral conformer computationally. The TPES is composed of broad, structureless bands because of unfavorable Franck–Condon factors for origin transitions upon ionization, populating the D0–D7 cationic states from the most stable neutral conformer, g′Gg′. The adiabatic ionization energy of ethanolamine is calculated at 8.940 ± 0.010 eV, and the 0 K appearance energies of aminomethylium, NH2CH2+ (+CH2OH), and methyleneammonium, NH3CH2+ (+H2CO), are determined experimentally to be 9.708 ± 0.010 eV and 9.73 ± 0.03 eV, respectively. The former is used to re-evaluate the ethanolamine enthalpy of formation in the gas and liquid phases as ΔfH 298K [NH2(CH2)2OH, g] = −208.2 ± 1.2 kJ mol−1 and ΔfH 298K [NH2(CH2)2OH, l] = −267.8 ± 1.2 kJ mol−1. This represents a substantial correction of the previous experimental determination and is supported by ab initio calculations. [ABSTRACT FROM AUTHOR]

The stable low energy states of the HPS and DPS molecules have been studied through multi-reference ab initio methods in conjunction with large atomic basis sets. Stable states for these species have been examined up to 7 eV above the ground state minimum. We found six stable electronic states that are mostly mono-configurational. These states may be involved in the photodynamics and photodissociation of this molecule. In particular, the 2 1A′ state presents two minima on the potential energy surface, one of them close to linear configuration. This state may be populated after the absorption of a visible photon from the ground state and gives rise to large amplitude motions that may eventually induce isomerization to electronically excited HSP. Moreover, we characterized these states spectroscopically to facilitate the assignment of the vibronic spectra of the HPS and DPS species. For these low-energy states, we thus computed vertical and adiabatic excitation energies, and for the stable ones, a full set of spectroscopic constants including harmonic frequencies and anharmonic vibrational, rotational, and centrifugal distortion constants. The calculated potential energy surfaces for these states have been used in a variational procedure to deduce the pattern of vibrational levels up to 4000 cm−1 above the corresponding vibrationless level. Our data may serve for the assignment of the IR and Vis spectra of HPS and DPS. [ABSTRACT FROM AUTHOR]

Collisional energy transfer under cold conditions is of great importance from the fundamental and applicative point of view. Here, we investigate low temperature collisions of the SH- anion with He. We have generated a three-dimensional potential energy surface (PES) for the SH-(X¹Σ+)-He(¹S) van der Waals complex. The ab initio multi-dimensional interaction PES was computed using the explicitly correlated coupled cluster approach with simple, double, and perturbative triple excitation in conjunction with the augmented-correlation consistent-polarized valence triple zeta Gaussian basis set. The PES presents two minima located at linear geometries. Then, the PES was averaged over the ground vibrational wave function of the SH- molecule and the resulting two-dimensional PES was incorporated into exact quantum mechanical close coupling calculations to study the collisional excitation of SH- by He. We have computed inelastic cross sections among the 11 first rotational levels of SH- for energies up to 2500 cm-1. (De-)excitation rate coefficients were deduced for temperatures ranging from 1 to 300 K by thermally averaging the cross sections. We also performed calculations using the new PES for a fixed internuclear SH- distance. Both sets of results were found to be in reasonable agreement despite differences existing at low temperatures confirming that accurate predictions require the consideration of all internal degrees of freedom in the case of molecular hydrides. The rate coefficients presented here may be useful in interpreting future experimental work on the SH- negative ion colliding with He as those recently done for the OH- -He collisional system as well as for possible astrophysical applications in case SH- would be detected in the interstellar medium. [ABSTRACT FROM AUTHOR]

We present a theoretical investigation of neutral and ionic C7 molecules. Since carbon chains present isomerism and the number of possible structures increases fast with the number of carbon atoms, a B3LYP/aug-cc-pVTZ search of stationary points has been achieved. For C7, we found twelve minimal structures. Among these forms, eleven C7 isomers are located into the lowest singlet hyper potential energy surface. The most stable form of C7 is linear and possesses a 1Σg+ symmetry species. For C7¯ , we characterized fifteen stable forms, where twelve are of doublet spin-multiplicity. The global minimum of C7¯ is a 2Πg doubly degenerate Renner-Teller structure. For C7+ cation, we found eleven doublet and three quartet isomers with a 7-atom cycle, C7+ (X2A1) ground state. For the most stable forms, explicitly correlated (R)CCSD(T)-F12 calculations have been performed for the determination of equilibrium geometries and for the spectroscopic characterization of C7, C7¯, and C7+, providing accurate rotational constants and harmonic frequencies. Vertical excitation energies to the lowest electronic states have been computed at the CASSCF/MRCI/aug-cc-pVTZ level. Thirty five electronic states of C7, suitable of being involved in reactive processes, lie below 7 eV. Fourteen metastable electronic states of C7¯ have been found below 3.5 eV. For linear-C7, we compute the electron affinity and the ionization energy to be 3.38 eV and 10.42 eV, respectively. [ABSTRACT FROM AUTHOR]

In many cases, 5-fluorouracil (5-FU) is the first-line drug used in combined chemotherapy and radiotherapy treatments due to its radio-sensitization properties. It could participate in a tautomerization process similar to that of uracil, where 5-FU may couple to adenine in DNA. At present, we performed structural and spectroscopic studies using quantum chemical methods of neutral and cationic isolated 5-FU anticarcinogenic drug tautomers, either interacting with a water molecule or embedded into an implicit water solvent. Also, we determined the stationary points (both stable structures and transition states) on their ground potential energy surfaces playing a role during the tautomerization processes. For neutral and ionic species in the gas phase and in solvent, the ordering of the tautomers is found to be the same, where the di-keto form of 5-FU is the most stable structure, followed by the keto–enol and di-enol structural forms. The energy barriers for tautomerization are strongly reduced in solvent (< 0.5 eV) compared to isolated species (∼2 eV). The patterns of their lowest electronic states are also computed. Our data may help for the identification of these species in vivo and in the laboratory. [ABSTRACT FROM AUTHOR]

In the present work, we investigate the bonding, structures, stability and spectra of the Znq+Im (where q = 0, 1, and 2) complexes, which are zeolitic imidazolate frameworks (ZIFs) and Zn-enzyme sub-units. Through a benchmark work, we used density functional theory (DFT) with dispersion correction and standard and explicitly correlated ab initio methods. For neutral Zn0Im, we found two stable weakly bound forms: (i) a stacked ferrocene-like complex and (ii) a planar σ-type complex. This is the first report of the Zn0 organic compound with a stacked ferrocene-like structure. The most stable isomers of the ionic species consist of σ-type bonded complexes. The role of various types of covalent and noncovalent interactions within these complexes is discussed after performing vibrational, NBO, charge and orbital analyses. For neutral species, van der Waals (vdWs) and charge transfer through covalent as well as noncovalent interactions are in action; whereas the bonding is dominated by charge transfer from Zn to Im within the ionic species. These findings are important to understand, at the microscopic level, the structure and the bonding within the ZIFs and the Zn-enzymes. Moreover, we establish the ability and reliability of M05-2X and PBE0 functionals for the simultaneous correct description of covalent and noncovalent interactions since this DFT leads to a close agreement with post-Hartree–Fock methods. The newly launched M11 functional is also suited for the description of noncovalent interactions. Therefore, M05-2X and PBE0 functionals are recommended for studying the larger complexes formed by Zn and Im, such as the ZIFs and Zn-enzymes. [ABSTRACT FROM AUTHOR]

Using an ab initio methodology, we performed a detailed theoretical study of the gas phase WC2+ dication. These calculations were done using a multiconfigurational method in connection with a large basis set, where relativistic effects were taken into account. This dication is identified here as the first thermochemically stable doubly charged diatomic carbide in the gas phase. Our work hence confirms the stability of this dication in the gas phase and its earlier observations by atom probe mass spectrometry. Our calculations show that the shape of the potential energy curves of its lowest electronic states changes drastically upon consideration of relativistic effects. For instance, the electronic ground state possesses a Morse-like potential without spin–orbit that evolves to the usual volcanic behavior, and with a columbic 1/R evolution at large internuclear separation after inclusion of spin–orbit. We predict a set of thermochemical and spectroscopic data for this molecular species. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the [3+2] cycloaddition (32CA) reactions of N-benzyl fluoro nitrone with a series of maleimides producing isoxazolidines. We use the Molecular Electron Density Theory at the MPWB1K/6-311G(d) level. We focus on the reaction mechanism, selectivity, solvent, and temperature effects. In addition, we perform topological analyses at the minimal and transition states to identify the intermolecular interactions. Electron Localization Function approach classifies the N-benzyl fluoro nitrone as zwitterionic (zw-) three-atom components (TACs), associated with a high energy barrier. The low polar character of the reaction is evaluated using the Conceptual Density Functional Theory analysis of the reactants, confirmed by the low global electron density transfer computed at the transition states. Computations show that these 32CA reactions follow a one-step mechanism under kinetic control, with highly asynchronous bond formation and no new covalent bond is formed at the TS. Besides, the potential energy surfaces along the reaction pathways in gas phase and in solvent are mapped. The corresponding Gibbs free energy profiles reveal that the exo-cycloadducts are kinetically and thermodynamically more favored than endo-cycloadducts, in agreement with the exo-selectivity observed experimentally. In particular, we found that solvent and temperature did not affect this selectivity and mainly influence the activation energies and the exothermic character of these 32CA reactions., (© 2023 Wiley Periodicals LLC.)

This computational study of line-broadening effects is based on an accurate, analytical representation of the intermonomer potential energy surface (PES) of the CO 2  ⋅ Ar van der Waals (vdW) complex. The PES is employed to compute collisional broadening coefficients for rovibrational lines of CO 2 perturbed by Ar. The semiclassical computations are performed using the modified Robert-Bonamy approach, including real and imaginary terms, and the exact trajectory model. The lines investigated are in the 10001←00011, 01101←00001, 00011←00001, and 00031←00001 vibrational bands and the computations are repeated at multiple temperatures. The computed results are in good agreement with the available experimental values, validating both the intermonomer PES developed and the methodology used. For lines in the 01101←00001 band of CO 2 , temperature-dependent Ar-broadening coefficients are reported for the first time. The parameters presented should prove useful, among other applications, for the accurate experimental determination of CO 2 and Ar abundances in planetary atmospheres., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Interfacial interactions of protonated water clusters adsorbed at aromatic surfaces play an important role in biology, and in atmospheric, chemical and materials sciences. Here, we investigate the interaction of protonated water clusters ((H + H 2 O) n (where n=1-3)) with benzene (Bz), coronene (Cor) and dodecabenzocoronene (Dbc)). To study the structure, stability and spectral features of these complexes, computations are done using DFT-PBE0(+D3) and SAPT0 methods. These interactions are probed by AIM electron density topography and non-covalent interactions index (NCI) analyses. We suggest that the excess proton plays a crucial role in the stability of these model interfaces through strong inductive effects and the formation of Eigen or Zundel features. Also, computations reveal that the extension of the π-aromatic system and the increase of the number of water molecules in the H-bounded water network led to a strengthening of the interactions between the corresponding aromatic compound and protonated water molecules, except when a Zundel ion is formed. The present findings may serve to understand in-depth the role of proton localized at aqueous medium interacting with large aromatic surfaces such as graphene interacting with acidic liquid water. Besides, we give the IR and UV-Vis spectra of these complexes, which may help for their identification in laboratory., (© 2023 Wiley-VCH GmbH.)

Accurate modeling of anionic abundances in the interstellar and circumstellar media requires calculations of collisional data with the most abundant species that are usually He atoms and H 2 molecules. In this paper, we focus on smaller cyclic molecular anion, c-C 3 H - , an astrophysical candidate, following the detection of larger C n H - carbon chains. From a new three-dimensional potential energy surface, the rotational (de-)excitation of the c-C 3 H - (X 1 A 1 ) anion by collision with He is investigated. The surface is obtained in the supermolecular approach at the CCSD(T)-F12/aug-cc-pVTZ level of theory. Fully quantum close-coupling calculations of inelastic integral cross sections are performed on a grid of collisional energies large enough to ensure the convergence of the state-to-state rate coefficients for the 34 first rotational levels up to j K a ,K c = 7 7,0 of c-C 3 H - and temperatures ranging from 5 to 100 K. For this collisional system, rate coefficients exhibit a strong dominance in favor of 2 1,2 → l 1,1 downward transition. This transition was previously used for the detection of the cyclic parent c-C 3 H. The c-C 3 H - -He rate coefficients (∼10 -11  cm 3  s -1 ) are of the same order of magnitude as those of the detected anions C n H - (as C 2 H - , C 4 H - , and C 6 H - ) in collision with He and one order of magnitude smaller than those with H 2 . The critical densities of H 2 were also estimated, and a discussion on the validity of the local thermodynamic equilibrium conditions is carried out. This work represents the contribution to understanding and modeling abundances and chemistry of hydrocarbon radicals, C n H, in astrophysical media.

The aim of this work is to contribute to the research in finding lead compounds for clinical use, to identify new drugs that target the SARS-CoV-2 virus main protease (Mpro). In this study, we used molecular docking strategies to analyze 2.5-diaminobenzophenone compounds against Malaria and to compare results with the Nelfinavir as a FDA-approved HIV-1 protease inhibitor recommended for the treatment of COVID-19. These efforts identified the potential compounds against SAR-COV-2 Mpro with the docking scores ranges from -6.1 to -7.75 kcal/mol, which exhibited better interactions than the Nelfinavir. Among thirty-six studied, compounds 20c, 24c, 30c, 34c, 35c and 36c showed the highest affinity and involved in forming hydrophobic interactions with Glu166, Thr24, Thr25, and Thr26 residues and forming H-bonding interactions with Gln189, Cys145, and His41residues. Pharmacokinetic properties and toxicity (ADMET) were also determined for identified compounds. This study result in the identification of two compounds 35 and 36 having high binding affinity, good pharmacokinetics properties and lowest toxicity. The structural stability and dynamics of lead compounds within the active site of 3CLpro was also examined using molecular dynamics (MD) simulation. Essential dynamics demonstrated that the two complexes remain stable during the entire duration of simulation. We have shown that these two lead molecules would have the potential to act as promising drug-candidates and would be of interest as starting point for designing compounds against the SARS-CoV-2., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2021 Published by Elsevier B.V. on behalf of King Saud University.)

The site-specific first microsolvation step of furan and some of its derivatives with methanol is explored to benchmark the ability of quantum-chemical methods to describe the structure, energetics, and vibrational spectrum at low temperature. Infrared and microwave spectra in supersonic jet expansions are used to quantify the docking preference and some relevant quantum states of the model complexes. Microwave spectroscopy strictly rules out in-plane docking of methanol as opposed to the top coordination of the aromatic ring. Contrasting comparison strategies, which emphasize either the experimental or the theoretical input, are explored. Within the harmonic approximation, only a few composite computational approaches are able to achieve a satisfactory performance. Deuteration experiments suggest that the harmonic treatment itself is largely justified for the zero-point energy, likely and by design due to the systematic cancellation of important anharmonic contributions between the docking variants. Therefore, discrepancies between experiment and theory for the isomer abundance are tentatively assigned to electronic structure deficiencies, but uncertainties remain on the nuclear dynamics side. Attempts to include anharmonic contributions indicate that for systems of this size, a uniform treatment of anharmonicity with systematically improved performance is not yet in sight.

Using configuration interaction ab initio methods, we investigate the lowest electronic states of doublet and quartet spin multiplicities of SSNO where the one-dimensional cuts of the six-dimensional potential energy surfaces of these electronic states along the stretching and bending coordinates are computed. Mainly, these electronic states are found to be repulsive along the central SN distance. A high density of electronic states is computed even at low excitation energies that may favor their couplings. Therefore, the dynamics of the SSNO electronic states is expected to be very complex. We also characterized the bound electronic states spectroscopically where we derived their equilibrium structures and vibrational frequencies. Our calculations show the importance of taking into account of dynamical correlation, in addition to static correlation, for the accurate description of SSNO electronic excited states and more generally for those of R-NO molecular species. Finally, we highlighted the potential role of SSNO in light-induced NO delivery from SSNO related species in biological media.

Results are presented that suggest that thiazyl hydride (HSN)/thionitrosyl hydride (sulfimide, HNS) can be used as light-sensitive compounds for NO-delivery in biological media, as well as markers for the possible detection of intermediates in nitrites + H2S reactions at the cellular level. They are expected to be more efficient than the HNO/HON isovalent species and hence they should be considered instead. A set of characteristic spectroscopic features are identified that could aid in the possible detection of these species in the gas phase or in biological environments. The possibility of intramolecular dynamical processes involving excited states that are capable of interconverting HNS and its isomeric form HSN is examined.