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Two ketones of atmospheric interest, methyl glyoxal and methyl vinyl ketone, are studied using explicitly correlated coupled cluster theory and core-valence correlation-consistent basis sets. The work focuses on the far-infrared region. At the employed level of theory, the rotational constants can be determined to within a few megahertz of the experimental data. Both molecules present two conformers, trans/cis and antiperiplanar (A

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

9 pags., 8 figs., 1 tab., 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 H2 molecules. In this paper, we focus on smaller cyclic molecular anion, c-C3H-, an astrophysical candidate, following the detection of larger CnH- carbon chains. From a new three-dimensional potential energy surface, the rotational (de-)excitation of the c-C3H-(X1A1) 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 jKa,Kc = 77,0 of c-C3H- and temperatures ranging from 5 to 100 K. For this collisional system, rate coefficients exhibit a strong dominance in favor of 21,2 → l1,1 downward transition. This transition was previously used for the detection of the cyclic parent c-C3H. The c-C3H-He rate coefficients (∼10-11 cm3 s-1) are of the same order of magnitude as those of the detected anions CnH- (as C2H-, C4H-, and C6H-) in collision with He and one order of magnitude smaller than those with H2. The critical densities of H2 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, CnH, in astrophysical media., This project was funded by the National Plan for Science, Technology and Innovation (MAARIFAH), King Abdulaziz City for Science and Technology, Kingdom of Saudi Arabia, Award No. 1600-100-10-17-2. The authors acknowledge the use of the service of the “SANAM” supercomputer at “King Abdulaziz City for Science and Technology” (KACST), Saudi Arabia.

Quantitative structure-activity relationships and drug-likeness evaluations were investigated for 33 compounds of 1,2-diazole derivatives as anti-mycobacterium tuberculosis. MLR procedures were used to obtain QSAR models. The predictivity of the models was estimated using cross-validation with the leave-one-out method. The results show a high correlation between the experimental and predicted activity values, indicating the good quality of the QSAR model.

Iodine oxide (IO) is an important tropospheric molecule. In the present paper, we mapped the potential energy surfaces (PESs) of the doubly degenerate IO(X-2 pi)-Ar van der Waals system using single- and double-excitation coupled cluster approaches with non-iterative perturbation treatment of triple excitations [RCCSD(T)] extrapolated to the complete basis set (CBS) limit. In addition to bent local minima, we identified a linear Ar-IO complex as a global minimum. Afterwards, we performed scattering calculations on these PESs, considering the non-zero spin-orbit contribution and the Renner-Teller effect. The integral cross-sections exhibit an oscillatory structure vs. the final rotational state, as already observed for the NO(X-2 pi)-Ar system. Moreover, computations reveal that the Ar-IO complex is stable toward dissociation into IO and Ar. Therefore, it can be found in the atmosphere and participates in iodine compound physical chemical processes occurring there.

Herein, a novel Zinc Ferrite nanocubes (ZnFe2O4 NCs) decorated reduced graphene oxide (rGO) nanocomposite have been designed through a sonochemical method. After then, as-synthesized ZnFe2O4 NCs/rGO was characterized by XPS, XRD, HRTEM and EIS. Furthermore, the ZnFe2O4 NCs/rGO nanocomposite modified GCE (glassy carbon electrode) shows excellent electrochemical sensing performance towards biomarker of 4-nitroquinoline N-oxide (4-NQ) with fast detection. 4-NQ is one of the important cancer biomarker. Moreover, the fabricated sensor showed a wide linear window for 4-NQ between 0.025 and 534.12 µM and nanomolar detection limit (8.27 nM). Further, the as-prepared ZnFe2O4 NCs/rGO/GCE has been applied to the determination of 4-NQ in human blood and urine samples with excellent recovery results.

The structure, stability, and adsorption mechanism on the Au(111) surface of hydrophilic/hydrophobic ionic liquids (ILs) with various lengths of the alkyl chain group in the cation were investigate...

Graphical abstract, 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.

10 pags., 4 figs., 5 tabs., Geometric and spectroscopic parameters are determined using explicitly correlated coupled cluster ab initio calculations (CCSD(T)-F12) for five monosubstituted isotopologues of acetone containing 18O, 13C, and D. The far-infrared region is explored with a variational procedure of reduced dimensionality that takes the interconversion of the nine minima of the potential energy surface into consideration. The methyl torsional barrier of the main isotopologue, computed to be 245.7 cm-1, varies slightly with the isotopic substitution. In the monodeuterated species, the two inequivalent internal rotors are hindered by two inequivalent barriers of 244.0 and 244.7 cm-1. The torsional fundamentals of the main variety are localized at 78.636 cm-1 (ν12) and 128.904 cm-1 (ν17). The differences between splitting components are lower than 0.02 and 0.2 cm-1 in the main isotopologue and in the isotopologues containing 18O and 13C, respectively. In the monodeuterated species the subcomponents are separated by ∼15 cm-1., This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie Grant Agreement No. 872081. This research was supported by the Ministerio de Ciencia, Innovación y Universidades of Spain through the Grants EIN2019-103072 and FIS2016-76418-P. This work has received funding from the CSIC i-coop+2018 Program under the Reference Number COOPB20364. The authors acknowledge the CTI (CSIC), CESGA, and the “Red Española de Computación” for Grants AECT-2020-2-0008 and RES-AECT2020-3-0011 for the computing facilities.

The spectra of helium-dominated white dwarf stars with hydrogen in their atmosphere present a distinctive broad feature centered around 1160~\AA\/ in the blue wing of the Lyman-$\alpha$ line. It is extremely apparent in WD 1425+540 recently observed with HST COS. With new theoretical line profiles based on ab initio atomic interaction potentials we show that this feature is a signature of a collision-induced satellite due to an asymptotically forbidden transition. This quasi-molecular spectral satellite is crucial to understanding the asymmetrical shape of Lyman-$\alpha$ seen in this and other white dwarf spectra. Our previous work predicting this absorption feature was limited by molecular potentials that were not adequate to follow the atomic interactions with spectroscopic precision to the asymptotic limit of large separation. A new set of potential energy curves and electronic dipole transition moments for the lowest electronic states of the H--He system were developed to account accurately for the behavior of the atomic interactions at all distances, from the chemical regime within 1~\AA\/ out to where the radiating H atoms are not significantly perturbed by their neighbors. We use a general unified theory of collision-broadened atomic spectral lines to describe a rigorous treatment of hydrogen Lyman-$\alpha$ with these potentials and present a new study of its broadening by radiative collisions of hydrogen and neutral helium. These results enable ab initio modeling of radiative transport in DBA white dwarf atmospheres., Comment: 9 pages, 7 figures

The journal of chemical physics 152(16), 164303 (2020). doi:10.1063/5.0004465, 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., Published by American Institute of Physics, Melville, NY

Herein, we report a super-active electrocatalyst of copper(II) oxide nanoparticles (CuO NPs) decorated functionalized multiwalled carbon nanotubes (CuO NPs@f-MWCNTs) by the ultrasonic method. The as-synthesized CuO NPs@f-MWCNTs was characterized through the FESEM, XPS, XRD and electrochemical impedance spectroscopy (EIS). The combination of highly active CuO NPs and highly conductive f-MWCNTs film with rapid detection enables this nanohybrid to display excellent electrochemical performance towards anesthesia drug. Furthermore, the hybrid electrocatalyst modified SPCE was developed for the determination of flunitrazepam (FTM) for the first time. FTM is important anesthesia drug with high adverse effect in human body. Benefiting from the synergistic reaction of CuO NPs and f-MWCNTs, this nanohybrid exhibited high sensitivity and specificity towards FTM electro-reduction. The CuO NPs@f-MWCNTs film modified SPCE exhibits outstanding electrochemical activity including excellent reproducibility, wide linear range from 0.05 to 346.6 µM with nanomolar limit of detection for FTM detection. Further, the as-modified CuO NPs@f-MWCNTs/SPCE has been applied to determination of FTM in biological and drug samples with satisfactory recovery results, thereby showing a notable potential for extensive (bio) sensor applications.

Herein, a novel Zinc Ferrite nanocubes (ZnFe

We report here the facile synthesis of a new series of hydroxy-thioxo-imidazole carboxylates in good yields using the cyanomethyl anion as an electrogenerated base which is formed when dry acetonitrile is electrolyzed at constant current, followed by addition of different thioureas and diazirine-3,3-dicarboxylate. The mechanism of the reaction, NMR shifts and IR are discussed and compared to density functional theory calculations.

Carbon disulfide is a prototype molecular system for studies of photophysical processes in molecules at different time scales and is also relevant to astrophysics. Here, reliable molecular properties are computed for linear SCS, bent

International audience; Using multi configurational ab initio methodologies, we compute the potential energy curves (PECs) of the lowest electronic states of the diatomic CsS. These computations are performed using internally contracted multi reference interaction configuration including Davidson correction (MRCI+Q) with and without considering spin-orbit effects. The shapes of the PECs are governed by the interactions between the two ionic states, 2+ and 2, correlating at large internuclear separations (RCsS) to the first ionic dissociation limit and the other electronic states correlating to the three lowest neutral dissociation limits. Computations show the importance of considering large amount of electron correlation for the accurate description of the PECs and spectroscopy of this molecular system. As expected, these PECs are also strongly affected by the spin-orbit interaction. For the bound states, we report a set of spectroscopic parameters including equilibrium distances, dissociation energies, vibrational and rotational constants. The effects of spin-orbit-induced changes on these parameters are also discussed. Moreover, we show that the 22 state presents a “bowl” potential with a rather flat region extending to large RCsS distances. After being promoted to this state, wavepackets should undergo strong oscillations, similar to those observed by Zewail and co-workers for the NaI molecule. These should provide information on the shape of the PEC for the 22 state and also on the couplings between this and the neighbouring states.

The stable isomers and electronic states of [S,S,N,O]

High-level ab initio electronic structure calculations were performed to characterize SNP isomers. In addition to the known linear SNP, cyc-PSN, and linear SPN isomers, we identified a fourth isomer, linear PSN, which is located ∼2.4 eV above the linear SNP isomer. The low-lying singlet and triplet electronic states of the linear SNP and SPN isomers were investigated using a multi-reference configuration interaction method and large basis set. Several bound electronic states were identified. However, their upper rovibrational levels were predicted to pre-dissociate, leading to S + PN, P + NS products, and multi-step pathways were discovered. For the ground states, a set of spectroscopic parameters were derived using standard and explicitly correlated coupled-cluster methods in conjunction with augmented correlation-consistent basis sets extrapolated to the complete basis set limit. We also considered scalar and core-valence effects. For linear isomers, the rovibrational spectra were deduced after generation of their 3D-potential energy surfaces along the stretching and bending coordinates and variational treatments of the nuclear motions.

The journal of chemical physics 148(1), 1-13 (2018). doi:10.1063/1.5009011, Published by American Institute of Physics, Melville, NY

International audience; Adenine, a DNA base, exists as several tautomers and isomers that are closely lying in energy and that may form a mixture upon vaporization of solid adenine. Indeed, it is challenging to bring adenine into the gas phase, especially as a unique tautomer. The experimental conditions were tuned to prepare a jet-cooled canonical adenine (9H-adenine). This isolated DNA base was ionized by single VUV photons from a synchrotron beamline and the corresponding slow photoelectron spectrum was compared to ab initio computations of the neutral and ionic species. We report the vibronic structure of the X+ 2A′′ (D0), A+ 2A′ (D1) and B+ 2A′′ (D2) electronic states of the 9H adenine cation, from the adiabatic ionization energy (AIE) up to AIE + 1.8 eV. Accurate AIEs are derived for the 9H-adenine ([X with combining tilde] 1A′) + hν → 9H-adenine+ (X+ 2A′′, A+ 2A′, B+ 2A′′) + e− transitions. Close to the AIE, we fully assign the rich vibronic structure solely to the 9H-adenine (X 1A′) + hν → 9H-adenine+ (X+ 2A′′) transition. Importantly, we show that the lowest cationic electronic states of canonical adenine are coupled vibronically. The present findings are important for understanding the effects of ionizing radiation and the charge distribution on this elementary building block of life, at ultrafast, short, and long timescales.

Density Functional Theory (BMK and B3LYP) and ab initio complete basis set (CBS-QB3) methods are used to study the stability order and tautomerization processes of all possible 37 tetraphosphoadenine tautomers in the gas phase for the first time. Adiabatic ionization energy (IE) and electron affinity (EA) of all tetraphosphoadenine tautomers were computed at B3LYP/6–311 + G(d,p) level of theory at 0 K. Positive calculated EA values suggest that the tetraphosphoadenine molecule is an attractive candidate for electron capture. It has been found that all tautomers of tetraphosphoadenine exists within the energy range of 0–150 kJ mol −1 . Similar to adenine, canonical tautomers PA7 and PA9 of tetraphosphoadenine are shown to be the most stable tautomeric forms as predicted by all of the above computational methods. The transition states for the tetraphosphadenine tautomerization processes were investigated for selected systems at B3LYP/6–311 + G(d,p) level of theory in the gas phase. Energy barrier for the proton transfer processes of tetraphosphadenine, is up to 97 kJ mol −1 . Dipole moment, full atomic natural charges and bond orders have been computed and discussed.

8 pags, 2 figs., 3 tabs., This work emphasizes the stability of CN linear carbon chains and carbon clusters containing three-body rings. CN possesses at least 44 neutral isomers and 38 and 35 isomers with a negative or a positive charge. The lowest-energy structures, which can be candidates for laboratory and astrophysical detection, were studied with RCCSD(T)-F12 and MRCI/CASSCF, specifying properties for various electronic states. Neutral CN displays two prominent equilibrium structures, a nitrogen-terminated linear form (XΠ) and a form (XB) containing a three-carbon ring. They are separated by 0.21 eV. For the linear one, Renner-Teller and spin-orbit effects are expected. Its equilibrium spin-orbit constant |A|was predicted to be 29.09 cm, the dipole moment was computed to be 0.2059 D, and B was computed to be 868.20 MHz, very close to the experimental value (B(exp)-B(calc) ∼ 4.9 MHz). The anion presents two stable forms, a linear triplet (XΣ) and a (XA) isomer, whereas for the cation most stable structures are both linear. For the linear anion and the two linear cations B was estimated to be 870.05 MHz, 875.72 MHz, and 917.36 MHz and μ was estimated to be 4.4200 D, 4.2013D, and 0.7828D. For the neutral form, Ae = 45048.74 MHz, Be = 1062.78 MHz, Ce = 1038.30 MHz, and μ = 0.8840 D, whereas for the negative form, Ae = 40087.48 MHz, Be = 1067.35 MHz, Ce = 1039.67 MHz, and μ = 6.2854 D. Below the electron affinity of the most stable isomer (EA = -3.42 eV), the linear anion displays three probably existing electronic states. Detectability is discussed in terms of the symmetry and spin multiplicity of the ground electronic states., The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at king Saud University for funding research group No. (RGP-333), the MINECO of Spain for the grants FIS2013-40626-P and FIS2016-76418-P, and the COST Actions CM1401 “Our Astrochemical History” and CM1405 “MOLIM.” This work is supported by the French National Research Agency through the project Anion Cos Chem (ANR-14-CE33-0013). The authors acknowledge the CTI (CSIC) and CESGA for computing facilities.

The hydroxymethyl peroxy (HMOO) radical is a product of the oxidation of non-methane hydrocarbons. The present study provides the first accurate computational determination of critical spectroscopic features of the title radical that should aid in its experimental characterization. Structure, energetics, vibrational frequencies, and rotational parameters are reported for the three stable isomers on the ground electronic state of HMOO. While preliminary computations have been carried out using density functional theory as well as second-order Møller-Plesset perturbation theory, for the accurate structural and spectroscopic characterization we made use of coupled-cluster techniques, herewith considering both standard and explicitly correlated methods. The "CCSD(T)/CBS + CV" composite scheme, a state-of-the-art composite approach based on the coupled-cluster theory including single and double excitations together with a perturbative treatment of triples that accounts for extrapolation to the complete basis-set limit as well as core-valence correlation effects, is used to obtain accurate structural and energetic data, in particular for the decomposition reaction to HO

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.

We demonstrated the time-resolved dynamics of laser action from the conductive oligomer (CO) 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). Absorption and fluorescence spectra were studied for BECV-DHF in different solvents under a wide range of concentrations. The Fourier-transform infrared spectroscopy (FTIR) spectrum was measured using simulation and experiments. The Ultraviolet-Visible (UV-VIS) spectra of the BECV-DHF were simulated in two different solutions. This CO formed a dimer and had two vibration bands in nonpolar solvents, partially dissolved in polar protic solvents, and created an H-type aggregate in polar aprotic solvents. BECV-DHF produced amplified spontaneous emission (ASE) at 464 nm in many solvents. The high efficiency of ASE is due to the waveguiding and self-assembly nature of the oligomer, which is very rare for optically pumped systems. However, BECV-DHF did not produce ASE in polar protic solvents. BECV-DHF produced ASE in both longitudinal and transverse pumping, and the full-width half maximum (FWHM) was 4 nm and 8 nm respectively for different solvents, such as toluene and acetone. The CO had a very low threshold pump energy (~0.5 mJ). The ASE efficiency was approximately 20%. The time-resolved spectroscopy (TRS) studies showed a temporal Gaussian-shaped ASE output from this CO. BECV-DHF shows remarkably high stability compare to the conjugated polymer (CP) PFO-co-pX.

8 pags., 4 figs., 4 tabs., Spectroscopic and structural properties of methoxymethyl radical (CH3OCH2, RDME) are determined using explicitly correlated ab initio methods. This radical of astrophysical and atmospheric relevance has not been fully characterized at low temperatures, which has delayed astrophysical research. We provide rovibrational parameters, excitations to the low energy electronic states, torsional and inversion barriers, and low vibrational energy levels. In the electronic ground state (X2A), which appears “clean” from nonadiabatic effects, the minimum energy structure is an asymmetric geometry whose rotational constants and dipole moment have been determined to be A0 = 46 718.67 MHz, B0 = 10 748.42 MHz, and C0 = 9272.51 MHz, and 1.432D (μA = 0.695D, µB = 1.215D, µC = 0.302D), respectively. A variational procedure has been applied to determine torsion-inversion energy levels. Each level splits into 3 subcomponents (A1/A2 and E) corresponding to the three methyl torsion minima. Although the potential energy surface presents 12 minima, at low temperatures, the infrared band shapes correspond to a surface with only three minima because the top of the inversion Vα barrier at α = 0° (109 cm−1) stands below the zero point vibrational energy and the CH2 torsional barrier is relatively high (∼2000 cm−1). The methyl torsion barrier was computed to be ∼500 cm−1 and produces a splitting of 0.01 cm−1 of the ground vibrational state., This research was supported by the FIS2016-76418-P project of the “Ministerio de Ciencia, Innovación y Universidades” of Spain and the CSIC i-coop 2018 programme No COOPB20364. The authors acknowledge the COST Actions CM1401 “Our Astrochemical History” and CM1405 “MOLIM.” The calculations have been performed in the CESGA and CTI-CSIC computer centers. M.C. also acknowledges the financial support from the Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía, and European Regional Development Fund (ERDF), ref. SOMM17/6105/UGR.

Novel 1,3-bis(N 1 -4-amino-6-methoxypyrimidine-benzenesulfonamide-2,2,4,4-ethane-1,2-dithiol)-2,4-dichlorocyclodiphosph(V)azane (L), was prepared and their coordinating behavior towards the lanthanide ion Er(III) was studied. The structures of the isolated products are proposed based on elemental analyses, IR, UV–VIS., 1 H NMR, 13 C NMR, 31 P NMR, SEM, XRD, mass spectra, effective magnetic susceptibility measurements and thermogravimetric analysis (TGA). Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of L and its binuclear Er(III) complex. Different tautomers of the ligand were optimized at the ab initio DFT level. Keto-form structure is about 17.7 kcal/mol more stable than the enol form (taking zpe correction into account). Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV–VIS spectra which compared by the measured electronic spectra.

Novel hexachlorocyclophosph(V)azane of sulfamonomethoxine (L), was prepared and their coordinating behavior toward the lanthanide ion erbium (III) was studied. The structures of the isolated products were proposed based on elemental analyses, IR, UV–VIS, 1 H NMR, 31 P NMR, SEM, TEM, XRD, mass spectra, effective magnetic susceptibility measurements and thermogravimetric analysis (TGA). The coordination polyhedra of the eight donor atoms around the two erbium (III) ions are best described as distorted dodecahedral. Computational studies were carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of L and its binuclear erbium (III) complex. Different tautomers of the ligand were optimized at the ab initio DFT level. Keto-form structure is about 30.5 kcal/mol more stable than the enol form (taking zpe correction into account). Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV–VIS spectra in gas phase and DMF.

International audience; Biological entities, such as DNA bases or proteins, possess numerous tautomers and isomers that lie close in energy, making the experimental characterization of a unique tautomer challenging. We apply VUV synchrotron-based experiments combined with state-of-the-art ab initio methodology to determine the adiabatic ionization energies (AIEs) of specific gas-phase cytosine tautomers produced in a molecular beam. The structures and energetics of neutral and cationic cytosine tautomers were determined using explicitly correlated methods. The experimental spectra correspond to well-resolved bands that are attributable to the specific contributions of five neutral tautomers of cytosine prior to ionization. Their AIEs are experimentally determined for the first time with an accuracy of 0.003 eV. This study also serves as an important showcase for other biological entities presenting a dense pattern of isomeric and tautomeric forms in their spectra that can be investigated to understand the charge redistribution in these species upon ionization.

We report the results of a detailed theoretical study of the electronic ground and excited states of the gas-phase doubly charged ion AlO2+ using high-level ab initio computer calculations. Both standard and explicitly correlated methods were used to calculate their potential energy curves and spectroscopic parameters. These computations show that the ground state of AlO2+ is X2Π. The internuclear equilibrium distance of AlO2+(X2Π) is computed 1.725 A. We also deduced the adiabatic double ionization and charge stripping energies of AlO to be about 27.45 eV and 17.80 eV, respectively.

Ab initio methods in conjunction with a large basis set are used to compute the potential energy surfaces of the 12 lowest electronic states of the HNS(+) and HSN(+) isomeric forms. These potentials are used in discussions of the metastability of these cations and plausible mechanisms for the H(+)/H + SN(+)/SN, S/S(+) + NH(+)/NH, N/N(+) + SH(+)/SH ion-molecule reactions. Interestingly, the low rovibrational levels of HSN(+)(1(2)A″) and HNS(+)(1(2)A″) electronically excited ions are predicted to be long-lived. Both ions are suggested to be a suitable candidate for light-sensitive NO(⋅) donor in vivo and as a possible marker for the detection of intermediates in nitrites + H2S reactions at the cellular level. The full spin rovibronic levels of HNS(+) are presented, which may assist in the experimental identification of HNS(+) and HSN(+) ions and in elucidating their roles in astrophysical and biological media.

International audience

Using first-principles methodologies, the equilibrium structures and the relative stability of CO2 @[Zn(q+) Im] (where q=0, 1, 2; Im=imidazole) complexes are studied to understand the nature of the interactions between the CO2 and Zn(q+) -imidazole entities. These complexes are considered as prototype models mimicking the interactions of CO2 with these subunits of zeolitic imidazolate frameworks or Zn enzymes. These computations are performed using both ab initio calculations and density functional theory. Dispersion effects accounting for long-range interactions are considered. Solvent (water) effects were also considered using a polarizable continuum model approach. Natural bond orbital, charge, frontier orbital and vibrational analyses clearly reveal the occurrence of charge transfer through covalent and noncovalent interactions. Moreover, it is found that CO2 can adsorb through more favorable π-type stacking as well as σ-type hydrogen-bonding interactions. The inter-monomer interaction potentials show a significant anisotropy that might induce CO2 orientation and site-selectivity effects in porous materials and in active sites of Zn enzymes. Hence, this study provides valuable information about how CO2 adsorption takes place at the microscopic level within zeolitic imidazolate frameworks and biomolecules. These findings might help in understanding the role of such complexes in chemistry, biology and material science for further development of new materials and industrial applications.

Carbon disulfide is a prototype molecular system for studies of photophysical processes in molecules at different time scales and is also relevant to astrophysics. Here, reliable molecular properties are computed for linear SCS, bent cyc-CS2, and linear CSS forms using highly correlated post Hartree-Fock methods in conjunction with large basis sets. Structures are identified using explicitly correlated and standard coupled cluster techniques. Evolution of the lowest-lying singlet and triplet electronic states of the three isomers along the SS and CS stretching coordinates and along the bending angle are mapped at the multireference configuration interaction (MRCI)/aug-cc-pV(5+d)Z level of theory. The computations suggest that the 1B2(1Σ+) electronic state of the SCS isomer plays an important role in the photoconversion of CS2 to cyc-CS2 and CSS. Photoconversion competes with photodissociation. Plausible mechanisms for the production of S2 and CS diatomics after the photoexcitation of SCS are proposed. To aid in the identification of CSS in the laboratory and in astrophysical media, a set of spectroscopic constants and rovibrational levels for CSS are reported.

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.

The state-to-state photodissociation of CO2 is investigated in the VUV range of 11.94-12.20 eV by using two independently tunable vacuum ultraviolet (VUV) lasers and the time-sliced velocity-map-imaging-photoion (VMI-PI) method. The spin-allowed CO(X(1)Σ(+); v = 0-18) + O((1)D) and CO(X(1)Σ(+); v = 0-9) + O((1)S) photoproduct channels are directly observed from the measurement of time-sliced VMI-PI images of O((1)D) and O((1)S). The total kinetic energy release (TKER) spectra obtained based on these VMI-PI images shows that the observed energetic thresholds for both the O((1)D) and O((1)S) channels are consistent with the thermochemical thresholds. Furthermore, the nascent vibrational distributions of CO(X(1)Σ(+); v) photoproducts formed in correlation with O((1)D) differ significantly from that produced in correlation with O((1)S), indicating that the dissociation pathways for the O((1)D) and O((1)S) channels are distinctly different. For the O((1)S) channel, CO(X(1)Σ(+); v) photoproducts are formed mostly in low vibrational states (v = 0-2), whereas for the O((1)D) channel, CO(X(1)Σ(+); v) photoproducts are found to have significant populations in high vibrationally excited states (v = 10-16). The anisotropy β parameters for the O((1)D) + CO(X(1)Σ(+); v = 0-18) and O((1)S) + CO(X(1)Σ(+); v = 0-9) channels have also been determined from the VMI-PI measurements, indicating that CO2 dissociation to form the O((1)D) and O((1)S) channels is faster than the rotational periods of the VUV excited CO2 molecules. We have also calculated the excited singlet potential energy surfaces (PESs) of CO2, which are directly accessible by VUV excitation, at the ab initio quantum multi-reference configuration interaction level of theory. These calculated PESs suggest that the formation of CO(X(1)Σ(+)) + O((1)S) photoproducts occurs nearly exclusively on the 4(1)A' PES, which is generally repulsive with minor potential energy ripples along the OC-O stretching coordinate. The formation of CO(X(1)Σ(+)) + O((1)D) photofragments can proceed by non-adiabatic transitions from the 4(1)A' PES to the lower 3(1)A' PES of CO2via the seam of conical intersections at a near linear OCO configuration, followed by the direct dissociation on the 3(1)A' PES. The theoretical PES calculations are consistent with the experimental observation of prompt CO2 dissociation and high rotational and vibrational excitations for CO(X(1)Σ(+)) photoproducts.

We report on the vibronic structure of the ground state X̃(2)A″ of the thymine cation, which has been measured using a threshold photoelectron photoion coincidence technique and vacuum ultraviolet synchrotron radiation. The threshold photoelectron spectrum, recorded over ∼0.7 eV above the ionization potential (i.e., covering the whole ground state of the cation) shows rich vibrational structure that has been assigned with the help of calculated anharmonic modes of the ground electronic cation state at the PBE0/aug-cc-pVDZ level of theory. The adiabatic ionization energy has been experimentally determined as AIE = 8.913 ± 0.005 eV, in very good agreement with previous high resolution results. The corresponding theoretical value of AIE = 8.917 eV has been calculated in this work with the explicitly correlated method/basis set (R)CCSD(T)-F12/cc-pVTZ-F12, which validates the theoretical approach and benchmarks its accuracy for future studies of medium-sized biological molecules.

We treat theoretically 2-quinolinol(lactam), an analog of carbostyril and DNA bases. We characterized the ground state structure of 2-quinolinol and its isomer(lactim) using density functional theory(DFT). The reaction profile and energetics for lactam–lactim tautomerization and cis -lactim to trans -lactim isomerization predicted with explicitly correlated methods. We explored the pattern of the lowest singlet and triplet manifolds of states and electronic S 1 ← S 0 transitions using multiconfigurational methodologies. The theoretical results are compared with available experimental data and used to interpret the on-going photoelectron study of 2-quinolinol. Our analysis should help to understand the effect of tautomerism and aromaticity on the DNA bases.