Predicting the structure and vibrational frequencies of ethylene using harmonic and anharmonic approaches at the Kohn-Sham complete basis set limit

Experimental and theoretical characterization of chelidonic acid structure

Chelidonic acid (4-oxo-4H-pyran-2,6-dicarboxylic acid) is present in plants of Papaveraceae family, especially in Chelidonium majus. Due to its anticancer, antibacterial, hepatoprotective, and antioxidant properties, it has been used in medical treatments. In this work, the X-ray structure of methanol solvate of chelidonic acid was determined. Layers of chelidonic acid are held by hydrogen bonds via COOH and C = O fragments and additionally bridged by methanol. The formed H-bond network between two acid units is different from typical –COOH dimers observed, e.g., in crystals of isophtalic acid. The molecular structure of 2,6-dimethyl-γ-pyrone (2Me4PN) and chelidonic acid, a 2,6-dicarboxylic derivate of γ-pyrone (4PN), was verified in silico using density functional theory (DFT-B3LYP) combined with large correlation-consistent basis sets. The impact of –CH3 and –COOH substituents on 4PN ring structure, dipole moments, geometric/magnetic indexes of aromaticity, and NBO charges was assessed following unconstrained geometry optimization in the gas phase, chloroform, methanol, DMSO, and water with solvent effect introduced using the polarized continuous model (PCM). H-bond network formed in chelidonic acid–methanol complex was analyzed and their interaction energy estimated. Theoretical modeling enabled prediction of accurate structural parameters, dipole moments, and geometric/magnetic indexes of aromaticity of the studied 4PN, 2Me4PN, and chelidonic acid molecules.

Weakly Bound Complex Formation between HCN and CH3Cl: A Matrix-Isolation and Computational Study

The matrix-isolated infrared spectrum of a hydrogen cyanide-methyl chloride complex was investigated in a solid argon matrix. HCN and CH₃Cl were co-condensed onto a substrate held at 10 K with an excess of argon gas, and the infrared spectrum was measured using Fourier-transform infrared spectroscopy. Quantum chemical geometry optimization, harmonic frequency, and natural bonding orbital calculations indicate stabilized hydrogen- and halogen-bonded structures. The two resulting weakly bound complexes are both composed of one CH₃Cl molecule bound to a (HCN)₃ subunit, where the three HCN molecules are bound head-to-tail in a ring formation. Our study suggests that─in the presence of CH₃Cl─the formation of (HCN)₃ is promoted through complexation. Since HCN aggregates are an important precursor to prebiotic monomers (amino acids and nucleobases) and other life-bearing polymers, this study has astrophysical implications toward the search for life in space.

On the impact of side methyl groups on the structure and vibrational properties of β-carotenoids. The case of butadiene and isoprene

Theoretical consideration about the impact of methyl groups on the structure and vibrational properties of β-carotenoids, using medium size molecules of trans-butadiene and trans-isoprene, are reported. Density functional theory (DFT) calculations with correlation-consistent and polarization-consistent basis sets were applied to trans-1,3-butadiene and trans-isoprene as the smallest building bricks of β-carotenoids. Their structure and harmonic vibrations were estimated in the complete basis set limit (CBS) using the non-linear least square fit. Optimized geometries and harmonic frequencies, obtained with B3LYP and BLYP density functionals and large basis sets, were favorably reproduced by a significantly faster approach, using a recently modified STO(1M)-3G Slater-type basis set. Selected density functionals with STO(1M)-3G and 6-311++G** basis sets were also successful in predicting β-carotene structures and harmonic vibrations. This work demonstrates the potential applicability of the proposed level of theory for larger molecules, including β-carotenoids, present in numerous natural food sources. The proposed scheme of molecular modeling, applied to biologically active compounds in food, could provide a deeper insight into their function in vivo, which is directly related to their structure and spectroscopic properties. It could also support the experimental qualitative analysis, based on peak assignment of β-carotenoids in various food sources.

Dehydrogenation of Ethylene on Supported Palladium Nanoparticles: A Double View from Metal and Hydrocarbon Sides

Adsorption of ethylene on palladium, a key step in various catalytic reactions, may result in a variety of surface-adsorbed species and formation of palladium carbides, especially under industrially relevant pressures and temperatures. Therefore, the application of both surface and bulk sensitive techniques under reaction conditions is important for a comprehensive understanding of ethylene interaction with Pd-catalyst. In this work, we apply in situ X-ray absorption spectroscopy, X-ray diffraction and infrared spectroscopy to follow the evolution of the bulk and surface structure of an industrial catalysts consisting of 2.6 nm supported palladium nanoparticles upon exposure to ethylene under atmospheric pressure at 50 °C. Experimental results were complemented by ab initio simulations of atomic structure, X-ray absorption spectra and vibrational spectra. The adsorbed ethylene was shown to dehydrogenate to C2H3, C2H2 and C2H species, and to finally decompose to palladium carbide. Thus, this study reveals the evolution pathway of ethylene on industrial Pd-catalyst under atmospheric pressure at moderate temperatures, and provides a conceptual framework for the experimental and theoretical investigation of palladium-based systems, in which both surface and bulk structures exhibit a dynamic nature under reaction conditions.

Direct Trace Fitting of Experimental Data Using the Master Equation: Testing Theory and Experiments on the OH + C2H4 Reaction

Laser flash photolysis coupled with laser-induced fluorescence observation of OH has been used to observe the equilibration of OH + C₂H₄ ↔ HOC₂H₄ over the temperature range 563-723 K and pressures of bath gas (N₂) from 58 to 250 Torr. The time-resolved OH traces have been directly and globally fitted with a master equation in order to extract Δ_RH₀⁰, the binding energy of the HOC₂H₄ adduct, with respect to reagents. The global approach allows the role that OH abstraction plays at higher temperatures to be identified. The resultant value ofΔ_RH₀⁰, 111.8 kJ mol^-1, is determined to be better than 2 kJ mol^-1 and is in agreement with our ab initio calculations (carried out at the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level), 111.4 kJ mol^-1, and other state of the art calculations. Parameters for the abstraction channel are also in good agreement with previous experimental studies. To effect this analysis, the MESMER master equation code was extended to directly incorporate secondary chemistry: diffusional loss from the observation region and reaction with the photolytic precursor. These extensions, which, among other things, resolve issues related to the merging of chemically significant and internal energy relaxation eigenvalues, are presented.

A comprehensive study on crystal structure of a novel sulfonamide-dihydroquinolinone through experimental and theoretical approaches

Quinolinones and sulfonamides are moieties with biological potential that can be linked to form new hybrid compounds with improved potential. However, there are few hybrids of these molecules reported. In this sense, this work presents a structural description of a new sulfonamide-dihydroquinolinone (E)-2-(2-methoxyphenyl)-3-(3-nitrobenzylidene)-1-(phenylsulfonyl)-2,3 dihydroquinolin-4(1H)-one (DHQ). The molecular structure of DHQ was elucidated by X-ray diffraction, nuclear magnetic resonance and infrared spectroscopy, and both molecular packing and intermolecular interactions were analyzed by Hirshfeld surfaces and fingerprint maps. In addition, theoretical calculations on frontier orbitals, molecular electrostatic potential maps, and assignments were performed. The crystal packing of DHQ was found to be stabilized by a dimer through a weak C-H⋯O interaction along the c axis. Moreover, the structure is stabilized mainly by C-H⋯O and C-H⋯π interactions, since the interaction C25-H25⋯π contributes to a chain formation. The Hirshfeld normalized surface shows that the closest interactions are around the atoms linked to the dimer formation. The calculations indicate that DHQ possesses electrophilic sites near O atoms and depleted electrons around the H atoms. There is a band GAP of 3.29 eV between its frontier orbitals, which indicates that DHQ is more reactive than other analogues published.

Analysis of two novel 1-4 quinolinone structures with bromine and nitrobenzyl ligands

The scientific community has shown particular interest in the study of quinolinones-a class of bicyclic organic compounds. An example of these compounds are the 4-quinolinones, considered to be very useful building blocks, since they can adapt their molecular structures with different ligands for applications in various fields such as pharmacy, medicine, physics and engineering. The compounds (E)-3-(benzylidene)-2-(3-nitrophenyl)-2,3-dihydro-1-(phenylsulfonyl)-quinolin-4-(1H)-one (NFQ) and (E)-3-(benzylidene)-2-(4-bromophenyl)-2,3-dihydro-1-(phenylsulfonyl) quinolin-4-(1H)-one (BFQ) were synthesized and characterized by infrared spectroscopy, ¹H and ¹³C NMR, and melting point. NFQ crystallized in the orthorhombic Pbca space group while BFQ appears in the monoclinic P2₁/n space group. X-ray diffraction was used to evaluate their crystallographic structures, and Hirshfeld surface evaluates the intermolecular interactions, supramolecular arrangement and packaging. Theoretical vibrational assignments and calculated electronic properties also demonstrate acceptable agreement between experimental and theoretical results.

Calculation of 15N NMR chemical shifts: Recent advances and perspectives

Recent advances in computation of ¹⁵N NMR chemical shifts are reviewed, concentrating mainly on practical aspects of computational protocols and accuracy factors. The review includes the discussion of the level of theory, the choice of density functionals and basis sets together with taking into account solvent effects, rovibrational corrections and relativistic effects. Computational aspects of ¹⁵N NMR are illustrated for the series of neutral and protonated open-chain nitrogen-containing compounds and nitrogen heterocycles, coordination and intermolecular complexes.

The vibrational properties of the bee-killer imidacloprid insecticide: A molecular description

The chemical imidacloprid belongs to the neonicotinoids insecticide class, widely used for insect pest control mainly for crop protection. However, imidacloprid is a non-selective agrochemical to the insects and it is able to kill the most important pollinators, the bees. The high toxicity of imidacloprid requires controlled release and continuous monitoring. For this purpose, high performance liquid chromatography (HPLC) is usually employed; infrared and Raman spectroscopy, however, are simple and viable techniques that can be adapted to portable devices for field application. In this communication, state-of-the-art quantum level simulations were used to predict the infrared and Raman spectra of the most stable conformer of imidacloprid. Four molecular geometries were investigated in vacuum and solvated within the Density Functional Theory (DFT) approach employing the hybrid meta functional M06-2X and the hybrid functional B3LYP. The M062X/PCM model proved to be the best to predict structural features, while the values of harmonic vibrational frequencies were predicted more accurately using the B3LYP functional.

Thermodynamic DFT analysis of natural gas

Density functional theory was performed for thermodynamic predictions on natural gas, whose B3LYP/6-311++G(d,p), B3LYP/6-31+G(d), CBS-QB3, G3, and G4 methods were applied. Additionally, we carried out thermodynamic predictions using G3/G4 averaged. The calculations were performed for each major component of seven kinds of natural gas and to their respective air + natural gas mixtures at a thermal equilibrium between room temperature and the initial temperature of a combustion chamber during the injection stage. The following thermodynamic properties were obtained: internal energy, enthalpy, Gibbs free energy and entropy, which enabled us to investigate the thermal resistance of fuels. Also, we estimated an important parameter, namely, the specific heat ratio of each natural gas; this allowed us to compare the results with the empirical functions of these parameters, where the B3LYP/6-311++G(d,p) and G3/G4 methods showed better agreements. In addition, relevant information on the thermal and mechanic resistance of natural gases were investigated, as well as the standard thermodynamic properties for the combustion of natural gas. Thus, we show that density functional theory can be useful for predicting the thermodynamic properties of natural gas, enabling the production of more efficient compositions for the investigated fuels. Graphical abstract Investigation of the thermodynamic properties of natural gas through the canonical ensemble model and the density functional theory.

SEI-forming electrolyte additives for lithium-ion batteries: development and benchmarking of computational approaches

SEI-forming additives play an important role in lithium-ion batteries, and the key to improving battery functionality is to determine if, how, and when these additives are reduced. Here, we tested a number of computational approaches and methods to determine the best way to predict and describe the properties of the additives. A wide selection of factors were evaluated, including the influences of the solvent and lithium cation as well as the DFT functional and basis set used. An optimized computational methodology was employed to assess the usefulness of different descriptors.

Quantum chemical and spectroscopic investigations of 4-Hydroxy-7-methyl-1,8-naphthyridine-3-carboxylic acid

The FTIR (4000–400[Formula: see text]cm[Formula: see text]) and the FT-Raman spectra (4000–50[Formula: see text]cm[Formula: see text]) of 4-Hydroxy-7-methyl-1,8-naphthyridine-3-carboxylic acid are recorded and investigated. The spectra are interpreted using anharmonic frequency computations by VPT2, VSCF and PT2-VSCF methods within DFT/6-311G(d,p) framework. The root mean square (RMS) values indicate that VSCF computed frequencies are in close agreement with the observed frequencies. The combination and overtone bands are also identified in the FTIR spectrum. The intermolecular O-H[Formula: see text]O hydrogen bonding interactions are discussed in the dimer structure of the molecule. The magnitudes of the coupling between pair of modes are also computed. The electronic spectra in water and ethanol solvents are analyzed using TD-B3LYP/6-311[Formula: see text]G(d,p) level of theory. Molecular electrostatic potential (MEP) and HOMO-LUMO analysis are also performed.

DFT studies on the structural and vibrational properties of polyenes

Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C = C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae. BLYP/6-311++G** calculated ν(C = C) and ν(C-C) frequencies for all-trans and all-cis polyenes containing up to 14 carbon-carbon double bonds were used to estimate these values for very long chains. Correction of raw, unscaled vibrational data was performed by comparing theoretical and experimental wavenumbers for polyenes chains containing 3 to 12 conjugated C = C units with both ends substituted by tert-butyl groups. The corrected ν(C = C) and ν(C-C) wavenumbers for all-trans molecules were used to estimate the presence of 9 - 12 C = C units in all-trans polyene pigment in red coral.