Quantum Chemical Structure Research Articles

Computational Screening of T-Muurolol for an Alternative Antibacterial Solution against Staphylococcus aureus Infections: An In Silico Approach for Phytochemical-Based Drug Discovery.

Staphylococcus aureus infections present a significant threat to the global healthcare system. The increasing resistance to existing antibiotics and their limited efficacy underscores the urgent need to identify new antibacterial agents with low toxicity to effectively combat various S. aureus infections. Hence, in this study, we have screened T-muurolol for possible interactions with several S. aureus-specific bacterial proteins to establish its potential as an alternative antibacterial agent. Based on its binding affinity and interactions with amino acids, T-muurolol was identified as a potential inhibitor of S. aureus lipase, dihydrofolate reductase, penicillin-binding protein 2a, D-Ala:D-Ala ligase, and ribosome protection proteins tetracycline resistance determinant (RPP TetM), which indicates its potentiality against S. aureus and its multi-drug-resistant strains. Also, T-muurolol exhibited good antioxidant and anti-inflammatory activity by showing strong binding interactions with flavin adenine dinucleotide (FAD)-dependent nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase, and cyclooxygenase-2. Consequently, molecular dynamics (MD) simulation and recalculating binding free energies elucidated its binding interaction stability with targeted proteins. Furthermore, quantum chemical structure analysis based on density functional theory (DFT) depicted a higher energy gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital (EHOMO-LUMO) with a lower chemical potential index, and moderate electrophilicity suggests its chemical hardness and stability and less polarizability and reactivity. Additionally, pharmacological parameters based on ADMET, Lipinski's rules, and bioactivity score validated it as a promising drug candidate with high activity toward ion channel modulators, nuclear receptor ligands, and enzyme inhibitors. In conclusion, the current findings suggest T-muurolol as a promising alternative antibacterial agent that might be a potential phytochemical-based drug against S. aureus. This study also suggests further clinical research before human application.

Crystal structure, theoretical calculations, mechanoluminescence feature and antimicrobial activity based on a double-armed Salamo-type ligand and its trinuclear Cu(Ⅱ) complex

A double-armed salamo-type ligand H4L and its Cu(Ⅱ) complex have been designed and synthesized. The stoichiometric ratios of the prepared H4L and its Cu(Ⅱ) complex were structurally characterized by a variety of analytical and spectroscopic techniques, including elemental analysis, FT-IR, UV–visible, fluorescence spectroscopy, and X-ray crystal diffraction. The results showed that H4L is a linear molecule, while the Cu(Ⅱ) complex is a trinuclear structure with three copper atoms exhibiting different coordination modes due to varying coordination cavities and bridging atoms. The quantum chemical parameters and molecular structures of the H4L and the Cu(Ⅱ) complex have been theoretically calculated and studied. Using molecular electrostatic potential (MEP) and density functional theory (DFT) calculations to understand the selectivity of the H4L and the Cu(Ⅱ) complex chemistry and related reactions. Detailed energy level transitions of the H4L and the Cu(Ⅱ) complex can be determined through time-dependent density functional theory (TD-DFT) calculations. In studying the fluorescence properties of liquid and solid states, it was observed that increasing water content leads to the formation of excimer in both the H4L and its Cu(Ⅱ) complex, the ligand H4L shown good mechanoluminescence, but the Cu(Ⅱ) complex did not. We studied the antimicrobial effectiveness of the H4L and the Cu(Ⅱ) complex against E. coli., the Cu(Ⅱ) complex showed higher inhibition of the pathogenic microorganisms.

The hybrid anti-symmetrized coupled channels method (haCC) for the tRecX code

We present a new implementation of the hybrid antisymmetrized Coupled Channels (haCC) method in the framework of the tRecX (Scrinzi, 2022 [6]). The method represents atomic and molecular multi-electron functions by combining CI functions, Gaussian molecular orbitals, and a numerical single-electron basis. It is suitable for describing high harmonic generation and the strong-field dynamics of ionization. Fully differential photoemission spectra are computed by the tSurff method. The theoretical background of haCC is outlined and key improvements compared to its original formulation are highlighted. We discuss control of over-completeness resulting from the joint use of the numerical basis and Gaussian molecular orbitals by pseudo-inverses based on the Woodbury formula. Further new features of this tRecX release are the iSurff method, new input features, and the AMOS gateway interface. The mapping of haCC into the tRecX framework for solving the time-dependent Schrödinger equation is shown. Use, performance, and accuracy of haCC are discussed on the examples of high-harmonic generation and strong-field photo-emission by short laser pulses impinging on the Helium atom and on the linear molecules N2 and CO. Program summaryProgram title: tRecX — time-dependent Recursive indeXing (tRecX=tSurff+irECS)CPC Library link to program files:https://doi.org/10.17632/m9g2jc82sw.1Developer's repository link:https://gitlab.physik.uni-muenchen.de/AG-Scrinzi/tRecXLicensing provisions: GNU General Public License 2Programming language: C++External libraries: Eigen, arpack, lapack, blas, boost, FFTW (optional)Journal Reference of previous version: A. Scrinzi, Comp. Phys. Comm., 270:108146, 2022.Does the new version supersede the previous version: YesReasons for the new version: Major new functionality: haCC — hybrid antisymmetrized coupled channels methodSummary of revisions: Main additions are haCC and iSurff. Code usage and compilation were improved.Nature of problem: tRecX is a general solver for time-dependent Schrödinger-like problems, with applications mostly in strong field and attosecond physics. There are no technical restrictions on the spatial dimension of the problem with up to 6 spatial dimensions realized in the strong-field double ionization of Helium. Gaussian-based quantum chemical multi-electron atomic and molecular structure can be combined with the numerical basis. A selection of coordinate systems is available and any Hamiltonian involving up to second derivatives and arbitrary up to three dimensional potentials can be defined on input by simple scripts.Solution method: The method of lines is used with spatial discretization by a flexible combination of one dimensional basis sets, DVR representations, discrete vectors, expansions into higher-dimensional eigenfunctions of user-defined operators, and Gaussian based molecular orbitals. Multi-electron Gaussian-based CI (configuration interaction) functions for neutrals and ions are combined with the numerical basis. Photo-emission spectra are calculated using the time-dependent surface flux method (tSurff) in combination with infinite range exterior complex scaling (irECS) for absorption. The code is object oriented and makes extensive use of tree-structures and recursive algorithms. Parallelization is by MPI. Code design and performance allow use in production as well as for graduate level training.

Photoelectron velocity map imaging spectroscopy of group 14 elements and iron tetracarbonyl anionic clusters MFe(CO)4- (M = Si, Ge, Sn).

The heteronuclear group 14 M-iron tetracarbonyl clusters MFe(CO)4- (M = Si, Ge, Sn) anions have been generated in the gas phase by laser ablation of M-Fe alloys and detected by mass and photoelectron spectroscopy. With the support of quantum chemical calculations, the geometric and electronic structures of MFe(CO)4- (M = Si, Ge, Sn) are elucidated, which shows that all the MFe(CO)4- clusters have the M-Fe bonded, iron-centered, and carbonyl-terminal M-Fe(CO)4 structure with the C2v symmetry and a 2B2 ground state. The M-Fe bond can be considered a double bond, which includes one σ electron sharing bond and one π dative bond. The C-O bonds in those anionic clusters are calculated to be elongated to different extents, and in particular, the C-O bonds in SiFe(CO)4- are elongated more. The Si-Fe alloy thus turns out to be a better collocation to activate the C-O bonds in the gas phase among group 14. The present findings have important implications for the rational development of high-performance catalysts with isolated metal atoms/clusters dispersed on supports.

Mass spectrometric stochastic dynamic 3D structural analysis of mixture of steroids in solution – Experimental and theoretical study

There is explored, herein, functional relation: Experimental mass spectrometric phenomenon, obeying a certain scientific law ⇔ 3D molecular conformations and electronic structures of analytes obtained for quantum chemical theories. The paper answers to questions: (a) What evidence claims these actual relations among measurable and theoretical parameters, experimental factors and molecular properties; (b) how the provided evidence is collected and used; and (c) how empirical proof relates to assign and explain mass spectrometric phenomena of steroids afforded by our innovative stochastic dynamic mass spectrometric formula, D″SD = 2.6388.10−17.(<I2>–<I>2), quantum chemical 3D conformations, electronic structures and energetics of molecules, respectively. The paper address issue concerning empirical evidence at very high-to-exact level of assignment of 3D molecular conformations of steroids to experimental mass spectrometric fragment ions, accounting precisely for (i) effect of protonation; (ii) intramolecular rearrangement for A–D rings of steroidal skeleton and proton transfer effect, if any; in addition to (iii) examination of enantiomers of steroids in mixture with different stereochemistry, (R) and (S), of a set of six atoms of the molecular backbone of hydrocortisone (1), deoxycorticosterone (2), progesterone (3) and methyltestosterone (4), respectively. Results from testosterone (5) are discussed, as well. There are used ultra-high resolution atmospheric pressure chemical ionization mass spectrometric data on analytes (1)–(4) at ng.(mL)-1 concentration levels in mixtures in solution obtained for positive operation mode. High accuracy static and molecular dynamic quantum chemical computations and chemometrics are also utilized. Experimental 3D structural parameters of steroids obtained for stochastic dynamic diffusion theory are correlated with available crystallographic data.

Computational Estimation of the Acidities of Pyrimidines and Related Compounds.

Pyrimidines are key components in the genetic code of living organisms and the pyrimidine scaffold is also found in many bioactive and medicinal compounds. The acidities of these compounds, as represented by their pKas, are of special interest since they determine the species that will prevail under different pH conditions. Here, a quantum chemical quantitative structure–activity relationship (QSAR) approach was employed to estimate these acidities. Density-functional theory calculations at the B3LYP/6-31+G(d,p) level and the SM8 aqueous solvent model were employed, and the energy difference ∆EH2O between the parent compound and its dissociation product was used as a variation parameter. Excellent estimates for both the cation → neutral (pKa1, R2 = 0.965) and neutral → anion (pKa2, R2 = 0.962) dissociations were obtained. A commercial package from Advanced Chemical Design also yielded excellent results for these acidities.

An Ordered Alite Cement Clinker Phase (Ca3SiO5, aP162) from Flux Synthesis

AbstractCalcium silicates are the main components in cement clinkers. Alite, the nesosilicate or island silicate Ca3SiO5, also named C3S in cement chemistry notation, represents the main phase in Portland cement clinkers. Due to the metastability of Alite at room temperature, quenching from high temperatures is mandatory for phase preservation and impurities are important structure directing factors. Those two aspects result in a plethora of published polymorphs. Many Alite polymorphs described in the literature are characterized by various degrees of disorder within the Si−O substructure which is a direct consequence of afore mentioned features (i. e. quenching and presence of impurities). Here we report on the CaCl2‐flux mediated synthesis and structural characterization of an aP162 Alite featuring a fully‐ordered [SiO4] tetrahedron substructure. The orientation of the [SiO4] tetrahedron substructure is discussed based on the Nishi and Takéuchi nomenclature and is equivalent to the Golovastikov model reported in 1975. Rietveld analyses of a synthetic clinker and three commercial CEM I clinker substantiate that the aP162 model can successfully be applied for clinker phase analysis. Besides the structural characterization, quantum chemical band structure calculations based on Density Functional Theory methods illustrate the expected electrically isolating character of Ca3SiO5.

Kinetics, structural effects and transformation pathways for norfloxacin oxidation using the UV/chlorine process

The UV/chlorine process is a novel light-driven oxidation technique. In this study, norfloxacin (NOR), a typical quinolone contaminant, was degraded by using the UV/chlorine process. The effects of the process parameters were also investigated. The UV/chlorine process was observed to be capable of fully removing NOR in 360 s with a high degradation rate constant of 0.0196 s−1. NOR degradation was found to be positively correlated with chlorine dose and UV intensity but negatively correlated with ammonia. FMO, MSPA, and CDFT quantum chemical structure analyses reveal the most reactive sites for electrophilic or radical attack are the N6 or N5 atoms in the piperazine ring of the NOR molecule, which are also potential starting reaction sites for the degradation process. Thirteen degradation intermediates were detected and identified by UPLC/Q-TOF HRMS. Three sub-pathways are present during the degradation process, including cleavage and removal of the piperazine ring, transformation and cleavage of the quinolone structure, and chlorination reaction with chlorine active matter (RCS). The full elimination of NOR does not ensure a decrease in acute toxicity. Environmental risks associated with the UV/chlorine process need to be assessed further.

Euphopias D–F from Euphorbia L.: quantum chemical calculation-based structure elucidation and their bioactivity of inhibiting NLRP3 inflammasome activation

Euphopias D–F (1–3), three novel carbon skeleton diterpenoids with an inhibitory effect on NLRP3 inflammasome, were isolated and identified from the whole plants of Euphorbia helioscopia.

Zinc binding promotes greater hydrophobicity in Alzheimer's Aβ42 peptide than copper binding: Molecular dynamics and solvation thermodynamics studies.

The aggregation of Aβ42 peptides is considered as one of the main causes for the development of Alzheimer's disease. In this context, Zn2+ and Cu2+ play a significant role in regulating the aggregation mechanism, due to changes in the structural and the solvation free energy of Aβ42. In practice, experimental studies are not able to determine the latter properties, since the Aβ42-Zn2+ and Aβ42-Cu2+ peptide complexes are intrinsically disordered, exhibiting rapid conformational changes in the aqueous environment. Here, we investigate atomic structural variations and the solvation thermodynamics of Aβ42, Aβ42-Cu2+ , and Aβ42-Zn2+ systems in explicit solvent (water) by using quantum chemical structures as templates for a metal binding site and combining extensive all-atom molecular dynamics (MD) simulations with a thorough solvation thermodynamic analysis. Our results show that the zinc and copper coordination results in a significant decrease of the solvation free energy in the C-terminal region (Met35-Val40), which in turn leads to a higher structural disorder. In contrast, the β-sheet formation at the same C-terminal region indicates a higher solvation free energy in the case of Aβ42. The solvation free energy of Aβ42 increases upon Zn2+ binding, due to the higher tendency of forming the β-sheet structure at the Leu17-Ala42 residues, in contrast to the case of binding with Cu2+ . Finally, we find the hydrophobicity of Aβ42-Zn2+ in water is greater than in the case of Aβ42-Cu2+ .

COSMOperm: Mechanistic Prediction of Passive Membrane Permeability for Neutral Compounds and Ions and Its pH Dependence.

We present a new and entirely mechanistic COSMOperm method to predict passive membrane permeabilities for neutral compounds, as well as anions and cations. The COSMOperm approach is based on compound-specific free energy profiles within a membrane of interest from COSMO-RS (conductor-like screening model for realistic solvation) calculations. These are combined with membrane layer-specific diffusion coefficients, for example, in the water phase, the polar head groups, and the alkyl tails of biochemical phospholipid bilayers. COSMO-RS utilizes first-principle quantum chemical structures and physically sound intermolecular interactions (electrostatic, hydrogen bond, and van der Waals). For this reason, it is unbiased toward different application scenarios, such as in cosmetics and industrial chemical or pharmaceutical industries. A fully predictive calculation of passive permeation through phospholipid bilayer membranes results in a performance of r2 = 0.92; rmsd = 0.90 log10 units for neutral compounds and anions, as compared to gold standard black lipid membrane experiments. It will be demonstrated that new membrane types can be generated by the related COSMOplex method and directly used for permeability studies by COSMOperm.

Towards an Understanding of the Mode of Action of Human Aromatase Activity for Azoles through Quantum Chemical Descriptors-Based Regression and Structure Activity Relationship Modeling Analysis

Aromatase is an enzyme member of the cytochrome P450 superfamily coded by the CYP19A1 gene. Its main action is the conversion of androgens into estrogens, transforming androstenedione into estrone and testosterone into estradiol. This enzyme is present in several tissues and it has a key role in the maintenance of the balance of androgens and estrogens, and therefore in the regulation of the endocrine system. With regard to chemical safety and human health, azoles, which are used as agrochemicals and pharmaceuticals, are potential endocrine disruptors due to their agonist or antagonist interactions with the human aromatase enzyme. This theoretical study investigated the active agonist and antagonist properties of “chemical classes of azoles” to determine the relationships of azole interaction with CYP19A1, using stereochemical and electronic properties of the molecules through classification and multilinear regression (MLR) modeling. The antagonist activities for the same substituent on diazoles and triazoles vary with its chemical composition and its position and both heterocyclic systems require aromatic substituents. The triazoles require the spherical shape and diazoles have to be in proper proportion of the branching index and the number of ring systems for the inhibition. Considering the electronic aspects, triazole antagonist activity depends on the electrophilicity index that originates from interelectronic exchange interaction (ωHF) and the LUMO energy (), and the diazole antagonist activity originates from the penultimate orbital () of diazoles. The regression models for agonist activity show that it is opposed by the static charges but favored by the delocalized charges on the diazoles and thiazoles. This study proposes that the electron penetration of azoles toward heme group decides the binding behavior and stereochemistry requirement for antagonist activity against CYP19A1 enzyme.

Synthesis and DFT characterisation of 2-arylamino-1,4-benzoquinone derivatives as potential electron transfer mediators

A series of new potential electron transfer mediators, 2-substituted 1,4-benzoquinone derivatives bearing an arylamino group with various substituents in o-, m- and p-positions of an aromatic ring were synthesised by adding a solution of aniline derivatives in aqueous acetic acid to an aqueous solution of 1,4-benzoquinone. The structure and properties of synthesised compounds were investigated by NMR spectroscopy methods in detail. The redox ability of 2-arylamino-1,4-benzoquinone derivatives has been estimated by calculations of quantum chemical structure– activity relationship (QSAR) descriptors within the framework of density functional theory.

Structure Elucidation of a Melam-Melem Adduct by a Combined Approach of Synchrotron X-ray Diffraction and DFT Calculations.

Melam-melem (1:1), an adduct compound that can be obtained from dicyandiamide in autoclave reactions at 450 °C and elevated ammonia pressure, had previously been described based on mass spectrometry and NMR spectroscopy, but only incompletely characterized. The crystal structure of this compound has now been elucidated by means of synchrotron microfocus diffraction and subsequent quantum-chemical structure optimization applying DFT methods. The structure was refined in triclinic space group P based on X-ray data. Cell parameters of a=4.56(2), b=19.34(8), c=21.58(11) Å, α=73.34(11)°, β=89.1(2)°, and γ=88.4(2)° were experimentally obtained. The resulting cell volumes agree with the DFT optimized value to within 7 %. Molecular units in the structure form stacks that are interconnected by a vast array of hydrogen bridge interactions. Remarkably large melam dihedral angles of 48.4° were found that allow melam to interact with melem molecules from different stack layers, thus forming a 3D network. π-stacking interactions appear to play no major role in this structure.

Mechanistic skin penetration model by the COSMOperm method: Routes of permeation, vehicle effects and skin variations in the healthy and compromised skin

A computational skin model has been constructed, representing the composition of a human skin, including short- and long chain ceramides, cholesterol and fatty acids in the stratum corneum, and differentiated model systems in the viable epidermis. The COSMOperm based method uses a set of membrane systems to predict skin permeabilities with an accuracy of rmsd = 0.72 log kp units for both non-polar and polar substances, including ionic protonation states. The membrane systems can be varied to model different grades of hydration and skin penetration enhancers. In addition, the release of substances from vehicle matrices is taken into account. The COSMOperm method calculates substance-specific free energy and diffusion profiles within a biological barrier of interest from COSMO-RS calculations. They are based on first-principle quantum chemical structures and surface polarities. The skin model was constructed using a new methodology called COSMOplex, originally developed for a self-consistent simulation of inhomogeneous surfactant, micelle and microemulsion systems. The skin penetration results are obtained quickly within minutes, i.e., many orders of magnitude faster than with molecular dynamics simulations. It will be shown that this mechanistic model should be able to cover variations of the skin composition and penetration pathways in the healthy and compromised skin.

Synthesis of 2-aminofluorene bis-Schiff base and corrosion inhibition performance for carbon steel in HCl

Three new bis-Schiff bases, including bis(2-aminofluorene) glyoxal(L1), bis(2-aminofluorene) p-phthalaldehyde (L2) and bis(2-aminofluorene) 4,4′-biphenyldicarboxaldehyde (L3), were synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR) and mass spectrometry (MS). Weight loss methods indicated that all these inhibitors have good resistance to 1.0 mol·L−1 hydrochloric acid corrosion, and the highest inhibition efficiency was 98.2% at 65 °C for L3. Polarization curves and electrochemical impedance spectroscopy (EIS) indicated that L3 exhibited excellent inhibition effect when concentration was 1.0 mmol·L−1. Moreover, the L3 was adsorbed spontaneously onto the surface by both physisorption and chemisorption, which followed the Langmuir adsorption isotherm. The relationship between molecular structure and quantum chemical structure parameters of three bis-Schiff base corrosion inhibitors was studied by Quantum chemistry calculation performed by density function theory (DFT) method. Results showed that L3 had excellent inhibition performance, which was consistent with experimental results.

Microwave Spectra and Structure of Ar-1,3-Difluorobenzene.

The microwave spectrum of the dimer Ar-1,3-difluorobenzene from 2 to 18 GHz is reported. The spectrum has been observed using a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer that has recently been expanded to include the 2-6 GHz region of the electromagnetic spectrum. Details of this upgraded spectrometer are reported. Eighty-seven transitions were observed for the parent dimer spectrum, which was adequately fit to a semirigid rotational Hamiltonian consisting of A, B, and C as well as four quartic centrifugal distortion constants. Observations of 13C species in natural abundance were aided by utilizing smaller chirp ranges of 7-9 and 9-11 GHz for 1.9 million and 3.73 million averages, respectively. Assignment of 13C isotopologues allowed for determination of the Kraitchman coordinates of the carbon atoms as well as inertial fits of the complex. The quantum-chemical structure predicts an Ar to monomer center of mass distance of 3.48 Å, compared with 3.564(1) Å determined from experimental structural analysis. This new study indicates that in fluorinated benzene-Ar dimers, when the fluorines are separated by more carbon atoms, the Ar-ring center distance decreases.

Combining Ion Mobility and Cryogenic Spectroscopy for Structural and Analytical Studies of Biomolecular Ions.

Ion mobility spectrometry (IMS) has become a valuable tool in biophysical and bioanalytical chemistry because of its ability to separate and characterize the structure of gas-phase biomolecular ions on the basis of their collisional cross section (CCS). Its importance has grown with the realization that in many cases, biomolecular ions retain important structural characteristics when produced in the gas phase by electrospray ionization (ESI). While a CCS can help distinguish between structures of radically different types, one cannot expect a single number to differentiate similar conformations of a complex molecule. Molecular spectroscopy has also played an increasingly important role for structural characterization of biomolecular ions. Spectroscopic measurements, particularly when performed at cryogenic temperatures, can be extremely sensitive to small changes in a molecule's conformation and provide tight constraints for calculations of biomolecular structures. However, spectra of complex molecules can be heavily congested due to the presence of multiple stable conformations, each of which can have a distinct spectrum. This congestion can inhibit spectral analysis and complicate the extraction of structural information. Even when a single conformation is present, the conformational search process needed to match a measured spectrum with a computed structure can be overwhelming for peptides of more than a few amino acids, for example. We have recently combined ion mobility spectrometry and cryogenic ion spectroscopy (CIS) to characterize the structures of gas-phase biomolecular ions. In this Account, we illustrate how the coupling of IMS and CIS is by nature synergistic. On the one hand, IMS can be used as a conformational filter to reduce spectral congestion that arises from heterogeneous samples, facilitating structural analysis. On the other hand, highly resolved, cryogenic spectra can serve as a selective detector for IMS that can increase the effective resolution and hence the maximum number of distinct species that can be detected. Taken together, spectra and CCS measurements on the same system facilitates structural analysis and strengthens the conclusions that can be drawn from each type of data. After describing different approaches to combining these two techniques in such a way as to simplify the data obtained from each one separately, we present two examples that illustrate the type of insight gained from using spectra and CCS data together for characterizing gas-phase biomolecular ions. In one example, the CCS is used as a constraint for quantum chemical structure calculations of kinetically trapped species, where a lowest-energy criterion is not applicable. In a second example, we use both the CCS and a cryogenic infrared spectrum as a means to distinguish isomeric glycans.

Equilibrium molecular structures of vinyl carbon chains: Vinyl acetylene, vinyl diacetylene, and vinyl cyanide

Semi-experimental equilibrium and high-level quantum-chemical structures are reported for three hydrocarbons containing the vinyl (H2C = CH–) group: vinyl acetylene, vinyl diacetylene and vinyl cyanide. Semi-experimental equilibrium structures have been obtained through a combination of new experimental results from Fourier transform microwave spectroscopy combined with force field calculations performed at the coupled-cluster singles and doubles model augmented by a perturbative correction for triple excitations, CCSD(T), level of theory. Comparison against equilibrium structures obtained by high-level CCSD(T) computations employing large correlation-consistent basis sets with up to 1090 basis functions yields excellent agreement. From this combined study, we find the carbon atom backbone in the vinyl group is largely unaffected when bound to different substituents, such as –H, –CCH, –C4H, –CN.

An experimental and theoretical investigation into the electronically excited states of para-benzoquinone

We report on a combination of experimental and theoretical investigations into the structure of electronically excited para-benzoquinone (pBQ). Here synchrotron photoabsorption measurements are reported over the 4.0–10.8 eV range. The higher resolution obtained reveals previously unresolved pBQ spectral features. Time-dependent density functional theory calculations are used to interpret the spectrum and resolve discrepancies relating to the interpretation of the Rydberg progressions. Electron-impact energy loss experiments are also reported. These are combined with elastic electron scattering cross section calculations performed within the framework of the independent atom model–screening corrected additivity rule plus interference (IAM-SCAR + I) method to derive differential cross sections for electronic excitation of key spectral bands. A generalized oscillator strength analysis is also performed, with the obtained results demonstrating that a cohesive and reliable quantum chemical structure and cross section framework has been established. Within this context, we also discuss some issues associated with the development of a minimal orbital basis for the single configuration interaction strategy to be used for our high-level low-energy electron scattering calculations that will be carried out as a subsequent step in this joint experimental and theoretical investigation.