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► The PES for the unimolecular reaction of ethyl acetate is explored. ► The rate coefficients are calculated by TST and RRKM theories. ► The major reaction is the channel producing ...ethylene and acetic acid. ► Some reactions could contribute to the overall rate constant at high temperatures.
The potential energy surface of the gas-phase unimolecular decomposition of ethyl acetate is investigated by using various quantum chemical methods including CCSD(T), GBS-QB3, BB1K, M06-2X, MP2 and B3LYP. Modified strong collision/RRKM theory was used to calculate the unimolecular rate constants of different reaction channels as a function of pressure and temperature. It is found that the major reaction pathway is the channel producing ethylene and acetic acid. Some reaction channels could contribute to the overall rate constant at high temperatures. The computed rate constants are compared with the available experimental data.
The retaining the excitation degree (RE) partitioning R.F. Fink, Chem. Phys. Lett. 428 (2006) 461(20 September) is reformulated and applied to multi-reference cases with complete active space (CAS) ...reference wave functions. The generalised van Vleck perturbation theory is employed to set up the perturbation equations. It is demonstrated that this leads to a consistent and well defined theory which fulfils all important criteria of a generally applicable ab initio method: The theory is proven numerically and analytically to be size-consistent and invariant with respect to unitary orbital transformations within the inactive, active and virtual orbital spaces. In contrast to most previously proposed multi-reference perturbation theories the necessary condition for a proper perturbation theory to fulfil the zeroth order perturbation equation is exactly satisfied with the RE partitioning itself without additional projectors on configurational spaces. The theory is applied to several excited states of the benchmark systems CH2, SiH2, and NH2, as well as to the lowest states of the carbon, nitrogen and oxygen atoms. In all cases comparisons are made with full configuration interaction results. The multi-reference (MR)-RE method is shown to provide very rapidly converging perturbation series. Energy differences between states of similar configurations converge even faster.
Quantum chemical methods and molecular mechanics approaches face a lot of challenges in drug metabolism study because of either insufficient accuracy, huge computational cost, or lack of clear ...molecular level pictures for building computational models. Low-cost QSAR methods can often be carried out, even though molecular level pictures are not well defined; however, they show difficulty in identifying the mechanisms of drug metabolism and delineating the effects of chemical structures on drug toxicity because a certain amount of molecular descriptors are difficult to be interpreted.
In order to make a breakthrough of QSAR, mechanistically interpretable molecular descriptors were used to correlate with biological activity to establish structure-activity plots. The biological activity is the lethality of anthracycline anticancer antibiotics denoted as log LD50. The mechanistically interpretable molecular descriptors include electrophilicity and the mathematical function in the London formula for dispersion interaction.
The descriptors were calculated using quantum chemical methods.
The plots for electrophilicity, which is interpreted as redox reactivity of anthracyclines, can describe oxidative degradation for detoxification and reductive bioactivation for toxicity induction. The plots for the dispersion interaction function, which represents the attraction between anthracyclines and biomolecules, can describe efflux from and influx into the target cells of toxicity. The plots can also identify three structural scaffolds of anthracyclines that have different metabolic pathways, resulting in their different toxicity behavior.
This structure-dependent toxicity behavior revealed in the plots can provide perspectives on drug design and drug metabolism study.
We show that on solid electrodes held at constant potential in an electrolyte all defect formation energies and activation energies for surface transport become potential dependent. The rapid ...smoothening of rough metal electrodes for (mostly) positive electrode potentials (“electrochemical annealing”) is therefore the consequence of the specific thermodynamic boundary condition of constant electrode potential. The potential dependence can be related to the surface charge density and the dipole moments of the defects. With dipole moments calculated by ab initio methods the theory is applied to experimental data on two-dimensional Ostwald ripening on Au(1
0
0) electrodes. The theory is further discussed in the context of other experiments.
The electronic structure and chemical properties of catalysts prepared by the electroless deposition (ED) of Ag onto Pt/SiO
2 were studied using a combination of X-ray photoelectron spectroscopy ...(XPS) and density functional theory (DFT) calculations. XPS studies revealed a negative shift (up to −0.75
eV) in the Ag 3
d binding energy (BE) relative to bulk Ag. Both the magnitude and direction of the shift are consistent with DFT calculations of model Ag/Pt(1
1
1) surfaces. DFT calculations have also been employed to study the adsorption of two probe molecules, carbon monoxide and 1-epoxy-3-butene (EpB), on the model surfaces. Combined with previously published reports, the results presented here suggest that (1) the AgPt/SiO
2 catalysts that are most active for hydrogenation of the EpB olefin function consist of an adlayer of Ag on Pt rather than a surface or bulk alloy and that (2) the higher activity and selectivity of ED-prepared Ag–Pt/SiO
2 catalysts for C
C hydrogenation of EpB to 1-epoxybutane are consistent with computed electronic (ligand) and bifunctional effects.
We present the results of calculations of the energy levels of defects at the (001) surface of MgO relative to the top of the valence band and values of defect ionisation potentials and electron ...affinities. The calculations were made using an embedded cluster method in which a cluster of several tens of ions treated quantum mechanically is embedded in a finite array of polarisable and point ions modelling the crystalline potential and the classical polarisation of the host lattice. The calculated ionisation potential of the ideal surface, which fixes the position of the top of the valence band with respect to the vacuum level, is about 6.7
eV. This value is used as a reference for positioning the energy levels of three charge states of a surface anion vacancy, which are also calculated as ionisation energies with respect to the vacuum level. The surface and vacancy electron affinities are calculated using the same method. As a prototype low-coordinated surface site, we have considered a cube corner. Our calculations predict the splitting of the corner states from the top of the surface valence band by about 1.0
eV. Both unrelaxed and relaxed holes are strongly localised at the corner oxygen ion. The ionisation energies and electron affinities of the corner anion vacancy are calculated. The electrons in the F and F
+ centres at the corner are shown to be significantly delocalised over surrounding Mg ions.
Supramolecular, electronic, and chemical structures of petroleum asphaltene molecules are studied. The investigations are carried out by quantum chemistry and molecular mechanics methods. The quantum ...chemical calculation of the structure-chemical parameters of dimers and trimers of petroleum asphaltenes is made using DFT/B3LYP. The refined values of the ionization potential and electron affinity of petroleum asphaltene molecules, their dimers and trimers agree well with the electron spectroscopy data. The results of the study of geometric structures of petroleum asphaltene dimers and trimers confirm the non-planar structure of asphaltenes.
