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Faced with the contradictory results of two recent experimental studies [Jara‐Toro et al., Angew. Chem. Int. Ed. 2017, 56, 2166 and Chao et al., Angew. Chem. Int. Ed. 2019, 58, 5013] of the possible catalytic effect of water vapor on CH3OH + OH reaction, we report calculations that corroborate the conclusion made by Chao et al. and extend the rate constant evaluation down to 200 K. The rate constants of the CH3OH + OH reaction catalyzed by a water molecule are computed as functions of temperature and relative humidity using high‐level electronic structure and kinetics calculations. The Wuhan–Minnesota Scaling (WMS) method is used to provide accurate energetics to benchmark a density functional for direct dynamics. Both high‐frequency and low‐frequency anharmonicities are included. Variational and tunneling effects are treated by canonical variational transition state theory with multidimensional small‐curvature tunneling. And, most significantly, we include multistructural effects in the rate constant calculations. Our calculations show that the catalytic effect of water vapor is not observable at 200–400 K. [ABSTRACT FROM AUTHOR]

Silicon hydride, as a new efficient catalyst for CO2 conversion to CO, is receiving ever‐increasing attention. Thus, a precise catalytic mechanism is needed to provide a guideline for the design of new efficient catalysts based on silicon hydride. Qian et al. recently proposed a one‐step mechanism for the catalytic process. The present work, based on the recently proposed WMS and revM06 quantum mechanical model chemistries, provides a multistep mechanism that has a lower free energy of activation than the one‐step model. A key point in favor of the new mechanism is that it is consistent with experimental details of the infrared spectrum that cannot be explained by the previous mechanism. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) as photocatalysts and photocatalyst supports combine several advantages of homogeneous and heterogeneous catalyses, including stability, post‐reaction separation, catalyst reusability, and tunability, and they have been intensively studied for photocatalytic applications. There are several reviews that focus mainly or even entirely on experimental work. The present review is intended to complement those reviews by focusing on computational work that can provide a further understanding of the photocatalytic properties of MOF photocatalysts. We first present a summary of computational methods, including density functional theory, combined quantum mechanical and molecular mechanical methods, and force fields for MOFs. Then, computational investigations on MOF‐based photocatalysis are briefly discussed. The discussions focus on the electronic structure, photoexcitation, charge mobility, and photoredox catalysis of MOFs, especially the widely studied UiO‐66‐based MOFs. [ABSTRACT FROM AUTHOR]

Electron momentum spectroscopy, scanning tunneling microscopy, and photoelectron spectroscopy provide unique information about electronic structure, but their interpretation has been controversial. This essay discusses a framework for interpretation. Although this interpretation is not new, we believe it is important to present this framework in light of recent publications. The key point is that these experiments provide information about how the electron distribution changes upon ionization, not how electrons behave in the pre‐ionized state. Therefore, these experiments do not lead to a "selection of the correct orbitals" in chemistry and do not overturn the well‐known conclusion that both delocalized molecular orbitals and localized molecular orbitals are useful for interpreting chemical structure and dynamics. The two types of orbitals can produce identical total molecular electron densities and therefore molecular properties. Different types of orbitals are useful for different purposes. [ABSTRACT FROM AUTHOR]

Motivated by the need to calculate liquid‐phase free energies of species and equilibria involving halogen bonding, recent experimental data were used to optimize new Coulomb radii for Br and I for use in the SMD universal solvation model for calculating free energies of solvation. The use of the SMD model with these parameters for Br and I and the SMD values of all other parameters is called SMD18. After parametrization, the SMD18 model was tested for data not used in the parametrization. These data are standard‐state free energies (equivalent to equilibrium constants) for 18 ionic equilibria involving Cl, Br, and I halogen bonding in acetonitrile, and the agreement of theory and experiment is satisfactory. The SMD18 model is then used to compare hydrogen bonding to halogen bonding and to reassess the interpretation of recent experiments. Experimental data on halogen bonded complexes has been used to reoptimize the iodine and bromine radius in the SMD intrinsic solvation model. Subsequent testing of this new SMD18 model on several ionic equilibria provided very good agreement between experiment and theory. [ABSTRACT FROM AUTHOR]

Abstract: The concept of oxidation state (OS) is based on the concept of Lewis electron pairs, in which the bonding electrons are assigned to the more electronegative element. This approach is useful for keeping track of the electrons, predicting chemical trends, and guiding syntheses. Experimental and quantum‐chemical results reveal a limit near +8 for the highest OS in stable neutral chemical substances under ambient conditions. OS=+9 was observed for the isolated [IrO4]+ cation in vacuum. The prediction of OS=+10 for isolated [PtO4]2+ cations is confirmed computationally for low temperatures only, but hasn't yet been experimentally verified. For high OS species, oxidation of the ligands, for example, of O−2 with formation of .O−1 and O−O bonds, and partial reduction of the metal center may be favorable, possibly leading to non‐Lewis type structures. [ABSTRACT FROM AUTHOR]

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Rechargeable batteries with organic electrodes are preferred to those with transition-metal-containing electrodes for their environmental friendliness, and resource availability, but all such batteries reported to date are based on organic electrolytes, which raise concerns of safety and performance. Here an aqueous-electrolyte all-organic rechargeable battery is reported, with a maximum operating voltage of 2.1 V, in which polytriphenylamine (PTPAn) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA)-derived polyimide (PNTCDA) serve as cathode and anode material, respectively. A key feature of the design is use of a 'water-in-salt' electrolyte to bind 'free' water; this impedes the side reaction of water oxidation, thereby enabling excellent reversibility in aqueous solution. The battery can deliver a maximum energy density of 52.8 Wh kg−1, which is close to most of the all-organic batteries with organic electrolytes. The battery exhibits a supercapacitor-like high power of 32 000 W kg−1 and a long cycle life (700 cycles with capacity retention of 85 %), due to the kinetics not being limited by ion diffusion at either electrode. [ABSTRACT FROM AUTHOR]

A strategy is presented to chemically bind sulfur and its discharge products with a graphene‐supported N/B‐rich carbon layer with various N sites and a unique N = B/N‐B site in the surface carbon frameworks, prepared by polymerizing and carbonizing ionic liquids ([Emim]BF4) onto the graphene. [ABSTRACT FROM AUTHOR]

Electronic singlet excitations of stacked adenine-thymine (AT) and guanine-cytosine (GC) complexes have been investigated with respect to local excitation and charge-transfer (CT) characters. Potential energy curves for rigid displacement of the nucleobases have been computed to establish the distance dependence of the CT states. The second-order algebraic diagrammatic construction [ADC(2)] method served as reference approach for comparison to a selected set of density functionals used within the time-dependent density functional theory (TD-DFT). Particular attention was dedicated to the performance of the recently developed family of M06 functionals. The calculations for the stacked complexes show that at the ADC(2) level, the lowest CT state is S for the AT and as S for the GC pair. At the reference geometry, the actual charge transferred is found to be 0.73 e for AT. In case of GC, this amount is much smaller (0.17 e). With increasing separation of the two nucleobases, the CT state is strongly destabilized. The M06-2X version provides a relatively good reproduction of the ADC(2) results. It avoids the serious overstabilization and overcrowding of the spectrum found with the B3LYP functional. On the other hand, M06-HF destabilizes the CT state too strongly. TD-DFT/M06-2X calculations in solution (heptane, isoquinoline, and water) using the polarizable continuum model show a stabilization of the CT state and an increase in CT character with increasing polarity of the solvent. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011 [ABSTRACT FROM AUTHOR]

This paper is a response to an invitation to share my viewpoint by writing an opinion piece (not a review) on proton tunneling, especially from the point of view of whether it has a greater importance in enzymatic reactions than in other reactions. The paper begins with a discussion of the emergence of a conceptual framework for including tunneling in reaction rate calculations; the framework is general enough to include not only transfer of protons but also transfer of hydrogen atoms and hydride ions and their isotopes, and not only enzymatically catalyzed reactions but also nonenzymatic reactions. Then the paper discusses the special issues that arise when the reaction rate under consideration is for an enzyme-catalyzed reaction. The emphasis is on physical considerations in reaction rate calculations, not on system-specific comparison of results for different modes of reaction. It is argued that enzymatic and nonenzymatic reactions may be treated within the same basic framework except that ensemble averaging, which is not usually required for gas-phase reactions, is essential for treating enzyme reactions. Enzymes explicitly discussed include methylamine dehydrogenase, aromatic amine dehydrogenase, E. coli dihydrofolate reductase, hyperthermophilic dihydrofolate reductase, liver alcohol dehydrogenase, methylmalonyl-CoA mutase, soybean lipoxygenase, copper amine oxidase, pentaerythritol tetranitrate reductase, morphinone reductase, enolase, xylose isomerase, and 4-oxalocrotonate tautomerase. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In a recent paper, Wang et al. found an iridium-containing compound with a formal oxidation state of 9. This is the highest oxidation state ever found in a stable compound. To learn if this is the highest chemical oxidation state possible, Kohn-Sham density functional theory was used to study various compounds, including PdO42+, PtO42+, PtO3F22+, PtO4OH+, PtO5, and PtO4SH+, in which the metal has an oxidation state of 10. It was found that PtO42+ has a metastable state that is kinetically stable with a barrier height for decomposition of 31 kcal mol−1 and a calculated lifetime of 0.9 years. All other compounds studied would readily decompose to lower oxidation states. [ABSTRACT FROM AUTHOR]

Holthausen has recently provided a comprehensive study of density functional theory for calculating the s/d excitation energies of the 3d transition metal cations. This study did not include the effects of scalar relativistic effects, and we show here that the inclusion of scalar relativistic effects significantly alters the conclusions of the study. We find, contrary to the previous study, that local functionals are more accurate for the excitation energies of 3d transition method cations than hybrid functionals. The most accurate functionals, of the 38 tested, are SLYP, PBE, BP86, PBELYP, and PW91. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [ABSTRACT FROM AUTHOR]

This essay provides a perspective on several issues in valence bond theory: the physical significance of semilocal bonding orbitals, the capability of valence bond concepts to explain systems with multireferences character, the use of valence bond theory to provide analytical representations of potential energy surfaces for chemical dynamics by the method of semiempirical valence bond potential energy surfaces (an early example of specific reaction parameters), by multiconfiguration molecular mechanics, by the combined valence bond-molecular mechanics method, and by the use of valence bond states as coupled diabatic states for describing electronically nonadiabatic processes (photochemistry). The essay includes both ab initio and semiempirical approaches. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2007 [ABSTRACT FROM AUTHOR]

This paper provides an overview of a new method developed to include quantum mechanical effects and free energy sampling in calculations of reaction rates in enzymes. The paper includes an overview of variational transition state theory with optimized multidimensional tunneling for simple gas‐phase reactions and then shows how this is extended to incorporate free energy effects and to include protein motions in the reaction coordinate by ensemble averaging. Finally we summarize recent comparisons to experiment for primary and secondary kinetic isotope effects for proton and hydride transfer reactions catalyzed by enzymes. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 [ABSTRACT FROM AUTHOR]

A subject of great practical importance that has not received much attention is the question of the sensitivity of molecular dynamics simulations to the initial X-ray structure used to set up the calculation. We have found two cases in which seemingly similar structures lead to quite different results, and in this article we present a detailed analysis of these cases. The first case is acyl-CoA dehydrogenase, and the chief difference of the two structures is attributed to a slight shift in a backbone carbonyl that causes a key residue (the proton-abstracting base) to be in a bad conformation for reaction. The second case is xylose isomerase, and the chief difference of the two structures appears to be the ligand sphere of a Mg2+ metal cofactor that plays an active role in catalysis. [ABSTRACT FROM AUTHOR]

DFT electronic structure calculations indicate the existence of oxidation state 10 in the Td structure of PtO42+. [ABSTRACT FROM AUTHOR]

DFT and coupled-cluster calculations show that the B2N2O4 molecule has a triplet ground state and therefore is paramagnetic. [ABSTRACT FROM AUTHOR]

Review: [117 refs. [ABSTRACT FROM AUTHOR]