In Situ Formation of Nano Ni-Co Oxyhydroxide Enables Water Oxidation Electrocatalysts Durable at High Current Densities.

The oxygen evolution reaction (OER) limits the energy efficiency of electrocatalytic systems due to the high overpotential symptomatic of poor reaction kinetics; this problem worsens over time if the performance of the OER electrocatalyst diminishes during operation. Here, a novel synthesis of nanocrystalline Ni-Co-Se using ball milling at cryogenic temperature is reported. It is discovered that, by anodizing the Ni-Co-Se structure during OER, Se ions leach out of the original structure, allowing water molecules to hydrate Ni and Co defective sites, and the nanoparticles to evolve into an active Ni-Co oxyhydroxide.

Exciting clusters, what does off-resonance actually mean?

Noble metal clusters have unique photophysical properties, especially as a new class of materials for multiphoton biomedical imaging. The previously studied AuSR exhibits "giant" two-photon absorbance cross sections. Herein, we investigate the origins of the large two photon absorption for AuSR, as well as 10 other Au and Ag clusters using femtosecond pump/probe transient absorption spectroscopy (fsTAS).

Pseudodiagonalization-based wavefunction optimization with contracted planewave basis functions.

Electronic structure calculations representing the molecular orbitals (MOs) with contracted planewave basis functions (CPWBFs) have been reported recently. CPWBFs are Fourier-series representations of atom-centered basis functions. The mathematical features of CPWBFs permit the construction of matrix-vector products, FC , involving the application of the Fock matrix, F, to the set of occupied MOs, C , without the explicit evaluation of F.

Direct inversion of the iterative subspace with contracted planewave basis functions.

Ways to reduce the computational cost of periodic electronic structure calculations by using basis functions corresponding to linear combinations of planewaves have been examined recently. These contracted planewave (CPW) basis functions correspond to Fourier series representations of atom-centered basis functions, and thus provide access to some beneficial properties of planewave (PW) and localized basis functions. This study reports the development and assessment of a direct inversion of the iterative subspace (DIIS) method that employs unique properties of CPW basis functions to efficiently converge electronic wavefunctions.

Molecular structure and interactions of water intercalated in nickel hydroxide.

The structure and properties of α-Ni(OH)2 containing water and nitrate have been investigated computationally. The adsorption of water molecules on the Ni(OH)2 surface is also investigated to provide insight into the nature of the water-Ni(OH)2 interactions. The spectroscopic and dynamical behaviour of the intercalated species has been characterized and used to explain experimental findings reported for this material.

Density-functional tight-binding investigation of the structure, stability and material properties of nickel hydroxide nanotubes.

Nickel hydroxide is a material composed of two-dimensional layers that can be rolled up to form cylindrical nanotubes belonging to a class of inorganic metal hydroxide nanotubes that are candidates for applications in catalysis, energy storage, and microelectronics. The stabilities and other properties of this class of inorganic nanotubes have not yet been investigated in detail. The present study uses self-consistent-charge density-functional tight-binding calculations to examine the stabilities, mechanical properties, and electronic properties of nickel hydroxide nanotubes along with the energetics associated with the adsorption of water by these systems.

N-Heterocyclic Carbene Self-assembled Monolayers on Copper and Gold: Dramatic Effect of Wingtip Groups on Binding, Orientation and Assembly.

Self-assembled monolayers of N-heterocyclic carbenes (NHCs) on copper are reported. The monolayer structure is highly dependent on the N,N-substituents on the NHC. On both Cu(111) and Au(111), bulky isopropyl substituents force the NHC to bind perpendicular to the metal surface while methyl- or ethyl-substituted NHCs lie flat.

Exact exchange with non-orthogonal generalized Wannier functions.

The evaluation of exact exchange (EXX) is an important component of quantum chemical calculations performed with ab initio and hybrid density functional methods. While evaluating exact exchange is routine in molecular quantum chemical calculations performed with localized basis sets, the non-local nature of the exchange operator presents a major impediment to the efficient use of exact exchange in calculations that employ planewave basis sets. Non-orthogonal generalized Wannier functions (NGWFs) corresponding to planewave expansions of localized basis functions are an alternative form of basis set that can be used in quantum chemical calculations.

Effects of reduced dimensionality on the properties of magnesium hydroxide and calcium hydroxide nanostructures.

Metal hydroxides are a class of layered materials that contain two-dimensional metal hydroxide layers that can be isolated to form layered nanostructures. In this work, density functional theory (DFT) and self-consistent-charge density-functional tight-binding (SCC-DFTB) methods have been used to investigate the properties of magnesium hydroxide and calcium hydroxide nanostructures. The properties of single layer and multi layer structures with up to 10 metal hydroxide sheets and nanoparticles containing more than 2000 atoms have been calculated and compared with the bulk properties of these systems.

High pressure chemistry of thioaldehydes: A first-principles molecular dynamics study.

First-principles molecular dynamics simulations are used to investigate the chemical behavior of bulk thioacetaldehyde (MeC(H)S) in response to changes in pressure, P. The simulations show that these molecules oligomerize in response to applied P. Oligomerization is initiated through C-S bond formation, with constrained dynamics simulations showing that the barrier to this reaction step is lowered significantly by applied P.

Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing.

The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state.

Differences in the Abilities to Mechanically Eliminate Activation Energies for Unimolecular and Bimolecular Reactions.

Mechanochemistry, i.e. the application of forces, F, at the molecular level, has attracted significant interest as a means of controlling chemical reactions.

Computing the Anharmonic Vibrational Spectrum of UF6 in 15 Dimensions with an Optimized Basis Set and Rectangular Collocation.

The anharmonic vibrational spectrum of UF6 is computed in full dimensionality directly from ab initio data, i.e., bypassing the construction of a potential energy surface (PES).

Theoretical Approaches for Understanding the Interplay Between Stress and Chemical Reactivity.

The use of mechanical stresses to induce chemical reactions has attracted significant interest in recent years. Computational modeling can play a significant role in developing a comprehensive understanding of the interplay between stresses and chemical reactivity. In this review, we discuss techniques for simulating chemical reactions occurring under mechanochemical conditions.

Systematic study of the synthesis and coordination of 2-(1,2,3-triazol-4-yl)-pyridine to Fe(II), Ni(II) and Zn(II); ion-induced folding into helicates, mesocates and larger architectures, and application to magnetism and self-selection.

With its facile synthesis, the pyridine-1,2,3-triazole chelate is an attractive building block for coordination-driven self-assembly. When two such chelates are bridged by a spacer and exposed to cations of octahedral geometrical preference, they generally self-assemble into dinuclear triple-stranded structures in the solid state and in solution in the presence of non-coordinating counter-ions. In solution, a wider range of architectures may nevertheless form, depending on the nature of the spacer.

Tuning the mesomorphic properties of phenoxy-terminated smectic liquid crystals: the effect of fluoro substitution.

The mesomorphic properties of phenoxy-terminated 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine liquid crystals can be tuned in a predictable fashion with fluoro substituents on the phenoxy end-group. We show that an ortho-fluoro substituent promotes the formation of a tilted smectic C (SmC) phase whereas a para-fluoro substituent promotes the formation of an orthogonal smectic A (SmA) phase. The balance between SmA and SmC phases may be understood in terms of the energetic preference of the phenoxy end-groups to self-assemble via arene-arene interactions in a parallel or antiparallel geometry, and how these non-covalent interactions may cause either a suppression or enhancement of out-of-layer fluctuations at the interface of smectic layers.

Ultra stable self-assembled monolayers of N-heterocyclic carbenes on gold.

Since the first report of thiol-based self-assembled monolayers (SAMs) 30 years ago, these structures have been examined in a huge variety of applications. The oxidative and thermal instabilities of these systems are widely known, however, and are an impediment to their widespread commercial use. Here, we describe the generation of N-heterocyclic carbene (NHC)-based SAMs on gold that demonstrate considerably greater resistance to heat and chemical reagents than the thiol-based counterparts.

DFT computational study of the methanolytic cleavage of DNA and RNA phosphodiester models promoted by the dinuclear Zn(II) complex of 1,3-bis(1,5,9-triazacyclododec-1-yl)propane.

A density functional theory study of the cleavage of a DNA model [p-nitrophenyl methyl phosphate (2)] and two RNA models [p-nitrophenyl 2-hydroxypropyl phosphate (3) and phenyl 2-hydroxypropyl phosphate (4)] promoted by the dinuclear Zn((II)) complex of 1,3-bis(1,5,9-triazacyclododec-1-yl)propane formulated with a bridging methoxide (1a) was undertaken to determine possible mechanisms for the transesterification processes that are consistent with experimental data. The initial substrate-bound state of 2:1a or 3:1a has the two phosphoryl oxygens bridging Zn((II))1 and Zn((II))2. For each of 2 and 3, four possible mechanisms were investigated, three of which were consistent with the overall free energy for the catalytic cleavage step for each substrate.

Photo- and thermal-induced multistructural transformation of 2-phenylazolyl chelate boron compounds.

The new N,C-chelate boron compounds B(2-phenylazolyl)Mes2 [Mes = mesityl; azolyl = benzothiazolyl (1a), 4-methylthiazolyl (2a), benzoxazolyl (3a), benzimidazolyl (4a)] undergo an unprecedented multistructural transformation upon light irradiation or heating, sequentially producing isomers b, c, d, and e. The dark isomers b generated by photoisomerization of a undergo a rare thermal intramolecular H-atom transfer (HAT), reducing the azole ring and generating new isomers c, which are further transformed into isomers d. Remarkably, isomers d can be converted to their diastereomers e quantitatively by heating, and e can be converted back to d by irradiation at 300 nm.

Controlled synthesis and alkaline earth ion binding of switchable formamidoxime-based crown ether analogs.

The partial positive charge of amide protons is used to promote macrocyclization and form crown-ether analogs. Their deprotonation generates very selective pH-switchable alkaline earth ion receptors only in the presence of an appropriate substrate.

Stepwise intramolecular photoisomerization of NHC-chelate dimesitylboron compounds with C-C bond formation and C-H bond insertion.

C,C-chelate dimesitylboron (BMes(2)) compounds containing an N-heterocyclic carbene (NHC) donor have been obtained. Single-crystal X-ray diffraction analyses established that the boron atom in these compounds is bound by four carbon atoms in a distorted tetrahedral geometry. Compared to previously reported N,C-chelate dimesitylboron compounds, the new C,C-chelate boron compounds have a much larger HOMO-LUMO energy gap (>3.

Prediction of reaction barriers and force-induced instabilities under mechanochemical conditions with an approximate model: a case study of the ring opening of 1,3-cyclohexadiene.

Mechanochemistry, the use of mechanical stresses to activate chemical reactions, has emerged as a topic of significant interest. The present study examines the use of an approximate model for the prediction of reaction barriers under mechanochemical conditions using the ring opening of 1,3-cyclohexadiene along conrotatory and disrotatory directions as a specific test case. To do this, reaction barriers are evaluated using quantum chemical methods with an external force applied between various pairs of atoms.

The tensile strengths of heterogeneous interfaces: a comparison of static and dynamic first-principles calculations.

First-principles molecular dynamics (FPMD) simulations and static quantum chemical (QC) calculations are used to evaluate the tensile strengths, σ(c), of interfaces consisting of (0001) surfaces of α-Al(2)O(3) separated by small organic species. The evaluation of σ(c) with FPMD was achieved by performing simulations in which the simulation cell was extending in a direction normal to the fracture plane until rupture of the interface occurred. The static QC calculations employed an approach which treated fracture of the interface as a competition between uniform extension of the simulation cell and crack formation at the rupture site, which is analogous to that used in the construction of universal binding energy relationships.

Methanolysis of thioamide promoted by a simple palladacycle is accelerated by 10(8) over the methoxide-catalyzed reaction.

Palladacycle 1 catalyzes the methanolytic cleavage of N-methyl-N-(4-nitrophenyl)thiobenzamide (4) via a mechanism involving formation of a Pd-bound tetrahedral intermediate (TI). The rate constant for decomposition of the complex formed between 1, methoxide, and 4 is 9.3 s(-1) at 25 °C; this reaction produces methyl thiobenzoate and N-methyl-4-nitroaniline.