FP-LMTO investigations of mechanical stability and high pressure of platinum nitride compounds

We report local density functional calculations using the full potential linear muffin-tin orbital (FP-LMTO) method for binary platinum nitride (PtN), in five different crystal structures, the rock salt (B1), zinc-blende (B3), wurtzite (B4), nickel arsenide (B8), and PbS (B10) phases. The ground state properties such as the equilibrium lattice constant, elastic constants, the bulk modulus and its pressure derivative of PtN in these phases are determined and compared with the other available experimental and theoretical works.Our calculations confirm in the B3 structure that PtN is found to be mechanically stable with a large bulk modulus B=232.45 GPa and at a sufficiently high pressure the B8₁ structure would be favoured.The theoretical transition pressure from zinc blende (B3) to NiAs (B8₁), zinc-blende (B3) to rock-salt (B1) and zinc-blende (B3) to PbO (B10) is determined to be 9.10 GPa, 9.85 GPa and 69.35 GPa, respectively. Our calculation shows also in five different structures for PtN a high bulk modulus is a good indicator of a hard material.     

Sliding droplets on superomniphobic zinc oxide nanostructures

This study reports on liquid-repellency of zinc oxide nanostructures (ZnO NS). The ZnO NS are synthesized by an easy and fast chemical bath deposition technique. Three different nanostructured surfaces consisting of nanorods, flowers, and particles are prepared, depending on the deposition time and the presence of ethanolamine in the reaction mixture. Chemical functionalization of the ZnO NS with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS) in liquid (PFTS L) and vapor phase (PFTS V) or through octafluorobutane (C(4)F(8)) plasma deposition led to the formation of superomniphobic surfaces. A comprehensive characterization of the wetting properties (static contact angle and contact angle hysteresis) has been performed using liquids composed of deionized water and various concentrations of ethanol (surface tension between 35 and 72.6 mN/m). Depending on the nanostructures morphology, coating nature and liquid employed, high static apparent contact angles θ ≈ 150-160°, and low contact angle hysteresis Δθ ≈ 0° are obtained. The different ZnO NS are characterized using scanning electron microscopy (SEM) and contact angle measurements. The results reported in this work permit preparation of sliding omniphobic surfaces using a simple and low cost technique.     

Stability of the gold/silica thin film interface: electrochemical and surface plasmon resonance studies

This article reports chemical stability studies of a gold film electrode coated with thin silicon oxide (SiOx) layers using electrochemical, surface plasmon resonance (SPR) and atomic force microscopy (AFM) techniques. Silica films with different thicknesses (d = 6.4, 9.7, 14.5, and 18.5 nm) were deposited using a plasma-enhanced chemical vapor deposition technique (PECVD). For SiOx films with d >/= 18.5 nm, the electrochemical behavior is characteristic of a highly efficient barrier for a redox probe. SiOx films with thicknesses between 9.5 and 14.5 nm were found to be less efficient barriers for electron transfer. The Au/SiOx interface with 6.4 nm of SiOx, however, showed an enhanced steady-state current compared to that of the other films. The stability of this interface in solutions of different pH was investigated. Whereas a strongly basic solution led to a continuous dissolution of the SiOx interface, acidic treatment produced a more reticulated SiOx film and improved electrochemical behavior. The electrochemical results were corroborated by SPR measurements in real time and AFM studies.     

Effect of surface roughness and chemical composition on the wetting properties of silicon-based substrates

The article reports on the wetting properties of silicon-based materials as a function of their roughness and chemical composition. The investigated surfaces consist of hydrogen-terminated and chemically modified atomically flat crystalline silicon, porous silicon and silicon nanowires. The hydrogenated surfaces are functionalized with 1-octadecene or undecylenic acid under thermal conditions. The changes occurring upon surface functionalization are characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) spectroscopy and water contact angle measurements. By increasing the surface roughness, the static water contact angle increases. The combination of high surface roughness with chemical functionalization with water repellent coating (1-octadecene) enables reaching superhydrophobicity (water contact angle greater than 150°) for silicon nanowires.     

Distinction between surface hydroxyl and ether groups on boron-doped diamond electrodes using a chemical approach

While it is clearly established that oxidation of as-grown boron-doped diamond (BDD) interfaces results in the introduction of different surface oxygen functions such as ether, carbonyl and hydroxyl groups, there is no reported approach which can clearly distinguish between the different surface functions. For further surface functionalization, it is important to quantify the presence of each group on the diamond surface. In this paper, the presence and amount of surface hydroxyl groups is identified using esterification of the COH groups with trifluoroacetic acid. The presence of CF₃ group in the acid allowed the identification and estimation of the amount of surface hydroxyl groups using X-ray photoelectron spectroscopy (XPS).     

Preparation of superhydrophobic silicon oxide nanowire surfaces

The paper reports on the preparation of superhydrophobic amorphous silicon oxide nanowires (a-SiONWs) on silicon substrates with a contact angle greater than 150 degrees by means of surface roughness and self-assembly. Nanowires with an average mean diameter in the range 20-150 nm and 15-20 microm in length were obtained by the so-called solid-liquid-solid (SLS) technique. The porous nature and the high roughness of the resulting surfaces were confirmed by AFM imaging. The superhydrophobicity resulted from the combined effects of surface roughness and chemical modification with fluorodecyl trichlorosilane.     

Palladium catalyzed mild reduction of α,β-unsaturated compounds by triethylsilane

The palladium(II) chloride/triethylsilane system has been successfully applied for the selective hydrogenation of the carbon-carbon double bond of α,β-unsaturated ketones to yield the corresponding saturated carbonyl compounds. The reaction takes place under mild conditions and affords high yields.     

Leading RNA tertiary interactions: structures, energies, and water insertion of A-minor and P-interactions. A quantum chemical view

Complex molecular shapes of ribosomal RNA molecules are stabilized by recurrent types of tertiary interactions involving highly specific and conserved non-Watson-Crick base pairs, triplets, and quartets. We analyzed the intrinsic structure and stability of the P-motif and the four basic types of A-minor interactions (types I, II, III, and 0), which represent the most prominent RNA tertiary interaction patterns refined in the course of evolution. In the studied interactions, the electron correlation component of the stabilization usually exceeds the Hartree-Fock (HF) term, leading to a strikingly different balance of forces as compared to standard base pairing stabilized primarily by the HF term. In other words, the A-minor and P-interactions are considerably more influenced by the dispersion energy as compared to canonical base pairs, which makes them particularly suitable to zip the folded RNA structures that are substantially hydrated even in their interior. Continuum solvent COSMO calculations confirm that the stability of the canonical GC base pair is affected (reduced) by the continuum solvent screening considerably more than the stability of the A-minor interaction. Among the studied systems, the strong A-minor II and weak A-minor III interactions require water molecules to stabilize the experimental geometry. Gas-phase optimization of the canonical A-minor II A/CG triplet without water results in a geometry that is clearly inconsistent with the RNA structure. The gas-phase structure of the P-interaction and the most stable A-minor I interaction nicely agrees with the geometries occurring in the ribosome. A-minor I can also adopt an alternative water-mediated substate rather often observed in X-ray and molecular dynamics studies. The A-minor I water bridge, however, does not appear to stabilize the tertiary contact, and its role is to provide structural flexibility to this binding pattern within the context of the RNA structure. Interestingly, the insertion of a polar water molecule in the A-minor I A/CG tertiary contact occurring in the A/C tertiary pair is stabilized primarily by the HF (electrostatic) interaction energy, while the dispersion-controlled A/G contact remains firmly bound. Thus, the intrinsic balance of forces as revealed by quantum mechanics (QM) calculations nicely correlates with many behavioral aspects of the studied interactions inside RNA. The comparison of interaction energies computed using quantum chemistry and an AMBER force field reveals that common molecular mechanics calculations perform rather well, except that the strength of the P-interaction is modestly overestimated. We also briefly discuss the non-negligible methodological differences when evaluating simple base-base nucleic acids base pairs and the complex RNA tertiary base pairing patterns using QM procedures.     

Substituent Effects on EI-MS Fragmentation Patterns of 5-Allyloxy-1-aryl-tetrazoles and 4-Allyl-1-aryl-tetrazole-5-ones; Correlation with UV-Induced Fragmentation Channels

1,4- and 1,5-disubstituted tetrazoles possess enriched structures and versatile chemistry, representing a challenge for chemists. In the present work, we unravel the fragmentation patterns of a chemically diverse range of 5-allyloxy-1-aryl-tetrazoles and 4-allyl-1-aryl-tetrazolole-5-ones when subjected to electron impact mass spectrometry (EI-MS) and investigate the correlation with the UV-induced fragmentation channels of the matrix-isolated tetrazole derivatives. Our results indicate that the fragmentation pathways of the selected tetrazoles in EI-MS are highly influenced by the electronic effects induced by substitution. Multiple pathways can be envisaged to explain the mechanisms of fragmentation, frequently awarding common final species, namely arylisocyanate, arylazide, arylnitrene, isocyanic acid and hydrogen azide radical cations, as well as allyl/aryl cations. The identified fragments are consistent with those found in previous investigations concerning the photochemical stability of the same class of molecules. This parallelism showcases a similarity in the behaviour of tetrazoles under EI-MS and UV-irradiation in the inert environment of cryogenic matrices of noble gases, providing efficient tools for reactivity predictions, whether for analytical ends or more in-depth studies. Theoretical calculations provide complementary information to articulate predictions of resulting products.     

Far-UV laser flash photolysis in solution. A study of the chemistry of 1,1-dimethylsilene in hydrocarbon solvents

The far-UV (193 nm) laser flash photolysis of nitrogen-saturated isooctane solutions of 1,1-dimethylsiletane allows the direct detection of 1,1-dimethylsilene as a transient species, which (at low laser intensities) decays with pseudo-first-order kinetics (τ 10 μs) and exhibits a UV absorption spectrum with λ_max 255 nm. Characteristic rapid quenching is observed for the silene with methanol (k_McOH = (4.9 ± 0.2) × 10⁹ M⁻¹ s⁻¹), tert-butanol (k_BuOH = (1.8 ± 0.1) × 10⁹ M⁻¹ s⁻¹) and oxygen (k_O2 = (2.0 ± 0.5) × 10⁸ M⁻¹ s⁻¹). The Arrhenius activation parameters for the reaction with methanol have been determined to be E_a = −2.6 ± 0.6 kcal mol⁻¹ and log A = 7.7 ± 0.3.