DFT calculations, DRIFT spectroscopy and kinetic studies on the hydrolysis of isocyanic acid on the TiO2-anatase (1 0 1) surface

The co-adsorption of isocyanic acid (HNCO) and water (H₂O) and their reaction to ammonia and carbon dioxide on the anatase phase of TiO₂ were studied with ab initio density functional theory (DFT) calculations using a cluster model as well as with in situ DRIFTS investigations and kinetic experiments. We found that isocyanic acid can in principle adsorb both molecularly and dissociatively on the TiO₂(1 0 1) surface, but the moment at which water gets involved in the process, is vital for determining the further course of the surface reaction. In the absence of water, it was found that HNCO can adsorb in molecular form on the TiO₂ surface. Assuming this case to be the first step of the HNCO hydrolysis, the surface HNCO rearranges into an intermediate complex with a modified NCO skeleton. After decarboxylation water attacks the complex from the gas phase and ammonia is finally formed.

However, when water is present at the beginning of the hydrolysis reaction, it immediately attacks the NCO group present at the surface, yielding a carbamic acid complex, which is further transformed into a carbamate complex. After decarboxylation an NH₂ group remains at the surface. Finally, NH₃ is formed by hydrogen transfer from molecularly adsorbed water at a neighboring titanium center and the hydrolysis reaction is completed.

Since water is always present in diesel exhaust gas, only the second mechanism is relevant under practical conditions. Moreover, the calculated energy barrier is lower for the second mechanism compared to the first reaction pathway. The comparison between the sum of the theoretical vibrational spectra of the reaction intermediates with the in situ DRIFT spectra also strongly supports the accuracy of the second reaction pathway. The experimental investigation of the kinetics of the HNCO hydrolysis on TiO₂-anatase revealed a second order reaction—first order with respect to HNCO and first order with respect to water, which can only be reconciled with the second mechanism.     

Three-dimensional structural analysis of eukaryotic flagella/cilia by electron cryo-tomography

Electron cryo-tomography is a potential approach to analyzing the three-dimensional conformation of frozen hydrated biological macromolecules using electron microscopy. Since projections of each individual object illuminated from different orientations are merged, electron tomography is capable of structural analysis of such heterogeneous environments as in vivo or with polymorphism, although radiation damage and the missing wedge are severe problems. Here, recent results on the structure of eukaryotic flagella, which is an ATP-driven bending organelle, from green algae Chlamydomonas are presented. Tomographic analysis reveals asymmetric molecular arrangements, especially that of the dynein motor proteins, in flagella, giving insight into the mechanism of planar asymmetric bending motion. Methodological challenges to obtaining higher-resolution structures from this technique are also discussed.     

Static field ionization of the spherically confined hydrogen atom

The ionization of the hydrogen atom confined in a spherical potential well and subjected to a static electric field is studied, using the diffusion Monte Carlo (DMC) method. Atomic ionization within a potential well is found to be a stationary, gradual, and reversible process. The value of the electric field at the onset of ionization is of the order of 0.1 atomic units, and depends on the symmetry of the atomic wave function and on the confinement dimension. By decreasing the confinement sphere, the difference between the bound and ionized states disappears, showing that strict confinement leads to pressure ionization of the atom. The off-center case is studied characterizing the potential energy surface (PES), and the transition between field-induced and pressure-induced ionization is confirmed. Except for very weak fields, the minimum of the PES is reached when the proton is in contact with the boundary of the well.     

High‐Throughput Metabolomics by 1D NMR

Metabolomics deals with the whole ensemble of metabolites (the metabolome). As one of the ‐omic sciences, it relates to biology, physiology, pathology and medicine; but metabolites are chemical entities, small organic molecules or inorganic ions. Therefore, their proper identification and quantitation in complex biological matrices requires a solid chemical ground. With respect to for example, DNA, metabolites are much more prone to oxidation or enzymatic degradation: we can reconstruct large parts of a mammoth's genome from a small specimen, but we are unable to do the same with its metabolome, which was probably largely degraded a few hours after the animal's death. Thus, we need standard operating procedures, good chemical skills in sample preparation for storage and subsequent analysis, accurate analytical procedures, a broad knowledge of chemometrics and advanced statistical tools, and a good knowledge of at least one of the two metabolomic techniques, MS or NMR. All these skills are traditionally cultivated by chemists. Here we focus on metabolomics from the chemical standpoint and restrict ourselves to NMR. From the analytical point of view, NMR has pros and cons but does provide a peculiar holistic perspective that may speak for its future adoption as a population‐wide health screening technique.     

SAC-CI general-R study of the ionization spectrum of HCl

The valence ionization spectrum of HCl is studied by symmetry-adapted-cluster configuration-interaction general-R and SD-R methods. The general-R method describes well the peak positions and intensities of seven satellite lines observed below the double ionization threshold. The twinning shake-up states due to the (4σ)⁻¹ state and the Rydberg states of HCl⁺ are correctly reproduced. Received: 26 June 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999     

Determination of the rate constants for the gas-phase reactions of methyl butenol with OH radicals,ozone, NO3 radicals,and Cl atoms

Using a relative rate method, rate constants for the gas-phase reactions of 2-methyl-3-buten-2-ol (MBO) with OH radicals, ozone, NO₃ radicals, and Cl atoms have been investigated using FTIR. The measured values for MBO at 298±2 K and 740±5 torr total pressure are: k_OH=(3.9±1.2)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹, k_O3=(8.6±2.9)×10⁻¹⁸ cm³ molecule⁻¹ s⁻¹, k=(8.6±2.9)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹, and k_Cl=(4.7±1.0)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. Atmospheric lifetimes have been estimated with respect to the reactions with OH, O₃, NO₃, and Cl. The atmospheric relevance of this compound as a precursor for acetone is, also, briefly discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 589–594, 1998     

Modeling the photophysics and photochromic potential of 1,2-dihydronaphthalene (DHN): a combined CASPT2//CASSCF-topological and MMVB-dynamical investigation

The photochemical ring opening of 1,2-dihydronaphthalene (DHN) was investigated using two complementary computational approaches. CASPT2//CASSCF minimum energy paths were characterized for reaction channels on the three lowest-energy singlet excited states, describing initial evolution of the spectroscopic bright (ionic) state and its subsequent decay to dark (covalent) states of benzene-like and hexatriene-like character. Although the benzene-like state is unreactive and can radiate, the hexatriene-like state has indirect access to a low-energy conical intersection seam, at which radiationless decay to the ground state and subsequent product formation can take place. An MMVB molecular dynamics simulation was carried out on the reactive hexatriene-like excited state, suggesting that intramolecular vibrational energy redistribution (IVR) controls the radiationless decay and the photoproduct distribution (which is qualitatively reproduced).     

Characterisation of the different hands in the composition of a 14th century breviary by means of portable XRF analysis and complementary techniques

A 14th‐century breviary known as Breviario di San Michele della Chiusa, produced at the disposal of the monks of Sacra di San Michele abbey (near Turin, Italy) has been analysed in order to identify the different authors who contributed in its making. The study aimed at revealing how many scribes composed the text and the musical notations and how many artists worked for miniatures and for the decorations of initials. All inks and decorative features have been analysed by means of portable X‐ray fluorescence spectrometry for determining elemental distribution and by means of ultraviolet–Visible diffuse reflectance spectrophotometry with optic fibres and spectrofluorimetry for identifying colourants. The results on non‐invasive measurements highlighted that at least 11 persons (six scribes for the text, two scribes for the musical notations, two artists for initials and filigrees and one artist for the full‐page miniature at f. 208v) were at work at the Breviario. Moreover, the black inks used for text and notes have an anomalous composition, being iron gall inks with a larger than usual amount of zinc, possibly as a consequence of the use of vitriols made from goslarite; this suggests that the scribes could come from Northern Europe. The presence of traces of bismuth in blue paints also suggested the provenance of azurite from Central or Northern Europe. Copyright © 2017 John Wiley & Sons, Ltd.