Screening for crystalline salts via mechanochemistry

Neat grinding and solvent-drop grinding methods are found to be effective screening tools for indicating the potential for crystalline salt formation involving a given acid-base pair, as demonstrated with two model pharmaceuticals.     

Generation of chemisorbed benzyl radicals on silica nanoparticles

Functionalized silica nanoparticles (NP) were obtained by esterification of the silanol groups of fumed silica nanoparticles with benzyl alcohol. These particles were characterized by Fourier transform infrared spectroscopy, ¹³C and ²⁹Si NMR spectroscopy, thermogravimetry, total organic carbon, Brunauer–Emmett–Teller analysis, UV-visible spectroscopy, and transmission electron microscopy. NP suspensions in water/acetonitrile mixtures were used as quenchers of benzophenone (BP) phosphorescence in time-resolved experiments at the excitation wavelength of 266 nm. The phosphorescence signals obtained in the presence of the nanoparticles were fitted to biexponential decays. Both decays were accelerated in the presence of increasing amounts of NP. A model, including the reversible adsorption of BP on the NP, which was supported by computer simulations accounts for the observed results. Laser flash-photolysis experiments with excitation at 266 nm of NP suspensions in water/acetonitrile in the presence of BP generated benzyl radicals that were attached to the silica surface. These radicals were detected at their absorption maxima (320 nm) by transient optical techniques.     

Role of direct microbial electron transfer in corrosion of steels

It has recently been discovered that many microbial species have the capacity to connect their metabolism to solid electrodes, directly exchanging electrons with them through membrane-bound redox compounds, nevertheless such a direct electron transfer pathway has been evoked rarely in the domain of microbial corrosion. Here was evidenced for the first time that the bacterium Geobacter sulfurreducens is able to increase the free potential of 304 L stainless steel up to 443 mV in only a few hours, which represents a drastic increase in the corrosion risk. In contrast, when the bacterial cells form a locally well-established biofilm, pitting potentials were delayed towards positive values. The microscopy pictures confirmed an intimate correlation between the zones where pitting occurred and the local settlement of cells. Geobacter species must now be considered as key players in the mechanisms of corrosion.     

Theoretical Study on Hydrogen‐Bond Effects in IR Spectra of High‐ and Low‐Temperature Phases of Nitric Acid Dihydrate

The low‐ and high‐temperature phases (α and β, respectively) of solid nitric acid dihydrate (NAD) are studied in depth by DFT methods. Each phase contains two types of complex structures (H₃O⁺) ? (H₂O), designated A and B, with different hydrogen‐bonding (HB) characteristics. The theoretical study reveals that type A complexes are weakly bound and could be described as (H₃O)⁺ and H₂O aggregates, with decoupled vibrational modes, whereas in type B structures the proton is situated close to the centre of the O ??? O bond and induces strong vibrational coupling. The proton‐transfer mode is predicted at quite different wavenumbers in each complex, which provides an important differentiating spectral feature, together with splitting of some bands in β‐NAD. Theoretical spectra are estimated by using two GGA parameterizations, namely, PBE and BLYP. The potential‐energy surface for each type of HB in NAD is also studied, as is the spectral influence of displacement of the shared H atom along the O? O bond. The results are compared to literature infrared spectra recorded by different techniques, namely, transmission and reflection–absorption, with both normal and tilted incident radiation. This work provides a thorough assignment of the observed spectra, and predictions for some spectra not yet available. The usefulness of high‐level theoretical calculations as performed herein to discriminate between two phases of a solid crystal is thus evidenced.     

Raman and X‐ray investigations of the incorporation of Ca2+ and Cd2+ in the ZrO2 structure

The formation of solid solution and ZrO₂ phase stabilization were investigated by Raman spectroscopy and X‐ray diffraction (XRD) in calcium‐containing and cadmium‐containing zirconium oxide samples heated at 1073 K in air. The adopted preparation procedure led to the incorporation of calcium and cadmium in solid solution into the zirconia structure. The solid solution favored the tetragonal and cubic zirconia phases at the expense of the thermodynamically stable monoclinic modification. Combined macro‐ and micro‐Raman spectroscopy disclosed that instead of forming a homogeneous phase t″, intermediate between the tetragonal t′ and the cubic phase, the tetragonal and cubic phases coexisted in the range 9.49–13.89 mol% for Ca and 11.88–17.23 mol% for Cd. At higher dopant contents the cubic form stabilized. The impurity content necessary to stabilize the high‐symmetry phases was defined. Copyright © 2007 John Wiley & Sons, Ltd.     

Tris(tetramethylethylenediamine-sodium)-9,9-bianthryl—The Salt of a π Hydrocarbon Radical Trianion with Three Na+–Cπ Contacts to One Molecular Half

Quite unexpectedly, all three electrons are taken up by the same anthryl moiety when 9,9′-bianthryl is reduced with an excess of sodium metal. Thanks to the “right” ligand/solvent mixture the first radical trianion salt (depicted on the right) could be isolated. It is a contact-ion quadruple of bianthryl in which all three Na⁺ counterions coordinate to the same half of the hydrocarbon molecule.     

Chiral Single-Molecule Potentiometers Based on Stapled ortho- Oligo(phenylene)ethynylenes

We report on the chemical design of chiral molecular junctions with stress-dependent conductance, whose helicity is maintained during the stretching of a single molecule junction due to the stapling of both ends of the inner helix. In the reported compounds, different conductive pathways are observed, with clearly different conductance values and plateau-length distributions, attributed to different conformations of the helical structures. The large chiro-optical responses and the potential use of these molecules as unimolecular spin filters have been theoretically proved using state-of-the-art Density Functional Theory (DFT) calculations, including a fully ab-initio estimation of the CISS-originating spin polarization which is done, for the first time, for a realistic molecular system.