Metallization and Schottky-barrier formation for Se-passivated GaAs(1 0 0) interfaces

Using a molecular dynamics DFT-LDA code, we have analyzed the Schottky-barrier formation of a Se-passivated GaAs(1 0 0)-2×1 reconstruction. In our approach we consider, first, the energetically most favorable interfaces formed by the deposition of either one or two Ga atoms per surface unit cell; then, we analyze the electron density of states and calculate the interface Fermi level and the Schottky-barrier height. We show that the height depends essentially on the very same interface geometry. In particular, the effect of exchanging Ga and Se atoms at the interface (an intermixing process) yields a normal Schottky-barrier height, while the normal passivated surface yields an ohmic contact.     

Biosynthetic studies of the DSP toxin skeleton

Marine toxins have drawn wide interest because their economical impact and disastrous effect upon the shellfish industry and public health in many parts of the world. One of the most interesting group of substances of marine toxins, from structural and pharmacological points of view are polyether compounds, which generally present a great diversity in size and potent biological activities. The subject of this work was about to biosynthesis of okadaic acid skeleton as leader as DSP toxins. Its biosynthesis attracts considerable attention since the carbon skeleton has been shown to be synthesised via an unusual route. In this paper we report on stable isotope incorporation experiments on DSP toxin in artificial cultures of dinoflagellate. The comparison of the degrees of incorporation in these samples measured by different methods led to contradictory results. This implies that further experimental data is needed in order to propose a logical biogenetic scheme.     

Strong light‐matter coupling between a molecular vibrational mode in a PMMA film and a low‐loss mid‐IR microcavity

Microcavity devices exhibiting strong light‐matter coupling in the mid‐infrared spectral range offer the potential to explore exciting open physical questions pertaining to energy transfer between heat and light and can lead to a new generation of efficient wavelength tunable mid‐infrared sources of coherent light based on polariton Bose‐Einstein Condensation. Vibrational transitions of organic molecules, which often have strong absorption peaks in the infrared and considerably narrower linewidths than organic excitonic resonances, can generate polaritonic states in the mid‐infrared spectral range using microcavity devices. Here, narrow linewidth polaritonic resonances are exhibited in the mid‐infrared by coupling the carbonyl stretch vibrational transition of a polymethyl methacrylate film to the photonic resonance of a low optical‐loss mid‐infrared microcavity, which consisted of two Ge/ZnS dielectric Bragg reflectors. Rabi‐splitting of 14.3 meV is observed, with a 4.4 meV polariton linewidth at anti‐crossing. The large Rabi‐splitting relative to linewidth indicates efficient impedance‐matching between the bare vibrational and photonic states, and suggests molecular‐vibration polaritons incorporated in dielectric microcavities can be an enabling step towards realizing polariton optical switching and polariton condensation in the mid‐infrared spectral range.     

New features on the fragmentation and differentiation of C-glycosidic flavone isomers by positive electrospray ionization and triple quadrupole mass spectrometry

Six flavone mono-C-glucosides, four standards (beta-D-glucopyranosyl-(1 --> C-6)- and -(1 --> C-8)- apigenin and luteolin) and two others from lemon juice (beta-D-glucopyranosyl-(1 --> C-6)- and -(1 --> C-8)-diosmetin) have been studied in order to analyze their fragmentation patterns. Initial separation was carried out using high-performance liquid chromatography with diode-array detection (HPLC/DAD) coupled to an electrospray ionization (ESI) interface and a triple quadrupole mass spectrometer. Several systematic differences between collision-induced dissociation tandem mass (CID-MS/MS) spectra of C-6- and C-8-isomers have been found and some general guidelines and two new diagnostic product ions have been proposed for the differentiation of C-6- and C-8-flavonoid glycosides. These results have been successfully applied to the characterization of two flavone C-glycosides found in lemon juice, and mass spectra of a flavone di-C-glycoside detected in lemon juice have been studied and interpreted.     

Synthesis, crystal structure and non-linear optical properties of boronates derivatives of salicylideniminophenols

The condensation in one step of a series of salicylaldehydes and 2-amino-5-nitrophenol with 1-naphthylboronic acid, 2-naphthylboronic acid, and o-tolylboronic acid to give the corresponding boronates 1a-3a, 1b-3b and 1c-3d, is reported. The X-ray crystal structures of 1a, 2b and 3b allowed determining the α- and β-angle between the stilbene skeleton and the aryl or naphthylboronic fragments; these values are indicative of different conformations for the aryl moieties around the (B-C) boron-carbon bond which could potentially modulate the electronic properties on the boron stilbene compounds. All compounds were characterized by ¹H, ¹¹B and ¹³C NMR spectroscopy, UV, IR and mass spectrometry. Second- and third-order non-linear optical characterizations were also performed by EFISH and THG Maker Fringe techniques, respectively. Compounds 3a-3d containing an -N(Et)₂ donor group gave the best NLO response in second- and third-order.     

TTF-based bent-core liquid crystals

The synthesis and characterization of bent-core liquid crystals which incorporate TTF groups is reported; different bent-core mesophases are induced depending on the molecular structure and properties derived from their compact packing have been studied.     

Giant Volume Change and Topological Gaps in Temperature‐ and Pressure‐Induced Phase Transitions: Experimental and Computational Study of ThMo2O8

By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo₂O₈, allowing the formation of an unexpected new ThMo₂O₈ polymorph (high‐temperature/high‐pressure (HT/HP) orthorhombic ThMo₂O₈). Compared with the other three ThMo₂O₈ polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP–orthorhombic ThMo₂O₈ is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high‐pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo₂O₈ phases are based on three‐dimensional (3D) frameworks constructed from corner‐sharing ThO_x (x=6, 8, or 9) polyhedra and MoO₄ tetrahedra. The HT/HP–orthorhombic ThMo₂O₈, however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO₁₁ and MoO₄₊₁ polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo₂O₈ polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings.