Direct synthesis of 2,5-polychloro-1,2-epoxycyclopentane-1-carboxylic acids and their alkyl esters

The treatment of 3,3,6,6-tetrachloro-1,2-cyclohexanedione with sodium hydroxide gave 2,5,5-trichloro-1,2-epoxycyclopentane-1-carboxylic acid in almost quantitative yield. 3,6,6-Trichloro-2-hydroxy-2-cyclohexen-1-one was also found to be able to undergo a similar reaction providing c-2,t-5-dichoro-1,2-epoxy-r-1-cyclopentanecarboxylic acid, whose structure was confirmed by X-ray crystallographic analysis. The reactions with alkali metal alcoholates gave the corresponding esters in fair to good yields. In contrast to the properties described for further α-chloroepoxides, the prepared compounds show remarkable stability.     

Mass spectra of 1,1-bis(acylamido)-1-deoxyalditol acetates

The mass spectra of fourteen 1,1-bis(acylamido)-1-deoxyalditol acetates and of two model compounds have been recorded. The most important feature of the fragmentation of these derivatives is the cleavage of the C–1–C–2 bond which produces fragment None of the alditol derivatives yields the molecular ion.     

The role of atomic scale investigation in the development of nanoscale materials for information storage applications.

It is well established that the response of devices based on the giant magnetoresistance (GMR) effect depends critically on film microstructure, with parameters such as interfacial abruptness, the roughness and waviness of the layers, and grain size being crucial. Such devices have applications in information storage systems, and are therefore of great technological interest as well as being of fundamental scientific interest. The layers must be studied at high spatial resolution if the microstructural parameters are to be characterized with sufficient detail to enable the effects of fabrication conditions on properties to be understood, and the techniques of high resolution electron microscopy, transmission electron microscopy chemical mapping, and atom probe microanalysis are ideally suited. This article describes the application of these techniques to a range of materials including spin valves, spin tunnel junctions, and GMR multilayers.     

FCclasses3: Vibrationally-resolved spectra simulated at the edge of the harmonic approximation

We introduce FCclasses3, a code to carry out vibronic simulations of electronic spectra and nonradiative rates, based on the harmonic approximation. Key new features are: implementation of the full family of vertical and adiabatic harmonic models, vibrational analysis in curvilinear coordinates, extension to several electronic spectroscopies and implementation of time-dependent approaches. The use of curvilinear valence internal coordinates allows the adoption of quadratic model potential energy surfaces (PES) of the initial and final states expanded at arbitrary configurations. Moreover, the implementation of suitable projectors provides a robust framework for defining reduced-dimensionality models by sorting flexible coordinates out of the harmonic subset, so that they can then be treated at anharmonic level, or with mixed quantum classical approaches. A set of tools to facilitate input preparation and output analysis is also provided. We show the program at work in the simulation of different spectra (one and two-photon absorption, emission and resonance Raman) and internal conversion rate of a typical rigid molecule, anthracene. Then, we focus on absorption and emission spectra of a series of flexible polyphenyl molecules, highlighting the relevance of some of the newly implemented features. The code is freely available at http://www.iccom.cnr.it/en/fcclasses/ .     

A model for oxidation-driven surface segregation and transport on Pt-alloys studied by atom probe tomography

Using a purpose-built 3D atom probe, we have previously shown that exposure to oxidising gases (NO, N₂O, O₂) induces Rh surface segregation in Pt–Rh alloys, the extent of which is strongly dependent on treatment temperature, crystallographic plane and the presence of ternary alloy additions. In this paper, the segregation trends identified on three different crystallographic surfaces of Pt–Rh are analysed using thermodynamic and kinetic arguments. The segregation model we present is generic for diffusion on alloy surfaces in the presence of active gases. From it we obtain activation energies and diffusion coefficients for the processes of metal-oxide species diffusion both perpendicular to and laterally across the surface. Using these we propose a simple model for the interaction of chemically active gases with the surfaces of such alloys. Applying this understanding to sequential oxidation/reduction treatments would in principle allow improved control of the surface composition of alloy catalysts. Related applications of this model include optimisation of core–shell catalyst nanoparticles.     

Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry of beta-(1 --> 3), beta-(1 --> 4)-xylans from Nothogenia fastigiata using nor-harmane as matrix

Three xylan fractions isolated from the red seaweed Nothogenia fastigiata (Nemaliales) were analyzed by ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOFMS). UV-MALDI-TOFMS was carried out in the linear and reflectron modes, and as routine in the positive and negative ion modes. Of the several matrices tested, nor-harmane was the only effective one giving good spectra in the positive ion mode. The number-average molar masses of two of the fractions, calculated from the distribution profiles, were lower than those determined previously by (1)H NMR analysis, suggesting a decrease in the ionization efficiency with increasing molecular weight; weight-average molar mass and polydispersity index were also determined. As the xylans retained small but significant quantities of calcium salts, the influence of added Ca(2+) as CaCl(2) on UV-MALDI-MS was investigated. The simultaneous addition of sodium chloride and calcium chloride was also analyzed. Addition of sodium chloride did not change the distribution profile of the native sample showing that the inhibitory effect is due to Ca(2+) and not to Cl(-). Addition of calcium chloride with 1:1 analyte/salt molar ratio gave spectra with less efficient desorption/ionization of oligomers; the signals of these oligomers were completely suppressed when the addition of the salt became massive (1:100 analyte/salt molar ratio).     

Synthesis of unsymmetrical diarylmethanes by cross-coupling between aryl triflates and tetrabutylammonium difluorotribenzylstannate

The benzylation of aryl triflates can be achieved by cross-coupling between aryl triflates and the new hypervalent tin reagent (n-Bu(4)N)(+)(Bn(3)SnF(2))(-).     

The High-Resolution 1H NMR Spectra and Conformations of N-Acetyl-α-D-Galactopyranosylamine Peracetate and 1,1-Bis(Acetamido)-1-Deoxy-D-Glucitol Peracetate in Aqueous Medium

Abstract

In contrast with the spectra previously measured with lower resolution equipment, the 500-MHz ¹H NMR spectra of 1,1-bis(acetamido)-1-deoxy-d-glucitol peracetate and N-acetyl-α-d-galactopyranosylamine peracetate in aqueous solution were amenable to full resolution. The former compound shows a “sickle” conformation produced by rotation of the C2-C3 bond out of the planar, zigzag arrangement, while the latter has a ⁴C₁ conformation.     

Three-dimensional atomic scale analysis of nanostructured materials

The 3-dimensional atom probe (3DAP) has been used to provide atomic-scale microcharacterisation of a number of nanostructured materials. Grain boundary segregation has been investigated in electrodeposited nanocrystalline nickel and Ni-P. In the nanocrystalline nickel, there was no observable grain boundary segregation in the as-deposited condition. After annealing, carbon and sulphur contamination was found at the boundary of an abnormally-grown grain. In the as-deposited Ni-P alloy, only limited grain boundary segregation of P is seen, but annealing produces significant segregation and the formation of Ni₃P precipitates at grain boundaries. The phase chemistry in a melt-spun amorphous Fe-Si-Cu-Nb-B-Al (FINEMET-type) alloy has also been studied, and the hetereogeneous nucleation of Fe-Si nanocrystals at Cu precipitates shown conclusively. It is found that at early stages of crystallisation, there is only limited partitioning of the Si between the nanocrystals and the amorphous matrix. Atom probe studies of thin layered films have historically been limited by specimen preparation problems, but recent advances have now yielded data on metallic multilayer films. This has allowed atomic-scale measurements of interface chemistry in these films for the first time.