Carbon Dioxide as a Protecting Group: Highly Efficient and Selective Catalytic Access to Cyclic cis‐Diol Scaffolds

The efficient and highly selective formation of a wide range of (hetero)cyclic cis‐diol scaffolds using aminotriphenolate‐based metal catalysts is reported. The key intermediates are cyclic carbonates, which are obtained in high yield and with high levels of diastereo‐ and chemoselectivity from the parent oxirane precursors and carbon dioxide. Deprotection of the carbonate structures affords synthetically useful cis‐diol scaffolds with different ring sizes that incorporate various functional groups. This atom‐efficient method allows the simple construction of diol synthons using inexpensive and accessible precursors and green metal catalysts and showcases the use of CO₂ as a temporary protecting group.     

Spatial distribution profiles of magnesium and strontium in speleothems using laser-induced breakdown spectrometry

Laser-induced breakdown spectrometry (LIBS) has been applied to spatially locate several atomic species in speleothems taken from the Nerja’s Cave (Málaga, Spain). Spatial distribution profiles of Mg at 285.21 nm and Sr at 407.77 nm were obtained while the laser was rastered through different paths along the sample. These elements were selected due to their importance as palaeoclimatic indicators. The 532 nm output of a Nd:YAG laser was used to irradiate the samples and generate the plasma that was spectrally analyzed and detected by using an intensified CCD detector. The signals were normalized to the Ca line to minimize pulse-to-pulse fluctuations in the laser source. Several studies were carried out to check for the point-to-point heterogeneity of the natural speleothem.     

Time-resolved laser-induced plasma spectrometry for determination of minor elements in steelmaking process samples

A pulsed Nd:YAG laser operating on the fourth (266 nm) and second (532 nm) harmonics has been used to generate plasmas on the target surface in air at atmospheric pressure. The influence of wavelength on quantitative analysis of 4 minor elements in stainless steel samples (Si, Ti, Nb and Mo) was investigated. Stainless steel samples with different elemental concentrations were prepared and analyzed by laser-induced plasma spectrometry (LIPS). The effect of laser wavelength on analytical figures of merit (calibration curves, correlation coefficients, linear dynamic ranges, analytical precision, and accuracy values) was found to be negligible when internal standardization (an Fe line) and time-resolved laser-induced plasma are employed. For both wavelengths, the calibration curves presented a good linearity and an acceptable linear dynamic range in the concentration interval investigated. For the four elements studied, limits of detection lower than 150 microg g(-1) were achieved. To evaluate the influence of wavelength on precision and accuracy, a set of fifteen high-alloyed steel samples from different stages of steelmaking process have been analyzed. Finally, the long-term stability of the analytical measurements for Mo with 532 nm wavelength has been discussed. RSD values were lower than 5.3% for the elements studied.     

Studies of sample preparation for surface-enhanced raman spectrometry on silver hydrosols

Surface-enhanced Raman spectra (SERS) on silver hydrosols of p-nitrobenzoic acid, p-aminobenzoic acid and aniline are reported. Several theoretical and practical aspects of the hydrosol preparation protocols and sample preparation procedures, and their effects on the sensitivity and reproducibility of the Raman signals are discussed. The effect of acidity on SERS signal intensity is shown to depend on the time of observation of the Raman spectra, illustrating the relevance of time to quantitative SERS data. the identification power of SERS at trace levels for closely related compounds (p-nitrobenzoic acid, p-aminobenzoic acid and aniline) is illustrated.     

Intermediate coupling model description of55Fe and57Fe

The properties of the negative parity states of⁵⁵Fe and⁵⁷Fe are investigated in the framework of the intermediate coupling model. In the model, a neutron or a quasineutron is coupled to anharmonic vibrations of the core. Anharmonicities of the vibrations are estimated through the observed properties of the core. Energy levels, spectroscopic factors and electromagnetic properties have been calculated. The results of the present calculations are also compared with available experimental results and other theoretical results. The model reasonably accounts for many of the properties of the low-lying states.     

Novel microscopic mechanism of intermixing during growth on soft metallic substrates

Generic computer simulations using empiric interatomic potentials suggest a new, collective mechanism that could be responsible for mixing at heteroepitaxial interfaces. Even if single adsorbate atoms diffuse by hopping on the substrate surface and do not mix at the terraces, two-dimensional islands formed by nucleation may become unstable above a certain critical size and explode upwards forming clusters of several atomic layers. This process is accompanied by strong distortions of the underlying atomic layers, and on soft materials it can result in surface etching and incorporation of substrate atoms into the islands.