Fifty years of M?ssbauer spectroscopy: from alloys and oxides to glasses and nanoparticles

The M?ssbauer Effect was discovered in 1957. In 1960 M?ssbauer spectroscopy was born when two important papers appeared on (i) the magnetic hyperfine interaction and (ii) the electric monopole (isomer shift) and quadrupole interactions. These transformed an interesting phenomenon into a method for probing solids. Applications to magnetism, metals and alloys, chemical compounds, biological molecules, geology, archaeology and other sciences followed and are still of current interest. Two areas of research where M?ssbauer spectroscopy is making unique contributions are in determining oxidation states in (i) glasses and (ii) nanoparticles. Some recent measurements are described.     

Characterization and Control of Residual Stress and Curvature in Anodically Bonded Devices and Substrates with Etched Features

While anodic bonding is commonly used in a variety of microelectromechanical systems (MEMS) applications, devices and substrates that incorporate this processing technique are often subjected to significant residual stress and curvature that create post-processing and reliability issues. Here, using an anisothermal anodic bonding procedure, residual stresses and the resulting wafer curvature in these structures are controlled by varying the initial bond temperatures of the silicon and Pyrex wafers independently. Residual stresses are quantified by measuring bulk wafer curvature and, locally, stress concentrations are measured using infrared photoelasticity accompanied by 3-D thermomechanical finite element analysis. Based on the good agreement between numerical predictions and experimental results, this process can be used to determine the bulk post-bond wafer curvature and to reduce the likelihood of structural failure at these sites, by changing the residual stresses from tensile in nature, which may drive initiation and growth of cracks, to compressive, which can suppress such failures.     

Full assignment of the proton and carbon-13 nmr spectra of 2,3,6 -tri-o-methyl-β-cyclodextrin

The proton and carbon-13 NMR spectra of 2,3,6 -tri-O-methyl-β-cyclodextrin in deuteriochloroform have been fully and unambiguously assigned using homonuclear and selective heteronuclear spin decoupling and two-dimensional homo- and heteronudear correlation NMR spectroscopy. Corrections are made to some earlier literature assignments.     

A reversible safety-catch method for the hydrogenolysis of N-benzyl moieties

The benzyl groups of β-hydroxy-N-benzyl sulfonamides are labile toward hydrogenolysis-unlike N-benzyl sulfonamides lacking the β-hydroxy moiety. We find that N-acyl-N-benzyl sulfonamides undergo hydrogenolysis under very mild conditions. Based upon these observations, we developed a reversible safety-catch method using tert-butoxycarbonyl moieties to activate N-benzyl sulfonamides toward hydrogenolysis. We also explored the utility of the safety-catch activation method for other nitrogen-based functionality such as N-benzyl carboxamides, imides, and related functionality.     

Phase transformation in He+ and H+ ion irradiated type 304 stainless steel

γ (fcc)→α (bcc) phase transformation in type 304 stainless steel has been observed after irradiation of He⁺ and H⁺ ions up to fluence levels of 10¹⁷ and 10¹⁹ ions/cm², respectively. Depth selective conversion Mössbauer spectroscopy and surface-sensitive X-ray diffractometry were employed to study the effect of irradiation. It is shown that the amount of the ion induced phase is highly sensitive to the fluence, the ion species and depth from the surface. It is worth noting that H⁺ ion irradiation is rather ineffective in inducing the transformation.     

素理想完全分裂的一个判别法则

本文给出了数域K内一个素理想在K的有限次正规扩域L内完全分裂的一个判别法则。     

Use of a urea and guanidine-HCl-propanol solvent system to purify a growth inhibitory glycopeptide by high-performance liquid chromatography

Reversed-phase high-performance liquid chromatography was used to purify an inhibitory glycopeptide where resolution and recovery were enhanced by using urea or guanidine-HCl-isopropanol-water as a solvent system. Isopropanol alone or other solvent systems that have been proposed for such purification steps were not effective in eluting hydrophobic proteins from the reversed-phase column. The application of the urea or guanidine-HCl solvent systems in the separation and purification of membrane proteins, and other hydrophobic macromolecules, could greatly enhance recovery and efficiency of purification.     

Isotopic oxygen exchange rates between [V18O42]12− and water

Summary From kinetic studies of¹⁸O-exchange between aqueous solutions of K₁₂V₁₈O₄₂ · 16H₂O and water it is concluded that [V₁₈O₄₂]^12– exists as a discrete ion in this medium. The rate of exchange is relatively slow (t_1/2 ca. 6×10⁴s at 0°C) and obeys the McKay equation within the precision obtainable. The sensitivity of the ion to its environment in the solid state, leading to induced exchange, prevented a decision as to whether all oxygens are kinetically equivalent. It is clear, however, that the ions remains intact for long periods in solution in the absence of air.