2-Aminobenzamide and 2-Aminobenzoic Acid as New MALDI Matrices Inducing Radical Mediated In-Source Decay of Peptides and Proteins

One of the mechanisms leading to MALDI in-source decay (MALDI ISD) is the transfer of hydrogen radicals to analytes upon laser irradiation. Analytes such as peptides or proteins may undergo ISD and this method can therefore be exploited for top-down sequencing. When performed on peptides, radical-induced ISD results in production of c- and z-ions, as also found in ETD and ECD activation. Here, we describe two new compounds which, when used as MALDI matrices, are able to efficiently induce ISD of peptides and proteins: 2-aminobenzamide and 2-aminobenzoic acid. In-source reduction of the disulfide bridge containing peptide Calcitonin further confirmed the radicalar mechanism of the ISD process. ISD of peptides led, in addition to c- and z-ions, to the generation of a-, x-, and y-ions both in positive and in negative ion modes. Finally, good sequence coverage was obtained for the sequencing of myoglobin (17 kDa protein), confirming the effectiveness of both 2-aminobenzamide and 2-aminobenzoic acid as MALDI ISD matrices.     

Fluxionality in the chemical reactions of transition metal oxide clusters: the role of metal, spin state, and the reactant molecule

The phenomenon of fluxionality in the reactions of transition metal oxide clusters provides many opportunities in various catalytic and industrial processes. To gain a better understanding into the various factors influencing this phenomenon, we have carried out an electronic structure investigation of the fluxionality pathways when W(3)O(6)(-) and Mo(3)O(6)(-) clusters react with hydrogen sulfide and ammonia. The study illustrates how the metal (W vs Mo), different spin states of the anionic metal oxide cluster (doublet vs quartet), and the nature of the nonmetal in the small molecule (O vs S vs N), all affect the fluxionality pathway. The thermodynamically facile fluxionality pathway with H(2)S detaches both the hydrogens from hydrogen sulfide and can thus be very useful in the petrochemical and desulfurization industries. The fluxionality pathway with NH(3) results in interesting metal-bound imines and bridged amines. However, the overall fluxionality process with NH(3) is found to be thermodynamically unfavorable.     

Synthesis of silicophosphates containing SiO6-octahedra under ambient conditions--reactions of anhydrous H3PO4 with alkoxysilanes

Anhydrous H(3)PO(4) reacts in diethylether solution at room temperature with ethoxysilanes to form silicophosphates which contain SiO(6)-units. A single crystal X-ray structure provides evidence for silicophosphate structures comprised of alternating SiO(4)- and PO(4)-tetrahedra as well as SiO(6)-octahedra.     

Evolution of structural properties of iron oxide nano particles during temperature treatment from 250 °C-900 °C: X-ray diffraction and Fe K-shell pre-edge X-ray absorption study

Iron oxide nano particles with nominal Fe₂O₃ stoichiometry were synthesized by a wet, soft chemical method with heat treatment temperatures from 250 °C to 900 °C in air. The variation in the structural properties of the nano particles with the heat treatment temperature was studied by X-ray diffraction and Fe K-shell X -ray absorption spectroscopy. X-ray diffractograms show that at lower annealing temperatures the nano particle comprise both maghemite and hematite phases. With increasing temperature, the remainder of the maghemite phase transforms completely to hematite. Profile analysis of the leading Bragg reflections reveals that the average crystallite size increases from 50 nm to 150 nm with increasing temperature. The mean primary particle size decreases from 105 nm to 90 nm with increasing heat treatment temperature. The X-ray diffraction results are paralleled by systematic changes in the pre-edge structure of the Fe K-edge X-ray absorption spectra, in particular by a gradual decrease of the t_2g/e_g peak height ratio of the two leading pre-edge resonances, confirming oxidation of the Fe from Fe²⁺ towards Fe³⁺. Transmission electron microscopy (TEM) on the samples treated at temperatures as high as 900 °C showed particles with prismatic morphology along with the formation of stacking fault like defects. High resolution TEM with selected area electron diffraction (SAED) of samples heat treated above 350 °C showed that the nano particles have well developed lattice fringes corresponding to that of (110) plane of hematite.     

Two-dimensional x-ray grating interferometer

We report on the design and experimental realization of a 2D x-ray grating interferometer. We describe how this interferometer has been practically implemented, discuss its performance, and present multidirectional scattering (dark-field) maps and quantitative phase images that have been retrieved using this device.     

An investigation of the relation between sibilant production and somatosensory and auditory acuity

The relation between auditory acuity, somatosensory acuity and the magnitude of produced sibilant contrast was investigated with data from 18 participants. To measure auditory acuity, stimuli from a synthetic sibilant continuum ([s]-[?]) were used in a four-interval, two-alternative forced choice adaptive-staircase discrimination task. To measure somatosensory acuity, small plastic domes with grooves of different spacing were pressed against each participant's tongue tip and the participant was asked to identify one of four possible orientations of the grooves. Sibilant contrast magnitudes were estimated from productions of the words 'said,' 'shed,' 'sid,' and 'shid'. Multiple linear regression revealed a significant relation indicating that a combination of somatosensory and auditory acuity measures predicts produced acoustic contrast. When the participants were divided into high- and low-acuity groups based on their median somatosensory and auditory acuity measures, separate ANOVA analyses with sibilant contrast as the dependent variable yielded a significant main effect for each acuity group. These results provide evidence that sibilant productions have auditory as well as somatosensory goals and are consistent with prior results and the theoretical framework underlying the DIVA model of speech production.     

Holes and Ledges Created by Multilayer Assembly on Polyelectrolyte Brushes: A Novel Route for the Three‐Dimensional Nanoscale Design of Surfaces

The layer‐by‐layer (LBL) assembly of poly(diallyldimethylammonium chloride) and poly(sodium styrene sulfonate) on poly(sulfo propyl methacrylate) brushes resulted in films with nanometer‐ and micrometer‐sized holes and ledges, observed by atomic force microscopy and scanning electron microscopy. Polyelectrolyte assembly was followed by the quartz microbalance technique. The formation of ledges and holes is explained by the interaction of the brush polymers with the incoming polyelectrolytes during the LBL assembly, inducing a spatially localized and self‐organized accumulation of the assembled polymers.

     

Synthesis and reactivity of new chiral bicyclic phospholanes as acyl-transfer catalysts

[structure: see text] Synthesis of chiral phosphines 1a, 14a, and 18a as nucleophilic catalysts for anhydride activation and kinetic resolution of alcohols is described. Radical cyclization of alkenylphosphines produced the phosphabicyclooctane (PBO) core of catalysts 1a and 14a, while 18a was made by quenching a metallocycle precursor with dichlorophenylphosphine. Catalysts 1a and 14a are less reactive, while 18a is comparable to the most reactive catalysts in the PBO family. The preferred ground-state geometries of phosphine-boranes were identified using computational methods, and were correlated with the catalytic reactivity of the corresponding free phosphines.     

Preliminary evidence for the use of microseismic cues for navigation by the Namib golden mole

Insect prey of the Namib golden mole congregate beneath clumps of grass scattered among the sand dunes of the Namib Desert. In the presence of the light winds that typically blow over the Namib Desert, these grass clumps emit low-amplitude vibrations that are transmitted through the sand. While foraging in the sand-swimming mode (a few centimeters below the surface of the sand), some moles apparently were attracted toward manmade sources emitting vibrations matching those recorded from the grass clumps. This is the first direct evidence that these desert mammals use seismic cues for navigation.