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Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques

Columns packed with microsized titanium dioxide particles have been used effectively as precolumns for enriching phosphopeptides from complex mixtures. Nanosized titanium dioxide particles have a higher specific surface area and, hence, potentially higher trapping capacities toward phosphopeptides than do microsized particles. Thus, in this study, we employed TiO2-coated magnetic (Fe3O4/TiO2 core/shell) nanoparticles to selectively concentrate phosphopeptides from protein digest products. Because of their magnetic properties, the Fe3O4/TiO2 core/shell nanoparticles that are conjugated to the target peptides can be isolated readily from the sample solutions by employing a magnetic field. In this paper, we also demonstrate that the Fe3O4/TiO2 core/shell nanoparticles behave as an effective SALDI matrix:  our upper detectable mass limit was ∼24 000 Da, whereas the detection limit for peptides was in the low-femtomole range. That is to say, the target analytes trapped by the Fe3O4/TiO2 nanoparticles can be id...

https://ir.nctu.edu.tw:443/bitstream/11536/13265/1/000231919400016.pdf

Fe3O4/TiO2 Core/Shell Nanoparticles as Affinity Probes for the Analysis of Phosphopeptides Using TiO2 Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

Recent years have seen a large increase of the research effort focused on framework materials, including the nowadays-ubiquitous metal–organic frameworks but also dense coordination polymers, covalent organic frameworks, and molecular frameworks. With the quickly increasing number of structures synthesized and characterized, one pattern emerging is the common occurrence of flexibility. More specifically, an important number of framework materials are stimuli-responsive: their structure can undergo changes of large amplitude in response to physical or chemical stimulation. They can display transformations induced by temperature, mechanical pressure, guest adsorption or evacuation, light absorption, etc. and are sometimes referred to as smart materials, soft crystals, or dynamic materials. This Perspective highlights recent progress in this field, showcasing some of the most novel and unusual responses to stimuli, as well as advances in the fundamental understanding of flexible framework materials.

https://hal.archives-ouvertes.fr/hal-02269625/document

Responsive Metal–Organic Frameworks and Framework Materials: Under Pressure, Taking the Heat, in the Spotlight, with Friends

Incorporation of Ti into the framework of aluminium-free zeolite Beta has been achieved in F- medium and has produced hydrophobic selective oxidation catalysts. The Ti−Beta(F) materials have been characterized by X ray diffraction, infrared, Raman, ultraviolet, XANES, EXAFS, 29Si MAS NMR, and 1H→29Si CP MAS NMR spectroscopies, adsorption microcalorimetry, and catalytic testing. At near neutral pH the incorporation of Ti into the framework appears to present an upper limit of ca. 2.3 Ti/uc, beyond which anatase is detected in the calcined materials. However, at higher pH (ca. 11) larger amounts of Ti can be incorporated without anatase formation. After calcination, Ti incorporation in the framework is characterized by an increase in the unit cell volume, the appearance of one Raman band and three infrared bands in the region near 960 cm-1 and the presence of a strong absorption band in the 205−220 nm ultraviolet spectrum. By 29Si MAS NMR, 1H→29Si CP MAS NMR, and infrared spectroscopies it is concluded that...

Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite

Publisher Summary This chapter focuses on the microporous crystalline titanium silicates. Titanium containing materials have been investigated for various reactions, but selective oxidations with H2O2 as the oxidant have attracted the most interest. For these reactions, the formation of surface titanium peroxo compounds with H2O2 and the subsequent transfer of the peroxidic oxygen to the organic reactants have been proposed to explain the mechanism by which titanium participates in the catalytic cycle. H2O2 has the advantage of giving environmentally benign water as its by-product. Furthermore, H2O2 ranks first in terms of available oxygen in the list of oxygen donors.The unusual properties of titanium silicalites have been attributed to the presence of TiIV in framework positions of the SiO2 lattice. It is important to realize that there is a limit to the extent of substitution; the exact value is still under discussion, but is certainly not more than a few percent. Very likely, the structure of crystalline silica is not stable at higher degrees of substitution. The discovery of the new titanium silicates and of their catalytic properties in H2O2 oxidation reactions has had a major impact in catalytic science and its industrial applications.

A. Lopez

Papers

19F MAS n.m.r. studies of crystalline microporous solids synthesized in the fluoride medium

Titanium in MFI-Type Zeolites: A Characterization by XANES, EXAFS, IR, and 74, 49Ti and 17O MAS NMR Spectroscopy and H2O Adsorption

Temperature-induced monoclinic/orthorhombic transition in germanium MFI-type zeolites

EXAFS study of germanium-rich MFI-type zeolites