Hybrid Organic-Inorganic Materials Derived from a Monosilylated Hoveyda-Type Ligand as Recyclable Diene and Enyne Metathesis Catalysts.

Polar olefin metathesis catalysts bearing a pendant electron-withdrawing (EWG) onium group are reviewed. The presence of this group not only activates the catalysts electronically, but renders them more hydrophilic. Catalysts can, therefore, be efficiently used not only in traditional media such as methylene chloride and toluene, but also in technical-grade alcohols, alcohol–water mixtures, and in neat water. In addition, some onium-tagged catalysts can act as inisurfs (initiator + surfactant molecules), promoting metathesis under heterogeneous aqueous conditions. Finally, some of these catalysts can be used in ionic liquids. Various ring-closing-, cross- and enyne metathesis reactions were conducted with these catalysts.

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Hybrid silica materials derived from Hoveyda–Grubbs ruthenium carbenes. Electronic effects of the nitro group on the activity and recyclability as diene and enyne metathesis catalysts

Tetrahedron ◽

10.1016/j.tet.2008.04.113 ◽

2008 ◽

Vol 64 (28) ◽

pp. 6770-6781 ◽

Cited By ~ 34

Author(s):

Xavier Elias ◽

Roser Pleixats ◽

Michel Wong Chi Man

Keyword(s):

Nitro Group ◽

Enyne Metathesis ◽

Electronic Effects ◽

Hybrid Silica ◽

Silica Materials ◽

Ruthenium Carbenes ◽

Metathesis Catalysts

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Limits for high-resolution electron microscopy of inorganic materials?

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100125117 ◽

1987 ◽

Vol 45 ◽

pp. 4-5

Author(s):

David J. Smith

Keyword(s):

Electron Microscopy ◽

Spherical Aberration ◽

High Resolution Electron Microscopy ◽

Inorganic Materials ◽

Atomic Scale ◽

Resolution Limit ◽

Contrast Transfer Function ◽

Existing Problems ◽

Resolution Electron ◽

Electron Microscopes

The era of atomic-resolution electron microscopy has finally arrived. In virtually all inorganic materials, including oxides, metals, semiconductors and ceramics, it is possible to image individual atomic columns in low-index zone-axis projections. A whole host of important materials’ problems involving defects and departures from nonstoichiometry on the atomic scale are waiting to be tackled by the new generation of intermediate voltage (300-400keV) electron microscopes. In this review, some existing problems and limitations associated with imaging inorganic materials are briefly discussed. The more immediate problems encountered with organic and biological materials are considered elsewhere.Microscope resolution. It is less than a decade since the state-of-the-art, commercially available TEM was a 200kV instrument with a spherical aberration coefficient of 1.2mm, and an interpretable resolution limit (ie. first zero crossover of the contrast transfer function) of 2.5A.

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Scanning tunneling microscopy (STM) of DNA and RNA

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100152148 ◽

1989 ◽

Vol 47 ◽

pp. 34-35

Author(s):

Patricia G. Arscott ◽

Gil Lee ◽

Victor A. Bloomfield ◽

D. Fennell Evans

Keyword(s):

Molecular Structures ◽

Inorganic Materials ◽

Resolving Power ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Form And Function ◽

Dna And Rna ◽

Calf Thymus ◽

And Function ◽

The Relationship

STM is one of the most promising techniques available for visualizing the fine details of biomolecular structure. It has been used to map the surface topography of inorganic materials in atomic dimensions, and thus has the resolving power not only to determine the conformation of small molecules but to distinguish site-specific features within a molecule. That level of detail is of critical importance in understanding the relationship between form and function in biological systems. The size, shape, and accessibility of molecular structures can be determined much more accurately by STM than by electron microscopy since no staining, shadowing or labeling with heavy metals is required, and there is no exposure to damaging radiation by electrons. Crystallography and most other physical techniques do not give information about individual molecules.We have obtained striking images of DNA and RNA, using calf thymus DNA and two synthetic polynucleotides, poly(dG-me5dC)·poly(dG-me5dC) and poly(rA)·poly(rU).

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Shot-noise simulations of HREM images of polymer crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153683 ◽

1989 ◽

Vol 47 ◽

pp. 342-343

Author(s):

Philippe Pradère ◽

Edwin L. Thomas

Keyword(s):

Low Dose ◽

Molecular Level ◽

High Resolution Electron Microscopy ◽

Crystal Defects ◽

Inorganic Materials ◽

Photographic Emulsion ◽

Polymer Crystals ◽

Resolution Electron ◽

Recent Developments ◽

Lattice Images

High Resolution Electron Microscopy (HREM) is a very powerful technique for the study of crystal defects at the molecular level. Unfortunately polymer crystals are beam sensitive and are destroyed almost instantly under the typical HREM imaging conditions used for inorganic materials. Recent developments of low dose imaging at low magnification have nevertheless permitted the attainment of lattice images of very radiation sensitive polymers such as poly-4-methylpentene-1 and enabled molecular level studies of crystal defects in somewhat more resistant ones such as polyparaxylylene (PPX) [2].With low dose conditions the images obtained are very noisy. Noise arises from the support film, photographic emulsion granularity and in particular, the statistical distribution of electrons at the typical doses of only few electrons per unit resolution area. Figure 1 shows the shapes of electron distribution, according to the Poisson formula :

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A Super-High-Resolution HVEM (H-1500) Newly Installed in NIRIM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100179464 ◽

1990 ◽

Vol 48 (1) ◽

pp. 142-143

Author(s):

S. Horiuchi ◽

Y. Matsui

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Chromatic Aberration ◽

Inorganic Materials ◽

Electron Gun ◽

Resolving Power ◽

National Budget ◽

Voltage Electron ◽

Specimen Holder ◽

The Magnetic Field

A new high-voltage electron microscope (H-1500) specially aiming at super-high-resolution (1.0 Å point-to-point resolution) is now installed in National Institute for Research in Inorganic Materials ( NIRIM ), in collaboration with Hitachi Ltd. The national budget of about 1 billion yen including that for a new building has been spent for the construction in the last two years (1988-1989). Here we introduce some essential characteristics of the microscope.(1) According to the analysis on the magnetic field in an electron lens, based on the finite-element-method, the spherical as well as chromatic aberration coefficients ( Cs and Cc ). which enables us to reach the resolving power of 1.0Å. have been estimated as a function of the accelerating As a result of the calculaton. it was noted that more than 1250 kV is needed even when we apply the highest level of the technology and materials available at present. On the other hand, we must consider the protection against the leakage of X-ray. We have then decided to set the conventional accelerating voltage at 1300 kV. However. the maximum accessible voltage is 1500 kV, which is practically important to realize higher voltage stabillity. At 1300 kV it is expected that Cs= 1.7 mm and Cc=3.4 mm with the attachment of the specimen holder, which tilts bi-axially in an angle of 35° ( Fig.1 ). In order to minimize the value of Cc a small tank is additionally placed inside the generator tank, which must serve to seal the magnetic field around the acceleration tube. An electron gun with LaB6 tip is used.

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