Chemical nature of the lewis acid center of dehydroxylated aluminosilicate catalysts

Theoretical studies on the dimers formed by CO with the halides of multivalent astatine as a Lewis-acid center are carried out to examine the typical characteristics of supervalent halogen bonds.

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ChemInform Abstract: TRIVALENT ARSENIC AS A LEWIS ACID CENTER, A NEW TYPE OF BONDING IN ARSENIC CHEMISTRY

Chemischer Informationsdienst ◽

10.1002/chin.197814293 ◽

1978 ◽

Vol 9 (14) ◽

Author(s):

F. KOBER

Keyword(s):

Lewis Acid ◽

Acid Center ◽

Trivalent Arsenic ◽

Lewis Acid Center ◽

New Type

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Release of Neurosecretion in the Crayfish Sinus Gland

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100100494 ◽

1968 ◽

Vol 26 ◽

pp. 150-151

Author(s):

Richard R. Shivers

Keyword(s):

Chemical Nature ◽

Storage Site ◽

Neurosecretory Granules ◽

Sinus Gland ◽

Diameter Class ◽

Dense Membrane ◽

Neurohemal Organ ◽

Dense Vesicles

The sinus gland is a neurohemal organ located in the crayfish eyestalk and represents a storage site for neurohormones prior to their release into the circulation. The sinus gland contains 3 classes of dense, membrane-limited granules: 1) granules measuring less than 1000 Å in diameter, 2) granules measuring 1100-1400 Å in diameter, and 3) granules measuring 1500-2000 Å in diameter. Class 3 granules are the most electron-dense of the granules found in the sinus gland, while class 2 granules are the most abundant. Generally, all granules appear to undergo similar changes during release.Release of neurosecretory granules may be initiated by a preliminary fragmentation of the “parent granule” into smaller, less dense vesicles which measure about 350 Å in diameter (V, Figs. 1-3). A decrease in density of the granules prior to their fragmentation has been observed and may reflect a change in the chemical nature of the granule contents.

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Freeze-fracture cytochemistry: A goal set by Russell Steere in 1957

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010014614x ◽

1993 ◽

Vol 51 ◽

pp. 60-61

Author(s):

Nicholas J Severs

Keyword(s):

Chemical Nature ◽

Biological Systems ◽

Freeze Fracture ◽

Structural Components ◽

Major Goal ◽

Membrane Biology ◽

Routine Application ◽

The Future ◽

Freeze Etching

In his pioneering demonstration of the potential of freeze-etching in biological systems, Russell Steere assessed the future promise and limitations of the technique with remarkable foresight. Item 2 in his list of inherent difficulties as they then stood stated “The chemical nature of the objects seen in the replica cannot be determined”. This defined a major goal for practitioners of freeze-fracture which, for more than a decade, seemed unattainable. It was not until the introduction of the label-fracture-etch technique in the early 1970s that the mould was broken, and not until the following decade that the full scope of modern freeze-fracture cytochemistry took shape. The culmination of these developments in the 1990s now equips the researcher with a set of effective techniques for routine application in cell and membrane biology.Freeze-fracture cytochemical techniques are all designed to provide information on the chemical nature of structural components revealed by freeze-fracture, but differ in how this is achieved, in precisely what type of information is obtained, and in which types of specimen can be studied.

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