scholarly journals Dihaloborenium cations stabilized by a four-membered N-heterocyclic carbene: electron deficiency compensation by asymmetric structural changes

2014 ◽  
Vol 43 (41) ◽  
pp. 15313-15316 ◽  
Author(s):  
Madelyn Qin Yi Tay ◽  
Balasubramanian Murugesapandian ◽  
Yunpeng Lu ◽  
Rakesh Ganguly ◽  
Kinjo Rei ◽  
...  
Keyword(s):  
Structural Changes ◽  
Electron Deficiency ◽  
Cyclic Fragment

Coordination of the four membered carbene ligand to electron deficient dihaloborenium moieties has resulted in asymmetric structural changes for the ligand's CN2P cyclic fragment.

Fine Structural Changes in the Microvasculature of the Mouse Pinna: Aging and Radiation Injury

1974 ◽  
Vol 32 ◽  
pp. 54-55
Author(s):  
S. Phyllis Steamer ◽  
Rosemarie L. Devine
Keyword(s):  
Structural Changes ◽  
Radiation Treatment ◽  
Arterial Stenosis ◽  
Ultrastructural Changes ◽  
Vascular Effects ◽  
Microvascular Changes ◽  
Surrounding Connective Tissue ◽  
Fission Neutrons ◽  
Total Body

The importance of radiation damage to the skin and its vasculature was recognized by the early radiologists. In more recent studies, vascular effects were shown to involve the endothelium as well as the surrounding connective tissue. Microvascular changes in the mouse pinna were studied in vivo and recorded photographically over a period of 12-18 months. Radiation treatment at 110 days of age was total body exposure to either 240 rad fission neutrons or 855 rad 60Co gamma rays. After in vivo observations in control and irradiated mice, animals were sacrificed for examination of changes in vascular fine structure. Vessels were selected from regions of specific interest that had been identified on photomicrographs. Prominent ultrastructural changes can be attributed to aging as well as to radiation treatment. Of principal concern were determinations of ultrastructural changes associated with venous dilatations, segmental arterial stenosis and tortuosities of both veins and arteries, effects that had been identified on the basis of light microscopic observations. Tortuosities and irregularly dilated vein segments were related to both aging and radiation changes but arterial stenosis was observed only in irradiated animals.

Evaluation of single-electron movies of glutamine synthetase molecules

1983 ◽  
Vol 41 ◽  
pp. 280-281
Author(s):  
W. Kunath ◽  
E. Zeitler ◽  
M. Kessel
Keyword(s):  
Electron Microscope ◽  
Glutamine Synthetase ◽  
Electron Irradiation ◽  
Structural Damage ◽  
Structural Changes ◽  
Single Electron ◽  
Continuous Series ◽  
Digital Recording ◽  
Recording Device ◽  
Low Exposure

The features of digital recording of a continuous series (movie) of singleelectron TV frames are reported. The technique is used to investigate structural changes in negatively stained glutamine synthetase molecules (GS) during electron irradiation and, as an ultimate goal, to look for the molecules' “undamaged” structure, say, after a 1 e/Å2 dose.The TV frame of fig. la shows an image of 5 glutamine synthetase molecules exposed to 1/150 e/Å2. Every single electron is recorded as a unit signal in a 256 ×256 field. The extremely low exposure of a single TV frame as dictated by the single-electron recording device including the electron microscope requires accumulation of 150 TV frames into one frame (fig. lb) thus achieving a reasonable compromise between the conflicting aspects of exposure time per frame of 3 sec. vs. object drift of less than 1 Å, and exposure per frame of 1 e/Å2 vs. rate of structural damage.

Fine Structural Changes in the Adenohypophyses of Rats Following Destruction of the Pituitary Stalk

1977 ◽  
Vol 35 ◽  
pp. 496-497
Author(s):  
K. Kovacs ◽  
E. Horvath ◽  
J. M. Bilbao ◽  
F. A. Laszlo ◽  
I. Domokos
Keyword(s):  
Structural Changes ◽  
Tissue Injury ◽  
Anterior Lobe ◽  
Uranyl Acetate ◽  
Male Rats ◽  
Pituitary Stalk ◽  
Sequence Of Events ◽  
Pituitary Glands ◽  
Electrolytic Lesions ◽  
Ultrathin Sections

Electrolytic lesions of the pituitary stalk in rats interrupt adenohypophysial blood flow and result in massive infarction of the anterior lobe. In order to obtain a deeper insight into the morphogenesis of tissue injury and to reveal the sequence of events, a fine structural investigation was undertaken on adenohypophyses of rats at various intervals following destruction of the pituitary stalk.The pituitary stalk was destroyed electrolytically, with a Horsley-Clarke apparatus on 27 male rats of the R-Amsterdam strain, weighing 180-200 g. Thirty minutes, 1,2,4,6 and 24 hours after surgery the animals were perfused with a glutaraldehyde-formalin solution. The skulls were then opened and the pituitary glands removed. The anterior lobes were fixed in glutaraldehyde-formalin solution, postfixed in osmium tetroxide and embedded in Durcupan. Ultrathin sections were stained with uranyl acetate and lead citrate and investigated with a Philips 300 electron microscope.

Membrane Changes in Polymorphonuclear Leukocytes During Ionophore (A23187) - Induced Lysosomal Release

1977 ◽  
Vol 35 ◽  
pp. 482-483
Author(s):  
P.L. Moore ◽  
P.L. Sannes ◽  
H.L. Bank ◽  
S.S. Spicer
Keyword(s):  
Structural Changes ◽  
Calcium Release ◽  
Clear Understanding ◽  
Ionophore A23187 ◽  
Enzyme Release ◽  
Extracellular Medium ◽  
Pmn Leukocytes ◽  
Intracellular Ion Concentrations ◽  
Membrane Changes ◽  
Pmn Leukocyte

It is thought that calcium and/or magnesium may play important roles in polymorphonuclear (PMN) leukocyte functions such as chemotaxis, adhesion and phagocytosis. Yet, a clear understanding of the biological roles of these ions has awaited the development of techniques which permit a selective alteration of intracellular ion concentrations. Recently, treatment of cells with the ionophore A23187 has been used to alter intracellular divalent cation concentrations. This ionophore is a lipid soluble antibiotic produced by Streptomyces chartreusensis that complexes with both calcium and magnesium (3) and is believed to carry these ions across biological membranes (4). Biochemical investigations of human PMN leukocytes demonstrate that cells treated with A23187 and extracellular calcium release their lysosomal enzymes into the extracellular medium without rupturing and releasing their soluble cytoplasmic enzymes (5,6). The aim of the present study and and a companion report (7) was to investigate the structural changes that occur in leukocytes during ionophore-induced lysosomal enzyme release.

The Reaction of Brain Structures with OsO4-Zinc-Iodide Stain

1971 ◽  
Vol 29 ◽  
pp. 272-273
Author(s):  
Werner J. Niklowitz
Keyword(s):  
Electron Microscope ◽  
Structural Changes ◽  
Mossy Fiber ◽  
Toxic Metal ◽  
Staining Technique ◽  
Brain Structures ◽  
Oxidase Inhibitor ◽  
Fiber Layer ◽  
Hippocampal Tissue ◽  
Zinc Iodide

After intoxication of rabbits with certain substances such as convulsant agents (3-acetylpyridine), centrally acting drugs (reserpine), or toxic metal compounds (tetraethyl lead) a significant observation by phase microscope is the loss of contrast of the hippocampal mossy fiber layer. It has been suggested that this alteration, as well as changes seen with the electron microscope in the hippocampal mossy fiber boutons, may be related to a loss of neurotransmitters. The purpose of these experiments was to apply the OsO4-zinc-iodide staining technique to the study of these structural changes since it has been suggested that OsO4-zinc-iodide stain reacts with neurotransmitters (acetylcholine, catecholamines).Domestic New Zealand rabbits (2.5 to 3 kg) were used. Hippocampal tissue was removed from normal and experimental animals treated with 3-acetylpyridine (antimetabolite of nicotinamide), reserpine (anti- hypertensive/tranquilizer), or iproniazid (antidepressant/monamine oxidase inhibitor). After fixation in glutaraldehyde hippocampal tissue was treated with OsO4-zinc-iodide stain and further processed for phase and electron microscope studies.

Embedding Procedure for Water Swollen Samples

1970 ◽  
Vol 28 ◽  
pp. 504-505
Author(s):  
Ann M. Thomas ◽  
Virginia Shemeley
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Ion Exchange ◽  
Structural Changes ◽  
Cross Linking ◽  
Ion Exchange Resins ◽  
Transmission Electron ◽  
First Pass ◽  
Exchange Resins

Those samples which swell rapidly when exposed to water are, at best, difficult to section for transmission electron microscopy. Some materials literally burst out of the embedding block with the first pass by the knife, and even the most rapid cutting cycle produces sections of limited value. Many ion exchange resins swell in water; some undergo irreversible structural changes when dried. We developed our embedding procedure to handle this type of sample, but it should be applicable to many materials that present similar sectioning difficulties.The purpose of our embedding procedure is to build up a cross-linking network throughout the sample, while it is in a water swollen state. Our procedure was suggested to us by the work of Rosenberg, where he mentioned the formation of a tridimensional structure by the polymerization of the GMA biproduct, triglycol dimethacrylate.

Anisotropic radiation damage of potassium tetracyano platinate (KCP)

1978 ◽  
Vol 36 (1) ◽  
pp. 392-393
Author(s):  
N. Uyeda ◽  
E. J. Kirkland ◽  
B. M. Siegel
Keyword(s):  
Electron Diffraction ◽  
Radiation Damage ◽  
Structural Changes ◽  
High Resolution Electron Microscopy ◽  
Radiation Sensitivity ◽  
Resolution Electron ◽  
Damage Process ◽  
Diffraction Patterns ◽  
Fading Rate

The direct observation of structural change by high resolution electron microscopy will be essential for the better understanding of the damage process and its mechanism. However, this approach still involves some difficulty in quantitative interpretation mostly being due to the quality of obtained images. Electron diffraction, using crystalline specimens, has been the method most frequently applied to obtain a comparison of radiation sensitivity of various materials on the quantitative base. If a series of single crystal patterns are obtained the fading rate of reflections during the damage process give good comparative measures. The electron diffraction patterns also render useful information concerning the structural changes in the crystal. In the present work, the radiation damage of potassium tetracyano-platinate was dealt with on the basis two dimensional observation of fading rates of diffraction spots. KCP is known as an ionic crystal which possesses “one dimensional” electronic properties and it would be of great interest to know if radiation damage proceeds in a strongly asymmetric manner.

An atomic resolution study of a carbide phase in platinum

1992 ◽  
Vol 50 (1) ◽  
pp. 20-21
Author(s):  
M.J. Witcomb ◽  
M.A. O'Keefe ◽  
CJ. Echer ◽  
C. Nelson ◽  
J.H. Turner ◽  
...  
Keyword(s):  
Solid Solution ◽  
Carbon Atom ◽  
Carbide Phase ◽  
Structural Changes ◽  
Critical Role ◽  
Alloy System ◽  
Atomic Resolution ◽  
Excess Carbon ◽  
Interstitial Carbon ◽  
Resolution Study

Under normal circumstances, Pt dissolves only a very small amount of interstitial carbon in solid solution. Even so, an appropriate quench/age treatment leads to the formation of stable Pt2C {100} plate precipitates. Excess (quenched-in) vacancies play a critical role in the process by accommodating the volume and structural changes that accompany the transformation. This alloy system exhibits other interesting properties. Due to a large vacancy/carbon atom binding energy, Pt can absorb excess carbon at high temperatures in a carburizing atmosphere. In regions rich in carbon and vacancies, another carbide phase, Pt7C which undergoes an order-disorder reaction was formed. The present study of Pt carburized at 1160°C and aged at 515°C shows that other carbides in the PtxC series can be produced.

Structural changes in silicon-on-insulator material during post-implantation annealing

1986 ◽  
Vol 44 ◽  
pp. 736-737
Author(s):  
C. O. Jung ◽  
S. J. Krause ◽  
S.R. Wilson
Keyword(s):  
Integrated Circuits ◽  
Oxide Layer ◽  
High Speed ◽  
Structural Changes ◽  
Device Fabrication ◽  
Silicon On Insulator ◽  
High Quality ◽  
Radiation Hardened ◽  
Post Implantation ◽  
Very High

Silicon-on-insulator (SOI) structures have excellent potential for future use in radiation hardened and high speed integrated circuits. For device fabrication in SOI material a high quality superficial Si layer above a buried oxide layer is required. Recently, Celler et al. reported that post-implantation annealing of oxygen implanted SOI at very high temperatures would eliminate virtually all defects and precipiates in the superficial Si layer. In this work we are reporting on the effect of three different post implantation annealing cycles on the structure of oxygen implanted SOI samples which were implanted under the same conditions.

Cryo-electron microscopy of two-dimensional crystals of reduced type B botulinum neurotoxin

1992 ◽  
Vol 50 (1) ◽  
pp. 530-531
Author(s):  
P. F. Flicker ◽  
V.S. Kulkarni ◽  
J. P. Robinson ◽  
G. Stubbs ◽  
B. R. DasGupta
Keyword(s):  
Disulfide Bonds ◽  
Clostridium Botulinum ◽  
Structural Changes ◽  
Two Dimensional ◽  
Type B ◽  
Single Chain ◽  
Muscle Paralysis ◽  
Cryo Electron Microscopy ◽  
Disulfide Linkages ◽  
Intracellular Action

Botulinum toxin is a potent neurotoxin produced by Clostridium botulinum. The toxin inhibits release of neurotransmitter, causing muscle paralysis. There are several serotypes, A to G, all of molecular weight about 150,000. The protein exists as a single chain or or as two chains, with two disulfide linkages. In a recent investigation on intracellular action of neurotoxins it was reported that type B neurotoxin can inhibit the release of Ca++-activated [3H] norepinephrine only if the disulfide bonds are reduced. In order to investigate possible structural changes in the toxin upon reduction of the disulfide bonds, we have prepared two-dimensional crystals of reduced type B neurotoxin. These two-dimensional crystals will be compared with those of the native (unreduced) type B toxin.

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