Direct Observation of a Stannyl Radical in the Reactions of the Tributylstannyl Anion with Alkyl Halides by a Stopped-Flow Technique

1998 ◽  
Vol 17 (10) ◽  
pp. 1913-1915 ◽  
Author(s):  
Masanobu Wakasa ◽  
Tsuyoshi Kugita
Keyword(s):  
Direct Observation ◽  
Alkyl Halides ◽  
Stopped Flow

scholarly journals Reactions of DOPA (3,4-dihydroxyphenylalanine) decarboxylase with DOPA

1979 ◽  
Vol 183 (2) ◽  
pp. 361-368 ◽  
Author(s):  
A Minelli ◽  
A T Charteris ◽  
C B Voltattorni ◽  
R A John
Keyword(s):  
Steady State ◽  
Time Scales ◽  
Direct Observation ◽  
Equilibrium Constants ◽  
Active Part ◽  
Stopped Flow ◽  
Step Rate ◽  
Multiple Reactions ◽  
Absorbing Material ◽  
Different Time Scales

The study of DOPA (3,4-dihydroxyphenylalanine) decarboxylase by steady-state methods is difficult because multiple reactions occur. The reaction with DOPA was studied at enzyme concentrations between 20 and 50 micrometer by direct observation of the bound coenzyme by using stopped-flow and conventional spectrophotometry. Four processes were observed on different time scales and three of these were attributed to stages in the decarboxylation. The fourth was attributed to an accompanying transamination that renders the enzyme inactive. It was clear that much, if not all, of the 330 nm-absorbing coenzyme present in the free enzyme plays an active part in the decarboxylation, since it is converted into 420 nm-absorbing material in the first observable step. An intermediate absorbing maximally at 390 nm is formed in a slower step. Rate and equilibrium constants have been determined and the ratio of decarboxylation to transamination was estimated to be 1200:1.

Kinetic studies of reactions of the stannyl anion with primary alkyl halides by a stopped-flow technique

1998 ◽  
Vol 1 (10) ◽  
pp. 386-388 ◽  
Author(s):  
Tsuyoshi Kugita ◽  
Masanobu Wakasa ◽  
Junsei Tamura ◽  
Hisaharu Hayashi
Keyword(s):  
Kinetic Studies ◽  
Alkyl Halides ◽  
Stopped Flow

Direct Observation of Heat Exchanger Deposits by Cross Sectioning

1967 ◽  
Vol 25 ◽  
pp. 364-365
Author(s):  
R. W. Anderson ◽  
D. L. Senecal
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Heat Exchanger ◽  
Direct Observation ◽  
Cross Sections ◽  
Preparation Method ◽  
Specimen Preparation ◽  
Flowing Water ◽  
Transmission Electron ◽  
Deposit Layer

A problem was presented to observe the packing densities of deposits of sub-micron corrosion product particles. The deposits were 5-100 mils thick and had formed on the inside surfaces of 3/8 inch diameter Zircaloy-2 heat exchanger tubes. The particles were iron oxides deposited from flowing water and consequently were only weakly bonded. Particular care was required during handling to preserve the original formations of the deposits. The specimen preparation method described below allowed direct observation of cross sections of the deposit layers by transmission electron microscopy.The specimens were short sections of the tubes (about 3 inches long) that were carefully cut from the systems. The insides of the tube sections were first coated with a thin layer of a fluid epoxy resin by dipping. This coating served to impregnate the deposit layer as well as to protect the layer if subsequent handling were required.

Application of a Simple Cold Stub to the Direct Observation of Frozen Hydrated Sand

1973 ◽  
Vol 31 ◽  
pp. 212-213
Author(s):  
John M. Wehrung ◽  
Richard J. Harniman
Keyword(s):  
United States ◽  
Surface Water ◽  
Direct Observation ◽  
Controlled Study ◽  
Clay Particles ◽  
Organic Debris ◽  
Rock Formations ◽  
Water Tables ◽  
Permeable Rock ◽  
Natural Means

Water tables in aquifer regions of the southwest United States are dropping off at a rate which is greater than can be replaced by natural means. It is estimated that by 1985 wells will run dry in this region unless adequate artificial recharging can be accomplished. Recharging with surface water is limited by the plugging of permeable rock formations underground by clay particles and organic debris.A controlled study was initiated in which sand grains were used as the rock formation and water with known clay concentrations as the recharge media. The plugging mechanism was investigated by direct observation in the SEM of frozen hydrated sand samples from selected depths.

Direct Observation of the Diffusionless β → β + ω Transformation in Titanium Alloys

1971 ◽  
Vol 29 ◽  
pp. 122-123
Author(s):  
N. E. Paton ◽  
D. de Fontaine ◽  
J. C. Williams
Keyword(s):  
Electron Microscope ◽  
Titanium Alloys ◽  
Direct Observation ◽  
Dark Field ◽  
X Ray Diffraction ◽  
Resistivity Measurements ◽  
Selected Area Electron Diffraction ◽  
Ti Alloys ◽  
Thin Foils ◽  
Field Device

The electron microscope has been used to study the diffusionless β → β + ω transformation occurring in certain titanium alloys at low temperatures. Evidence for such a transformation was obtained by Cometto et al by means of x-ray diffraction and resistivity measurements on a Ti-Nb alloy. The present work shows that this type of transformation can occur in several Ti alloys of suitable composition, and some of the details of the transformation are elucidated by means of direct observation in the electron microscope.Thin foils were examined in a Philips EM-300 electron microscope equipped with a uniaxial tilt, liquid nitrogen cooled, cold stage and a high resolution dark field device. Selected area electron diffraction was used to identify the phases present and the ω-phase was imaged in dark field by using a (101)ω reflection. Alloys were water quenched from 950°C, thinned, and mounted between copper grids to minimize temperature gradients in the foil.

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