The radiation chemistry of aqueous ferrous sulfate solutions at natural pH

1983 ◽  
Vol 36 (7) ◽  
pp. 1305 ◽  
Author(s):  
RW Matthews
Keyword(s):  
Hydrogen Atom ◽  
Ferrous Sulfate ◽  
Experimental Error ◽  
Absorbed Dose ◽  
Radiation Chemistry ◽  
Ion Concentration ◽  
Sulfate Solutions ◽  
Diffusion Controlled ◽  
Wide Range ◽  
Γ Rays

The yield of FeIII species has been determined in FeSO4 solutions irradiated at natural pH with 60Co γ-rays for a wide range of solute conditions. The stoichiometry of the hydrogen peroxide reaction was investigated and found to be abnormal if H2O2 is present in excess. If, however, FeS04 is present in excess, as it is in the irradiation of FeSO4 solutions, deviations from the normal stoichiometry are trivial. In nitrous oxide saturated solutions initial G(FeIII) values were found to be from 6.90 to 7.72 for FeSO4 concentrations in the range (0.5-2.0) × 10-3 M. Non-linearity in the yield of ferric ion concentration against dose plots was attributed to competition between hydrogen atom reduction of ferric species with hydrogen atom oxidation of ferrous species. The reaction between hydrogen atom and the ferric species was estimated to be close to diffusion controlled. In aerated solutions, the FeIII yield was, within experimental error, a linear function of dose for FeSO4 concentrations in the range (0.5 - 2.0) × 10.-3 M with G(FeIII) values of 12.27 ± 0.06, 12.62 ± 0.07 and 12.77 ± 0.10 for 0.5, 1.0 and 2.0 × M respectively. At lower FeSO4 concentrations. deviation from linearity was noticeable. The deviation was attributed to competition between FeII and FeIII species for the O2- radical anion. k(O2-· + FeII)/k(O2-·+ FeIII) was determined to be about 4.0. In deaerated solu- tion, the FeIII yield against absorbed dose for 1 × M FeSO4 solution was followed to extended doses. A limiting FeIII yield of about 0.75 times the aerated solution yield was observed in the closed system. The data were quite well described by values calculated from the reaction mechanism, published rate constants and the rate ratio of 0.016 for k(H· + FeII)/k(H· + FeIII) determined from the N2O experiments, and demonstrate the importance of reducing radical reactions with insoluble ferric species.

scholarly journals To scavenge or not to scavenge, that is STILL the question

2012 ◽  
Vol 20 (1) ◽  
pp. 23-36 ◽  
Author(s):  
Elizabeth G. Allan ◽  
Melissa C. Kander ◽  
Ian Carmichael ◽  
Elspeth F. Garman
Keyword(s):  
Crystal Size ◽  
Chemical Species ◽  
Absorbed Dose ◽  
Dose Dependence ◽  
Radiation Chemistry ◽  
X Ray ◽  
On Line ◽  
Crystallization Conditions ◽  
Effects Of Radiation ◽  
Dose Tolerance

An extensive radiation chemistry literature would suggest that the addition of certain radical scavengers might mitigate the effects of radiation damage during protein crystallography diffraction data collection. However, attempts to demonstrate and quantify such an amelioration and its dose dependence have not yielded consistent results, either at room temperature (RT) or 100 K. Here the information thus far available is summarized and reasons for this lack of quantitative success are identified. Firstly, several different metrics have been used to monitor and quantify the rate of damage, and, as shown here, these can give results which are in conflict regarding scavenger efficacy. In addition, significant variation in results from data collected from crystals treated in nominally the same way has been observed. Secondly, typical crystallization conditions contain substantial concentrations of chemical species which already interact strongly with some of the X-ray-induced radicals that the added scavengers are intended to intercept. These interactions are probed here by the complementary technique of on-line microspectrophotometry carried out on solutions and crystals held both at 100 K and RT, the latter enabled by the use of a beamline-mounted humidifying device. With the help of computational chemistry, attempts are made to assign some of the characteristic spectral features observed experimentally. A further source of uncertainty undoubtedly lies in the challenge of reliably measuring the parameters necessary for the accurate calculation of the absorbed dose (e.g.crystal size and shape, beam profile) and its distribution within the volume of the crystal (an issue addressed in detail in another article in this issue). While microspectrophotometry reveals that the production of various species can be quenched by the addition of scavengers, it is less clear that this observation can be translated into a significant gain in crystal dose tolerance for macromolecular crystallographers.

scholarly journals Dual Cobalt and Photoredox Catalysis Enabled Intermolecular Oxidative Hydrofunctionalization

2020 ◽  
Author(s):  
Han-Li Sun ◽  
Fan Yang ◽  
Wei-Ting Ye ◽  
Jun-Jie Wang ◽  
Rong Zhu
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Electrochemical Analysis ◽  
Hydrogen Atom Transfer ◽  
Redox Process ◽  
Photochemical Oxidation ◽  
Atom Transfer ◽  
Photoredox Catalysis ◽  
Wide Range ◽  
Selective Alkylation

A general protocol has been developed for the Markovnikov-selective intermolecular hydrofunctionalization based on visible-light-mediated Co/Ru dual catalysis. The key feature involves the photochemical oxidation of an organocobalt(III) intermediate derived from hydrogen atom transfer, which is supported by electrochemical analysis, quenching studies and stoichiometric experiments. This unique redox process enables the efficient branch-selective alkylation of pharmaceutically important nucleophiles (phenols, sulfonamides and various N-heterocycles) using a wide range of alkenes including moderately electron-deficient ones. Moreover, light-gated polar functionalization via organocobalt species was demonstrated.

Dependence of Cardiac Contractility on Myofibrillar Calcium Sensitivity

Physiology ◽  
1987 ◽  
Vol 2 (5) ◽  
pp. 179-182
Author(s):  
JC Ruegg
Keyword(s):  
Calcium Ion ◽  
Sarcomere Length ◽  
Cardiac Contractility ◽  
Calcium Sensitivity ◽  
Ion Concentration ◽  
Free Calcium ◽  
Wide Range ◽  
Heart Contractility ◽  
Calcium Ion Concentration

In the heart, contractility may be varied over a wide range. It is determined mainly by the myoplasmic free calcium ion concentration. However, alteration of the responsiveness of the myofilaments to calcium may also be important in regulating cardiac contractility, in particular following changes in sarcomere length, or in hypoxia, or after interventions with certain novel cardiotonic drugs.

scholarly journals A Colorimetric Method for Studying the Dissociation of Oxyhæmocyanin suitable for Class Work

1925 ◽  
Vol 13 (4) ◽  
pp. 970-980 ◽  
Author(s):  
C. F. A. Pantin ◽  
Lancelot T. Hogben
Keyword(s):  
Marked Effect ◽  
Colorimetric Method ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Dissociation Curve ◽  
Hydrogen Ion Concentration ◽  
Laboratory Class ◽  
Wide Range ◽  
Increasing Temperature ◽  
Limits Of Error

1. A simple colorimetric method for plotting the dissociation curve of haemocyanin is indicated. The limits of error are within 5 per cent. The simplicity of the method commends it for laboratory class work.2. The effect of hydrogen ion concentration on the dissociation of the hsemocyanins of the crustacean Palinurus and the pulmonate Helix have been compared. In the snail change of hydrogen ion concentration over a wide range was not found to affect the dissociation of the hsemocyanin: in 'the crustacean there is a marked effect similar to that seen in the dissociation of hæmoglobin.3. The similarity of crustacean hsemocyanin to haemoglobin is also seen in that increasing temperature depresses the dissociation curve. The effects of certain salts upon haemocyanin. have also been recorded.

scholarly journals Effects of Austenitization Temperature and Pre-Deformation on CCT Diagrams of 23MnNiCrMo5-3 Steel

Materials ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5116
Author(s):  
Ivo Schindler ◽  
Rostislav Kawulok ◽  
Petr Opěla ◽  
Petr Kawulok ◽  
Stanislav Rusz ◽  
...  
Keyword(s):  
Phase Transformations ◽  
Deformation Temperature ◽  
True Strain ◽  
Austenitization Temperature ◽  
Diffusion Controlled ◽  
Significant Acceleration ◽  
Wide Range ◽  
Mean Grain Size ◽  
Cct Diagrams ◽  
Kinetics Of

The combined effect of deformation temperature and strain value on the continuous cooling transformation (CCT) diagram of low-alloy steel with 0.23% C, 1.17% Mn, 0.79% Ni, 0.44% Cr, and 0.22% Mo was studied. The deformation temperature (identical to the austenitization temperature) was in the range suitable for the wire rolling mill. The applied compressive deformation corresponded to the true strain values in an unusually wide range. Based on the dilatometric tests and metallographic analyses, a total of five different CCT diagrams were constructed. Pre-deformation corresponding to the true strain of 0.35 or even 1.0 had no clear effect on the austenite decomposition kinetics at the austenitization temperature of 880 °C. During the long-lasting cooling, recrystallization and probably coarsening of the new austenitic grains occurred, which almost eliminated the influence of pre-deformation on the temperatures of the diffusion-controlled phase transformations. Decreasing the deformation temperature to 830 °C led to the significant acceleration of the austenite → ferrite and austenite → pearlite transformations due to the applied strain of 1.0 only in the region of the cooling rate between 3 and 35 °C·s−1. The kinetics of the bainitic or martensitic transformation remained practically unaffected by the pre-deformation. The acceleration of the diffusion-controlled phase transformations resulted from the formation of an austenitic microstructure with a mean grain size of about 4 µm. As the analysis of the stress–strain curves showed, the grain refinement was carried out by dynamic and metadynamic recrystallization. At low cooling rates, the effect of plastic deformation on the kinetics of phase transformations was indistinct.

60Co γ-RADIOLYSIS OF HYDROGEN HALIDES AT 77 °K

1966 ◽  
Vol 44 (2) ◽  
pp. 191-197
Author(s):  
R. C. Rumfeldt ◽  
D. A. Armstrong
Keyword(s):  
Liquid Phase ◽  
Hydrogen Atom ◽  
Experimental Error ◽  
Dose Dependence ◽  
Solid Matrix ◽  
Reactive Intermediate ◽  
Hydrogen Atoms ◽  
Hydrogen Halides ◽  
Atoms And Molecules ◽  
The Difference

Yields of hydrogen formed in the 60Co γ-radiolyses of pure polycrystalline samples of HBr and HCl at 77 °K decrease with increasing dose in the range 0 to 1 × 1018 eV per g. The true initial yields are G(H2)solidHClat77°K = 6.3 ± 0.2 and G(H2)solidHBrat77°K = 12.3 ± 0.3. Within experimental error these are the same as the respective liquid-phase yields at −79 °C. For doses in excess of 2 × 1018 eV per g the dose dependence is no longer significant and the yields tend toward plateau values of 3.2 ± 0.1 and 10.3 ± 0.1 for HCl and HBr respectively. The dose dependence of the hydrogen yields is attributed to the scavenging of a reactive intermediate by the halogen atoms and molecules which accumulate in the solid matrix as the dose increases.In independent experiments with an apparatus of the Klein–Scheer type it was shown that hydrogen atoms react readily with films of HBr at 77 °K. There is, however, no evidence of a significant reaction with HCl at this temperature. The difference in behavior of the two hydrogen halides may be explained by their different activation energies for reaction with hydrogen atoms. The results of the γ-radiolyses are discussed in the light of these experiments and it is suggested that the dose dependence may be a result of the scavenging of an ionic intermediate rather than a thermal hydrogen atom.

scholarly journals Nature of the silver precipitation obtained by cementation from thiosulphate solutions

2011 ◽  
Vol 9 (1) ◽  
pp. 180-184 ◽  
Author(s):  
O. Kuntyi ◽  
G. Zozulya ◽  
I. Saldan ◽  
V. Kree ◽  
S. Korniy ◽  
...  
Keyword(s):  
Electrochemical Behaviour ◽  
Ion Concentration ◽  
Solution Temperature ◽  
Electrochemical Reactions ◽  
Redox Potentials ◽  
Pure Silver ◽  
Magnesium Metal ◽  
Current Limit ◽  
Wide Range ◽  
Silver Precipitation

AbstractThe morphology and composition of the deposits formed on the surface of magnesium disk during cementation from thiosulphate solutions (0.0025–0.1M) [Ag(S2O3)2]3− + 0.5M S2O3 2− have been studied. A porous deposit with low adhesion is formed on the surface of the magnesium metal substrate. Within a wide range of [Ag(S2O3)2]3− ion concentrations, sulfur as well as silver are constituents of the deposit at the initial stages of cementation and at the end of the reaction. This is attributed to the electrochemical behaviour of magnesium in thiosulphate solutions resulting in the exceeding of current limit on cathode for pure silver reduction. Hence, parallel electrochemical reactions take place that are very close in their values to the standard redox potentials of reduction of [Ag(S2O3)2]3− ions to Ag0 and S2O32− ions to S2−. Sulfur content in the cement deposits increases with the decrease in [Ag(S2O3)2]3− ion concentration and increase in cementation time. This tendency is also observed with the decreasing solution temperature.

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