Evolution isotopes

Dimethyl sulfate (16 g) is added to a mixture of dimethyl carbonate (400 g) and deuterium oxide (1(X) g) in a 1 liter flask. Two reflux condensers and a drying tube are attached in series (initial rapid evolution of carbon dioxide may entrain some liquid), and the reaction mixture is heated under reflux for 72 hr. The methanol-OD is distilled directly from the reaction flask through a 30 cm Vigreux column. Redistillation from a small amount of sodium yields 275 g of pure methanol-OD bp 66-66.5° isotopic purity, 98.6%. ... 

This enzyme is of wide occurrence in bacteria where it is concerned with the reduction of nitrate and CO2 as well as sulphur. Methods for its estimation depend on measuring some activity of hydrogenase by (a) dye reduction (benzyl viologen or methylene blue), (b) isotopic exchange and (c) evolution of molecular hydrogen. Interpretation of quantitative results is difficult due to the complex relationship between the enzyme cell structure and the particular method selected. ... 

Now consider the simultaneous evolution of and c)D. Suppose an air mass having initial compositions 3, = 0 cools and precipitates, always as an equilibrium process. According to the preceding analysis, measurements of both isotopic ratios in precipitation will plot on a curve with a slope approximately given by... 

Ambrose, S.H. 1986 Stable carbon and nitrogen isotope analysis of human and animal diet in Mrica. Journal of Human Evolution 15 707-731. 

Bocherens, H., Fizet, M., Mariotti, A., Lange-Badre, B., Vandermeersch, B., Borel, J.P and Bellon, G. 1991a Isotopic biogeochemistry ( C, N) of fossil vertebrate collagen implications for the study of fossil food web including Neandertal Man. Journal of Human Evolution 20 481 92. 

Cerling, T., Harris, J.M., Ambrose, S.H., Leakey, M.G. and Solounias, N. 1998 Dietary and environmental reconstruction with stable isotope analyses of herbivore tooth enamel from the Miocene locality of Fort Tsmaa. Journal of Human Evolution 33 635-650. 

Lee-Thorp, J.A., van der Merwe, N.J. and Brain, C.K. 1989b Isotopic evidence for dietary differences between two extinct baboon species from Swartkrans. Journal of Human Evolution 18 183-190. 

Stable isotope studies in human evolution. Evolutionary Anthropology 4 83—98. 

In aqueous solutions, approximately one atom of deuterium, D, is present for every 7000 atoms of the ordinary hydrogen isotope (protium, H). In the evolntion of heavy hydrogen, HD, the polarization is approximately 0.1 V higher than in the evolution of ordinary hydrogen, H2. Hence during electrolysis the gas will be richer in protium, and the residual solution will be richer in deuterium. The relative degree of enrichment is called the separation factor (S) of the hydrogen isotopes,... 

A process involving water electrolysis is the production of heavy water. During cathodic polarization the relative rates of deuterium discharge and evolution are lower than those of the normal hydrogen isotope. Hence, during electrolysis the solution is enriched in heavy water. When the process is performed repeatedly, water with a D2O content of up to 99.7% can be produced. Electrochemical methods are also used widely in the manufacture of a variety of other inorganic and organic substances. 

Until the advent of modem physical methods for surface studies and computer control of experiments, our knowledge of electrode processes was derived mostly from electrochemical measurements (Chapter 12). By clever use of these measurements, together with electrocapillary studies, it was possible to derive considerable information on processes in the inner Helmholtz plane. Other important tools were the use of radioactive isotopes to study adsorption processes and the derivation of mechanisms for hydrogen evolution from isotope separation factors. Early on, extensive use was made of optical microscopy and X-ray diffraction (XRD) in the study of electrocrystallization of metals. In the past 30 years enormous progress has been made in the development and application of new physical methods for study of electrode processes at the molecular and atomic level. 

Shikazono, N. (1988a) Oxygen and carbon isotopic ratios of calcite and evolution of hydrothermal activities in the Seigoshi gold-silver mining district, Japan. Mining Geology Special Issue, 12, 1-16. 

Shikazono, N. (1989) Oxygen and carbon isotopic compositions of carbonates from the Neogene epithermal vein-type deposits of Japan Implication for evolution of terrestrial geothermal activity. Chem. Geol, 76, 239-247. 

Shimizu, M., Shikazono, M. and Tsunoda, K. (1995) Sulphur isotopic characteristics of hydrothermal mineral deposits in the southern Fossa Magna region, Japan Implications for the tectonic and geologic evolution in the southern Fossa Magna region after middle Mioceme age. Memoirs Fac. Ed. Yamanashi U., 46, 40-48. 

Blichert-Toft J, Alberede F (1997) The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crast system. Earth Planet Sci Lett 148 243-258... 

O Hara MJ (1968) The bearing of phase equilibria studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks. Earth Sci Rev 4 69-133 O Nions RK, McKenzie D (1993) Estimates of mantle thorium/uranium ratios from Th, U and Pb isotope abundances in basaltic melts. Phil Trans Royal Soc 342 65-77 Oversby V, Gast PW (1968) Lead isotope compositions and uranium decay series disequilibrium in reeent volcanic rocks. Earth Planet Sci Lett 5 199-206... 

Baeza A, del Rio M, Miro C, et al. 1999. Recent evolution of the multi-isotopic radioactive content in ice of Livingston Island, Antarctica. Bull Environ Contain Toxicol 63 139-149. 

The isotope effect (i.e. the difference in the rates of evolution of hydrogen from H20 and D20) on hydrogen evolution is very important for theoretical and practical reasons. The electrolysis of a mixture of H20 and D20 is characterized, like in other separation methods, by a separation factor... 

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