Isotopes isolation

M. Quack, U. Schmitt, and M. A. Suhm, FTIR spectroscopy of hydrogen fluoride clusters in synchronously pulsed supersonic jets Isotopic isolation, substitution and 3 D condensation. Chem. Phys. Lett. 269, 29 38 (1997). 

On the other hand, the weak bands centered around 2270 cm4 in the spectra of deuterated NMP are probably due to N-D stretches of the isotopically isolated NH3D+ ions. 

The subject for further investigations in frameworks of proposed method for calculation of phase equilibriums is description of equilibrium isotopic effect in intermetallic hydrides the method is used for isotope isolation and hydrogen... 

The isotopic isolation of in each tree ring had crucial implications for future radiocarbon studies and continues to be very much a part of current research. Specifically, the examination of the radiocarbon contents in tree-ring-dated samples of wood provided the principal data that permits an in-depth examination of the assumption that the production of radiocarbon by cosmic rays had been maintained at a constant level. For archaeologists especially, it is important to know if there have been... 

The partial H/D-substitution technique has provided precise insight into the structure of water in hydrated saccharinates. Correspondences between the numbers of (OD) or (OH) stretchings isotopically isolated in H2O or D2O matrices, respectively, and the structurally nonequivalent OH oscillators have been regularly observed <1997JST(408)333, 1998MI231>. Unexpectedly, a high (OD) frequency (2531 cm ) was observed in case of D-[Cu(H20)(py)2(sac)2] <1999JST(482)121>. 

Spectra of water in the sodiun salt of Nafion were studied in considerable detail in ref. 4, with special attention to the spectral profiles of the stretching fundamentals of isotopically isolated HDO. Isotopic isolation is achieved experimentally by observing the OD stretching fundamental of a sample with D/H ratio of 1/10 or less, or alternatively the OH stretching fundamental of a sample with H/D ratio of 1/10 or less. These bands are much simpler and thus easier to interpret structurally than the stretching fundamentals of either H20 or D20. The spectra described in ref. 4 have been fully confirmed by further work in the author s laboratory, except that the samples described as "fully hydrated" have now been found to correspond to water content below 3 H20/-S03 whereas full hydration for sodium Nafion corresponds to some 14 H20/-S0o . With this re-interpretation, the results of ref. 4 will be summarized in the next two sections. 

Eighteen isotopes of niobium are known. The metal can be isolated from tantalum, and prepared in several ways. 

The isotope produced was the 20-hour 255Fm. During 1953 and early 1954, while discovery of elements 99 and 100 was withheld from publication for security reasons, a group from the Nobel Institute of Physics in Stockholm bombarded 238U with 160 ions, and isolated a 30-min alpha-emitter, which they ascribed to 250-100, without claiming discovery of the element. This isotope has since been identified positively, and the 30-min half-life confirmed. 

In an extension of the work described m the preceding section Bender showed that basic ester hydrolysis was not concerted and like acid hydrolysis took place by way of a tetrahedral intermediate The nature of the experiment was the same and the results were similar to those observed m the acid catalyzed reaction Ethyl benzoate enriched m 0 at the carbonyl oxygen was subjected to hydrolysis m base and samples were isolated before saponification was complete The recovered ethyl benzoate was found to have lost a por tion of Its isotopic label consistent with the formation of a tetrahedral intermediate... 

Isotope Dilution Another important quantitative radiochemical method is isotope dilution. In this method of analysis a sample of analyte, called a tracer, is prepared in a radioactive form with a known activity. Ax, for its radioactive decay. A measured mass of the tracer, Wf, is added to a sample containing an unknown mass, w, of a nonradioactive analyte, and the material is homogenized. The sample is then processed to isolate wa grams of purified analyte, containing both radioactive and nonradioactive materials. The activity of the isolated sample, A, is measured. If all the analyte, both radioactive and nonradioactive, is recovered, then A and Ax will be equal. Normally, some of the analyte is lost during isolation and purification. In this case A is less than Ax, and... 

The concentration of insulin in a production vat is determined by the method of isotope dilution. A 1.00-mg sample of insulin labeled with with an activity of 549 cpm, is added to a 10.0-mL sample taken from the production vat. After homogenizing the sample, a portion of the insulin is separated and purified, yielding 18.3 mg of pure insulin. The activity for the isolated insulin is measured at 148 cpm. How many milligrams of insulin are in the original sample ... 

A major example of isotope-dilution analysis lies in the procedure itself, which does not require any quantitative isolation of the elements being investigated. The relation between the abundance of the element under investigation and the spike is such that, once the spike has been intimately mixed with the sample, any losses of sample have no effect on the result (Figure 48.14). 

Helium-3 [14762-55-1], He, has been known as a stable isotope since the middle 1930s and it was suspected that its properties were markedly different from the common isotope, helium-4. The development of nuclear fusion devices in the 1950s yielded workable quantities of pure helium-3 as a decay product from the large tritium inventory implicit in maintaining an arsenal of fusion weapons (see Deuterium AND TRITIUM) Helium-3 is one of the very few stable materials where the only practical source is nuclear transmutation. The chronology of the isolation of the other stable isotopes of the hehum-group gases has been summarized (4). 

The overall biosynthetic pathway to the tetracychnes has been reviewed (74). Studies (75—78) utilising labeled acetate and malonate and nmr analysis of the isolated oxytetracycline (2), have demonstrated the exclusive malonate origin of the tetracycline carbon skeleton, the carboxamide substituent, and the folding mode of the polyketide chain. Feeding experiments using [1- 02] acetate and analysis of the nmr isotope shift effects, led to the location of... 

The occurrence and extent of rearrangement of the 2-butyl cation have also been investigated by solvolysis studies using isotopic labeling. When 2-butyl tosylate is solvolyzed in acetic acid, C-2/C-3 rearrangement occurs only to the extent of 9% in the 2-butyl acetate which is isolated.Thus, under these conditions, most of the reaction proceeds by direct participation of the solvent. 

Two techniques, electrochemical reduction (section IIl-C) and Clem-mensen reduction (section ITI-D), have previously been recommended for the direct reduction of isolated ketones to hydrocarbons. Since the applicability of these methods is limited to compounds which can withstand strongly acidic reaction conditions or to cases where isotope scrambling is not a problem, it is desirable to provide milder alternative procedures. Two of the methods discussed in this section, desulfurization of mercaptal derivatives with deuterated Raney nickel (section IV-A) and metal deuteride reduction of tosylhydrazone derivatives (section IV-B), permit the replacement of a carbonyl oxygen by deuterium under neutral or alkaline conditions. 

Homogeneous catalytic deuteration of various unsaturated 5a-spirostane derivatives is an excellent method for the preparation of side chain labeled analogs. Thus, saturation of the double bonds at positions 20(21), 23 and 24 provided the corresponding deuterated compounds (144), (145) and (146) in high isotopic purity. The preparation of (146) is a rare example of the saturation of an isolated trisubstituted double bond in the steroid field. 

Element 86, the final member of the group, is a short-lived, radioactive element, formerly known as radium-emanation or niton or, depending on which radioactive series it originates in (i.e. which isotope) as radon, thoron, or actinon. It was first isolated and studied in 1902 by E. Rutherford and F. Soddy and is now universally known as radon (from radium and the termination-on adopted for the noble gases Latin radius, ray). 

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