Isotope tracer studies

Although many overall rearrangements can be formulated as a series of 1,2-shifts, both isotopic tracer studies and con utational work have demonstrated foe involvement of other species. These are bridged ions in which hydride or alkyl groups are partially bound to two other carbons. Such structures can be transition states for hydride and alkyl-group shifts, but some evidence indicates that these structures can also be intermediates. 

Thus we shall be concerned with properties that furnish information about the nature of the ligands, the oxidation state of the metal, and the geometry of the field of ligands. Techniques such as radio-isotope tracer studies, neutron-activation analysis, and electron microscopy are powerful methods for locating a metal within constituents of the cell and are particularly suited to heavy-metal rather than organic drugs but since they do not provide information about the chemical environment of the metal they will not concern us here. After each section below we shall give an example, not necessarily from platinum chemistry, where the method has been used with success in biochemistry. 

Unidirectional, first-order transfer rates (day1) between compartments were developed for 6 age groups, and intermediate age-specific values are obtained by linear interpolation. The range of age-specific transfer rate values are given in Table 2-8. The total transfer rate from diffusible plasma to all destinations combined is assumed to be 2,000 day"1, based on isotope tracer studies in humans receiving lead via injection or inhalation. Values for transfer rates in various tissues and tissue compartments are based on measured deposition fractions, or instantaneous fractional outflows of lead between tissue compartments (Leggett 1993). 

Bell, J., and R. I. Reed Isotopic Tracer Studies of Pyrolytic Reactions. 

On treatment with aluminum chloride in benzene, 1-benzene-Hulfooyl- 2-bromomethylftziridme gives an open-chain benzenes ulfon-amide (Eq. 73). Evidence provided by an isotopic-tracer study (discussed in further detail in the accompanying chapter on azetidinea) fa that flic reaction occurs by way of an ozetidine.1 .177 ... 

Termination in autoxidations is rather more complex than in the chain reactions we have considered so far. As we have noted briefly earlier (Section 9.2, p. 488), the peroxy radicals first combine to an unstable tetroxide, ROOOOR.124 The existence of these compounds when R is tertiary is inferred from isotope tracer studies,125 and the equilibrium 9.72 is observable by electron... 

The use of isotopic tracers has demonstrated that the selective oxidation of propylene proceeds via the formation of a symmetrical allyl species. Probably the most convincing evidence is presented by the isotopic tracer studies utilizing, 4C-labeled propylene and deuterated propylene. Adams and Jennings 14, 15) studied the oxidation of propylene at 450°C over bismuth molybdate and cuprous oxide catalysts. The reactant propylene was labeled with deuterium in various positions. They analyzed their results in terms of a kinetic isotope effect, which is defined by the probability of a deuterium atom being abstracted relative to that of a hydrogen atom. Letting z = kD/kH represent this relative discrimination probability, the reaction paths shown in Fig. 1 were found to be applicable to the oxidation of 1—C3He—3d and 1—QH —1 d. 

The classic Horiuti-Polanyi mechanism proposed in 1934 for hydrogenation of ethylene on Ni is shown in Scheme 1. Since then isotopic tracer studies,... 

Within the carbonaceous deposit, there is mixing of both the carbon and the hydrogen as revealed by isotopic tracer studies. 

Vitamin Be requirements have been estimated both by isotopic tracer studies to determine turnover of the body pool (Section 9.6.1) and also by depletion/ repletion studies using a variety of indices of status (Section 9.6.2). These studies have generally been conducted on young adults, and there is inadequate information to determine the requirements of elderly people, because apparent status assessed by a variety of indices declines with increasing age, despite intake as great as in younger people (Bates et al., 1999a). As discussed in Section 9.6.3, there is also inadequate information to estimate the requirements of infants. 

Cobelli, C., TofFolo, G., Bier, D. M., and Nosadini, R. (1987). Models to interpret kinetic data in stable isotope tracer studies. Am. J. Physiol. 253, E551—E564. 

Reaction of hydroxylamine with nitrous acid has been the subject of kinetic - " and isotopic-tracer " ° studies. In addition to formation of nitrous oxide (2), there is a minor reaction (3) forming hyponitrous acid. 

Jahn B. M. (1999) Sm-Nd isotope tracer study of UHP metamorphic rocks implications for continental subduction and collisional tectonics. Int. Geol. Rev. 41, 859-885. 

Normal pentane oxidation was also the subject of an investigation by Cullis and Hirschler [189] with respect to the formation of 1- and 2-pentene, and the effect of their addition to pentane + oxygen mixtures. Mechanisms of reaction were interpreted from radioactive isotope tracer studies by addition of substituted pentenes to the reactants [189], albeit under conditions involving appreciable temperature change. In an earlier study, Chung and Sandler [26] showed that the proportion of pentenes formed during pentane oxidation in a flow system reached a maximum at a reactor temperature of about 750 K. 

Further reports have appeared on the reaction of trivalent phosphorus compounds with acetylene dicarboxylates. In the first, alkyl diphenylphosphinites (e.g.57) are shown to react with dialkylacetylene dicarboxylates (e.g.58) in the presence of carbon dioxide to form 1,2-oxaphosphol-3-enes (e.g.59) which in the presence of excess phosphinite decompose via (60) to give di-ylids (e.g.61). On the other hand, the phosphoranes (62) from phosphonites and phosphites react with a further phosphorus component to give the ylids (63) which are readily converted by treatment with alcohol into phosphonates (65) apparently via ketene intermediates (64) as evidenced by and isotopic tracer studies. ... 

C. M. Scrimgeour, W.M. Bennet, A.A. Connacher (1988) A convenient method of screening glucose for C C ratio for use in stable isotope tracer studies. Biomed. Environ. Mass Spectrom. 17, 265-266... 

A multifaceted characterization effort to stndy these materials as a function of thermal treatment has been undertaken. The techniques include BET surface area measurements. X-ray diffraction, chemisorption, scanning and high-resolution transmission electron microscopy, analytical electron microscopy, neutron activation analysis, atomic absorption spectroscopy, FTIR and isotopic tracer studies. The details of catalyst preparation have been previously... 

Data Analysis. - The vocabulary and principles used in stable isotope tracer studies have been reviewed. " ... 

Although isotope-tracer studies have shown that most mammals can synthesize DHA from the essential fatty acid LNA, there is considerable debate over the capacity of... 

Lupton J. E. (1983) Terrestrial inert gases isotope tracer studies and clues to primordial components in the mantle. Ann. Rev. Earth Planet. Sci. 11, 371-414. 

Dingley, K. H., Roberts, M. L., Velsko, C. A., and Xurteltaub, K. W. (1998). Attomole detection of 3H in biological samples using accelerator mass spectrometry Application in low-dose, dual-isotope tracer studies in conjunction with 14C accelaata- mass spectrometry. Chem Res Toxicol 11, 1217-1222. 

Blaedel and Haupert (28) demonstrated the feasibility of using this phenomenon as a preconcentration technique using isotope tracer studies on the ions Na4", Cs4", Zn24", and later Blaedel and Christensen (29) extended the work to include the anions 1 and HP01 . They found anion transport to be much slower than the previously reported cation transport. Coion transport in the anion exchange membranes was much higher and apparently dependent on the anionic charge of the bulk electrolyte. Further studies with more recently available membranes (1) seem to be needed. 

MK biosynthesis by the OSB pathway has been elucidated on the basis of isotopic tracer experiments, isolation of mutants blocked in the various steps, isolation and identification of intermediates accumulated by the mutants, and by enzyme assays. Early isotopic tracer experiments with various bacteria established that methionine and prenyl PPi contribute to the methyl and prenyl substituents of the naphthoquinone. The early isotopic tracer studies and other work have been reviewed by Bentley and Meganathan. " In 1964, Cox and Gibson observed that [G- " C] shikimate was incorporated into both MK and ubiquinone by E. coli, thus providing the first evidence for the involvement of the shikimate pathway." Chemical degradation of the labeled isolated menaquinone (MK-8) showed that essentially all of the radioactivity was retained in the phthalic anhydride. It was concluded that the benzene ring of the naphthoquinone (sic) portion of vitamin K2 arises from shikimate in E. coli The authors further suggested that shikimate was first converted to chorismate before incorporation into MK. A more complete chemical degradation of the MK derived from... 

---