Radio-tracer studies

Early studies on oxide films stripped from iron showed the presence of chromium after inhibition in chromate solutionand of crystals of ferric phosphate after inhibition in phosphate solutions. More recently, radio-tracer studies using labelled anions have provided more detailed information on the uptake of anions. These measurements of irreversible uptake have shown that some inhibitive anions, e.g. chromateand phosphate are taken up to a considerable extent on the oxide film. However, other equally effective inhibitive anions, e.g. benzoate" pertechnetate and azelate , are taken up to a comparatively small extent. Anions may be adsorbed on the oxide surface by interactions similar to those described above in connection with adsorption on oxide-free metal surfaces. On the oxide surface there is the additional possibility that the adsorbed anions may undergo a process of ion exchange whereby... 

Radio tracer studies, and adsorption of perchlorate ions on copper, 94 Raman s scattering, and differential capacitance, 80... 

In this section we summarise the manner in which i -metals. Fig. 6, and where possible specifically the platinum complexes of concern here, interact with biological molecules. Some radio-tracer studies have been carried out on the distribution of platinum complexes in whole bacteria grown in media inocculated with the metal ion. The results are summarised in Table 11. It is noteworthy that the bacteriocidal complex [PtClg]2- was taken up almost entirely by the cytoplasmic protein whereas the filamentous forming neutral species, [Pt(NHs)2Cl4], was... 

Ethylphenoxy)triethylamine and 2-(3,4-dimethoxyphenoxy)triethylamine markedly reduce the biosynthesis of limonoids in citrus leaves, presumably by inhibition of cyclase activity. Radio-tracer studies have revealed that limonoids are synthesized in the leaves of citrus and transported to the fruit. The fruit tissue does not appear to be capable of the de novo synthesis of limonoids from acetate or mevalonate. 

Figure 1. Hydrolytic pathway of metabolism of the insecticide carbaryl Once considered the only route of metabolism, radio-tracer studies later showed that oxidation, hydrolysis and conjugation reactions resulted in over a dozen metabolites being formed by some organisms.

Atlas E, Velasco A, Sullivan K, et al. 1983. A radio tracer study of air-water exchange of synthetic organic compounds. Chemosphere 12 1251-1258. 

The main problem of the in situ radio-tracer study of electrosorption phenomena originates from the very nature of the method, because the radiation measured consists of two main parts. The first one is that coming from the solution phase or from the solution layer contacting the electrode. The second radiation component is the radiation coming from the adsorption... 

G. Horanyi and G. Inzelt, Anion-involvement in electrochemical transformations of polyaniline. A radio-tracer study, Electrochim. Acta ii 947 (1988). 

Radio-tracers have been used to study silver deposition, and it has been shown that when certain inhibitors or complexing agents are present the displacement reaction may be markedly affected ... 

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. 

M. Simonyi, I. Fitos, Z. Tegyey, and L. Otvos, Stationary uitrafiltration a radio-tracer technique for studying stereoselective binding of racemic ligands, Biochem. Biof ys. Res. Commun., 97 1 (1980). 

Stone and Tilley have shown that the spectral changes which occur on spinel formation can be related to the extent of reaction of the component oxides, although the kinetics were also followed by chemical analysis. Keyser et have studied the reaction of zirconium silicate with calcium oxide by a radio tracer method. Wagenblast and Damask have used internal friction measurements to study the rate of precipitation of carbon in iron. The rate of decrease of the Snoek peak can be related to the growth kinetics of the iron carbon precipi-... 

A PET study begins with the injection or inhalation of a radiotracer, followed by scanning. When the radiotracer decays, it emits a positron that travels a short distance and annihilates with an electron (Eig. 5.1). Annihilation produces two 511-keV photons, which propagate at approximately 180° apart These photons can be detected within a short time window called the coincidence time window (-10 ns). Many such events are summed to provide the distribution of the radiotracer. Radio-tracer transport, washout and retention can be monitored by PET and, if cah-brated, the PET images can yield quantitative estimates of the amount of radiotracer... 

Radiopharmaceuticals with very high specific activity (5-15 Ci mmol ) are used in PET studies so as to retain the pharmaceutical, biological, and biochemical properties of the compound being studied. This section reviews the common radiosynthetic methods, the selection of a suitable radio-tracer, and limitations in the preparation of radiopharmaceuticals. 

Surface self-diffusion is the two-dimensional analogue of the Brownian motion of molecules in a liquid bulk. Measurements of self-diffusion have to be performed in complete absence of any Marangoni flow caused by surface tension differences. Such experimental conditions are best established in an insoluble monolayer where one part consists of unlabelled and the other of radio-tracer labelled molecules. The movement of molecules within the surface monolayer can be now observed by using a Geiger-Miiller counter. There are possible effects of liquid convective flow in the sublayer which was discussed for example by Vollhardt et al. (1980a). With e special designed apparatus Vollhardt et al. (1980b) studied the self-difihision of different palmitic and stearic acid and stearyl alcohol and obtained self-diffusion coefficients between l-i-4 lO cm /s. 

A more detailed study of the dehydration of 2-phenyl-1-propanol was reported and a radio tracer technique using C was used to delineate the mechanism. Of the reaction products, the allyl benzene formed was labelled only on the benzylic carbon and was thus produced by y hydrogen abstraction and concerted phenyl migration. In the a-methylstyrene, the label was equally distributed between the I and 3 carbon atoms and this product arose either through a symmetrical cyclopropane intermediate or a tertiary carbonium ion. viz-... 

Another type of poisoning which has been extensively studied by radio-tracer techniques is the loss of catalytic activity due to the accumulation on the surface of strongly retained carbonaceous species, sometimes referred to as coke. Radiotracer experiments with [14-C]labelled ethylene, hex-1-ene, and cyclohexene on Pt black showed that catalyst deactivation was accompanied by progressive build-up of hydrocarbon residues on the surface. ... 

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