Initiators radiolabeled

The elucidation of the biosynthetic pathway for the production of various metabolites has been extensively examined through the use of techniques that use isotopic labeling (stable isotopes and radioactive isotopes). Initially, radiolabeled precursors were introduced into plants and the resultant radioactive compounds were chemically degraded to identify the positions of the label. As the development of analytical instrumentation advanced, the isotopically labeled natural products were analyzed by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy instead of chemical degradation. 

The AMAPs (2-[ arylmethyl amino]-l,3-propanediols) are a class of planar polycyclic aromatic derivatives, which contain polar side-chains. They are known to be DNA intercalators and possess broad spectrum antitumour activity. An approach to C-radiolabelled AMAP derivative 40 used the Bucherer reaction as an initial starting reaction. 2-Naphthol was reacted with 4-bromophenylhydrazine 38 in the presence of sodium metabisulfite and HCl to afford 39. Subsequent derivatisation of 39 afforded 40. 

The best labeling system in this regard is isotopic labeling since it involves the minimum change from the standard initiator. Methods based on radiolabeling and stable isotopes detectable by NMR are described in Sections 3.5.4.1 and 3.5.4.2 respectively. 

Polymer formed using radiolabeled initiators may be isolated and analyzed to determine the concentration of initiator-derived residues and calculate the initiator efficiency. Radiolabeled initiators have also been used extensively to establish the relati ve reactivity of monomers towards radicals. 107,5 -5 2... 

Berger and Mcycrhoff150 also reported that termination involves substantial disproportionation. They determined the initiator fragments per molecule in PS prepared with radiolabeled AIBN and conducted a detailed kinetic analysis of the system. They also found a marked temperature dependence for k k. Values of kt fkK ranged from 0.168 at 30 °C to 0.663 at 80 °C. 

Park and Smith 170 attempted to allow for chain transfer in their examination of the termination mechanism during VC polymerization at 30 and 40 °C in chlorobenzene. They determined the initiator-derived ends in PVC prepared with radiolabeled AIBN and concluded that kjk = 3.0. However, questions have been raised regarding the reliability of these measurements.171 172 Atkinson et al.x72 applied the gelation technique (Section 5.2.2.2) to VC polymerization and proposed that termination involves predominantly combination. 

Both H-thymidine incorporation and radiolabeled leucine incorporation techniques have been recently used to determine bacterial activity and growth in the rhizosphere of barley seedling (28), Bacteria were initially released from the rhizosphere using homogenization and centrifugation before adding the labeled substrates. The cell incorporation rate was twice as high in the rhizosphere than in bulk soil. In addition, both the leucine and thymidine incorporation rates increased with the distances from the root tip (28). 

The use of microbial siderophores by dicotyledonous plants appears to involve uptake of the entire metallated chelate (42-44), or an indirect process in which the siderophore undergoes degradation to release iron (45). As demonstrated in initial studies examining this question, there was concern that iron uptake from microbial siderophores may be an artifact of microbial iron uptake in which radiolabeled iron is accumulated by root-colonizing microorganisms (46). Consequently, evidence for direct uptake of iron from microbial siderophores has required the use of axenic plants. In experiments with cucumber, it was shown that the microbial siderophore ferrioxamine B could be used as an iron source at concentrations as low as 5 pM and that the siderophore itself entered the plant (42). 

Diisopropyl methylphosphonate is initially distributed to the liver by way of the portal circulation after absorption from the intestines, and then to the kidneys for excretion (Hart 1976). High concentrations of radiolabel were detected in the urinary bladder itself, exclusive of any urine of mice at 15 minutes and persisted for up to 6 hours. A similar pattern of distribution to the liver, kidney, and urinary bladder was seen in rats over the first 6 hours after oral administration of diisopropyl methylphosphonate. 

Acrylonitrile is rapidly distributed throughout the body after inhalation exposure. Measurable amounts of acrylonitrile derived radiolabel were present in the brain, stomach, liver, kidney, lung and blood within 1 hour of initiation of exposure (Pilon et al. 1988b). 

The following operations should be done using standard safety procedures for working with radioactive compounds. All steps involving SASD prior to initiation of the photoreaction should be done protected from light to avoid loss of phenyl azide activity. The radiolabeling procedure should be done quickly to prevent excessive loss of NHS ester activity due to hydrolysis. 

Amphipod, Gammarus pseudolimnaeus PCBs 8, 15, 32, 155, 101 initial water concentrations of 70-210 pg/L Mysid, Mysls rellcta-, exposed to radiolabeled PCB 153 for 6 h at 4°C, then transferred to clean water for 26 days Amphipod, Pontoporeia hoy r, exposed to radiolabeled PCB 153 for 6 h at 4°C, then transferred to clean water for 26 days... 

Expired air. For 14C-labeled chemicals, the tracer carbon may be incorporated in vivo into carbon dioxide, a possible metabolic product. Therefore, when the position of the radiolabel indicates the potential for biological instability, a pilot study to collect expired air and monitor its radioactivity content should be conducted prior to initiating a full-scale study. Expired air studies should also be performed in situations where the radiolabel has been postulated to be stable but analyses of urine and feces from the toxicokinetic study fail to yield complete recovery (mass balance) of the dose. 

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