Radiolabelled ammonia

Figure 23 further shows that after changing the flow to NHs/He, [ N]-NH3 desorbs and travels as a pulse through the reactor. This indicates that [13N]-NH3 exchanges rapidly with [ Nj-NHs. At first sight, this exchange process is very similar to the experiment shown in Figure 22. However, in this case, radio-labelled ammonia is not in full equilibrium on 7-almnina. After switching to imlabelled ammonia, first of all, the available Lewis sites are saturated. The time to satmate the 7-alumina bed with ammonia, measured with the mass spectrometer at the outlet of the reactor, is equal to the retention time of radiolabelled ammonia in the catalyst bed. Thus, the radiolabelled ammonia moves with the saturation front, where aimnonia adsorption/desorption is in quasi equilibrium. We conclude that gas phase anunonia clearly facilitates desorption of [ Nj-NHs it remains adsorbed at the same bed position without ammonia in the gas phase. This proves that Adsorption Assisted Desorption takes place for aimnonia desorption from 7-alumina.

Method. The sample of thiol is added to a 5-ml glass vial which is fitted with a plastic cap. Two syringe needles are inserted through the cap and nitrogen gas is introduced. A 0.1 M ammonia-ammonium chloride buffer (pH 9.0,6 10-SA/ in EDTA and 0.8 M in urea) is added to bring the total volume to 3.0 ml. A four-fold molar excess of radiolabeled methylmercuric nitrate is then added and the contents of the vial are mixed gently. A 0.1-0.5-ml aliquot portion of the resulting solution is placed on a column of Sephadex G-10F and eluted with 0.1 M citrate (pH 2.0,1% in Hyamine 2389 surfactant) at a flow-... 

The urea breath test measures radiolabelled COj in expired air after ingestion of labelled urea, exploiting the fact that the organism produces urease and can convert urea to ammonia. 

The UBT is based on HP urease activity. The carbon (nonradioac-tive isotope) and " carbon (radioactive isotope) tests require that the patient ingest radiolabeled urea, which is then hydrolyzed by HP (if present in the stomach) to ammonia and radiolabeled bicarbonate. The radiolabeled bicarbonate is absorbed in the blood and excreted in the breath. A mass spectrometer is used to detect carbon, whereas " carbon is measured using a scintillation counter. The stool antigen test is approved by the Food and Drug Administration (FDA), but availability in the United States is limited. It is less expensive and easier to perform than the UBT, and may be useful in children. Although comparable to the UBT in the initial detection of HP, the stool antigen test is less accurate when used to confirm HP eradication posttreatment. Salivary and urine antibody tests are under investigation. ... 

Histidine ammonia lyase (HAL, histidinase, histidine-a-deaminase, E.C. 4.3.1.3) is capable of abstracting ammonia from L-histidine (17), resulting in the formation of urocanoic acid [Scheme 12.6-4, (6)], an intermediate in the metabolism of l-histidine,n). HAL has also been identified as a key enzyme in the synthesis of secondary metabolites such as Nikkomycin in Streptomyces tendae,ul The mechanism of the enzyme has been investigated and seems to proceed via the carbanion intermediate111, 13]. Synthetic applications of HAL are difficult to achieve, particularly as the enzyme is sensitive to oxygen1131. The utility of HAL is limited to niche applications such as the synthesis of radiolabeled urocanic acids as tracers of histidine metabolism1"1. 

The first report of enzyme catalyzed esterification of lAA was made by Kopcewicz et al. [117], who studied the synthesis of lAA esters by incubating radiolabeled lAA with a com endosperm enzyme preparation. Following incubation, ammonia was added to the incubation mixture and the amount of labeled indole-3-acetamide formed was used as a measure of the amount of lAA ester synthesized. Ester synthesis was found to be stimulated by ATP and CoASH, suggesting acyl group activation. Later studies by Michalczuk and Bandurski [118,119] used a more direct assay procedure, and indicated the following two step reaction mechanism involving sugar, not lAA, activation ... 

Ethynylestradiol, 19-nor-17a-pregna-l,3,5(10)-trien-20-yne-3,17p-diol a synthetic estrogen, M, 296.41, m.p. 146°C, [a][, + 1 ° (dioxan). Administered subcutaneously, E. and estradiol have the same biological potency, but when administered orally, E. is much more active and is therefore used in oral contraceptives. It is synthesized by addition of ethyne (acetylene) to estrone in the presence of sodium in liquid ammonia. Small scale synthesis of E. (e.g. for synthesis of radiolabeled E.) is achieved by addition of lithium acetylide to estrone in dimethyl sulfoxide. 

Then, using radiolabeled ( C) bromobenzene (CeHsBr), it was shown that the aniline (aminobenzene, C6H5NH2) resulting from the reaction with sodium amide in liquid ammonia was a 1 1 mixture of ipso- and ortho-[ Ci]-anihnes (aminoben-zenes) (Equation 7.65). 

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