Potassium-40, positron emission

Poor Metabolizer Phenotype Population Pharmacokinetics Positron Emission Tomography Post-translational Modification Potassium Channels Potassium Competitive Acid Blockers PP... 

A lunar expedition brought back some moon rocks. Analysis of the rocks showed them to contain 17% potassium-40 and 83% argon by mass. The half-life of K-40 is 1.2 x 10 years. K-40 decays through positron emission. Ar-40 is the decay product of the reaction. How old was the rock sample (in years) ... 

Dichloropentane (1) and 1,6-dibromohexane (2) can be converted to the monofluoro derivatives 3 and 4 by heating with potassium fluoride in ethylene glycol at 125 C. The yields are low (< 20 %).74 These compounds are of interest because they can be converted to fluoroal-kylamines for use as synthetic intermediates in the preparation of histamine receptor ligands for use in positron emission tomography. 

Self-Test 17.3A Identify the nuclides that result from (a) electron capture by potassium-40 and (b) positron emission by sodium-22. 

To monitor tumor response to capecitabine therapy noninvasively, Zheng and co-workers, from the Indiana University School of Medicine, developed the synthesis of the fluorine- 18-labeled capecitabine as a potential radiotracer for positron emission tomography (PET) imaging of tumors.28 Cytosine (20) was nitrated at the C-5 position with nitric acid in concentrated sulfuric acid at 85°C, followed by neutralization to provide 5-nitrocytosine (27) in moderate yield. This nitro pyrimidine was then carried through the glycosylation and carbamate formation steps, as shown in the Scheme below, to provide the 6/s-protected 5-nitro cytidine 28 in 47% for the three-step process. Precursor 28 was then labeled by nucleophilic substitution with a complex of 18F-labeled potassium fluoride with cryptand Kryptofix 222 in DMSO at 150 °C to provide the fluorine-18-labe led adduct. This intermediate was not isolated, but semi-purified and deprotected with aqueous NaOH in methanol to provide [l8F]-capecitabine in 20-30% radiochemical yield for the 3-mg-scale process. The synthesis time for fluorine-18 labeled capecitabine (including HPLC purification) from end of bombardment to produce KI8F to the final formulation of [18F]-1 for in vivo studies was 60-70 min. 

In nuclear equations for positron emission, the electron is written as either P" ", +ie, or je. Potassium-40, which is important in geologic dating, undergoes positron emission ... 

Radioactive xenon-133 is used to measure lung capacity. It shifts toward stability by emitting beta particles. Write the nuclear equation for this reaction. Write the nuclear equation for the positron emission of potassium-40. 

Positron emission tomography Potassium blood urine... 

Additional examples include the electrophilic arylations of sodium arenesulflnates [866], potassium car-bonotrithioates [867] and benzazoles [868] using diaryliodonium salts in ionic liquids and the arylations of anilines [869], sodium tetraphenylborate [870] and vinyUndiums [871]. Particularly important are the reactions of diaryliodonium salts with fluoride anion as nucleophile. This reaction is widely applied for introduction of the radioactive F isotope into different organic substrates to obtain labeled agents for positron emission tomography. This topic is covered separately in Chapter 7 due to its importance and wide usage. 

Potassium ion is present in foods and is an essential nutrient in the human body. One of the naturally occurring isotopes of potassium, potassium-40, is radioactive. Potassium-40 has a natural abundance of 0.0117% and a half-life ti/2 = 1.28 X 10 yr. It undergoes radioactive decay in three ways 98.2% is by electron capture, 1.35% is by beta emission, and 0.49% is by positron emission, (a) Why should we expect to be radioactive (b) Write the nuclear equations for the three modes by which decays, (c) How many °K ions are present in 1.00 g of KCl (d) How long does it take for 1.00% of the K in a sample to undergo radioactive decay ... 

The table to the right gives the number of protons (p) and neutrons ( ) for four isotopes, (a) Write the symbol for each of the isotopes, (b) Which of the isotopes is most likely to be unstable (c) Which of the isotopes involves a magic number of protons and/or neutrons (d) Which isotope will yield potassium-39 following positron emission ... 

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