Mechanism of nitrogen-13-labeled ammonia formation in a cryogenic water target

Biocatalysis in radiochemistry: Enzymatic incorporation of PET radionuclides into molecules of biomedical interest

“…More commonly, [ 13 N]NH 3 can be generated directly in the target by the addition of ethanol, hydrogen gas, or methane to the pure water, which act as scavengers and prevent radiolytic oxidation of ammonia. Ammonia can be also produced in‐target using cryogenic targets …”

“…Ammonia can be also produced in-target using cryogenic targets. 29 Besides direct application as flow and perfusion marker, [30][31][32] [ 13 N]NH 3 is the main precursor for the synthesis of natural amino acids. In general, [ 13 N]NH 3 can be incorporated into amino acids through 3 main enzymatic routes ( Figure 2): (1) using amino acid dehydrogenases that catalyze the reductive amination of α-ketoacids using nicotinamide adenine dinucleotide (NADH) as redox cofactor and [ 13 N]NH 3 as the amine source 10, 11, 33-40; (2) using amino acid synthetases that catalyze the insertion of [ 13 N]NH 3 into the ω-carboxylic group of acidic amino acids by using adenosine triphosphate (ATP) 11,36,37,41 and (3) using a bi-enzymatic system integrated by an amino acid dehydrogenase (usually glutamate dehydrogenase) that catalyzes the reductive amination of α-ketoglutarate to produce L-[ 13 N]glutamate that is concurrently used by a transaminase that transfers the radiolabeled amine group to the target α-ketoacid to form the desired L-[ 13 N]amino acid.…”

Labelling with positron emitters of pnicogens and chalcogens

“…4,8 The target material of the proton irradiation is natural water, which leads to a mixture of [ 13 N]nitrogen, [ 13 N]nitrite, [ 13 N]nitrate, and [ 13 N]ammonia. [35][36][37][38] [ 13 N]N 2 has been used as a PET tracer in the context of studying both pulmonary function in humans 39 and nitrogen fixation in root nodules of legumes. 40 Several methods were developed for the in-target production of elemental [ 13 N]N 2 .…”

“…Several nuclear reactions were studied for the production of 13 N; however, today the 16 O(p,α) 13 N reaction is the method of choice for routine production of this positron emitter . The target material of the proton irradiation is natural water, which leads to a mixture of [ 13 N]nitrogen, [ 13 N]nitrite, [ 13 N]nitrate, and [ 13 N]ammonia …”

Nitrogen‐13: historical review and future perspectives

“…Krizek and co-workers described 1 year later that irradiation of water in the liquid phase with protons yielded a mixture of [ 13 23 The radiochemical purity of the […”