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The Chemical Form of N Produced in 13
Various Nuclear Reactions and Chemical Environments: A Review
Downloaded by AUBURN UNIV on September 25, 2017 | http://pubs.acs.org Publication Date: March 1, 1982 | doi: 10.1021/ba-1981-0197.ch013
ROY S. TILBURY
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Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021
The literature on the chemistry of recoil N-13 atoms is reviewed with emphasis on the chemical form of the N-13 atom in various nuclear reactions and target materials. The nuclear reactions considered are: C(d,n) N, O(p,α) N (n,2n) N. The mechanisms of the reaction of the N re coils are discussed. 12
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'•phe chemistry of excited nitrogen atoms or molecules has an extensive -•-literature [see, for example, the book "Active Nitrogen' by Wright and Winkler (1) and the more recent review by Brown and Winkler (2)]. The hot atom or recoil chemistry of nitrogen-13, a radioactive isotope with half-life of 10.0 min, has been studied for many years as basic research into the mechanisms of reactions of excited nitrogen atoms. The more recent use of N-labeled compounds as tracers for studying biological and medical problems has given renewed interest and importance to these studies. In this chapter I shall review the various methods for producing of nitrogen-13 and the chemical forms of the N-labeled compounds formed in various target materials. 13
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Deuterons on Carbon-Containing Compounds A common method of making N-13 is the (d,n) nuclear reaction on carbon-12. This reaction has a Q value of —0.28 MeV and a coulomb barrier of 1.8 MeV, and so it will occur with deuterons of energy greater Current address: Nuclear Medical Section, M . D . Anderson Hospital, 6723 Bertner Avenue, Houston, TX 77030. 1
0065-2393/81/0197-0261$05.00/0 © 1981 American Chemical Society
Root and Krohn; Short-Lived Radionuclides in Chemistry and Biology Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
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SHORT-LIVED RADIONUCLIDES
than 1.8 MeV. The maximum cross section occurs at about 5 MeV, and yields of about 10 mCi/fjA at saturation can be achieved with 8-MeV deuterons. Schmied and Koski (3) studied the N-labeled products when various organic compounds were irradiated with 2-MeV deuterons. When methyl bromide, methyl chloride, or chloroform was irradiated, H C N was the main product. In CHC1 , C1C N was also observed. In CCI4, C1C N was the main product. Also, N N and NO were formed from traces of nitrogen and oxygen in the target chamber. No significant amounts of N H were detected, indicating that no abstraction of hydrogen occurred, which agrees with the earlier work on active nitrogen. Perkins and Koski (4) irradiated methane, methanol, and ethanol with 2-MeV deuterons and detected H C N , C H C N , and C H C N . Again, no N H was detected. Dubrin et al. (5) also reported H C N as the major product of the deuteron irradiation of methane and ethylene, but they stress that these were volatile products only. 13
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Welch (6) irradiated carbon dioxide with 7-MeV deuterons and found N N and N • N O to be formed in approximately equal amounts over a range of dose from 0.008 to 0.2 eV/molecule and with nitrogen present in the range 0.2-10%. At higher doses the N • N O content decreased due to its radiolytic decomposition. Welch and Lifton (7) irradiated several inorganic carbides with 7-MeV deuterons and measured the N-labeled products produced on acid dissolution. A1 C , a methanide, gave 80% N H and 20% C H N H as the major products, while CaC , an acetylide, gave 20% N H , 40% C N " , and 30% C H C N as the major products. These products and yields were correlated with the crystal structure of the metallic carbides. Tilbury et al. (8) irradiated methane flowing through a glass tube with 7.8-MeV deuterons and bubbled the irradiated gas through water or isotonic saline solution. The solution was analyzed by radio-gas chroma tography and was found to contain 95% N H , 2% C H N H , and 0.2% C H N H . Less than 3% H C N and no C H C N were detected. These results were strikinkly different from those of Koski et al. (3,4). Welch and Straatmann (9) suggested a mechanism involving water and oxygen impurities to account for the observations of Tilbury et al., with H atoms being formed radiolytically ( M represents a third body): 1 3
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H + 0 + M->H0 - + M 2
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N:+ H0 --» NH: 2
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Root and Krohn; Short-Lived Radionuclides in Chemistry and Biology Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
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Chemical Form of N
TILBURY
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Dewhurst (JO) found significant amounts of ammonia when active nitrogen was reacted with silanes and hydrocarbons. He thought it unlikely that ammonia was formed by hydrogen abstraction reactions, since in the first step immine radicals are formed, which very likely disproportionate to hydrogen and nitrogen. He therefore postulated that ammonia was formed by combination of nitrogen and hydrogen atoms and that this may also be the mechanism of formation of N H . Straatman and Welch (11), on irradiating methane with 7-MeV deuterons and bubbling the gas through dilute acid, found, by highpressure liquid chromatography ( H P L C ) on an anion-exchange column, a large unidentified N-labeled component near the solvent front as well as N H . This unidentified peak disappeared on gas chromatography and was presumably decomposed to N H , giving the same product distribution as observed by Tilbury et al. A l l the above methods of producing N H yielded significant quan tities of nonradioactive ammonia that interfered with the enzymatic synthesis of amino acids, and for this reason most workers have subse quently used the proton irradiation of water to produce N H (see below). Stewart et al. (12) studied the reactions of recoil N atoms in the gas phase with C 0 , N , 0 , N 0 , and N O . Recoil nitrogen atoms were generated by the C ( d , n ) N reaction using C 0 as the target molecule and 1.7-MeV deuterons. The only products observed were N • N and N • NO. Other products sought but not detected were N O , N 0 , and C N radicals. The N • N O yield was independent of C 0 concentration but increased rapidly with the addition of oxygen. It was concluded that recoil N atoms do not react directly with C 0 .
Downloaded by AUBURN UNIV on September 25, 2017 | http://pubs.acs.org Publication Date: March 1, 1982 | doi: 10.1021/ba-1981-0197.ch013
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Protons on Oxygen-Containing Compounds Probably the most common method for making N for labeled compound synthesis is now the (p,«) nuclear reaction on O , usually in the form of water. Several groups have used this reaction to produce N H (13-16). This reaction has a Q value of - 5 . 2 MeV, a threshold energy of 5.52 MeV, and a peak cross section of about 200 mb at 8 MeV. A yield of 25 mCi/juA at saturation can be achieved with 14.5-MeV protons (17). Welch and Straatmann (9) studied the reaction of N recoil atoms produced in a variety of organic compounds and i n water, and they reported 7% N H , 93% N 0 " at dose rates less than 1 eV/molecule and 0.3% N H , 99.7% NO
