Freitas M A, O'Hair R A, Schmidt J A, Tichy S E, Plashko B E, Williams T D
Department of Chemistry, Kansas State University, Manhattan 66506-3701, USA.
J Mass Spectrom. 1996 Oct;31(10):1086-92. doi: 10.1002/(SICI)1096-9888(199610)31:10<1086::AID-JMS399>3.0.CO;2-H.
The gas-phase reactions of the nitrosonium ion, NO+ with the amino acids glycine, alanine and valine and their N-methyl derivatives were investigated under chemical ionization mass spectrometric (CIMS) conditions. Two products were observed in all cases: the formation of the iminium ion and the formation of an [M-H]+ ion. The latter product is consistent with a reaction channel involving hydride abstraction by NO+, and was confirmed by (i) examining the Ar+CI mass spectra of the same amino acids under similar source conditions and (ii) examining the unimolecular fragmentation reactions of the [M + H]+ ions of the N-nitroso-N-methyl derivatives of each of the amino acids in a tandem mass spectrometer. Further insights into the reaction of glycine with NO+ were obtained by performing ab initio calculations (at the MP2/6-31G* parallel HF/6-31G* level). These results indicate that four reactions are thermodynamically viable for glycine: (i) hydride abstraction; (ii) iminium ion formation (with concomitant loss of HONO and CO); (iii) diazonium ion formation; and (iv) diazonium ion formation followed by loss of N2. Possible reasons why reactions (iii) and (iv) are not observed are discussed, and comparisons with solution reactivity and the gas-phase reactivity of NO+ are also made.
在化学电离质谱（CIMS）条件下，研究了亚硝鎓离子（NO⁺）与氨基酸甘氨酸、丙氨酸和缬氨酸及其N-甲基衍生物的气相反应。在所有情况下均观察到两种产物：亚胺离子的形成和[M-H]⁺离子的形成。后一种产物与涉及NO⁺夺取氢负离子的反应通道一致，并通过以下方式得到证实：（i）在相似的源条件下检查相同氨基酸的Ar⁺CI质谱，以及（ii）在串联质谱仪中检查每种氨基酸的N-亚硝基-N-甲基衍生物的[M + H]⁺离子的单分子碎裂反应。通过从头算计算（在MP2/6-31G*//HF/6-31G*水平）获得了关于甘氨酸与NO⁺反应的进一步见解。这些结果表明，甘氨酸有四个反应在热力学上是可行的：（i）夺取氢负离子；（ii）形成亚胺离子（同时失去HONO和CO）；（iii）形成重氮离子；以及（iv）形成重氮离子后失去N₂。讨论了未观察到反应（iii）和（iv）的可能原因，并与溶液反应活性以及NO⁺的气相反应活性进行了比较。
