Gas-phase reactions of glycine, alanine, valine and their N-methyl derivatives with the nitrosonium ion, NO+.
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.
Freitas
M A
MA
Department of Chemistry, Kansas State University, Manhattan 66506-3701, USA.
O'Hair
R A
RA
Schmidt
J A
JA
Tichy
S E
SE
Plashko
B E
BE
Williams
T D
TD
D000409:Alanine / Q000737:chemistry*; D005740:Gases; D005998:Glycine / Q000737:chemistry*; D007202:Indicators and Reagents; D013058:Mass Spectrometry; D008745:Methylation; D008968:Molecular Conformation; D009603:Nitroso Compounds / Q000737:chemistry*; D013816:Thermodynamics; D014633:Valine / Q000737:chemistry*
D005740:Gases; D007202:Indicators and Reagents; D009603:Nitroso Compounds; D014633:Valine; D000409:Alanine; D005998:Glycine