TY - JOUR
T1 - Competitive Deprotonation and Superoxide [O2 -•] Radical-Anion Adduct Formation Reactions of Carboxamides under Negative-Ion Atmospheric-Pressure Helium-Plasma Ionization (HePI) Conditions
AU - Hassan, Isra
AU - Pinto, Spencer
AU - Weisbecker, Carl
AU - Attygalle, Athula B.
N1 - Publisher Copyright:
© 2015 American Society for Mass Spectrometry.
PY - 2016/3/1
Y1 - 2016/3/1
N2 - Carboxamides bearing an N-H functionality are known to undergo deprotonation under negative-ion-generating mass spectrometric conditions. Herein, we report that N-H bearing carboxamides with acidities lower than that of the hydroperoxyl radical (HO-O•) preferentially form superoxide radical-anion (O2 -•) adducts, rather than deprotonate, when they are exposed to the glow discharge of a helium-plasma ionization source. For example, the spectra of N-alkylacetamides show peaks for superoxide radical-anion (O2 -•) adducts. Conversely, more acidic amides, such as N-alkyltrifluoroacetamides, preferentially undergo deprotonation under similar experimental conditions. Upon collisional activation, the O2 -• adducts of N-alkylacetamides either lose the neutral amide or the hydroperoxyl radical (HO-O•) to generate the superoxide radical-anion (m/z 32) or the deprotonated amide [m/z (M - H)-], respectively. For somewhat acidic carboxamides, the association between the two entities is weak. Thus, upon mildest collisional activation, the adduct dissociates to eject the superoxide anion. Superoxide-adduct formation results are useful for structure determination purposes because carboxamides devoid of a N-H functionality undergo neither deprotonation nor adduct formation under HePI conditions. [Figure not available: see fulltext.]
AB - Carboxamides bearing an N-H functionality are known to undergo deprotonation under negative-ion-generating mass spectrometric conditions. Herein, we report that N-H bearing carboxamides with acidities lower than that of the hydroperoxyl radical (HO-O•) preferentially form superoxide radical-anion (O2 -•) adducts, rather than deprotonate, when they are exposed to the glow discharge of a helium-plasma ionization source. For example, the spectra of N-alkylacetamides show peaks for superoxide radical-anion (O2 -•) adducts. Conversely, more acidic amides, such as N-alkyltrifluoroacetamides, preferentially undergo deprotonation under similar experimental conditions. Upon collisional activation, the O2 -• adducts of N-alkylacetamides either lose the neutral amide or the hydroperoxyl radical (HO-O•) to generate the superoxide radical-anion (m/z 32) or the deprotonated amide [m/z (M - H)-], respectively. For somewhat acidic carboxamides, the association between the two entities is weak. Thus, upon mildest collisional activation, the adduct dissociates to eject the superoxide anion. Superoxide-adduct formation results are useful for structure determination purposes because carboxamides devoid of a N-H functionality undergo neither deprotonation nor adduct formation under HePI conditions. [Figure not available: see fulltext.]
KW - Adducts
KW - Carboxamides
KW - Helium-plasma ionization (HePI)
KW - Superoxide radical anion
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U2 - 10.1007/s13361-015-1296-6
DO - 10.1007/s13361-015-1296-6
M3 - Article
AN - SCOPUS:84958182566
SN - 1044-0305
VL - 27
SP - 394
EP - 401
JO - Journal of the American Society for Mass Spectrometry
JF - Journal of the American Society for Mass Spectrometry
IS - 3
ER -