Hydrogen-deuterium exchange at non-labile sites: A new reaction facet withbroad implications for structural and dynamic determinations

Hydrogen-deuterium exchange at non-labile sites is reported. The conjugate bases of isophthalic acid (m-C6H4(CO2H)(2)), 2-oxoglutaric acid (HO2CCOCH2C H2CO2H), and 2-methylisophthalic acid (2-CH3-1,3-C6H4(CO2H)(2)) undergo scr ambling with 1, 2, and 3 carbon-centered hydrogens under a variety of condi tions. Likewise, protonated 2-(m-methoxyphenyl)ethylamine ((m-CH3OC6H4)CH2C H2NH2) undergoes up to 5 H/D exchanges upon gentle activation whereas the c onjugate acid of 2-phenylethylamine (C6H5CH2CH2NH2) requires the presence o f ammonia-d(3) in order to be pushed to undergo up to 8 H/D exchanges. The very act of electrospraying ions can result in extensive movement of deuter ium to carbon centers and, in some cases, could not be prevented. These fin dings offer great promise for future exploitation but also suggest that the interpretation of many H/D exchange experiments using mass spectrometry as the analytical tool could be in error. (C) 2001 American Society for Mass Spectrometry.