ACETONE CHEMICAL-IONIZATION STUDIES - IX - AMINO-ACIDS AND NUCLEOBASES

Acetone chemical ionization mass spectra of 16 natural alpha-amino aci ds and 5 free nucleobases show characteristic ions corresponding to [M +H](+), [M+43](+) and [M+59](+) ions. The proton affinities of the sub strates are found to control the formation of the above ions, The site of acetylation of amino acids under acetone chemical ionization condi tions has been studied by the comparison of collision induced dissocia tion mass spectra of [M+43](+) ions from the amino acids with those of [M+H]+ ions from the corresponding N-acetyl amino acids, generated un der both methane chemical ionization and liquid secondary ion mass spe ctrometric conditions, It is concluded that the site of acetylation de pends on the nature of the functional groups present, The structure of the [M+43](+) ions of nucleobases is indicated to be an ion-neutral c omplex between the protonated nucleobase and ketene. (C) 1997 John Whe y & Sons, Ltd.