Chiral recognition and the deprotonation reaction of gas-phase cytochrome c ions

Gas-phase deprotonation reactions of cytochrome c ions by chiral amines (2-butylamine and 1-amino-2-propanol) exhibit strong chiral specificity. The R-isomer of 2-butylamine is at most 10 times more reactive than the S-isomer. With 1-amino-2-propanol, the S-isomer is as much as two times more reactive than the S isomer. The specificity decreases with increasing charge states. For the 12+ state, the (2R)-2-butylamine is only 50% more reactive than the S isomer, compared to 10 times for the 9+ state. Reactions of the racemic mixture of 1-amino-2-propanol and double resonance experiments suggest a complicated proton transfer mechanism possibly involving a diadducted intermediate-the protein with two alkyl amine adducts. Variable temperature experiments are also performed to illustrate the presence of a barrier in the proton transfer reaction. (C) 1999 Elsevier Science B.V.