CONFORMATION OF DOUBLY PROTONATED PEPTIDES STUDIED BY CHARGE-SEPARATION REACTIONS IN MASS-SPECTROMETRY

Charge-separation metastable processes were investigated by mass spect rometry and kinetic energy release (KER) distributions were determined from the measured metastable peak profiles. Benzene, p-N,N-dimethylam inoaniline and pipecuronium bromide (Arduan) were investigated as refe rence compounds to confirm that there is a well defined relationship b etween the KER distribution and the distance of the two charged center s. For these 'rigid' systems relatively narrow I(ER distributions were found, and the average values sere in good agreement with the interch arge distances determined by a semi-empirical (MNDO) molecular orbital calculation. Two metastable processes of bradykinin, a nonapeptide an d one of trilysine were studied. The distribution of KER suggests that the conformation of bradykinin is fairly rigid, whereas that of trily sine is flexible. The observed KER values clearly indicate far smaller intercharge distances than those corresponding to extended geometries . This is clear experimental evidence that medium-sized doubly charged peptides have a folded and not an extended geometry in the gas phase. (C) 1997 by John Wiley & Sons, Ltd.