Rearrangement chemistry of a ions probed by IR spectroscopy

Proton Mobility in b2 Ion Formation and Fragmentation Reactions of Histidine-Containing Peptides

“…The fragmentation chemistry of a 2 ions derived from protonated PheHis-OMe and HisPhe-NH 2 , and protonated cyclo-(HisPhe), is a lot more similar than the b 2 ion case. Nevertheless differences in the structures or, more likely, the distribution of structures generated from the preceding collisional activation are apparent at lower collisional energies, consistent with the premise that how the ions are made can have a noticeable effect on the product ion population distributions [59][60][61][62][63][64].…”

Fragmentation reactions of an (n=4–8) ions containing only alanine residues

“…This probably is due to the much shorter time frame of the present experiments. There is increasing evidence [22,26,[34][35][36][37] that the time frame of observation can be an important parameter in determining the structure or mixture of structures observed.…”

“…loss of the Gly residue from the a 4 * ion of nominal sequence YGGF. Since this early work there have been a number of studies [19,[23][24][25][26] of a variety of a 4 ions using primarily IRMPD and computational methods. These studies have shown that a 4 ions largely have undergone rearrangement as shown in Scheme 1 with the major species observed being the amide species M. Following proton transfer this species can readily lose NH 3 to form the a 4 * ion with an oxazolone at the C-terminus.…”

Improved Infrared Spectra Prediction by DFT from a New Experimental Database

“…Agreement between experimental IRMPD and calculated spectra is generally satisfying, in particular for band positions, but some small differences are often observed. Mismatches between the calculated and experimental spectra can occur from isomerization of the studied molecule if this is rapid on the timescale of the multiphoton absorption process, as has recently been observed for a n ions . If IR spectra are calculated by DFT methods that use harmonic approximations, discrepancies can arise as a result of anharmonic and finite temperature effects .…”