Comparison of infrared photodissociation in a Fourier transform mass spectrometer with metastable ion decay in a double-focusing mass spectrometer

Near-UV Photodissociation of Tryptic Peptide Cation Radicals. Scope and Effects of Amino Acid Residues and Radical Sites

“…Thus, it is difficult to distinguish from the pulse dependence alone whether the ion undergoes only photodissociation or whether the dissociation is accompanied by the formation of another photoactive isomer. Distinction has been made for [ • AFAR + ] ions using single-pulse action spectroscopy that clearly indicated the presence of two [z 4 + H] +• ion isomers produced by ETD [27]. It should be noted that the data reported in Ref 27 were obtained at a lower laser power (0.8-2.1 mJ/pulse) than the present 355 nm data, which accounts for the different α eff .…”

“…Likewise, the internal Lys residue did not undergo extensive radical side-chain dissociations [37], the main side-chain loss of C 2 H 8 N 3 occurring from the C-terminal Arg residue. An interesting comparison can be made for [z 4 + H] +• ions containing residues that are known to favor cascade N-C oe bond cleavages leading to [z 2 + H] +• ions (Asp, Asn, Phe, His, and Trp) [30,31]. Among these, Asp, Asn, and His gave abundant [z 2 + H] +• photofragments that competed with the formation of the [y n ] + ions.…”

“…The laser beam at 355 nm was produced from an EKSPLA NL 301 HT Nd-YAG laser (Altos Photonics, Bozeman, MT, USA) providing the third harmonics line at 355 nm, as described previously [19]. The photodissociation yields were measured as a function of the laser power for the [z 4 + H] +• (m/z 487) ion from AAWAR and showed approximately linear increase in the range of 3.3-9 mJ/pulse, indicating single photon absorption (Supplementary Figure S1). The computational methods used are described in the Supplement.…”

“…P hotodissociation is one of the tools for accomplishing dissociations of gas-phase ions [1][2][3][4] that more recently has been widely applied to biomolecular ions [5][6][7][8][9][10][11][12][13]. Photodissociation in the far UV (157 nm [14,15]) and middle UV (193 nm [16]) regions of the spectrum has been used to dissociate peptide ions.…”

“…We selected to study UVPD of the following types of z-ions. The first type is [ • AXAB + ], or [z 4 + H] +• , ions (for nomenclature see Ref [32]), that have the C α -radical defect at the deaminated N-terminal Ala residue and contain a common chromophore for all combinations of X and B. Second, ETD fragment ions by loss of ammonia from peptides of the Lys-C-terminated (AAXAK) series were studied.…”