Peptide Radicals and Cation Radicals in the Gas Phase

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, where X = A, C, D, E, F, G, H, K, L, M, N, P, Y, and W, were generated by electron transfer dissociation of peptide dications and investigated by MS 3 -nearultraviolet photodissociation (UVPD) at 355 nm. Laser-pulse dependence measurements indicated that the ion populations were homogeneous for most X residues except phenylalanine. UVPD resulted in dissociations of backbone CO─NH bonds that were accompanied by hydrogen atom transfer, producing fragment ions of the [y n ] + type. Compared with collision-induced dissociation, UVPD yielded less sidechain dissociations even for residues that are sensitive to radical-induced side-chain bond cleavages. The backbone dissociations are triggered by transitions to second (B) excited electronic states in the peptide ion R-CH • -CONH-chromophores that are resonant with the 355-nm photon energy. Electron promotion increases the polarity of the B excited states, R-CH + -C • (O -)NH-, and steers the reaction to proceed by transfer of protons from proximate acidic C α and amide nitrogen positions.

Section: Introductionmentioning

confidence: 99%

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

Nguyen

Tureček

2017

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“…W hereas isolated peptide molecules and ions are inherently stable species with closed-electronic shells, perturbation of their electronic structure results in novel and often unexpected chemistry [1]. There are now several ways of generating peptide radicals and cation radicals in the gas phase to be investigated by mass spectrometry.…”

Section: Introductionmentioning

confidence: 99%

“…Thermal [10] or light-induced [11] homolytic bond dissociations in suitably derivatized peptide ions have also been developed into methods of peptide cation radical generation. All these techniques produce peptide cation radicals that are stoichiometrically equivalent to neutral peptide molecules and because they do not contain additional hydrogens from protonation, they are called Bhydrogen deficient [ 1]. Of note is that the structures of hydrogen-deficient peptide cation radicals, wherever the charge and radical sites are known, depend on the particular activation method.…”

Section: Introductionmentioning

confidence: 99%

Ground and Excited-Electronic-State Dissociations of Hydrogen-Rich and Hydrogen-Deficient Tyrosine Peptide Cation Radicals

Viglino

Lai

et al. 2016

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Abstract. We report a comprehensive study of collision-induced dissociation (CID) and near-UV photodissociation (UVPD) of a series of tyrosine-containing peptide cation radicals of the hydrogen-rich and hydrogen-deficient types. Stable, long-lived, hydrogen-rich peptide cation radicals, such as [AAAYR + 2H] +• and several of its sequence and homology variants, were generated by electron transfer dissociation (ETD) of peptide-crown-ether complexes, and their CID-MS 3 dissociations were found to be dramatically different from those upon ETD of the respective peptide dications. All of the hydrogen-rich peptide cation radicals contained major (77%-94%) fractions of species having radical chromophores created by ETD that underwent photodissociation at 355 nm. Analysis of the CID and UVPD spectra pointed to arginine guanidinium radicals as the major components of the hydrogen-rich peptide cation radical population. Hydrogen-deficient peptide cation radicals were generated by intramolecular electron transfer in Cu II (2,2′:6′,2″-terpyridine) complexes and shown to contain chromophores absorbing at 355 nm and undergoing photodissociation. The CID and UVPD spectra showed major differences in fragmentation for [AAAYR] +• that diminished as the Tyr residue was moved along the peptide chain. UVPD was found to be superior to CID in localizing C α -radical positions in peptide cation radical intermediates.

“…ECD/ETD is initiated by electron attachment/transfer to multiply-protonated molecules, which induces cleavage at N-C α bonds in the peptide backbone. Several ECD/ETD mechanisms have been investigated in order to understand this phenomenon [6][7][8][9][10][11]. In one such mechanism, the so-called Cornell model, the recombination of an electron and an excess proton in a multiply protonated molecule, followed by the transfer of the resulting hydrogen atom to a carbonyl group in the peptide backbone, eventually forms a c'/z • fragment pair [6].…”

Section: Introductionmentioning

confidence: 99%

Difference of Electron Capture and Transfer Dissociation Mass Spectrometry on Ni²⁺-, Cu²⁺-, and Zn²⁺-Polyhistidine Complexes in the Absence of Remote Protons

Asakawa

Pauw

2016

Abstract. Electron capture dissociation (ECD) and electron transfer dissociation (ETD) in metal-peptide complexes are dependent on the metal cation in the complex. The divalent transition metals Ni 2+ , Cu 2+ , and Zn 2+ were used as charge carriers to produce metal-polyhistidine complexes in the absence of remote protons, since these metal cations strongly bind to neutral histidine residues in peptides. In the case of the ECD and ETD of Cu 2+ -polyhistidine complexes, the metal cation in the complex was reduced and the recombination energy was redistributed throughout the peptide to lead a zwitterionic peptide form having a protonated histidine residue and a deprotonated amide nitrogen. The zwitterion then underwent peptide bond cleavage, producing a and b fragment ions. In contrast, ECD and ETD induced different fragmentation processes in Zn 2+ -polyhistidine complexes. Although the N-C α bond in the Zn 2+ -polyhistidine complex was cleaved by ETD, ECD of Zn 2+ -polyhistidine induced peptide bond cleavage accompanied with hydrogen atom release. The different fragmentation modes by ECD and ETD originated from the different electronic states of the charge-reduced complexes resulting from these processes. The details of the fragmentation processes were investigated by density functional theory.