Rearrangements in Model Peptide‐Type Radicals <i>via</i> Intramolecular Hydrogen‐Atom Transfer

Moran, Damian; Jacob, Rebecca; Wood, Geoffrey P. F.; Coote, Michelle L.; Davies, Michael J.; O’Hair, Richard A. J.; Easton, Christopher J.; Radom, Leo

doi:10.1002/hlca.200690210

Cited by 40 publications

(36 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is consistent with the high radical mobility indicated by theoretical and experimental observations [26,46]. As shown in Scheme 2, after the radical moves to the side-chain ␤-carbon via hydrogen abstraction, it facilitates the cleavage of backbone C ␣ -C(O) bonds, forming an even-electron a-type ion after loss of an odd-electron carbonyl radical.…”

Section: Collisional Dissociation Of Radical Ionssupporting

confidence: 87%

Radical-driven dissociation of odd-electron peptide radical ions produced in 157 nm photodissociation

Zhang

Reilly

2009

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

Odd-electron a ϩ 1 radical ions generated in the 157 nm photodissociation of peptide ions were investigated in an ion trap mass spectrometer. To localize the radical, peptide backbone amide hydrogens were replaced with deuterium. When the resulting radical ions underwent hydrogen elimination, no H/D scrambling was obvious, suggesting that without collisional activation, the radical resides on the terminal ␣-carbon. Upon collisional excitation, oddelectron radical ions dissociate through two favored pathways: the production of a-type ions at aromatic amino acids via homolytic cleavage of backbone C ␣ -C(O) bonds and side-chain losses at nonaromatic amino acids. When aromatic residues are not present, nonaromatic residues can also lead to a-type ions. In addition to a-type ions, serine and threonine yield c n-1 and a n-1 ϩ 1 ions where n denotes the position of the serine or threonine. All of these fragments appear to be directed by the radical and they strongly depend on the amino acid side-chain structure. In addition, thermal fragments are also occasionally observed following cleavage of labile Xxx-Pro bonds and their formation appears to be kinetically competitive with radical migration. (J Am Soc Mass

show abstract

Section: Collisional Dissociation Of Radical Ionssupporting

confidence: 87%

Radical-driven dissociation of odd-electron peptide radical ions produced in 157 nm photodissociation

Zhang

Reilly

2009

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

show abstract

“…The Gly-Gly dipeptide radical has been recently studied as a benchmark for hydrogen transfer reactions in peptides. 38 In the current study, the ⌬E, ⌬G 298 , and forward and reverse ⌬G ‡ are reported. Moran et al found the ⌬E and barriers at the G3͑MP2͒-RAD level of theory to be −5.5, 18.4, and 23.9 kcal/ mol, respectively.…”

Section: Quantum Mechanical Peptide Radical Rearrangementmentioning

confidence: 99%

Vibrational subsystem analysis: A method for probing free energies and correlations in the harmonic limit

Woodcock

Zheng

Ghysels

et al. 2008

The Journal of Chemical Physics

View full text Add to dashboard Cite

A new vibrational subsystem analysis ͑VSA͒ method is presented for coupling global motion to a local subsystem while including the inertial effects of the environment. The premise of the VSA method is a partitioning of a system into a smaller region of interest and a usually larger part referred to as environment. This method allows the investigation of local-global coupling, a more accurate estimation of vibrational free energy contribution for parts of a large system, and the elimination of the "tip effect" in elastic network model calculations. Additionally, the VSA method can be used as a probe of specific degrees of freedom that may contribute to free energy differences. The VSA approach can be employed in many ways, but it will likely be most useful for estimating activation free energies in QM/MM reaction path calculations. Four examples are presented to demonstrate the utility of this method.

show abstract

“…It is usually initiated by hydrogen abstraction or proton transfer from the initial radical site generated in the ion formation step [35,36]. Reaction barriers for H atom transfer in several small model radicals have been reported by Moran et al [37]. They demonstrated that in the absence of side chains 1,4 [C↔C] hydrogen transfer along the peptide backbone is associated with substantial barriers of ca.…”

mentioning

confidence: 99%

Fragmentation ofα-radical cations of arginine-containing peptides

Laskin

Yang

et al. 2010

J. Am. Soc. Mass Spectrom.

103

View full text Add to dashboard Cite

Fragmentation pathways of peptide radical cations, M ϩ· , with well-defined initial location of the radical site were explored using collision-induced dissociation (CID) experiments. Peptide radical cations were produced by gas-phase fragmentation of Co III (salen)-peptide complexes [salen ϭ N,N'-ethylenebis (salicylideneiminato)]. Subsequent hydrogen abstraction from the ␤-carbon of the side-chain followed by C ␣ -C ␤ bond cleavage results in the loss of a neutral side chain and formation of an ␣-radical cation with the radical site localized on the ␣-carbon of the backbone. Similar CID spectra dominated by radical-driven dissociation products were obtained for a number of arginine-containing ␣-radicals, suggesting that for these systems radical migration precedes fragmentation. In contrast, proton-driven fragmentation dominates CID spectra of ␣-radicals produced via the loss of the arginine side chain. Radicaldriven fragmentation of large M ϩ· peptide radical cations is dominated by side-chain losses, formation of even-electron a-ions and odd-electron x-ions resulting from C ␣ -C bond cleavages, formation of odd-electron z-ions, and loss of the N-terminal residue. In contrast, charge-driven fragmentation produces even-electron y-ions and odd-electron b-ions. (n-1)ϩ· ions produced by capture of low-energy electrons by multiply protonated molecules or by electron-transfer processes [1][2][3][4][5]9], hydrogen deficient radical anions [M Ϫ nH] (n-1)-· generated by electron detachment and photodetachment from multiply deprotonated molecules [10,11], peptides cationized on lithium [12], or transition metals [13][14][15][16], and M ϩ· peptide radical cations. [In this study, we used standard notation for molecular radical cations, M ϩ· , which implies that the molecule has a charge and one unpaired electron, and specified the initial location of the radical site, when possible]. M ϩ· ions can be produced via gas-phase fragmentation of specially designed precursors. For example, radical cations of peptides without additional H atoms are produced by collision-induced dissociation (CID) of ternary metal-ligand-peptide complexes [17][18][19][20][21][22][23][24][25]. In addition, M ϩ· peptide ions have been generated through free radical-initiated reactions [26,27], CID of nitrosopeptides [28], and peptides containing labile serine and homoserine nitrate esters [29], photolysis of peptides containing iodinated tyrosine residues [30,31], and photodissociation of protonated peptides [32,33].Fragmentation of small peptide radical cations has been recently reviewed [7,34]. It is usually initiated by hydrogen abstraction or proton transfer from the initial radical site generated in the ion formation step [35,36]. Reaction barriers for H atom transfer in several small model radicals have been reported by Moran et al. [37]. They demonstrated that in the absence of side chains 1,4 [C↔C] hydrogen transfer along the peptide backbone is associated with substantial barriers of ca. 100 kJ/mol, while 1,5 and 1,6 [C↔N] hydrogen shift...

show abstract

Rearrangements in Model Peptide‐Type Radicals via Intramolecular Hydrogen‐Atom Transfer

Cited by 40 publications

References 38 publications

Radical-driven dissociation of odd-electron peptide radical ions produced in 157 nm photodissociation

Radical-driven dissociation of odd-electron peptide radical ions produced in 157 nm photodissociation

Vibrational subsystem analysis: A method for probing free energies and correlations in the harmonic limit

Fragmentation ofα-radical cations of arginine-containing peptides

Contact Info

Product

Resources

About