Formation of molecular radical cations of aliphatic tripeptides from their complexes with CuII(12-crown-4).
Molecular radical cations have proven to be difficult to generate from aliphatic peptides under electrospray ionization mass spectrometry (ESI-MS) conditions. For a family of small aliphatic peptides GGX, where X = G, A, P, I, L and V, these cations have been generated by electrospraying a mixture of Cu.2+, 12-crown-4 and GGX in methanol/water. GGX.+ is readily formed from the collision-induced dissociation (CID) of [CuII(12-crown-4)(GGX)].2+. The formation of these aliphatic peptide radical ions from these complexes, in cases where it is not possible from the corresponding complexes involving a series of amine ligands instead of 12-crown-4, is likely due to the second ionization energy of the [CuI(12-crown-4)(GGX)]+ complex being higher than that of the corresponding [CuI(amine)(GGX)]+ complex. Using these 12-crown-4 complexes, GGI can be differentiated from the isomeric GGL by comparing the CID spectra of their [a3 + H].+ ions.
Chu
Ivan K
IK
Department of Chemistry, The University of Hong Kong, SAR China. ivankchu@hku.hk
Siu
S O
SO
Lam
Corey N W
CN
Chan
Jenny C Y
JC
Rodriquez
Christopher F
CF
D002412:Cations; D003300:Copper / Q000737:chemistry*; D008667:Metalloproteins / Q000737:chemistry*; D009842:Oligopeptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
D002412:Cations; D008667:Metalloproteins; D009842:Oligopeptides; D003300:Copper