Publication: Histidine, Lysine, and Arginine Radical Cations: Isomer Selection via the Choice of Auxiliary Ligand (L) in the Dissociation of [CuII(L)(amino acid)]â¢2+ Complexes
All || By Area || By Year| Title | Histidine, Lysine, and Arginine Radical Cations: Isomer Selection via the Choice of Auxiliary Ligand (L) in the Dissociation of [CuII(L)(amino acid)]â¢2+ Complexes | Authors/Editors* | Yuyong Ke, Junfang Zhao, Udo H. Verkerk, Alan C. Hopkinson, K. W. Michael Siu |
|---|---|
| Where published* | J. Phys. Chem. B |
| How published* | Journal |
| Year* | 2007 |
| Volume | 111 |
| Number | |
| Pages | 14318-14328 |
| Publisher | |
| Keywords | Radical Cations, Collision-Induced Dissociation, Auxiliary Ligand, Ternary Copper(II) Complexes |
| Link | http://dx.doi.org/10.1021/jp0746648 |
| Abstract |
Histidine, lysine and arginine radical cations have been generated through collisioninduced-dissociation (CID) of complexes [Cu (auxiliary ligand) (amino acid)]â¢2+ using tri-, bi-, as well as monodentate auxiliary ligands. Based on the observed CID products, the existence of two isomeric amino-acid populations is postulated. The type 1 radical cations of histidine and lysine, stable on the mass spectrometer timescale, were found to lose water, followed by the loss of carbon monoxide under more energetic CID conditions. The arginine type 1 radical cation behaved differently, losing dehydroalanine. The type 2 radical cations were metastable and easily fragmented by the loss of carbon dioxide, effectively preventing direct observation. Radical cations of type 1 are proposed to result from neutral (canonical) amino-acid coordination, whereas type 2 radical cations are from zwitterionic amino-acid coordination to copper in the complex. The ratio of type 1/type 2 ions was found to be dependent on the auxiliary ligand, providing a method of controlling which radical cation would be formed primarily. Density Functional calculations at B3LYP/6-311++G(d,p) have been used to determine the relative energies of five [His]â¢+ isomers. Barriers against interconversion between the isomers and against fragmentation have been calculated, giving insight as to why type 1 ions are stable, while only fragmentation products of type 2 ions are observable under CID conditions. |
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