Publication: Dissociations of Copper(II)-Containing Complexes of Aromatic Amino Acids: Radical Cations of Tryptophan, Tyrosine, and Phenylalanine
All || By Area || By Year| Title | Dissociations of Copper(II)-Containing Complexes of Aromatic Amino Acids: Radical Cations of Tryptophan, Tyrosine, and Phenylalanine | Authors/Editors* | Chi-Kit Siu, Yuyong Ke, Yuzhu Guo, Alan C. Hopkinson, and K. W. Michael Siu |
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| Where published* | Physical Chemistry Chemical Physics |
| How published* | Journal |
| Year* | 2008 |
| Volume | 10 |
| Number | |
| Pages | 5908-5918 |
| Publisher | |
| Keywords | |
| Link | |
| Abstract |
The dissociations of two types of copper(II)-containing complexes of tryptophan (Trp), tyrosine (Tyr), or phenylalanine (Phe) are described. The first type is the bis-amino acid complex, [CuII(M)2]dot2+, where M = Trp, Tyr, or Phe; the second [CuII(4Cl-tpy)(M)]dot2+, where 4Cl-tpy is the tridendate ligand 4Î-chloro-2,2Î:6Î,2ÎÎ-terpyridine. Dissociations of the Cu(II) bis-amino acid complexes produce abundant radical cation of the amino acid, Mdot+, and/or its secondary products. By contrast, dissociations of the 4Cl-tpy-bearing ternary complexes give abundant Mdot+ only for Trp. Density functional theory (DFT) calculations show that for Tyr and Phe, amino-acid displacement reactions by H2O and CH3OH (giving [CuII(4Cl-tpy)(H2O)]dot2+ and [CuII(4Cl-tpy)(CH3OH)]dot2+) are energetically more favorable than dissociative electron transfer (giving Mdot+ and [CuI(4Cl-tpy)]+). The fragmentation pathway common to all these [CuII(4Cl-tpy)(M)]dot2+ ions is the loss of NH3. DFT calculations show that the loss of NH3 proceeds via a âphenonium-typeâ intermediate. Dissociative electron transfer in [CuII(4Cl-tpy)(M â NH3)]dot2+ results in [M â NH3]dot+. The [Phe â NH3]dot+ ion dissociates facilely by eliminating CO2 and giving a metastable phenonium-type ion that rearranges readily into the styrene radical cation. |
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