Solvent dependence of intramolecular electron transfer in a helical oligoproline assembly.

b2m metal-to-ligand charge-transfer (MLCT) excitation at 457 nm, electron-transfer quenching occurs, ultimately to give a redox-separated (RS) state containing a phenothiazine (PTZ) radical cation at the Pra(Ptzpn) site and an anthraquinone (ANQ) radical anion at the Pra(Anq) site. The redox-separated state was formed with 33-96% efficiency depending on the solvent, and the transient stored energy varied from -1.46 to -1.71 eV at 22 +/- 2 degrees C. The dominant quenching mechanism is PTZ reductive quenching of the initial RuIII(b2m*-) MLCT excited state which is followed by m*- --> ANQ electron transfer to give the RS state. Back electron transfer is highly exergonic and occurs in the inverted region. The rate constant for back electron transfer is solvent dependent and varies from 5.2 x 10(6) to 7.7 x 10(6) s-1 at 22 +/- 2 degrees C. It is concluded that back electron transfer occurs by direct ANQ*- --> PTZ*+ electron transfer. Based on independently evaluated kinetic parameters, the electron-transfer matrix element is HDA approximately 0.13 cm-1. -->
Substance Nomenclature: 0 (Anthraquinones)
0 (Coordination Complexes)
0 (Peptides)
0 (Phenothiazines)
0 (Solvents)
0 (tris(2,2-bipyridine)-ruthenium(II))
25191-13-3 (polyproline)
551W113ZEP (2,2'-Dipyridyl)
GS9EX7QNU6 (phenothiazine)
Entry Date(s): Date Created: 20040422 Date Completed: 20040806 Latest Revision: 20210623
Update Code: 20240829
DOI: 10.1021/ja0304289
PMID: 15099113
Autor: Striplin DR; Department of Chemistry, Davidson College, North Carolina 28036 USA., Reece SY, McCafferty DG, Wall CG, Friesen DA, Erickson BW, Meyer TJ
Jazyk: angličtina
Zdroj: Journal of the American Chemical Society [J Am Chem Soc] 2004 Apr 28; Vol. 126 (16), pp. 5282-91.
DOI: 10.1021/ja0304289
Abstrakt: The helical oligoproline assembly CH3-CO-Pro-Pro-Pro-Pra(Ptzpn)-Pro-Pro-Pra(RuIIb2m2+ -Pro-Pro-Pra(Anq)-Pro-Pro-Pro-NH2, having a spatially ordered array of functional sites protruding from the proline backbone, has been prepared. The 13-residue assembly formed a linear array containing a phenothiazine electron donor, a tris(bipyridine)ruthenium(II) chromophore, and an anthraquinone electron acceptor with the proline II secondary structure as shown by circular dichroism measurements. Following RuII --> b2m metal-to-ligand charge-transfer (MLCT) excitation at 457 nm, electron-transfer quenching occurs, ultimately to give a redox-separated (RS) state containing a phenothiazine (PTZ) radical cation at the Pra(Ptzpn) site and an anthraquinone (ANQ) radical anion at the Pra(Anq) site. The redox-separated state was formed with 33-96% efficiency depending on the solvent, and the transient stored energy varied from -1.46 to -1.71 eV at 22 +/- 2 degrees C. The dominant quenching mechanism is PTZ reductive quenching of the initial RuIII(b2m*-) MLCT excited state which is followed by m*- --> ANQ electron transfer to give the RS state. Back electron transfer is highly exergonic and occurs in the inverted region. The rate constant for back electron transfer is solvent dependent and varies from 5.2 x 10(6) to 7.7 x 10(6) s-1 at 22 +/- 2 degrees C. It is concluded that back electron transfer occurs by direct ANQ*- --> PTZ*+ electron transfer. Based on independently evaluated kinetic parameters, the electron-transfer matrix element is HDA approximately 0.13 cm-1.
Databáze: MEDLINE
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