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Conformational Analysis of the Electron-Transfer Kinetics across Oligoproline Peptides Using N,N-Dimethyl-1,4-benzenediamine Donors and Pyrene-1-sulfonyl Acceptors†
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and Stephan S. Isied*§
Section:Abstract
Photoinduced intramolecular charge separation across proline-bridged donor−acceptor complexes of the type Pyr-(Pro)n−DMPD (where Pyr = pyrene-1-sulfonyl and DMPD = N,N-dimethyl-1,4-phenylenediamine) was studied. The steady-state emission spectrum for n = 0, 1, 2, 3 showed an increase in emission intensity with the number of proline residues. Time-dependent emission measured by streak camera showed increasing emission signal amplitude with increasing n, along with a decrease in decay rate. In all these studies, Pyr-Pro was used as a control complex for the decay of the excited pyrene acceptor moiety without the donor DMPD. Detailed photon counting experiments carried out in DMF/water, DMF, and toluene showed single-exponential kinetics for n = 0, 1 and multiexponential kinetics for n = 2, 3. Rate constants observed in DMF are for n = 0, k = 
5 × 1010 s-1; n = 1, k = 9.70 × 108 s-1; n = 2, k = 35.9 × 108 s-1 (70%) and 5.58 × 108 s-1 (30%); and n = 3, k = 16.6 × 108 s-1 (55%) and 3.87 × 108 s-1 (45%). These results show that a significant percentage of the n = 2 and n = 3 molecules undergo faster electron transfer than for the n = 1 case. Conformational analysis for Pyr-(Pro)n−DMPD molecules in water showed that whereas only one conformation is possible for n = 1, eight are possible for n = 2, and 32 are possible for n = 3. Calculation of the free energy and electronic coupling for these conformers in water showed that only a few of these conformations have the appropriate energy and electronic coupling to be observed in the experimental time window from 20 ps to 20 ns. Assignment of the conformers undergoing electron transfer in Pyr-(Pro)n−DMPD for n = 2 and 3 was based on the values for the n = 1 case, for which the measured rate constant is 109 s-1 and the calculated electronic coupling matrix element Hda is 297 cm-1. The similarity in ground state energy between the cis and trans conformers for n = 2 and 3, their use in aqueous−organic and organic solvents, and the nature of the Pyr and DMPD acceptor and donor groups could be contributing causes for the multiexponential kinetics, which was not observed for the metal ion derivatives of proline peptides studied earlier in aqueous solution.
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This article has been cited by 4 ACS Journal articles (4 most recent appear below).
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Joseph B. Issa, Karsten Krogh-Jespersen, and Stephan S. IsiedThe Journal of Physical Chemistry C2010 114 (48), 20809-20812Electronic coupling across peptide bonds has been determined throughout the peptide bond conformational space. Using the side chains of tyrosine (Tyr) and tryptophan (Trp) as donors (D) and acceptors (A), respectively, a plot of the electronic coupling ...
Ultrafast Electron Transfer Dynamics in Micellar Media Using Surfactant as the Intrinsic Electron Acceptor
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Eun-Kyung Park, Bongjeong Park, Jun-Ho Choi, Kihang Choi and Minhaeng ChoThe Journal of Physical Chemistry B2009 113 (32), 11301-11305Conformations of proline-substituted chromophores are determined by using circular dichroism (CD) spectroscopy and quantum chemistry calculation method. Coumarin is chosen for the optical chromophore and proline amino acid is attached to its C7 position. ...
Ultrafast Bimolecular Electron Transfer Dynamics in Micellar Media
Manoj Kumbhakar, Prabhat K. Singh, Sukhendu Nath, Achikanath C. Bhasikuttan and Haridas PalThe Journal of Physical Chemistry B2008 112 (21), 6646-6652Ultrafast Bimolecular Electron Transfer Dynamics in Micellar Media
Manoj Kumbhakar, Prabhat K. Singh, Sukhendu Nath, Achikanath C. Bhasikuttan and Haridas PalThe Journal of Physical Chemistry B2008 112 (21), 6646-6652Ultrafast photoinduced bimolecular electron transfer (ET) dynamics between 7-aminocoumarin derivatives and N,N-dimethylaniline (DMAN) has been studied in neutral (TX100), cationic (DTAB) and anionic (SDS) micellar media. A very fast decay time constant (τ...
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- Published In Issue June 21, 2007
- Received February 26, 2007
Revised April 2, 2007
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