Conformational analysis of the electron-transfer kinetics across oligoproline peptides using N,N-dimethyl-1,4-benzenediamine donors and pyrene-1-sulfonyl acceptors

Joseph B. Issa, Abdu S. Salameh, Ed Castner, James F. Wishart, Stephan S. Isied

Research output: Contribution to journalArticle

11 Citations (Scopus)

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 H da 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.

Original languageEnglish
Pages (from-to)6878-6886
Number of pages9
JournalJournal of Physical Chemistry B
Volume111
Issue number24
DOIs
Publication statusPublished - Jun 21 2007

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Pyrene
pyrenes
Proline
Peptides
peptides
electron transfer
Kinetics
Conformations
Electrons
Water
Rate constants
kinetics
electronics
water
Streak cameras
Molecules
streak cameras
Toluene
polarization (charge separation)
Organic solvents

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Conformational analysis of the electron-transfer kinetics across oligoproline peptides using N,N-dimethyl-1,4-benzenediamine donors and pyrene-1-sulfonyl acceptors. / Issa, Joseph B.; Salameh, Abdu S.; Castner, Ed; Wishart, James F.; Isied, Stephan S.

In: Journal of Physical Chemistry B, Vol. 111, No. 24, 21.06.2007, p. 6878-6886.

Research output: Contribution to journalArticle

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title = "Conformational analysis of the electron-transfer kinetics across oligoproline peptides using N,N-dimethyl-1,4-benzenediamine donors and pyrene-1-sulfonyl acceptors",
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 H da 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.",
author = "Issa, {Joseph B.} and Salameh, {Abdu S.} and Ed Castner and Wishart, {James F.} and Isied, {Stephan S.}",
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T1 - Conformational analysis of the electron-transfer kinetics across oligoproline peptides using N,N-dimethyl-1,4-benzenediamine donors and pyrene-1-sulfonyl acceptors

AU - Issa, Joseph B.

AU - Salameh, Abdu S.

AU - Castner, Ed

AU - Wishart, James F.

AU - Isied, Stephan S.

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N2 - 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 H da 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.

AB - 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 H da 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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