ISSN:
0894-3230
Keywords:
photoinduced intramolecular electron transfer
;
dichromophore-appended α-helical peptides
;
preferred conformations
;
Chemistry
;
Theoretical, Physical and Computational Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The α-helical structure of donor-acceptor-substituted peptides 1 and 2 was established by circular dichroism and NMR spectroscopy. The photoproduction of a spatially separated radical ion pair was detected by transient absorption spectroscopy. The expected influence of the electric field along the helical pitch direction was established by monitoring S1 lifetimes. The complex kinetics of the observed decays indicate that even these rigid peptides exist in a distribution of conformations. This assertion is further supported by single-photon counting measurements, NMR spectroscopy (COSY, NOESY and variable-temperature 1H NMR) and extended MMS2 force-field model calculations. An estimate for the rotational thresholds of the appended chromophores was obtained, and the character of the electronic interaction between the appended chromophores was examined by semiempirical single-point calculations. Such calculations show the possible importance of through-bond interactions between the chromophores. The backbone conformational regularities of 1 and 2 are sufficient to establish the previously reported influence of a electrostatic field on photoinduced electron transfer rates, but side-chain conformational mobility of 1 and 2 imposes an inherent limitation on experimental observations. © 1997 John Wiley & Sons, Ltd.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
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