121445-55-4Relevant articles and documents
Photoinduced Electron Transfer on a Single α-Helical Polypeptide Chain
Sisido, Masahiko,Tanaka, Ryo,Inai, Yoshihito,Imanishi, Yukio
, p. 6790 - 6796 (2007/10/02)
Electron transfer on an α-helical polypeptide carrying the sequence L-p-(dimethylamino)phenylalanine (dmaPhe)-L-alanine-L-1-pyrenylalanine (pyrAla) at the midpoint of an α-helical poly(γ-benzyl L-glutamate) chain was studied.Conformational energy calculation for the side-chain orientations predicted that only one type of orientation is allowed for both the dmaPhe and the pyrAla units.The center-to-center (edge-to-edge) distance between the two chromophores was estimated to be 13.2 (9.4) Angstroem.The fluorescence spectrum showed no exciplex emission in thepolypeptide, in contrast to the strong exciplex observed for a model tripeptide having the same dmaPhe-Ala-pyrAla sequence.The rate of electron transfer was calculated from the decay times of pyrenyl fluorescence of the polypeptide in trimethyl phosphate and in tetrahydrofuran solutions.The ket was on the order of 1E5 (s-1).The activation enthalpy was 1.4 kcal mol-1 in trimethyl phosphate and smaller than 1 kcal mol-1 in less polar solvents near room temperature.It was even smaller at lower temperatures.The activation entropy was less than -25 eu, suggesting a nonadiabatic electron transfer.In contrast to the slow electron transfer in the polypeptide, the rate constant for the model tripeptide was on the order of 1E7-1E8 (s-1) around room temperature, and the activation enthalpy was higher than that in the polypeptide case.
