Photoinduced hole hopping through tryptophans in proteins
Hole hopping through tryptophan/tyrosine chains enables rapid unidirectional charge transport over long distances. We have elucidated structural and dynamical factors controlling hopping speed and efficiency in two modified azurin constructs that include a rhenium(I) sensitizer, Re(His)(CO) (dmp) ,...
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| Published in: | Proceedings of the National Academy of Sciences - PNAS Vol. 118; no. 11 |
|---|---|
| Main Authors: | , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
United States
16.03.2021
|
| Subjects: | |
| ISSN: | 1091-6490, 1091-6490 |
| Online Access: | Get more information |
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| Summary: | Hole hopping through tryptophan/tyrosine chains enables rapid unidirectional charge transport over long distances. We have elucidated structural and dynamical factors controlling hopping speed and efficiency in two modified azurin constructs that include a rhenium(I) sensitizer, Re(His)(CO)
(dmp)
, and one or two tryptophans (W
, W
). Experimental kinetics investigations showed that the two closely spaced (3 to 4 Å) intervening tryptophans dramatically accelerated long-range electron transfer (ET) from Cu
to the photoexcited sensitizer. In our theoretical work, we found that time-dependent density-functional theory (TDDFT) quantum mechanics/molecular mechanics/molecular dynamics (QM/MM/MD) trajectories of low-lying triplet excited states of Re
(His)(CO)
(dmp)
-W
(-W
) exhibited crossings between sensitizer-localized (*Re) and charge-separated [Re
(His)(CO)
(dmp
)/(W
or W
)] (CS1 or CS2) states. Our analysis revealed that the distances, angles, and mutual orientations of ET-active cofactors fluctuate in a relatively narrow range in which the cofactors are strongly coupled, enabling adiabatic ET. Water-dominated electrostatic field fluctuations bring *Re and CS1 states to a crossing where *Re(CO)
(dmp)
←W
ET occurs, and CS1 becomes the lowest triplet state. ET is promoted by solvation dynamics around *Re(CO)
(dmp)
(W
); and CS1 is stabilized by Re(dmp
)/W
electron/hole interaction and enhanced W
solvation. The second hop, W
←W
, is facilitated by water fluctuations near the W
/W
unit, taking place when the electrostatic potential at W
drops well below that at W
Insufficient solvation and reorganization around W
make W
←W
ET endergonic, shifting the equilibrium toward W
and decreasing the charge-separation yield. We suggest that multiscale TDDFT/MM/MD is a suitable technique to model the simultaneous evolution of photogenerated excited-state manifolds. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 1091-6490 1091-6490 |
| DOI: | 10.1073/pnas.2024627118 |