In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 118, No. 11 ( 2021-03-16)
Abstract:
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) 3 (dmp) + , and one or two tryptophans (W 1 , W 2 ). Experimental kinetics investigations showed that the two closely spaced (3 to 4 Å) intervening tryptophans dramatically accelerated long-range electron transfer (ET) from Cu I 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 I (His)(CO) 3 (dmp) + –W 1 (–W 2 ) exhibited crossings between sensitizer-localized (*Re) and charge-separated [Re I (His)(CO) 3 (dmp •– )/(W 1 •+ or W 2 •+ )] (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) 3 (dmp) + ←W 1 ET occurs, and CS1 becomes the lowest triplet state. ET is promoted by solvation dynamics around *Re(CO) 3 (dmp) + (W 1 ); and CS1 is stabilized by Re(dmp •– )/W 1 •+ electron/hole interaction and enhanced W 1 •+ solvation. The second hop, W 1 •+ ←W 2 , is facilitated by water fluctuations near the W 1 /W 2 unit, taking place when the electrostatic potential at W 2 drops well below that at W 1 •+ . Insufficient solvation and reorganization around W 2 make W 1 •+ ←W 2 ET endergonic, shifting the equilibrium toward W 1 •+ 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.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.2024627118
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2021
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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