B-side electron transfer promoted by absorbance of multiple photons in Rhodobacter sphaeroides R-26 reaction centers

Journal Article · Thu Jun 03 04:00:00 EDT 1999 · Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical

DOI:https://doi.org/10.1021/jp990303j· OSTI ID:355530

Lin, S; Jackson, J A; Taguchi, A K.W.; Woodbury, N W ^[1]

---

1. Arizona State Univ., Tempe, AZ (United States)

Femtosecond transient absorbance spectra of quinone-depleted Rhodobacter sphaeroides R-26 reaction centers in the Q{sub X} transition region have been measured at 15 K under various excitation conditions. This study focuses on the excitation wavelength dependence and excitation intensity dependence of the formation of charge-separated states on the A- and B-side of the reaction center, judging from the bleaching of the 533 nm (B-side) and 544 nm (A-side) ground-state transitions of the reaction center bacteriopheophytins (H{sub A} and H{sub B}). Upon low-intensity selective excitation directly into the bacteriopheophytin Q{sub Y} transitions (near 760 nm), bleaching of both ground-state bacteriopheophytin Q{sub X} transitions appeared immediately, showing that initially either the A- or B-side bacteriopheophytin could be excited. However, both excited states ultimately resulted in P{sup +}H{sub A}{sup {minus}} formation under these conditions. Low-intensity excitation at any of the various wavelengths showed no difference in the kinetics of the A-side charge separation forming P{sup +}H{sub A}{sup {minus}} and no substantial formation of the B-side charge-separated state, P{sup +}H{sub B}{sup {minus}}. In contrast, high-intensity 595 nm excitation resulted in substantial long-lived bleaching of the B-side bacteriopheophytin ground-state transition at 533 nm. This 533 nm bleaching was formed with essentially the same time constant as the bleaching at 544 nm due to A-side charge separation. Both bleaching bands persisted at the longest times measured in quinone-removed reaction centers. The long-lived bleaching at 533 nm using high-intensity excitation most likely represents the formation of P{sup +}H{sub B}{sup {minus}} with a relative yield of nearly 40%. One possible mechanism for B-side electron transfer is that two-photon excitation of the reaction center resulting in the state P{sup *}B{sub B}{sup *} makes P{sup +}B{sub B}{sup {minus}} thermodynamically accessible.

• Sponsoring Organization: National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
• DOE Contract Number: FG05-88ER75443; FG05-87ER75361
• OSTI ID: 355530
• Journal Information: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical Journal Issue: 22 Vol. 103; ISSN 1089-5647; ISSN JPCBFK
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
ELECTRON TRANSFER
PHOTOSYNTHESIS
PHOTOSYNTHETIC BACTERIA
PHOTOSYNTHETIC REACTION CENTERS