6 research outputs found
A DNA-Directed Light-Harvesting/Reaction Center System
A structurally
and compositionally well-defined and spectrally
tunable artificial light-harvesting system has been constructed in
which multiple organic dyes attached to a three-arm-DNA nanostructure
serve as an antenna conjugated to a photosynthetic reaction center
isolated from Rhodobacter sphaeroides 2.4.1. The light energy absorbed by the dye molecules is transferred
to the reaction center, where charge separation takes place. The average
number of DNA three-arm junctions per reaction center was tuned from
0.75 to 2.35. This DNA-templated multichromophore system serves as
a modular light-harvesting antenna that is capable of being optimized
for its spectral properties, energy transfer efficiency, and photostability,
allowing one to adjust both the size and spectrum of the resulting
structures. This may serve as a useful test bed for developing nanostructured
photonic systems
Reengineering the Optical Absorption Cross-Section of Photosynthetic Reaction Centers
Engineered
cysteine residues near the primary electron donor (P)
of the reaction center from the purple photosynthetic bacterium Rhodobacter sphaeroides were covalently conjugated
to each of several dye molecules in order to explore the geometric
design and spectral requirements for energy transfer between an artificial
antenna system and the reaction center. An average of 2.5 fluorescent
dye molecules were attached at specific locations near P. The enhanced
absorbance cross-section afforded by conjugation of Alexa Fluor 660
dyes resulted in a 2.2-fold increase in the formation of reaction
center charge-separated state upon intensity-limited excitation at
650 nm. The effective increase in absorbance cross-section resulting
from the conjugation of two other dyes, Alexa Fluor 647 and Alexa
Fluor 750, was also investigated. The key parameters that dictate
the efficiency of dye-to-reaction center energy transfer and subsequent
charge separation were examined using both steady-state and time-resolved
fluorescence spectroscopy as well as transient absorbance spectroscopy
techniques. An understanding of these parameters is an important first
step toward developing more complex model light-harvesting systems
integrated with reaction centers