Chapter 23
Ultrafast Energy Transfer of Biohybrid
Photosynthetic Antenna Complexes
in Molecular Assembly Systems
Takehisa Dewa, Yusuke Yoneda, Masaharu Kondo, Hiroshi Miyasaka,
and Yutaka Nagasawa
Abstract Photosynthesis in natural systems is one of the typical examples where the
interaction between multiple photons and multiple chromophores leads to the synergetic responses in three-dimensionally arranged molecular aggregates. Accordingly,
the investigation of primary events in the excited state could provide important information on the progress in the artificial photosynergetic systems. Along with this line,
we have prepared biohybrid light-harvesting complexes to study ultrafast dynamics
of excitation energy transfer in the present project. Light-harvesting 2 complex (LH2)
from photosynthetic purple bacteria is a molecular assembly, in which multiple photosynthetic chromophores are well organized. To expand high-harvesting activity of
LH2, we attached a fluorophore, Alexa647, to lysine residues on the LH2 polypeptide so as to cover broad solar spectrum. Ultrafast energy transfer from Alexa 647 to
the intrinsic chromophores B800 and B850 in LH2 was observed using femtosecond
transient absorption spectroscopy. Detailed analysis revealed two possible energy
transfer pathways. In addition, we made a LH2 mutant bearing reactive Cys residue
on the N-terminal region of LH2β polypeptide. The engineered LH2 allows us to
provide the defined position of Alexa647. Together with the system in which LH2
was dissolved in micellar solution, a lipid bilayer system in which the bioengineered
LH2 was incorporated was applied to control the location of the external fluorophore.
Keywords Light-harvesting complex 2 (LH2) · Photosynthesis · Biohybrid ·
Ultrafast energy transfer · Fluorophore
T. Dewa (B) · M. Kondo
Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya
Institute of Technology, Gokiso-Cho, Showa-Ku, Nagoya 466-8555, Japan
e-mail: takedewa@nitech.ac.jp
Y. Yoneda · H. Miyasaka
Graduate School of Engineering Science, Division of Frontier Materials Science, Osaka
University, Toyonaka, Osaka 530-8531, Japan
Y. Nagasawa
Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1
Noji-Higashi, Kusatsu, Shiga 525-8577, Japan
© Springer Nature Singapore Pte Ltd. 2020
H. Miyasaka et al. (eds.), Photosynergetic Responses in Molecules
and Molecular Aggregates, https://doi.org/10.1007/978-981-15-5451-3_23
389
Ultrafast Energy Transfer of Biohybrid
Photosynthetic Antenna Complexes
in Molecular Assembly Systems
Takehisa Dewa, Yusuke Yoneda, Masaharu Kondo, Hiroshi Miyasaka,
and Yutaka Nagasawa
Abstract Photosynthesis in natural systems is one of the typical examples where the
interaction between multiple photons and multiple chromophores leads to the synergetic responses in three-dimensionally arranged molecular aggregates. Accordingly,
the investigation of primary events in the excited state could provide important information on the progress in the artificial photosynergetic systems. Along with this line,
we have prepared biohybrid light-harvesting complexes to study ultrafast dynamics
of excitation energy transfer in the present project. Light-harvesting 2 complex (LH2)
from photosynthetic purple bacteria is a molecular assembly, in which multiple photosynthetic chromophores are well organized. To expand high-harvesting activity of
LH2, we attached a fluorophore, Alexa647, to lysine residues on the LH2 polypeptide so as to cover broad solar spectrum. Ultrafast energy transfer from Alexa 647 to
the intrinsic chromophores B800 and B850 in LH2 was observed using femtosecond
transient absorption spectroscopy. Detailed analysis revealed two possible energy
transfer pathways. In addition, we made a LH2 mutant bearing reactive Cys residue
on the N-terminal region of LH2β polypeptide. The engineered LH2 allows us to
provide the defined position of Alexa647. Together with the system in which LH2
was dissolved in micellar solution, a lipid bilayer system in which the bioengineered
LH2 was incorporated was applied to control the location of the external fluorophore.
Keywords Light-harvesting complex 2 (LH2) · Photosynthesis · Biohybrid ·
Ultrafast energy transfer · Fluorophore
T. Dewa (B) · M. Kondo
Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya
Institute of Technology, Gokiso-Cho, Showa-Ku, Nagoya 466-8555, Japan
e-mail: takedewa@nitech.ac.jp
Y. Yoneda · H. Miyasaka
Graduate School of Engineering Science, Division of Frontier Materials Science, Osaka
University, Toyonaka, Osaka 530-8531, Japan
Y. Nagasawa
Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1
Noji-Higashi, Kusatsu, Shiga 525-8577, Japan
© Springer Nature Singapore Pte Ltd. 2020
H. Miyasaka et al. (eds.), Photosynergetic Responses in Molecules
and Molecular Aggregates, https://doi.org/10.1007/978-981-15-5451-3_23
389