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T. Dewa et al.
(Fig. 23.2). Maleimide-C2-Alexa647 was directly attached to the Cys residue. The
numbers of Alexa647 attached to LH2 were ~9 and ~5 for the former and the latter
biohybrid LH2s, respectively. Hereafter, we call the two type of LH2 biohybrids as
LH2-A647 and LH2-NC-A647.
23.3 Energy Transfer Dynamics of LH2-A647
in the Micellar Solution System [9]
Figure 23.4a shows absorption spectrum of LH2-A647. The spectral profile can be
reproduced as a sum of A647 and the intrinsic chromophores (BChl and Car). The
absorption bands and circular dichroism (CD) signals of the intrinsic chromophores
in LH2 were well preserved, indicating that modification with A647 does not perturb
the environment of the chromophores. In addition, CD and linear dichroism spectra
suggested no excitonic coupling and particular orientation of A647 attached to LH2.
Upon excitation at 650 nm, significant quenching of A647 and prominent emission
from B850 were observed for LH2-A647. This result clearly indicates energy transfer
from A647 to B800/B850. Figure 23.4b shows comparison of fluorescence excitation
and absorptance (1 – T) spectra of LH2-A647 indicating that the efficient energy
transfer of 83% takes place from A647 to B800/B850. When free A647 was simply
mixed with LH2 in solution, no energy transfer was observed. This result indicates
that the efficient energy transfer is established by conjugation of LH2 and A647
external chromophore.
Energy transfer dynamics was observed with femtosecond transient absorption
(TA) spectroscopy. Figure 23.5 shows TA spectra upon excitation at 650 nm. Immediately, after the photoexcitation, the TA spectrum exhibits a negative band with a
minimum at 657 nm and positive bands with maxima at 517 and 454 nm within the
response time of the apparatus. The negative band is ascribed to the superposition of
ground state bleach (GSB) and stimulated emission (SE) of A647, and the positive
Fig. 23.4 a Absorption spectra of LH2-A647, LH2, and A647 in the micellar solution. b Fluorescence excitation and absorptance (1 – T) spectra of LH2-A647. Figures modified with permission
from American Chemical Society Ref. [9] Copyright 2015
T. Dewa et al.
(Fig. 23.2). Maleimide-C2-Alexa647 was directly attached to the Cys residue. The
numbers of Alexa647 attached to LH2 were ~9 and ~5 for the former and the latter
biohybrid LH2s, respectively. Hereafter, we call the two type of LH2 biohybrids as
LH2-A647 and LH2-NC-A647.
23.3 Energy Transfer Dynamics of LH2-A647
in the Micellar Solution System [9]
Figure 23.4a shows absorption spectrum of LH2-A647. The spectral profile can be
reproduced as a sum of A647 and the intrinsic chromophores (BChl and Car). The
absorption bands and circular dichroism (CD) signals of the intrinsic chromophores
in LH2 were well preserved, indicating that modification with A647 does not perturb
the environment of the chromophores. In addition, CD and linear dichroism spectra
suggested no excitonic coupling and particular orientation of A647 attached to LH2.
Upon excitation at 650 nm, significant quenching of A647 and prominent emission
from B850 were observed for LH2-A647. This result clearly indicates energy transfer
from A647 to B800/B850. Figure 23.4b shows comparison of fluorescence excitation
and absorptance (1 – T) spectra of LH2-A647 indicating that the efficient energy
transfer of 83% takes place from A647 to B800/B850. When free A647 was simply
mixed with LH2 in solution, no energy transfer was observed. This result indicates
that the efficient energy transfer is established by conjugation of LH2 and A647
external chromophore.
Energy transfer dynamics was observed with femtosecond transient absorption
(TA) spectroscopy. Figure 23.5 shows TA spectra upon excitation at 650 nm. Immediately, after the photoexcitation, the TA spectrum exhibits a negative band with a
minimum at 657 nm and positive bands with maxima at 517 and 454 nm within the
response time of the apparatus. The negative band is ascribed to the superposition of
ground state bleach (GSB) and stimulated emission (SE) of A647, and the positive
Fig. 23.4 a Absorption spectra of LH2-A647, LH2, and A647 in the micellar solution. b Fluorescence excitation and absorptance (1 – T) spectra of LH2-A647. Figures modified with permission
from American Chemical Society Ref. [9] Copyright 2015