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Photosynthesis Research by Means of
Optical Spectroscopy:
Energy Transfer
Charge Transfer
Protein Dynamics
Biosensors
Renewable Energy
Solar energy: 3,850,000x1018 J per year per
Earth; (and will last for millions of years)
Photosynthetic Pigment-Protein Complexes: Harvesting Light
and Funneling it into the Reaction Center (where Primary
Photochemistry Takes Place) with nearly 100% Effectiveness.
Top view of plant
Photosystem I:
Blue: protein
Grey: antenna chlorophylls
Red, orange: quinones and
iron-sulfur clusters of the
RC
What makes these seemingly chaotic (with a few exceptions)
antenna arrangements so efficient?
WHY
=
?
Can we learn something useful from Mother Nature for
designing more efficient solar energy harvesting systems?
Factors affecting pigments (e.g. Chlorophylls) transition energies:
Interactions with surrounding protein (static and dynamic);
Inter-pigment interactions
Quantum effects
Protein Structure and Dynamics
Tertiary protein structure, which determines protein’s function, is
determined by electrostatic interactions between peptides and
between peptides and water…
How do proteins “know” how to fold?
Levinthal Paradox:
A polypeptide of just 100 residues will have 99
peptide bonds, and therefore 198 different φ and
θ bond angles. If each of these bond angles can
be in one of just three stable conformations, the
protein may mis-fold into a maximum of 3198=
3x1094 different conformations.
Therefore if a protein were to attain its correctly folded configuration by randomly
sampling all possible conformations, it would require a time longer than the age of
the universe to arrive at its correct conformation even if conformations are sampled
at rapid (ns-1 or ps-1) rates. In reality, folding is very fast, and 100 amino acid
proteins fold (correctly) in milliseconds…
Predicting tertiary structure from primary sequence is ineffective:
Need to study actual energy landscapes
Scan number
Pigments as Sensitive Probes to Local Protein Environment.
Photosynthetic complexes have pigments in wide range of local
protein environments… and without any genetic engineering!
Wavelength (nm)
Hofmann, C., Aartsma, T. J.,
Michel, H., Köhler, J., New
Journal of Physics 6, 2004, 8.
© Christopher M. Dobson
Spectral Hole Burning and
Single Molecule Spectroscopy
Line/hole Width ~
[energy transfer time]-1
High-Resolution Optical Spectroscopy …
…in Frequency Domain (in our case)
Spectroscopy CCD with QE>90%
And avalanche photodiode
Tunable CW laser system (532 nm + dye + Ti-S)
Liquid helium cryostat
Spectrograph and single entity (including
graphene Raman) optical setup
Biosensors for Photosynthesis Inhibitors,
Including Herbicides and Explosives
lumen
ChlzD1
TNT
ChlzD2
D2
OEC
D1
stroma
No inhibitor
Working electrode (PS II)
Reference electrode
Photo-current (nA)
140
120
Increasing concentration of
inhibitor
100
80
60
40
20
0
4103
8103
Time (sec)
1.2104