Photosynthesis Research by Means of Optical Spectroscopy:

Energy TransferCharge Transfer

Protein DynamicsBiosensors

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.

What makes these seemingly chaotic (with a few exceptions) antenna arrangements so efficient?

Top view of plant Photosystem I:Blue: protein

Grey: antenna chlorophyllsRed, orange: quinones and iron-sulfur clusters of the

RC

=

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 interactionsQuantum effects

?

Protein Structure and DynamicsTertiary 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:

Predicting tertiary structure from primary sequence is ineffective: Need to study actual energy landscapes

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…

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)

Scan

num

ber

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)

Tunable CW laser system (532 nm + dye + Ti-S)

Liquid helium cryostat

Spectroscopy CCD with QE>90%And avalanche photodiode

Spectrograph and single entity (including graphene Raman) optical setup

Working electrode (PS II)

Reference electrode

Time (sec)

No inhibitor

Increasing concentration of inhibitor

0 4103 8103 1.2104

140

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TNT

Biosensors for Photosynthesis Inhibitors, Including Herbicides and Explosiveslumen

stroma

ChlzD2

ChlzD1

D1D2 OEC

Pho

to-c

urre

nt (

nA)