Quantifying the Limited Role of Quantum Dynamics in Biomolecular Function

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Speaker: Professor Ross McKenzie (University of Queensland)
Date: 3rd June 2011

Quantum effects such as coherence, interference, tunnelling, and entanglement are well established for atoms and small molecules in a vacuum. But could quantum “weirdness” also occur in large biomolecules which are in thermal equilibrium with water at room temperature? I will describe a quantitative model for the quantum decoherence of the excited states of optically active biomolecules in a native environment [1]. Key physics includes the multiple time, energy, and length scales associated with the dielectric relaxation of proteins and of water. A wide range of experiments show that quantum decoherence typically occurs on time scales less than 1 picosecond and for distances less than 10 nanometers. These results provide a framework to critically evaluate the claims of some physicists (and New Age pop psychology gurus) that quantum effects are important in biology.¬† Such speculations have increased in the past few years stimulated by some experimental results for photosynthe!
tic systems. I contend that most claims of “quantum biology” are based on wishful thinking and involve (i) debatable data analysis with an excessive reliance on curve fitting, (ii) a misunderstanding of what biological evolution implies about the efficiency of specific processes in biomolecules, and/or (iii) speculations which go far beyond what the experimental data actually establish. Nevertheless, there is a lot of interesting physics involved in understanding the role of quantum decoherence in biomolecular function at sub-nanosecond timescales. One important challenge is to define an effective Hamiltonian for a specific class of biomolecular processes. This must find a balance between the distinctively different levels of detail normally used in physics, chemistry, and biology. I will briefly illustrate this with¬† recent work on Green Fluorescent Proteins [2]. A second challenge is solving the quantum dynamics in realistic parameter regimes where there is no simple sepa!
ration of time scales.

[1] J. Gilmore and R.H. McKenzie, J. Phys. Chem. A 112, 2162 (2008).

[2] S. Olsen and R.H. McKenzie, J. Chem. Phys. 130, 184302 (2009).