Abstract
We describe the activation of out-of-equilibrium collective oscillations of a macromolecule as a classical phonon condensation phenomenon. If a macromolecule is modeled as an open system—that is, it is subjected to an external energy supply and is in contact with a thermal bath to dissipate the excess energy—the internal nonlinear couplings among the normal modes make the system undergo a nonequilibrium phase transition when the energy input rate exceeds a threshold value. This transition takes place between a state where the energy is incoherently distributed among the normal modes and a state where the input energy is channeled into the lowest-frequency mode entailing a coherent oscillation of the entire molecule. The model put forward in the present work is derived as the classical counterpart of a quantum model proposed a long time ago by Fröhlich in an attempt to explain the huge speed of enzymatic reactions. We show that such a phenomenon is actually possible. Two different and complementary THz near-field spectroscopic techniques—a plasmonic rectenna and a microwire near-field probe—have been used in two different labs to eliminate artifacts. By considering an aqueous solution of a model protein, the bovine serum albumin, we find that this protein displays a remarkable absorption feature around 0.314 THz, when driven in a stationary out-of-thermal equilibrium state by means of optical pumping. The experimental outcomes are in very good qualitative agreement with the theory developed in the first part of the paper and in excellent quantitative agreement with the theoretical result, allowing us to identify the observed spectral feature with a collective oscillation of the entire molecule.
- Received 1 November 2017
- Revised 25 June 2018
DOI:https://doi.org/10.1103/PhysRevX.8.031061
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Living cells host a complex network of biochemical reactions, in which the molecular players seem to know where to go and when. A long-standing hypothesis surmises that these interactions could be driven by electrodynamic forces between biomolecular partners in these reactions. However, electrodynamic interactions between biomolecules have eluded detection. Here, we provide theoretical and experimental confirmation of a crucial prerequisite for this hypothesis: the activation of a collective vibration of a macromolecule subject to an external supply of energy.
We first develop a theoretical model that describes out-of-equilibrium collective oscillations of a macromolecule as a classical phonon condensation phenomenon. Internal couplings among the normal modes of the molecule trigger a phase transition when the energy input rate exceeds some threshold, channeling the input energy into a coherent oscillation of the entire molecule.
Next, we experimentally show that this phenomenon is possible. We find that a model protein, bovine serum albumin, has an absorption feature around 0.314 THz when driven in a stationary out-of-thermal equilibrium state by means of optical pumping. The experimental outcomes are in excellent agreement with theory, allowing us to identify the absorption feature with a collective oscillation of the entire molecule.
Our results could lead to a better understanding of the dynamics of biomolecular encounters and recognition in living cells by opening a broad domain of systematic investigations. We foresee the possibility of modulating biochemical reactions like enzymatic chains, DNA duplication and repair, and gene expression through externally applied electromagnetic fields, with numerous medical applications.
