Abstract
In the first part of the present paper (theoretical), the activation of out-of-equilibrium collective oscillations of a macromolecule is described 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 non-equilibrium 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, to 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 long time ago by H. Fr\"ohlich in the attempt to explain the huge speed of enzymatic reactions. In the second part of the present paper (experimental), we show that such a phenomenon is actually possible. Two different and complementary THz near-field spectroscopic techniques, a plasmonic rectenna, and a micro-wire near-field probe, have been used in two different labs to get rid of artefacts. By considering a aqueous solution of a model protein, the BSA (Bovine Serum Albumin), we found 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, and in excellent quantitative agreement with a theoretical result allowing to identify the observed spectral feature with a collective oscillation of the entire molecule.
Highlights
Recent progress in terahertz technology has enabled us to look at biological systems with terahertz radiation, that is, in an energy domain of the order of the activation energy of many biological processes
We describe the activation of out-of-equilibrium collective oscillations of a macromolecule as a classical phonon condensation phenomenon
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
Summary
Recent progress in terahertz technology has enabled us to look at biological systems with terahertz radiation, that is, in an energy domain (a few meV) of the order of the activation energy of many biological processes. The first important question addressed in the present work is whether a phonon condensation phenomenology can be retrieved in a classical framework and out of thermal equilibrium To this aim, by resorting to a dequantization method, we have worked out a classical version of the original Fröhlich model, finding that—remarkably—in a classical context too, Bose-like phonon condensation is possible [16]. By resorting to a dequantization method, we have worked out a classical version of the original Fröhlich model, finding that—remarkably—in a classical context too, Bose-like phonon condensation is possible [16] This possibility requires us to consider a biomolecule as an open system—that is, far from thermal equilibrium with its environment—through which energy flows under the simultaneous actions of an external energy supply and of dissipation due to radiative, dielectric, and viscous energy losses.
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