Abstract
In the present paper we address the problem of the energy downconversion of the light absorbed by a protein into its internal vibrational modes. We consider the case in which the light receptors are fluorophores either naturally co-expressed with the protein or artificially covalently bound to some of its amino acids. In a recent work [Phys. Rev. X 8, 031061 (2018)], it has been experimentally found that by shining a laser light on the fluorophores attached to a protein the energy fed to it can be channeled into the normal mode of lowest frequency of vibration thus making the subunits of the protein coherently oscillate. Even if the phonon condensation phenomenon has been theoretically explained, the first step - the energy transfer from electronic excitation into phonon excitation - has been left open. The present work is aimed at filling this gap.
Highlights
In the present paper we address the problem of the energy downconversion of the light absorbed by a protein into its internal vibrational modes
A continuous energy supply of this kind was experimentally found effective to excite the vibrational modes of the proteins and, with an energy supply rate exceeding a suitable threshold, this eventually led to a phonon condensation phenomenon into the lowest vibrational frequency
Summarizing the physical meaning of the results reported in the present work, we have to keep in mind that the parameter space of the system investigated here is very large, we have limited our investigation to a basic choice of physically meaningful parameters to tackle the fast process that we aimed at modelling, as stated in the Introduction
Summary
In order to sketch the conceptual framework of the present work and what has motivated it, let us begin by quoting a recent work[1] where the activation of out-of-equilibrium collective intramolecular vibrations of a model protein has been reported This phenomenon has been induced by light pumping, realised by shining a laser light on an aqueous solution of BSA (Bovine Serum Albumin) protein molecules each one carrying a few fluorophores covalently attached to their Lysine residues. The reason is that, at thermal equilibrium, a macromolecule vibrates incoherently with a broad spectrum of modes, whereas the action of an external source of energy promoting a phenomenon of phonon condensation can induce the coherent motion of the molecular subunits, so that, the resulting collective vibration can bring about a large oscillating dipole moment Under this condition long-range and resonant ( selective) electrodynamic forces can be activated. Besides linear interactions among the thermal baths modes and the biomolecule modes, k k mode-mode interactions among the biomolecule normal modes are considered to be mediated by the modes of the former thermal bath
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