Detection of long-range electrostatic interactions between charged molecules by means of fluorescence correlation spectroscopy

Abstract

The present paper deals with an experimental feasibility study concerning the detection of longrange intermolecular interactions through molecular diffusion behavior in solution. This follows previous analyses, theoretical and numerical, where it was found that inter-biomolecular long-range force fields of electrodynamic origin could be detected through deviations from Brownian diffusion. The suggested experimental technique was Fluorescence Correlation Spectroscopy (FCS). By considering two oppositely charged molecular species in watery solution, that is, Lysozyme protein and a fluorescent dye molecule (Alexa488), the diffusion coefficient of the dye has been measured by means of the FCS technique at different values of the concentration of Lysozyme molecules, that is, at different average distances between the oppositely charged molecules. For the model considered long-range interactions are built-in as electrostatic forces, the action radius of which can be varied by changing the ionic strength of the solution. The experimental outcomes clearly prove the detectability of long-range intermolecular interactions by means of the FCS technique. Molecular Dynamics simulations provide a clear and unambiguous interpretation of the experimental results.

Out-of-Equilibrium Collective Oscillation as Phonon Condensation in a Model Protein

“…Thus our results explain why electrodynamic interactions between biomolecules have hitherto eluded detection, in fact no attempt has ever been done to detect them by involving biomolecules vibrating out-of-equilibrium. Consequently, our work also motivates new efforts to detect these electrodynamic intermolecular interactions [59,60].…”

Collective behavior of oscillating electric dipoles

“…These long range electrodynamic interactions are predicted by standard classical electrodynamics, thus they necessarily exist, the point is whether these can attain a sufficient strength to overcome all the dissipation mechanisms that would be activated together with the collective vibration [5]. In our preliminary investigations in [6] and [7,8] we have put forward the idea that an answer to this conundrum could come from the study of how the diffusion behavior of biomolecules in solution could change when their concentration is varied (that is, when the average intermolecular distance is varied) as a consequence of the action of surmised electrodynamic interactions. The experimental technique envisaged in [7,8] was Fluorescence Correlation Spectroscopy (FCS), a well established experimental technique [9][10][11].…”

Energy transfer to the phonons of a macromolecule through light pumping

“…Actually, this is a longstanding theoretical scenario [4][5][6] which, for several reasons, has been discarded. However, the upgrade of Fröhlich's theoretical proposition in 1,2 and the experimental outcomes reported in 1 , represent a first crucial leap forward to ascertain whether the above mentioned hypotheses can be given experimental confirmation or refutation that can be attempted with the nowadays available technology 7,8 .…”