Heat Transfer Pathways in Proteins

Abstract

Proteins propagate excess thermal energy surprisingly fast and efficient. The theoretical description of thermal transport dynamics in proteins is challenging as it involves both fast quantum vibrations as well as more classical slow conformational changes. Existing protein Molecular Dynamics methods describe these conformational changes well but perform poorly for fast quantum degrees of freedom. Dye labeled Azido-PEG oligomers are experimentally well studied model systems for excess energy transport. Relaxation-assisted two-dimensional infrared (RA 2DIR) spectroscopy has been applied 1) 2) to measure the time-dependent correlation of frequencies belonging to the dye and the Azido group.Thermal energy is generated at the dye and propagates through the flexible oligomer chain (intramolecular) as well as into the solvent (intermolecular). The oligomer chain undergoes conformational changes on the ps time scales of the transfer process. These slow changes were sampled using Molecular Dynamics trajectories. The resulting structural ensemble was used to map the mode coupling pathways for the fast quantum degrees of freedom. All pairwise mode-mode coupling potentials along pairs of dynamic normal mode vectors were calculated. A molecular heat map was generated using the spatial delocalization of the modes and the inter mode coupling strengths. Molecular heat maps have the potential to extend the theoretical understanding of intramolecular heat transduction pathways in proteins.1) Lin, Z., Rubtsov, I.V., PNAS, 2012, 105, 5, 1413-14182) Lin, Z., Rubtsov, I.V., et al., Phys. Chem. Chem. Phys., 2012, 14, 10445-10454