Solvation of charged species plays a fundamental role for electron and ion transport in water and for the structure and function of hydrated biomolecules [1]. The electric dipole moment of water molecules gives rise to strong electric fields in the liquid which, due to thermally activated molecular motions, fluctuate in a time range from tens of femtoseconds to several picoseconds. This talk addresses two aspects of electric fields and interactions in water, the field-driven generation and subsequent solvation of electrons [2,3] and the role of contact ion pairs in stabilizing hydrated RNA structure [4,5].<br/>Fluctuating intermolecular electric fields induce spontaneous tunneling ionization of water molecules which can be made irreversible by imposing an external directed terahertz (THz) field on the liquid. Time-resolved nonlinear THz spectroscopy maps charge separation, transport, and localization of the released electron on a few-picosecond time scale. The highly polarizable localized electrons modify the THz absorption spectrum and refractive index of water, a manifestation of a highly nonlinear response. The many-body Coulomb interactions in the liquid give solvated electrons distinct polaronic properties, resulting in coupled electron and water motions in the (sub-)THz frequency range.<br/>The formation of stable tertiary RNA and DNA structures requires a balance of repulsive and attractive electric interactions, mediated by ions and the water shell. Vibrational excitations of the negatively charge phosphate groups in the RNA and DNA backbones serve as noninvasive probes of local hydration geometries and related electric fields. Two-dimensional infrared spectroscopy with a femtosecond time resolution identifies contact pairs of phosphate groups with magnesium ions (Mg<sup>2+</sup>) from the environment as a key feature stabilizing tertiary RNA structure. Results are presented for short RNA duplexes and the cloverleaf structure of transfer RNA. The spectroscopic results together with MD simulations give quantitative insight in electric interactions at the RNA-water interface.

Charge solvation in water – ultrafast dynamics and electric interactions

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.