Computational modeling of overhauser dynamic nuclear polarization in liquids

Official URL: http://risc01.sabanciuniv.edu/record=b1640300 (Table of Contents)

Since its discovery, nuclear magnetic resonance (NMR) spectroscopy has been a vital tool for molecular structure and function determination. Inherently, NMR signals suffer from lack of sensitivity, however Overhauser Dynamic Nuclear Polarization (ODNP) offers a substantial enhancement in the NMR signals exploiting the stochastic modulation of hyperfine interaction between electron and nuclear spins. The origin of the hyperfine interaction is known to comprise of dipolar and scalar couplings whose magnitudes can change depending on the nuclear spin. For instance, 1H ODNP is dominated by dipolar interaction while 13C may be influenced by both interactions. Therefore, prediction of the enhancement necessitates the knowledge of separate contributions. Although the dipolar contribution can be predicted via analytical models which exploit its geometric nature, the contribution of scalar interaction is impossible to predict using such analytical models since its magnitude depends on the electron spin density on the nucleus. Recently, a methodology based on molecular dynamics simulations was developed for predicting ODNP enhancements influenced by dipolar interaction. In this work, the strategy is successfully applied for proton ODNP of acetone and DMSO liquids doped with nitroxide TEMPOL. Due to its high sensitivity on ODNP enhancements, the fidelity of the rotational motion of the simulated molecules is also assessed by dielectric relaxation analysis. The scope of methodology is extended to take scalar interaction into account by performing DFT calculations. The functional and basis set dependency of the DFT calculations is investigated and quantitative agreement with the experiment is achieved for the carbons of acetone and chloroform.