Methodology and software was developed to simulate molecular dynamics and relaxation of LLS and nuclear spin states conventionally measured in NMR. Singlet relaxation mechanisms of a a maleate derivative was studied in collaborative project (article 3). Singlet relaxation mechanisms of a a maleate derivative was studied in collaborative project (article 3, recently accepted in PhysChemChemPhys). The singlet lifetime was explicable with conventional relaxation mechanisms (including coupling with paramagnetic oxygen). This article, which is now accepted for publication, describes the first successful treatment of nuclear singlet relaxation by a combination of molecular dynamics and computational chemistry, almost free from adjustable parameters, and marks the substantial achievement of the main project goals.
As part of the project, computational chemistry techniques were employed to study the interaction of a 3He atom with an encapsulating fullerene molecule. These tasks were relevant for verifying and optimizing the computational methodology involved in the relaxation calculations, and led to two high-profile publications (articles 1 and 2).
Theory and software for the calculation of the interaction parameters for the spin-nuclear-motion (SNM) relaxation mechanism was also developed. To obtain the parameters, the software post-processes spin-rotation tensor calculations (calculated by the Dalton software package). Gamma-picoline (4-methylpyridine, see attached figure) was chosen as an example system to study and understand SNM contribution to LLS relaxation. Gamma-picoline is pyridine with one of the protons replaced by the methyl group (opposed to the nitrogen atom). The methyl group is reported to have a low rotational barrier, and we, therefore, considered it to be an ideal candidate to study internal rotation coupling to nuclear spins. However, while our developed model was able to explain the lifetimes of the LLS by good approximation, it was unable to explain the relaxation of the conventional nuclear spin states. As in conventional NMR relaxation simulations, the used methodology couples classical molecular dynamics to the nuclear spins. The failure of our model may be explained by the sparsity of the accessible rotational states of the methyl group, which means that the quantum mechanical nature of the methyl rotation must be taken into account when it is coupled with the nuclear spins. It should be noted that our model explains the relaxation of the atoms of the pyridine in this system. The fellow and the host group investigated the possibility to derive theory and methodology for coupling quantum mechanical molecular dynamics of the internal motion to the nuclear spins. However, this was judged to be a very significant task which would require an entirely new approach to the problem of nuclear relaxation. This project would require several years of work and additional resources, and was not completed at the time the fellow left the project.
