Fast-field-cycling
relaxometry is a nuclear magnetic resonance
method growing in popularity; yet, theoretical interpretation is limited
to analytical models of uncertain accuracy. We present the first study
calculating fast-field-cycling dipolar coupling directly from a molecular
dynamics simulation trajectory. In principle, the frequency-resolved
dispersion contains both rotational and translational diffusion information,
among others. The present joint experimental/molecular dynamics study
demonstrates that nuclear magnetic resonance properties calculated
from the latter reproduce measured dispersion curves and temperature
trends faithfully. Furthermore, molecular dynamics simulations can
verify interpretation model assumptions by providing actual diffusion
coefficients and correlation times.
The nuclear Overhauser
effect (NOE) is a powerful tool in molecular
structure elucidation, combining the subtle chemical shift of NMR
and three-dimensional information independent of chemical connectivity.
Its usage for intermolecular studies, however, is fundamentally limited
by an unspecific long-ranged interaction behavior. This joint experimental
and computational work shows that proper selection of interacting
isotopes can overcome these limitations: Isotopes with strongly differing
gyromagnetic ratios give rise to short-ranged intermolecular NOEs.
In this light, existing NOE experiments need to be re-evaluated and
future ones can be designed accordingly. Thus, a new chapter on intermolecular
structure elucidation is opened.
This computational study deals with the collective structure and dynamics as well as their interaction seen from a dielectric viewpoint in zwitterionic reverse micelles for which a force field was designed de novo. For this end, a dualistic strategy is followed: the raw data are generated by extensive microscopic molecular dynamics (MD) simulations while the subsequent analysis has a focus on mesoscopic dielectric properties. The unusually low dielectric signals as well as the remarkable acceleration of collective dynamics is elucidated in great detail. This structural and dynamic behaviour is caused essentially by non-specific micellar boundary conditions. We found that in these ion lacking reverse micelles the water core and the water sheath compensate each other dielectrically which can be understood as a LeChatelier phenomenon facilitating the transition from highly polar encapsulated water to the non-polar low dielectric medium octane. In addition, specific chemical effects are brought about by the perturbing influence of the surfactants. This comprehensive analysis aids both in understanding and designing the dipolar properties of liquid polar spherical colloids dispersed in a hydrophobic medium.
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