Solid-State NMR Studies on the Non-Platonic Solid Geometries of Crystalline Cubane and Dodecahedrane Hydrocarbons
Sprache des Vortragstitels:
Englisch
Original Tagungtitel:
The 9th Alpine Conference on Solid-State NMR
Sprache des Tagungstitel:
Englisch
Original Kurzfassung:
Internuclear distance information can be determined by exploiting the ~r^-3
dependence of the direct dipolar coupling interaction. This attractive relation
explains the substantial experimental (fast-MAS) and theoretical (C/R-type pulse
sequences) efforts made to disentangle spectral dependence on dipolar coupling
from that on other spin interactions. This goal becomes experimentally most
demanding if the dipolar coupling is substantially smaller (long range) than
e.g. chemical shielding anisotropy (CSA). Additional modulations of the desired
pure dipolar polarisation transfer potentially leads to a misinterpretation of
data in terms of extracted internuclear distances. The problem of data
interpretation often comes together with a severe experimental loss of spectral
intensity.
We demonstrate how nature-inspired genetic algorithms can be used to approach
this conundrum from a numerical point of view. Homonuclear direct dipolar
recoupling experiments of the C/R symmetry framework are compared to our
genetically evolved pulse sequences that are widely independent of any CSA
influence and provide very high spectral intensity. At the same time it is
demonstrated that genetic algorithms offer the means to easily implement
optimisation of multiple objectives simultaneously. This is especially important
since a well performing NMR experiment typically requires multiple objectives to
be met (high efficiency, various degrees of broadbandedness, low-power
irradiation, small number of pulses, etc.).
Forschungs-