Solid-State NMR Studies on the Non-Platonic Solid Geometries of Crystalline Cubane and Dodecahedrane Hydrocarbons

Description

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.).

Period	13 Sept 2015
Event title	The 9th Alpine Conference on Solid-State NMR
Event type	Conference
Location	FranceShow on map