Communication: Molecular dynamics and 1H NMR of n -hexane in liquid crystals

• Published in: The Journal of chemical physics 2015-07, Vol.143 (1)
• Main Authors: Weber, Adrian C. J., Burnell, E. Elliott, Meerts, W. Leo, de Lange, Cornelis A., Dong, Ronald Y., Muccioli, Luca, Pizzirusso, Antonio, Zannoni, Claudio
• Format: Article
• Language: English
• Subjects: Biological evolution; Chemical industry; Computer simulation; Couplings; Covariance matrix; Crystal structure; Deuteration; Liquid crystals; Molecular dynamics; Nematic crystals; NMR; Nuclear magnetic resonance; Physics
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4923253

The NMR spectrum of n-hexane orientationally ordered in the nematic liquid crystal ZLI-1132 is analysed using covariance matrix adaptation evolution strategy (CMA-ES). The spectrum contains over 150 000 transitions, with many sharp features appearing above a broad, underlying background signal that results from the plethora of overlapping transitions from the n-hexane as well as from the liquid crystal. The CMA-ES requires initial search ranges for NMR spectral parameters, notably the direct dipolar couplings. Several sets of such ranges were utilized, including three from MD simulations and others from the modified chord model that is specifically designed to predict hydrocarbon-chain dipolar couplings. In the end, only inaccurate dipolar couplings from an earlier study utilizing proton-proton double quantum 2D-NMR techniques on partially deuterated n-hexane provided the necessary estimates. The precise set of dipolar couplings obtained can now be used to investigate conformational averaging of n-hexane in a nematic environment.