Molecular Structure in Liquid Crystals Studied by NMR

University dissertation from Stockholm : Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi

Abstract: This thesis is focused on structure determinations of molecules in liquid crystals using NMR. The systems described here exhibit orders ranging from nearly isotropic to essentially solid. The structure is determined by interpreting, mainly dipolar couplings, but also J-couplings and NOE data using conformational distribution functions (cdfs) to capture both the structure and the flexibility of the molecules. The models used in the analysis of the NMR parameters are: a statistical approach denoted Maximum Entropy (ME), a mean field method named Additive Potential (AP) and a synthesis of the two named APME. The thesis covers some background on liquid crystals, NMR, dipolar couplings and their role in structure determination as well as the aforementioned models used for this purpose.The thesis also discusses four papers: 1st being a comparison of the ME, AP and APME models in the structure determination of diphenylmethane. The 2nd covering a test of the APME method, reproducing the cdf of dimyristoylphosphatidylcholine in a lipid bilayer obtained through a molecular dynamics simulation using the APME method on dipolar couplings calculated from the MD trajectory. The 3rd paper deals with a discotic molecule 2, 3, 6, 7, 10, 11-hexahexyl-thiotriphenylene, HHTT displaying a polymorphism which is investigated, using NMR, determining the characteristics of three of its phases. Finally the 4th paper is a structure investigation of ?-cyclodextrin employing the ME method using experimental J-couplings, NOEs and dipolar couplings.

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