Fluorine labelling for in situ ¹⁹F NMR in oriented systems

The focus of this project is to take advantage of the large NMR chemical shift anisotropy of ¹⁹F to determine the orientation of fluorine labeled biomolecules in situ in oriented biological systems such as muscle. The difficulty with a single fluorine atom is that the orientation determined from a chemical shift is not singlevalued in the case of a fully anisotropic chemical shift tensor. The utility of a labeling approach with two fluorine labels in a fixed molecular framework where one of the labels has an axially symmetric chemical shift anisotropy such as a CF₃ group and the other has a fully asymmetric chemical shift anisotropy such as 5-fluorotryptophan is evaluated. The result is that the orientation of the label can be determined straightforwardly from a single one-dimensional ¹⁹F NMR spectrum. The potential applications are widespread and not limited to biological applications.