Mapping Molecular Perturbations by a New Form of Two-Dimensional Spectroscopy

We propose a new general form of two-dimensional spectroscopy where the indirect "evolution" dimension is derived using the Radon transform. This idea is applicable to several types of spectroscopy but is illustrated here for the case of NMR spectroscopy. This "projection spectroscopy" displays characteristic correlation peaks that highlight perturbations of chemical shifts caused by temperature, pressure, solvent, molecular binding, chemical exchange, hydrogen bonding, pH variations, conformational changes, or paramagnetic agents. The results are displayed in a convenient format that allows the chemist to see all of the chemical shift perturbations at a glance and assess their rates of change and directions. As a proof of principle, we present two simple, practical examples that display two-dimensional representations of the effects of temperature and solvent on NMR spectra.