Measuring the J HH coupling by a simple 2D-intra-HNCA IP/AP-E.COSY with simultaneous encoding of N chemical shift and J HC evolution.

The J coupling values are commonly used in biomolecular NMR to extract structural information. Here we present a novel intra HNCA IP/AP E.COSY pulse sequence that allows to measure J HH coupling constants by a simple and rapid two-dimensional H-N correlation experiment where the N frequency is encoded at the same time as the J HC coupling evolution. The advantage with respect to the conventional 3D HNCA E.COSY pulse sequence is the dimensionality reduction to a simple 2D experiment, which decreases acquisition time and facilitates data analysis. The performance of this new experiment is demonstrated with an ubiquitin sample at 500 MHz.