Fast multi-dimensional Hadamard spectroscopy.

Multi-dimensional NMR spectroscopy can be speeded up by large factors by replacing the time-domain evolution dimensions by direct irradiation at signal-bearing sites with a frequency-domain multiplex scheme. There is no loss in sensitivity per unit time. The excitation and transfer operations are encoded according to Hadamard matrices and the detected NMR signals are decoded by reference to the same matrices. Most traditional multi-dimensional NMR pulse sequences can be readily converted into this new Hadamard mode. Three-dimensional TOCSY-HSQC experiments on strychnine at 700 MHz bear out these ideas, indicating that the measurement time can be reduced by as much as three orders of magnitude in favorable cases.