Auto-offsetting and -referencing in biomolecular NMR experiments

A frequency ratio RatioXH associated with two carrier frequencies in ppm is introduced for achieving auto-offsetting and -referencing (AOR) in biomolecular NMR. Once the center of 1H is referenced, all the offsets in other dimensions are automatically determined and the centers of the spectral widths provide accurate indirect references. Since the scale in ppm is independent of the magnetic field strength, the AOR does not require manually updating carrier frequencies from time to time, making the multidimensional NMR experiments greatly simplified and reliable. It is extremely valuable when molecules need to be run a large number of experiments at different times and the data (chemical shifts, for example) need to be compared with each other. In AOR, the error arising from improper referencing of 1H is handed down in the same amount to the other nuclei being referenced. This error-inheritance provides a measure of accuracy in indirect referencing. The temperature dependence of the frequency ratio of DSS is derived with the first-order approximation and it can be used for temperature dependent AOR. For nuclei other than 13C, certain frequency ratios regarding TMS need to be derived (rather than measured) based on the recommended frequency ratios of DSS, thus avoiding conflicts and unifying the two standards.