Python code to help with the determination of signs of chemical shift differences using the R_1ρ method. The code takes a p_b, k_ex and a list of chemical shift differences, and determines optimal B₁ fields and offsets from numerically evolving the appropriate Louvillian. Effects of differences in transverse relaxation between exciting both upfield and downfield of the resonance of interest are calculated. Varian input macros files are produced, so that you only need type ‘go’ at the spectrometer. The program uses nmrPipe and nmrGlue to process data and will also analyze everything for you. Signs made simple!

Measurement of the signs of methyl chemical shift differences between ground and excited protein states by R_1ρ: an application to αB-crystallin
Baldwin AJ, Kay LE
J. Biol. NMR (2012) 53(1) 1 pdf