CEST

CEST (Chemical Exchange Saturation Transfer) experiments detect the presence of minor conformational states through their effect on the major-state peak intensity. A weak radiofrequency field is applied at a variable saturation offset; when the offset matches the resonance frequency of a minor-state spin, saturation is transferred to the major-state peak via chemical exchange, reducing its intensity. The resulting Z-spectrum (also called a CEST profile) reveals both the major-state and minor-state chemical shifts.

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Usage

The input is a single pseudo-3D dataset where the first plane is the reference spectrum (recorded without saturation) and subsequent planes are saturation spectra recorded at increasing saturation offsets.

using NMRAnalysis

cest2d("11"; B1=15, Tsat=0.3)

# Read everything from the pulse-sequence annotations
cest2d("11")

• B1: Saturation field strength in Hz. Typical values are 5–50 Hz for ¹⁵N CEST. If you don't give it, it is calculated from the annotated saturation power (cest.power), calibrated against the reference pulse of the annotated channel (cest.channel).
• Tsat: Saturation time in seconds, otherwise read from the cest.duration annotation.
• offsets: Saturation offsets in ppm, one per plane, otherwise read from the cest.offset annotation or the fq3list.
• skipplanes: Saturation planes to leave out of the fit. The reference, plane 1, can't be skipped.

Anything that can't be found is asked for before the window opens.

Output

Clicking Save to folder writes all results to results.csv. Each row is one peak, with the per-offset amplitudes (amp[1], amp[2], …) that make up the Z-spectrum (normalised intensity $I(\omega_\text{sat})/I_0$), plus the fitted R1/R2 rates and uncertainties. See Peak Lists and Output Files for the full format.