CPMG Relaxation Dispersion

CPMG (Carr-Purcell-Meiboom-Gill) relaxation dispersion experiments detect conformational exchange processes on the microsecond-to-millisecond timescale. The effective transverse relaxation rate R₂,eff depends on the CPMG pulse frequency νCPMG: residues undergoing exchange show elevated R₂,eff at low νCPMG that decreases as νCPMG increases.

The effective relaxation rate is calculated from the intensity ratio:

\[R_{2,\text{eff}}(\nu_\text{CPMG}) = -\frac{1}{T_\text{relax}} \ln\!\frac{I(\nu_\text{CPMG})}{I_\text{ref}}\]

where $T_\text{relax}$ is the total CPMG relaxation period and $I_\text{ref}$ is the reference plane intensity (zero CPMG pulses).

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Usage

The input is a single pseudo-3D dataset where the first plane is the reference spectrum and subsequent planes are recorded at increasing CPMG frequencies.

using NMRAnalysis

# Specify CPMG frequencies directly (Hz); use 0 for the reference plane
cpmg2d("11"; Trelax=0.04, vCPMG=[0, 25, 50, 75, 100, 200, 500])

# Alternatively, specify the number of CPMG cycles per plane (vCPMG = ncyc / Trelax)
ncyc = [0, 1, 2, 3, 4, 8, 20]
cpmg2d("11"; Trelax=0.04, ncyc=ncyc)

# Or read the cycle numbers from the vclist
cpmg2d("11"; Trelax=0.04)

If neither vCPMG nor ncyc is given, the cycle numbers are read from the vclist, and if Trelax or the cycle numbers can't be found you are asked for them. skipplanes leaves planes out of the fit, as long as at least one reference plane remains.

Output

Clicking Save to folder writes all results to results.csv. Each row is one peak, with the per-plane amplitudes (amp[1], amp[2], …) from which the R₂,eff dispersion profile is computed, and the derived reference rate R20, R20_err (R₂,₀, s⁻¹). See Peak Lists and Output Files for the full format.