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)

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.