Cross-Correlated Relaxation (CCR)

Cross-correlated relaxation (CCR) experiments measure the interference between two relaxation mechanisms — for example, between dipole-dipole coupling and chemical shift anisotropy — and are used to determine bond vector orientations, order parameters, and rotational correlation times.

The CCR rate η is extracted by comparing the buildup and decay of spin-state-selective coherences:

\[\tanh(\eta T) = \frac{I_\text{buildup}}{I_\text{decay}}\]

For symmetric reconversion experiments, where two buildup and two decay spectra are recorded to suppress contributions from auto-relaxation:

\[\tanh(\eta T) = \sqrt{\frac{I_{\text{bu},1} \cdot I_{\text{bu},2}}{I_{\text{dec},1} \cdot I_{\text{dec},2}}}\]

Usage

Single decay / buildup pair

using NMRAnalysis

ccr2d("decay", "buildup", 0.08)

Symmetric reconversion (two pairs)

ccr2d(
    ["decay1", "decay2"],
    ["buildup1", "buildup2"],
    0.08
)

The third argument T is the relaxation time constant in seconds during which the CCR rate acts. Experiments can also be given as Bruker experiment numbers, individually or as a list/range (e.g. ccr2d(1, 2, 0.08) or ccr2d(1:2, 3:4, 0.08)).

Output

Clicking Save to folder writes all results to results.csv. The derived columns are:

See Peak Lists and Output Files for the full format. Plot η against residue number with summaryplot("output-folder/").