Abstract
2D homonuclear NMR spectroscopy is an essential technique to characterize small and large molecules, such as organic compounds, metabolites, and biomacromolecules at atomic resolution. However, for complex samples 2D homonuclear spectra display poor resolution, making spectral assignment very cumbersome. Here, we propose a new method that exploits the differential T2* relaxation times of individual resonances and resolves the 2D NMR peaks into pseudo-3D spectra, where time is the 3rd dimension. T2* weIghted DEconvolution or TIDE analyzes individual free induction decays (FIDs) and dissects them into sub-FIDs that are transformed into pseudo-3D spectra combining Fourier transformation and covariance NMR. TIDE achieves higher resolution and sensitivity for NMR spectra than classical covariance NMR reducing offset-dependent artifacts. We demonstrate the performance of TIDE for magic angle spinning (MAS) [13C,13C]-DARR NMR spectra of single- and multi-span membrane proteins embedded in lipid bilayers. Since TIDE is applicable to all type of homonuclear correlation experiments for liquid and solid samples, we anticipate that it will be a general method for processing NMR data of biomacromolecules, complex mixtures of metabolites as well as material samples.
Highlights
Where i and j represent row and column index of the covariance matrix, respectively, k is the index of the free induction decays (FIDs) in the t1 dimension, N1 is the total number of time points in the indirect dimension and 〈S(i)〉 = 1/N1∑k S(k, i) is the mean of ith column vector of S
TIDE extends the dimensionality of the 2D homonuclear correlation spectroscopy by retaining time-frequency information encoded in the FID
It can be applied to data sets acquired with standard pulse sequences without modifications of experimental parameters and requires only real points in the indirect dimension, reducing the experimental time by 50%. Another benefit shared by covariance NMR and TIDE is the improved resolution even in the presence of asymmetry in the peak intensities with respect to the diagonal
Summary
For covariance NMR (Fig. S1), the time-domain signals, S (t1, t2), are first Fourier transformed along the direct dimension t2, obtaining S (t1, ω2). Note that if we used FT in this step, which relies on initial phases of the signals in the t1 dimension, we would introduce first-order phase distortions in the spectra resulting from the missing time points and dwell time in the sub-FIDs. In contrast, we opted for covariance transformation, which avoids phase distortions.
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