Improved proton assignment for DNA by application of aliasing and dispersive-absorptive phasing to two-quantum COSY spectra.

A unique combination of aliasing and dispersive-absorptive (DA) phasing of two-quantum correlated spectroscopy (2 Q-COSY) NMR data is shown to enhance proton chemical-shift assignments in DNA oligonucleotides by (i) reducing the time necessary for acquiring NMR data or, alternatively, improving the spectral resolution in a given time, (ii) reducing the number of spectra necessary for NMR data processing and analysis, and (iii) increasing the complexity of oligonucleotide sequences and structures which are accessible to 2D NMR analysis. Aliasing allows a reduction in the size of the acquired data without significant risk of losing information. Phasing the 2Q-COSY dispersive in the F2 dimension reduces the primary antiphase doublet into a pseudo-singlet and increases the apparent signal-to-noise. A single 2Q-COSY spectrum can provide an amount of chemical-shift information comparable to that from a series of COSY, relayed-COSY, and/or spin-lock COSY spectra optimized for various coupling constants. The low signal-to-noise inherent in the most popular two-quantum-filtered correlated spectroscopy (2QF-COSY) of samples with naturally broad lines is largely avoided due to less cancellation. There is no diagonal in a 2Q-COSY which can obscure correlations between protons which are nearly isochronous. As an example of this efficient application, the assignment of 139 of the 143 proton resonances from a single 2Q-COSY and a 2D-NOE spectrum of the DNA hexadecamer [d(AAATATAGCTATATTT)]2 is demonstrated.