Simplifying DOSY spectra with selective TOCSY edited preparation.

Abstract

Diffusion-ordered NMR spectroscopy, while quite powerful, is limited by its inability to resolve signals that are severely overlapped in the proton spectrum. We present here a DOSY experiment that uses selective TOCSY as an editing/preparation period. With this method, well-resolved signals of the analytes are selectively excited and the magnetization subsequently transferred by isotropic mixing to resonances buried in the matrix background, which are then resolved by the ensuing DOSY sequence. Key to the success of our proposed method is the incorporation of a highly effective zero-quantum filter into the selective TOCSY preparation period, which prevents zero-quantum coherence from being carried into the DOSY part of the pulse sequence. Further improvement in spectral resolution can be obtained by expanding the proposed experiment into a 3D sequence and utilizing the homonuclear decoupling feature of the BASHD-TOCSY technique. Both pulse sequences were found to greatly simplify the DOSY spectrum of a 'dirty' sucrose/raffinose mixture, as the complex matrix background is no longer present to obscure or overlap with the signals of interests. Furthermore, complete resolution of the relevant signals was achieved with the 3D sequence.