Natural product mixture analysis by matrix-assisted DOSY using Brij surfactants in mixed solvents

Abstract

The assignment of NMR signals to specific components in a mixture is a challenging task. Diffusion-Ordered Spectroscopy (DOSY) has provided important progress in this area, allowing the signals originating from individual components of different molecular sizes to be distinguished. However, when the sizes of the compounds are similar and/or the spectra are overlapped, signal assignment can easily become intractable. The use of a co-solute in a matrix-assisted DOSY (MAD) experiment can be a useful solution, improving diffusional (and sometimes spectral) resolution by exploiting selective binding to the matrix. MAD has generated promising results in the study of several types of mixtures, including those of functional and structural isomers. The challenge is to apply MAD to molecules with high structural similarity, for example in natural product mixtures. Various surfactants, including SDS, AOT and CTAB have previously been shown to be effective in MAD analysis. Here we present an important addition, the Brij family of nonionic surfactants. We demonstrate the use of Brij micelles in mixed solvents with a variety of mixtures relevant to natural products.