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

Two flavonoid glycosides derived from rhamnopyranoside (1) and arabinofuranoside (2) have been isolated from leaves of Persea caerulea for the first time. The structures of 1 and 2 have been established by H NMR, C NMR, and IR spectroscopy, together with LC-ESI-TOF and LC-ESI-IT MS spectrometry. From the MS and MS/MS data, the molecular weights of the intact molecules as well as those of quercetin and kaempferol together with their sugar moieties were deduced. The NMR data provided information on the identity of the compounds, as well as the α and β configurations and the position of the glycosides on quercetin and kaempferol. We have also explored the application of sodium dodecyl sulfate (SDS) normal micelles in binary aqueous solution, at a range of concentrations, to the diffusion resolution of these two glycosides, by the application of matrix-assisted diffusion ordered spectroscopy (DOSY) and pulse field gradient spin echo (PGSE) methodologies, showing that SDS micelles offer a significant resolution which can, in part, be rationalized in terms of differing degrees of hydrophobicity, amphiphilicity, and steric effects. In addition, intra-residue and inter-residue proton-proton distances using nuclear Overhauser effect build-up curves were used to elucidate the conformational preferences of these two flavonoid glycosides when interacting with the micelles. By the combination of both diffusion and nuclear Overhauser spectroscopy techniques, the average location site of kaempferol and quercetin glycosides has been postulated, with the former exhibiting a clear insertion into the interior of the SDS-micelle, whereas the latter is placed closer to the surface. Copyright © 2016 John Wiley & Sons, Ltd.

Section: Resultssupporting

confidence: 81%

Flavonoid glycosides from Persea caerulea. Unraveling their interactions with SDS‐micelles through matrix‐assisted DOSY, PGSE, mass spectrometry, and NOESY

Álvarez

Raya-Barón

Nieto

et al. 2016

“…Different analytes bind to the matrix to different extents, leading to different diffusion coefficients, allowing isomer signals to be differentiated in the diffusion dimension. Such experiments are sometimes referred to as Matrix‐Assisted DOSY (MAD), or in the case of surfactant matrices, Micelle‐Assisted DOSY . The purpose of the micelles here is simply to provide a means of differentiating between the signals of different compounds using diffusion.…”

Section: Introductionmentioning

confidence: 99%

¹⁹F NMR matrix‐assisted DOSY: a versatile tool for differentiating fluorinated species in mixtures

Poggetto

Antunes

Nilsson

et al. 2016

Self Cite

NMR is the most versatile tool for the analysis of organic compounds and, in combination with Diffusion-Ordered Spectroscopy ('DOSY'), can give information on compounds in complex mixtures without the need for physical separation. In mixtures where the components' diffusion coefficients are nearly identical, for example because of similar sizes, Matrix-Assisted DOSY ('MAD') can help separate the signals of different constituents, resolving their spectra. Unfortunately, DOSY (including MAD) typically fails where signals overlap, as is common in H NMR. Using F NMR avoids such problems, because the great sensitivity of the F chemical shift to local environment leads to very well-dispersed spectra. Another advantage is the absence of any F background signals from the matrices typically used, avoiding interference with the analyte signals. In this study, differentiation among fluorophenol and fluoroaniline isomers was evaluated using normal and reverse micelles-of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and dioctyl sodium sulfosuccinate (AOT)-as matrices. These surfactants provide useful diffusion separation in these difficult mixtures, with all the solutes interacting with the matrices to different extents, in some cases leading to differences in diffusion coefficient of more than 30%. The best matrices for separating the signals of both acid and basic species were shown to be AOT and CTAB, which are useful over a wide range of surfactant concentration. Copyright © 2016 John Wiley & Sons, Ltd.

“…Matrix‐assisted DOSY holds great potential for the NMR analysis of difficult mixtures such as natural product extracts, chemical reaction mixtures, and foods and beverages, and for metabolite identification. Its efficacy has been demonstrated for a number of classes of problem species, including positional isomers, epimers, enantiomers, and natural product mixtures . However, our understanding of how to choose a matrix for a particular type of sample is just in its infancy, and largely empirical.…”

Section: Introductionmentioning

confidence: 99%

“…Its efficacy has been demonstrated for a number of classes of problem species, including positional isomers, [7,13] epimers, [18] enantiomers, [16] and natural product mixtures. [12,19] However, our understanding of how to choose a matrix for a particular type of sample is just in its infancy, and largely empirical. In this publication, we investigate the effects of various matrices on a representative mixture, illustrating the process of choosing a matrix tailored to the species under study.…”

Section: Introductionmentioning

confidence: 99%

Matrix‐assisted diffusion‐ordered spectroscopy: choosing a matrix

Gramosa

Ricardo

Adams

et al. 2016

Self Cite

Diffusion‐ordered spectroscopy (DOSY) is an important technique for separating the NMR signals of the components in a mixture, and relies on differences in diffusion coefficient. Standard DOSY experiments therefore struggle when the components of a mixture are of similar size, and hence diffuse at similar rates. Fortunately, the diffusion coefficients of solutes can be manipulated by changing the matrix in which they diffuse, using matrix components that interact differentially with them, a technique known as matrix‐assisted DOSY. In the present investigation, we evaluate the performance of a number of new, previously used, and mixed matrices with an informative test mixture: the three positional isomers of dihydroxybenzene. The aim of this work is to present the matrix‐assisted DOSY user with information about the potential utility of a set of matrices (and combinations of matrices), including ionic and non‐ionic surfactants, complexing agents, polymers, and mixed solvents. A variety of matrices improved the diffusion resolution of the signals of the test system, with the best separation achieved by mixed micelles of sodium dodecyl sulfate and cetyl trimethylammonium bromide. The use of mixed matrices offers great potential for the analyst to tailor the matrix to a particular sample under study. © 2016 The Authors Magnetic Resonance in Chemistry Published by John Wiley & Sons, Ltd.