Showing papers by "Gareth A. Morris published in 2009"
TL;DR: This study describes a general alternative to existing methods for the calibration of NMR diffusion measurements which is parameterised as the exponential of a power series.
110 citations
96 citations
TL;DR: The use of micelle-assisted DOSY to resolve the NMR spectra of isomers is illustrated for the case of the three dihydroxybenzenes in aqueous solution containing sodium dodecyl sulfate micelles, and in chloroform solution containing AOT reversed micells.
Abstract: Diffusion-ordered NMR spectroscopy ("DOSY") is a useful tool for the identification of mixture components. In its basic form it relies on simple differences in hydrodynamic radius to distinguish between different species. This can be very effective where species have significantly different molecular sizes, but generally fails for isomeric species. The use of surfactant co-solutes can allow isomeric species to be distinguished by virtue of their different degrees of interaction with micelles or reversed micelles. The use of micelle-assisted DOSY to resolve the NMR spectra of isomers is illustrated for the case of the three dihydroxybenzenes (catechol, resorcinol, and hydroquinone) in aqueous solution containing sodium dodecyl sulfate micelles, and in chloroform solution containing AOT reversed micelles.
62 citations
TL;DR: A DOSY investigation of the solubilisation capacity of micelles of sodium dodecyl sulphate for artemisinin and curcumin, individually and in combination suggests a potentially useful combination of the surface activity and antioxidant properties of the novel binary SDS:ASC8 system.
47 citations
15 Dec 2009
TL;DR: Diffusion-ordered spectroscopy (DOSY) as discussed by the authors is a mixture analysis technique based on pulsed field gradient spin (PFGSE) or stimulated echo measurements, which can be used to distinguish the NMR signals from species of different sizes.
Abstract: Diffusion-ordered spectroscopy (DOSY) is a mixture analysis technique based on pulsed field gradient spin (PFGSE) or stimulated (PFGSTE) echo measurements. In such experiments, the measured signal intensity depends on timing, diffusion coefficient, and gradient amplitude, so measurements made with a range of gradient strengths allow the diffusion coefficients for different signals to be determined. Since the diffusion coefficient is characteristic of a given molecule, the NMR signals from species of different sizes can be distinguished. The name DOSY refers to the use of a set of diffusion-attenuated spectra to synthesize a multidimensional spectrum in which signals are spread out according to diffusion coefficient in one of the dimensions. Thus, in an ideal 2-D DOSY spectrum, all the signals of a given species appear at the same diffusion coefficient, allowing the NMR spectra of complex mixtures to be analyzed. In this article, the principles of DOSY are explained, practical methods of data acquisition and analysis are discussed, and examples are given both of 2-D and 3-D DOSY spectra and of multivariate analysis of DOSY data.
Keywords:
DOSY;
pulsed field gradients;
diffusion;
diffusion-ordered spectroscopy
46 citations
TL;DR: Measurement of diffusion-weighted NMR spectra as a function of time allows the time-dependence of concentration and the isolated spectrum to be found for each component in a reaction, without prior assumptions about spectra, kinetics or diffusion behaviour, by data decomposition using the PARAFAC algorithm.
38 citations
TL;DR: An improved constant time gradient HSQC–iDOSY pulse sequence is presented, and the corresponding form of the Stejskal–Tanner equation is derived.
Abstract: An improved constant time gradient HSQC-iDOSY pulse sequence is presented, and the corresponding form of the Stejskal-Tanner equation is derived. The pulse sequence is particularly well suited to the problem of analysing mixtures of chemically cognate species, where the high spectral resolution afforded by H-1-C-13 correlation methods is needed for DOSY experiments to give good diffusion resolution. Its use is illustrated for a mixture of rutin and its aglycone quercetin. Copyright (C) 2009 John Wiley & Sons, Ltd.
26 citations
TL;DR: In order to improve the ability of DOSY to distinguish between different species, relaxation has been incorporated into diffusion experiments, as a further dimension, resulting in a locally trilinear data set which can be decomposed with multivariate statistical methods such as PARAFAC.
Abstract: DOSY (diffusion-ordered spectroscopy) is one of the most commonly employed methods for identifying compounds in mixtures by nuclear magnetic resonance (NMR). However, it struggles to resolve component spectra when there is severe signal overlap and/or diffusion coefficients are very similar. In order to improve the ability of DOSY to distinguish between different species, here, relaxation has been incorporated into diffusion experiments, as a further dimension. This results, to a first approximation, in a locally trilinear data set which, in contrast with a bilinear data set (e.g., a standard DOSY data set), can be decomposed with multivariate statistical methods such as PARAFAC (parallel factor analysis). This enables overlapping multiplets from different species, and by extension whole spectra, to be separated.
24 citations
TL;DR: A study of the acyl nitroso Diels-Alder (ANDA) reaction of sorbate esters and sorbic alcohol derivatives, using alkoxycarbonyl nitro so dienophiles, and presents a novel HMBC/HSQC ((1)H-(15)N) criterion for ready distinction of regioisomers arising from such ANDA reactions.
Abstract: We present a study of the acyl nitroso Diels–Alder (ANDA) reaction of sorbate esters and sorbic alcohol derivatives, using alkoxycarbonyl nitroso dienophiles. An optimisation of the reaction conditions for ethyl sorbate is first presented, and the product is used in an efficient synthesis of 5-methylornithine. Structure–reactivity trends in sorbic alcohol (E,E-2,4-hexadien-1-ol) and its acylated analogues are then discussed. We present single-crystal X-ray structural proof for key adducts in both series and present in detail a novel HMBC/HSQC (1H–15N) criterion for ready distinction of regioisomers arising from such ANDA reactions.
13 citations