Diffusion ordered spectroscopy

A. M. Gil, I. Duarte, E. Cabrita, B. J. Goodfellow, M. Spraul, R. Kerssebaum 2004, (Exploratory applications of diffusion ordered spectroscopy to liquid food an aid towards spectral assignment), Anal. Chim. Acta 506 (2), 215—223. 

The study of molecular diffusion in solution by NMR methods offers insights into a range of physical molecular properties. Different mobility rates or diffusion coefficients may also be the basis for the separation of the spectra of mixtures of small molecules in solution, this procedure being referred to as diffusion-ordered spectroscopy (DOSY) [271] (Figure 5.11). In this 2D experiment, the acquired FID is transformed with respect to 2 (the acquisition time). 

DOSY is a technique that may prove successful in the determination of additives in mixtures [279]. Using different field gradients it is possible to distinguish components in a mixture on the basis of their diffusion coefficients. Morris and Johnson [271] have developed diffusion-ordered 2D NMR experiments for the analysis of mixtures. PFG-NMR can thus be used to identify those components in a mixture that have similar (or overlapping) chemical shifts but different diffusional properties. Multivariate curve resolution (MCR) analysis of DOSY data allows generation of pure spectra of the individual components for identification. The pure spin-echo diffusion decays that are obtained for the individual components may be used to determine the diffusion coefficient/distribution [281]. Mixtures of molecules of very similar sizes can readily be analysed by DOSY. Diffusion-ordered spectroscopy [273,282], which does not require prior separation, is a viable competitor for techniques such as HPLC-NMR that are based on chemical separation. 

An important technical development of the PFG and STD experiments was introduced at the beginning of the 1990s the Diffusion Ordered Spectroscopy, that is DOSY.69 70 It provides a convenient way of displaying the molecular self-diffusion information in a bi-dimensional array, with the NMR spectrum in one dimension and the self-diffusion coefficient in the other. While the chemical-shift information is obtained by Fast Fourier Transformation (FFT) of the time domain data, the diffusion information is obtained by an Inverse Laplace Transformation (ILT) of the signal decay data. The goal of DOSY experiment is to separate species spectroscopically (not physically) present in a mixture of compounds for this reason, DOSY is also known as "NMR chromatography."... 

Olson, B.F. 1999. Analysis of the Diffusion Coefficients in Gelatinizated Starch-Water Systems over Time Using Diffusion-Ordered Spectroscopy . Masters Thesis, University of Illinois, Urbana-Champaign, IL. 

Pelta, M.D., Morris, G.A., Stchedroff, M.J., and Hammond, SJ. 2002. A one-shot sequence for high-resolution diffusion-ordered spectroscopy. Magn. Reson. Chem. 40, S147-S152. 

A complete NMR approach has been employed to evaluate the complexation process of catechin A with p-CD and synthetic analogues.125 The analysis of the variation of the proton chemical shifts indicated the formation of a 1 1 stoichiometric complex. 2D-ROESY provided detailed spatial information of the complex while the binding constants were obtained by using diffusion-order spectroscopy (DOSY) techniques. 

PGSE diffusion measurements can also be presented as a 2D spectrum where the chemical shift is displayed in the first dimension and the diffusion coefficient in the second one. Such an experiment is called DOSY (Diffusion Ordered Spectroscopy) [274, 322, 323] and has also been referred to as NMR chromatography , for its ability to facilitate and visualize the resolution and assignment of complex mixtures. Although used in several areas of chemistry, such as micelles [324], polymers [325-328], resins [329], biochemistry [330-332] and organic chemistry [333-336],... 

High Resolution Diffusion Ordered Spectroscopy TABLE 1... 

Nilsson, M. et al., high-resolution NMR and diffusion-ordered spectroscopy of Port wine, J. Agric. Food Chem., 52, 3736, 2004. 

Self-diffusion coefficients have been obtained by diffusion-ordered spectroscopy (DOSY [24,25]). For the [C2CiIm]Cl/AlCl3 system, the diffusion constants for all [CjCjIm] proton resonances were identical. A linear relationship between diffusion constants and conductivihes of the melts demonstrated the fact that the transport properties are determined by the molar quantities (and not by the properties of the individual ions). 

Wu, D. H., Ghen, A. D., and Johnson, C. S., An improved diffusion-ordered spectroscopy experiment incorporating bipolar-gradient pulses, /. Magn. Reson., Ser A, 115, 260,1995. 

Giernoth, R. and Bankmann, D., Application of diffusion-ordered spectroscopy (DOSY) as a solvent signal filter for NMR in neat ionic liquids., Eur.. Org. Chem., 4529,2005. 

Diffusions NMR spectroscopy (e.g. PGSE = Pulsed Gradient Spin Echo STE = Stimulated Echo DOSY = Diffusion Ordered Spectroscopy) is a straightforward and accurate method for determination of the self-diffusion coefficient of a molecule. Its principal use in dendrimer chemistry is for size determination of dissolved dendrimers since the self-diffusion coefficient is directly correlated with the hydrodynamic radius of the molecule via the Stokes-Einstein equation [24]. Although one-dimensional and multidimensional diffusion NMR experiments can thus make an important contribution to structural characterisation of dendrimers, they have been used comparatively rarely until recently [25, 26]. 

Diffusion-ordered spectroscopy (DOSY) provides a means for virtual separation of compounds by providing a 2D map in which one axis is the chemical shift, while the other is that of the diffusion coefficient. 45 The direct combination of 19F NMR and DOSY has been shown to be very useful for studying drug formulations with fluorine-containing compounds that are part of a complex mixture.46... 

Diffusion-ordered spectroscopy (DOSY)45 is a NMR spectroscopic technique that separates the NMR signals of different compounds according to their diffusion coefficient (D, their rate of diffusion in a particular medium). A series of spin echo spectra is measured with different pulsed field gradient strengths, and the signal decays are fitted to give diffusion coefficients for each compound present. In 2D DOSY this... 

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