Diffusion ordered spectroscopy DOSY

Diffusion Ordered SpectroscopY (DOSY) is a solution 2D technique that is rapidly gaining importance, because it correlates NMR spectroscopic properties with a physical parameter that otherwise does not 

This enables us to determine the sizes of many molecules in solution independently, provided we have suitably separated resonances. Note that r refers to spherical objects molecules are not spherical, so these calculated radii do not have absolute meaning, and should only be used to compare molecules. 

Consider Ti -(C5Me5)SiN(SiMe3)2 (4.XXVI), which is colorless in solution, but forms intense yellow crystals, which are shown by X-ray diffraction to be dimeric (4.XXVII) [47]. The NMR spectra in CeDs solution do not distinguish between dimer and monomer structures. 

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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). 

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. 

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). 

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. 

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... 

The sole Nano-probe paper published in 2004 of which the author is aware was the study by Claeyssens and co-workers220 of the enzymatic hydrolysis products of Nothogenia erinacea seaweed xylan, which is a linear homopolymer with mixed / — (1 —3)// — (1 —4) linkages. The sequence of the residues was determined from a combination of nuclear overhauser effect spectroscopy (NOESY) correlations between the anomeric protons and a proton of the residue to which it is glycosidically linked and gHMBC data, that were acquired using Nano-probe capabilities. Finally, in early 2005, Bradley et al.221 compared the ability of cryogenic, Nano- and conventional NMR probes to acquire diffusion-ordered spectroscopy (DOSY) spectra of dilute mixtures of compounds. 

Fig. 10. Radiofrequency and gradient pulse sequence for diffusion-ordered spectroscopy (DOSY) owing to Morris and Johnson [1992] in which a PGSE pulse pair (Gj) represents the first (t,) domain and the acquisition time provides the second (tj) domain. Note the storage period 7], which allows for eddy current decay prior to data collection.

Often it is impossible to resolve the signals from different molecular species in complex polymer mixtures by simple ID- and 2D-NMR. However, development of diffusion-ordered spectroscopy (DOSY), which employs PEGs, provides another method of separating the resonances of different polymer species. In DOSY experiments, the normal ID spectrum is obtained in one dimension of the 2D spectrum and these spectra are dispersed in a second dimension based on the structure s diffusion coefficient. It is possible to resolve separate spectra of small monomer and large polymer molecules ... 

Morris, G.A. Diffusion-ordered spectroscopy (DOSY). End. Nucl. Magn. Reson. 2002,9, 35-44. 

There has also been a recent assessment of different methods for the processing of diffusion ordered spectroscopy (DOSY) NMR experiments. This included the evaluation of iterative single channel methods including single channel methods such as... 

One of the most important developments in the field of diffusion NMR in the last decade seems to be the introduction of diffusion-ordered spectroscopy (DOSY) by Johnson Jr. [15, 17]. DOSY vould appear to be one of the main reasons for the recent increase in popularity of diffusion NMR among non-expert users. This method uses the inverse Laplace transform (ILT), and provides a 2-D-map (like those in 2-D NMR) in which one axis is the chemical shift while the other is that of the diffusion coefficient. Figure 6.5 shows a simulated DOSY spectrum of four components having different diffusion coefficients. 

The basic idea behind the DOSY concept is similar to the one behind multidimensional NMR. In 2-D NMR, a modulation in the phase or signal intensity with respect to a known time increment is recovered by inverse FT. In a DOSY experiment, the diffusion coefficient is recovered from the signal decay as a function of a diffusion increment by an ILT. In fact, the approximate ILT of the signal amplitude with respect to q, where q is defined as ygSf (t), yields the second dimension of the spectrum which correlates the chemical shift with the diffusion coefficient. Therefore, it was termed diffusion ordered spectroscopy (DOSY). However, unlike the FT of the time domain signal that yields a unique solution, ILT does not yield a unique solution. Therefore, several software packages were developed to overcome this problem. Readers interested in more details concerning the DOSY techniques can consult a recent extensive review on the subject [17]. 

PNMR = Pulse gradient-field spin echo (PGSE) NMR, DNMR = diffusion ordered spectroscopy (DOSY) NMR, Elec = Electrochemistry, ENMR = fringe field NMR. 

For analysis of complex mixtures the quasi 2D diffusion-ordered spectroscopy (DOSY) method could be applied [22, 23]. 

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