Diffusion editing

In an experiment, tcp is to be varied systematically to obtain the 2D data matrix. For the spin-echo and stimulated-echo based sequences, molecular diffusion causes signal decay in the first segment, thus both are called diffusion-editing sequences. 

Two-dimensional D-T2 map generated from saturation of53%was measured. Figure taken the diffusion-editing measurements and ana- from Ref. [58] with permission, lyzed using FLI. There are two distinct peaks... 

When the measurement of a distribution of diffusivity is desired, improved signal-to-noise is needed. This can be achieved by using a diffusion-editing pulse sequence [7] rather than the CPMG sequence with varying echo spacing. This... 

NMR interpretation has made significant advances with diffusion-editing pulse sequences and two-dimensional inversion of diffusivity and T2 relaxation [7,40-44]. The 2D inversion can also be used to compare Tj and T2 relaxation with each other [42]. Distributions of these two characteristic parameters can now be displayed on a 2D map and the relationship between them more easily visually interpreted. The 2D distribution map can be interpreted by comparing the measured distribution with the line for the bulk diffusivity of water and the correlation lines for the hydrocarbon components in crude oils, shown in Figure 3.6.10 as dashed lines [40-46]. Figure... 

M. Flaum, J. Chen, G. J. Hirasaki 2004, NMR Diffusion Editing For D-T2 Maps Application To Recognition Of Wettability Change, Petrophysics 46 (2), 113-123. 

As noted by Liu et al. [42], there is a resurgence of interest in measuring diffusion coefficients using NMR spectroscopy, particularly in complex biological fluids which contain a number of molecules having a broad range of molecular weights and concentrations. These authors demonstrated the use of two-dimensional diffusion-edited total correlation NRM spectroscopy to measure diffusion coefficients in human blood samples. 

M Lui, JK Nicholson, JA Parkinson, JC Lindon. Measurement of bimolecular diffusion coefficients in blood plasma using two-dimensional 1II-1 II diffusion-edited total-correlation NMR spectroscopy. Anal Chem 69 1504-1509, 1997. 

Hajduk, P. J., et al., One-dimensional relaxation- and diffusion-edited NMR methods for screening compounds that bind to macromolecules. J Am ChemSoc, 1997,119,12257-12261. 

On the basis of data from DOSY and diffusion editing, we now know that the components soluble in aqueous base tend not to be macromolecular (Simpson et al., 2002), at least not to the extents considered previously. More detail needs to be known about the nature of the associations that give pseudo-macromolecular properties. 

Diffusion edited JH NMR spectroscopy DE Only large molecules, macromolecular domains, and stable aggregates are observed. Often simplifies the ID H as signals from small molecules (including solvents and water) are removed. A very powerful approach that is underutilized. Diffusion editing is relates to molecular selfdiffusion in solution. It should not be confused with spin diffusion in solids, which is completely unrelated. 

Lin M, Shapiro MJ, Wareing JR, Diffusion-edited NMR affinity NMR for direct observation of molecular interactions, J. Am. Chem. Soc., 119 5249-5250, 1997. 

All the spectroscopic approaches applied for structural characterization of mixtures derive from methods originally developed for screening libraries for their biological activities. They include diffusion-ordered spectroscopy [15-18], relaxation-edited spectroscopy [19], isotope-filtered affinity NMR [20] and SAR-by-NMR [21]. These applications will be discussed in the last part of this chapter. As usually most of the components show very similar molecular weight, their spectroscopic parameters, such as relaxation rates or selfdiffusion coefficients, are not very different and application of these methodologies for chemical characterization is not straightforward. An exception is diffusion-edited spectroscopy, which can be a feasible way to analyze the structure of compounds within a mixture without the need of prior separation. This was the case for the analysis of a mixture of five esters (propyl acetate, butyl acetate, ethyl butyrate, isopropyl butyrate and butyl levulinate) [18]. By the combined use of diffusion-edited NMR and 2-D NMR methods such as Total Correlation Spectroscopy (TOCSY), it was possible to elucidate the structure of the components of this mixture. This strategy was called diffusion encoded spectroscopy DECODES. Another example of combination between diffusion-edited spectroscopy and traditional 2-D NMR experiment is the DOSY-NOESY experiment [22]. The use of these experiments have proven to be useful in the identification of compounds from small split and mix synthetic pools. 

Dyrby, M., Petersen, M., Whittaker, A.K., Lambert, L., Norgaard, L., Bro, R., and Engelsen, S.B., Analysis of lipoproteins using 2D diffusion-edited NMR spectroscopy and multi-way chemometrics, Analytica Chimica Acta, 531, 209-216, 2005. 

New methods for editing TOCSY NMR spectra of biofluids have been proposed based on differences in molecular diffusion coefficients and this has been termed Diffusion Edited TOCSY (DETOCSY). This approach complements the editing of TOCSY NMR spectra based on coherence selection and promises to provide an efficient alternative strategy for assignment of resonances in complex mixtures such as biofluids and cell extracts. - ... 

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