DOSY analysis

Sawada H, Takami K, Asahi S. A toxicogenomic approach to drug-induced phosphoUpi-dosis Analysis of its induction mechanism and establishment of a novel in vitro screening system. Toxicol Sci 2005 83 282-292. 

A detailed analysis of the proton high field NMR spectra of tomato juice and pulp has recently been acquired [15]. The combination of suitable selective and two-dimensional techniques (J-resolved, COSY, TOCSY, DOSY, etc.) was used for... 

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. 

Linssen and de Vries [285] have examined 1 % di-f-butyl-p-cresol (DBPC) in low-MW poly(tetrahydro-furan) by means of DOSY (Figure 5.13). DOSY is a powerful tool for the analysis of polydisperse samples and complex mixtures, such as anionic surfactants. It is not to be expected that DOSY will rapidly become a standard tool in polymer/additive analysis. 

The use of NMR continues to improve existing methods, and to develop new concepts. By cleverly combining existing pulse-sequences, new sequences are formed with improved properties. An example is the combination of the COSY and DOSY sequence to a new 3D-NMR COSY-IDOSY sequence with improved sensitivity, a 32-fold decrease in experiment time, and an improved resolution resulting in better data analysis [34]. 

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. 

S. Trefi, C. Routaboul, S. Hamieh, V. Gilard, M. Malet-Martino and R. Martino, Analysis of illegally manufactured formulations of tadalafil (Cialis ) by H NMR, 2D DOSY H NMR and Raman spectroscopy, J. Pharm. Biomed. Anal, 47, 103-113 (2008). 

The HR-DOSY method outlined here is potentially a very powerful tool for the NMR analysis of complex mixtures. There are significant technical challenges in its successful implementation, but early results suggest that the method could greatly reduce the labour involved in analyzing complex mixtures such as biofluids and tissue extracts. 

In secondary ion mass spectrometry (SIMS) the sample surface is sputtered by an ion beam and the emitted secondary ions are analyzed by a mass spectrometer (review Ref. [360]). Due to the sputtering process, SIMS is a destructive method. Depending on the sputtering rate we discriminate static and dynamic SIMS. In static SIMS the primary ion dosis is kept below 1012 ions/cm2 to ensure that, on average, every ion hits a fresh surface that has not yet been damaged by the impact of another ion. In dynamic SIMS, multiple layers of molecules are removed at typical sputter rates 0.5 to 5 nm/s. This implies a fast removal of the topmost layers of material but allows quantitative analysis of the elemental composition. 

The study of the composition of a mixture is an extremely common problem in analytical and bioanalytical chemistry. While chromatography and solvent extraction are commonly employed to simplify the analysis prior to characterization of the constituents, NMR has provided a series of tools that help in unravelling the components of complex samples, when a previous separation of the pure compounds is not feasible or complete. Thus, TOCSY, NMR diffusometry (DOSY, among all) and heteronuclear correlation experiments are widely used to this purpose, for example, for the characterization of small molecules in biologically relevant samples, such as in metabolomics,1 plant extracts analysis,2 food quality control,3 4 to name a few cases. 

Conventional methods for mixture analysis have been supplemented by DOSY (see Section X.B), which could be useful when the components differ in molecular size. While... 

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. 

Barjat H, Morris GA, Smart S, Swanson AG, Williams SCR, High-resolution diffusion-ordered 2-D spectroscopy (HR-DOSY)—A new tool for the analysis of complex mixtures, /. Magn. Reson. B, 108 170-172, 1995. 

Giuseppone N, Schmitt J-L, Allouche L, Lehn J-M (2008) DOSY NMR experiments as a tool for the analysis of constitutional and motional dynamic processes implementation for the driven evolution of dynamic combinatorial libraries of helical strands. Angew Chem Int Ed 47 2235-2239... 

Analysis of the genuine formulation of Cialis using conventional and 2D DOSY... 

Trefi, S., Gilard, V., Balayssac, S., et al. (2008) Quality assessment of fluoxetine and fluvoxamine pharmaceutical formulations purchased in different countries or via the Internet by 19F and 2D DOSY I I NMR. Journal of Pharmaceutical and Biomedical Analysis, 46(4), 707-722. 

The method has been given the name DOSY for diffusion-ordered spectroscopy. It is related to mobility-ordered spectroscopy (MOSY) for analysis of electrophoretic mobilities [Heil, Holl, Joh2, Mor4]. By using shielded gradients with amplitudes larger than... 

In the case of 2D diffusion-weighted NMR spectra a transformation exists, which is able to transform the second dimension directly into the desired diffusion coefficient (D). In this form, the spectra are known as 2D DOSY and the diffusion coefficients can be extracted directly without using further mathematical analysis. However, this transformation - the inverse Laplace transform - is ill-posed, i.e. the solution can be highly inaccurate without adequate regularisation. A wiser choice may be to analyse the original diffusion-weighted data using three-way methods, as exemplified in Section 3.3. 

Examples of the application of MCR to both 2D DOSY NMR data23 and 3D [jH-15N] HSQC NMR data24 can be found. In the latter case, the reaction between 15N-labelled cisplatin and the amino acid-nucleotide hybrid (Phac-met-linker p5 dG) is monitored and both analysis of the individual 2D HSQC spectra as well as the simultaneous analysis of all 2D HSQC spectra over time is performed in which case the kinetic reaction profiles can be obtained. The authors found that sub-structures involved in local unfolding as a consequence of the addition of denaturant could be identified, and that this would hardly have been possible without multivariate analysis of the data. 

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

In this section, we shall consider the operation of more widely used diffusion sequences and their variants, and consider methods for processing the acquired data. This essentially falls into two possible approaches, either direct regression analysis to provide values of the diffusion coefficients or treatments that present the pseudo-2D DOSY spectra mentioned above. To understand the process of measuring diffusion coefficients by NMR, we shall first consider the simplest gradient spin-echo experiment. 

---