Characterization of Dimethylsulfoxide / Glycerol Mixtures: A Binary Solvent System for the Study of "Friction-Dependent" Chemical Reactivity

The properties of binary mixtures of dimethylsulfoxide and glycerol, measured by several techniques, are reported. Special attention is given to those properties contributing or affecting chemical reactions. In this respect the investigated mixture behaves as a relatively simple solvent and it is especially well suited for studies on the influence of viscosity in chemical reactivity. This is due to the relative invariance of the dielectric properties of the mixture. However, special caution must be taken with specific solvation, as the hydrogen-bonding properties of the solvent changes with the molar fraction of glycerol.Comment: 49 pages including appendix, 20 figures and 89 reference

Rapid Multidimensional NMR: High Resolution by Spectral Aliasing

Spectral aliasing consists in setting the spectral window of multidimensional NMR experiments below the full range of chemical shifts in order to increase the spectral resolution. The improvement factor can reach two orders of magnitude when applied to small molecules. The ambiguities in the observed chemical shifts can be resolved using diverse sources of complementary information discussed in the article. The advantages of spectral aliasing are very easy implementation with almost any standard pulse sequence, and reliance on the classical linear sampling of data points processed using the Fourier transform. Applications to small molecules and proteins are discussed

High resolution in the indirectly detected dimension exploiting the processing of folded spectra

Multi-dimensional experiments using proton detection such as HSQC are often used to study organic and bioorganic molecules. Whereas the resolution in the directly detected dimension is normally high, the resolution in the indirectly detected dimension is often much lower, limiting the unambiguous assignment to carbon or nitrogen atoms. The principle exploited here consists in taking advantage of the fact that spectral resolution increases when spectral widths are reduced. The price to pay for such resolution enhancement is that signals fold into the smaller window, making their chemical shift ambiguous. The software presented here efficiently assists spectroscopists to choose the correct chemical shift out of a large number of possibilities. It checks for their compatibility with signals in reference spectra. When the indirectly detected dimension is not too crowded, such processing is straightforward and unambiguous. It thereby permits one to attain the natural linewidth in the indirectly detected dimension. In the case of HSQC spectra it reaches the resolution available in proton decoupled one-dimensional spectra. A program for processing folded two-dimensional spectra is available. It was applied to the 1H- 13C HSQC of cholesterol

Human- and computer-accessible 2D correlation data for a more reliable structure determination of organic compounds

The introduction of a universal data format to report the correlation data of 2D NMR spectra such as COSY, HSQC and HMBC spectra will have a large impact on the reliability of structure determination of small organic molecules. These lists of assigned cross peaks will bridge signals found in NMR 1D and 2D spectra and the assigned chemical structure. The record could be very compact, human and computer readable so that it can be included in the supplementary material of publications and easily transferred into databases of scientific literature and chemical compounds. The records will allow authors, reviewers and future users to test the consistency and, in favorable situations, the uniqueness of the assignment of the correlation data to the associated chemical structures. Ideally, the data format of the correlation data should include direct links to the NMR spectra to make it possible to validate their reliability and allow direct comparison of spectra. In order to take the full benefits of their potential, the correlation data and the NMR spectra should therefore follow any manuscript in the review process and be stored in open-access database after publication. Keeping all NMR spectra, correlation data and assigned structures together at all time will allow the future development of validation tools increasing the reliability of past and future NMR data. This will facilitate the development of artificial intelligence analysis of NMR spectra by providing a source of data than can be used efficiently because they have been validated or can be validated by future users

Damien Jeannerat, maître d’enseignement et de recherche au Département de chimie organique de Faculté de sciences de l'UNIGE. <p>--------</p>Damien Jeannerat, senior Lecturer in the Department of Organic Chemistry at the Faculty of science at UNIGE.

Damien Jeannerat, maître d’enseignement et de recherche au Département de chimie organique de Faculté de sciences de l'UNIGE. --------Damien Jeannerat, senior Lecturer in the Department of Organic Chemistry at the Faculty of science at UNIGE

Exemple d’élément de spectre RMN avec les données au nouveau format NMReDATA.<p>--------</p>An example of NMR spectra data using the new NMReDATA.

Exemple d’élément de spectre RMN avec les données au nouveau format NMReDATA.--------An example of NMR spectra data using the new NMReDATA

Computer Optimized Spectral Aliasing in the indirect dimension of 1H- 13C Heteronuclear 2D NMR experiments. A new algorithm and examples of applications to small molecules

A new algorithm for optimizing spectral width in the indirect dimension of heteronuclear 2D experiments is introduced. It takes a list of carbon chemical shifts as input and calculates the optimal spectral width and number of time increments to use in the carbon dimension of 2D experiments such as HSQC, HMBC, etc. When using optimized conditions where signals are better distributed along the carbon dimension, the number of time increments needed to resolve all of the signals is reduced by one to two orders of magnitude. This decreases the experimental time by the same factors and makes the acquisition of spectra such as HSQC-TOCSY, HSQC-NOESY, etc. more practical. The new algorithm allows users to limit the maximal t(1) evolution time when relaxation is a concern, and can take lists of carbons that do not need to be resolved. For any carbon, insights regarding the position of signals in the proton dimension increase the efficiency of the optimization by allowing the overlap of pairs of carbons with incompatible proton dispersions. The application of a second optimization using a fully-resolved spectrum as a source of proton dispersion for the carbons allows the number of time increments to be reduced further. Application to cyclosporine A shows that the time taken to acquire fully resolved HSQC spectra can be 126 times less than would be required in a full-width spectrum with the same resolution. The most interesting applications concern experiments where series of HSQC-based experiments have to be acquired, for example in relaxation time measurements. It is shown that the acquisition of quickly acquired series of selective-TOCSY-HSQC can facilitate assignment in carbohydrates. Computer-optimized spectral aliasing (COSA) generally requires no modification of the pulse sequence and can therefore be easily applied by non specialists