Avances en resonancia magnética nuclear ultrarrápida

Abstract

Multidimensional nuclear magnetic resonance plays a number of essential roles in present day spectroscopy. It is also an integral part of the image formation protocol in magnetic resonance imaging (MRI). Traditional two-dimensional experiments are intrinsically time consuming because many t1 increments have to be acquired to obtain two-dimensional spectra with adequate digital resolution in the indirect dimension. Proposals for accelerating multidimensional NMR spectroscopy, including non-Fourier transform schemes, the acquisition of multiple NMR spectra in a single experiment, and ultrafast multidimensional NMR spectroscopy, also called UF-NMR, have been introduced. The latter methodology was inspired by echo planar imaging (EPI) and was developed by Frydman et al. It permits the collection of complete multidimensional NMR data sets within a single continuous acquisition.This new methodology offers an enormous improvement in speed for multidimensional NMR measurements. In this regard, a typical two-dimensional experiment can be completed in less than a second. This attractive feature enables ultrafast NMR to examine dynamic processes, that is, organic reactions and their mechanisms, as they happen in real time. To achieve this goal, some drawbacks related to the management of the technique must be overcome. In this thesis the author first focuses on the implementation of this new technique in standard NMR spectrometers and, secondly, on the evaluation and optimization of the different features of the UF-NMR sequences in order to apply these new methods to the study of organic dynamic systems. The UF-NMR sequences are not available on commercial spectrometers. Therefore, the pulse programs must be generated. As these sequences don’t work in the same way as traditional experiments, it is necessary to develop new programs that calculate the appropriate acquisition parameters and process the acquired data in order to get the UF spectrum. The first step will be the development of the pulse program to carry out the socalled basic, or mixing-less, UF experiment. The author will write the programs that calculate the acquisition parameters that will yield the desired spectral widths, as well as those necessary for processing the data to obtain the spectrum. Then various spatialencoding schemes will be evaluated. Different acquisition parameters will be estimated in order to find the sets that yield the optimum spectrum. Different homo- and heteronuclear UF sequences will be developed in order to study scalar and dipolar correlations. For each sequence, the optimum parameters will be evaluated...