Pulse-power Fourier transform spectroscopy

In the last three decades, nuclear magnetic resonance has become a powerful tool for investigating the structural and physical properties of matter. Today, nuclear magnetic resonance is the physical method most widely used in analytical chemistry. For special applications, e.g. relaxation time measurements, there is available a variety of modifications of the basic nuclear magnetic resonance experiments such as pulse and spin-echo methods. In the course of this development and when electronic computers were provided at a reasonable price, Fourier transform spectroscopy was applied to nuclear magnetic resonance in the middle of the sixties. At that time, Fourier methods were already used to a large extent in far infrared spectroscopy (see Refs. and references cited therein). 

While the two problems mentioned so far occur also in infrared Fourier transform spectroscopy , we have now to consider problems that are specific of FTNMR, Fig. 13 schematically describes a spectrometer for FTNMR. One coil is used to apply the 90°-pulse from the rf-generator (frequency cUr) and the power amplifier to the sample and to pick up the FID signal from the latter. After amplification, this rf-signal is mixed with the reference frequency co to obtain, after filtering the audio signal... 

New techniques for data analysis and improvements in instrumentation have now made it possible to carry out stmctural and conformational studies of biopolymers including proteins, polysaccharides, and nucleic acids. NMR, which may be done on noncrystalline materials in solution, provides a technique complementary to X-ray diffraction, which requires crystals for analysis. One-dimensional NMR, as described to this point, can offer structural data for smaller molecules. But proteins and other biopolymers with large numbers of protons will yield a very crowded spectrum with many overlapping lines. In multidimensional NMR (2-D, 3-D, 4-D), peaks are spread out through two or more axes to improve resolution. The techniques of correlation spectroscopy (COSY), nuclear Overhausser effect spectroscopy (NOESY), and transverse relaxation-optimized spectroscopy (TROSY) depend on the observation that nonequivalent protons interact with each other. By using multiple-pulse techniques, it is possible to perturb one nucleus and observe the effect on the spin states of other nuclei. The availability of powerful computers and Fourier transform (FT) calculations makes it possible to elucidate structures of proteins up to 40,000 daltons in molecular mass and there is future promise for studies on proteins over 100,000... 

The properties of weakly bonded van der Waals complexes in reactive systems are studied by pulsed Fourier Transform microwave spectroscopy, which is a powerful tool for investigating many complexes. 

A quite different approach to radiofrequency, microwave and infrared spectroscopy is that known as Fourier transform (FT) spectroscopy. As we shall see, this method of recording the spectra of transient molecular species is particularly appropriate in combination with the use of pulsed gas nozzles. For this reason it has proved to be a powerful technique for the study of weakly bound dimer complexes formed in supersonic gas expansions. It has, however, also been used for the study of diatomic molecules, both... 

The single most important development in nuclear magnetic resonance (NMR) spectroscopy since the initial observation of the NMR phenomenon in bulk phases in 1945 was undoubtedly the introduction of pulse Fourier transform NMR by Anderson and Ernst. This technique provided greatly increased sensitivity per unit time, making it feasible to obtain spectra for low sensitivity/low abundance nuclei such as More importantly, it allowed the development of a wide variety of sophisticated and powerful multipulse experiments which have revolutionized the use of NMR spectroscopy in studies of molecular structure and dynamics. This article provides an overview of pulse sequence experiments. Many individual experiments are discussed in other articles. 

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