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Selective radiofrequency multiplet single line excitation to interpret complicated multicomponent systems spectra

Keywords:

M.G. Morozov – Post-graduate Student, Faculty of Physics, Southern Federal University (Rostov-on-Don). E-mail:morozov.rf.nmr@gmail.com Yu.E. Chernysh – Dr. Sc. (Chem.), Southern Federal University (Rostov-on-Don). E-mail: yu.chern@rambler.ru G.P. Sinyavsky – Dr. Sc. (Phys.-Math.), Professor, Head of Department, Southern Federal University (Rostov-on-Don). E-mail: sinyavsky@sfedu.ru


There are many different ways to determine the structure of molecules and study their dynamic behavior. However, their success re-quires not only the proper equipment, but also the appropriate methods by which it is possible to perform optimal measurements of the spectral parameters and to conduct a thorough assessment of nuclear magnetic resonance (NMR) spectra. At present there are many non-selective and semi-selective NMR experiments devoted to the investigation of molecular behavior in liquids or the solid state, each associated with particular pulse sequence. Accordingly we would like to propose a new approach – Multiplet Single Line Excitation (MUSLE). The new experiment makes use of a two-pulse sequence, a combination of a single-line selective pulse and a nonselective pulse, or of two selective pulses. Each scheme is suitable for a specific dynamic NMR problem. Here we discuss the application to a weakly-coupled spin system AX, calculated according to the product operator formalism. Knowing of chemical shifts leads to decoding complex big molecules, that is reached due to simple combination of semi-selective and selective excitation. In this way each resonance signal is excited selectively that makes the free precession of multiplet signal resonance lines possible. Afterwards the Fourier transformation generates multiplet sub-spectra corresponding to the chosen resonance signal site. The series of these sub-spectra creates usual spectrum that represents all chemical shifts and couplings. By using selective excitation the chosen spectral lines group is excited in the way not to overlap neighbor groups. The radiation selectivity is reached by respectively «soft» pulses of long duration. The pulses intensity is set in such way that only chosen group of lines is greatly exposed, but excitation of other lines should be negligible small. In the limit one can excite just single line of the spin multiplet.
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