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Orientation effects of aromatic compounds in isotropic media as studied by total-line-shape analysis of 1H NMR spectraтезисы доклада
- Авторы: Sheberstov K.F., Cheshkov D.A., Chertkov V.A.
- Сборник: International Symposium and Summer School in Saint Petersburg “Nuclear Magnetic Resonance in Condenced Matter”, 10th Meeting “NMR in Life Sciences”, Saint-Peterburg
- Тезисы
- Год издания: 2013
- Издательство: Izd-vo Sankt-Peterburgskogo universiteta
- Местоположение издательства: Sankt-Peterburg, Russia (Federation)
- Первая страница: 111
- Последняя страница: 111
- Аннотация: Molecules with anisotropy of magnetic susceptibility exhibit partial orientation in strong magnetic field of the spectrometer. As a result, anisotropic nuclear spin interactions are incompletely averaged and thus residual couplings may show up in high-resolution NMR spectra. Thus, line widths, intensities and positions of peaks can be affected, and even additional line-splittings could be observed. Taking into account these orientation effects allows escape accuracy errors in interpreting spectra and also offers additional information about structure and properties of molecules studied. For the first time, we designed a computer program for total-line-shape analysis of 1H NMR spectra including dipole-dipole residual constants in calculations. Our algorithm separates contributions of the indirect coupling from the direct dipole-dipole coupling. Dipolar couplings D linearly depend on the squared magnetic induction B02. Thus, the program performs combine computation of the two spectra obtained in different magnetic fields. In our work we studied 15N enriched cis- and trans-azobenzene, substituted naphthalenes, styrene and tetrahydrofuran in different isotropic solvents. Degassed and sealed-off in vacuum samples were used. Experimental spectra were pre-processed with reference deconvolution technique for getting narrower lines (Lorenzian-shaped, width at half-maximum ~ 0.1 Hz). A series of high-resolution 1H NMR spectra recorded at 7.04 T and 14.09 T magnetic fields were analyzed in the framework of a unified approach with highest possible accuracy, see figure 1. The spin-spin coupling constants and the dipole-dipole coupling constants for all pairs of 1H nuclei of studied molecules were estimated (values of D constants achieve tenths of mHz, while accuracy of analysis is about 0.5 mHz). Taking into account, the orientation effects improves in all cases R-factors of the fit. Character of the slope for the linear dependences on the squared magnetic induction B02 can be used for the determination of absolute signs of the spin-spin coupling constants. Thus we determined signes of a series of small but important for conformational analysis 1H-15N constants in 15N enriched azobenzene.
- Добавил в систему: Чертков Вячеслав Алексеевич