A Brief Review on Bioactive Compounds from Species

Abstract

Gas-phase multinuclear magnetic resonance (MR) spectra allow the total elimination of intermolecular effects from magnetic shielding in molecules. Consequently, the resonance frequencies of isolated atoms and molecules are also available for reading from MR spectra. Following the connectivity between nuclear magnetic moments, resonance frequencies of two different nuclei in the same MR experiment and the shielding of helium-3, it is demonstrated that the direct shielding measurement is available on a nuclear MR spectrometer. As shown, the shielding parameters can completely replace the chemical shifts of numerous nuclei. The new method has also many additional advantages; as it allows for example the direct comparison of experimental and theoretical shielding constants and makes possible the determination of the first order isotope effect in shielding, which was not available in nuclear MR spectroscopy before.