Konstantin Ivanov, RU: Field-cycling NMR experiments in ultra-wide magnetic field range: relaxation and coherent polarization transfer

When: Monday, 11.5.2020, 16:00

Where: Joseph Loschmidt Lecture Hall, Faculty of Chemistry, Waehringerstrasse 42, 1090 Vienna

Fast-field cycling NMR methods offer the possibility to study various spin phenomena over a wide range of external magnetic fields. For instance, studies of NMR relaxation allow one to probe molecular mobility in different samples, including polymers, liquid crystals, biomolecules, etc. In recent years, studies of hyperpolarized nuclear spin systems at variable fields have become important for optimizing NMR signal enhancements of specific nuclei of choice.

We describe an experimental method allowing fast field-cycling NMR experiments over a wide range of magnetic fields from 5 nT to 10 T. The method makes use a hybrid technique: the high field range is covered by positioning the sample in the inhomogeneous stray field of the NMR spectrometer magnet. For fields below 2 mT a magnetic shield is mounted on top to the spectrometer; inside the shield the magnetic field is controlled by a specially designed coil system. This combination allows us to measure T1-relaxation times and nuclear Overhauser effect parameters over the full range in a routine way. For coupled proton-carbon spin systems relaxation with a common  is found at low fields, where the spins are “strongly coupled”. In some cases, experiments at ultralow fields provide access to heteronuclear long-lived spin states.

Efficient coherent transfer of polarization in heteronuclear spin systems, which is observed at ultralow fields, paves the way to a number of exciting experiments. Such transfer can be revealed by observation of quantum oscillations in the polarization evolution. Polarization transfer at ultralow fields can be efficiently exploited for polarizing “insensitive” NMR nuclei, such as 13C and 15N, by polarization transfer from primarily polarized protons, which is the case in parahydrogen induced polarization experiments. Transfer of polarization among heteronuclei can be utilized for designing novel 2D-NMR experiments, in which spin mixing is occurring at ultralow fields.

Prof. Dr. Konstantin L. Ivanov, Director of the International Tomography Center, Novosibirsk (Russia), http://www.tomo.nsc.ru/en/mtc/administrativno-upravlencheskiy-personal/

Faculty Colloquium Series - programme of summer term 2020

For students: If at least three of the four lectures have been attended, this course will have a credit of 0.5 ECTS.

(Copyright: Konstantin L. Ivanov)