Optical Rotation Constitutes a Novel Method for Nuclear Magnetic Resonance (NMR) Detection

07.10.2010

NMR is one of the most widely used techniques for characterization of materials and their properties. It has been proposed that magneto-optic effects involving circularly or linearly polarized light impinging on a sample could greatly enhance the sensitivity and spatial resolution of the NMR method. Novel theoretical description and first-principles computational evaluation nuclear spin optical rotation (NSOR) reveals optical chemical shifts between the signals observed for chemically non-equivalent nuclear sites. Through this discovery, a viable alternative to conventional NMR may be obtained.

In the Faraday effect, the magnetic field due to spin-polarized nuclei rotates the plane of polarization of an incident beam of linearly polarized light. This rotation angle, the NSOR, should convey distinct signals for non-equivalent nuclei in different chemical surroundings in order to provide information on molecular structure. First-principles electronic structure calculations carried out by the Molecular Magnetism and NMR Research groups at the Universities of Helsinki and Oulu have proven the existence of such chemical distinction between different molecules as well as for non-equivalent nuclei in the same molecule.

Calculations of the proton NSOR in the water molecule were found to be in quantitative agreement with recent groundbreaking experiments. It was also seen that 17O in water should convey a much larger signal. The magnitude of the effect is massively amplified if the wavelength of the laser in use is close to an optical resonance. Calculations involving wavelengths close to resonance for a retinal model exhibit enhanced distinction between chromophores. These theoretical predictions strongly encourage further experimental work.

Large-scale density-functional theory (DFT) quadratic response calculations using up to 128 parallel cores were carried out in the supercomputers of CSC and the local Linux cluster facilities in Helsinki and Oulu.

The work is due to a Finnish team consisting of M.Sc. Suvi Ikäläinen, docent, academy research fellow Perttu Lantto, and prof. Juha Vaara, in collaboration with the leading experimentalist in the field, prof. Michael V. Romalis of Princeton University. The project has been carried out within the Finnish Center of Excellence in Computational Molecular Science (CMS) funded by the Academy of Finland.

Additional information:

Prof. Juha Vaara, e-mail:  juha.vaara at oulu.fi, tel. +358 8 553 1343

S. Ikäläinen, M. V. Romalis, P. Lantto, and J. Vaara:
Chemical distinction by nuclear spin optical rotation,
Physical Review Letters 105, 153001 (2010).

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