Methodology

DNP (Dynamic Nuclear Polarization)

Nuclear Magnetic Resonance (NMR) is witnessing a revolution, being driven by the advent of new methods with high potential for achieving nuclear hyperpolarization. While NMR is a powerful spectroscopic tool for the characterization of molecular structure and dynamics in Chemistry and Biochemistry is well-established tool in medicine as an in vivo imaging (MRI) it suffers lack of sensitivity.  It has been recently demonstrated that new technologies based on dynamic nuclear polarization (DNP), whereby the large spin alignment characteristic of electron paramagnetic resonance is passed on to nuclear spins at low temperatures, can be used to increase the sensitivity of typical NMR and MRI experiments by >10,000 times. This dramatic gain in sensitivity promises nothing less than a true revolution in the application of magnetic resonance spectroscopy and imaging. NMR and MRI-oriented DNP experiments are currently being pursued in three different settings, each one seeking its own area of specific applications. These include (i) in situ solid-state DNP NMR investigations of the kind pioneered by Griffin et al at MIT, where polarization enhancements of ≈100-300 are sought at ≈90K and at the relatively high fields where actual high resolution solid state NMR measurements will take place; (ii) cryogenic (≈1K) solid-state DNP experiments where nuclear spins are aligned ≥10,000 times over their conventional degrees of order, and then suddenly melted and transferred to a spectrometer/scanner for an otherwise conventional liquid-state NMR/MRI measurement on the resulting metastable spin state; and (iii) in situ liquid high-field DNP NMR experiments, where polarization enhancements of ≈10 are obtained. Although there are numerous experimental results, of different amount and significance, among the three directions,  that show the potential of DNP, there are still many  open questions  and need for both methodological and technological development to realize the potential of the approach and turn it into a viable routine method.

Together with Prof. Shimon Vega and Dr. Akiva Feintuch we focus on understanding the underlying spin dynamics mechanisms of DNP. This is a project where high field EPR and NMR come together both in the experimental techniques, the instrumentation and the theoretical approach.  This project is part of a large German Israeli collaboration with Lucio Frydman (Weizmann), Thomas Prisner ( Frankfurt U.) and Hartmut oschkimat (Leibnitz Institute, Berlin).

Nanometer scale distance measurements in biomolecules

Methods for measuring nanometer scale distances between specific sites in bimolecules (proteins and nucleic acids) and their complexes are essential for analysis of their structure and function. In the last decade pulse EPR techniques, mainly pulse double-electron-electron resonance (DEER),  have been shown to be a very effective for measuring  distances between two spin labels attached to a bimolecule. DEER is routine for distances up to 5 nm and with some extra effort and favorable conditions distances as high as 8 nm can be accessed. So far such measurements have been applied mostly to biomolecules labeled with nitroxide stable radicals. The measurements are usually carried out at standard X-band frequencies (~9.5 GHz, 0.35 mT).

We are developing  new family of spin labels that are based on Gd³⁺ for DEER measurements at high frequencies, particularly W-band (95 GHz, ~3.5 T). The benefit such spin label offers is the considerable increase in sensitivity that reduces the amount of the biomolecule needed by more than an order of magnitude. Gd³⁺ has a spin of 7/2 and its unique ERP spectral properties turn it into an excellent spin label for distance measurements at high fields. 

This work is done in collaboration with Gottfried Otting and Thomas Huber (Australian national University), Arnold Raitsimring (University of Arizona),  Tom Meade(  Northwestern University), Songi Han and Mark Sherwin (University of California, Santa-Barbara).

High field Pulse EPR methodology

Although pulse EPR and ENDOR techniques are highly effective in the study of  paramagnetic systems, to fully exploit their potential , methods aiming at increasing the resolution and sensitivity need to be developed. In terms of hardware we are constantly improving our home build W-band spectrometer. In addition we concentrate on new experiments for sensitivity enhancement and design of  two-dimensional correlation experiments, involving electron-electron and electro-nuclear double or triple resonance experiments. Such techniques increase resolution and facilitate  signal assignment.