Double resonance structure for NMR and EPR measurements
INNOVECTIS Gesellschaft für Innovations-Dienstleistungen mbH
Nuclear magnetic resonance spectroscopy (NMR) is one oft he most important methods to elucidate the structure and dynamics of molecules, especially biomolecules. In studies of such molecules, the sensitivity of the spectrometer is a limiting factor.
The present invention solves this problem by a double resonance structure for a combined NMR/EPR spectrometer (EPR = Electron Para-magnetic Resonance) for the investigation of liquid samples by using DNP and/or ENDOR experiments (DNP = Dynamic Nuclear Polarization, ENDOR = Electron Nuclear Double Resonance).
The use of double resonance structures for DNP and ENDOR is already known. These structures usually consist of a cylindrical microwave resonator, also called helix resonator, producing a high-frequency magnetic field which is required for the experiments.
Disadvantage of this technique is the limited-purpose volume of samples for the examination. On the one hand, they are limited because of the dimension of the helix resonator which correlates to the wavelength of the excited microwave. On the other hand, large volumes of liquid, particularly aqueous samples are heated up, because of microwave irradiation.
The new double-resonant structure is formed by a combination of a strip resonator for generating high-frequency fields for NMR transitions and a microwave resonator for EPR transitions. Simultaneously, a part of the strip resonator acts as a flat mirror of the microwave resonator. There, irradiating microwaves are reflected quasi-optical. Thus, an open double-resonant structure, which offers enough space for the measurement of an up to 10 times higher sample volume (200 nl) compared to known helix resonators, is built.
Moreover the flat mirror forms a sample plate,which is used due to its good thermal conductivity as a heat sink. This allows investigations of larger volumes of liquid samples.
In addition, the arrangement has got a spherical mirror, comprising an iris, through which microwaves can be fed in the microwave resonator.
In Simulations it was shown, that the new double-resonant structure not only generates an increased magnetic high-frequency signal but also a strong magnetic microwave field within the sample, which shows a very homogeneous distribution.
Therefore a spectrometer with high signal sensitivity and high spectral resolution is provided. Alternatively, it is possible to form the high-frequency resonator, not only from a single strip resonator, but also from a number of parallel arranged electrically conductive strips. Compared to the use of only one stripe, the use of a number of stripes increases the resonators conversion factor. On the one hand, this provides a higher magnetic field strength. On the other hand an increased NMR-measuring sensitivity is achieved.
The new double structure is used for example in DNP experiments for the structural analysis of biomolecules, identification and monitoring of contaminants or to investigate dynamic molecular interactions.
Applications in ENDOR experiments are mainly in the investigation of defects in semiconductors, the chirality and fullerenes. Thus, the applications range from medical diagnostics to the material science.
- Measurement of an approximately 10-fold larger sample volume (200 nl) in comparison to known helix resonators
- Avoidance of overheating of the samples
- Improvement of the sensitivity and spectral resolution of DNP and ENDOR experiments
- reduces measurement times
- Easily implementable construction
A prototype of the invention has been designed and tested.
A German patent application is filed. There is another national application in USA.
Owners of the patent are Johann Wolfgang Goethe-Universität Frankfurt am Main and Johannes Gutenberg-Universität Mainz.
Licensing or assignment of the technology is possible as well as a cooperation for further development of the invention.