Instruments & Methods

In our laboratory we employ routine methods for materials characterization such as Small Angle X-ray Diffraction (SAX), transmission electron microscopy (TEM) and nitrogen absorption for surface area and pore size distribution. In addition we use Uv-vis spectroscopy for routine characterization of some of the proteins we work with.

In terms magnetic resonance spectroscopy (EPR and DNP), which is our specialty, we apply the following type of experimental techniques at both X- and W-band frequencies

Continuous wave EPR to record the EPR spectrum.
Pulse ENDOR (electron-nuclear double resonance) techniques to measure the nuclear frequencies (NMR) of nuclei coupled to the electron spin. From these we obtain the hyperfine and nuclear quadrupole interactions give the spatial and electronic structure.
ESEEM (electron spin echo envelope modulation) techniques that also provide NMR frequencies. In general, this family of methods can provide low nuclear frequencies that are difficult to observe in ENDOR. The ESEEM and ENDOR techniques are complementary. Two dimensional/experiments provide resolution and correlations needed for signal assignment.
ELDOR (electron-electron double resonance) - detected NMR. This is yet another double resonance based on the excitation of forbidden EPR transitions. It is particularly useful at high fields and closely related to DNP.
DEER (double electron-electron resonance) techniques which provide distances between paramagnetic centers in the range of 1.5-8 nm which we use it to trap intermediate in enzymatic reactions.
DNP (dynamic nuclear polarization) methods to enhance NMR signals through polarization transfer from electron spins.

We also have a special EPR freeze quench attachment to Biologic SFM300 stop-flow instrument which we use to investigate intermediate in enzymatic reaction.

Our spectrometers

X-band (9.5 GHz) pulse EPR spectrometer
Bruker Elexys 580 with electron-nuclear and electron-electron double resonance (ENDOR and ENLOR) capabilities and a temperature range of 3-300 K.

Home build pulsed/continuous wave W-band (95 GHz) spectrometer.
The spectrometer features electron – electron and electron nuclear double resonance capabilities (ENDOR and ENDOR). It employs a superconducting magnet with a solenoid-coil configuration that can reach a maximum field of 6T . The warm bore of 90 mm diameter is equipped with a superconducting sweep coil with permanent current leads to produce a sweep range of ±0.3 T. The magnet is fitted with a variable temperature insert with a temperature range from 2.5 to 300 K using liquid or gaseous helium for cooling. The probehead set-up is based on a cylindrical TE011 cavity, with an rf Helmholtz coil a round the cavity. In addition, there is a mechanism that allows for the rotation of the sample holder around the cavity axis for single-crystal measurements. Typical sample sizes are 0.8 mm o.d. tubes with a length of about 10 mm, out of which ~2 mm are in the active area of the cavity. A detailed description of the probehead in given in Reference 1, The MW bridge described in this reference has been replaced with a new bridge.
The new bridge features two pulse channels and a coherent heterodyne receiver. The two channels have independent frequency/power/phase controls. The maximum power at the output of the bridge is 700 mW. For the two channels π/2 pulse of 12-16 µs are easily achieved with a cavity with a Q~1000. Typical rf π pulses for protons (~144 MHz) are in the range of 15 -25 µs, whereas for deuterons it is ~ 40 µs.

The flexibility required for running multi-dimensional experiments and for implementing different acquisition modes is highly demanding in terms of the software that manages the spectrometer. Our spectrometer is controlled using SpecMan.

Home build W-band (95 GHz) DNP spectrometer.
This spectrometer is dedicated for low temperature solid state DNP measurements. It is specifically designed for systematic studies of the spin dynamics underlying DNP in solids at low temperatures. The spectrometer functions as a fully operational NMR spectrometer (144 MHz) and pulse EPR spectrometer (95 GHz) with a microwave (MW) power of up to 300 mW at the entrance of the probehead where the sample is placed, generating a MW B1 field as high as 670 KHz. The combined NMR/EPR probe comprises of an open-structure horn-reflector configuration that functions as a low Q EPR cavity and an RF coil that can accommodate a 30μl-50μl sample tube. (shared with Prof. Shimon Vega)

We are constantly engaged in instrumental developments, concentrating primarily on the EPR and DNP spectrometer where our goal is to increase the sensitivity and flexibility in terms of multiple resonance experiments.

In addition we also use X- and Q-band CW EPR spectrometers within the framework of the Chemical Infrastructure Laboratory of the Faculty of Chemistry.

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X-band (9.5 GHz) pulse EPR spectrometer

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W-band microwave bridge

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Home build pulsed/continuous wave W-band (95 GHz) spectrometer

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Instruments & Methods

Our spectrometers