Similar to nuclear magnetic resonance (NMR) spectroscopy, electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy looks at the characteristics of unpaired electrons rather than nuclei like protons. It is employed to investigate the electronic structure of metal complexes or organic radicals in the domains of chemistry, biology, material science, and physics.
Basements are frequently the location of the huge electromagnets used for EPR spectroscopy, which can weigh over a ton.
The US company Bridge12, which is situated close to Boston, has introduced a next-generation EPR spectrometer that can be installed on any floor of a building and is almost half the price of existing models. It is also a tenth of the size and weight. An Arbitrary Waveform Generator (AWG) to create the pulses and a Digitizer to record the returned signal are the two Spectrum Instrumentation cards at the center of the system.
Thorsten Maly, VP Magnetic Resonance at Bridge12, said, “As a start-up, we had a clean slate to design our EPR spectrometer enabling us to use the latest technologies to create a next generation product that is much more compact than existing products. This EPR spectrometer will open up the use of this methodology to a much greater audience of researchers. Most of our customers are university researchers who gain access to the method through collaborations. Having a cheaper, state-of-the-art instrument will increase access to this powerful method. Our third goal was to make it much easier to use than current devices that need an experienced operator so that any scientist can use it for their research which will make EPR spectroscopy more widely used. Our control software has been designed to be intuitive to use with many features automated so that the set-up is straightforward and it immediately shows if the experiment is working correctly. You don’t have to be an expert in EPR spectroscopy to obtain results.”
How EPR functions
spectrometer by Bridge 12 opens this
technology to many more scientists
In structural biology, for instance, EPR spectroscopy can be used to measure the separations between radicals in order to ascertain the folded structure of (membrane) proteins. This sheds light on the possible interactions between these proteins and other molecules or proteins.
This is accomplished by affixing two spin labels, or markers, to the protein and utilizing pulsed dipolar spectroscopy, a type of pulse EPR spectroscopy, to measure the separation between them. By stimulating the radical with a series of microwave pulses and measuring the reaction, EPR spectroscopy can identify the spin labels, which are specifically created, non-reactive radical molecules.
The distance between the two markers is directly related to the dipolar coupling between the spins. A three- dimensional model of the protein’s folding can be found by placing spin label pairs at various locations on the protein to produce a set of distances.
Low-noise and Modular components
“EPR spectroscopy can measure distances in the range of 1 – 100 Angstroms but requires very accurately generated pulse sequences which is why we used Spectrum Instrumentation cards as they have extremely low levels of noise,” said Maly. “In addition, our spectrometer is designed to be modular so that the customer can specify exactly what performance they want and then we select the perfect AWG and Digitizer from Spectrum’s extensive range without being forced to use an over specified card. What we particularly like about the Spectrum cards is that they come integrated into Netboxes that then connects to our PC through ethernet. That way we can use a compact PC and not one that must be big enough to insert cards or have a bulky rack solution. It makes it also much easier to service our instrument and replace components in the field.”
Operation in the 35 GHz Q band range
Over the past few decades, EPR spectroscopy has changed as a result of advancements in radar technology and mobile telecommunications, which produced equipment that could be utilized to construct EPR apparatus, which uses microwave technology and requires higher frequencies in order to achieve better resolution. EPR spectrometer have historically functioned at 10 GHz (X-Band), however new commercial equipment that can run at considerably higher frequencies, such 35 GHz (Q band), is now available thanks to 5G technology. This frequency is much more desirable for this kind of application and available in new EPR spectrometer.
As needed by the experiment, the AWG creates 10–100 ns long pulses in the 200–500 MHz region. These pulses are then up-converted to the Q band range after first being up-converted to the X band range using an RF I/Q mixer.
Before being delivered to the EPR resonator, the microwave pulses are first routed into a 100 W solid-state amplifier.
The reflected signal is then transmitted to the digitizer after being down-converted to an IF frequency between 200 and 500 MHz. The signal is typically down-converted to DC in EPR spectroscopy, but this novel method significantly minimizes noise and distortions.
Figure 2 illustrates the kind of AWG-generated pulses that are utilized in contemporary EPR experiments. Broadband microwave pulses known as WURST (Wideband, Uniform Rate, Smooth Truncation) pulses have an excitation bandwidth and profile significantly larger than that of a conventional rectangular pulse. Such pulses are essential for broadband excitation in EPR spectroscopy and are highly dependent on the AWG’s performance.
Strong Magnetic Fields Using Significantly Lighter Magnets
The ability to produce strong magnetic fields of 1 to 1.5 Tesla, which normally calls for a large, heavy electromagnet, is the other factor. Maly explained, “We are using a much smaller, super-conducting magnet to produce the required magnetic field strength. For this experiment, the sample always needs to be cooled to cryogenic temperatures using helium so we found a supplier of liquid cryogen-free (dry) magnets that are compact and can generate the high magnetic field of 1.2 Tesla but at a fraction of the size and weight at around 130 kg. Rather than using liquid helium, the instrument uses a cold-head and helium compressor, which is effectively a fridge achieving cryogenic temperatures in a closed cycle. This is crucial as liquid helium is becoming increasingly hard to obtain.”
Maly concluded, “Spectrum’s 5-year warranty gives us great piece of mind as these cards are key parts of our EPR spectrometer. The technical support was also first class in helping us set up the equipment so we know we can rely on Spectrum if any issues occur for our customers in the future.”
Bridge12 Technologies new EPS spectrometer is available for purchase now and further details are at: https://www.bridge12.com
