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New world-class research carried out on 2D-ELDOR ESR spectrometer with ELVA-1 95 GHz 2.5 ns FWHM Transceiver

11th February, 2021.
Recent progress is reported in developing 2D-ELDOR (2D electron-electron double resonance) techniques to better capture molecular dynamics in complex fluids, particularly in model and biological membranes. 

Microsecond Exchange Processes Studied by Two-Dimensional ESR at 95 GHz

A group of scientists from Cornell University’s ACERT Biomedical Research Center has published new article in the Journal of the American Chemical Society describing novel studies completed in 2020 utilizing a high-field, high-power electron-spin resonance (ESR) spectrometer built around a new design, high performance ELVA-1 95 GHz 2.5 ns transceiver, titled: “Microsecond Exchange Processes Studied by Two-Dimensional ESR at 95 GHz”, Boris Dzikovski, Valery V. Khramtsov, Siddarth Chandrasekaran, Curt Dunnam, Meera Shah, and Jack H. Freed. 

At 95 GHz, it becomes possible, in many cases, to resolve hidden spectral details of ESR probes such as nitroxides because of the increased g-factor resolution. Recent 95 GHz instrumental developments at ACERT now enable such studies.

For the first time, cross-peaks emerging due to chemical exchange processes were detected in ESR spectra of nitroxide radicals. Their analysis allowed for determination of the exchange rates. Studying cross-peaks is one of the most useful and powerful techniques in NMR, but in ESR their observation has been challenging due to resolution and timescale limitations. Recent 95 GHz instrumental developments at ACERT now enable such studies due to the increased g-factor resolution. The new capabilities were demonstrated using two examples: (A) the protonation/deprotonation process for a pH-sensitive imidazoline spin label in aqueous solution and (B) a nitroxide radical partitioning between polar (aqueous) and nonpolar (phospholipid) environments in multilamellar lipid vesicles.

 ACERT millimeter-wave instrumentation development in cooperation with millimeter wave specialists from ELVA-1 has resulted in substantial performance upgrade embodied in a new, highly stable “MK II” version of the spectrometer’s original 95 GHz transceiver, providing significantly increased receiver sensitivity and bandwidth, and advanced transmit-modulation versatility.

Most importantly for the published studies, the ELVA-1 95 GHz MKII transceiver is capable of producing well defined, highly stable spin excitation pulses down to 2.5 ns, compared to the 4.5 ns minimum pulse capability of the MK I transceiver, and is the world’s only ESR transceiver capable of directly producing such short pulses with minimal phase deviation during transitions. These millimeter-wave bursts are subsequently amplified to a level of 1.2KW by an extended-interaction klystron (CPI, Canada), marking this spectrometer as unique in its capability of directly producing extended trains of extremely short, high-power pulses.

Additional features of the transceiver include: frequency stability better than 1 ppm/h further enhances resolution over long averaging times; also, transmission bandwidth and versatility are based entirely on a heterodyne architecture, whereas the MK I transceiver relied upon frequency multiplication via bandwidth-limited IMPATT diode devices. In this architecture, the combined nanosecond-scale MK II transmitter pulse forming and QPSK modulation performance now permit a wider range of pulse patterns, with simultaneous wideband AWG.

“The quasi-optical bridge and state-of-the art MKII receiver section permits ACERT to access signals with T2 decay times that are as short as 15 ns, which is more than sufficient for the present project...", — reported in the article for the Journal of the American Chemical Society.

About the ELVA-1 95GHz MKII TRANSCEIVER for Cornell University

ELVA-1’s second-generation 95 GHz MKII heterodyne transceiver installed in the Cornell University National Biomedical Center for Advanced ESR Technology (ACERT) 95 GHz high-power pulse spectrometer has significantly improved noise figure of 4.5 dB, gated QPSK-encoded pulse widths as short as 2.5 ns and ±350 MHz wideband AWG modulation capability.

Visit the presentation page of ELVA-1 95 GHz MKII heterodyne transceiver for specifications and photos.