Improved sensitivity for W-band Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements with shaped pulses.

摘要: Abstract Chirp and shaped pulses have been recently shown to be highly advantageous for improving sensitivity in DEER (double electron–electron resonance, also called PELDOR) measurements due their large excitation bandwidth. The implementation of such pulse EPR has become feasible the availability arbitrary waveform generators (AWG) with high sampling rates support shaping tens nanoseconds duration. Here we present a setup obtaining chirp on our home-built W-band (95 GHz) spectrometer demonstrate its performance Gd(III)-Gd(III) nitroxide-nitroxide measurements. We carried out an extensive optimization procedure two model systems, Gd(III)-PyMTA–spacer–Gd(III)-PyMTA (Gd-PyMTA ruler; zero-field splitting parameter (ZFS) D ∼ 1150 MHz) as well nitroxide–spacer–nitroxide (nitroxide ruler) evaluate applicability Gd(III) complexes nitroxides, which are important classes spin labels used modern DEER/EPR experiments. applied findings ubiquitin, doubly labeled Gd-DOTA-monoamide (D ∼ 550 MHz) as a system small ZFS. Our experiments were focused questions (i) what best conditions positioning detection frequency, (ii) pump parameters (bandwidth, spectrum, length) yield signal-to-noise ratio (SNR) improvements when compared classical DEER, (iii) how do sample’s spectral influence experiment. For nitroxide ruler, report improvement up 1.9 total SNR, while Gd-PyMTA ruler was 3.1–3.4 ubiquitin it factor 1.8. Whereas setups maximum observe gave about same improvement, significant difference found. In general choice set depends D complex.