Making hyperfine selection in Mims ENDOR independent of deadtime

Abstract

A form of remote echo-detected ENDOR can be performed by adding an additional π pulse to the detection phase of a Mims three-pulse, stimulated-echo ENDOR experiment. The resulting four-pulse experiment, denoted refocused Mims (ReMims) ENDOR, retains the hyperfine selectivity of the Mims technique, but makes it possible to obtain arbitrarily short preparation intervals, τ 1, independent of the spectrometer deadtime. As a result, without resonator redesign, it is possible to study a wider range of hyperfine values without distortions from “blind-spots”. The hyperfine selectivity of the ReMims ENDOR sequence is demonstrated on the 1H and 14N ENDOR spectra from a single crystal of Cu(glycine) 2. Use of the ReMims protocol to augment the basic Mims and Davies ENDOR sequences is shown in two different types of situation: the sign of a 9 MHz coupled proton is assigned by the use of the implicit-TRIPLE effect in the proton ENDOR spectrum of nitrile hydratase; the true lineshape of the proton ENDOR spectrum of fluorometmyoglobin is determined without distortions by blindspots.