MAKING HYPERFINE SELECTION IN MIMS ENDOR INDEPENDENT OF DEADTIME

A form of remote echo-detected ENDOR can be performed by adding an add itional pi pulse to the detection phase of a Mims three-pulse, stimula ted-echo ENDOR experiment. The resulting four-pulse experiment, denote d refocused Mims (ReMims) ENDOR, retains the hyperfine selectivity of the Mims technique, but makes it possible to obtain arbitrarily short preparation intervals, tau(1), independent of the spectrometer deadtim e. As a result, without resonator redesign, it is possible to study a wider range of hypefine values without distortions from ''blind-spots' '. The hyperfine selectivity of the ReMims ENDOR sequence is demonstra ted on the H-1 and N-14 ENDOR spectra from a single crystal of Cu(glyc ine)(2). Use of the ReMims protocol to augment the basic Mims and Davi es ENDOR sequences is shown in two different types of situation: the s ign of a 9 MHz coupled proton is assigned by the use of the implicit-T RIPLE effect in the proton ENDOR spectrum of nitrile hydratase; the tr ue lineshape of the proton ENDOR spectrum of fluorometmyoglobin is det ermined without distortions by blindspots.