Chaoliang Fan

Quantitative studies of davies pulsed ENDOR

Abstract The results of quantitative and systematic studies of the dependence of two-pulse spin-echo intensity on the pulse widths and of the Davies ENDOR response on the width of the preparation pulse, t p are reported. A formula that describes the Davies ENDOR response as a function of the selectivity parameter, η η = A n t p is presented. These measurements, which employ a variety of small molecules and metalloenzymes, not only provide information about the Davies ENDOR technique, but also give a quantitative description of the recently described POSHE method for hyperfine selection of heteronuclear pulsed ENDOR spectra through manipulation of pulse widths in the Davies ENDOR sequence. This procedure involves suppression of weakly coupled proton pattern and optimization of strongly coupled heteronuclei signals. It is demonstrated with single-crystal data for Cu(II)-doped Zn(glycinato) 2 and frozen solution data for the blue copper protein Pseudomonas aeruginosa azurin.

A simple method for hyperfine-selective heteronuclear pulsed ENDOR via proton suppression

A major reason for the importance of ENDOR spectroscopy ( 1) in the study of metal complexes is that the technique is inherently broad-banded: all coupled nuclei having spin I > 0 can be detected with comparable sensitivity (2). Unfortunately, at X-band magnetic fields ( -0.3 T at g = 2) the proton ENDOR spectrum often overlaps with and obscures the spectra of important heteronuclei such as 14N, 13C 57Fe or 33S. One solution is to work at higher microwave frequency (2, 3). In adiitioi, three elegant, two-dimensional pulsed-ENDOR techniques (4) have been developed to address this problem by hyperfine selection at X band (57). We now describe a simple one-dimensional pulsed-ENDOR method for hyperfine selection of heteronuclear ENDOR signals through the suppression of the proton pattern. As the technique also leads to enhancement of the intensities of heteronuclear signals, we call it POSHEENDOR (proton suppression, heteronuclear enhancement). Two of the currently available pulsed-ENDOR techniques for hyperiine selection are formally equivalent and can be loosely grouped as ELDOR-ENDOR experiments. Buhlmann et al. (5) used field jumps within a Davies ENDOR sequence (4, 8) to achieve selection, whereas Thomann and Bernard0 (6) used microwave frequency jumps. However, these methods require two-dimensional experiments to obtain a complete hyperfme-selected spectrum and thus need large blocks of time for data acquisition. In addition, they require equipment beyond that necessary for ordinary Davies ENDOR. The third technique, developed by de Beer et al. ( 7)) utilizes a Mims ENDOR sequence (4, 9). In this method, hyperfine selection is achieved by systematic variation of time between the first and second microwave pulses in a stimulated-echo sequence. This procedure is restricted by the time required for a 2D experiment as well as by limitation of the Mims sequence to smaller hypetine couplings. The hyperfine selection technique we describe employs the fact that in a Davies ENDOR sequence,

Cytochrome c Oxidase: A Brief Introduction and Some New Results from High Field Endor Studies of The CuA and CuB Sites

A Mitchellian view of mitochondrial respiration is presented in Scheme I.1,2 This illustrates electron transfer from an electron rich material, NH, through quinone, Q, through Complex HI, into cytochrome c, and through Complex IV(cytochrome c oxidase) to O2, with accompanying proton translocations across the lipid bilayer.