Janet F. Bank

13 C CPMAS nuclear magnetic resonance study of the adsorption of 2-phenethylamine on clays

Abstract2-Phenethylamine 13C-enriched in the beta position was adsorbed on four different aluminum-exchanged clays: hectorite, Barasym, Laponite RD, and lithium taeniolite. The sites for adsorption were characterized by 13C high-resolution cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS-NMR) spectroscopy. Using differences in chemical shift values and linewidths, three different types of bound ammonium compounds and a motionally restricted bound compound were identified. Correlation with charge effects indicated that one of the clay sites was extremely acidic.The important catalytic sites for the different clays, the edge or platelet face, interlamellar and some combination of both, were probed by using the trimethylsilyl group as a clay-blocking agent. Silylation of aluminum-exchanged Laponite RD and Li taeniolite had little effect on amine adsorption. This indicates that, for these clays, amine adsorption occurred mainly at interlamellar sites. For hectorite, amine adsorption occurred at both surface and interlamellar sites, and silylation had the effect of reducing surface adsorption. Silylation of Barasym resulted in a very interesting shift of adsorption from one kind of surface site to a more acidic surface site.

Pulse field-sweep EPR of copper proteins

Abstract P ulse f ield-sweep EPR (PFSEPR) is developed as a low-power, microwave pulse technique to resolve hyperfine structure underlying inhomogeneously broadened EPR lines. PFSEPR arises from transfer of saturation due to spin state mixing from forbidden Δm I ≠ 0 EPR transitions. We report its first use to resolve large copper hyperfine couplings which are unresolved by standard X-band EPR. As applied to copper, PFSEPR has better sensitivity than ENDOR with comparable spectral resolution. The details of energy levels and state mixing which account for PFSEPR transitions in these copper systems are developed here. PFSEPR transitions from stellacyanin provide hyperfine and quadrupole couplings in good agreement with those predicted by various EPR simulations and determined by ENDOR. Copper couplings from the Cu A signal of cytochrome- c oxidase are comparable to previously published estimates, but PFSEPR suggests underlying state mixing of copper levels.

Conformational Transitions of Cytochrome c Oxidase Induced by Partial Reduction

The metal centers of cytochrome c oxidase obviously interact by transferring electrons. Potentiometric titrations of metal centers, as monitored optically and by EPR, indicate redox coupling between centers (1). This means that putting an electron on one redox center perturbs the redox potential of another center. It has been proposed that such redox interactions are in fact aspects of concomitant conformational change (2).

Newly Developed Time-Resolved EPR Techniques for the Study of Cytochrome C Oxidase

We present recent results from two new time-resolved EPR techniques used to probe structure and function of cytochrome c oxidase. The first of these, which we have used at cryogenic temperatures, is pulse field-sweep EPR. With this we can resolve hyperfine couplings of the CuA nucleus in cytochrome Oxidase, where such couplings are not directly resolved by straight EPR. This method is a technically simpler alternative to other double resonance techniques. The second technique is an ambient temperature technique to follow oxygen consumption by cytochrome oxidase. This technique uses an oxygen-sensitive spin probe to report the concentration of oxygen in solution. It is feasible to use this spin probe technique together with stopped flow. O2 kinetics have been followed both under aerobic conditions where O2 consumption is limited by cytochrome c reductant and under conditions where low oxygen concentration limits the rate of oxygen consumption.