Film-electrochemical EPR spectroscopy to investigate electron transfer in membrane proteins in their native environment.

Film-electrochemical electron paramagnetic resonance spectroscopy (FE-EPR) enables simultaneous electrochemical and spectroscopic characterisation of paramagnetic electron-transfer centres, including in soluble proteins. We now report a modified set-up FE-EPR with tuneable macroporous working electrodes and demonstrate the feasibility to investigate electron transfer in membrane proteins in their native membrane environment.

Operando film-electrochemical EPR spectroscopy tracks radical intermediates in surface-immobilized catalysts.

The development of surface-immobilized molecular redox catalysts is an emerging research field with promising applications in sustainable chemistry. In electrocatalysis, paramagnetic species are often key intermediates in the mechanistic cycle but are inherently difficult to detect and follow by conventional in situ techniques. We report a new method, operando film-electrochemical electron paramagnetic resonance spectroscopy (FE-EPR), which enables mechanistic studies of surface-immobilized electrocatalysts.

Controlling and exploiting intrinsic unpaired electrons in metalloproteins.

Electron paramagnetic resonance spectroscopy encompasses a versatile set of techniques that allow detailed insight into intrinsically occurring paramagnetic centers in metalloproteins and enzymes that undergo oxidation-reduction reactions. In this chapter, we discuss the process from isolating the protein to acquiring and analyzing pulse EPR spectra, adopting a practical perspective. We start with considerations when preparing the protein sample, explain techniques and procedures available for determining the reduction potential of the redox-active center of interest and provide details on methodologies to trap a given paramagnetic state for detailed pulse EPR studies, with an emphasis on biochemical and spectroscopic tools available when multiple EPR-active species are present.

Functional group introduction and aromatic unit variation in a set of π-conjugated macrocycles: revealing the central role of local and global aromaticity.

π-Conjugated macrocycles are molecules with unique properties that are increasingly exploited for applications and the question of whether they can sustain global aromatic or antiaromatic ring currents is particularly intriguing. However, there are only a small number of experimental studies that investigate how the properties of π-conjugated macrocycles evolve with systematic structural changes. Here, we present such a systematic experimental study of a set of [2.

Insights into metalloproteins and metallodrugs from electron paramagnetic resonance spectroscopy.

Metal ions play an important role in diverse biological processes, and much of the basic knowledge derived from studying native bioinorganic systems are applied in the synthesis of new molecules with the aim of diagnosing and treating diseases. At first glance, metalloproteins and metallodrugs are very different systems, but metal ion coordination, redox chemistry and substrate binding play essential roles in advancing both of these research fields. In this article, we discuss recent metalloprotein and metallodrug studies where electron paramagnetic resonance spectroscopy served as a major tool to gain a better understanding of metal-based structures and their function.

A sensitivity leap for X-band EPR using a probehead with a cryogenic preamplifier.

Inspired by the considerable success of cryogenically cooled NMR cryoprobes, we present an upgraded X-band EPR probehead, equipped with a cryogenic low-noise preamplifier. Our setup suppresses source noise, can handle the high microwave powers typical in X-band pulsed EPR, and is compatible with the convenient resonator coupling and sample access found on commercially available spectrometers. Our approach allows standard pulsed and continuous-wave EPR experiments to be performed at X-band frequency with significantly increased sensitivity compared to the unmodified setup.

H hyperfine spectroscopy and DFT modeling unveil the demethylmenasemiquinone binding mode to E. coli nitrate reductase A (NarGHI).

The quinol oxidation site Q in E. coli respiratory nitrate reductase A (EcNarGHI) reacts with the three isoprenoid quinones naturally synthesized by the bacterium, i.e.

Probing the Menasemiquinone Binding Mode to Nitrate Reductase A by Selective H and N Labeling, HYSCORE Spectroscopy, and DFT Modeling.

In vivo specific isotope labeling at the residue or substituent level is used to probe menasemiquinone (MSK) binding to the quinol oxidation site of respiratory nitrate reductase A (NarGHI) from E. coli. N selective labeling of His Nδ or Lys Nζ in combination with hyperfine sublevel correlation (HYSCORE) spectroscopy unambiguously identified His Nδ as the direct hydrogen-bond donor to the radical.