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The link of an antenna dye with an electron spin converter, in this case naphthalenediimide and C60, produces a system with a rich photophysics including the detection of more than one triplet state on the long timescale (tens of μs). Beside the use of optical spectroscopies in the ns and in the fs time scale, we used time‐resolved Electron Paramagnetic Resonance (TREPR) to study the system evolution following photoexcitation. TREPR keeps track of the formation path of the triplet states through specific spin polarization patterns observed in the spectra. The flexibility of the linker and solvent polarity play a role in favouring either electron transfer or energy transfer processes. [ABSTRACT FROM AUTHOR]

We present a novel pulsed electron paramagnetic resonance (EPR) spectroscopic ruler to test the performance of a recently developed spin-labeling method based on the photoexcited triplet state ( S=1). Four-pulse electron double resonance (PELDOR) experiments are carried out on a series of helical peptides, labeled at the N-terminal end with the porphyrin moiety, which can be excited to the triplet state, and with the nitroxide at various sequence positions, spanning distances in the range 1.8-8 nm. The PELDOR traces provide accurate distance measurements for all the ruler series, showing deep envelope modulations at frequencies varying in a progressive way according to the increasing distance between the spin labels. The upper limit is evaluated and found to be around 8 nm. The PELDOR-derived distances are in excellent agreement with theoretical predictions. We demonstrate that high sensitivity is acquired using the triplet state as a spin label by comparison with Cu(II)-porphyrin analogues. The new labeling approach has a high potential for measuring nanometer distances in more complex biological systems due to the properties of the porphyrin triplet state. [ABSTRACT FROM AUTHOR]

Gaining detailed information on the structural rearrangements associated with stimuli-induced molecular movements is of utmost importance for understanding the operation of molecular machines. Pulsed electron-electron double resonance (PELDOR) was employed to monitor the geometrical changes arising upon chemical switching of a [2]rotaxane that behaves as an acid-base-controlled molecular shuttle. To this aim, the rotaxane was endowed with stable nitroxide radical units in both the ring and axle components. The combination of PELDOR data and molecular dynamic calculations indicates that in the investigated rotaxane, the ring displacement along the axle, caused by the addition of a base, does not alter significantly the distance between the nitroxide labels, but it is accompanied by a profound change in the geometry adopted by the macrocycle. [ABSTRACT FROM AUTHOR]

A photosystem II (PSII) core complex lacking the internal antenna CP43 protein was isolated from the photosystem II of Synechocystis PCC6803, which lacks photosystem I (PSI). CP47–RC and reaction centre (RCII) complexes were also obtained in a single procedure by direct solubilization of whole thylakoid membranes. The CP47–RC subcore complex was characterized by SDS/PAGE, immunoblotting, MALDI MS, visible and fluorescence spectroscopy, and absorption detected magnetic resonance. The purity and functionality of RCII was also assayed. These preparations may be useful for mutational analysis of PSII RC and CP47–RC in studying primary reactions of oxygenic photosynthesis. [ABSTRACT FROM AUTHOR]

A pulsed electron paramagnetic resonance (EPR) spectroscopic ruler is reported for the measurement of distances and distance distributions based on a novel spin ‐ labelling strategy. The ruler consists of a series of α ‐ helical peptides, labelled at the N ‐ terminal end with a porphyrin moiety that can be excited to the triplet state, and with a nitroxide at various sequence positions, spanning distances in the range between 1.8 – 8 nm. The new labelling approach has a high potential for measuring nanometer distances in biological macromolecules due to the distinctive properties of the porphyrin triplet state. More information can be found in the Full Paper by M. Di Valentin et al. on page 17204 ff. [ABSTRACT FROM AUTHOR]

The geometrical changes arising upon chemical switching of a doubly spin ‐ labeled [2]rotaxane, which behaves as an acid – base ‐ controlled molecular shuttle, were monitored by pulsed electron – electron double resonance (PELDOR) spectroscopy. The ring displacement along the axle in the rotaxane is accompanied by a profound change in the geometry adopted by the macrocycle. More information can be found in the Communication by A. Credi, M. Di Valentin, M. Lucarini et al. on page 8745 ff. [ABSTRACT FROM AUTHOR]