The geometry of the secondary radical pair P700(+)A1(-), in photosystem I (PSI) from the deuterated and 15N-substituted cyanobacterium Synechococcus lividus, has been determined by high time resolution electron paramagnetic resonance (EPR), performed at three different microwave frequencies. Structural information is extracted from light-induced quantum beats observed in the transverse magnetization of P700(+)A1(-) at early times after laser excitation. A computer analysis of the two-dimensional Q-band experiment provides the orientation of the various magnetic tensors of with respect to a magnetic reference frame. The orientation of the cofactors of the primary donor in the g-tensor system of is then evaluated by analyzing time-dependent X-band EPR spectra, extracted from a two-dimensional data set. Finally, the cofactor arrangement of P700(+)A1(-) in the photosynthetic membrane is deduced from angular-dependent W-band spectra, observed for a magnetically aligned sample. Thus, the orientation of the g-tensor of P700(+) with respect to a chlorophyll based reference system could be determined. The angle between the g1(z) axis and the chlorophyll plane normal is found to be 29 +/- 7 degrees, while the g1(y) axis lies in the chlorophyll plane. In addition, a complete structural model for the reduced quinone acceptor, A1(-), is evaluated. In this model, the quinone plane of is found to be inclined by 68 +/- 7 degrees relative to the membrane plane, while the P700(+)-A1(-) axis makes an angle of 35 +/- 6 degrees with the membrane normal. All of these values refer to the charge separated state, observed at low temperatures, where forward electron transfer to the iron-sulfur centers is partially blocked. Preliminary room temperature studies of P700(+)A1(-), employing X-band quantum beat oscillations, indicate a different orientation of A1(-) in its binding pocket. A comparison with crystallographic data provides information on the electron-transfer pathway in PSI. It appears that quantum beats represent excellent structural probes for the short-lived intermediates in the primary energy conversion steps of photosynthesis.

Blue-light excitation of cryptochromes and homologs uniformly triggers electron transfer (ET) from the protein surface to the flavin-adenine dinucleotide (FAD) cofactor. A cascade of three conserved tryptophan residues has been considered to be critically involved in this photoreaction. If the FAD is initially in its fully oxidized (diamagnetic) redox state, light-induced ET via the tryptophan triad generates a series of short-lived spin-correlated radical pairs comprising an FAD radical and a tryptophan radical. Coupled doublet-pair species of this type have been proposed as the basis, e.g., of a biological magnetic compass in migratory birds, and were found critical for some cryptochrome functions in vivo. In this contribution, a cryptochrome-like protein (CRYD) derived from Xenopus laevis has been examined as a representative system. The terminal radical-pair state FAD•⋯W324• of X. laevis CRYD has been characterized in detail by time-resolved electron-paramagnetic resonance (TREPR) at X-band microwave frequency (9.68 GHz) and magnetic fields around 345 mT, and at Q-band (34.08 GHz) at around 1215 mT. Different precursor states – singlet versus triplet – of radical-pair formation have been considered in spectral simulations of the experimental electron-spin polarized TREPR signals. Conclusively, we present evidence for a singlet-state precursor of FAD•⋯W324• radical-pair generation because at both magnetic fields, where radical pairs were studied by TREPR, net-zero electron-spin polarization has been detected. Neither a spin-polarized triplet precursor nor a triplet at thermal equilibrium can explain such an electron-spin polarization. It turns out that a two-microwave-frequency TREPR approach is essential to draw conclusions on the nature of the precursor electronic states in light-induced spin-correlated radical pair formations.

The photoexcited triplet states of three 5,10,15-tris(pentafluorophenyl)corroles (tpfc), hosting Sn(IV) and AI(III) in their core, namely, Sn(Cl)(tpfc), Al(pyr)2(tpfc ) and Al(pyr)2(tpfc-Brs), were studied by time-resolved electron paramagnetic resonance (TREPR) spectroscopy in the nematic liquid crystal E7. Only two of these metallocorroles, namely, Sn(C1)(tpfc) and Al(pyr)2(tpfc-Br8), exhibit TREPR spectra following pulsed laser excitation. This result is rationalized in terms of a very low quantum yield of triplet formation in Al(pyr)2(tpfc ). Analysis of the spin polarized Q-band (34 GHz) EPR spectra of Sn(Cl)(tpfc) and Al(pyr)2(tpfc-Brs) provides detailed information on the magnetic and kinetic parameters of the triplet states as well as on the molecular ordering of the complexes in the liquid crystal. With the assignment of the zero-field splitting parameter D < 0 for the Sn(C1)(tpfc) and Al(pyr)2(tpfc-Brs), one can evaluate the dominant intersystem crossing path for these metallocorroles. Analysis reveals that in Sn(C1)(tpfc) the in-plane triplet sublevels are preferentially populated, i.e., A x, A r >> A z. This can be rationalized in terms of weak electronic interactions between the Sn(IV) ion and the corrole n-system, consistent with the domed structure of Sn(Cl)(tpfc). In Al(pyr)2(tpfc-Brs), however, the out-of-plane triplet sublevel is predominantly populated, i.e., A z > A x, Ar, which is attributed to a large increase in the spin-orbit coupling strength arising from the peripheral bromine atoms on the corrole skeleton.

Electrochemical energy storage using lignin as a renewable electrode material is a cheap and sustainable approach for future organic batteries. Previous reports mainly focus on lignosulfonates (LS) or composites with conductive polymer additives with inherent problems, such as still expensive monomers. Here, composite electrodes are used from more available Kraft lignin and sustainable conductive carbon. Charge storage is evaluated in terms of electrical double layer storage and redox reactions, aiming at a better understanding of desired lignin properties for electrochemical energy storage. Using unmodified, commercial lignin and high surface area conductive carbon, reasonable capacity of ≈80 mAh g−1 is achieved in samples in which a thin layer of lignin covers the interface of high surface area carbon. Non‐faradaic contribution to charge storage is as large as in comparable pure carbon electrodes, and redox reactions in lignin contribute to additional, faradaic charge storage, significantly enhancing capacity in these systems. Resulting electrodes are cheap, reliable, and stable.

The spin-polarized W-band EPR spectra of the secondary radical pair in plant photosystem I indicate a magneticfield-induced orientation of the photosynthetic reaction centers in the field of the EPR spectrometer. This orientation arises due to the anisotropy of the diamagnetic susceptibility of the reaction center protein. Analysis of the angular-dependent EPR spectra on the basis of the spin-correlated radical pair concept provides new information on the cofactor arrangement in plant photosystem I.

Characterization of the HNA-3 system allows identification of blood donors at risk to develop HNA-3-antibodies. FcγRIIIb (HNA-1) and CD177 (HNA-2) seem to be important in bacterial host defense. Activation of neutrophils by HNA-1 and HNA-2-antibodies potentially occurs via mPR3 and CD11b/CD18 (HNA-4a).

Aims. We announce the discovery of a quasar behind the disk of M 31, which was previously classified as a remarkable nova in our neighbour galaxy. It is shown here to be a quasar with a single strong flare where the UV flux has increased by a factor of ∼20. The present paper is primarily aimed at the remarkable outburst of J004457+4123 (Sharov 21), with the first part focussed on the optical spectroscopy and the improvement in the photometric database. Methods. We exploited the archives of photographic plates and CCD observations from 15 wide-field telescopes and performed targetted new observations. In the second part, we try to fit the flare by models of (1) gravitational microlensing due to a star in M 31 and (2) a tidal disruption event (TDE) of a star close to the supermassive black hole of the quasar. Results. Both the optical spectrum and the broad band spectral energy distribution of Sharov 21 are shown to be very similar to that of normal, radio-quiet type 1 quasars. We present photometric data covering more than a century and resulting in a long-term light curve that is densely sampled over the past five decades. The variability of the quasar is characterized by a ground state with typical fluctuation amplitudes of ∼0.2 mag aroundB ∼ 20.5, superimposed by a singular flare of ∼2 yr duration (observer frame) with the maximum at 1992.81. The total energy in the flare is at least three orders of magnitudes higher than the radiated energy of the most luminous supernovae, provided that it comes from an intrinsic process and the energy is radiated isotropically. The profile of the flare light curve is asymmetric showing in particular a sudden increase before the maximum, whereas the decreasing part can be roughly approximated by a t −5/3 power law. Both properties appear to support the standard TDE scenario where a ∼10 M giant star was shredded in the tidal field of a ∼2 . . . 5 × 10 8 M black hole. The short fallback time derived from the observed light curve requires an ultra-close encounter where the pericentre of the stellar orbit is deep within the tidal disruption radius. This simple model neglects, however, the influence of the massive accretion disk, as well as general-relativistic effects on the orbit of the tidal debris. Gravitational microlensing probably provides an alternative explanation, although the probability of such a high amplification event is very low.

The hydrophobic fluorescence dye 10-n-nonyl-acridinium-orange-chloride, NAO, stains specifically the mitochondria of living HeLa-cells. A dye concentration of 1 X 10(-8) M is sufficient for vital staining and at 5 X 10(-7) M an incubation time less than 1 min is enough to generate the bright green fluorescence of the mitochondria. The retention of NAO by the mitochondria is longer than 7 days. The dye accumulation is not affected by the ionophores valinomycin, nigericin, gramicidin, the uncoupling agents DNP, CCCP or by ouabain. In contrast to Rh 123 the trans-membrane potential is not the driving force of the NAO accumulation. We assume that NAO is bound to the hydrophobic lipids and proteins in the mitochondrial membranes by hydrophobic interaction. With valinomycin, 500 ng/ml, 10 min, the mitochondria in HeLa-cells swell. Now it is possible to observe some details in the enlarged mitochondria by light microscopy. After vital staining with NAO, 5 X 10(-7) M, 10 min, the periphery of the swollen mitochondria shows an intense green fluorescence, the inner part is dark. Obviously the dye is bound to the membranes. By electron microscopy it can be shown that the valinomycin treated and NAO stained mitochondria have outer and inner membranes and cristae. They differ from untreated mitochondria mainly in the size. After incubation of the HeLa-cells with relatively high NAO concentrations, 5 X 10(-6) M, 10 min, the mitochondria show a weak orange fluorescence. It is generated by the dimers D of NAO. Therefore the dye concentration in the mitochondrial membranes is locally very high and causes dye dimerisation. The weak orange fluorescence is instable and disappears within a few seconds. Instead we observe a green fluorescence with growing intensity that is generated by the monomers M of NAO. The intensity has its maximum value after a few seconds. Using low NAO concentrations for incubation, 1 X 10(-7) M, 10 min, we observe only the green fluorescence with increasing intensity. In this case the orange fluorescence is too weak for observation (concentration quenching). It can be shown by experiments and quantum mechanics that the orange fluorescence is assigned to an optical forbidden, the green fluorescence to an allowed electronic transition of D or M respectively. Our results indicate a dissoziation of D in 2 M by irradiation of the mitochondria under the fluorescence microscope.(ABSTRACT TRUNCATED AT 400 WORDS)