A large geometric distortion in the first photointermediate of rhodopsin, determined by double-quantum solid-state NMR

Double-quantum magic-angle-spinning NMR experiments were performed on 11,12-C-13(2)-retinylidene-rhodopsin under illumination at low temperature, in order to characterize torsional angle changes at the C11-C12 photoisomerization site. The sample was illuminated in the NMR rotor at low temperature (similar to 120 K) in order to trap the primary photointermediate, bathorhodopsin. The NMR data are consistent with a strong torsional twist of the HCCH moiety at the isomerization site. Although the HCCH torsional twist was determined to be at least 40A degrees, it was not possible to quantify it more closely. The presence of a strong twist is in agreement with previous Raman observations. The energetic implications of this geometric distortion are discussed

Removal and Reconstitution of the Carotenoid Antenna of Xanthorhodopsin

Salinixanthin, a C40-carotenoid acyl glycoside, serves as a light-harvesting antenna in the retinal-based proton pump xanthorhodopsin of Salinibacter ruber. In the crystallographic structure of this protein, the conjugated chain of salinixanthin is located at the protein–lipid boundary and interacts with residues of helices E and F. Its ring, with a 4-keto group, is rotated relative to the plane of the π-system of the carotenoid polyene chain and immobilized in a binding site near the β-ionone retinal ring. We show here that the carotenoid can be removed by oxidation with ammonium persulfate, with little effect on the other chromophore, retinal. The characteristic CD bands attributed to bound salinixanthin are now absent. The kinetics of the photocycle is only slightly perturbed, showing a 1.5-fold decrease in the overall turnover rate. The carotenoid-free protein can be reconstituted with salinixanthin extracted from the cell membrane of S. ruber. Reconstitution is accompanied by restoration of the characteristic vibronic structure of the absorption spectrum of the antenna carotenoid, its chirality, and the excited-state energy transfer to the retinal. Minor modification of salinixanthin, by reducing the carbonyl C=O double bond in the ring to a C-OH, suppresses its binding to the protein and eliminates the antenna function. This indicates that the presence of the 4-keto group is critical for carotenoid binding and efficient energy transfer

On the typology and the worship status of sacred trees with a special reference to the Middle East

This article contains the reasons for the establishment of sacred trees in Israel based on a field study. It includes 97 interviews with Muslim and Druze informants. While Muslims (Arabs and Bedouins) consider sacred trees especially as an abode of righteous figures' (Wellis') souls or as having a connection to their graves, the Druze relate sacred trees especially to the events or deeds in the lives of prophets and religious leaders. A literary review shows the existence of 24 known reasons for the establishment of sacred trees worldwide, 11 of which are known in Israel one of these is reported here for the first time. We found different trends in monotheistic and polytheistic religions concerning their current worship of sacred trees

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Charge transfer in molecular conductors - Oxidation or reduction?

We discuss the nature of charge transfer in molecular conductors upon connecting to two metallic contacts and imposing a voltage bias across them. The sign of the charge transfer (oxidation vs. reduction) depends on the position of the metal Fermi energy with respect to the molecular levels. In addition, the charge transfer depends on the strength of the coupling (chemisorption vs. physisorption) with the contacts. A convenient way to establish the nature and onset of the charge transfer and the corresponding features in the I-V is to draw an energy level diagram for each spin species. Starting from such a level diagram, we argue that transport in the Tour-Reed switching molecules, which consist of a central phenyl ring with a nitroamine redox center, involves the oxidation of a HOMO level. © 2002 Published by Elsevier Science B.V.link_to_subscribed_fulltex

Linear dichroism and the transition dipole moment orientation of the carotenoid in the LH2 antenna complex in membranes of Rhodopseudomonas acidophila strain 10050

Linear dichroism (LD) of the carotenoid, rhodopin glucoside, and the 800 and 850 nm absorbing bacteriochlorophylls in the LH2 antenna complex from membranes of Rhodopseudomonas acidophila strain 10050 squeezed in polyacrylamide gels is reported. A model is presented for computing the ratio of the LD-to-isotropic absorption (LD/A) for the pigments based on the crystal structure of the LH2 complex solved by X-ray diffraction methods. Semiempirical molecular orbital (MO) calculations have refined the structure of the protein-bound rhodopin glucoside and show that the transition moment of the carotenoid is not collinear with the long axis of the molecule. Rather, it is 9.1 ° off axis from the extended ð-electron conjugated chain. This rotation of the transition moment vector away from the structural long axis emerges as a result of the single/double bond alternation naturally present in all polyenes and carotenoids and is not due to environmental perturbations induced by binding of the molecule to the pigment-protein complex. Calculations of the intensity of polarized absorption for the rhodopin glucoside molecule predict a significant effect of the magnitude of the off-axis angle on the value of the observed LD/A. This paper employs semiempirical MO calculations and seeks to correlate the experimentally observed LD, which gives the orientation of the transition moment of the rhodopin glucoside in the membranes, with the X-ray diffraction results, which reveals the molecular structure of the carotenoid to atomic resolution