Expression of a ketolase gene mediates the synthesis of canthaxanthin in Synechococcus leading to tolerance against photoinhibition, pigment degradation and UV-B sensitivity of photosynthesis

The potential of ketocarotenoids to protect the photosynthetic apparatus from damage caused by excess light and UV-B radiation was assessed. Therefore, the cyanobacterium Synechococcus was transformed with a foreign beta-carotene ketolase gene under a strong promoter leading to the accumulation of canthaxanthin. This diketo carotenoid is absent in the original strain. Most of the newly formed canthaxanthin was located in the thylakoid membranes. The endogenous beta-carotene hydroxylase was unable to interact with the ketolase. Therefore, only traces of astaxanthin were found. The transformant was treated with strong light (500 or 1200 mumol m-2 s-1) and with UV-B radiation. In contrast to a nontransformed strain the overall photosynthesis, measured as oxygen evolution, was protected from inhibition by light of 500 mumol m-2 s-1 and UV-B radiation of 6.8 W m-2. Furthermore, degradation in the light of chlorophyll and carotenoids at an irradiance of 1200 mumol m-2 s-1, which was substantial in the nontransformed control, was prevented. These results indicate that in situ canthaxanthin, which is formed at the expense of zeaxanthin and replaces this hydroxy carotenoid within the photosynthetic apparatus, is a better protectant against solar radiation. These findings are discussed on the basis of the in vitro properties such as inactivating peroxyl radicals, quenching of singlet oxygen and oxidation stability of these different carotenoid structures.     

A facile route to a versatile synthon for preparation of cis-pyrethroids

$\text{cis}$-2-Cyano-3,3-dimethylcyclopropanecarboxylic acid was obtained in >50% overall yield starting with ethyl 3,3-dimethylacrylate. The key step involved a tandem Michael reaction - intramolecular displacement to afford stereoselectively a cyclopropanoid precursor of $\text{cis}$-pyrethroids.     

Quantitative Bestimmung des Zuckers im Blute

Ohne Zusammenfassung     

Optimizing the accuracy and precision of the single‐pulse Laue technique for synchrotron photo‐crystallography

The accuracy that can be achieved in single‐pulse pump‐probe Laue experiments is discussed. It is shown that with careful tuning of the experimental conditions a reproducibility of the intensity ratios of equivalent intensities obtained in different measurements of 3–4% can be achieved. The single‐pulse experiments maximize the time resolution that can be achieved and, unlike stroboscopic techniques in which the pump‐probe cycle is rapidly repeated, minimize the temperature increase due to the laser exposure of the sample.     

Diblock copolymer surfactant transport across the interface between two homopolymers

Dynamics of adsorption and desorption of a diblock copolymer to an interface between two homopolymers was measured using dynamic secondary-ion mass spectrometry (SIMS). Thin films were constructed consisting of a layer of saturated polybutadiene with 90% 1,2-addition (sPB90), followed by a layer of saturated polybutadiene with 63% 1,2-addition (sPB63), and finally by another layer of the sPB90 homopolymer. A sPB90-sPB63 diblock copolymer was initially included only in the top sPB90 layer of the film at a volume fraction of 0.05. The thin films were annealed at ambient temperature for times ranging between 0.2 and 108 h, and the concentration profiles of the diblock copolymer through the films were measured using SIMS. The dynamics of adsorption and desorption of the diblock copolymer at the two sPB90-sPB63 interfaces was gauged by comparing the different transient concentration profiles. The sorption process was modeled as diffusion in an external field, generated from self-consistent field theory (SCFT). All parameters for the model were determined independently. Although the model neglects the dynamics of conformational change, experimental results matched theory very well.     

A functional model for the cysteinate-ligated non-heme iron enzyme superoxide reductase (SOR)

Superoxide reductases (SORs) are cysteine-ligated, non-heme iron enzymes that reduce toxic superoxide radicals (O2-). The functional role of the trans cysteinate, as well as the mechanism by which SOR reduces O2-, is unknown. Herein is described a rare example of a functional metalloenzyme analogue, which catalytically reduces superoxide in a proton-dependent mechanism, via a trans thiolate-ligated iron-peroxo intermediate, the first example of its type. Acetic-acid-promoted H2O2 release, followed by Cp2Co reduction, regenerates the active Fe(II) catalyst. The thiolate ligand and its trans positioning relative to the substrate are shown to contribute significantly to the catalyst's function, by lowering the redox potential, changing the spin state, and dramatically lowering the nuFe-O stretching frequency well-below that of any other reported iron-peroxo, while leaving nuO-O high, so as to favor superoxide reduction and Fe-O, as opposed to O-O, bond cleavage. Thus we provide critical insight into the relationship between the SOR structure and its function, as well as important benchmark parameters for characterizing highly unstable thiolate-ligated iron-peroxo intermediates.     

Time-resolved EPR spectra of the triplet excited states of diaminoacridine guests in polar potassium hydrogen phthalate single crystals

Mixed crystals of potassium hydrogen phthalate containing 3,6-diaminoacridine were photoexcited with visible light and the resulting triplet excited states were analyzed by time resolved EPR spectroscopy. Spectra from discrete growth sectors were compared with powders and polycrystalline glasses prepared at various pHs. The data yield the predominant protonation state and orientation of the triplets in each of a pair of growth sectors bounding the positive and negative ends of the polar crystal.