The Occurrence of the psbS Gene Product in Chlamydomonas reinhardtii and in Other Photosynthetic Organisms and Its Correlation with Energy Quenching†

To avoid photodamage, photosynthetic organisms have developed mechanisms to evade or dissipate excess energy. Lumen overacidification caused by light‐induced electron transport triggers quenching of excited chlorophylls and dissipation of excess energy into heat. In higher plants participation of the PsbS protein as the sensor of low lumenal pH was clearly demonstrated. Although light‐dependent energy quenching is a property of all photosynthetic organisms, large differences in amplitude and kinetics can be observed thus raising the question whether a single common mechanism is in action. We performed a detailed study of PsbS expression/accumulation in Chlamydomonas reinhardtii and investigated its accumulation in other algae and plants. We showed that PsbS cannot be detected in Chlamydomonas under a wide range of growth conditions. Overexpression of the endogenous psbs gene showed that the corresponding protein could not be addressed to the thylakoid membranes. Survey of different unicellular green algae showed no accumulation of anti‐PsbS reactive proteins differently from multicellular species. Nevertheless, some unicellular species exhibit high energy quenching activity, suggesting that a PsbS‐independent mechanism is activated. By correlating growth habitat and PsbS accumulation in different species, we suggest that during the evolution the light environment has been a determinant factor for the conservation/loss of the PsbS function.     

Sequence stereoisomerism in calixarene-based pseudo[3]rotaxanes

Two calix[6]arene directional wheels can be ordered in the right stereosequence by their through-the-annulus threading with a rationally designed bis(benzylalkylammonium) axle. These stereoisomeric pseudo[3]rotaxanes can be considered as a minimal "informational system" because the "written information" on the thread is transferred to a specific sequence stereoisomer.     

Fixed or invertible calixarene-based directional shuttles

The first examples of rotaxanes based on calixarenes threaded by dialkylammonium ions, which also represent the first examples of calixarene-based molecular shuttles, are reported. The base/acid treatment demonstrated that these systems act as molecular shuttles, which move between three sites on the axle. When small OMe groups are appended at the calix[6]arene lower rim an unprecedented inversion of its shuttling direction is observed, which occurs through a cone-to-cone inversion of the macrocycle.     

Selective base-promoted synthesis of substituted selenophenes by carbocyclization of (Z)-benzylselenoenynes

We herein described the synthesis of several 3-benzyl-2,5-diarylselenophene derivatives in moderate to good yields using (Z)-benzylselenoenynes as starting material in carbocyclization reactions. The reactions were carried out under mild conditions using only t-BuOK as base, in the complete absence of transition metals or additives. The cyclized 3-benzyl-2,5-diarylselenophenes obtained in the current protocol appear highly promising and attractive intermediates for the synthesis of polysubstituted selenophenes. For instance, 3-benzyl-2,5-diphenylselenophene was treated with Br(2) provided the corresponding 3-benzyl-4-bromo-2,5-diphenylselenophene in high yield. 4-Bromoselenophene derivative was applied as substrate in the palladium catalyzed cross-coupling reactions with boronic acids to give the Suzuki type products in excellent yields.     

Inclusion properties of volatile organic compounds in a calixarene-based organic zeolite

The inclusion properties of a calixarene-based porous material have been studied to investigate the adsorption and the desorption of carbon tetrachloride, chloroform, and water in the zeolite-like structure. Uptake and release processes have been studied both by time-resolved powder X-ray diffraction and by thermogravimetric analysis to obtain structural and kinetic information. The selected guests are able to enter the structure with an increase in the host cell volume and with time-dependent diffusivity coefficients. Chloroform molecules act as a permanent porosity switch promoting a phase transition to non-porous triclinic form.     

Thiocyanate-free cyclometalated ruthenium sensitizers for solar cells based on heteroaromatic-substituted 2-arylpyridines

The first examples of thiocyanate-free thiophene-substituted Ru(ii) cyclometalated complexes, based on thiophene-derived 2-(2,4-difluorophenyl)pyridine ligands, are presented and investigated as photosensitizers in DSCs. Upon thiophene substitution the complexes presented enhanced optical properties compared to the reference dye with no thiophene substitution. DSCs based on the dithienyl-derived dye showed power conversion efficiencies up to 5.7%, more than twice that containing the complex without the thiophene substitution.     

Sugar composition of the moss Rhodobryum ontariense (Kindb.) Kindb

Although the second biggest terrestrial group of plants, bryophytes remain poorly known chemically compared to the angiosperms. In this article, the sugars of the moss Rhodobryum ontariense, an unstudied representative of the medicinally known genus, are reported. The chemical analysis revealed the usual plant sugar sucrose, and a new sugar, fructooligosaccharide 1-kestose, which is reported first not only for the genus Rhodobryum, but also for mosses. The trisaccharides have been scantily reported in bryophytes hitherto. This gives more significance to this study for further investigation of its role in the moss species. The health-promoting effect of 1-kestose is also briefly discussed.     

Acetylcholinesterase inhibition activity of acetylated depsidones from Lobaria pulmonaria

As part of our ongoing project of new acetylcholinesterase inhibitors from lower marine and terrestrial species, a phytochemical investigation was conducted on a foliose lichen, Lobaria pulmonaria (L.) Hoffm. (Lobariaceae), from Bosnia and Herzegovina. The study led to the isolation of a mixture of acetylated depsidones which showed a moderate activity (0.5?μg) in the acetylcholinesterase inhibition test on Thin-layer chromatography plate. Our results indicate for the first time the significance of depsidones, highly specific metabolites from lichen species, in searching for these inhibitors which still represent the best drugs currently available for the management of Alzheimer's disease.     

Social Influence Maximization in Hypergraphs

This work deals with a generalization of the minimum Target Set Selection (TSS) problem, a key algorithmic question in information diffusion research due to its potential commercial value. Firstly proposed by Kempe et al., the TSS problem is based on a linear threshold diffusion model defined on an input graph with node thresholds, quantifying the hardness to influence each node. The goal is to find the smaller set of items that can influence the whole network according to the diffusion model defined. This study generalizes the TSS problem on networks characterized by many-to-many relationships modeled via hypergraphs. Specifically, we introduce a linear threshold diffusion process on such structures, which evolves as follows. Let H=(V,E) be a hypergraph. At the beginning of the process, the nodes in a given set S⊆V are influenced. Then, at each iteration, (i) the influenced hyperedges set is augmented by all edges having a sufficiently large number of influenced nodes; (ii) consequently, the set of influenced nodes is enlarged by all the nodes having a sufficiently large number of already influenced hyperedges. The process ends when no new nodes can be influenced. Exploiting this diffusion model, we define the minimum Target Set Selection problem on hypergraphs (TSSH). Being the problem NP-hard (as it generalizes the TSS problem), we introduce four heuristics and provide an extensive evaluation on real-world networks.     

On the approximation performance of fictitious play in finite games

We study the performance of Fictitious Play (FP), when used as a heuristic for finding an approximate Nash equilibrium of a two-player game. We exhibit a class of two-player games having payoffs in the range $[0,1]$ that show that FP fails to find a solution having an additive approximation guarantee significantly better than $1/2$ . Our construction shows that for $n\times n$ games, in the worst case both players may perpetually have mixed strategies whose payoffs fall short of the best response by an additive quantity $1/2 - O(1/n^{1-\delta })$ for arbitrarily small $\delta $ . We also show an essentially matching upper bound of $1/2 - O(1/n)$ .