Tuning Electron Donor–Acceptor Hybrids by Alkali Metal Complexation

A zinc phthalocyanine endowed with four [18]‐crown‐6 moieties, ZnPc_TeCr, has been prepared and self‐assembled with either pyridyl‐functionalized perylenebisimides (PDI‐Py) or fullerenes (C₆₀‐Py) to afford a set of novel electron donor–acceptor hybrids. In the case of ZnPc_TeCr, aggregation has been circumvented by the addition of potassium or rubidium ions to lead to the formation of monomers and cofacial dimers, respectively. From fluorescence titration experiments, which gave rise to mutual interactions between the electron donors and the acceptors in the excited state, the association constants of the respective ZnPc_TeCr monomers and/or dimers with the corresponding electron acceptors were derived. Complementary transient‐absorption experiments not only corroborated photoinduced electron transfer from ZnPc_TeCr to either PDI‐Py or C₆₀‐Py within the electron donor–acceptor hybrids, but also the unexpected photoinduced electron transfer within ZnPc_TeCr dimers. In the electron donor–acceptor hybrids, the charge‐separated‐state lifetimes were elucidated to be close to 337 ps and 3.4 ns for the two PDI‐Pys, whereas the longest lifetime for the photoactive system that contains C₆₀‐Py was calculated to be approximately 5.1 ns.     

Ruthenoarenes versus Phenol Derivatives as Axial Linkers for Subporphyrazine Dimers and Trimers

The subporphyrazine (SubPz) dimer diboron(III) [μ‐1′,4′‐benzenediolato][bis‐(1,2,6,7,11,12‐hexapropylsubporphyrazinato)] ( 2 ) and trimer triboron(III)[μ‐1′,3′,5′‐benzenetriolato][tris‐(1,2,6,7,11,12‐hexapropylsubporphyrazinato)] ( 4 ), consisting of SubPz units assembled through their axial positions by hydroquinone‐ and phloroglucinol‐linkers, respectively, have been prepared. Selective ruthenium‐π‐coordination to the linking aromatic rings afforded SubPz arrays 8 and 9 , respectively. These latter systems displayed different degrees of electronic communication between the macrocycles relative to 2 and 4 as inferred from analyses of the ground‐ and excited‐state features. For instance, as revealed by time‐resolved pump probe transient absorption spectroscopy, the excited singlet states of dimer 2 and trimer 4 undergo rather rapid deactivation. In contrast, the presence of a ruthenoarene linker, as in 8 and 9 , serves to increase the SubPz singlet excited state lifetimes; these now reach values similar to those seen in the case of monomeric SubPz compounds that either do or do not contain ruthenoarene subunits (i.e., 7 and 6 , respectively). These findings are ascribed to the redox active nature of the hydroquinone and phloroglucinol linkers in 2 and 4 and a change in the electronics that results from organometallic functionalization.     

Stereoselective Syntheses,Structures, and Properties of Extremely Distorted Chiral Nanographenes Embedding Hextuple Helicenes

We report a molecular design and concept using π-system elongation and steric effects from helicenes surrounding a triphenylene core toward stable chiral polycyclic aromatic hydrocarbons (PAHs) with a maximal π-distortion to tackle their aromaticity, supramolecular and molecular properties. The selective syntheses, and the structural, conformational and chiroptical properties of two diastereomeric large multi-helicenes of formula C₉₀H₄₈ having a triphenylene core and embedding three [5]helicene units on their inner edges and three [7]helicene units at their periphery are reported based on diastereoselective and, when applicable, enantiospecific Yamamoto-type cyclotrimerizations of racemic or enantiopure 9,10-dibromo[7]helicene. Both molecules have an extremely distorted triphenylene core, and one of them exhibits the largest torsion angle recorded so far for a benzene ring (twist=36.9°).     

Progress on the development of uniform distributed Pd electroless based catalysts on MEA for PEMFC application

Envisaging the scale-up production of fuel cell electrodes, it was established an electrode manufacturing method that enables a uniform distribution of Pd-based catalyst over the MEA, ensuring simultaneously a low catalyst loading. The new procedure relies on the direct immobilization of the catalyst on the gas diffusion substrate by the electroless deposition after substrate activation by the electrodeposition of metal nucleus of Pd using the galvanostatic mode. The effect of the novel method on the catalyst distribution uniformity, morphology, and electrocatalytic activity towards the oxygen reduction reaction (ORR) in 0.1 M HClO₄ solution is compared to samples prepared by the conventional Sn/Pd sensitization—activation route. The performance of the PEMFC containing the same Pd load (0.09 mg cm^?2) reveals to be slightly higher on depositing the Pd nucleus by the galvanostatic electrodeposition than by the conventional sensitization/activation method. The new method opens up new approaches to extend the electroless deposition to the preparation of a wide range of alloy catalysts for the cathode and anode sides of PEMFCs.     

Influence of Perfluorohexane-Enriched Atmosphere on Viscoelasticity and Structural Order of Self-Assembled Semifluorinated Alkanes at the Air-Water Interface

Abstract : Semifluorinated alkanes FnHm self-assemble into nanometer-sized surface micelles at the air-water interface. In this study, we investigated how an atmosphere enriched with perfluorohexane (PFH) influences the interfacial viscoelasticity and structural order of a monolayer of FnHm by the combination of dilational rheology and grazing-incidence small-angle X-ray scattering (GISAXS). The monolayers behaved predominantly elastic which can be attributed to the strong dipole repulsions of the surface domains. Enrichment of the atmosphere with PFH lead to an increase of the compressibility and a decrease of the elastic modulus without altering the structural ordering of the FnHm molecules into highly correlated nanodomains, suggesting the adsorption of PFH molecules to the free spaces between the domains. The capability of FnHm domains to retain the structural integrity in the presence of PFH gas is promising for the fabrication of stable microbubbles for sonographic imaging.     

Enzymes of Opuntia ficus-indica (L.) Miller with potential industrial applications-I

We report on the screening of different enzymes such as arylamidases, lipases, proteinases, and glucosidases in plant extracts of the Cactaceae family, genus Opuntia, as well as on a newly purified plant proteases from O. ficus-indica fruit extracts. These proteinases showed the maximum activity at pH 5.2 and 55°C and FTC-casein was the best of the escreened substrates. Proteolytic activities were activated by anti-oxidant compounds and by some divalent cations. These proteinases were efficiently inhibited by cystein proteinase inhibitors and by 1,10-phenanth roline. The estimated M _t for the main proteolytic activity was about 23.2 kDa. The results on milk clotting characteristics suggest a potential use of the fruit cystein enzymes of this plant in dairy industries.     

Fibrations by curves with more than one nonsmooth point

Bertini’s theorem on variable singular pointsmay fail in positive characteristic, as was discovered by Zariski in 1944. In fact, he found fibrations by nonsmooth curves. In this work we continue to classify this phenomenon in characteristic three by constructing the first example, rising in the literature, of fibrations with more than one nonsmooth point. Our approach has been motivated by the close relation between it and the theory of regular but nonsmooth curves, or equivalently, nonconservative function fields in one variable. In analogy to the Kodaira-Néron classification of special fibers of minimal fibrations by elliptic curves, we also construct the minimal proper regular model of some fibrations by nonsmooth projective plane quartic curves and determine the structure of the bad fibers.     

Structure and composition of the nacre–prisms transition in the shell of <Emphasis Type="Italic">Pinctada margaritifera</Emphasis> (Mollusca,Bivalvia)

A microstructural, mineralogical, and chemical study of the nacre–prisms boundary in the shells of Pinctada margaritifera shows that this boundary is not an abrupt transition, but that there exists a distinct fibrous layer with clear topographic structures and evidence of growth lines. A three-step biomineralization process is proposed that involves changes in the chemical and biochemical composition of the last growth increments of the calcite prisms, formation of the fibrous layer, and development of regular tablets in the nacreous layer.     

Effect of temperature on the buildup of polyelectrolyte multilayers

The effect of temperature on the buildup of polyelectrolyte multilayers consisting of poly(styrenesulfonate) (PSS), poly(diallyldimethylammonium) (PDADMA), and poly(allylamine) (PAH) was studied by using a quartz crystal microbalance. The increase of temperature in the deposition process was shown to have a considerable effect on the rate of the layer-by-layer buildup. The effect of temperature on the PDADMA/PSS deposition was found to be stronger than on the PAH/PSS deposition. The increasing temperature was found to extend the exponential buildup regime in all of the studied systems. A buildup model was created to simulate the buildup and to explain the effect of temperature. The model is based on the assumption that each deposition step leads to a quasi-equilibrium between the concentration of the polymer repeating unit in solution and the composition of the layer. According to the model, the layer-by-layer buildup is inherently exponential, becoming linear whenever diffusion is not fast enough to carry the polymer within the entire thickness of the film. This buildup model is discussed jointly with the earlier published three-zone model of the polyelectrolyte multilayers. The rate of the buildup is characterized by growth exponent beta. The temperature dependence of the growth exponent is discussed in connection with the thermodynamic parameters of the deposition.