ANTENNA EFFECT IN LUMINESCENT LANTHANIDE CRYPTATES: A PHOTOPHYSICAL STUDY

Excited state emission and absorption decay measurements have been made on the cage-type cryptate complexes [M bpy.bpy.bpy]ⁿ⁺, where Mⁿ⁺= Na⁺, La³⁺, Eu³⁺, Gd³⁺ or Tb³⁺ and [bpy.bpy.bpy] is a tris-bipyridine macrobicyclic cryptand. Excitation has been performed in the high intensity ¹π-π* cryptand band with maximum at about 300 nm. Experiments have been carried out in H₂O or D₂O solutions and at 300 and 77 K to evaluate the rate constants of radiative and nonradiative decay processes. For Mⁿ⁺= Na⁺, La³⁺ and Gd³⁺ the lowest excited state of the cryptate is a ³ππ* level of the cryptand which decays in the microsecond time scale at room temperature in H₂O solution and in the second-millisecond time scale at 77 K in MeOH-EtOH. For Mⁿ⁺= Eu³⁺, the lowest excited state is the luminescent ⁵D₀ Eu³⁺ level which in H₂O solution is populated with 10% efficiency and decays to the ground state with rate constants 2.9 × 10³ s^_1 at room temperature and 1.2 × 10³ s^?′ at 77 K. The relatively low efficiency of ⁵D₀ population upon ¹ππ* excitation is attributed to the presence of a ligand-to-metal charge transfer level through which ¹ππ* decays directly to the ground state. For Mⁿ⁺= Tb³⁺ the lowest excited state is the luminescent ⁵D₄ Tb³⁺ level. The process of ⁵D₄ population upon ¹ππ* excitation is ?100% efficient, but at room temperature it is followed by a high-efficiency, activated back energy transfer from the ⁵D₄ Tb³⁺ level to the ³ππ* ligand level because of the relatively small energy gap between the two levels (1200 cm^_1) and the intrinsically long lifetime of ⁵D₄. At 77 K back energy transfer cannot take place and the ⁵D₄ Tb^3* level deactivates to the ground state with rate constant 5.9 × 10² s^-′ (H₂O solution). The relevance of these results toward the optimization of Eu³⁺ and Tb³⁺ cryptates as luminescent probes is discussed.     

Anion selectivities of trifluoroacetophenone derivatives as neutral ionophores in solvent-polymeric membranes

Trifluoroacetophenones with different substituents in the para-position are studied in order to examine their anion selectivities in solvent-polymeric membranes. The selectivities of the corresponding ion-selective electrodes and the hydration of the ligands in membranes depend on the Hammett constants σ of the substituents. Better selectivities for carbonate over chloride were reached throughout for ligands with substituents of high σ values.     

Pressurized liquid extraction-capillary electrophoresis-mass spectrometry for the analysis of polar antioxidants in rosemary extracts

A method based on capillary electrophoresis-electrospray-mass spectrometry (CE-ESI-MS) was developed to qualitatively characterize natural antioxidants from rosemary (Rosmarinus officinalis L.) in different fractions obtained by pressurized liquid extraction (PLE) using subcritical water. The parameters of CE-ESI-MS were adjusted allowing the separation and characterization of different compounds from rosemary in the PLE fractions. These parameters for CE are kind, pH and concentration of the separation buffer, parameters for ESI-MS are dry gas temperature and flow, nebulizing gas pressure, and make-up flow. The following analytical conditions were found most favorable: aqueous CE buffer (40 mM ammonium acetate/ammonium hydroxide, pH 9); sheath liquid containing 2-propanol-water (60:40, v/v) and 0.1% (v/v) triethylamine at a flow rate of 0.24 mL/h; drying gas flow rate equal to 7 L/min at 350 degrees C, nebulizing gas pressure of 13.8 kPa (2 psi), using a compound stability of 50%. Different antioxidant compounds (e.g., rosmarinic acid and carnosic acid) could be detected in the rosemary extracts by CE-ESI-MS without any additional treatment, enabling the determination of variations in the extract composition caused by the different PLE conditions (i.e., 60 and 100 degrees C). The results provide complementary information to HPLC analysis.     

Effect of Structure of Functionalizing Molecules on the Inter‐Macromolecular Reactions and Blending of Poly(ethylene‐co‐propylene) (EPM) with Poly(6‐aminohexanoic Acid) (PA6)

Two different functionalizing systems, i.e., monohexadecyl maleate (= hexadecyl hydrogen (2Z)‐but‐2‐enedioate) in the presence of dicumyl peroxide (= bis(1‐methyl‐1‐phenylethyl) peroxide) or 4‐carboxybenzenesulfonazide (= 4‐(azidosulfonyl)benzoic acid), were used in distinct experiments to perform in a one‐step procedure the formation of a EPM–PA6 graft copolymer, necessary to obtain a compatibilized blend, from a molten mixture of ethylene–propylene copolymer (EPM) and polyamide 6 (PA6). The characterization of the graft polymer by selective solvent extraction of the blends and the subsequent IR and NMR analysis of the various fractions established the occurrence of functionalization reactions preferentially onto the polyolefin with both reagents. Also the formation in good yield of graft copolymers at the phases interface was observed. Moreover, the morphology and thermal characterizations of the blends by means of SEM and DSC analyses were used to evaluate the compatibilization extent in comparison with blends obtained by the conventional two‐step procedure or by the one‐step procedure with commercial maleic acid derivatives.     

Variational and Perron–Wiener solutions in stratified Lie groups

We consider sub‐Laplacians in stratified Lie groups and we compare Perron–Wiener and weak‐variational solutions of the Dirichlet problem , where Ω is a bounded open set in and φ is the restriction to the boundary of a function such that . The result we obtained extends a previous theorem by Arendt and Daners, related to the classial Laplacian in .     

GPU-acceleration of waveform relaxation methods for large differential systems

It is the purpose of this paper to provide an acceleration of waveform relaxation (WR) methods for the numerical solution of large systems of ordinary differential equations. The introduced technique is based on the employ of graphics processing units (GPUs) in order to speed-up the numerical integration process. A CUDA solver based on WR-Picard, WR-Jacobi and red-black WR-Gauss-Seidel iterations is presented and some numerical experiments realized on a multi-GPU machine are provided.     

Protocell Communication through the Eyes of Synthetic Organic Chemists

The bottom-up fabrication of synthetic cells (protocells) from molecules and materials, is a major challenge of modern chemistry. A significant breakthrough has been the engineering of protocells capable of chemical communication using bio-derived molecules and ex situ stabilised cell machineries. These, however, suffer from short shelf-lives, high costs, and require mild aqueous conditions. In this Concept Article we analyse the chemistry at the heart of protocell communication to highlight new opportunities for synthetic chemists in protocell engineering. Specifically, we (i) categorise the main bio-derived chemical communication machineries in enzyme cascades, DNA strand displacement, and gene-mediated communication; (ii) review the chemistries of these signal transduction machineries; and (iii) introduce new types of bio-inspired, fully synthetic artificial enzymes to replace their natural counterparts. Developing protocells that incorporate synthetic analogues of bio-derived signal transduction machineries will improve the robustness, stability, and versatility of protocells, and broaden their applications to highly strategic fields such as photocatalysis and fine chemicals production.     

Unexpected Acid-Triggered Formation of Reversibly Photoswitchable Stenhouse Salts from Donor-Acceptor Stenhouse Adducts

Donor-acceptor Stenhouse adducts (DASAs) are reversibly photoswitchable dyes, which are able to interconvert between a red/NIR absorbing triene-like state and a colorless cyclic state. Although optically attractive for multiple applications, their low solubility and lack of photoswitching in water impede their use in aqueous environments. We developed water-soluble DASAs based on indoline as donor and methyl, or trifluoromethyl, pyrazolone-based acceptors. In acetonitrile, photophysical analysis and photochemical studies, accounted with a three-state kinetic model, confirmed the reversible photoswitching mechanism previously proposed. In water, the colorless cyclic state is a thermodynamic sink at neutral pH values. In contrast, in acidic conditions, we observed a fast scrambling of DASAs’ end-group resulting in the in situ formation of Stenhouse salts (StS), which are in turn capable of reversible photoswitching. We believe that this unexpected result is of interest not only for the future design of DASAs with improved stability, but also for further development and applications of StS as photoswitchable probes.