Epifluorescence imaging of electrochemically switchable Langmuir-Blodgett films of Nafion

A combination of electrochemistry and luminescence methods was exploited to obtain information on the electrochemical activity and homogeneity of Nafion Langmuir-Blodgett films. The redox behavior of the Ru(bpy)3(2+) probe incorporated in the Nafion film was monitored by epifluorescence microscopy. The photoluminescent images, recorded by a charge-coupled device (CCD) camera, reflect the distribution of the probe in the film, which resulted as very uniform, particularly in comparison with spin-coated films. Apparent diffusion coefficients (Dapp) determined by cyclic voltammetry for films of less than 10 layers are in the range of 1 x 10(-12) to 8 x 10(-12) cm(2) s(-1), that is, 2 orders of magnitude lower than values reported in the literature for spin-coated Nafion films. The application to the electrode of a potential able to oxidize the luminescent Ru(bpy)3(2+) to the nonluminescent Ru(bpy)3(3+) switched off the photoluminescence with a response time that for the LB films was much shorter than that for the spin-coated ones. Experimental evidence and calculations indicate that lowering of the film thickness down to the nanometric level is very effective in shortening the switching time, notwithstanding the lowering of the Dapp value in LB films.     

Conversion of oximes to carbonyl compounds by triscetylpyridinium tetrakis(oxodiperoxotungsto) phosphate (PCWP)-mediated oxidation with hydrogen peroxide

Aromatic and aliphatic oximes have been deoximated in chloroform-water to the corresponding aldehydes with dilute hydrogen peroxide and triscetylpyridinium tetrakis (oxodiperoxotungsto) phosphate as catalyst. The presence of dipolarophiles in the reaction mixtures allows a competitive reaction that converts oximes into isoxazole and isoxazoline derivatives via the intermediate formation of nitrile oxide species.     

Design and synthesis of bis-amide and hydrazide-containing derivatives of malonic acid as potential HIV-1 integrase inhibitors

HIV-1 integrase (IN) is an attractive and validated target for the development of novel therapeutics against AIDS. In the search for new IN inhibitors, we designed and synthesized three series of bis-amide and hydrazide-containing derivatives of malonic acid. We performed a docking study to investigate the potential interactions of the title compounds with essential amino acids on the IN active site.     

Combinatorial synthesis and characterization of metal-open frameworks in mild and friendly conditions: application to CO₂ adsorption

Combinatorial screening using precipitation methods at room temperature can lead to a great diversity of carboxylate based Metal Organic Frameworks (MOFs) including already known or original porous solids. The investigation of the synthesis of MOFs in different solvent and solvent mixtures includes the use of solvents such as alcohols and tetrahydrofuran (THF) which would greatly facilitate large scale production. We also show the application of Principal Component Analysis (PCA) and clustering techniques on large libraries of XRD diffraction files in order to identify classes of similar phases and peculiar phases. The combinatorial screening of 105 samples in the La/btc system has led to the identification of two phases which are solvent depending. On the La(btc) compound, the CO? adsorption measurements reveal a guest-host interactions as supported by XRD phase transformation upon thermal treatment. The mass transport can be assigned to a "single file diffusion" regime due to the one dimensional channel porous structure associated to small pore size.     

Conformational polymorphism of the PrP106-126 peptide in different environments: a molecular dynamics study

Extensive molecular dynamic simulations (approximately 240 ns) have been used to investigate the conformational behavior of PrP106-126 prion peptide in four different environments (water, dimethyl sulfoxide, hexane, and trifluoroethanol) and under both neutral and acidic conditions. The conformational polymorphism of PrP106-126 in solution observed in the simulations supports the role of this fragment in the structural transition of the native to the abnormal form of prion protein in response to changes in the local environmental conditions. The peptide in solution is primarily unstructured. The simulations show an increased presence of helical structure in an apolar solvent, in agreement with the results from circular dichroism spectroscopy. In water solution, beta-sheet elements were observed between residues 108-112 and either residues 115-121 or 121-126. An alpha-beta transition was observed under neutral conditions. In DMSO, the peptide adopted an extended conformation, in agreement with nuclear magnetic resonance experiments.     

Electronic transitions involved in the absorption spectrum and dual luminescence of tetranuclear cubane [Cu4I4(pyridine)4] cluster: a density functional theory/time-dependent density functional theory investigation

We present a combined density functional theory (DFT)/time-dependent density functional theory (TDDFT) study of the geometry, electronic structure, and absorption and emission properties of the tetranuclear "cubane" Cu4I4py4 (py = pyridine) system. The geometry of the singlet ground state and of the two lowest triplet states of the title complex were optimized, followed by TDDFT excited-state calculations. This procedure allowed us to characterize the nature of the excited states involved in the absorption spectrum and those responsible for the dual emission bands observed for this complex. In agreement with earlier experimental proposals, we find that while in absorption the halide-to-pyridine charge-transfer excited state (XLCT*) has a lower energy than the cluster-centered excited state (CC*), a strong geometrical relaxation on the triplet cluster-centered state surface leads to a reverse order of the excited states in emission.     

Ternary choices in repeated games and border collision bifurcations

Several recent contributions formalize and analyze binary choices games with externalities as those described by Schelling. Nevertheless, in the real world choices are not always binary, and players have often to decide among more than two alternatives. These kinds of interactions are examined in game theory where, starting from the well known rock-paper-scissor game, several other kinds of strategic interactions involving more than two choices are examined. In this paper we investigate how the dynamics evolve introducing one more option in binary choice games with externalities. The dynamics we obtain are always in a stable regime, that is, the structurally stable dynamics are only attracting cycles, but of any possible positive integer as period. We show that, depending on the structure of the game, the dynamics can be quite different from those existing when considering binary choices. The bifurcation structure, due to border collisions, is explained, showing the existence of so-called big-bang bifurcation points.