Fluorescent properties of antioxidant cysteine ABZ analogue

The antioxidant properties of aminobenzamide cysteine (ABZ Cys) makes it a molecule that can potentially be used as a drug in oxidative stress related diseases and delivered in the form of a nanoparticles. Here we have studied the photo-physical properties of ABZ Cys, a fluorescent analogue of a popular antioxidant N-acetyl cysteine (NAC). We have compared ABZ Cys steady state and time-resolved fluorescence properties with its parent compounds anthranilic acid and anthranilamide in solution as well as in poly-vinyl alcohol (PVA) polymer films. ABZ Cys did not show any significant shift in absorption after entrapment in PVA film, but there was a shift towards shorter wavelengths in the emission peak compared to the phosphate buffer solution. Fluorescence lifetimes and quantum yields indicated a slight quenching of ABZ Cys fluorescence in comparison to the cysteine-less parent compounds. We also demonstrated that very low concentrations of ABZ Cys, such as 100 nM, are readily detected by a commercial spectrofluorometer. Hence we have established the possible use of ABZ Cys in biomedical applications.     

Copper-catalyzed direct sulfoximination of azoles and polyfluoroarenes under ambient conditions

The direct dehydrogenative C-N coupling of azoles or polyfluoroarenes with N-H sulfoximines proceeds effectively in the presence of a copper catalyst at room temperature under air to afford the corresponding N-arylsulfoximines in good to high yields.     

Crystal structure and morphology evolution in the LaXO3, X = Al, Ga, In nano-oxide series. Consequences for the synthesis of luminescent phosphors

The LaXO(3):Tb(3+) (X = Al(3+), Ga(3+), In(3+)) perovskite nanoparticles were obtained using the nonhydrolytic treatment (Bradley reaction) of the molecular precursors of the La(O(i)Pr)(3), Al(O(i)Pr)(3), Ga(O(i)Pr)(3), In(5)O(O(i)Pr)(13), and Tb(acac)(3), respectively. It was shown that crystal structure and morphology evolution in the LaXO(3), X = Al, Ga, In nano-oxide series depended on the size and chemical properties of the X-metal atom. Formation of the LaInO(3):Tb(3+) nanoparticles is distinctly less thermodynamically demanding on contrary to the LaAlO(3):Tb(3+) and LaGaO(3):Tb(3+) since it provided crystalline product directly in the solution synthesis at 202 °C, which is the lowest reported synthesis temperature for this compound up-to-date. This behavior was ascribed to the effects directly connected with the dopant substitution (exchange of bigger La(3+) cation with smaller Tb(3+)) as well as reduction of the particle size. The size effects are mostly reflected in the expansion of the cell volume, changes of the cell parameters as well as shifting and broadening of the Raman bands. Indirectly, size reduction has also an effect on the luminescence properties through the higher probability of presence of surface and net defects as well as heterogeneous distribution of the Tb(3+) ions caused by high surface-to-volume ratio. The prepared nanophosphors show basically green emission with exception of white-green in case of the LaInO(3):Tb(3+). Strong emission quenching was found in the latter case being most likely a consequence of the nonradiative energy transfer between Tb(3+) and In(3+) as well as the presence of defects. In comparison to the Pechini's method, the LaXO(3) nanoparticles required significantly lower annealing temperature (700 °C) necessary for complete crystallization. Generally the resulting particles are distinctly smaller (5 to 25 nm) and less agglomerated (50-100 nm) depending on the reaction conditions as well as thermal treatment. For the first time, it was shown that the LaGaO(3):Tb(3+) nanopowder has crystallized in the high-temperature rhombohedral R3c phase.     

Kinetic study of the reaction of OH with CH2I2

Flash photolysis (FP) coupled to resonance fluorescence (RF) was used to measure the absolute rate coefficients (k(1)) for the reaction of OH(X(2)Π) radicals with diiodomethane (CH(2)I(2)) over the temperature range 295-374 K. The experiments involved time-resolved RF detection of the OH (A(2)Σ(+)→X(2)Π transition at λ = 308 nm) following FP of the H(2)O/CH(2)I(2)/He mixtures. The OH(X(2)Π) radicals were produced by FP of H(2)O in the vacuum-UV at wavelengths λ > 120 nm. Decays of OH radicals in the presence of CH(2)I(2) are observed to be exponential, and the decay rates are found to be linearly dependent on the CH(2)I(2) concentration. The results are described by the Arrhenius expression k(1)(T) = (4.2 ± 0.5) × 10(-11) exp[-(670 ± 20)K/T] cm(3) molecule(-1) s(-1). The implications of the reported kinetic results for understanding the atmospheric chemistry of CH(2)I(2) are discussed.     

On the transferability of folding and threading potentials and sequence-independent filters for protein folding simulations

Significant progress has recently been made in de novo protein structure prediction. The Rosetta method by Baker and colleagues, which is based on the idea of assembling putative models from a library of k-mer fragments derived from known three-dimensional protein structures, proved to be particularly successful. Critical components of the Rosetta approach are various sequence-dependent as well as sequence-independent measures that are used to rank alternative models and to enhance sampling of native-like conformations. In the present work we revisit several sequence-independent filters that have been used to enhance the discrimination of native and native-like structures from misfolded structures, such as the overall compactness of the structure and its contact order. We also propose a novel sequence-independent filter, based on the shape of the mean inter-residue radial distribution function. Using the Rosetta, Park–Levitt and CASP4 sets of decoys it is shown that sequence-independent filters are in fact more successful in distinguishing native structures in Rosetta and CASP4 tests than commonly used knowledge-based pairwise potentials. The latter are typically designed to distinguish native structures in a population of well-folded alternatives, and they fail to discriminate between native-like and non-physically packed misfolded structures from Rosetta simulations. Moreover, a rigorous attempt to optimize pairwise potentials for recognition of homologous structures in threading by using a linear programming approach leads to further deterioration of performance in terms of recognition of native structures from the Rosetta set. These findings shed light onto the success of tailored scoring functions used in the Rosetta protocol and provide support for explicit inclusion of both sequence dependent and sequence independent measures in the design of scoring functions. A Web server that enables ranking of decoy structures according to sequence independent filters considered here is available at http://sift.chmcc.org.     

The synthesis,crystal structure and thermal studies of a mixed-ligand 1,10-phenanthroline and hexamethylenetetramine complex of lanthanum nitrate. Insight into coordination sphere geometry changes of lanthanide(III) 1,10-phenanthroline complexes

The structure of tetraaqua-bis(nitrato-O,O′)-(1,10-phenanthroline-N,N′)-lanthanum(III) 1,3,5,7-tetraazatricyclo[3.3.1.1^3,7]decane nitrate dihydrate, [La(NO₃)₂ · phen · (H₂O)₄]⁺ · hmt · NO ₃ ⁻ · 2H₂O, is presented. The lanthanum ion exhibits tenfold coordination and the polyhedron can be described as tetradecahedron. The complex cations, nitrate ions, water and hexamethylenetetramine molecules are assembled via hydrogen bonds, H–π rings and π–π stacking interactions into 3D supramolecular network. The bond strength of coordination sphere was calculated by means of the bond-valence method. The influence of La:phen stoichiometry and additional ligand on the changes of lanthanum(III) coordination sphere geometry in ten-coordinated complexes with 1,10-phenanthroline was discussed. The infrared spectrum of structure optimised by means of quantum mechanical calculations was analysed and compared with measured one. The obtained compound was characterised by thermogravimetric analysis in conjunction with evolved gases in the air atmosphere.     

Cage-like ordered silica with large mesopore volume synthesized by doubling amount of polymer, adding sodium chloride and lowering acid concentration

Cage-like ordered mesoporous silica, FDU-1, with about twice the pore volume and a narrower pore size distribution compared with those for previously reported samples was synthesized in a much shorter time by doubling the amount of block copolymer, adding sodium chloride and lowering the acid concentration.     

Molecular weight dependent charge carrier mobility in poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene)

Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight.