A simple but effective dual redox and fluorescent ion pair receptor based on a ferrocene-imidazopyrene dyad

The ferrocene-imidazopyrene dyad, bearing the imidazole ring as the only receptor site, acts as a redox and optical molecular sensor for ion pairs, exhibiting an easily detectable signal change in the redox potential of the ferrocene/ferrocinium redox couple and in the emission spectrum. Perturbation of the emission spectrum follows the order Pb(2+) > Hg(2+) > Zn(2+) for cations and H(2)PO(4)(-) > AcO(-) for anions.     

Characterization of galactooligosaccharides derived from lactulose

Galactooligosaccharides are non-digestible carbohydrates with potential ability to modulate selectively the intestinal microbiota. In this work, a detailed characterization of oligosaccharides obtained by transgalactosylation reactions of the prebiotic lactulose, by using β-galactosidases of different fungal origin (Aspergillus oryzae, Aspergillus aculeatus and Kluveromyces lactis), is reported. Oligosaccharides of degree of polymerization (DP) up to 6 were detected and quantified by HPLC-ESI MS from a complex mixture produced by transgalactosylation reaction with A. oryzae (GOSLuAo), whereas only carbohydrates up to DP4 and DP5 were found for those obtained from the reaction with β-galactosidases from K. lactis (GOSLuKl) and A. aculeatus (GOSLuAa), respectively. Disaccharides (galactosyl-galactoses and galactosyl-fructoses) and trisaccharides were characterised in the three mixtures by GC-MS as their trimethylsilyl oximes. Galactosyl- and digalactosyl-glycerols were produced during the transgalactosylation reaction of lactulose with β-galactosidases from A. aculeatus and K. lactis, due to the presence of glycerol as enzyme stabiliser.     

Ferrocene-based heteroditopic receptors displaying high selectivity toward lead and mercury metal cations through different channels

The synthesis and electrochemical, optical, and ion-sensing properties of ferrocene-imidazophenazine dyads are presented. Dyad 4 behaves as a highly selective chemosensor molecule for Pb(2+) cations in CH(3)-CN/H(2)O (9:1). The emission spectrum (λ(exc) = 317 nm) undergoes an important chelation-enhanced fluorescence effect (CHEF = 47) in the presence of Pb(2+) cations, a new low-energy band appeared at 502 nm, in its UV/vis spectrun, and the oxidation redox peak is anodically shifted (ΔE(1/2) = 230 mV). The presence of Hg(2+) cations also induced a perturbation of the redox potencial although in less extension than those found with Pb(2+) cations. Dyad 7, bearing two fused pyridine rings, has shown its ability for sensing Hg(2+) cations selectively through three channels: electrochemical, optical, and fluorescent; the oxidation redox peak is anodically shifted (ΔE(1/2) = 200 mV), a new low-energy band of the absorption spectrum appeared at 485 nm, and the emission spectrum (λ(exc) = 340 nm) is red-shifted by 32 nm accompanied by a remarkable chelation-enhanced fluorescent effect (CHEF = 165). Linear sweep voltammetry revealed that Cu(2+) cations induced oxidation of the ferrocene unit in both dyads. (1)H NMR studies have been carried out to obtain information about the molecular sites which are involved in the binding process.     

Carbonic anhydrase inhibitors: X-ray crystallographic studies for the binding of N-substituted benzenesulfonamides to human isoform II

N-substituted benzenesulfonamides, incorporating the N-amino-, N-hydroxy- and N-methoxy-moieties at the sulfonamide zinc binding group, have been investigated as CAIs by means of inhibition and structural studies, unraveling interesting aspects related to their inhibition mechanism.     

Time resolved spectroscopy of 2-(dimethylamine)fluorene. Solvent effects and photophysical behavior

The effect of different solvents on the fluorescent properties of 2-(dimethylamine)fluorene (DAF) were studied. In aprotic solvents we detected a strongly emissive intramolecular charge transfer (ICT) state that decayed by intersystem crossing to triplet. In proton-accepting solvents DAF exhibits in the excited state an intramolecular proton transfer. An ionized species is postulated, which simultaneously twists to a rotated conformation in the excited state. Thus, the specific solvent interactions supplement but do not replace the twist mechanism and accompany the charge transfer accepted as the prerequisite for twisted intramolecular charged transfer (TICT) state formation.     

Absorption and emission spectra of fluorescent silica nanoparticles from TD-DFT/MM/PCM calculations

A multi-scale computational protocol, which combines Quantum Mechanics and Molecular Mechanics (QM/MM) calculations with the polarisable continuum model (PCM), has been used to study the tetramethylrhodamine isothiocyanate (TRITC) fluorophore, embedded in three different environments, namely in water, on an amorphous silica surface and covalently encapsulated in a silica nanoparticle (C dot). Absorption and emission spectra have been simulated by using TD-B3LYP/PCM calculations, performed on the TRITC ground and excited state geometries, optimized at the QM/MM level. The results are in good agreement with experimental data confirming the caging effect played by the silica shell on the mobility of the TRITC molecule when covalently encapsulated in silica nanoparticles. This could result in a decrease of the nonradiative decay rate and thus an increase of the quantum yield of the molecule.     

Influence of the alkyl and alkoxy side chains on the electronic structure and charge-transport properties of polythiophene derivatives

Density Functional Theory has been used to study the structural, electronic and charge-transport properties of two regio-regular head-to-tail polythiophene derivatives, i.e. poly(3-hexyl-thiophene), P3HT, and poly(3-oxyhexyl-thiophene), P3OHT. The effect of substituents on the electronic structure was analyzed by means of bandwidth, bandgap, effective mass, total and partial densities of states and crystal orbital overlap populations. Electronic couplings were estimated from band diagrams as the splitting of the valence band. The neutral and cationic states of isolated oligomers were optimized using the supercell approximation. The hole-transfer rates and mobilities were evaluated according to Marcus's theory. Results provide a compelling illustration of the effect of side chains on the crystal packing, electronic structure and charge-transport properties. Thus, the hole mobility calculated for the alkyl derivative was 0.15 cm(2) V(-1) s(-1) (experimental mobility is 0.10 cm(2) V(-1) s(-1)), while the alkoxy derivative has a theoretical mobility of 0.49 cm(2) V(-1) s(-1). The obtained results hopefully could motivate experimentalists to try out P3OHT for an improved charge carrier mobility.     

Effect of alkyl chain length and hydroxyl group functionalization on the surface properties of imidazolium ionic liquids

Properties of the surface of ionic liquids, such as surface tension, ordering, and charge and density profiles, were studied using molecular simulation. Two types of modification in the molecular structure of imidazolium cations were studied: the length of the alkyl side chain and the presence of a polar hydroxyl group at the end of the side chain. Four ionic liquids were considered: 1-ethyl-3-methylimidazolium tetrafluoroborate, [C(2)C(1)im][BF(4)]; 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate, [C(2)OHC(1)im][BF(4)]; 1-octyl-3-methylimidazolium tetrafluoroborate, [C(8)C(1)im][BF(4)] and 1-(8-hydroxyoctyl)-3-methylimidazolium tetrafluoroborate, [C(8)OHC(1)im][BF(4)]. The surface tension was calculated using both mechanical and thermodynamic definitions, with consistent treatment of the long-range corrections. The simulations reproduce the available experimental values of surface tension with a maximum deviation of ±10%. This energetic characterization of the interface is completed by microscopic structural analysis of orientational ordering at the interface and density profiles along the direction normal to the interface. The presence of the hydroxyl group modifies the local structure at the interface, leading to a less organized liquid phase. The results allow us to relate the surface tension to the structural ordering at the liquid-vacuum interface.     

Fluorescence spectra of organic dyes in solution: a time dependent multilevel approach

Classical all-atom molecular dynamics (MD) simulations and quantum mechanical (QM) time-dependent density functional theory (TD-DFT) calculations are employed to study the conformational and photophysical properties of the first emitter excited state of tetramethyl-rhodamine iso-thiocyanate fluorophore in aqueous solution. For this purpose, a specific and accurate force field has been parameterised from QM data to model the fluorophore's first bright excited state. During the MD simulations, the consequences of the π→π* electronic transition on the structure and microsolvation sphere of the dye has been analysed in some detail and compared to the ground state behaviour. Thereafter, fluorescence has been calculated at the TD-DFT level on configurations sampled from the simulated MD trajectories, allowing us to include time dependent solvent effects in the computed emission spectrum. The latter, when compared with the absorption spectrum, reproduces well the experimental Stokes shift, further validating the proposed multilevel computational procedure.