Beyond classical coordination: silver-pi interactions in metal dipyrrin complexes

Homo- and hetero-leptic Zn and Cu complexes of dipyrrin type ligands bearing mono- and di-cyanophenyl groups when combined with silver cations lead to the formation of Ag(I)-C=C double bond interactions unprecedented in the crystalline phase.     

Influence of structural factors on the enhanced activity of moxifloxacin: a fluorescence and EPR spectroscopic study

Partition coefficients of moxifloxacin in liposomes of dimyristoyl-L-α-phosphatidylcholine or dimyristoyl-L-α-phosphatidylglycerol and water were determined by spectrophotometry and fluorimetry. The K _p values obtained were larger than those reported for most of the other fluoroquinolones, a consequence of the structural changes observed in the molecule of moxifloxacin, which in turn change its acid/base properties. Introduction of a methoxy group at position 8 and a diazabicyclonyl ring at position 7 in the basic fluoroquinolone structure alters the charge distribution at the physiological pH of 7.4, and these changes seem to be responsible for its improved antibacterial potency and broader spectrum of activity. Location studies have also been performed using fluorescence and electron paramagnetic resonance (EPR) spectroscopies. The results show that moxifloxacin must be located near the phospholipid headgroups, similar to other fluoroquinolones, but contributions from a hydrophobic component were also detected. These results suggest that the enhanced activity of this drug may be related to a more facilitated entrance into the bacterial cell, perhaps including a mediator step involving electrostatic interaction with a hydrophobic component; this step then controls the extent or orientation of insertion and improves the electrostatic interaction.     

The Influence of the Amide Linkage in the FeIII‐Binding Properties of Catechol‐Modified Rosamine Derivatives

The two new fluorescent ligands RosCat1 and RosCat2 contain catechol receptors connected to rosamine platforms through an amide linkage and were synthesized by using microwave‐assisted coupling reactions of carboxyl‐ or amine‐substituted rosamines with the corresponding catechol units and subsequent deprotection. RosCat1 possesses a reverse amide, whereas RosCat2 has the usual oriented amide bond (HNCO vs. CONH, respectively). The ligands were characterized by means of NMR spectroscopy, mass‐spectrometry, and DFT calculations and X‐ray crystallography studies for RosCat1 . The influence of the amide linkage on the photophysical properties of the fluorescent ligands was assessed in different solvents and showed a higher fluorescence quantum yield for RosCat1 . The coordination chemistry of these ligands with a Fe^III center has been rationalized by mass‐spectrometric analysis and semiempirical calculations. Octahedral Fe^III complexes were obtained by the chelation of three RosCat1 or RosCat2 ligands. Interestingly, the unconventional amide connectivity in RosCat1 imposes the formation of an eight‐membered ring on the chelate complex through a “salicylate‐type” mode of coordination.     

Highly Fluorescent Green Fluorescent Protein Chromophore Analogues Made by Decorating the Imidazolone Ring

The synthesis and photophysical behavior of an unexplored family of green fluorescent protein (GFP)‐like chromophore analogues is reported. The compound (Z)‐4‐(4‐hydroxybenzylidene)‐1‐propyl‐2‐(propylamino)‐1H‐imidazol‐5(4 H)‐one (p‐HBDNI, 2 a ) exhibits significantly enhanced fluorescence properties relative to the parent compound (Z)‐5‐(4‐hydroxybenzylidene)‐2,3‐dimethyl‐3,5‐dihydro‐4H‐imidazol‐4‐one (p‐HBDI, 1 ). p‐HBDNI was considered as a model system and the photophysical properties of other novel 2‐amino‐3,5‐dihydro‐4H‐imidazol‐4‐one derivatives were evaluated. Time‐dependent DFT calculations were carried out to rationalize the results. The analogue AIDNI ( 2 c ), in which the 4‐hydroxybenzyl group of p‐HBDNI was replaced by an azaindole group, showed improved photophysical properties and potential for cell staining. The uptake and intracellular distribution of 2 c in living cells was investigated by confocal microscopy imaging.     

Micro solid phase spectrophotometry in a sequential injection lab-on-valve platform for cadmium,zinc, and copper determination in freshwaters

This work describes the development of a solid phase spectrophotometry method in a μSI-LOV system for cadmium, zinc, and copper determination in freshwaters. NTA (Nitrilotriacetic acid) beads with 60–160 μm diameter were packed in the flow cell of the LOV for a μSPE column of 1 cm length. The spectrophotometric determination is based on the colourimetric reaction between dithizone and the target metals, previously retained on NTA resin. The absorbance of the coloured product formed is measured, at 550 nm, on the surface of the NTA resin beads in a solid phase spectrophotometry approach.     

Hybrid Transported-Tabulated Strategy to Downsize Detailed Chemistry for Numerical Simulation of Premixed Flames

A strategy to introduce hydrocarbon combustion detailed chemistry into three-dimensional numerical simulation of flames is reported. Significant progress has been made recently in terms of accuracy and robustness in both chemical kinetics and flow computations. However, the highest resolution reached in simulation of practical burner does not yet ensure that the response of intermediate radical species is fully captured. In the method discussed, the full set of species and elementary reaction rates of the detailed mechanism are retained, but only species featuring non-zero concentration in fresh and burnt gases are transported with the flow. Intermediate chemical species, developing within thin flame layers, are expressed resorting to their self-similar properties observed in a series of canonical combustion problems, projected into an optimized progress variable defined from all transported species. The method is tested with success in various adiabatic and non-adiabatic laminar steady- and unsteady-strained premixed flames.     

Modelling of the effect of DC and AC electric fields on the stability of a lifted diffusion methane/air flame

The application of an external electric field is known to improve flame stability significantly. Until now, few studies have proposed modelling approaches for combustion in the presence of an externally applied voltage. In these numerical studies, the negative ions are overlooked, and only the displacement of positive ions and electrons under the effect of a direct electric field was examined. In the present paper, a simplified mathematical model including negative ions is proposed based on a kinetic mechanism featuring 39 ionic reactions and 5 charged species. This mechanism is first evaluated by comparison of a monodimensional premixed flame with the available experimental data. Then it is used to analyse the stabilisation mechanism of a diffusion lifted flame in the presence of direct or alternating electric fields. It was concluded that the role of negative ions is crucial, and they are not to be neglected. Moreover, the simulations have shown that the magnitude of the flame stabilisation improvement depends, mainly, on the intensity and polarity of the applied voltage. If the applied voltage is alternating, its frequency is also found to influence the extent of the flame stabilisation improvement.     

Simple one-step ultrasonic synthesis of anatase titania/polypyrrole nanocomposites

In this work, hybrid nanocomposites based on anatase titania:polypyrrole (TiO₂:PPy) were directly obtained from a simple, one-step, ultrasonic (UT)-assisted synthesis. The properties of these crystalline nanocomposites were compared with those of others fabricated using cold (Cold)-assisted synthesis without any UT assistance, which required a hydrothermal treatment (HT) to yield crystalline anatase titania in the nanocomposite (TiO₂:PPy) at low temperature (130 °C) and in a short time (3 h). The SEM results demonstrated that the UT-assisted synthesis is a feasible method to obtain anatase TiO₂:PPy nanocomposites with controlled morphology using low energy. The Fourier transform infrared (FT-IR) bands of the crystalline nanocomposites exhibited a shift with respect to neat components, which was attributed to the strong interaction between the secondary amine groups (N–H) of PPy and the oxygen from TiO₂. The acceptable absorption in the visible region (λ_max = 670 nm) indicates that these nanocomposites are good candidates for harvesting energy in solar cells. Devices based on these nanocomposites were built to evaluate their electrical properties. An increase in the photocurrent was observed for the devices prepared with the nanocomposites from the UT-assisted synthesis.     

Access to optically active 3-azido- and 3-aminopiperidine derivatives by enantioselective ring expansion of prolinols

The activation of N-alkyl prolinols by XtalFluor E allowed the formation of an aziridinium intermediate that can react with tetrabutylammonium azide (nBu(4)NN(3)) to produce 3-azidopiperidines and/or 2-(azidomethyl)pyrrolidines, in a ratio up to 100/0. These 3-azidopiperidines can be reduced to the corresponding 3-aminopiperidines.