Towards a molecular model for bismuth(III) subsalicylate. Synthesis and solid-state structure of [Bi(Hsal)3(bipy)(C7H8]2 and [Bi(Hsal)(sal)(1,10-phenanthroline)(C7H8]2

The synthesis and characterization of the first bismuth salicylate complexes, stabilized by chelating amine ligands, offers the possibility for detailed investigation of molecular precursors of the biologically significant compound bismuth subsalicylate (BSS).     

Using ultrapure water in ion chromatography to run analyses at the ng/L level

Thanks to enhanced capabilities, ion chromatography (IC) occupies an increasing position in many types of applications. Achieving ideal performances for an extended life-time can only be reached, however, if the IC system is operated in optimum experimental conditions. Among the various parameters that need to be controlled, water is particularly important, because it is used throughout the analysis, from sample preparation to column rinsing, elution, and mobile phase preparation. More and more, devices are included in IC systems to generate the eluent in situ, and ultrapure water becomes the major reagent. Data of pre-concentration of high purity water show that detection limits at the ng/L level can be expected with water purified using the right combination of technologies.     

A mechanically interlocked molecular system programmed for the delivery of an anticancer drug

The development of mechanically interlocked molecular systems programmed to operate autonomously in biological environments is an emerging field of research with potential medicinal applications. Within this framework, functional rotaxane- and pseudorotaxane-based architectures are starting to attract interest for the delivery of anticancer drugs, with the ultimate goal to improve the efficiency of cancer chemotherapy. Here, we report an enzyme-sensitive [2]-rotaxane designed to release a potent anticancer drug within tumor cells. The molecular device includes a protective ring that prevents the premature liberation of the drug in plasma. However, once located inside cancer cells the [2]-rotaxane leads to the release of the drug through the controlled disassembly of the mechanically interlocked components, in response to a determined sequence of two distinct enzymatic activations. Furthermore, in vitro biological evaluations reveal that this biocompatible functional system exhibits a noticeable level of selectivity for cancer cells overexpressing β-galactosidase.     

Electrochemical study of a nonheme Fe(ii) complex in the presence of dioxygen. Insights into the reductive activation of O2 at Fe(ii) centers

Recent efforts to model the reactivity of iron oxygenases have led to the generation of nonheme Fe^III(OOH) and Fe^IV(O) intermediates from Fe^II complexes and O₂ but using different cofactors. This diversity emphasizes the rich chemistry of nonheme Fe(ii) complexes with dioxygen. We report an original mechanistic study of the reaction of [(TPEN)Fe^II]²⁺ with O₂ carried out by cyclic voltammetry. From this Fe^II precursor, reaction intermediates such as [(TPEN)Fe^IV(O)]²⁺, [(TPEN)Fe^III(OOH)]²⁺ and [(TPEN)Fe^III(OO)]⁺ have been chemically generated in high yield, and characterized electrochemically. These electrochemical data have been used to analyse and perform simulation of the cyclic voltammograms of [(TPEN)Fe^II]²⁺ in the presence of O₂. Thus, several important mechanistic informations on this reaction have been obtained. An unfavourable chemical equilibrium between O₂ and the Fe^II complex occurs that leads to the Fe^III-peroxo complex upon reduction, similarly to heme enzymes such as P450. However, unlike in heme systems, further reduction of this latter intermediate does not result in O–O bond cleavage.     

Topological metastability and oxide ionic conduction in La(2)-(x)Eu(x)Mo(2)O(9)

The effect of partial substitution, up to x = 0.4, of La by trivalent Eu on the phase stability, thermal expansion, and transport properties of La2Mo2O9 are investigated using temperature-controlled X-ray powder diffraction, differential thermal analysis, and complex impedance spectroscopy. At low europium content (x < or = 0.1), the alpha-beta phase transition is observed at a temperature dependent on the sample shaping (powder, pellet, etc.). At high europium content (x > or = 0.25), the samples remain cubic (beta phase), regardless of the shaping. In the intermediate range of europium content (x = 0.15, 0.2), the phase stability is highly sensitive to the thermal history and the sample shaping, with a double-reversed beta-alpha-beta transition suppressed by the shaping/sintering process. The influence of the amount of europium on the transport mechanisms and parameters is studied in both low- (Arrhenius) and high-temperature (Vogel-Tammann-Fulcher = VTF) regimes. If the effect of substitution is rather mild and monotonous within each transport regime and crystallographic phase, an abrupt change in the Arrhenius parameters between the alpha- and beta-type phases is observed.     

Fluorescence of the DNA double helices (dAdT)n.(dAdT)n studied by femtosecond spectroscopy

Polymeric and oligomeric DNA helices, poly(dAdT).poly(dAdT) and (dAdT)(10).(dAdT)(10), composed of 200-400 and 20 adenine-thymine base pairs, respectively, are studied by fluorescence upconversion. Fluorescence decays, anisotropy decays and time-resolved spectra, obtained for this alternating base sequence, are compared with those determined previously for the homopolymeric sequence (dA)(n).(dT)(n). It is shown that identical fluorescence decays may correspond to quite different anisotropy decays and vice versa, both varying with the emission wavelength, the base sequence and the duplex size. Our observations cannot be explained in terms of monomer and excimer emission exclusively, as concluded in the past on the basis of steady-state measurements. Excitons also contribute to the fluorescence. These are rapidly trapped by excimers, characterized by long-lived weak emission.     

New water-soluble polyanionic dendrimers and binding to acetylcholine in water by means of contact ion-pairing interactions

A new water-soluble polyanionic dendrimer containing 81 benzoate termini (diameter: 11+/-1 nm from DOSY NMR spectroscopy) has been synthesized; it interacts with acetylcholine cations in water-soluble assemblies in which each carboxylate terminus reversibly forms contact ion pairs and aggregates at the tether termini, as shown by 1H NMR spectroscopy.