Clickety click: Click dendrimers, including the first click metallodendrimers, are synthesized in the presence of a stoichiometric amount of copper(I). The 1,2,3‐triazolylferrocenyl dendrimers (see picture) are selective electrochemical sensors for both transition‐metal cations and oxo anions.

Keggin and Dawson-type polyoxometalates (POMs) covalently grafted to heteroleptic cyclometalated iridium(III) complexes (POM-[Ir] dyads) have been prepared by postfunctionalization of organosilyl and organotin POM derivatives. Electronic properties of these 4 photosensitized POM-[Ir] dyads were evaluated by electrochemical measurements and theoretical calculations. These studies reveal that the electron acceptor character of the POMs vary with structural class (Keggin vs. Dawson) and chemical anchorage (organosilyl vs. organotin); they reveal the poor electronic interaction between the POMs and the chromophores. Combined transient absorption and spectroelectrochemical measurements provide evidence for the formation of photoinduced electron transfer from the chromophore to the POM. The lifetimes of the charge-separated states (ranging from ns to hundreds of ns) are the longest values reported for covalently bonded photosensitized POMs. The functionalization of the heteroleptic cyclometalated iridium(III) on the picolinate ligand provides directionality to the photoinduced electron transfer by enhancing charge separation and delaying charge recombination The kinetics of the photoinduced electron transfers are rationalized by Marcus theory. We conclude that the charge separation and charge recombination respectively occur in the Marcus normal and inverted regions.

We report the direct introduction of biological samples into a high-resolution mass spectrometer, the LTQ-Orbitrap, as a fast tool for metabolomic studies. A proof of concept study was performed on yeast cell extracts that were introduced into the mass spectrometer by using flow injection analysis, with an acquisition time of 3 min. Typical mass spectra contained a few thousand m/z signals, 400 of which were found to be analytically relevant (i.e., their intensity was 3-fold higher than that of the background noise and they occurred in at least 60% of the acquisition profiles under identical experimental conditions). The method was validated by studies of the matrix effect, linearity, and intra-assay precision. Accurate mass measurements in the Orbitrap discriminated between isobaric ions and also indicated the elemental composition of the ions of interest with mass errors below 5 ppm, for identification purposes. The proposed structures were then assessed by MSn experiments via the linear ion trap, together with accurate mass determination of the product ions in the Orbitrap analyzer. When applied to the study of cadmium toxicity, the method was as effective as that initially developed by using LC/ESI-MS/MS for a targeted approach. The same metabolic fingerprints were also subjected to multivariate statistical analyses. The results highlighted a reorganization of amino acid metabolism under cadmium conditions in order to increase the biosynthesis of glutathione.

A series of redox tunable polyoxometalate–bodipy conjugates display variable charge transfer dynamics occuring down to 54 ps.

High resolution mass spectrometry (HRMS) is increasingly used to produce metabolomics data. Thanks to its high mass resolution and mass measurement accuracy, it is also very useful for metabolite identification. Nevertheless, a rigorous methodology is required. This manuscript describes different steps involved in the structural elucidation of metabolites and demonstrates the utility of HRMS for such purpose. After a brief overview of HRMS performances in terms of mass measurement accuracy, peak resolution, isotopic clusters/patterns and the instrumentation used, the first section is devoted to the data processing generally performed to reduce the data set size. Based on the mass accuracy measurements, different post-acquisition data processing procedures have been developed for complex mixture analysis and can be used in metabolomics. The second section describes protocols used to process putative metabolite annotations or identifications with HRMS data, based on elemental composition determined from accurately measured m/z value and mass spectral databases. Non-classical approaches are also proposed for tentative structure elucidation of unknown metabolites. Finally, limitations of the proposed workflow for metabolite structure elucidation are discussed and possible improvements are proposed

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Reproducibility among different types of excitation modes is a major bottleneck in the field of tandem mass spectrometry library development in metabolomics. In this study, we specifically evaluated the influence of collision voltage and activation time parameters on tandem mass spectrometry spectra for various excitation modes [collision-induced dissociation (CID), pulsed Q dissociation (PQD) and higher-energy collision dissociation (HCD)] of Orbitrap-based instruments. For this purpose, internal energy deposition was probed using an approach based on Rice-Rampserger-Kassel-Marcus modeling with three thermometer compounds of different degree of freedom (69, 228 and 420) and a thermal model. This model treats consecutively the activation and decomposition steps, and the survival precursor ion populations are characterized by truncated Maxwell-Boltzmann internal energy distributions. This study demonstrates that the activation time has a significant impact on MS/MS spectra using the CID and PQD modes. The proposed model seems suitable to describe the multiple collision regime in the PQD and HCD modes. Linear relationships between mean internal energy and collision voltage are shown for the latter modes and the three thermometer molecules. These results suggest that a calibration based on the collision voltage should provide reproducible for PQD, HCD to be compared with CID in tandem in space instruments. However, an important signal loss is observed in PQD excitation mode whatever the mass of the studied compounds, which may affect not only parent ions but also fragment ions depending on the fragmentation parameters. A calibration approach for the CID mode based on the variation of activation time parameter is more appropriate than one based on collision voltage. In fact, the activation time parameter in CID induces a modification of the collisional regime and thus helps control the orientation of the fragmentation pathways (competitive or consecutive dissociations).

The charge state distribution of proteins was studied as a function of experimental conditions, to improve the understanding of the matrix-assisted laser desorption/ionization (MALDI) mechanisms. The relative abundances of the multiply-charged ions appear to be a function of the matrix chosen, the laser fluence and the matrix-to-analyte molar ratio. A correlation is found between the matrix proton affinity and the yield of singly- versus multiply-charged ions. These results are in good agreement with a model in which gas-phase intracluster reactions play a significant role in analyte ion formation. A new model for endothermic desolvation processes in ultraviolet/MALDI is presented and discussed. It is based upon the existence of highly-charged precursor clusters and, complementary to the ion survivor model of Karas et al., assumes that two energy-dependent processes exist: (i) a soft desolvation involving consecutive losses of neutral matrix molecules, leading to a multiply-charged analyte and (ii) hard desolvation leading to a low charge state analyte, by consecutive losses of charged matrix molecules. These desolvations pathways are discussed in terms of kinetically limited processes. The efficiency of the two competitive desolvation processes seems related to the internal energy carried away by clusters during ablation.