Sensing the chirality of Dawson lanthanide polyoxometalates [alpha1-LnP2W17O61]7- by multinuclear NMR spectroscopy

Lanthanide complexes of the chiral Dawson phosphotungstate [alpha(1)-P(2)W(17)O(61)](10-) were used to study the formation of diastereomers with optically pure organic ligands. The present work started with the full assignment of the (183)W NMR spectra of [alpha(1)-Yb(H(2)O)(4)P(2)W(17)O(61)](7-) at different temperatures and concentrations, which allowed the structure of the dimerized form in aqueous solution to be established. Different enantiopure amino acids and phosphonic acids were screened as ligands. Both types allowed chiral differentiation by multinuclear NMR spectroscopy under fast-exchange conditions. Functional groups with a good affinity for the oxo framework of the polyoxometalate were identified, and maps of the interactions between L-serine and N-phosphonomethyl-L-proline with [alpha(1)-Yb(H(2)O)(4)P(2)W(17)O(61)](7-) were established. This demonstrates the power of (183)W NMR spectroscopy to elucidate the molecular recognition of inorganic molecules by organic compounds. N-Phosphonomethyl-L-proline appears to be a convenient ligand to promote separation of the diastereomers and ultimately resolution of the enantiomers of [alpha(1)-Yb(H(2)O)(4)P(2)W(17)O(61)](7-).     

X‐Tream quality assurance in synchrotron X‐ray microbeam radiation therapy

Microbeam radiation therapy (MRT) is a novel irradiation technique for brain tumours treatment currently under development at the European Synchrotron Radiation Facility in Grenoble, France. The technique is based on the spatial fractionation of a highly brilliant synchrotron X‐ray beam into an array of microbeams using a multi‐slit collimator (MSC). After promising pre‐clinical results, veterinary trials have recently commenced requiring the need for dedicated quality assurance (QA) procedures. The quality of MRT treatment demands reproducible and precise spatial fractionation of the incoming synchrotron beam. The intensity profile of the microbeams must also be quickly and quantitatively characterized prior to each treatment for comparison with that used for input to the dose‐planning calculations. The Centre for Medical Radiation Physics (University of Wollongong, Australia) has developed an X‐ray treatment monitoring system (X‐Tream) which incorporates a high‐spatial‐resolution silicon strip detector (SSD) specifically designed for MRT. In‐air measurements of the horizontal profile of the intrinsic microbeam X‐ray field in order to determine the relative intensity of each microbeam are presented, and the alignment of the MSC is also assessed. The results show that the SSD is able to resolve individual microbeams which therefore provides invaluable QA of the horizontal field size and microbeam number and shape. They also demonstrate that the SSD used in the X‐Tream system is very sensitive to any small misalignment of the MSC. In order to allow as rapid QA as possible, a fast alignment procedure of the SSD based on X‐ray imaging with a low‐intensity low‐energy beam has been developed and is presented in this publication.     

Nitrosylation of Nitric‐Oxide‐Sensing Regulatory Proteins Containing [4Fe‐4S] Clusters Gives Rise to Multiple Iron–Nitrosyl Complexes

The reaction of protein‐bound iron–sulfur (Fe‐S) clusters with nitric oxide (NO) plays key roles in NO‐mediated toxicity and signaling. Elucidation of the mechanism of the reaction of NO with DNA regulatory proteins that contain Fe‐S clusters has been hampered by a lack of information about the nature of the iron‐nitrosyl products formed. Herein, we report nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT) calculations that identify NO reaction products in WhiD and NsrR, regulatory proteins that use a [4Fe‐4S] cluster to sense NO. This work reveals that nitrosylation yields multiple products structurally related to Roussin's Red Ester (RRE, [Fe₂(NO)₄(Cys)₂]) and Roussin's Black Salt (RBS, [Fe₄(NO)₇S₃]. In the latter case, the absence of ³²S/³⁴S shifts in the Fe?S region of the NRVS spectra suggest that a new species, Roussin's Black Ester (RBE), may be formed, in which one or more of the sulfide ligands is replaced by Cys thiolates.     

Chemiluminescent probe for the in vitro detection of protease activity

A strategy involving the use of a self-immolative linker has been investigated for the chemiluminescent sensing of proteases. The reactive linker enabled the release of a 1,2-dioxetane light precursor. As a proof of principle, caspase-3, a key peptidase involved in apoptosis has been targeted. An in vitro assay has been carried out and proved the decomposition of the linker and the selectivity for caspase-3.     

Asymmetric total synthesis of (-)-indicol by a carbene cyclization-cycloaddition cascade strategy

The first total synthesis of a secodolastane, (-)-indicol, has been accomplished. The key reaction is a rhodium(II)-mediated carbene cyclization-cycloaddition cascade, by which the core bicyclo[5.4.0]undecane skeleton was assembled. In this one-pot reaction, a domino series of transformations resulting in the construction of three sigma bonds and three stereocenters was realized in good yield.     

Versatile synthesis of rare nucleotide furanoses

Direct activation of unprotected thioimidoyl furanosides yielded in only one step and few minutes a panel of rare uridine 5'-diphospho-furanoses. Diastereoselectivity of the reaction was tightly connected with reaction time, temperature, and nature of the furanosyl donor. This approach was totally selective since no ring expansion from the initial five-membered ring to the more stable pyranose form was observed.     

Quasi-Stationarity of Discrete-Time Markov Chains with Drift to Infinity

We consider a discrete-time Markov chain on the non-negative integers with drift to infinity and study the limiting behavior of the state probabilities conditioned on not having left state 0 for the last time. Using a transformation, we obtain a dual Markov chain with an absorbing state such that absorption occurs with probability 1. We prove that the state probabilities of the original chain conditioned on not having left state 0 for the last time are equal to the state probabilities of its dual conditioned on non-absorption. This allows us to establish the simultaneous existence, and then equivalence, of their limiting conditional distributions. Although a limiting conditional distribution for the dual chain is always a quasi-stationary distribution in the usual sense, a similar statement is not possible for the original chain.     

Development of Sustainable Chemistry in Madagascar: Example of the Valuation of CNSL and the Use of Chromones as an Attractant for Mosquitoes

This article describes a part of the results obtained from the cooperation between the University of Lyon1 (France) and the University of Antananarivo (Madagascar). It shows (among others) that useful research can be carried out in developing countries of the tropics if their social, technical, and economic conditions are taken into account. The concepts and methods associated with so-called “green chemistry” are particularly appropriated for this purpose. To illustrate this approach, two examples are shown. The first deals with industrial ecology and concerns waste transformation from the production of cashew nut into an amphiphilic product, oxyacetic derivatives. This product was obtained with a high yield and in a single step reaction. It exhibited an important surfactant property similar to those of the main fossil-based ones but with a much lower ecological impact. The second talks about chemical ecology as an alternative to insecticides and used to control dangerous mosquito populations. New substituted chromones were synthesized and showed biological activities toward Aedes albopictus mosquito species. Strong repellent properties were recorded for some alkoxylated products if others had a significant attractant effect (Kairomone) depending on their stereochemistry and the length of the alkyl chain.     

Di‐μ‐benzoato‐bis­[di­carbonyl­(pyri­dine)­ruthenium(I)] (new polymorph) and di‐μ‐tri­fluoro­acetato‐bis­[di­carbonyl­(pyridine)­ruthenium(I)]

The syntheses and crystal structure determinations of a pair of `sawhorse' dimers are reported, viz. [Ru₂(C₆H₅CO₂)₂(C₅H₅N)₂(CO)₄] [a new polymorph, cf. Kepert, Deacon, Spiccia, Fallon, Skelton & White (2000). J. Chem. Soc. Dalton Trans. pp. 2867–2874] and [Ru₂(CF₃CO₂)₂(C₅H₅N)₂(CO)₄]. The Ru⋯Ru distances are 2.6724 (2) and 2.7122 (5) Å, respectively.     

UV dosimeters based on neotetrazolium chloride

A novel UV dosimeter is described comprising a tetrazolium dye, neotetrazolium chloride (NTC), dissolved in a film of polymer, polyvinyl alcohol (PVA). The dosimeter is pale yellow/colourless in the absence of UV light, and turns red upon exposure to UV light. The spectral characteristics of a typical UV dosimeter film and the mechanism through which the colour change occurs are detailed. The NTC UV dosimeter films exhibit a response to UV light that is related to the intensity and duration of UV exposure, the level of dye present in the films and the thickness of the films themselves. The response of the dosimeter is temperature independent over the range 20–40 °C and, like most UV dosimeters, exhibits a cosine-like response dependence upon irradiance angle. The introduction of a layer of a UV-screening compound which slows the rate at which the dosimeter responds to UVR enables the dosimeter response to be tailored to different UV doses. The possible use of these novel dosimeters to measure solar UV exposure dose is discussed.