Supercritical CO2: an effective medium for the chemo-enzymatic synthesis of block copolymers?

In this review, we describe the combination of enzymatic polymerisation and controlled free radical polymerisation in supercritical carbon dioxide. This combination facilitates the preparation of a range of block and graft copolymers, some of which cannot easily be obtained by conventional polymer synthesis. Biocatalysis in polymer science provides significant new opportunities and will open up a very broad range of new polymeric materials.     

Residue determination of captan and folpet in vegetable samples by gas chromatography/negative chemical ionization-mass spectrometry

A gas chromatography/negative chemical ionization-mass spectrometry (GC/NCI-MS) method has been developed for the simultaneous determination of the fungicides captan and folpet in khaki (persimmon; flesh and peel) and cauliflower. Samples were extracted with acetone in the presence of 0.1 M zinc acetate solution in order to avoid degradation of fungicides and were purified using solid-phase extraction with divinylbenzene polymeric cartridges. Purified extracts were evaporated and dissolved in hexane prior to injection into the GC/NCI-MS system. Isotope-labeled captan and folpet were used as surrogate/internal standards, and quantification was performed using matrix-matched calibration. The method showed linear response in the concentration range tested (50-2500 ng/mL). The method was fully validated with untreated blank samples of khaki (flesh and peel) and cauliflower spiked at 0.05 and 0.5 mg/kg. Satisfactory recoveries between 82 and 106% and relative standard deviations lower than 11% in all cases (n = 5) were obtained. The limit of detection for both compounds were estimated to be 0.01 mg/kg. The developed method has been applied to treated and untreated samples collected from residue trials.     

Synthesis of a New pH-Dependent Ligand: Conformational and Complexation Studies

A new macrocyclic ligand, 3, which exhibits pH-induced conformational changes, has been prepared. This ligand consists of a crown ether derived from a trans-anti-trans 1,2,4,5-tetrasubstituted cyclohexane. Due to the stereochemistry of the substituents on the carbocyclic ring, two different low-energy conformations of the crown ether are possible. Ligand 3 has been studied in solution by ¹H NMR spectroscopy at different values of pH and temperature, showing that the conformation of the crown ether, and thus its complexing ability, is strongly pH-dependent. The solid-state structure of the ligand has been determined by X-ray diffraction.     

Discrete iridium pyridonate chains with variable metal valence: nature and energetics of the Ir-Ir bonding from DFT calculations

The structure of the Ir(I) complex [Ir2(mu-OPy)2(CO)4] (Opy = 2-pyridonate) has been fully characterized in its head-to-head (A) configuration as a "dimer of dimers" AA in which two binuclear complexes are connected by means of a weak, but unsupported, iridium-iridium interaction (Ir(2)...Ir(2A) 2.9808(6) A). The head-to-tail isomer, referred to as B, was found in equilibrium with A in solution. It has been shown that this complex can be oxidized by diiodine to give iridium chains with highly selective configurations and general formula I-[Ir2(mu-OPy)2(CO)4]n-I (n = 1-3). The synthesis of IAI (1), of the isomers IAAI (2AA) and IABI (2AB), and of IABAI (3) is reported. DFT calculations have been carried out on A and B and on the known isomers of 1-3, as well as on two isomers of the hypothetic chain of eight Ir(1.25) atoms corresponding to n = 4. The stability of the metal chain is assigned to a 2-electron/2n-center sigma bond delocalized along the metal backbone and supplemented with a weak attractive interaction of the metallophilic type. Calculations confirm that further oxidation of the Ir chains corresponding to n > 1 by iodine, yielding the cleavage of one or two unsupported bond(s), is a highly exothermic process. The formation of the I-[Ir2(mu-OPy)2(CO)4]n-I chains is also computed to be exothermic, either highly for n = 1 or still significantly for n = 2 and 3. At variance with these results, the formation of an octanuclear chain is predicted to be no more than marginally exothermic (DeltaG = 1.7 kcal.mol(-1)), mainly because of interligand strain induced by the steric bulk of the amidate rings.     

Development and evaluation of a plastic scintillating resin for radioactive tin determination

Journal of Radioanalytical and Nuclear Chemistry - In the next few years, a large number of nuclear facilities will be closed. This will involve the measurement of large amounts of nuclear wastes...     

Simultaneous enzymatic ring opening polymerisation and RAFT-mediated polymerisation in supercritical CO2

This report presents the first simultaneous, metal-free synthesis of block copolymers through combination of enzymatic ring-opening polymerisation of epsilon-caprolactone with RAFT-mediated controlled radical polymerisation of styrene.