Oxidative double dehalogenation of tetrachlorocatechol by a bio-inspired CuII complex: formation of chloranilic acid

Copper(II) complexes of the potentially tripodal N,N,O ligand 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its conjugate acid HL1 have been synthesised and structurally and spectroscopically characterised. The reaction of equimolar amounts of ligand and CuII resulted in the complexes [Cu(L1)]n(X)n (X=OTf-, PF6(-); n=1,2), for which a new bridging coordination mode of L1 is inferred. Although these complexes showed moderate catecholase activity in the oxidation of 3,5-di-tert-butylcatechol, surprising reactivity with the pseudo-substrate tetrachlorocatechol was observed. A chloranilato-bridged dinuclear CuII complex was isolated from the reaction of [Cu(L1)]n(PF6)n with tetrachlorocatechol. This stoichiometric oxidative double dehalogenation of tetrachlorocatechol to chloranilic acid by a biomimetic copper(II) complex is unprecedented. The crystal structure of the product, [Cu2(ca)Cl2(HL1)2], shows a bridging bis-bidentate chloranilato (ca) ligand and ligand L1 coordinated as its conjugate acid (HL1) in a tridentate fashion. Magnetic susceptibility studies revealed weak antiferromagnetic coupling (J= -35 cm(-1)) between the two copper centres in the dinuclear complex. Dissolution of the green complex [Cu2(ca)Cl2(HL1)2] resulted in the formation of new pink-purple mononuclear compound [Cu(ca)(HL1)(H2O)], the crystal structure of which was determined. It showed a terminal bidentate chloranilato ligand and N,N-bidentate coordination of ligand HL1, which illustrates the flexible coordination chemistry of ligand L1.     

Incorporation of nonmethyl branches by isoprenoid-like logic: multiple beta-alkylation events in the biosynthesis of myxovirescin A1

Several polyketide secondary metabolites are predicted to undergo isoprenoid-like beta-alkylations during biosynthesis. One such secondary metabolite is myxovirescin A1, produced by Myxococcus xanthus. Myxovirescin is of special interest in that it appears to undergo two distinct beta-alkylations. Additionally, the myxovirescin biosynthetic gene cluster lacks tandem thiolation domains required in the synthesis of other beta-branched secondary metabolites. To probe the origins of the beta-branches in myxovirescin, we heterologously overexpressed the proteins predicted to be responsible for myxovirescin beta-alkylation and reconstituted their activities in vitro on model substrates. Our results confirm that myxovirescin undergoes two isoprenoid-like beta-alkylations during its biosynthesis, including an unprecedented beta-ethylation. The study of its biosynthesis should shed light on the scope and requirements for isoprenoid-like biosynthetic logic in a polyketide context.     

Synthesis of sugar nucleotides by application of phosphoramidites

A new method for the construction of pyrophosphates is reported based on the coupling of a sugar phosphate and a nucleoside phosphoramidite. The in situ formed phosphate-phosphite intermediate was subsequently oxidized with tBuOOH. Three UDP-N-acetylglucosamine derivatives were prepared using this one-pot procedure in good yields.     

The excited state dynamics of KLa(MoO4)2:Pr: From a case study to the determination of the energy levels of rare earth impurities relative to the bandgap in oxidising host lattices

The luminescence properties of KLa(MoO₄)₂ (KLM) single crystals doped with Pr³⁺ have been measured in the 10-600 K temperature range in order to investigate the mechanisms involved in the radiationless processes. At variance with previously studied scheelite-like molybdates activated with Pr³⁺, no effects attributed to the formation of intervalence charge transfer states have been observed. The model proposed in order to account for this behaviour allows the determination of the energy of the Pr³⁺ levels relative to the valence and conduction bands of the host. This model has firstly been confirmed for Tb³⁺-doped KLM, for which suitable experimental data are available, and then extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties. The obtained conclusions are finally supported in the light of the comparison with some other representative cases.     

Catalytic asymmetric conjugate addition of grignard reagents to alpha,beta-unsaturated sulfones

A highly efficient method is reported for the asymmetric conjugate addition of Grignard reagents to alpha,beta-unsaturated 2-pyridylsulfones. Using a Cu/TolBinap complex, excellent enantioselectivities and high yields are obtained for a wide variety of aliphatic substrates.     

Noise within the social context: annoyance reduction through fair procedures

The social context of noise exposure is a codeterminant of noise annoyance. The present study shows that fairness of the exposure procedure (sound management) can be used as an instrument to reduce noise annoyance. In a laboratory experiment (N = 117) participants are exposed to aircraft sound of different sound pressure level (SPL: 50 vs 70 dB A)--which is experienced as noise--while they work on a reading task. The exposure procedure (fair versus neutral) is modeled in line with findings from social justice theory. In the fair condition, participants can voice their preference for a certain sound sample, although they cannot deduce whether their preference is granted. In the neutral condition, participants are not asked to voice their preference. Results show the predicted interaction effect of sound pressure level and procedure on annoyance: Annoyance ratings are significantly lower in the fair condition than in the neutral condition, but this effect is found only in the 70 dB condition. When the SPL is considerably disturbing, fair procedures reduce noise annoyance. Consequences of the reported findings for both theory and practice are discussed.     

A Space–Time Integral Estimate For A Large Data Semi-linear Wave Equation on the Schwarzschild Manifold

We consider the wave equation with in . The wave equation on a spherically symmetric manifold with a single closed geodesic surface or on the exterior of the Schwarzschild manifold can be reduced to this form. Using a smoothed Morawetz estimate which does not require a spherical harmonic decomposition, we show that there is decay in for initial data in the energy class, even if the initial data is large. This requires certain conditions on the potentials V, V _L and f. We show that a key condition on the weight in the smoothed Morawetz estimate can be reduced to an ODE condition, which is verified numerically.      

Multicomponent supramolecular thermoplastic elastomer with peptide‐modified nanofibers

Bioactive nanofibers present a promising synthetic niche for in vivo applications due to their morphological and functional resemblance to the extracellular matrix. Potentially interesting nanofibers are constructed from the hard‐segment regimes in well‐defined thermoplastic elastomers (TPEs). The supramolecular interactions between these hard segments cause physical crosslinking by the formation of nanofibers and provide excellent mechanical properties. Here, we make use of a new class of biocompatible supramolecular TPEs, in which both the formation of the main chain and the hard block is based on multiple hydrogen‐bonding interactions. A self‐assembly process is explored to arrive at well‐defined peptide‐modified nanofibers embedded in a biocompatible soft matrix. Crucial for the success in the synthetic design is the use of an exact match between the molecular recognition units of the peptide and the supramolecular unit that takes care of forming the supramolecular nanofibers of the TPE. Evidence for the strong anchoring of the modified peptides in the hard‐segment nanofibers of the supramolecular TPE is provided by simple extraction experiments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A Cyclic Sulfate Approach to the Synthesis of 1,4-Dideoxy-1,4-imino Derivatives of L-Xylitol,L-Arabinitol and D-Xylitol

Polyhydroxylated pyrrolidines are readily accessible by ring opening of a 1,4-cyclic sulfate function in pentitol derivatives by nitrogen nucleophiles and further processing of the in situ generated charged sulfate group.     

Correction to: Complete enumeration of pure‐level and mixed‐level orthogonal arrays

We correct an error found in Schoen, Endebak, Nguyen, J Combin Designs 18 (2010), 123–140. © 2010 Wiley Periodicals, Inc. J Combin Designs 18: 488, 2010