Efficient CO2 Insertion and Reduction Catalyzed by a Terminal Zinc Hydride Complex

The terminal zinc hydride complex [Tntm]ZnH ( 2 ; Tntm=tris(6‐tert‐butyl‐3‐thiopyridazinyl)methanide) is an efficient hydrosilylation catalyst of CO₂ at room temperature without the need of Lewis acidic additives. The inherent electrophilicity of the system leads to selective formation of the monosilylated product (MeO)₃SiO₂CH (at room temperature with a TOF of 22.2 h^?1 and at 45 °C with a TOF of 66.7 h^?1). In absence of silanes, the intermediate formate complex [Tntm]Zn(O₂CH) ( 3 ) is quantitatively formed within 5 min. All complexes were fully characterized by ¹H and ¹³C NMR spectroscopy and single‐crystal X‐ray diffraction analyses. Density functional theory (DFT) calculations reveal a high positive charge on zinc and the increased preference of the ligand to adopt a κ³‐coordination mode.     

Über die Bestimmung der Oxalsäure

Analytical and Bioanalytical Chemistry -     

Structure-based approach for identification of novel phenylboronic acids as serine-β-lactamase inhibitors

β-Lactamases are bacterial enzymes conferring resistance to β-lactam antibiotics in clinically-relevant pathogens, and represent relevant drug targets. Recently, the identification of new boronic acids (i.e. RPX7009) paved the way to the clinical application of these molecules as potential drugs. Here, we screened in silico a library of ~1400 boronic acids as potential AmpC β-lactamase inhibitors. Six of the most promising candidates were evaluated in biochemical assays leading to the identification of potent inhibitors of clinically-relevant β-lactamases like AmpC, KPC-2 and CTX-M-15. One of the selected compounds showed nanomolar K _i value with the clinically-relevant KPC-2 carbapenemase, while another one exhibited broad spectrum inhibition, being also active on Enterobacter AmpC and the OXA-48 class D carbapenemase.     

Zeolites as model solids for investigations on the role of iron at the solid-liquid interface in particulate toxicity

In order to investigate the molecular mechanism whereby iron in asbestos and in other iron containing fibres plays a crucial role in fibre induced carcinogenicity, two Fe²⁺-exchanged zeolites (Y and H-ZSM-5) have been prepared and used as model solids. Fe-Y was active both in free radical generation via hydrogen abstraction and in single strand DNA damage, but lost both these properties when oxidized by hydrogen peroxide. Fe-ZSM-5, on the other hand, was nearly inactive. Iron chelators and reductants (ascorbate, citrate and EDTA) enhance the activity in DNA single strand breaks. Moreover, they reactivate oxidized Fe-Y and activate Fe-ZSM-5. Iron is mobilized and Fe³⁺ is partially reduced to Fe²⁺. The most pronounced effect was found when citrate was present together with ascorbate. H-abstraction turns out to be a rather general reaction, occurring also with peptides as target molecules. In this case EPR spectra show that more than one type of radical moiety is generated.     

Water‐soluble and Halogen‐free Hexaammine Complexes of Metal Ions of Group 9 – Synthesis,Crystal Structures,and Vibrational Spectra

Reaction of [M(NH₃)₆]Cl₃ (M = Co, Rh, Ir) and [Ir(NH₃)₅(OH₂)]Cl₃ with (NH₄)₂C₂O₄ · H₂O in aqueous solution resulted in the isolation of [M(NH₃)₆]₂(C₂O₄)₃ · 4 H₂O and [Ir(NH₃)₅(OH₂)]₂(C₂O₄)₃ · 4 H₂O, respectively. The complexes have been characterized by X‐ray crystallography, IR and UV/VIS spectroscopy. The isomorphous compounds crystallize in the orthorhombic space group Pnnm (No. 58). Four molecules of crystal water are involved in an extended three‐dimensional hydrogen bonding network. The librational modes of the lattice water around 600 cm^–1 allow the characterization of [Ir(NH₃)₆]₂(C₂O₄)₃ · 4 H₂O and [Ir(NH₃)₅(OH₂)]₂(C₂O₄)₃ · 4 H₂O, respectively, by IR spectroscopy. The band around 600 cm^–1 shows a significant frequency shift in the IR spectra of the hexaammine and aquapentaammine complex of iridium(III) and, by that, a distinction is possible.     

Chemical and Mechanical Characterization of Licorice Root and Palm Leaf Waste Incorporated into Poly(urethane-acrylate) (PUA)

A poly(urethane-acrylate) polymer (PUA) was synthesized, and a sufficiently high molecular weight starting from urethane-acrylate oligomer (UAO) was obtained. PUA was then loaded with two types of powdered ligno-cellulosic waste, namely from licorice root and palm leaf, in amounts of 1, 5 and 10%, and the obtained composites were chemically and mechanically characterized. FTIR analysis of final PUA synthesized used for the composite production confirmed the new bonds formed during the polymerization process. The degradation temperatures of the two types of waste used were in line with what observed in most common natural fibers with an onset at 270 °C for licorice waste, and at 290 °C for palm leaf one. The former was more abundant in cellulose (44% vs. 12% lignin), whilst the latter was richer in lignin (30% vs. 26% cellulose). In the composites, only a limited reduction of degradation temperature was observed for palm leaf waste addition and some dispersion issues are observed for licorice root, leading to fluctuating results. Tensile performance of the composites indicates some reduction with respect to the pure polymer in terms of tensile strength, though stabilizing between data with 5 and 10% filler. In contrast, Shore A hardness of both composites slightly increases with higher filler content, while in stiffness-driven applications licorice-based composites showed potential due to an increase up to 50% compared to neat PUA. In general terms, the fracture surfaces tend to become rougher with filler introduction, which indicates the need for optimizing interfacial adhesion.     

Insights into docking and scoring neuronal α4β2 nicotinic receptor agonists using molecular dynamics simulations and QM/MM calculations

A combined quantum mechanical (QM)‐polarized docking and molecular dynamics approach to study the binding mode and to predict the binding affinity of ligands acting at the α4β2‐nAChR is presented. The results obtained in this study indicate that the quantum mechanical/molecular mechanics docking protocol well describes the charge‐driven interactions occurring in the binding of nicotinic agonists, and it is able to represent the polarization effects on the ligand exerted by the surrounding atoms of the receptor at the binding site. This makes it possible to properly score agonists of α4β2‐nAChR and to reproduce the experimental binding affinity data with good accuracy, within a mean error of 2.2 kcal/mol. Moreover, applying the QM‐polarized docking to an ensemble of nAChR conformations obtained from MD simulations enabled us to accurately capture nAChR‐ligand induced‐fit effects. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Weak localization of light in superdiffusive random systems

Lévy flights constitute a broad class of random walks that occur in many fields of research, from biology to economy and geophysics. The recent advent of Lévy glasses allows us to study Lévy flights-and the resultant superdiffusion-using light waves. This raises several questions about the influence of interference on superdiffusive transport. Superdiffusive structures have the extraordinary property that all points are connected via direct jumps, which is expected to have a strong impact on interference effects such as weak and strong localization. Here we report on the experimental observation of weak localization in Lévy glasses and compare our results with a recently developed theory for multiple scattering in superdiffusive media. Experimental results are in good agreement with theory and allow us to unveil the light propagation inside a finite-size superdiffusive system.     

Programming scale-free optics in disordered ferroelectrics

Using the history dependence of a dipolar glass hosted in a compositionally disordered lithium-enriched potassium tantalate niobate (KTN:Li) crystal, we demonstrate scale-free optical propagation at tunable temperatures. The operating equilibration temperature is determined by previous crystal spiralling in the temperature/cooling-rate phase space.