Electronic structure of the water oxidation catalyst cis,cis-[(bpy)2(H2O)Ru(III)ORu(III)(OH2)(bpy)2]4+, the blue dimer

The first designed molecular catalyst for water oxidation is the "blue dimer", cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(OH(2))(bpy)(2)](4+). Although there is experimental evidence for extensive electronic coupling across the μ-oxo bridge, results of earlier DFT and CASSCF calculations provide a model with magnetic interactions of weak to moderately coupled Ru(III) ions across the μ-oxo bridge. We present the results of a comprehensive experimental investigation, combined with DFT calculations. The experiments demonstrate both that there is strong electronic coupling in the blue dimer and that its effects are profound. Experimental evidence has been obtained from molecular structures and key bond distances by XRD, electrochemically measured comproportionation constants for mixed-valence equilibria, temperature-dependent magnetism, chemical properties (solvent exchange, redox potentials, and pK(a) values), XPS binding energies, analysis of excitation-dependent resonance Raman profiles, and DFT analysis of electronic absorption spectra. The spectrum can be assigned based on a singlet ground state with specific hydrogen-bonding interactions with solvent molecules included. The results are in good agreement with available experimental data. The DFT analysis provides assignments for characteristic absorption bands in the near-IR and visible regions. Bridge-based dπ → dπ* and interconfiguration transitions at Ru(III) appear in the near-IR and MLCT and LMCT transitions in the visible. Reasonable values are also provided by DFT analysis for experimentally observed bond distances and redox potentials. The observed temperature-dependent magnetism of the blue dimer is consistent with a delocalized, diamagnetic singlet state (dπ(1)*)(2) with a low-lying, paramagnetic triplet state (dπ(1)*)(1)(dπ(2)*)(1). Systematic structural-magnetic-IR correlations are observed between ν(sym)(RuORu) and ν(asym)(RuORu) vibrational energies and magnetic properties in a series of ruthenium-based, μ-oxo-bridged complexes. Consistent with the DFT electronic structure model, bending along the Ru-O-Ru axis arises from a Jahn-Teller distortion with ∠Ru-O-Ru dictated by the distortion and electron-electron repulsion.     

Torch Design Modification Using Micro-jets to Suppress Fluid Dynamic Instabilities in Plasma Arc Cutting

Highly constricted plasma arcs are widely used for metal cutting. One important characteristic of the cutting process is the consistency of the cut edge around the perimeter of the workpiece. Cut edge properties, including surface roughness, edge shape and dross formation, are presumed to depend on the local temperature and chemical composition of the cutting arc adjacent to the cut edge. Fluid dynamic instabilities in the arc boundary leading to entrainment of the low temperature ambient gas can have a strong effect on cutting performance. This paper describes the use of micro-jets to suppress fluid dynamic instabilities in the boundary layer of a plasma cutting arc. Previously developed optical diagnostics and analysis methods are used to characterize the arc boundary layer. Multiple nozzle designs have been investigated to quantify the effects of utilizing micro-jet flow around the arc column, and some relationships between nozzle design and cut quality are presented.     

Molecular interactions in biofilms

A biofilm may be defined as a microbially derived, sessile community characterized by cells that attach to an interface, embed in a matrix of exopolysaccharide, and demonstrate an altered phenotype. This review covers the current understanding of the nature of biofilms and the impact that molecular interactions may have on biofilm development and phenotype using the motile gram-negative rod Pseudomonas aeruginosa and the nonmotile gram-positive cocci Staphylococcus aureus as examples.     

Endotrivial modules for the general linear group in a nondefining characteristic

Suppose that \(G\) is a finite group such that \(\mathrm{SL }(n,q)\subseteq G \subseteq \mathrm{GL }(n,q)\), and that \(Z\) is a central subgroup of \(G\). Let \(T(G/Z)\) be the abelian group of equivalence classes of endotrivial \(k(G/Z)\)-modules, where \(k\) is an algebraically closed field of characteristic \(p\) not dividing \(q\). We show that the torsion free rank of \(T(G/Z)\) is at most one, and we determine \(T(G/Z)\) in the case that the Sylow \(p\)-subgroup of \(G\) is abelian and nontrivial. The proofs for the torsion subgroup of \(T(G/Z)\) use the theory of Young modules for \(\mathrm{GL }(n,q)\) and a new method due to Balmer for computing the kernel of restrictions in the group of endotrivial modules.     

Skew products over rotations with exotic properties

We show that a $\text{ Z}_{2}$ skew product of a badly approximable rotation can be minimal and not uniquely ergodic. This construction is used to construct a Z skew product of a rotation where the orbit of a.e. point is dense but Lebesgue measure is not ergodic.     

Every transformation is disjoint from almost every non-classical exchange

A natural generalization of interval exchange maps are linear involutions, first introduced by Danthony and Nogueira (Ann Sci École Norm Sup (4) 26(6):645–664, 1993). Recurrent train tracks with a single switch which are called non-classical interval exchanges (Gadre in Ergod Theory Dyn Syst 32(06):1930–1971, 2012), form a subclass of linear involutions without flips. They are analogs of classical interval exchanges, and are first return maps for non-orientable measured foliations associated to quadratic differentials on Riemann surfaces. We show that every transformation is disjoint from almost every irreducible non-classical interval exchange. In the “Appendix”, we prove that for almost every pair of quadratic differentials with respect to the Masur–Veech measure, the vertical flows are disjoint.     

Bioinspired Colorimetric Detection of Calcium(II) Ions in Serum Using Calsequestrin‐Functionalized Gold Nanoparticles

Seeing is sensing : Calsequestrin (CSQ) functionalized gold nanoparticles undergo calcium‐dependent CSQ polymerization, which results in a clear color change (see picture) together with precipitation. The sensing system is specific for Ca²⁺ ions and the differences between normal and disease‐associated abnormal (hypercalcemia) Ca²⁺ ion levels in serum can be distinguished with the naked eye.

     

Identification of the Biotransformation Products of 2-Ethylhexyl 4-(N,N-Dimethylamino)benzoate

Nowadays, 2-ethylhexyl 4-(N,N-dimethylamino)benzoate (EDP) is one of the most widely used UV filters in sunscreen cosmetics and other cosmetic products. However, undesirable processes such as percutaneous absorption and biological activity have been attributed to this compound. The in vitro metabolism of EDP was elucidated in the present work. First of all, the phase I biotransformation was studied in rat liver microsomes and two metabolites, N,N-dimethyl-p-aminobenzoic acid (DMP) and N-monomethyl-p-aminobenzoic acid (MMP), were identified by GC-MS analysis. Secondly, the phase II metabolism was investigated by means of LC-MS. The investigated reactions were acetylation and glucuronidation working with rat liver cytosol and with both human and rat liver microsomes, respectively. Analogue studies with p-aminobenzoic acid (PABA) were carried out in order to compare the well established metabolic pathway of PABA with the unknown biotransformation of EDP. In addition, a method for the determination of EDP and its two phase I metabolites in human urine was developed. The methodology requires a solid-phase extraction prior to LC-MS analysis. The method is based on standard addition quantification and has been fully validated. The repeatability of the method, expressed as relative standard deviation, was in the range 3.4–7.4% and the limit of detection for all quantified analytes was in the low ng mL^?1 range.     

Synthesis of substituted (S)-2-aminotetralins via ring-opening of aziridines prepared from l-aspartic acid β-tert-butyl ester

This paper describes the total synthesis of the hydrochloride salts of (2S)-2-amino-7-methoxytetralin (21-HCl) and (2S)-2-amino-6-fluoro-7-methoxytetralin (ST1214), from a common enantiomerically pure aziridine 4b, which was available from l-aspartic acid β-tert-butyl ester. The synthesis of 21-HCl and ST1214 proceeded in nine steps and 5 and 6% overall yields, respectively. Key steps are the regioselective ring-opening of 4b with ArMgBr/CuBr·SMe₂ and the intramolecular Friedel-Crafts cyclisation providing α-tetralone. Substituted naphthalenes were formed as side products in the latter reaction.     

N-activated β-lactams as versatile reagents for acyl carrier protein labeling

Acyl carrier proteins are critical components of fatty acid and polyketide biosynthesis. Their primary function is to shuttle intermediates between active sites via a covalently bound phosphopantetheine arm. Small molecules capable of acylating this prosthetic group will provide a simple and reversible means of introducing novel functionality onto carrier protein domains. A series of N-activated β-lactams are prepared to examine site-specific acylation of the phosphopantetheine-thiol. In general, β-lactams are found to be significantly more reactive than our previously studied β-lactones. Selectivity for the holo over apo-form of acyl carrier proteins is demonstrated indicating that only the phosphopantetheine-thiol is modified. Incorporation of an N-propargyloxycarbonyl group provides an alkyne handle for conjugation to fluorophores and affinity labels. The utility of these groups for mechanistic interrogation of a critical step in polyketide biosynthesis is examined through comparison to traditional probes. In all, we expect the probes described in this study to serve as valuable and versatile tools for mechanistic interrogation.