Voltammetric monitoring of laccase-catalysed mediated reactions

Six different compounds capable of mediating laccase-catalysed reactions have been tested by cyclic voltammetry. They exhibited quasi-reversible electrodic behaviour with formal redox potentials ranging from 150 to 800 mV (E(0)' vs. SCE). The immersion of a laccase-coated glassy carbon electrode (GCE) in mediator solutions generated large cathodic catalytic currents easily recorded by cyclic voltammetry at low-potential scan rates. This current showed two well-defined pH profiles, which correlated with the variation of the mediator redox potentials at the pH range tested. The relevant effect of temperature on the activity of laccase has been assessed here. Likewise, it was shown that the current record varied with the substrate concentration. This trend fitted Michaelis-Menten kinetics, which allowed us to give an estimation of the affinity of the fungal laccase for the different mediators.     

Control of Excited‐State Conformations in B,N‐Acenes

We present a new concept to control the conformations of molecules in the excited state through harvesting negative hyperconjugation. The strategy was realized with the 2,3,1,4‐benzodiazadiborinane scaffold, which was prepared by a new synthetic procedure. Photochemical studies identified dual light emission, which was assigned to well‐defined conformers. The emission at longer wavelength can be switched off by restricting the rotational degrees of freedom in the solid state as well as by controlling the energy levels of the excited states through adjusting the solvent polarity.     

Atomic‐Scale Observation of the Metal–Promoter Interaction in Rh‐Based Syngas‐Upgrading Catalysts

The direct conversion of syngas to ethanol, typically using promoted Rh catalysts, is a cornerstone reaction in CO₂ utilization and hydrogen storage technologies. A rational catalyst development requires a detailed structural understanding of the activated catalyst and the role of promoters in driving chemoselectivity. Herein, we report a comprehensive atomic‐scale study of metal–promoter interactions in silica‐supported Rh, Rh–Mn, and Rh–Mn–Fe catalysts by aberration‐corrected (AC) TEM. While the catalytic reaction leads to the formation of a Rh carbide phase in the Rh–Mn/SiO₂ catalyst, the addition of Fe results in the formation of bimetallic Rh–Fe alloys, which further improves the selectivity and prevents the carbide formation. In all promoted catalysts, Mn is present as an oxide decorating the metal particles. Based on the atomic insight obtained, structural and electronic modifications induced by promoters are revealed and a basis for refined theoretical models is provided.     

15‐Hydroperoxy‐PGE2: Intermediate in Mammalian and Algal Prostaglandin Biosynthesis

Arachidonic‐acid‐derived prostaglandins (PGs), specifically PGE₂, play a central role in inflammation and numerous immunological reactions. The enzymes of PGE₂ biosynthesis are important pharmacological targets for anti‐inflammatory drugs. Besides mammals, certain edible marine algae possess a comprehensive repertoire of bioactive arachidonic‐acid‐derived oxylipins including PGs that may account for food poisoning. Described here is the analysis of PGE₂ biosynthesis in the red macroalga Gracilaria vermiculophylla that led to the identification of 15‐hydroperoxy‐PGE₂, a novel precursor of PGE₂ and 15‐keto‐PGE₂. Interestingly, this novel precursor is also produced in human macrophages where it represents a key metabolite in an alternative biosynthetic PGE₂ pathway in addition to the well‐established arachidonic acid‐PGG₂‐PGH₂‐PGE₂ route. This alternative pathway of mammalian PGE₂ biosynthesis may open novel opportunities to intervene with inflammation‐related diseases.     

Synthesis and structure‐activity relationship of several aromatic ketone‐based two‐photon initiators

Several novel aromatic ketone‐based two‐photon initiators containing triple bonds and dialkylamino groups were synthesized and the structure‐activity relationships were evaluated. Branched alkyl chains were used at the terminal donor groups to improve the solubility in the multifunctional monomers. Because of the long conjugation length and good coplanarity, the evaluated initiators showed large two‐photon cross section values, while their fluorescence lifetimes and quantum yields strongly depend on the solvent polarity. All novel initiators exhibited high activity in terms of two‐photon‐induced microfabrication. This is especially true for fluorenone‐based derivatives, which displayed much broader processing windows than well‐known highly active initiators from the literature and commercially available initiators. While the new photoinitiators gave high reactivity in two‐photon‐induced photopolymerization at concentration as low as 0.1% wt, these compounds are surprisingly stable under one photon condition and nearly no photo initiation activity was found in classical photo DSC experiment. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Liquid crystalline polyfluorenes for blue polarized electroluminescence

A series of 9,9‐dialkyl‐poly(fluorene‐2,7‐diyl)s containing linear and branched alkyl substituents with a M_n of up to 200000 g/mol has been synthesized. Moreover, some of the polymers were end capped with a suitable hole transport functionality, such as a triphenylamine derivative, to improve their charge transport properties and to control the molecular weight. The thermal alignment of these novel polymers on a rubbed polyimide layer led to highly anisotropic film formation with dichroic ratios (absorption parallel and perpendicular to the rubbing direction) of up to 26 in absorption and 21 in emission.     

Atomic force microscopy study of the adsorption and electrostatic self-organization of poly(amidoamine) dendrimers on mica

The adsorption behavior of poly(amidoamine) dendrimers to mica surfaces was investigated as a function of ionic strength and pH. The conformation and lateral distribution of the adsorbed dendrimers of generations G8 and G10 were obtained ex situ by tapping mode atomic force microscopy (AFM). The deposition kinetics of the dendrimers was found to follow a diffusion-limited process. Fractional surface coverage and pair correlation functions of the adsorbed dendrimers were obtained from the AFM images. The data are interpreted in terms of the random sequential adsorption (RSA) model, where electrostatic repulsion due to overlapping double layers is considered. Although the general trends typical for an RSA-determined process are well-reproduced, quantitative agreement is lacking at low ionic strengths.     

The Henicosaphosphide Iodides of Potassium and Rubidium,K4P21I and Rb4P21I

The novel ternary polyphosphides M₄P₂₁I (M = K, Rb) have been synthesized from the elements in single crystalline form, representing further examples for the formation of mixed crystals between simple salts and binary phosphides. They form as ruby‐red platelets and dark‐red prisms, respectively, and are only slightly sensitive to moisture and oxygen. The compounds are isotypic (Ccmm (no 63); Z = 4; oP104; K₄P₂₁I: a = 12.853Å; b = 21.795Å; c = 9.748Å; 1168 hkl, R = 0.033; Rb₄P₂₁I: a = 13.281Å; b = 21.868Å; c = 9.771Å; 777 hkl, R = 0.053) and feature corrugated 2D networks formed from two different types of polymerized P₇ units. The networks form large cavities filled by M⁺ and I^‐ ions. Zigzag chains of condensed trigonal M₆ prisms, centered by the I^‐ anions, separate the polyphosphide nets. The mean homoatomic P‐P bond length (d = 2.216Å) corresponds to a P‐P single bond. However, the individual P‐P distances vary with position and function (2.126 ‐ 2.247Å) and these are compared with those of the isolated P₂₁^‐3 anion.