Selective catalytic reduction of NOx by hydrocarbons enhanced by hydrogen peroxide over silver/alumina catalysts

It is shown that hydrogen peroxide enhances substantially selective reduction of NOx to nitrogen with hydrocarbons over Ag/alumina catalysts.     

Highly Functionalized Cyclopentane Derivatives by Tandem Michael Addition/Radical Cyclization/Oxygenation Reactions

Densely functionalized cyclopentane derivatives with up to four consecutive stereocenters are assembled by a tandem Michael addition/single‐electron transfer oxidation/radical cyclization/oxygenation strategy mediated by ferrocenium hexafluorophosphate, a recyclable, less toxic single‐electron transfer oxidant. Ester enolates were coupled with α‐benzylidene and α‐alkylidene β‐dicarbonyl compounds with switchable diastereoselectivity. This pivotal steering element subsequently controls the diastereoselectivity of the radical cyclization step. The substitution pattern of the radical cyclization acceptor enables a switch of the cyclization mode from a 5‐exo pattern for terminally substituted olefin units to a 6‐endo mode for internally substituted acceptors. The oxidative anionic/radical strategy also allows efficient termination by oxygenation with the free radical 2,2,6,6‐tetramethyl‐1‐piperidinoxyl, and two C?C bonds and one C?O bond are thus formed in the sequence. A stereochemical model is proposed that accounts for all of the experimental results and allows the prediction of the stereochemical outcome. Further transformations of the synthesized cyclopentanes are reported.     

Phases of the K2TaF7–TaF5 binary system

The phase equilibria in the K₂TaF₇–TaF₅ binary system were determined up to x _TaF5 = 0.5 by means of differential scanning calorimetry. XRD diffraction analysis of solidified mixtures was performed. Besides the K₂TaF₇ and KTaF₆ phases, the presence of a third phase was observed, as well. It was suggested that the last phase melts incongruently. Correspondence: B. Kubikova, Institute of Inorganic Chemistry SAS, Dúbravská cesta 9, Bratislava, 845 36, Slovakia.     

Determination of hydroxycamptothecin affinities to albumin and membranes by steady-state fluorescence anisotropy measurements

Camptothecin (CPT) and its hydroxycamptothecin analogs are fluorescent compounds exhibiting strong anticancer properties. They exist in two forms: active lactone and inactive carboxylate. The deactivation proceeds via hydrolysis in neutral and base solutions. A serious limitation to the clinical application of CPT is the strong affinity of its carboxylate form to human serum albumin (HSA) which destabilizes its active lactone form. However, binding to membranes in blood improves the stability of the lactone form of CPT and its analogs. A high-throughput screening assay based on the steady-state fluorescence anisotropy method was used to determine the protein- and membrane-binding properties of 10 hydroxycamptothecin (10-OH-CPT), 7-ethyl-10-hydroxycamptothecin (SN-38) and 7-tert-butyldimethylsil-10-hydroxycamptothecin (DB-67). The relative affinities of hydroxycamptothecins to HSA and model membranes in the form of DMPC liposomes were determined, and DB-67 exhibited the most desirable properties including the highest affinity to membranes in its lactone form and low affinity to HSA in its carboxylate form.     

Light absorption properties of the rabbit cornea repeatedly irradiated with UVB rays

Under normal conditions, the cornea absorbs the majority of UVB (ultraviolet B, 280-320 nm) rays, which is very important for the protection of the inner eye against their damaging effect. Our previous studies have shown that repeated irradiation of the rabbit cornea with UVB rays for 5 days (daily dose of 1.01 J cm(- 2)) caused photokeratitis accompanied by swelling (hydration) of the corneal stroma, thinning of the corneal epithelium and decrease in antioxidants. The purpose of this study was to examine the light absorption properties of such damaged rabbit cornea. Results of both spectrophotometry of the whole corneal buttons and corneal tissue dissolved in sodium hydroxide show that because of above mentioned disturbances, UVB-irradiated cornea absorbs more light throughout the whole measurable UV-VIS spectral range than the normal cornea. Increased corneal thickness (result of hydration), changes of corneal transparency (the cornea becomes grayish) and some increase in protein content all contribute to the increased light absorption of UVB irradiated corneas. We suggest that the UVB-irradiated cornea, although damaged and nearly without antioxidants, might actually through its higher UV absorbance protect the inner eye against further damage from UVB rays.     

Metadynamics in essential coordinates: free energy simulation of conformational changes

We propose an approach that combines an extraction of collective motions of a molecular system with a sampling of its free energy surface. A recently introduced method of metadynamics allows exploration of the free energy surface of a molecular system by means of coarse-grained dynamics with flooding of free energy minima. This free energy surface is defined as a function of a set of collective variables (e.g., interatomic distances, angles, torsions, and others). In this study, essential coordinates determined by essential dynamics (principle component analysis) were used as collective variables in metadynamics. First, dynamics of the model system (explicitly solvated alanine dipeptide, Ace-Ala-Nme) was simulated by a classical molecular dynamics simulation. The trajectory (1 ns) was then analyzed by essential dynamics to obtain essential coordinates. The free energy surface as a function of the first and second essential coordinates was then explored by metadynamics. The resulting free energy surface is in agreement with other studies of this system. We propose that a combination of these two methods (metadynamics and essential dynamics) has great potential in studies of conformational changes in peptides and proteins.     

GCxGC/TOF MS technique-A new tool in identification of insect pheromones: Analysis of the persimmon bark borer sex pheromone gland

Conventional gas chromatography with electroantennographic detection (GC-EAD) and two-dimensional (GC × GC) gas chromatography using a time-of-flight mass spectrometric detector (TOFMS), were combined to analyse the female sex pheromone gland extract of the persimmon bark borer, Euzophera batangensis. GC-EAD analysis produced two EAD responses in GC areas where no compounds were detected by FID detection. GC × GC/TOFMS analysis of this area indicated the presence of several chemicals, including (Z9,E12)-tetradeca-9,12-dien-1-ol and (Z9)-tetradec-9-en-1-ol, pheromone components of closely related Euzophera species. Spectral characteristics, retention behaviour and the ability to elicit GC-EAD responses imply that both identified unsaturated alcohols are candidates for E. batangensis sex pheromone components. GC × GC/TOFMS facilitated the analysis of complex matrices on a subnanogram level and was shown to have great potential as a powerful tool in the analysis of insect pheromones.     

Comparison of SERRS and RRS excitation profiles of [Fe(tpy)2]2+ (tpy = 2,2':6',2'‐terpyridine) supported by DFT calculations: effect of the electrostatic bonding to chloride‐modified Ag nanoparticles on its vibrational and electronic structure

Nonresonance (or normal) Raman scattering (NRS), resonance Raman scattering (RRS), surface‐enhanced Raman scattering (SERS), and surface‐enhanced RRS (SERRS) spectra of [Fe(tpy)₂]²⁺ complex dication (tpy = 2,2':6',2''‐terpyridine) are reported. The comparison of RRS/NRS and SERRS/SERS excitation profiles of [Fe(tpy)₂]²⁺ spectral bands in the range of 445–780 nm is supported by density functional theory (DFT) calculations, Raman depolarization measurements, comparison of the solid [Fe(tpy)₂](SO₄)₂ and solution RRS spectra, and characterization of the Ag nanoparticle (NP) hydrosol/[Fe(tpy)₂]²⁺ SERS/SERRS active system by surface plasmon extinction spectrum and transmission electron microscopy image of the fractal aggregates (D = 1.82). By DFT calculations, both the Raman active modes and the electronic states of the complex have been assigned to the symmetry species of the D_2d point group. It has been demonstrated that upon the electrostatic bonding of the complex dication to the chloride‐modified Ag NPs, the geometric and ground state electronic structure of the complex and the identity of the three different metal‐to‐ligand charge transfer (¹MLCT) electronic transitions remain preserved. On the other hand, the effect of ion pairing manifests itself by a slight change in localization of one of the electronic transitions (with max. at 552 nm) as well as by promotion of the Herzberg–Teller activation of E modes resulting from coupling of E and B₂ excited electronic states. Finally, the very low, 1 × 10⁻¹¹ M SERRS spectral detection limit of [Fe(tpy)₂]²⁺ at 532‐nm excitation is attributed to a concerted action of the electromagnetic and molecular resonance mechanism, in conjunction to the electrostatic bonding of the complex dication to the chloride‐modified Ag NP surface. Copyright © 2014 John Wiley & Sons, Ltd.