Addition of dipropylamine to multiacrylate and its model compound catalyzed by lithium dipropylamide

The nucleophilic addition reaction of dipropylamine to vinyl groups of multiacrylate - poly(2-acryloyloxyethyl methacrylate) and to 2-butyrylethyl acrylate as model compound has been investigated. Based on the results obtained, it has been shown that the addition reaction rate of dipropylamine to multiacrylate and 2-butyrylethyl acrylate is proportional to [CH₂=CH-] and to [(C₃H₇)₂NLi] with the ratio [(C₃H₇)₂NH]_o/[(C₃H₇)₂NLi]_o = 20. Second-order addition reaction rate constants and activation energies for the systems under investigation have been determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Monanchoxymycalin C with anticancer properties,new analogue of crambescidin 800 from the marine sponge Monanchora pulchra

A new pentacyclic guanidine alkaloid, monanchoxymycalin C (1) was isolated from a new collection of marine sponge Monanchora pulchra along with the known monanchoxymycalin A (2). The structure of 1 was elucidated on the basis of spectroscopic data. Monanchoxymycalin C exhibits cytotoxic activity against human cancer HeLa cells at low micromolar concentrations, induces apoptosis-related death of malignant cells and inhibits cancer cell colony formation. In addition, synergistic and additive effects have been observed in combination with cisplatin.     

Control of Metal–Organic Framework Crystallization by Metastable Intermediate Pre‐equilibrium Species

There is an increasing amount of interest in metal–organic frameworks (MOFs) for a variety of applications, from gas sensing and separations to electronics and catalysis. However, the mechanisms by which they crystallize remain poorly understood. Herein, an important new insight into MOF formation is reported. It is shown that, prior to network assembly, crystallization intermediates in the canonical ZIF‐8 system exist in a dynamic pre‐equilibrium, which depends on the reactant concentrations and the progress of reaction. Concentration can, therefore, be used as a synthetic handle to directly control particle size, with potential implications for industrial scale‐up and gas sorption applications. These findings enable the rationalization of apparent contradictions between previous studies of ZIF‐8 and opens up new opportunities for the control of crystallization in network solids more generally.     

Simultaneous sampling of volatile and non-volatile analytes in beer for fast fingerprinting by extractive electrospray ionization mass spectrometry

By gently bubbling nitrogen gas through beer, an effervescent beverage, both volatile and non-volatile compounds can be simultaneously sampled in the form of aerosol. This allows for fast (within seconds) fingerprinting by extractive electrospray ionization mass spectrometry (EESI-MS) in both negative and positive ion mode, without the need for any sample pre-treatment such as degassing and dilution. Trace analytes such as volatile esters (e.g., ethyl acetate and isoamyl acetate), free fatty acids (e.g., caproic acid, caprylic acid, and capric acid), semi/non-volatile organic/inorganic acids (e.g., lactic acid), and various amino acids, commonly present in beer at the low parts per million or at sub-ppm levels, were detected and identified based on tandem MS data. Furthermore, the appearance of solvent cluster ions in the mass spectra gives insight into the sampling and ionization mechanisms: aerosol droplets containing semi/non-volatile substances are thought to be generated via bubble bursting at the surface of the liquid; these neutral aerosol droplets then collide with the charged primary electrospray ionization droplets, followed by analyte extraction, desolvation, ionization, and MS detection. With principal component analysis, several beer samples were successfully differentiated. Therefore, the present study successfully extends the applicability of EESI-MS to the direct analysis of complex liquid samples with high gas content.

Electron capture dissociation of polypeptides using a 3 Tesla Fourier transform ion cyclotron resonance mass spectrometer

Electron capture dissociation (ECD) of polypeptides has been demonstrated using a commercially available 3 Tesla Fourier transform ion cyclotron resonance (FTICR) instrument. A conventional rhenium filament, designed for high-energy electron impact ionisation, was used to effect ECD of substance P, bee venom melittin and bovine insulin, oxidised B chain. A retarding field analysis of the effective electron kinetic energy distribution entering the ICR cell suggests that one of the most important parameters governing ECD for this particular instrument is the need to employ low trapping plate voltages. This is shown to maximise the abundance of low-energy electrons. The demonstration of ECD at this relatively low magnetic field strength could offer the prospect of more routine ECD analysis for the wider research community, given the reduced cost of such magnets and (at least theoretically) the greater ease of electron/ion cloud overlap at lower field.     

Efficiency assessment of wastewater treatment plant based on SPMD sampling

The efficiency of treatment processes forboth municipal and industrial wastewater (treatment plant-Ostrava, Czech Republic) focused on persistent organic pollutants (POPs) was assessed. Semipermeable membrane devices (SPMDs) as a sampling system were applied. Exposed SPMDs were analyzed both for chemical contaminants of POPs and toxicity response. The chemical analyses of PAHs were made by HPLC-FLD, PCDD/Fs and PCBs were analysed by GC/MS/MS on GCQ or PolarisQ (Thermoquest). Ecotoxicity data on chlorococcal alga Desmodesmus subspicatus (Scenedesmus subspicatus) and luminescent bacteria Vibrio fischeri are presented here. All toxicity data as effective volume Vtox are expressed. The results show good treatment ability of the treatment plant and proved used system as an appropriate tool for efficiency assessment of treatment and/or decontamination processes.     

Microscopic visualization of alamethicin incorporation into model membrane monolayers

Lipid interactions and cooperative assembly properties are fundamental determinants for the action of antimicrobial membrane-active peptides. Here we analyze the interactions and aggregation properties of alamethicin, an antimicrobial pore-forming peptide, with films formed at the air/water interface. Surface-area/pressure isotherms, Brewster angle microscopy, and fluorescence-confocal microscopy provided detailed information on the morphologies and structural properties of the peptide and its effect on the film components. The pressure-area analysis and microscopy experiments facilitated unprecedented visualization of the structural consequences of alamethicin association at the air/water interface, with pure phospholipid films, and within mixed phospholipid/polydiacetylene (PDA) films. The analysis exposed the kinetic features and the interplay between the peptide aggregates and film constituents. In particular, the results demonstrate the use of phospholipid/PDA film assemblies for studying membrane-peptide association and interactions within two-dimensional films.     

Chemical Bonding and Pressure‐Induced Change of the Electron Configuration of Ytterbium in β‐YbAgGa2

Single‐phase polycrystalline samples of the intermetallic compound β‐YbAgGa₂ were synthesized by inductive heating and subsequent annealing for eight weeks at 670 K. Magnetic properties were characterized by susceptibility measurements and indicated intermediate valence of ytterbium at ambient pressure. Angle‐dispersive X‐ray powder diffraction data of orthorhombic β‐YbAgGa₂ indicate stability of the phase in the investigated pressure range from 0.1 MPa (ambient pressure) to 19 GPa. The pressure‐induced volume decrease is accompanied by an increase of the effective valence from 2.17 at ambient conditions to 2.71 at 16 GPa as evaluated by X‐ray absorption spectroscopy at the Yb L_III threshold. Analysis of the chemical bonding in β‐YbAgGa₂ by integrating the electron density of the polyanion in basins as defined by the electron localization function results in an electron count Yb^2.7+[(Ag^0.2—)(Ga1(3b)^1.0—)(Ga2(4b)^1.5—)]. This finding is close to the expected values calculated by means of the Zintl rules and fits well the results of magnetic susceptibility measurements and XAS investigations.     

Electrocatalytic reduction of ROOH by iron porphyrins

Electrocatalytic reduction of a series of chemical oxidants of different power (tert-butyl hydroperoxide, potassium peroxomonosulfate, peracetic acid, and m-chloroperbenzoic acid) at iron-porphyrin-modified graphite electrodes is studied in buffered aqueous solutions by rotating disk and ring-disk voltammetry. Both ferric and ferrous porphyrins are catalytically active. Turnover of ferric catalysts is slower than that of the ferrous analogues and involves competing catalytic reduction and disproportionation. The kinetic data are consistent with reactant binding being the rate-determining step in catalysis by Fe(III). In catalysis by Fe(II), the turnover is controlled by the first electron transfer. The covalently linked proximal imidazole ligand is found to be crucial for achieving the Fe(III) catalysis.