Uniform structure of eukaryotic plasma membrane: lateral domains in plants

Current models of the plasma membrane (PM) organization focus on the lateral heterogeneity of the membrane and its relation to the cell function. Increasing evidence in mammals and yeast supports the direct relationship between PM lateral microdomains and specific cell processes and functions (nutrient transport, signaling, protein and lipid sorting, endocytosis, pathogen entry etc.). However, for the present the functional significance of an enrichment of specific proteins and possibly lipids in plant PM domains as well as the underlying molecular mechanism driving the lateral PM segregation remain unaddressed. Here we summarize recent findings on the plant PM organization and its role in signaling pathways, with the special emphasis on auxin transport.     

Interpretation of substituent effects on 13C and 15N NMR chemical shifts in 6-substituted purines

A range of purine derivatives modified at position 6 of the basic purine skeleton exhibit a variety of biological activities. Several derivatives are used or tested nowadays for pharmacological treatments. The present work aims to analyze the effects of substituents on the electron distribution in the purine core as reflected by NMR chemical shifts. We collected a comprehensive set of experimental NMR data for a variety of 6-substituted purines (-NH(2), -NHMe, -NMe(2), -OMe, -Me, -CCH, and -CN) and determined the molecular and crystal structures of three derivatives (-NHMe, -CCH, and -CN) by X-ray diffraction. The density-functional methods calibrated in our recent study (Phys. Chem. Chem. Phys., 2010, 12, 5126) have been employed to enable understanding of the substituent-induced changes in the NMR chemical shifts of the atoms in the purine skeleton. Analyses of the nuclear shielding using localized molecular orbitals (LMOs), specifically the natural LMOs (NLMOs) and Pipek-Mezey LMOs, were used to break down the values of the isotropic (13)C and (15)N NMR chemical shifts and the chemical shift tensors into the contributions of the individual LMOs. The experimental and calculated trends in the chemical shift of the N-3 atom correlate nicely with the Hammett constants (σ(para)) and the calculated natural charges on N-3, whereas the contributions of the LMOs to the N-1 and C-6 chemical shifts are found to be more complex.     

The morphology of aerosol particles consisting of hydrophobic and hydrophilic phases: hydrocarbons, alcohols and fatty acids as the hydrophobic component

The morphology of bi-phase aerosol particles containing phase separated hydrophobic and hydrophilic components is considered, comparing simulations based on surface and interfacial tensions with measurements made by aerosol optical tweezers. The competition between the liquid phases adopting core-shell and partially engulfed configurations is considered for a range of organic compounds including saturated and unsaturated hydrocarbons, aromatics, alcohols, ketones, carboxylic acids, esters and amines. When the solubility of the organic component and the salting-out of the organic component to the surface by the presence of concentrated inorganic solutes in the aqueous phase are considered, it is concluded that the adoption of a partially engulfed structure predominates, with the organic component forming a surface lens. The aqueous surface can be assumed to be stabilised by a surface enriched in the organic component. The existence of acid-base equilibria can lead to the dissociation of organic surfactants and to significant lowering of the surface tension of the aqueous phase, further supporting the predominance of partially engulfed structures. Trends in morphology from experimental measurements and simulations are compared for mixed phased droplets in which the organic component is decane, 1-octanol or oleic acid with varying relative humidity. The consequences of partially engulfed structures for aerosol properties are considered.     

Photoluminescence blue shift of indium phosphide nanowire networks with aluminum oxide coating

This paper describes our finding that optical properties of semiconductor nanowires were modified by depositing a thin layer of metal oxide. Indium phosphide nanowires were grown by metal organic chemical vapor deposition on silicon substrates with gold catalyst resulting in three‐dimensional nanowire networks, and optical properties were obtained from the collective nanowire networks. The networks were coated with an aluminum oxide thin film deposited by plasma‐enhanced atomic layer deposition. We studied the dependence of the peak wavelength of photoluminescence spectra on the thickness of the oxide coatings. A continuous blue shift in photoluminescence spectra was observed when the thickness of the oxide coating was increased. The observed blue shift is attributed to the Burstein–Moss effect due to increased carrier concentration in the nanowire cores caused by repulsion from intrinsic negative fixed charges located at the inner oxide surface. Samples were further characterized by scanning electron microscopy, Raman spectroscopy, transmission electron microscopy, and selective area diffractometry to better understand the physical mechanisms for the blue shift. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fractionation and Chemical Analysis of Urban Air Particulate Extracts

Abstract

Urban air samples were collected using Hi-Vol PM₁₀ samplers during 24 hours periods. Samples were collected from October 1993 to September 1994 both in Teplice and Prachatice and from October 1996 to April 1997 in Teplice, CR. Organic material (EOM) was extracted from filters with methylene chloride in a Soxhlet apparatus. Acid base partitioning of the crude extract was carried out and neutral compounds were further fractionated by silica gel column chromatography. More than one hundred and seventy compounds were identified by GC-MS in the fractions. Levels of PAHs and the distribution profile was similar at both sampling locations. Higher concentrations of PAHs, nitro-PAHs, polycyclic aromatic ketones and organic acids and bases were observed in winter period when the fuel consumption for home heating is high.     

Interactions Between Alkyl Triphenyl Phosphonium Bromides and Polyvinylpyrrolidones in Aqueous Media

The interactions of polyvinylpyrrolidones with alkyl triphenyl phosphonium bromide in aqueous media were investigated with conductometric, fluorimetric and tensiometric techniques. Formation of surfactant-polymer aggregates was detected in the case of C₁₆ and C₁₄ surfactant by these techniques. Tensiometric technique proved to be very sensitive to detect the early stage of association at very low concentrations. The Gibbs free energy of micellization and the dielectric constant values of the micellar interface values were obtained and discussed in terms of strength of interaction between the polymers and surfactants.     

Total Synthesis,Proof of Absolute Configuration,and Biosynthetic Origin of Stylopsal,the First Isolated Sex Pheromone of Strepsiptera

The asymmetric total synthesis of the diastereomers of stylopsal establishes the absolute configuration of the first reported sex pheromone of the twisted‐wing parasite Stylops muelleri as (3R,5R,9R)‐trimethyldodecanal. The key steps for the diastereo‐ and enantiodivergent introduction of the methyl groups are two different types of asymmetric conjugate addition reactions of organocopper reagents to α,β‐unsaturated esters, whereas the dodecanal skeleton is assembled by Wittig reactions. The structure of the natural product was confirmed by chiral gas chromatography (GC) techniques, GC/MS and GC/electroantennography (EAD) as well as field tests. An investigation into the biosynthesis of the pheromone revealed that it is likely to be produced by decarboxylation of a 4,6,10‐trimethyltridecanoic acid derivative, which was found in substantial amounts in the fat body of the female, but not in the host bee Andrena vaga. This triple‐branched fatty acid precursor thus seems to be biosynthesized de novo through a polyketide pathway with two consecutive propionate‐propionate‐acetate assemblies to form the complete skeleton. The simplified, motionless and fully host‐dependent female exploits a remarkable strategy to maximize its reproductive success by employing a relatively complex and potent sex pheromone.     

The use of copper solid amalgam electrodes for determination of the pesticide thiram

The complexes formed between copper and thiram and between mercury and thiram have been electrochemically (voltammetrically) investigated in the present work. Their structure was confirmed using electrospray ionization mass spectrometry. Due to formation of the complex between copper (from copper solid amalgam electrode) and thiram, the concentration of this pesticide can be determined. The voltammetric behavior of thiram was investigated at polished (p-CuSAE) and mercury meniscus modified (m-CuSAE) copper solid amalgam electrodes (inner diameter 1.5 mm) by differential pulse voltammetry (DPV) and by direct current voltammetry (DCV). Optimum conditions for DPV determination of thiram were found in Britton–Robinson buffer. The reaction mechanism was investigated using DCV and elimination voltammetry with linear scan. DPV with optimized parameters was applied for determination of thiram in analyzed solutions. The limits of detection were calculated as 16 nmol?L^?1 (t _acc?=?100 s) for m-CuSAE and 23 nmol?L^?1 (t _acc?=?60 s) for p-CuSAE. The proposed method was successfully applied for thiram determination in real sample solutions.     

A comparative study of fragment screening methods on the p38�� kinase: new methods, new insights

The stress-activated kinase p38α was used to evaluate a fragment-based drug discovery approach using the BioFocus fragment library. Compounds were screened by surface plasmon resonance (SPR) on a Biacore(?) T100 against p38α and two selectivity targets. A sub-set of our library was the focus of detailed follow-up analyses that included hit confirmation, affinity determination on 24 confirmed, selective hits and competition assays of these hits with respect to a known ATP binding site inhibitor. In addition, functional activity against p38α was assessed in a biochemical assay using a mobility shift platform (LC3000, Caliper LifeSciences). A selection of fragments was also evaluated using fluorescence lifetime (FLEXYTE(?)) and microscale thermophoresis (Nanotemper) technologies. A good correlation between the data for the different assays was found. Crystal structures were solved for four of the small molecules complexed to p38α. Interestingly, as determined both by X-ray analysis and SPR competition experiments, three of the complexes involved the fragment at the ATP binding site, while the fourth compound bound in a distal site that may offer potential as a novel drug target site. A first round of optimization around the remotely bound fragment has led to the identification of a series of triazole-containing compounds. This approach could form the basis for developing novel and active p38α inhibitors. More broadly, it illustrates the power of combining a range of biophysical and biochemical techniques to the discovery of fragments that facilitate the development of novel modulators of kinase and other drug targets.