Major Distinctions in the Molecular and Supramolecular Structures of Selenium‐containing Organotins, (o‐MeSe‐C6H4CH2)SnPh3–nCln (n = 0, 1, 2)

The synthesis and characterization of selenium‐containing stannanes, (o‐MeSeC₆H₄CH₂)Sn(Ph)_3–nCl_n [n = 0 ( 1Se ); 1 ( 2Se ); 2 ( 3Se )], is presented. The increasing Lewis acidity at tin in the series 1Se → 2Se → 3Se is reflected in their respective solid state arrangements and supramolecular architecture by interactions of the type Se ··· Se, Sn ··· Se, and Cl ··· H–C. Overall the capacity of the selenium atom to form bidentate interactions creates geometric assemblies distinctly different to those of the oxygen and sulfur analogs.     

Development of lightning rod for lightning protection standard in Europe,especially in Czech lands

This article presents a precise evaluation of the technological and social significance of the first European lightning rod, constructed in the Czech lands by the priest Václav Prokop Divi? at P?ímětice in Moravia on June 15, 1754. Discussions on the protection against lightning are known to have a rich tradition in the Czech lands (in the Habsburg monarchy) as well as in Europe as a whole. Especially the Czech lands, when compared with other countries, ranked among the leaders in terms of installed lightning rods. As for its overall impact, Divi?'s lightning rod had a significant international overlap; it proved to be of great importance even beyond the borders of the then Habsburg monarchy.The article offers not only a comparison of the efficiency and size of the protective zone of the first lightning rod by means of a computer model and contemporary mathematical and computing methods (method of the rolling sphere and the apex angle method), but it also highlights the unique social milieu in which Divi? developed his initial idea. It was an interplay of dogmatic religious scholastics and rational enlightenment in physics and natural sciences that was eventually conducive to the construction of one of the first devices for the protection against direct lightning impact. In their article, the authors also examine the transfer of knowledge on the protection against lightning impact from and to the Czech lands. A key approach to the protection against lightning was correct understanding and assessment of lightning charge, an analysis of the contact tip phenomenon and many issues relating to electrostatic phenomena. Seen in a historical perspective, the Czech lands had established an efficient platform of scientific centres, which linked up to and developed the pioneering work of Prokop Divi? several decades later. Viewed in a historical time scale, the Czech lands were represented in the branch of lightning protection primarily by Karel Václav Emanuel Zenger, Franti?ek Běhounek, Josef Postránecký, Ladislav V. ?íhánek, Franti?ek Popolanský and many others.Also in terms of standardization, the Czech Republic has been active on a long-term basis, while espousing the European standards with its own ?SN EN 62 305 standard. In many other respects, this country has been loyal to traditions; after all, the very first decree on the protection of gunpowder depots against lightning in the Habsburg monarchy came from Empress Maria Theresa and was published shortly after 1778. The lightning protection standard, issued by the Czechoslovak Electrical Engineering Union in the 1950s, had introduced a fundamentally new concept that served for the implementation of most protective systems in this branch until 2006.     

Effect of backbone flexibility on charge transfer rates in peptide nucleic acid duplexes

Charge transfer (CT) properties are compared between peptide nucleic acid structures with an aminoethylglycine backbone (aeg-PNA) and those with a γ-methylated backbone (γ-PNA). The common aeg-PNA is an achiral molecule with a flexible structure, whereas γ-PNA is a chiral molecule with a significantly more rigid structure than aeg-PNA. Electrochemical measurements show that the CT rate constant through an aeg-PNA bridging unit is twice the CT rate constant through a γ-PNA bridging unit. Theoretical calculations of PNA electronic properties, which are based on a molecular dynamics structural ensemble, reveal that the difference in the CT rate constant results from the difference in the extent of backbone fluctuations of aeg- and γ-PNA. In particular, fluctuations of the backbone affect the local electric field that broadens the energy levels of the PNA nucleobases. The greater flexibility of the aeg-PNA gives rise to more broadening, and a more frequent appearance of high-CT rate conformations than in γ-PNA.     

Cluster glass magnetism in the phase-separated Nd2/3Ca1/3MnO3 perovskite

A detailed study of the low-temperature magnetic state and the relaxation in the phase-separated colossal magnetoresistance Nd_2/3Ca_1/3MnO₃ perovskite has been carried out. Clear experimental evidence of the cluster-glass magnetic behavior of this compound has been revealed. Well defined maxima in the in-phase linear ac susceptibility χ′(T) were observed, indicative of the magnetic glass transition at T_g∼60 K. Strongly divergent zero-field-cooled and field-cooled static magnetizations and frequency dependent ac susceptibility are evident of the glassy-like magnetic state of the compound at low temperatures. The frequency dependence of the cusp temperature T_max of the χ′(T) susceptibility was found to follow the critical slowing down mechanism. The Cole–Cole analysis of the dynamic susceptibility at low temperature has shown extremely broad distribution of relaxation times, indicating that spins are frozen at “macroscopic” time scale. Slow relaxation in the zero-field-cooled magnetization has been experimentally revealed. The obtained results do not agree with a canonical spin-glass state and indicate a cluster glass magnetic state of the compound below T_g, associated with its antiferromagnetic–ferromagnetic nano-phase segregated state. It was found that the relaxation mechanisms below the cluster glass freezing temperature T_g and above it are strongly different. Magnetic field up to about μ₀H∼0.4 T suppresses the glassy magnetic state of the compound.     

Comparison of SERS effectiveness of copper substrates prepared by different methods: what are the values of enhancement factors?

Surface‐enhanced Raman scattering (SERS) spectroscopy is an analytical method for the detection of low amounts of analytes adsorbed on an appropriate coinage metal (Au, Ag, Cu) surface. Generally, the values of the enhancement factor are the highest on silver, lower on gold and relatively very low on copper. In this study, we have focused on the estimation of the enhancement factors of copper surface/substrates formed by different preparation procedures. The SERS activity of large electrochemically prepared substrates and colloidal systems is compared. The surface morphology of the large substrates was studied using scanning electron microscopy and atomic force microscopy. The size distribution of colloidal nanoparticles was monitored by dynamic light scattering. The values of enhancement factor are in both cases more than 10⁵ for the FT‐SERS spectra, demonstrating the fundamental role of nanostructured copper as a substrate material at the excitation wavelength (1064 nm) used. Copyright © 2011 John Wiley & Sons, Ltd.     

A role for the membrane protein M6 in the Drosophila visual system

Background

Members of the proteolipid protein family, including the four-transmembrane glycoprotein M6a, are involved in neuronal plasticity in mammals. Results from our group previously demonstrated that M6, the only proteolipid protein expressed in Drosophila, localizes to the cell membrane in follicle cells. M6 loss triggers female sterility, which suggests a role for M6 in follicular cell remodeling. These results were the basis of the present study, which focused on the function and requirements of M6 in the fly nervous system.

Results

The present study identified two novel, tissue-regulated M6 isoforms with variable N- and C- termini, and showed that M6 is the functional fly ortholog of Gpm6a. In the adult brain, the protein was localized to several neuropils, such as the optic lobe, the central complex, and the mushroom bodies. Interestingly, although reduced M6 levels triggered a mild rough-eye phenotype, hypomorphic M6 mutants exhibited a defective response to light.

Conclusions

Based on its ability to induce filopodium formation we propose that M6 is key in cell remodeling processes underlying visual system function. These results bring further insight into the role of M6/M6a in biological processes involving neuronal plasticity and behavior in flies and mammals.     

Size-dependant heating rates of iron oxide nanoparticles for magnetic fluid hyperthermia

Using the thermal decomposition of organometallics method we have synthesized high-quality, iron oxide nanoparticles of tailorable size up to ∼15 nm and transferred them to a water phase by coating with a biocompatible polymer. The magnetic behavior of these particles was measured and fit to a log-normal distribution using the Chantrell method and their polydispersity was confirmed to be very narrow. By performing calorimetry measurements with these monodisperse particles we have unambiguously demonstrated, for the first time, that at a given frequency, heating rates of superparamagnetic particles are dependent on particle size, in agreement with earlier theoretical predictions.     

Preparation of a GdCaAl3O7 matrix by the non-hydrolytic sol-gel route

Due to their stable physical and chemical properties, inorganic matrices have been widely employed as hosts for lasers and phosphors. We have prepared a GdCaAl₃O₇ matrix by the non-hydrolytic sol-gel route and have investigated the influence of heating treatment on sample structure. Europium III chloride was added as a structural probe, and the structure was analyzed by thermal analyses (TG/DTA/DSC), X-ray diffraction (XRD), and photoluminescence (PL). The XRD analysis revealed that initial crystallization took place at 400 °C. The peaks corresponding to the GdCaAl₃O₇ and GdAlO₃ phases were observed at 800 and 1000 °C. PL data revealed the characteristic transition bands arising from the ⁵D₀→⁵F_J (J=0, 1, 2, 3, and 4) manifolds under maximum excitation at 275, 391 and 463 nm for all the samples. All the analyses gave evidence that this methodology leads to the formation of a GdCaAl₃O₇ phase.     

Gold-copolymer nanoparticles: Poly(ε-caprolactone)/poly(N-vinyl-2-pyrrolydone) Biodegradable triblock copolymer as stabilizer and reductant

Block copolymers have been extensively used in the synthesis of many types of nanoparticles, where generally are considered as stabilizer and protective agent. In this work a double function of the biodegradable triblock copolymer poly(N-vinyl-2-pyrrolidone)-b-poly(ε-caprolactone)-b-poly(N-vinyl-2-pyrrolidone), (PVP-PCL-PVP) in the gold nanoparticle-copolymer synthesis is reported.Gold-copolymer composed nanoparticles were synthesized using the triblock copolymer (PVP-PCL-PVP) and potassium tetrachloro aurate (III), both in aqueous solution. The copolymer work as both, reductant and stabilizer agent. The obtained nanoparticles were characterized by FT-IR, dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The shape and the size of the obtained nanoparticles are dependent on the copolymer/salt of gold concentration ratio used in the synthesis.To complement the experimental results about the copolymer role in the nanoparticles synthesis, computational tools were used to characterize the reactivity of the reactant species.