Phototransformations of azetidine radical cations stabilized in freonic matrices

It has been established that transformations of azetidine radical cations observed in freonic matrices under the action of light with λ = 436 nm (T = 77 K) are associated with C-N bond cleavage which corresponds to the cyclic form yielding a mixture of open distonic C-centered radical cations of the following structure: ·CH2CH2CH=NH 2 + © 2014 Pleiades Publishing, Ltd

Magnetic studies and scanning electron microscopy — X-ray energy dispersive spectroscopy analyses of road sediments, soils and vehicle-derived emissions

27 Pag., 2 Tabl., 6 Fig. The definitive version is available at: http://www.springerlink.com/content/0039-3169/Human health and environmental problems related to particulate matter emission from vehicles has become a topic of research interest in recent years. These airborne particles can not only be directly inhaled, but are also present as suspended and deposited particles on paved areas and roadside soils. Here we report on magnetic studies, scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and chemical analyses of vehicle-derived particles collected from both primary sources and as deposited particles on roads and soils. Preliminary results, recently published by the authors, have revealed that the magnetic signal of such particles is controlled by a magnetite-like phase with magnetic grain size ranging between 0.1 µm and 5 µm. An enrichment of some trace elements: Ba, Cr, Cu, Zn and Pb was also found. In this study we focus on SEM and EDS complementary studies of magnetic extracts. SEM observations showed small individual particles or spherulites, small aggregates in the form of chains or clusters, large aggregates of spherules, flake-like bodies, fibre-like particles, sheet-like particles, irregular debris and large particle agglomerates, i.e. a wide variety of shapes. Grain size distribution is also in agreement with magnetic grain size estimations. Additionally the following elements: C, O, Na, Mg, Al, Si, S, K, Ca, V, Ba, Ti, Cr, Mn, Fe, Cu, Zn and Pb were detected by EDS analysis.The authors would like to thank the CONICET, UNCPBA and UNMdP. Financial support was also received from a PICT-2005 of the ANPCYT, project No. 38050 and by the CICYT project MEDEROCAR (CGL2008-0831).Peer reviewe

In Situ SERS Sensing by a Laser-Induced Aggregation of Silver Nanoparticles Templated on a Thermoresponsive Polymer

A stimuli-responsive (pH- and thermoresponsive) micelle-forming diblock copolymer, poly(1,2-butadiene) 290 - block -poly( N , N -dimethylaminoethyl methacrylate) 240 (PB- b -PDMAEMA), was used as a polymer template for the in situ synthesis of silver nanoparticles (AgNPs) through Ag + complexation with PDMAEMA blocks, followed by the reduction of the bound Ag + with sodium borohydride. A successful synthesis of the AgNPs on a PB- b -PDMAEMA micellar template was confirmed by means of UV–Vis spectroscopy and transmission electron microscopy, wherein the shape and size of the AgNPs were determined. A phase transition of the polymer matrix in the AgNPs/PB- b -PDMAEMA metallopolymer hybrids, which results from a collapse and aggregation of PDMAEMA blocks, was manifested by changes in the transmittance of their aqueous solutions as a function of temperature. A SERS reporting probe, 4-mercaptophenylboronic acid (4-MPBA), was used to demonstrate a laser-induced enhancement of the SERS signal observed under constant laser irradiation. The local heating of the AgNPs/PB- b -PDMAEMA sample in the laser spot is thought to be responsible for the triggered SERS effect, which is caused by the approaching of AgNPs and the generation of “hot spots” under a thermo-induced collapse and the aggregation of the PDMAEMA blocks of the polymer matrix. The triggered SERS effect depends on the time of a laser exposure and on the concentration of 4-MPBA. Possible mechanisms of the laser-induced heating for the AgNPs/PB- b -PDMAEMA metallopolymer hybrids are discussed

Self-Assembled Multivalent (SAMul) Polyanion Binding – Impact of Hydrophobic Modifications in the Micellar Core on DNA and Heparin Binding at the Peripheral Cationic Ligands

This paper reports a small family of cationic surfactants designed to bind polyanions such as DNA and heparin. Each molecule has the same hydrophilic cationic ligand, and a hydrophobic aliphatic group with eighteen carbon atoms with either one, two or three alkene groups within the hydrophobic chain (C18-1, C18-2 and C18-3). Dynamic light scattering indicates that more alkenes lead to geometric distortion, giving rise to larger self-assembled multivalent (SAMul) nanostructures. Mallard Blue and Ethidium Bromide dye displacement assays demonstrate that heparin and DNA have markedly different binding preferences, with heparin binding most effectively to C18-1, and DNA to C18-3, even though the molecular structural differences of these SAMul systems are buried in the hydrophobic core. Multiscale modelling suggests that adaptive heparin maximises enthalpically-favourable interactions with C18-1, while shape-persistent DNA forms a similar number of interactions with each ligand display, but with slightly less entropic cost for binding to C18-3 – fundamental thermodynamic differences in SAMul binding of heparin or DNA. This study therefore provides unique insight into electrostatic molecular recognition between highly charged nanoscale surfaces in biologically-relevant systems