Contact probe electrochemical characterization and metal speciation of silver LLDPE nanocomposite films

A contact probe methodology, based on the voltammetry of immobilized microparticle approach, is used for characterizing silver species present in linear low density polyethylene (LLDPE) films with different Ag(I)/Ag(0) ratios and silver nanoparticle features usable as food contact polymers. The films displayed characteristic voltammetric features in contact with aqueous acetate buffer, in particular signals for the stripping oxidation of nanoparticulate Ag systems. Significant differences between the studied films were also observed by means of electrochemical impedance spectroscopy and detected at the nanoscopic scale using electrochemical scanning microscopy. Differences in optical and thermal properties of the studied films are associated with the presence of silver nanoparticles. The silver oxidation state as well as nanoparticle size also had influence on the oxidative resistance of the LLDPE films; indeed, films containing cationic silver showed the lowest oxidation induction time value.     

Experimental and computational studies of ring‐opening polymerization of ethylene brassylate macrolactone and copolymerization with ε‐caprolactone and TBD‐guanidine organic catalyst

The ring‐opening polymerization (ROP) of ethylene brassylate, catalyzed by the cyclic guanidine 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) is reported. Several experimental parameters were evaluated for bulk ROP process and polyesters, resulting in molecular weights between 3 and 15 kg mol^?1. End‐group analysis by ¹H nuclear magnetic resonnance (NMR) and matrix assisted laser desorption ionization time of flight computational studies supports the dual behavior of TBD, which can act as both a catalyst and initiator of the polymerization process. Under optimum conditions, semicrystalline poly(ethylene brassylate‐co‐ε‐caprolactone) random copolymers were synthesized. Depending on the comonomer content, our results showed a range of melting temperatures between 39 and 69 °C. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 552–561     

A linear matrix equation: a criterion for block similarity

In this paper we study a homogeneous linear matrix equation related to the block similarity of rectangular matrices. We obtain the dimension of the vector space of its solutions and we describe these solutions. We give a characterization of the block similarity by rank tests. We extend Roth's criterion to the corresponding non homogeneous equation.     

Multipliers of weak type on locally compact Vilenkin groups

Let be a locally compact Vilenkin group with dual group . We give a sufficient condition for to be a multiplier of weak type on . Some applications of our result are given. We also prove that our result is sharp.

     

Synthesis of the aminocyclopentitol moieties of the hopanoids of Zymomonas mobilis and 'Anacystis montana'

The first synthesis of the cyclopentitol units in bacterial hopanoids has been accomplished from D-glucosamine and the possible biological activity of the free cyclitols as glycosidase inhibitors has been studied.     

Excess Gibbs free energies at several temperatures and excess enthalpies and volumes at 298.15 K of butanenitrile with 2-methyl-1-propanol or 2-methyl-2-propanol

Vapour pressures of butanenitrile +2-methyl-1-propanol or +2-methyl-2-propanol at several temperatures between 278.15 and 323.15 K were measured by a static method. Excess molar enthalpies and volumes were also measured at T = 298.15 K. Reduction of the vapour pressures to obtain activity coefficients and excess molar Gibbs free energies was carried out by fitting the vapour pressure data to the Redlich-Kister correlation according to Barker's method. Azeotropic mixtures with a minimum boiling temperature were observed over the whole temperature range, except for 2-methyl-2-propanol at T = 323.15 K.     

Nanoscale investigation of the structural and chemical changes induced by oxidation on carbon black surfaces: a scanning probe microscopy approach

Scanning tunneling microscopy (STM) and noncontact tapping mode atomic force microscopy (AFM) have been employed to study on a local scale the structural and, for the first time, the chemical changes of carbon black (CB) particles following plasma oxidation. STM imaging of the pristine, untreated particles revealed a relatively ordered structure of tiny crystallites with a few amorphous regions. After plasma treatment, the crystallites were no longer observed and the CB particle surface exhibited a noticeable and ubiquitous increase in atomic-scale disorder. Phase contrast images obtained with noncontact tapping mode AFM indicated that the untreated CB particles were essentially hydrophobic as a pristine basal surface of graphite, but with occasional hydrophilic patches. By contrast, their plasma-treated counterparts displayed enhanced hydrophilicity as a result of the introduction of oxygen onto the CB surface, the presence of which was evidenced by X-ray photoelectron spectroscopy, but most significantly, such enhancement was observed to be quite uniform at a local scale of individual particles. The possibility of investigating on a very local scale the chemical behavior of oxidized CB particles should be useful for the control and optimization of their dispersion properties in different systems.     

Rhodium/iridium-titanium azaheterometallocubanes

Treatment of [[Ti(eta5-C5Me5)(mu-NH)]3(mu3-N)] (1) with the diolefin complexes [[MCl(cod)]2] (M = Rh, Ir; cod = 1,5-cyclooctadiene) in toluene afforded the ionic complexes [M-(cod)(mu3-NH)3Ti3(eta5-C5Me5)3(mu3-N)]Cl [M = Rh (2), Ir (3)]. Reaction of complexes 2 and 3 with [Ag(BPh4)] in dichloromethane leads to anion metathesis and formation of the analogous ionic derivatives [M(cod)(mu3-NH)3Ti3-(eta5-C5Me5)3(mu3-N)][BPh4] [M = Rh (4), Ir (5)]. An X-ray crystal structure determination for 5 reveals a cube-type core [IrTi3N4] for the cationic fragment, in which 1 coordinates in a tripodal fashion to the iridium atom. Reaction of the diolefin complexes [[MCl(cod))2] (M = Rh, Ir) and [[RhCl(C2H4)2]2] with the lithium derivative [[Li(mu3-NH)2(mu3-N)-Ti3(eta5-C5Me5)3(mu3-N)]2] x C7H8 (6 C7H8) in toluene gave the neutral cube-type complexes [M(cod)(mu-NH)2(mu3-N)Ti3-(eta5-C5Me5)3(mu3-N)] [M = Rh (7), Ir (8)] and [Rh(C2H4)2(mu3-NH)2(mu3-N)Ti3(eta5-C5Me5)3(mu3-N)] (9), respectively. Density functional theory calculations have been carried out on the ionic and neutral azaheterometallocubane complexes to understand their electronic structures.     

Importance of Micropore–Mesopore Interfaces in Carbon Dioxide Capture by Carbon‐Based Materials

Mesoporous carbonaceous materials (Starbons®) derived from low‐value/waste bio‐resources separate CO₂ from CO₂/N₂ mixtures. Compared to Norit activated charcoal (AC), Starbons® have much lower microporosities (8–32 % versus 73 %) yet adsorb up to 65 % more CO₂. The presence of interconnected micropores and mesopores is responsible for the enhanced CO₂ adsorption. The Starbons® also showed three–four times higher selectivity for CO₂ adsorption rather than N₂ adsorption compared to AC.     

Exploitation of Dimeric Cyclic Cysteine as Helix Inducer in Ultra-Short Peptides for Cu(II)-Catalyzed Asymmetric Michael Addition on Chalcones

A dimeric cyclic cysteine analogue, i.e. (1R,1′R,2R,2′R)-2,2′-disulfanediylbis (aminocyclohexane-1-carboxylic acid), was used as a constrained unnatural amino acid and as a folding inducer in ultra-short Leu-Val-containing peptide. Our results showed that both free dimer amino acid L1 and its peptide derivative L2 are able to chelate Cu(II). The obtained complexes resulted to be catalytically active in Michael addition reaction of nitromethane on different types of chalcones. L1-Cu(II) was shown more reactive in terms of conversion, while, in neat conditions, L2-Cu(II) allows to obtain an interesting 60 % e.e. on pyridine chalcone.