Synthesis of octahedral zirconium complex bearing [NHC?O] ligands,and its behavior as catalyst in the polymerization of olefins

The synthesis and characterization of a zirconium complex, having two alkoxide functionalized N‐heterocyclic carbene ligands, and its behavior as catalyst in the polymerization of ethylene and propylene, have been reported. NMR analysis showed that more than one species was obtained during synthesis. These data were confirmed by ethylene polymerization that gave rise to a linear polyethylene having a high Molecular weight and a polydispersity index (MDI) > 2 and often bimodal. The same catalytic system was able to produce highly isotactic polypropylene together with an atactic fraction. DFT studies on the complex stereoisomer stability gave indications on the species possibly involved in the polymerizations. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

<Emphasis Type="Italic">ϕ</Emphasis>-pairs and common fixed points in cone metric spaces

In this paper we introduce a contractive condition, called ϕ-pair, for two mappings in the framework of cone metric spaces and we prove a theorem which assures existence and uniqueness of common fixed points for ϕ-pairs. Also we obtain a result on points of coincidence. These results extend and generalize well-known comparable results in the literature. The authors are supported by Università degli Studi di Palermo, R. S. ex 60%.     

Invilappi di sfere sulle cui focali si corrispondono le linee di curvatura e le linee asintotiche

Sunto. In questa Memoria vengono formati gl'inviluppi di sfere, sulle cui focali si corrispondono le linee di curvatura e le linee asintotiche, con la considerazione della congruenzaaggiunta; il problema è ridotto ad un sistema diCauchy e la soluzione generale dipende da quattro funzioni arbitrarie di una sola variabile.     

Una trasformazione delle congruenze cicliche

Sunto. In questa Memoria è stabilita una trasformazione di una data congruenza ciclica(G) in una nuova congruenza ciclica (G ₁), attraverso un sistema di cinque sfere a due a due ortogonali. L'equazione diLaplace per i parametri direttori della rettaG ₁ èl'aggiunta di quella relativa a(G). La (G ₁) è generale se tale è la(G).     

Intorno alle congruenze sulle cui superficie focali si corrispondono le linee di curvatura

Sunto Nel presente lavoro è stabilita una trasformazione delle congruenzeW, secondo la quale il problema della determinazione di tali congruenze è ridotto alla formazione di una reteO dello spazio a quattro dimensioni, e di due altre tali reti equivalenti adO per trasformazioni conformi. Il caso in cui sulle superficie focali della congruenza si corrispondono le linee di curvatura, è caratterizzato da una relazione fra le curvature isotrope delle retiO, da cui dipende il problema.     

Liquid chromatography coupled to quadruple time‐of‐flight tandem mass spectrometry for microcystin analysis in freshwaters: method performances and characterisation of a novel variant of microcystin‐RR

Cyanobacteria, also called blue‐green algae, occur worldwide within water blooms in eutrophic lakes and drinking water reservoirs, producing several biotoxins (cyanotoxins). Among these, microcystins (MCs) are a group of cyclic heptapeptides showing potent hepatotoxicity and activity as tumour promoters. So far, at least 89 MCs from different cyanobacteria genera have been characterised. Herein, ion trap, matrix‐assisted laser desorption/ionisation time‐of‐flight (MALDI‐ToF) and quadruple time‐of‐flight (Q‐ToF) mass spectrometry (MS)‐based methods were tested and compared for analysing MCs in freshwaters. Method performances in terms of limit of detection, limit of quantification, mean recoveries, repeatability, and specificity were evaluated. In particular, a liquid chromatography/electrospray ionisation (LC/ESI)‐Q‐ToF‐MS/MS method was firstly described to analyse MCs in freshwaters; this technique is highly selective and sensitive, and allowed us to characterise the molecular structure of an unknown compound. Indeed, the full structural characterisation of a novel microcystin variant from a bloom of Planktothrix rubescens in the Lake Averno, near Naples, was attained by the study of the fragmentation pattern. The new cyanotoxin was identified as the 9‐acetyl‐Adda variant of microcystin‐RR. Copyright © 2009 John Wiley & Sons, Ltd.