RAFT Polymerization: Adding to the Picture

SUMMARY: Factors affecting the choice of RAFT agent [RSC(Z) = S] for a given polymerization are discussed. For polymerization of methyl methacrylate (MMA), tertiary cyanoalkyl trithiocarbonates provide very good control over molecular weight and distribution and polymerizations show little retardation. The secondary trithiocarbonate RAFT agents with R = CHPh(CN) also gives good control but an inhibition period attributed to slow reinitiation is manifest. Radical induced reduction with hypophosphite salts provides a clean and convenient process for removal of thiocarbonylthio end groups of RAFT-synthesized polymers. Two methods providing simultaneous control over stereochemistry and molecular weight distribution of chains formed by radical polymerization are reported. Polymerization of MMA in the presence of scandium triflate provides a more isotactic PMMA. A similar RAFT polymerization with trithiocarbonate RAFT agents also provides control and avoids issues of RAFT agent instability seen with dithiobenzoate RAFT agents in the presence of Lewis acids. RAFT polymerization of tetramethylammonium methacrylate at 45 °C provides a more syndiotactic PMMA of controlled molecular weight and distribution (after methylation; mm:mr:rr 2:21:77 compared to 3:35:62 when formed by bulk polymerization of MMA).     

Evaluation by chemical parameters of the pollution state of the agricultural-industrial settlement of the Fucino Plain

In the present work are reported the results of a monitoring on a vast scale, carried out through evaluation of opportune chemical parameters, of the pollution state of the agricultural-industrial settlement of the Fucino Plain. The parameters took into consideration have been the presence of wide consumption pesticides and of ionic species as Cl-, NO2-, NO3-, NH4+, the quantification of the dissolved oxygen, of the temperature, of the conductivity, of pH and eH. Collected data are used for chemometric elaboration. The water systems examined, by means of drawing campaigns carried out at regular intervals in winter, spring, summer, and autumnal seasons, are represented by superficial waters constituting a network of irrigation canals fed by stratum and meteoric waters. In this work are reported the results relative to the drawing campaigns.     

A simple mathematical model for seasonal planktonic blooms

We show how the inclusion of the defense strategy by different species can alter the prediction of simple models. One of the defense strategy by the phytoplankton population against their grazer is the release of toxic chemicals. In turn the zooplankton population reduces there predation rate over toxin producing phytoplankton (TPP) to protect themselves from those toxic chemicals. Thus, when the level of toxicity is high, the grazing pressure is low and when the level of toxicity is low or when the toxin is absent, the grazing pressure is high. Here we have considered a TPP–zooplankton system where the rate of toxin liberation and the predation rate vary with zooplankton abundance. We observe that our proposed model has the potential to show different dynamical behaviour that are similar to that seen in real‐world situations. Further, we consider three different functional forms for the distribution of the toxins and compare them using latin hypercube sampling technique and found that the functional forms seem to have no effect in determining the final outcome of the system. Copyright © 2009 John Wiley & Sons, Ltd.     

Penkvilksite‐2O: Na2TiSi4O11·2H2O

The crystal structure of synthetic penkvilksite‐2O, disodium titanium tetrasilicate dihydrate, Na₂TiSi₄O₁₁·2H₂O, a microporous titanosilicate, confirms the major features of a previous model that had been obtained by order–disorder (OD) theory from the known structure of penkvilksite‐1M. An important difference from the previous model involves the hydrogen bonding of the water molecule which, on the basis of a Raman spectrum and the finding of only one of the two H atoms, is proposed to be disordered about a fixed O–H direction. The structure of penkvilksite‐2O is based on (100) silicate layers linked by isolated TiO₆ octahedra to form a heteropolyhedral framework. The layer is strongly corrugated, based on interlaced spiral chains, and is crossed by two different channels that have an effective channel width of about 3 Å.     

Reactivity of lithium 2,3-dihydro-1-benzothiophene-1-oxide toward aldehydes and imines and DFT calculations

The sulfinyl carbanion derived from 2,3-dihydro-1-benzothiophene-1-oxide and its lithium salt has been investigated by DFT calculations. The lithium carbanion was treated with aldehydes and imines to give chiral hydroxy and amino derivatives, with high stereoselectivity at the carbon α to the sulfoxide group (trans diastereoisomers), but with low diastereoselectivity at the hydroxyl or amine group. DFT calculations were used to rationalize the different stereochemical behavior of cyclic and acyclic lithiated sulfoxides in the reaction with aldehydes and azomethines.     

Minimal volume invariants,topological sphere theorems and biorthogonal curvature on 4‐manifolds

The goal of this article is to establish estimates involving the Yamabe minimal volume, mixed minimal volume and some topological invariants on compact 4‐manifolds. In addition, we provide topological sphere theorems for compact submanifolds of spheres and Euclidean spaces, provided that the full norm of the second fundamental form is suitably bounded.     

Modeling the depletion of dissolved oxygen in a water body located near a city

Water bodies located nearby cities are much prone to pollution, especially in the developing countries, where effluents treatment facilities are generally lacking. The main reason for this phenomenon is the increasing population in the cities, and the large number of industries located near them. This leads to generation of huge amounts of domestic and industrial sewage that is discharged into the water bodies, increasing their organic pollutant load and resulting in the depletion of dissolved oxygen. In this paper, we propose a mathematical model for this situation, focusing especially on the resulting quality of the water, determined by the level of dissolved oxygen. The model also accounts for resources needed for the population survival and for the industrial operations. In addition, we describe also the decomposition of organic pollutants by bacteria in the aquatic medium. Feasibility conditions and stability criteria of the system's equilibria are determined analytically. The results show that human population and industries are relevant influential factors responsible for the increase in organic pollutants and the decrease in dissolved oxygen in the water body, in the sense that they may exert a destabilizing effect on the system. The numerical simulations confirm the analytical results. Copyright © 2016 John Wiley & Sons, Ltd.     

A fast and efficient one-pot microwave assisted synthesis of variously di-substituted 1,2,4-oxadiazoles

A one-pot two-step microwave assisted synthesis of variously disubstituted 1,2,4-oxadiazoles from carboxylic acids and amidoximes is reported. This methodology is characterized by short reaction times, is versatile, robust and high-yielding and allows for the preparation of heterocycles with a stereocenter with 100% enantiomeric purity.     

On Hypersurfaces of Spheres with Two Principal Curvatures

In this paper we obtain a classification of hypersurfaces in the Euclidean sphere having two principal curvatures; for some of the results we impose that the sectional curvature (Ricci curvature, resp.) is non-negative Ricci.