The effect of different catalytic chain transfer agents on particle nucleation and the course of the polymerization in ab initio batch emulsion polymerization of methyl methacrylate

The effect a Co(II) based catalytic chain transfer agent (CCTA) has on the course of the polymerization and the product properties of an emulsion polymerization is governed by the intrinsic activity and the partitioning behavior of the catalyst. The effect on the conversion time history, the molecular weight distribution and the particle size distribution is evaluated in batch emulsion polymerization of methyl methacrylate for three different CCTAs, which cover a range of intrinsic activities and partitioning behaviors. It was demonstrated that radical desorption from the particle phase to the aqueous phase preceded by chain transfer is the main kinetic event controlling the course of the polymerization and the product properties in terms of the particle size distribution. The experimental results show that the aqueous phase solubility of the CCTA is the key parameter controlling the course of the polymerization and the particle size distribution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1038–1048, 2010     

Development of an in vitro system combining aqueous and lipid phases as a tool to understand gastric nitrosation

Nitrite has long been considered a potential pre‐carcinogen for gastric cancer. Acidification of salivary nitrite, derived from dietary nitrate, produces nitrosative species such as NOSCN, NO⁺ and N₂O₃, which can form potentially carcinogenic N‐nitroso compounds. Ascorbic acid inhibits nitrosation by converting the nitrosative species into nitric oxide (NO). However, NO diffuses rapidly to adjacent lipids, where it reacts with oxygen to reform nitrosative species. Nitrosation has been studied in vitro in aqueous systems and less frequently in organic systems; however, there is a need to investigate acid‐catalysed nitrosation in a system combining aqueous and lipid environments, hence providing a physiologically relevant model. Here, we describe a two‐phase system, which can be used as a tool to understand acid‐catalysed nitrosation. Using gas chromatography/ion trap tandem mass spectrometry, we investigated the nitrosation of secondary amines as a function of the lipid phase composition and reaction mixing. An increased interface surface area was a driver for nitrosation, while incorporation of unsaturated fatty acids affected morpholine and piperidine nitrosation differently. Linoleic acid methyl esters did not affect morpholine nitrosation and only had a limited effect on N‐nitrosopiperidine formation, while incorporation of free linoleic acid to the lipid phase significantly reduced N‐nitrosopiperidine formation, but increased N‐nitrosomorpholine formation at low levels. The mechanisms driving these effects are thought to involve amine partitioning, polarity and unsaturated fatty acids acting as scavengers of nitrosating species, findings relevant to the nitrosative chemistry occurring in the stomach, where the gastric acid meets a range of dietary fats which are emulsified during digestion. Copyright © 2010 John Wiley & Sons, Ltd.     

Fully Discrete Error Estimation by the Method of Lines for a Nonlinear Parabolic Problem

A posteriori error estimates for a nonlinear parabolic problem are introduced. A fully discrete scheme is studied. The space discretization is based on a concept of hierarchical finite element basis functions. The time discretization is done using singly implicit Runge-Kutta method (SIRK). The convergence of the effectivity index is proven.     

A limit theorem for the Shannon capacities of odd cycles I

This paper contains a construction for independent sets in the powers of odd cycles. It follows from this construction that the limit as goes to infinity of is zero, where is the Shannon capacity of the graph .

     

Theoretical study of the mechanism of the formation of 3-unsubstituted 4,4-disubstituted beta-lactams by silver-induced ring expansion of alkoxycyclopropylamines: a new synthetic route to 4-alkoxycarbonyl-4-alkyl-2-azetidinones

The mechanisms of formation of 4,4-dialkyl- and 4-alkoxycarbonyl-4-alkyl-2-azetidinones by silver-induced ring expansion of the corresponding 2,2-disubstituted N-chloro-1-hydroxycyclopropylamines were theoretically investigated by means of the B3LYP method and the PCM solvation model. The obtained results indicate that these reactions are facile two-step regioselective processes proceeding through a short-life nitrenium intermediate. The theoretical results thus predict that this synthetic strategy, which has already been used to obtain 4,4-dialkyl-2-azetidinones, could also be a new route to efficiently obtain in a regio- and stereoselective way 4-alkoxycarbonyl-4-alkyl-2-azetidinones, which are precursors of conformationally constrained amino acids.