3D Study of the Morphology and Dynamics of Zeolite Nucleation

The principle aspects and constraints of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na‐rich aluminosilicate system. A detailed time‐series EMT‐type zeolite crystallization study in the model hydrogel system was performed to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods was employed to analyze the gel evolution and complement the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core–shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of the gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels.     

On approximations of the de Rham complex and their cohomology

For a commutative algebra R, its de Rham cohomology is an important invariant of R. In the paper, an infinite chain of de Rham-like complexes is introduced where the first member of the chain is the de Rham complex. The complexes are called approximations of the de Rham complex. Their cohomologies are found for polynomial rings and algebras of power series over a field of characteristic zero.     

Influence of the PVOH molar mass on the morphology and functional properties of EVOH/PVOH films prepared by melt blending

The influences of the molar mass (low, medium, and high) and content of poly(vinyl alcohol) (PVOH) dispersed by melt-blending in an ethylene vinyl alcohol (EVOH) copolymer on the morphology, microstructure, thermal, mechanical, and oxygen barrier properties were investigated. Multilayer films with external low-density polyethylene layers and inner EVOH/PVOH blend layer and respective monolayer films were elaborated and characterized. EVOH/PVOH blends exhibited a good compatibility because of the initial presence of PVOH segments in EVOH. The detailed quantitative analysis of the morphology performed for all blends showed that the finest dispersion was obtained with the PVOH with the lowest molar mass. The properties of the films as a function of the PVOH content and its molar mass were determined herein. Significant improvement of barrier properties was obtained at moderated water activities (up to a_w = 0.6) by using the PVOH with the lowest molar mass. Compared to the neat EVOH material, the oxygen permeability coefficients decreased by a factor 2 by adding 15 vol% PVOH while the thermal and mechanical properties remained similar.     

Rank properties of certain semigroups

In this paper we consider certain ranks of some semigroups. These ranks are r ₁(S),r ₂(S),r ₃(S),r ₄(S) and r ₅(S) as defined below. We have r ₁≤r ₂≤r ₃≤r ₄≤r ₅. The semigroups are CL _n ,CL _m ×CL _n ,Z _n and SL _n . Here CL _n is a chain with n elements, Z _n is the zero semigroup on n elements and SL _n is the free semilattice generated by n elements and having 2 ⁿ −1 elements. We find many of the ranks for these classes of semigroups.     

Effects of fire on the state of several elements in some soils of Sardinia

In order to individuate the modifications induced in the soil by fires relatively to the mobility of metals and rare earth three soils of Sardinia which differ in their mineralogical and physico-chemical characteristics were sampled. The analytical results obtained on the samples drawn at different depths (0-5 and 10-30 cm) three months after a fire and on the tests indicate that only the surface layer underwent significant modifications. The dynamics of metals and the distribution of the rare earths were found to depend, besides the amount and quality of the burned material, on the different behaviour of elements towards leaching. The diffractometric analysis showed that the soil surface layer of all the samples did not exceed 400 degrees C.     

Pyridylalkylamine ligands and their palladium complexes: structure and reactivity revisited by NMR

Pyridylmethylamines or pma are versatile platforms for different catalytic transformations. Five pma‐ligands and their respective Pd complexes have been studied by liquid state NMR. By comparing ¹H, ¹³C and ¹⁵N chemical shifts for each pma/pma–Pd couple, a general trend for the metallacycle atoms concerns variations of the electronic distribution at the pendant arm, especially at the nitrogen atom of the ligand. Moreover, the increase of the chemical shift of the pendant arm nitrogen atom from primary to tertiary amine is also related to the increase of crowding within the complex. This statement is in good agreement with X‐ray data collected for several complexes. Catalytic results for the Suzuki–Miyaura reaction involving the pma–Pd complexes showed within this series that a sterically crowded and electron‐rich ligand in the metallacycle was essential to reach the coupling product with a good selectivity. In this context, NMR study of chemical shifts of all active nuclei especially in the metallacycle could give a trend of reactivity in the studied family of pma–Pd complexes. Copyright © 2014 John Wiley & Sons, Ltd.     

Exploring the binding of serotonin to the 5-HT3 receptor by density functional theory

The 5-HT3 receptor is a typical ligand-gated ion channel of the Cys-loop superfamily, which is activated by binding of serotonin (5-HT). Models of the binding site of this protein reveal potential interactions between 5-HT and Tyr143, Tyr153, and Tyr234. Here we describe a series of ab initio calculations, based on density functional theory, to assess the effects of mutating these tyrosine residues on the binding of 5-HT. A series of mutations to these tyrosines, previously studied experimentally, were tested, and the binding energies compared with the available experimental data. Our results show that Tyr153 could form a hydrogen bond with the tertiary amine of 5-HT, and that mutation in this location revealed binding energies broadly in line with experimentally determined EC50s. Tyr143 could also form a hydrogen bond, but as EC50s do not relate to binding energies, it is unlikely that such a bond is formed here. Tyr234 is quite distinct in that it may interact with 5-HT via a mixed hydrogen bond/cation-pi interaction.