Surface modification of calcium carbonate nanofillers by fluoro- and alkyl-alkoxysilane: Consequences on the morphology,thermal stability and gas barrier properties of polyvinylidene fluoride nanocomposites

Nano-sized precipitated silica coated calcium carbonate fillers (PCC-Si) were modified by an alkyl- and a fluoro-alkoxysilane derivative, respectively. PCC-Si surface modification was characterized by elemental analysis, Fourier transform infrared analysis and X-ray photoelectron spectroscopy. The modification conditions used for surface treatment led to a similar grafting density (around 3.2 μmol m^?2) for the two alkoxysilane derivatives. A significant decrease of filler hydrophilicity was observed after the alkoxysilane treatment. Nanocomposites prepared by melt mixing the modified fillers (10 wt.%) with polyvinylidene fluoride (PVDF) depicted no color change, an enhanced filler dispersion state with an homogeneous dispersion of very small filler aggregates (less than 150 nm diameter size), an increase of the thermal stability at high temperature and no change of the PVDF crystalline morphology. The oxygen permeability decrease measured on the nanocomposite prepared from the perfluorooctyltriethoxysilane modified filler was in good agreement with Maxwell law. The permeability increase evidenced for the nanocomposite based on the octyltriethoxysilane modified PCC suggested the formation of weak interfaces in this system.     

A two-step,single pot procedure for the synthesis of substituted dihydropyrazolo-pyrimidines

In this study, we report a two-step, one pot tandem microwave-assisted reaction of 3-formylchromones with aminopyrazoles followed by a tin-free radical addition. A library of alkyl substituted dihydropyrazolopyrimidines was prepared using this new process.     

Some modular relations for Ramanujan’s function k(q)=r(q)r^2(q^2)

In both his second and lost notebooks, Ramanujan introduced and studied a function \(k(q)=r(q)r^2(q^2)\) , where \(r(q)\) is the Rogers–Ramanujan continued fraction. Ramanujan also recorded five beautiful relations between the Rogers–Ramanujan continued fraction \(r(q)\) and the five continued fractions \(r(-q)\) , \(r(q^2)\) , \(r(q^3)\) , \(r(q^4)\) , and \(r(q^5)\) . Motivated by those relations, we present some modular relations between \(k(q)\) and \(k(-q)\) , \(k(-q^2)\) , \(k(q^3)\) , and \(k(q^5)\) in this paper.     

Investigation of the Hydroxylation Mechanism of Noncoupled Copper Oxygenases by Ab Initio Molecular Dynamics Simulations

In Nature, the family of copper monooxygenases comprised of peptidylglycine α‐hydroxylating monooxygenase (PHM), dopamine β‐monooxygenase (DβM), and tyramine β‐monooxygenase (TβM) is known to perform dioxygen‐dependent hydroxylation of aliphatic C? H bonds by using two uncoupled metal sites. In spite of many investigations, including biochemical, chemical, and computational, details of the C? H bond oxygenation mechanism remain elusive. Herein we report an investigation of the mechanism of hydroxylation by PHM by using hybrid quantum/classical potentials (i.e., QM/MM). Although previous investigations using hybrid QM/MM techniques were restricted to geometry optimizations, we have carried out ab initio molecular dynamics simulations in order to include the intrinsic flexibility of the active sites in the modeling protocol. The major finding of this study is an extremely fast rebound step after the initial hydrogen‐abstraction step promoted by the cupric–superoxide adduct. The hydrogen‐abstraction/rebound sequence leads to the formation of an alkyl hydroperoxide intermediate. Long‐range electron transfer from the remote copper site subsequently triggers its reduction to the hydroxylated substrate. We finally show two reactivity consequences inherent in the new mechanistic proposal, the investigation of which would provide a means to check its validity by experimental means.     

Generalizations of some conjectures of Sun on the relations between N(a, b, c, d; n) and T(a, b, c, d; n)

The Ramanujan Journal - We derive some new finite sums involving the sequence $$s_{2}\left( n\right) ,$$ the sum-of-digits of the expansion of n in base 2. These functions allow us to generalize...     

Dioxygen activation at a mononuclear Cu(I) center embedded in the calix[6]arene-tren core

The reaction of a cuprous center coordinated to a calix[6]arene-based aza-cryptand with dioxygen has been studied. In this system, Cu(I) is bound to a tren unit that caps the calixarene core at the level of the small rim. As a result, although protected from the reaction medium by the macrocycle, the metal center presents a labile site accessible to small guest ligands. Indeed, in the presence of O2, it reacts in a very fast and irreversible redox process, leading, ultimately, to Cu(II) species. In the coordinating solvent MeCN, a one electron exchange occurs, yielding the corresponding [CalixtrenCu-MeCN](2+) complex with concomitant release of superoxide in the reaction medium. In a noncoordinating solvent such as CH2Cl2, the dioxygen reaction leads to oxygen insertions into the ligand itself. Both reactions are proposed to proceed through the formation of a superoxide-Cu(II) intermediate that is unstable in the Calixtren environment due to second sphere effects. The transiently formed superoxide ligand either undergoes fast substitution for a guest ligand (in MeCN) or intramolecular redox evolutions toward oxygenation of Calixtren. Interestingly, the latter process was shown to occur twice on the same ligand, thus demonstrating a possible catalytic activation of O2 at a single cuprous center. Altogether, this study illustrates the oxidizing power of a [CuO2](+) adduct and substantiates a mechanism by which copper mono-oxygenases such as DbetaH and PHM activate O2 at the Cu(M) center to produce such an intermediate capable of C-H breaking before the electron input provided by the noncoupled Cu(H) center.     

Oxidation of UO2(s) in aqueous solution

In this review the kinetics and mechanism of oxidative dissolution of UO₂(s), mainly under conditions of relevance for the safety assessment of a deep geological repository for spent nuclear fuel, are discussed. Rate constants for the elementary processes involved (oxidation of UO₂ and dissolution of oxidized UO₂) are used to calculate the rates of oxidative UO₂(s) dissolution under various conditions (type of oxidant, oxidant concentration and HCO₃ ⁻/CO₃ ²⁻ concentration) for which experimental data are also available. The calculated rates are compared to the corresponding experimental values under the assumption that the experimental numbers reflect the steady-state conditions of the system. The agreement between the calculated rates and the corresponding experimental ones is very good, in particular for the higher rates. In general, the calculated rates are somewhat higher than the experimental numbers. This can be due partly to the use of initial concentrations rather than steady-state concentrations in the calculations. The kinetic data are also used to quantitatively discuss the dynamics of spent nuclear fuel dissolution under deep geological repository conditions.