Synthesis of new 3,5-diarylisoxazolidines by cycloaddition of oxaziridines and alkenes

This article reports a novel process of cycloaddition of C-aryloxaziridines with a variety of alkenes to afford stable, five-membered heterocycles 13–24. The steric hindrance of the tert-butyl group on the nitrogen atom of the oxaziridine is responsible for the high stereoselectivity of the cycloaddition reaction.     

Guerbet condensation of methanol with n-propanol to isobutyl alcohol over heterogeneous copper chromite/Mg–Al mixed oxides catalysts

The synthesis of isobutyl alcohol (ⁱBuOH) from methanol (MeOH) and n-propanol (PrOH) through the Guerbet condensation has been studied at 200 °C and under inert atmosphere (3.0 MPa of N₂), using a two-component heterogeneous catalytic system based on pre-activated copper chromite and Mg–Al mixed oxides deriving from hydrotalcite-type (HT) precursors with different Mg/Al ratios. All the investigated catalysts displayed a significant activity, with an almost complete selectivity to ⁱBuOH. Unlike the copper chromite/soluble sodium methoxide system, the catalysts were tolerant of the co-produced water and did not display any appreciable deactivation during the course of the reaction. The catalyst productivity was found to increase by reducing the Mg/Al ratio in the heterogeneous base, according to the increase of the fraction of medium–strong and strong basic sites which favour the aldol condensation between the aldehydes derived from MeOH and PrOH.     

Ziegler-Natta catalytic systems

A calorimetric investigation on the reactions of TiCl₄ with phthalates in 1,1,2,2-tetrachloroethane (TCE) is presented in order to better understand the complex interactions present in Ziegler-Natta catalytic systems. The Lewis bases diethyl isophthalate (L1), diethyl terephthalate (L2) and the ortho-isomer diethylphthalate (L3), have been chosen to study how the substituent positions could influence the energy and the stoichiometry of the complexation reactions. FTIR spectroscopy was used to obtain information on the coordination mode of the ligands and diffusion measurements by NMR was carried out to verify the presence of oligo-or polymeric species. Experimental results were compared with theoretical calculations based on Density Functional Theory (DFT).     

On the Asymptotic Behavior of Dilution Parameters for Gaussian and Hole–Gaussian Log-Conductivity Covariance Functions

Using a Lagrangian approach, the authors have previously shown that the kinetics of concentration variance and dilution of passive solutes in heterogeneous aquifers depend on the ratio between two- and one-particle covariances. Extending this approach, it is here demonstrated that, for point injections, the two-particle covariance coincides with the variance of the centroid location. Then, based on an Eulerian formulation, analytical first-order approximations are obtained for the two-particle covariance, for two types of log-conductivity covariance. For Gaussian covariance functions, whereas the transverse moments are asymptotically constant, the longitudinal moment tends to increase logarithmically over time. For hole–Gaussian covariances, both transverse and longitudinal moments tend to constant values. In both cases, the longitudinal two-particle correlation, which plays a crucial role in determining the dynamics of the concentration fluctuations, is controlled by the magnitude of the local dispersivity. The theoretical predictions are compared to the data collected at the Cape Cod site in terms of time derivative of the longitudinal two-particle moment, for Gaussian log-conductivity covariance and resorting to maximum likelihood estimates. Generally, good agreement is there, between experimental data and analytical expressions.     

Influence of Film Structure and Precursor Composition on Rhodamine B Retention in Dye-Dopped Ormosils

The interplay between the chemical structure of the precursors, internal organization in the end materials and dye retention was investigated for composites (ormosils) doped with rhodamine B. Besides formulations with triethoxysilanes (RTES) only, we synthesized as well organic–inorganic hybrids with addition of titanium isopropoxide (TIP) and maleic anhydride (MA). The organic (R) functionality of RTES was changed from methyl (MeTES), to phenyl (PTES) and octyl (OTES). Atomic force microscopy and electron microscopy, coupled with thermogravimetric analysis prove that hydrophobicity increase stimulates the transition of film structure: from well-defined, compact particles (for MeTES), to a mixture of porous particles and non-granular material (for MeTES/PTES), with extreme results observed for octyl-based composites. For this latter, the apparent homogeneity comes from cluster-like organization, where the primary entities are pseudo—granules produced by hydrophobic interactions of oligomeric siloxanes. Controlling the composition and gelation procedure resulted in doped composites with good optical transparency and rhodamine B fluorescence emission bands at around 580 nm. Dye transport inside the inorganic structure is not facilitated when: (a) the particles have a compact (nonporous) inner structure and (b) the recipe does not contain the TIP/MA combination. For silica-based films, the dye is located in the macropores (between the granules) of the material and could be easy removed by washing with acetone. On the contrary, using TIP/MA changes not only the internal composition of the granular-like material (by creating a microporous titania-rich outer-shell of the particles) but also the affinity of the Rh-B to permeate and reside inside these new structures.     

Magnetic anisotropy and molecular assembling in d complex cation–f complex anion type coordination compounds

The system [Fe(bpca)₂][Er(NO₃)₄(H₂O)₂] (1) (Hbpca = bis(2-pyridil-carbonyl) amine) is a complex cation–complex anion type coordination compound consisting of distinct d and f units, interlinked by hydrogen bonds. Particularly, the association of f-type complex anions in dimers is remarked and discussed. The energy decomposition analyses based on DFT calculations offered supplementary insight into the coordination effects at the lanthanide ions and the hydrogen bond driven supramolecular association of the complex units. Special ab initio procedures and subsequent modeling afforded the computation of anisotropic magnetization tensors of the [Er(NO₃)₄(H₂O)₂]^? f-type units. The computed results are in line with the experimental data for compound 1.     

Expedient synthesis of pseudo-Pro-containing peptides: towards constrained peptidomimetics and foldamers

The reaction of sulfonyl peptides containing L- or D-configured Ser or Thr with bis(succinimidyl) carbonate in the presence of a catalytic amount of a base affords, in solution or in the solid phase, the corresponding peptides with one or two, consecutive or alternate oxazolidin-2-ones (Oxd). The Oxd ring can be regarded to as a pseudo-Pro with an exclusively trans conformation of the preceding peptide bond; homochiral Oxd-containing peptides adopt extended conformations, while the presence of a D-configured Oxd favours folded conformations.     

Adsorption of formic acid on Si(111)7 × 7 at room temperature: a valence band photoemission and Si2p photodesorption study

Formic acid is the simplest of the carboxylic acids and a model adsorption system for several surfaces. In spite of the simple structure, formic acid reactivity and photoreactivity may be quite complex. In this paper, a study is presented on the deuterated formic acid adsorption on Si(111)7 × 7 at room temperature. The study is performed both by valence band photoemission and by photon‐stimulated desorption as a function of time and of photon energy in the 90–120 eV range. A primarily adsorption on rest atoms is found. This is verified by monitoring rest atoms and adatom intensity as a function of formic acid exposure. Further checks were made to control that surface adatoms were still free to react after the adsorption of formic acid. The photon stimulated desorption produces 5 single positively charged fragments: D⁺, O⁺, OD⁺ CO⁺ and CDO⁺. Possible fragmentation mechanisms are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

The Complexation Reactions of N-methylated Polyamines with Silver(I) in Dimethylsulfoxide

Abstract

The thermodynamic parameters for the complex formation reactions in dimethylsulfoxide (dmso) between Ag(I) and the following polyamines: N,N′-dimethylethylenediamine (dmen), N,N,N′,N′-tetramethylethylenediamine (dmen), N,N″-dimethyl-diethylenetriamine (dmdien) and N,N,N′,N″, N″-pentamethyldiethylenetriamine (pmdien) have been determined by potentiometric and calorimetric techniques at 298 K and 0.1 mol dm^?3 ionic strength (NEt₄ClO₄). Only mononuclear complexes are formed (AgL_j ⁺ j = 1,2) where the ligands act prevalently as chelate agents. All the complexes are enthalpy stabilized whereas the entropy changes counteract the complex formation. The results are discussed in terms of different basicities and steric requirements of both the ligands and the complexes formed.     

Highly Selective Water Adsorption in a Lanthanum Metal–Organic Framework

We present a new metal–organic framework (MOF) built from lanthanum and pyrazine‐2,5‐dicarboxylate (pyzdc) ions. This MOF, [La(pyzdc)_1.5(H₂O)₂] ? 2 H₂O, is microporous, with 1D channels that easily accommodate water molecules. Its framework is highly robust to dehydration/hydration cycles. Unusually for a MOF, it also features a high hydrothermal stability. This makes it an ideal candidate for air drying as well as for separating water/alcohol mixtures. The ability of the activated MOF to adsorb water selectively was evaluated by means of thermogravimetric analysis, powder and single‐crystal X‐ray diffraction and adsorption studies, indicating a maximum uptake of 1.2 mmol g^?1 MOF. These results are in agreement with the microporous structure, which permits only water molecules to enter the channels (alcohols, including methanol, are simply too large). Transient breakthrough simulations using water/methanol mixtures confirm that such mixtures can be separated cleanly using this new MOF.