Aqueous alteration of five-oxide silicate glasses: Experimental approach and Monte Carlo modeling

The alteration behavior of glass comprising five oxides (61 ? x)SiO₂–17B₂O₃–18Na₂O–4CaO–xZrO₂ was studied during static leach tests in a buffer solution at 90 °C and with a glass-surface-area-to-solution-volume (SA/V) ratio of 15 cm^?1. The morphological evolution of altered glasses investigated by small-angle X-ray scattering (SAXS) exhibits a strong dependence with the zirconium content in the glass. The experiments were compared with modeling results using Monte Carlo simulation. The model has been improved to simulate the alteration kinetics and alteration layer morphology, considering zirconium atoms at coordination number 6. The simulations exhibit very good agreement with experimental results, showing relations between the alteration rate and the restructuring altered layer. The model is used to interpret experimental observations by proposing a porosity closure mechanism in the altered layer to account for the diminishing alteration rate. For high zirconium concentrations, the simulation highlights the existence of percolation pathways responsible for a complete alteration of the glass. Zirconium has a hardening effect that limits the dissolution of neighboring atoms; this effect is favorable in terms of the glass alteration kinetics, but by inhibiting silicon recondensation it prevents complete closure of the porosity and the glass is completely altered.     

The Vilsmeier reagent as an efficient acid activator for the synthesis of β-lactams

The Vilsmeier reagent (chloromethylenedimethylammonium chloride) has been used as an efficient and cheap acid activator for the one-step Staudinger reaction of substituted acetic acids and imines under mild conditions. This reaction is clean and the by-products are DMF and triethylamine hydrochloride which were removed by simple aqueous work-up.     

Phase stability,mechanical and thermodynamic properties of orthorhombic and trigonal MgSiN2: an ab initio study

Structural stability and mechanical and thermodynamic properties of the orthorhombic and trigonal MgSiN₂ polymorphs (or-MgSiN₂ and tr-MgSiN₂) were investigated through density functional theory and quasi-harmonic Debye model (QHDM). Our calculations show that or-MgSiN₂ is energetically the stable polymorph at low pressure, in agreement with previous experimental and theoretical study. Under pressure, a crystallographic transition from the orthorhombic structure to the trigonal one occurs around 25, 17.45 and 19.05 GPa as obtained from the generalized gradient approximation of Perdew-Wang (GGA-PW91), the generalized gradient approximation parameterized recently by Perdew et al (GGA-PBEsol) and the local density approximation developed by Ceperley and Alder and parameterized by Perdew and Zunger (LDA-CAPZ), respectively. Single-crystalline and polycrystalline elastic constants and related properties, namely Vickers hardness, acoustic Grüneisen parameter, minimum thermal conductivity, isotropic sound velocities and Debye temperature, were numerically estimated for both or-MgSiN₂ and tr-MgSiN₂. We have showed that the hardness of tr-MgSiN₂ is comparable to that of the harder materials like c-BN and B₆O. Temperature and pressure dependencies of volume, bulk modulus, thermal expansion, Grüneisen parameter, heat capacities and Debye temperature were investigated using QHDM.     

Ceric Ammonium Nitrate on Silica Gel for Solid–Solid Phase N-Dearylation of β -Lactams

Silica gel–supported ceric ammonium nitrate (CAN-SiO ₂ ) has been found to be an effective reagent for the solid–solid phase and solvent-free N-dearylation of β-lactams. The results have been compared with CAN alone in solution and solid–solid phase.     

Synthesis of mono-, bis-spiro- and dispiro-β-lactams and evaluation of their antimalarial activities

Some new mono-, bis-spiro- and dispiro-β-lactams have been synthesized from imines derived from 9H-fluoren-9-one and a ketene derived from 9H-xanthene-9-carboxylic acid or phenoxyacetic acid by a [2+2] cycloaddition reaction in good to excellent yields varying from 45 to 83%. The biological activity of these monocyclic β-lactams was successfully investigated against Plasmodium falciparum K14 resistant strain with excellent EC₅₀ values up to 5 μM.     

On-column N-dearylation of 2-azetidinones by silica-supported ceric ammonium nitrate

A modified traditional preparative chromatographic column can be used to achieve quantitative N-dearylation of N-(alkoxyphenyl), N-(alkoxynaphthyl), and N-(alkoxybenzyl)-2-azetidinones under mild conditions. Starting materials are charged on top of the column and the pure N-unsubstituted 2-azetidinones leave the column minutes later without need for other purifications. The yields are good-to-excellent and the reaction condition is mild, easy, efficient, and cheap.     

Synthesis of novel N-sulfonyl monocyclic beta-lactams as potential antibacterial agents

New cis monocyclic beta-lactams were synthesized by [2+2] Staudinger cycloaddition reactions of the imine (3,4-dimethoxybenzylidene)-(4-methoxyphenyl)-amine and ketenes derived from different acyl chlorides and Et3N. These monocyclic beta-lactams were then cleaved by ceric ammonium nitrate (CAN) to give NH-monocyclic beta-lactams, which in turn were converted to N-sulfonyl monocyclic beta-lactams by treatment with four different sulfonyl chlorides in the presence of Et3N and 4,4-dimethyl-aminopyridine (DMAP).     

Sequential determination of iron(II) and iron(III) in pharmaceutical by flow-injection analysis with spectrophotometric detection.

A flow injection procedure for the sequential spectrophotometric determination of iron(II) and iron(III) in pharmaceutical products is described. The method is based on the catalytic effect of iron(II) on the oxidation of iodide by bromate at pH = 4.0. The reaction was monitored spectrophotometrically by measuring the absorbance of produced triiodide ion at 352 nm. The activating effect for the catalysis of iron(II) was extremely exhibited in the presence of oxalate ions, while oxalate acted as a masking agent for iron(III). The iron(III) in a sample solution could be determined by passing through a Cd-Hg reductor column introduced in the FIA system to reduce iron(III) to iron(II), which allows total iron determination. Under the optimum conditions, iron(II) and iron(III) could be determined over the range of 0.05 - 5.0 and 0.10 - 5.0 microg ml(-1), respectively with a sampling rate of 17 +/- 5 h(-1). The experimental limits of detection were 0.03 and 0.04 microg ml(-1) for iron(II) and iron(III), respectively. The proposed method was successfully applied to the speciation of iron in pharmaceutical products.     

Synthesis of new nanocopolymer containing β-lactams

Several new monocyclic β-lactam monomers bearing the NO₂ group 2a–g were synthesized via a [2 + 2] ketene–imine cycloaddition reaction (Staudinger reaction). Calculation of coupling constant of H-3 and H-4, and the X-ray crystallography of β-lactam 2e confirmed the cis stereochemistry of these β-lactams. Then aminophenyl β-lactams were synthesized by the reduction of NO₂ to NH₂ group in the presence of Raney Ni and hydrazine hydrate. Treatment of these aminophenyl β-lactams with acryloyl chloride and sodium bicarbonate (NaHCO₃), afforded the monomers bearing the NHCOCH=CH₂ group. These acrylated β-lactam monomers were dissolved in a warm mixture of butyl acrylate and styrene and then were converted to the corresponding polyacrylate nano β-lactams by emulsion polymerization in water. A unique feature of this methodology is the ability to incorporate water-insoluble compounds directly into the nanoparticle framework. Structures of the synthesized compounds were confirmed by physical and spectral analyses. Dynamic light scattering analysis and transmission electron microscopy of the final emulsions show that the nanoparticles were about 50–70 nm in diameter.