Structure control in PMMA/silica hybrid nanoparticles by surface functionalization

Hydrophilic silica particles need to be hydrophobized to be encapsulated in a polymeric environment, which can be achieved by different methods. We report on the relationship between different hydrophobization techniques of silica and the final structure of poly(methyl methacrylate)/silica hybrid nanoparticles obtained by miniemulsion polymerization. Hydrophobization by cetyltrimethylammonium chloride (CTMA-Cl) uses the ionic interaction between the positively charged ammonium salt and the negatively charged silica surface, as shown by isothermal titration calorimetry. In this case, the interaction between polymer and silica surface needs to be enhanced, so 4-vinylpyridine (4-VP) was used as a co-monomer. Alternatively, the condensation reactions of 3-methacryloxypropyltrimethoxysilane (MPS) and octadecyltrimethoxysilane (ODTMS) were used to provide a covalent bond to the silica surface. The condensation reaction of the trimethoxysilane groups onto the silica surface was proven by Fourier transform infrared spectroscopy and thermogravimetric analysis. Hybrid nanoparticles were successfully formed with silica particles functionalized with the different functionalization agents. However, the structure of the resulting hybrid particles (i.e., the distribution of the silica particles within the polymer matrix) depends on the agent. The MPS-functionalized silica particles copolymerize with poly(methyl methacrylate), leading to a fixation of the silica particles inside the polymer and to a homogeneous distribution. The CTMA-Cl- and ODTMS-functionalized silica particles cannot copolymerize, but aggregate at the interface, leading to a Janus-like structure.     

Optimization of matrix solid-phase dispersion conditions for organic fungicides determination in soil samples

A simplified sample preparation method, based on the matrix solid-phase dispersion technique, is proposed for the sensitive determination of 15 organic fungicides in vineyard soils by gas chromatography-mass spectrometry (GC-MS). Under final working conditions, sieved samples (0.5 g) were blended and dispersed with 2 g of C18 and transferred to a polypropylene syringe containing 1 g of diatomaceous earth. Analytes were recovered using 10 mL of ethyl acetate, this extract was concentrated to 1 mL and fungicides determined by GC-MS, without additional cleanup. The method provided recoveries in the range from 74 to 122% for soils with total carbon contents up to 5.5% and it allowed the use of external standard as quantification technique. Inter-day precision, given as relative standard deviations, stayed between 3 and 13%, and the limits of quantification were comprised between 0.6 and 15 ng g(-1). Several fungicides were found in the top layer of vineyard soils with the highest detection frequency and maximum concentration corresponding to iprovalicarb. Some real samples were also submitted to pressurized liquid extraction. Measured concentrations were in excellent agreement with those obtained by matrix solid-phase dispersion, which reinforces the accuracy of the latter methodology.     

Studies on stereoselective [2+2] cycloadditions between N,N-dialkylhydrazones and ketenes

Staudinger-like cycloadditions between chiral, non-racemic N,N-dialkylhydrazones 1 and functionalized ketenes constitute an efficient methodology for the stereoselective construction of the beta-lactam ring. The potential for fine tuning of the dialkylamino auxiliary structure, the availability of a high-yielding deprotection method for the release of the free azetidinones, and the high thermal and chemical stability of hydrazones as N-dialkylamino imines are highlighted as the key elements for the success of the strategy. This last aspect is of particular importance concerning generality: even hydrazones from easily enolizable aldehydes or from formaldehyde reacted to afford the corresponding cycloadducts with high chemical and stereochemical yields. The syntheses of the beta-amino-alpha-hydroxyacids (2R,3S)-phenylisoserine (42) and (2R,3S)-norstatin (45) were accomplished as illustrative examples of the synthetic utility of this procedure. A model system for the cycloaddition of g series auxiliaries was studied by ab initio computational methods. The collected results support a two-step mechanism through zwitterionic intermediates, and explain the observed absolute and relative stereochemistry in terms of the preferred outward cycloaddition to the Re face of the hydrazone.     

Improved conditions for the asymmetric synthesis of α-amino acids using Cinchona-derived anthracenylmethyl ammonium salts as chiral phase-transfer organocatalysts

Cinchonidine and cinchonine-derived monomeric anthracenylmethyl ammonium salts bearing different counter-anions are used as chiral organocatalysts in the enantioselective alkylation of a benzophenone-imine tert-butyl glycinate under phase-transfer conditions. Generally, an improvement of the enantioselectivity is observed when the counterions are tetrafluoroborate and hexafluorophosphate using 50% aqueous KOH as the base and toluene/chloroform as the solvent. The enantioselectivities achieved are comparable and frequently higher, even working under simpler and less-strict reaction conditions and with lower organocatalyst loading, than those reported previously.     

Intramolecular Cannizzaro desymmetrization of tetraethylene glycol assisted by a cation binding template

The synthesis of desymmetrized tetraethylene glycol possessing a benzyl alcohol and a benzoic acid end group via a Cannizzaro reaction is reported. The barium cation template used was found to be essential for a successful transformation.     

The QCD spin chain S matrix

Beisert et al. have identified an integrable SU(2,2)$\mathit{SU}(2,2)$ quantum spin chain which gives the one-loop anomalous dimensions of certain operators in large Nc$N_c$ QCD. We derive a set of nonlinear integral equations (NLIEs) for this model, and compute the scattering matrix of the various (in particular, magnon) excitations.     

Indolylgold(I) derivatives and indole as π-arene ligands in cationic rhodium(I) complexes

The reaction of LAuIn (L = P(C₆H₅)₃, P(2-MeC₆H₄)₃ or P(4-MeC₆H₄)₃; In = indolyl group) with the solvated complexes [(diolefin)Rh(Me₂CO)_x]ClO₄ gives the novel heterometallic complexes [(diolefin)Rh(μ-In)AuL]ClO₄. The mononuclear arene derivatives [(diolefin)Rh(η⁶-HIn)]ClO₄ react with methanolic KOH to give the binuclear complexes [(diolefin)Rh(μ-OMe)]₂, while [(COD)Rh(η⁶-HIn)]ClO₄ reacts with KOH in water/acetone to give the hydroxo-bridged complex [(COD)Rh(μ-OH)]₂.     

Shock models under a Markovian arrival process

A device submitted to shocks arriving randomly and causing damage is considered. Every shock can be fatal or not. The shocks follow a Markovian arrival process. When the shock is fatal, the device is instantaneously replaced. The Markov process governing the shocks is constructed, and the stationary probability vector calculated. The probability of the number of replacements during a time is determined. A particular case in which the fatal shock occurs after a fixed number of shocks is introduced, and a numerical application is performed. The expressions are in algorithmic form due to the use of matrix-analytic methods. Computational aspects are introduced. This model extends others previously considered in the literature.     

Surfaces of Constant Mean Curvature Bounded by Convex Curves

This paper proves that an embedded compact surface in the Euclidean space with constant mean curvature H bounded by a circle of radius 1 and included in a slab of width is a spherical cap. Also, we give partial answers to the problem when a surface with constant mean curvature and planar boundary lies in one of the halfspaces determined by the plane containing the boundary, exactly, when the surface is included in a slab.     

A Novel Method for Surface Free-Energy Determination of Powdered Solids

Interfacial solid/liquid interactions play a crucial role in wetting, spreading, and adhesion processes. In the case of a flat solid surface, contact angle measurements are commonly utilized for the determination of the solid surface free energy and its components. However, if such a surface cannot be obtained, then the contact angle can not be measured directly. Usually methods based on imbibition of probe liquids into a thin porous layer or column are applied. In this paper a novel method, also based on the capillary rise, is proposed for the solid surface free-energy components determination. Actually, it is a modification of the thin column wicking method; similar theoretical background can be applied together with that appropriate for the capillary rise method of liquid surface tension determination. The proposed theoretical approach and procedure are verified by using single glass capillaries, and then alumina and ground glass powders were used for the method testing. Thus obtained surface free-energy components for these solids, for both glass and alumina, agree well with the literature values.