Studies on decarboxylation reactions. Part 5 . Micellar catalysis and mixed solvents effects on the decarboxylation of some N-alkyl- or N-aryl-substituted 5-amino-1,3,4-oxadiazole-2-carboxylic acids

The effect of micelles and mixed solvents on the decarboxylation of some N-alkyl- or N-aryl-substituted 5-amino-1,3,4-oxadiazole-2-carboxylic acids has been studied. The data support the unimolecular decarboxylation mechanism proposed by us. Moreover, they show that mixed solvents and micelles have different effects on reactivity of the amino acids under study.     

Synthesis of core‐shell structured carboxylated microparticles with a straightforward procedure and their evaluation as a polymer support

Poly(trimethylolpropane trimethacrylate) microspheres with a narrow size distribution were obtained by precipitation polymerization. They were subsequently modified by surface grafting with acrylic acid in a polar ethanol–water reaction medium, without stabilizer, yielding core‐shell particles with diameters in the micrometer range. The resulting polymeric material was characterized by SEM and potentiometric titration, FTIR spectroscopy, and thermal analysis. It was shown that the particle characteristics (size, size distribution, and functionality) obtained by this straightforward procedure can be controlled by modifying the synthesis parameters (monomer concentration, agitation rate, and temperature). The high functionality, the chemical and physico‐mechanical stability, as well as the possibility to control the performances of the resulting polymeric materials by synthesis allow its applications in various areas. Envisaging separation and catalysis domains, Cu(II), Cd(II), and Cr(III) uptake capacity from aqueous solutions was investigated under noncompetitive conditions as a function of synthesized particle functionality, time, and pH range. It was also found that the addition of the carboxylated microparticles to polyethylene stabilized with α‐tocopherol improved the thermo‐oxidative behaviour of the polymeric material. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5889–5898, 2005     

Reversible click chemistry at the service of macromolecular materials. Part 1: Kinetics of the Diels-Alder reaction applied to furan-maleimide model compounds and linear polymerizations

The model Diels-Alder reaction of furfuryl acetate with N-methylmaleimide and the linear polymerization of the corresponding difunctional monomers were followed by both UV and ¹H NMR spectroscopy. The results obtained from this study provided clear-cut indications about the most appropriate conditions to be applied in the preparation of novel macromolecular materials based in part on renewable resources and possessing thermoreversible, mendable and recycling features, among other properties.     

An algorithm for ordinal sorting based on ELECTRE with categories defined by examples

This work proposes a Progressive Assisted Sorting Algorithm (PASA) based on a multicriteria evaluation ELECTRE-type method. The purpose of the PASA is to aid a decision maker to progressively sort a set of alternatives into a set of categories, which we considered are ordered (ordinal sorting), following a consistency principle. We consider the principle that if an alternative outranks (is as good as) a second one, then it must belong to the same category or to a better category. The set of alternatives already sorted by the decision maker will implicitly define the categories, and will constrain the range of categories where other alternatives may be sorted. We show how the same idea may be used in an aggregation/disaggregation approach, considering some parameters of ELECTRE are not fixed a priori, but are constrained only by the examples provided. In this context, we establish a “convex-shape property” stating that the range of possible categories for an alternative is always an interval of categories. A discussion contrasting this approach with ELECTRE TRI is included in the conclusions.     

Photoluminescence in Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>-doped silica-titania inverse opal structures

Er³⁺ photoluminescence (PL) and Yb³⁺ → Er³⁺ energy transfer (ET) phenomena in the near infrared (NIR) have been studied in three-dimensional (3-D) inverse opal (IO) structures synthesized by a colloidal/sol–gel route, starting with the deposition of polystyrene microsphere (235 nm and 460 nm diameter) direct opal templates by convective self-assembly, followed by infiltration of the interstices with Er³⁺/Yb³⁺-doped silica, titania and silica-titania sols and heat-removal of the polymeric template material. The crystalline quality of the IOs has been optimized through suitable substrate treatments, plus the control of temperature and humidity during deposition of the templates. The structural and optical properties of the 3-D opal and IO structures have been studied by field emission scanning electron microscopy and visible-NIR reflection spectroscopy, in order to assess the relationship between microstructure and the photonic properties obtained. Photonic bandgaps have been evidenced by the corresponding stop bands in the reflection spectra. The shape and the intensity of the Er^{3+ 4}I_13/2 → ⁴I_15/2 transition at ~1.5 μm were modified in most IOs relatively to similar matrix deposits without a photonic crystal structure, particularly in the case of pure silica and titania IOs, where the PL peak narrowed and intensified. It was not possible at this stage to detect Yb³⁺ → Er³⁺ ET phenomena in the IOs structures.     

Composition and antioxidant activity of Thymus vulgaris volatiles: Comparison between supercritical fluid extraction and hydrodistillation

Supercritical fluid extraction (SFE) of the volatile oil from Thymus vulgaris L. aerial flowering parts was performed under different conditions of pressure, temperature, mean particle size and CO₂ flow rate and the correspondent yield and composition were compared with those of the essential oil isolated by hydrodistillation (HD). Both the oils were analyzed by GC and GC‐MS and 52 components were identified. The main volatile components obtained were p‐cymene (10.0–42.6% for SFE and 28.9–34.8% for HD), γ‐terpinene (0.8–6.9% for SFE and 5.1–7.0% for HD), linalool (2.3–5.3% for SFE and 2.8–3.1% for HD), thymol (19.5–40.8% for SFE and 35.4–41.6% for HD), and carvacrol (1.4–3.1% for SFE and 2.6–3.1% for HD). The main difference was found to be the relative percentage of thymoquinone (not found in the essential oil) and carvacryl methyl ether (1.0–1.2% for HD versus t?0.4 for SFE) which can explain the higher antioxidant activity, assessed by Rancimat test, of the SFE volatiles when compared with HD. Thymoquinone is considered a strong antioxidant compound.     

Basic ingredients of free energy calculations: A review

Methods to compute free energy differences between different states of a molecular system are reviewed with the aim of identifying their basic ingredients and their utility when applied in practice to biomolecular systems. A free energy calculation is comprised of three basic components: (i) a suitable model or Hamiltonian, (ii) a sampling protocol with which one can generate a representative ensemble of molecular configurations, and (iii) an estimator of the free energy difference itself. Alternative sampling protocols can be distinguished according to whether one or more states are to be sampled. In cases where only a single state is considered, six alternative techniques could be distinguished: (i) changing the dynamics, (ii) deforming the energy surface, (iii) extending the dimensionality, (iv) perturbing the forces, (v) reducing the number of degrees of freedom, and (vi) multi‐copy approaches. In cases where multiple states are to be sampled, the three primary techniques are staging, importance sampling, and adiabatic decoupling. Estimators of the free energy can be classified as global methods that either count the number of times a given state is sampled or use energy differences. Or, they can be classified as local methods that either make use of the force or are based on transition probabilities. Finally, this overview of the available techniques and how they can be best used in a practical context is aimed at helping the reader choose the most appropriate combination of approaches for the biomolecular system, Hamiltonian and free energy difference of interest. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

On the role of the colloidal stability of mesoporous silica nanoparticles as gene delivery vectors

Mesoporous silica nanoparticles have been synthesized and functionalized with four different types of molecules containing amino groups, i.e., with primary amines only, with quaternary amines, with quaternized cyclic amines, or with polyethylenimine (PEI), which is formed by primary, secondary, and tertiary amines. These nanoparticles were then incubated with reporter plasmids and the ability of the resulting complexes to transfect human cells was studied. Only nanoparticles functionalized with PEI were efficient for transfection. The agglomeration behavior and the electrokinetic potential of the nanoparticle–plasmid complexes have been studied, as well as their cell internalization behavior using a fluorescent-labeled plasmid that allows its monitorization by confocal microscopy. The results indicate that the efficiency of PEI-functionalized nanoparticles for transfection resides to some extent in the different characteristics imparted to the nanoparticles regarding agglomeration and surface charge behavior.