Association: A Possible Explanation for Anomalies in Ebulliometric Measurements with Polyethylene

In a recent paper [1], anomalies in ebulliometric measurements with polyethylene in different solvents were reported. Anomalies were claimed because the elevation of the boiling point ΔT exhibited an unusual concentration dependence. A strong increase of ΔT with c was followed by a weaker one and again by a strong increase. The anomalies at low concentrations were attributed to unaccounted-for factors.     

Stereocontrol in DL-Leucine N-Carboxyanhydride Polymerizations

L-Leucine and DL-leucine N-carboxyanhydride were polymerized in 1,4-dioxane at 25°C with either benzylamine or L-a-methylbenzylamine as initiator, using a constant volume reactor for rate studies. A rapid initiation period was followed by two pseudo-first-order propagation periods for the racemic (DL) monomer and by three pseudo-first-order propagation periods for the L-monomer. The ratio of rate constants of the L- to the DL-polymerization is about 2 for any given polymerization period, independent of initiator type. Such a behavior is expected for stereoselective propagations without crossover, leading to blends of isotactic polymers.     

A Novel Series of 3,4‐Disubstituted Dihydropyrazoles: Synthesis and Evaluation for MAO Enzyme Inhibition

In this study, the authors have designed and synthesized a novel series of 3‐acyl‐4‐aryl‐4,5‐dihydropyrazoles, with the aim to obtain new potential scaffolds for the inhibition of both isoforms of monoamine oxidase (MAO) enzyme. The synthetic pathway to these compounds includes as a key step the 1,3‐dipolar cycloaddition reaction of diazomethane with a chalcone. All the compounds were fully characterized by means of spectroscopic and analytical data and showed specific inhibition against MAO A.     

Ageing and thermal stability studies on quasi-solid composite electrolytes for Grätzel-type solar cells

Loss of volatile components from two types of quasi-solid gel electrolytes to be used in Grätzel (or dye-sensitized, DSSC)-type alternative solar cells are checked time to time by thermogravimetry (TG) to follow the stability or changes of composites during storage at ambient. One of the gel samples, labeled as P2000 and based on UreaSil 2000, a 3D-cage precursor compound, has been found quite stable, while the related P230 sample based on UreaSil 230 seems to have a bit higher deviation in heterogeneity and some tendencies losing gradually from its volatile content, time to time. In addition, two online coupled evolved gas analytical tools (TG–EGA–FTIR and TG/DTA–EGA–MS) are applied to check the gel electrolytes for thermal vaporization, degradation, and decomposition processes as a function of temperature during dynamic heating in air. Initial minor elimination of ethyl acetate has been detected by both in situ coupled mass spectroscopy and FTIR spectroscopic gas cell. According to both evolved gas analytical systems, the other liquid ingredients, acetic acid (AcOH) and sulfolane are also released in the order of their volatility. Above 300 °C, an oxidative thermal degradation of UreaSil-type host matrices is indicated by the occurrence of, among others, formaldehyde or ammonia for electrolyte samples P2000 and P230, respectively. Evolution of various alkyl iodides with short chain length has only been detected by the mass spectroscopic evolved gas analysis method only.     

Characterization of surface plasmon energy transduction in gold nanoparticle/polymer composites by photo-DSC

In this study, we investigate the formulation and optimization of stimulus-responsive composites consisting of gold nanoparticles in polyethylene glycol diacrylate (PEGDA) matrices, which can be remotely heated through localized surface plasmon resonance (SPR). In these materials, laser radiation is absorbed by the nanoparticles and transduced into thermal energy. Optothermal properties of the polymer/nanoparticle composites are characterized using an adaptation of photo-differential scanning calorimetry (photo-DSC), in which a sample is characterized in isothermal mode in the presence and absence of optical illumination. Au/PEGDA composite samples are determined by photo-DSC to transduce energy from a 532 nm optical source with high efficiencies (>80%). UV/Vis/NIR spectrophotometry is used to characterize the optical properties of the samples. Nanoparticle dispersion and size within composite polymer matrices are characterized using transmission electron microscopy (TEM). It is shown that the magnitude and rate of energy transduction can be tuned by varying both nanoparticle concentration and dispersion.     

Bringing about matrix sparsity in linear-scaling electronic structure calculations

The performance of linear-scaling electronic structure calculations depends critically on matrix sparsity. This article gives an overview of different strategies for removal of small matrix elements, with emphasis on schemes that allow for rigorous control of errors. In particular, a novel scheme is proposed that has significantly smaller computational overhead compared with the Euclidean norm-based truncation scheme of Rubensson et al. (J Comput Chem 2009, 30, 974) while still achieving the desired asymptotic behavior required for linear scaling. Small matrix elements are removed while ensuring that the Euclidean norm of the error matrix stays below a desired value, so that the resulting error in the occupied subspace can be controlled. The efficiency of the new scheme is investigated in benchmark calculations for water clusters including up to 6523 water molecules. Furthermore, the foundation of matrix sparsity is investigated. This includes a study of the decay of matrix element magnitude with distance between basis function centers for different molecular systems and different methods. The studied methods include Hartree–Fock and density functional theory using both pure and hybrid functionals. The relation between band gap and decay properties of the density matrix is also discussed.     

Cadmium telluride nanocrystals as luminescent sensitizers in flow analysis

A fully automated multipumping flow system (MPFS) using water-soluble CdTe quantum dots (QD) as sensitizers is proposed for the chemiluminometric determination of the anti-diabetic drugs gliclazide and glipizide in pharmaceutical formulations. The nanocrystals acted as enhancers of the weak CL emission produced upon oxidation of sulphite by Ce(IV) in acidic medium, thus improving sensitivity and expanding the dynamical analytical concentration range. By interacting with the QD, the two analytes prevented their sensitizing effect yielding a chemiluminescence quenching of the Ce(IV)-SO₃²⁻CdTe QD system. The pulsed flow inherent to MPFS assured a fast and efficient mixing of all solutions inside the flow cell, circumventing the need for a reaction coil and facilitating the monitoring of the short-lived generated chemiluminescent species. QD crystal size, concentration and spectral region for measurement were investigated.     

Size-controllable synthesis of functional heterostructured TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> core–shell nanoparticles

Mono and bicomponent TiO₂ and WO₃ nanoparticles were synthesized inside Vycor^® glass pores, by cycles of impregnation of the glass with the respective oxide precursor followed by its thermal decomposition. The impregnation-decomposition cycle (IDC) methodology promoted a linear mass increase of the glass matrix, and allowed tuning the nanoparticle size. X-ray diffraction and Raman spectroscopy data allowed identifying the formation of TiO₂ as anatase phase, while WO₃ is a mixture of the γ-WO₃ (monoclinic) and δ-WO₃ (triclinic) phases. High resolution transmission electron microscopy images revealed that for 3, 5, and 7 IDC, the TiO₂ nanoparticles obtained presented average diameters of 3.4, 4.3, and 5.1 nm, and the WO₃ nanoparticles have 2.9, 4.6, and 5.7 nm sizes. These TiO₂ and WO₃ monocomponent nanoparticles were submitted to IDC with the other oxide precursor, resulting in bicomponent nanoparticles. The broadening and shift of the Raman bands related to titanium and tungsten oxides suggest the formation of hetero-structure core–shell nanoparticles with tunable core sizes and shell thicknesses.     

Quantitative Analysis of Flame Instabilities in a Hele-Shaw Burner

We show in this paper that a Hele-Shaw burner can be used for studying the development of premixed flame instabilities in a quasi-two dimensional configuration. It is possible to ignite a plane flame at the top of the cell, and to measure quantitatively the growth rates of the instability by image analysis. Experiments are performed with propane and methane-air mixtures. It is found that the most unstable wavelength, and the maximum linear growth rate of perturbations, directly measured in the present experiments, have the same order of magnitude as those previously measured on flames propagating freely downwards in wide tubes.     

Evolution of the commutation concept associated with the development of flow analysis

Evolution of the commutation concept has lead to the proposal and development of different generations of flow analyzers. Since the inception of the air-segmented flow systems till the availability of modern flow injection, sequential-injection and other flow-based analytical systems, a noteworthy improvement of the commutating devices has been noted.

Multi-functional manifold is described as a polyvalent approach for methodology implementation in a flow analyzer. It permits the investigation of mixing conditions under different flow patterns (unsegmented, segmented, monosegmented) with optional exploitation of the stopped-flow approach. For this purpose, spectrophotometric or turbidimetric measurements eventually affected by Schlieren noise were considered. Potentialities and limitations of the manifold are discussed in relation with methods based on relatively fast or slow chemical reactions. As applications, phosphate and chloride determinations in plant digests and natural waters were selected.

The manifold is characterized by high versatility and may work in connection with different flow configurations. Development will certainly lead to simple, versatile and miniaturized analyzers, able to run samples in a personalized fashion. In addition, random reagent selection, full automation, expansion of the analytical application range and increasing potentialities of the already existing methodologies are devised.