Monitoring the polyamide 11 degradation by thermal properties and X‐ray fluorescence spectrometry allied to chemometric methods

The influence of temperature (110 and 120 °C) on the ageing of piping made from polyamide 11 (PA‐11) containing 10–12% of plasticizer was studied using deionized water (pH ≈ 7.0). A clean analytical methodology has been employed for quality control of polymeric materials: energy‐dispersive X‐ray fluorescence spectrometry (ED‐XRF). It provides a fast and suitable technique to characterize chemical elements because of its multielemental capability, good sensitivity, high precision, short analytical time, and nondestructive nature. Herein, the content of additive in PA‐11 was monitored from ED‐XRF measurements where the abundance of the S line is directly related to the ageing time, agreeing with the thermogravimetric analysis. The XRF data were allied to chemometric treatment to classify PA‐11 samples according to the amount of additive and weight average molar mass change, predicting the ageing time, and viscosity values of PA‐11. Therefore, the XRF can be used as a clean analytical methodology to monitor the PA‐11 degradation, thus eliminating the use of toxic organic solvents (necessary to viscosity measurements) and reducing the working time. Also, the effect of hydrolysis on the structure over time and the material morphology were monitored through measurements of dynamic mechanical analysis and differential scanning calorimetry. Copyright © 2012 John Wiley & Sons, Ltd.     

Phase transfer of hydrophilic, cyclodextrin-modified gold nanoparticles to chloroform solutions.

The preparation and characterization of gold nanoparticles (approximately 3 nm in diameter) capped with thiolated alpha- and beta-cyclodextrins (alpha and beta-CD) is described. The CD-capped nanoparticles are hydrophilic and bind ferrocene derivatives as evidenced by electrochemical and (1)H NMR spectroscopic measurements. The binding interactions of the CD-capped nanoparticles with a series of five alkyldimethyl(ferrocenylmethyl)ammonium ions (the alkyl group is propyl for compound 1, heptyl for 2, dodecyl for 3, hexadecyl for 4, and docosyl for 5) can be utilized for the phase transfer of the hydrophilic, CD-capped nanoparticles into a nonpolar chloroform phase. Only 3, 4, and 5 act as effective phase transfer agents, since 1 and 2 do not have enough amphiphilic character. The structure of the aggregates formed upon transfer of the CD-capped nanoparticles to the chloroform solution is postulated to resemble that of reverse micelles, as the nanoparticles template the peripheral arrangement of the cationic ferrocene amphiphiles, counterions and water molecules around their surfaces.     

Confidence intervals for quantile estimation using Jackknife techniques

We consider the inference on quantiles, Q _y (β), with jackknife techniques, in finite populations of a variable, Y, using the quantile information on an auxiliary variable, X. Jackknife techniques are applied to estimate quantiles and the behaviour of these estimators is analyzed. Their properties are studied for simple random sampling. We also examine the confidence intervals obtained with jackknife variances.     

1,3-Cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride as a spectrophotometric reagent for the determination of lodate in acetic and perchloric acid media

1,3-Cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride produces colored solutions with iodate ions in acid medium. The yellow color obtained has been used to proposed Spectrophotometric methods for determination of IO₃^? in the concentration range 1.0–11.0 ppm in acetic acid medium (molar absorptivity 1.08 × 10⁴ liters mol^?1 cm^?1 at a wavelength of 415 nm) and 0.5–8.0 ppm in perchloric acid medium (molar absorptivity 2.05 × 10⁴ liters mol^?1 cm^?1 at a wavelength of 400 nm).     

Spectroscopy characterization of MnSe nanoclasters randomly distributed in HgMnTe single crystal

New semimagnetic semiconductor Hg_0.91Mn_0.09Te-MnSe mixture, grown by Bridgman method, was investigate by Atomic Force Microscopy, X-ray and far-infrared spectroscopy, in order to obtain the necessary feedback information to determine the optimal conditions for crystal growth. The investigated mixture consists of MnSe nanoclasters randomly distributed in Hg_0.91Mn_0.09Te matrix. Far-infrared reflectivity spectrum of the Hg_0.91Mn_0.09Te-MnSe mixture was measured in the 80–500 cm^?1 range at a room temperature. The analysis of the far-infrared spectrum was made by the fitting procedure. The Maxwell-Garnett effective medium theory is used for modeling an effective dielectric function, and on that way calculating both electron and phonon response.     

Dendritic cavitands: preparation and electrochemical properties

A new series of dendrimers containing a central cavitand core with four appended Fréchet-type dendrons, linked to the core through 4,4'-bipyridinium (viologen) subunits, have been synthesized, characterized and their electrochemical properties investigated using cyclic voltammetric measurements.     

Metabolic profiling for the identification of Huntington biomarkers by on‐line solid‐phase extraction capillary electrophoresis mass spectrometry combined with advanced data analysis tools

In this work, an untargeted metabolomic approach based on sensitive analysis by on‐line solid‐phase extraction capillary electrophoresis mass spectrometry (SPE‐CE‐MS) in combination with multivariate data analysis is proposed as an efficient method for the identification of biomarkers of Huntington's disease (HD) progression in plasma. For this purpose, plasma samples from wild‐type (wt) and HD (R6/1) mice of different ages (8, 12, and 30 weeks), were analyzed by C₁₈‐SPE‐CE‐MS in order to obtain the characteristic electrophoretic profiles of low molecular mass compounds. Then, multivariate curve resolution alternating least squares (MCR‐ALS) was applied to the multiple full scan MS datasets. This strategy permitted the resolution of a large number of metabolites being characterized by their electrophoretic peaks and their corresponding mass spectra. A total number of 29 compounds were relevant to discriminate between wt and HD plasma samples, as well as to follow‐up the HD progression. The intracellular signaling was found to be the most affected metabolic pathway in HD mice after 12 weeks of birth, when mice already showed motor coordination deficiencies and cognitive decline. This fact agreed with the atrophy and dysfunction of specific neurons, loss of several types of receptors, and changed expression of neurotransmitters.     

Catalyzing aldehyde hydrosilylation with a molybdenum(VI) complex: a density functional theory study

[MoCl(2)O(2)] catalyzes the hydrosilylation reaction of aldehydes and ketones, as well as the reduction of other related groups, in apparent contrast to its known behavior as an oxidation catalyst. In this work, the mechanism of this reaction is studied by means of density functional theory calculations using the B3LYP functional complemented by experimental data. We found that the most favorable pathway to the first step, the Si--H activation, is a [2+2] addition to the Mo=O bond, in agreement with previous and related work. The stable intermediate that results is a distorted-square-pyramidal hydride complex. In the following step, the aldehyde approaches this species and coordinates weakly through the oxygen atom. Two alternative pathways can be envisaged: the classical reduction, in which a hydrogen atom migrates to the carbon atom to form an alkoxide, which then proceeds to generate the final silyl ether, or a concerted mechanism involving migration of a hydrogen atom to a carbon atom and of a silyl group to an oxygen atom to generate the silyl ether weakly bound to the molybdenum atom. In this Mo(VI) system, the gas-phase free energies of activation for both approaches are very similar, but if solvent effects are taken into account and HSiMe(3) is used as a source of silicon, the classical mechanism is favored. Several unexpected results led us to search for still another route, namely a radical path. The energy involved in this and the classical pathway are similar, which suggests that hydrosilylation of aldehydes and ketones catalyzed by [MoCl(2)O(2)] in acetonitrile may follow a radical pathway, in agreement with experimental results.     

One-pot synthesis of MWW zeolite nanosheets using a rationally designed organic structure-directing agent

A new material MIT-1 comprised of delaminated MWW zeolite nanosheets is made in a one-pot synthesis using a rationally designed organic structure-directing agent (OSDA). The OSDA consists of a hydrophilic head segment that resembles the OSDA used to synthesize the zeolite precursor MCM-22(P), a hydrophobic tail segment that resembles the swelling agent used to swell MCM-22(P), and a di-quaternary ammonium linker that connects both segments. MIT-1 features high crystallinity and surface areas exceeding 500 m² g^–1, and can be synthesized over a wide synthesis window that includes Si/Al ratios ranging from 13 to 67. Characterization data reveal high mesoporosity and acid strength with no detectable amorphous silica phases. Compared to MCM-22 and MCM-56, MIT-1 shows a three-fold increase in catalytic activity for the Friedel–Crafts alkylation of benzene with benzyl alcohol.     

Surface phase transitions in one-dimensional channels arranged in a triangular cross-sectional structure: theory and Monte Carlo simulations

Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior in a submonolayer lattice-gas of interacting monomers adsorbed on one-dimensional channels arranged in a triangular cross-sectional structure. Two kinds of lateral interaction energies have been considered: (1) w(L), interaction energy between nearest-neighbor particles adsorbed along a single channel and (2) w(T), interaction energy between particles adsorbed across nearest-neighbor channels. We focus on the case of repulsive transverse interactions (w(T)>0), where a rich variety of structural orderings are observed in the adlayer, depending on the value of the parameters k(B)Tw(T) (being k(B) the Boltzmann constant) and w(L)w(T). For w(L)w(T)=0, successive planes are uncorrelated, the system is equivalent to the triangular lattice, and the well-known ([square root] 3 x [square root] 3) [([square root] 3 x ([square root] 3)(*)] ordered phase is found at low temperatures and a coverage, theta, of 13. In the more general case (w(L)/w(T) not equal 0), a competition between interactions along a single channel and a transverse coupling between sites in neighboring channels leads to a three-dimensional adsorbed layer. Consequently, the ([square root] 3 x ([square root] 3) and (([square root] 3 x ([square root] 3)(*) structures "propagate" along the channels and new ordered phases appear in the adlayer. Each ordered phase is separated from the disordered state by a continuous order-disorder phase transition occurring at a critical temperature, T(c), which presents an interesting dependence with w(L)/w(T). The Monte Carlo technique was combined with the recently reported free energy minimization criterion approach (FEMCA) [F. Roma et al., Phys. Rev. B 68, 205407 (2003)] to predict the critical temperatures of the order-disorder transformation. The excellent qualitative agreement between simulated data and FEMCA results allows us to interpret the physical meaning of the mechanisms underlying the observed transitions.