Chemometrics study of the kinetics of the Griess reaction

The kinetics of the Griess reaction in which 3‐nitroaniline acts as a nitrosation agent and 1‐naphtylamine as a coupling reagent was studied by chemometrics methods. The kinetic reaction was investigated under pH 1.0 and 25°C by UV‐vis spectrophotometry. The concentrations of nitrite, 3‐nitroaniline and 1‐naphtylamine were such that a second‐order kinetic reaction took place. Data explorations based on principal component analysis and multivariate curve resolution–alternating least squares were performed to obtain information about the reaction. Calculation of band boundaries of the multivariate curve resolution–alternating least squares solutions showed that the rotational ambiguities associated with the calculation of spectra and concentration profiles have been completely removed. The decrease in the ambiguity of the recovered solutions was closely related to the application of the equality constraint. The results of the exploratory data analysis showed that the kinetic reaction proceeds through a two‐step mechanism. Moreover, the two‐steps are second order. Data analysis approaches based on hard modeling and global hard modeling were used to resolve profiles of the reactants, intermediates and products and to evaluate the rate constants. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of laser pulse wavelength and laser fluence on the characteristics of silver nanoparticle generated by laser ablation

Electrically pumped ultraviolet random lasing was achieved in metal-insulator-semiconductor (MIS) diodes based on ZnO films at room temperature. The ZnO films were grown by plasma assisted molecular beam epitaxy. Two different kinds of insulator layers, SiO _x (0<x≤2) and AlO _x (0<x≤1.5) were deposited by electron beam evaporation. X-ray diffraction experiments found these oxide layers were amorphous (or microcrystals), and X-ray photoelectron spectroscopy confirmed the Si and Al were fully oxidized. Compared with devices using SiO _x as the insulator layer, diodes with evaporated AlO _x layers showed a lower working threshold forward current (～20 mA to ～26 mA) and higher emission intensity. Periodic features indicating formation of closed-loop paths were deduced by the power Fourier transform of electroluminescence spectra. The cavity length of both devices increased as forward currents increased, while a larger cavity length was always obtained in the AlO _x -involved device under the same working current. The improved performance was attributed to larger hole amount in AlO _x layers. These results revealed that evaporated AlO _x can serve as good electron blocking and hole supplying layers for hetero-structures.     

The fractional q-differential transformation and its application

In this paper, the definitions and operations of the one-dimensional and two-dimensional fractional q-differential transform is proposed. A distinctive feature of the fractional q-differential transform is its ability to solve linear and nonlinear ordinary/partial fractional q-differential equations.     

Me3SiCl and Et3SiI‐promoted one‐pot synthesis of 1,4‐dihydropyridine derivatives

An efficient synthesis of 1,4‐dihydropyridine derivatives has been achieved by the one‐pot cyclocondensation reaction of methyl 3‐aminocrotonate and a range of aldehydes in the presence of chlorotrimethylsilane as a promoter under solvent‐free conditions. The cyclocondenstion reaction requires a very short time and takes place in good to excellent yields. Furthermore iodotriethylsilane, generated in situ by the reaction of triethylsilane and methyl iodide in the presence of palladium chloride, has been investigated for the synthesis of 1,4‐dihydropyridine derivatives. This facile and efficient method affords high yields for the preparation of 1,4‐dihydropyridines at room temperature and short reaction times. Copyright © 2009 John Wiley & Sons, Ltd.     

RuIII(OTf)SalophenCH2–NHSiO2–Fe: an efficient and magnetically recoverable catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane

Efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by ruthenium(III) complex of chloromethylated Salophen supported on nanomagnetic materials is reported. First, the iron nanomagnets were silica coated, functionalized with amine and then ruthenium CM‐Salophen was successfully bonded to their surface. The catalyst, Ru^III(OTf)SalophenCH₂–NHSiO₂–Fe, was characterized by elemental analysis, FT‐IR and UV–visible spectroscopic techniques, transmission electron microscopy and inductively coupled plasma (ICP). The Ru^III(OTf)SalophenCH₂–NHSiO₂–Fe catalyzed trimethylsilylation of primary and secondary alcohols as well as phenols, and the corresponding TMS ethers were obtained in high yields and short reaction times at room temperature. This new heterogenized trimethylsilylation catalyst is easily recovered with a magnet and showed no appreciable loss of activity even after five consecutive runs. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetics and mechanism of the dehydration reaction of sarcosine to a bislactame through diacyclperoxide intermediate in strong acidic medium

The influence of substitution on the amine functional group of glycine in the permanganic oxidation of such an α‐amino acid in moderately concentrated sulfuric acid medium has been investigated. Reaction products analysis has revealed that contrary to the usual α‐amino acid oxidation product, which is an aldehyde species, a valuable compound, namely 1,4‐dimethylpiperazine‐2,5‐dione, has been obtained as the main product via a cheap, simple, efficient, and novel method. Sarcosine has been chosen as a substituted derivative of glycine, and the kinetics and mechanism of its permanganic oxidation have been investigated using a spectrophotometric technique. Conclusive evidence has proven delayed autocatalytic activity for Mn(II) in this reaction, analogous to some α‐amino acids. It has been revealed that such activity can show up when a certain concentration ratio of Mn(II) to sarcosine is built up in the medium, which we call the “critical ratio.” The magnitude of the latter ratio depends on the sulfuric acid concentration. Considering the “delayed autocatalytic behavior” of Mn(II) ions, rate equations satisfying observations for both catalytic and noncatalytic routes have been presented. The reaction shows first‐order dependence on permanganate ions and sarcosine concentrations in both catalytic and noncatalytic pathways, and apparent first‐order dependence on Mn²⁺ ions in catalytic pathways. The correspondence of pseudo‐order rate constants of the catalytic and noncatalytic pathways to Arrhenius and Eyring laws has verified “critical ratio” as well as “delayed autocatalytic behavior” concepts. The activation parameters associated with both pathways have been computed and discussed. Mechanisms for both catalytic and noncatalytic routes involving radical intermediates as well as a product having a diketopiperazine skeleton have been reported for the first time. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 689–703, 2009     

Potentiometric determination of silver(I) by selective membrane electrode based on derivative of porphyrin.

The performance of silver metal complexes with meso-tetraphenylporphyrin ([H2T(4-CH3)]PP) as ionophores for ion-selective electrodes was studied. The electrode exhibited linear response with Nernstian slope of 59.2 +/- 1.0 mV per decade within the concentration range of 1.0 x 10(-7)-1.0 x 10(-1) M silver ions. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot, was 1.0 x 10(-7) M. The response time of the electrode was < 10 s over the entire concentration range. The silver-selective electrode exhibited good selectivity for Ag(I) with respect to alkali, alkaline earth and heavy metal ions. The electrodes could be used at least three months without a considerable divergence in their potential. The electrodes are suitable for use in aqueous solutions in a wide pH range of 3.0-9.0. They were used as indicator electrodes in titration of Ag(I) with sodium iodide solution and were successfully applied to direct determination of silver in real samples.     

Application of chemometrics methods with kinetic constraints for estimation of rate constants of second order consecutive reactions.

To determine the rate constants for the second order consecutive reactions of the form U + V -(k1)--> W -(k2)--> P, a number of chemometrics and hard modeling-based methods are described. The absorption spectroscopic data from the reaction were utilized for performing the analysis. Concentrations and extinctions of components were comparable, and all of them were absorbing species. The number of steps in the reaction was less than the number of absorbing species, which resulted in a rank-deficient response matrix. This can cause difficulties for some of the methods described in the literature. The standard MATLAB functions were used for determining the solutions of the differential equations as well as for finding the optimal rate constants to describe the kinetic profiles. The available knowledge about the system determines the approaches described in this paper. The knowledge includes the spectra of reactants and products, the initial concentrations, and the exact kinetics. Some of this information is sometimes not available or is hard to estimate. Multiple linear regression for fitting the kinetic parameters to the obtained concentration profiles, rank augmentation using multiple batch runs, a mixed spectral approach which treats the reaction using a pseudo species concept, and principal components regression are the four groups of methods discussed in this study. In one of the simulated datasets the spectra are quite different, and in the other one the spectra of one reactant and of the product share a high degree of overlap. Instrumental noise, sampling error are the sources of error considered. Our aim was the investigation of the relative merits of each method.     

Portfolio optimization with linear and fixed transaction costs

We consider the problem of portfolio selection, with transaction costs and constraints on exposure to risk. Linear transaction costs, bounds on the variance of the return, and bounds on different shortfall probabilities are efficiently handled by convex optimization methods. For such problems, the globally optimal portfolio can be computed very rapidly. Portfolio optimization problems with transaction costs that include a fixed fee, or discount breakpoints, cannot be directly solved by convex optimization. We describe a relaxation method which yields an easily computable upper bound via convex optimization. We also describe a heuristic method for finding a suboptimal portfolio, which is based on solving a small number of convex optimization problems (and hence can be done efficiently). Thus, we produce a suboptimal solution, and also an upper bound on the optimal solution. Numerical experiments suggest that for practical problems the gap between the two is small, even for large problems involving hundreds of assets. The same approach can be used for related problems, such as that of tracking an index with a portfolio consisting of a small number of assets.