Kinetic Study of the CCl2 Radical Recombination Reaction by Laser‐Induced Fluorescence Technique

An experimental setup that coupled IR multiple‐photon dissociation (IRMPD) and laser‐induced fluorescence (LIF) techniques was implemented to study the kinetics of the recombination reaction of dichlorocarbene radicals, CCl₂, in an Ar bath. The CCl₂ radicals were generated by IRMPD of CDCl₃. The time dependence of the CCl₂ radicals’ concentration in the presence of Ar was determined by LIF. The experimental conditions achieved allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C₂Cl₄. The rate constant for this reaction was determined in both the falloff and the high‐pressure regimes at room temperature. The values obtained were k₀ = (2.23 ± 0.89) × 10^?29 cm⁶ molecules^?2 s^?1 and k_∞ = (6.73 ± 0.23) × 10^?13 cm³ molecules^?1 s^?1, respectively.     

Synthesis and characterization of Pd(II) complexes of 2‐ and 3‐thiophenecarbaldehyde immobilized on silica obtained from sepiolite

Silica obtained by acid treatment of sepiolite was used as a support for catalysts consisting of palladium complexes of 2‐ and 3‐thiophenecarbaldehyde. The support and the catalysts were characterized by X‐ray diffraction, and solid‐state ²⁹Si and ¹³C nuclear magnetic resonance spectroscopies. The supported palladium catalysts were used in the Suzuki reaction of bromobenzene with phenylboronic acid. Copyright © 2013 John Wiley & Sons, Ltd.     

Insight into industrial PLA aging process by complementary use of rheology,HPLC, and MALDI

Nowadays, there is a growing availability of biodegradable industrial materials intended to food contact applications whose service life behavior needs to be further investigated. This article is focused on the degradation of two materials based on polylactic acid. The correlation between the rate of degradation and the amount of trapped degradation products was investigated applying three characterization techniques in parallel, namely rheology, high‐performance liquid chromatography (HPLC), and matrix‐assisted laser desorption/ionization (MALDI). The rate of degradation was studied through the evaluation of their rheological properties and calculation of the number of average molecular weights, and weight‐average molecular weights. Water‐soluble oligomers and lactic acid were quantified by HPLC‐ultraviolet. Changes in cyclic and linear oligomers were monitored by MALDI‐time‐of‐flight mass spectrometry. Specimens of 4‐mm thickness of each biopolymer were subjected to hydrolysis in deionized water up to 6 months at two temperatures, simulating service conditions of food packaging. The diminution in viscosity and consequently in molecular weight distribution (20–60%) showed the degradation of the molecular structure of both polylactic acids. The chain scission was followed through the increasing values of lactic acid and hydrolyzed oligomers (twofold to eightfold), and the predominant signal of the linear oligomers over the cyclic ones with aging. Rheology, HPLC, and MALDI showed to be complementary tools to better understand the changes in the molecular structure. The obtained results showed the necessity of adding suitable stabilizers for each particular food packaging application. Copyright © 2013 John Wiley & Sons, Ltd.     

Assay of Kanamycin A by HPLC with Direct UV Detection

The development of a simple reversed phase ion pair liquid chromatographic method for the assay of kanamycin A has been described. Because of the lack of a UV chromophore in the structure of kanamycin A, borate complexation was used to allow direct UV detection at 205 nm. Three columns were evaluated in this study: Zorbax Extend C18 (4.6 mm × 250 mm; 5 μm), XBridge C18 (4.6 mm × 250 mm; 5 μm) and apHera C18 (4.6 mm × 250 mm; 5 μm). The mobile phase was a mixture of 0.1 M disodium tetraborate (pH 9.0) and water (20:80, v/v) supplemented with 0.5 g L^?1 sodium octanesulphonate. Final chromatographic conditions were achieved on the XBridge column at 50 °C. The method was validated according to ICH guidelines and applied to a commercially available sample. It is much faster and more specific than the current microbiological assay prescribed in the European Pharmacopoeia. No expensive equipment is necessary to perform this assay making it a viable replacement.     

Permutation Cellular Automata

Permutation cellular automata are cellular automata defined by using finite maximal prefix codes. The overall dynamics of onesided and twosided permutation cellular automata is studied. For some classes of permutation cellular automata including the class of those defined by using finite maximal bifix codes, the overall dynamics is completely or partially described in terms of the codes used to define them.     

Disclosing the Structure/Activity Correlation in Trivalent Boron‐Containing Compounds: A Tendency Map

Most trivalent boron reagents are electrophiles owing to the vacancy for two electrons to fill the outer orbital of boron; however, interestingly, trivalent boron compounds can change their electrophilic character to a nucleophilic character by only changing the nature of the substituents on the boron atoms. With the help of computational tools, we have analyzed the structural‐ and electronic properties of boryl fragments that were either bonded to main‐group metals or coordinated to transition‐metals/rare‐earth‐metals and we have designed a map that might help to identify certain trends. This trend map will be useful for selecting an appropriate trivalent boron compound, depending on the sought reactivity.