CuII‐Containing 1‐Aminocyclopropane Carboxylic Acid Oxidase Is an Efficient Stereospecific Diels–Alderase

In the context of developing ecofriendly chemistry, artificial enzymes are now considered as promising tools for synthesis. They are prepared in particular with the aim to catalyze reactions that are rarely, if ever, catalyzed by natural enzymes. We discovered that 1‐aminocyclopropane carboxylic acid oxidase reconstituted with Cu^II served as an efficient artificial Diels–Alderase. The kinetic parameters of the catalysis of the cycloaddition of cyclopentadiene and 2‐azachalcone were determined (K_M=230 μm , k_app=3 h^?1), which gave access to reaction conditions that provided quantitative yield and >99 % ee of the (1S,2R,3R,4R) product isomer. This unprecedented performance was rationalized by molecular modeling as only one docking pose of 2‐azachalcone was possible in the active site of the enzyme and this was the one that leads to the (1S,2R,3R,4R) product isomer.     

Styrene—Acrylonitrile Copolymerization: Effect of Remote Units on the Reactivity of the Styrene-Ended Radicals

Application of the gas-liquid chromatographic method to the analysis of the process of styrene-acrylonitrile radical copolymerization, especially with a monomer mixture rich in styrene, provided evidence for penultimate and antepenultimate effects. Methods are given for the determination of the corresponding reactivity ratios:

r _A ≈ 0, r _AS = 0.55, r _ASS = 0.50, r _SSS = 0.25     

Acid-Catalyzed Methanolysis of Vinyl Acetate Polymers and Copolymers. I. Polyvinyl Acetate

Acid (HCL) catalyzed methanolysis of polyvinyl acetate and of model compounds was carried out in solvent mixtures with various amounts of methanol and tetrahydrofuran. The initial rate was first order vs methanol concentration. The acceleration was mainly dependent on the extension of the chain and was enhanced by a tighter coiling of the macromolecule; it is suggested that coiling favors the trapping of the catalyst ions.     

First Evidence for the Existence of Hexafluoroantimonic(V) Acid

By reacting IPr ? InBr₃ with AgSbF₆ in dichloroethane at room temperature, we could obtain single crystals comprising [{(IPr ? InBr₃)(Ag ? (CH₂Cl)₂)}₂][SbF₆]₂ ( 1 ) and two identical HSbF₆ units. It is presumed that the reaction gave rise to [IPr ? InBr_3?x][SbF₆]_x (x=1, 2, or 3) which reacted with adventitious water to give HSbF₆ and [IPr ? InBr_3?x(OH)][SbF₆]_x?1. The experiment was reproduced at 60 °C, eventually leading to the indium hydroxide [{IPr ? In(OH)_0.5(H₂O)_4.5}₂][SbF₆]₅ ( 2 ).     

Surfactants with transfer agent properties (transurfs) in styrene emulsion polymerization

Styrene emulsion polymerization has been carried out at 70°C using 2–2 Azobis (2 methyl, N-(2 hydroxyethyl) propionamide as initiator and thiol-ended surfactants (I) HS-C₁₁ H₂₂- (OCH₂ CH₂) _n OH withn from 17 to 90 units. The kinetics of monomer conversion, the evolution of particle size, particle size distribution, molecular weight, and molecular weight distribution have been studied. After washing the final latex, the incorporation yield of the surfactant moieties in the particles has been measured. Most of the experiments have been carried out in batch; complementary experiments used semi batch or seeded process. In some experiments the two functions of transfer agent and surfactants have been decoupled using either dodecylmercaptan (oil soluble) or thioglycolic acid (water soluble) as transfer agent and the bromine ended precursor of (I) as surfactant. The discussion of the results is chiefly oriented towards both the molecular weight distribution and the incorporation of the surfactant to the latex.     

Quantitative analysis of five tobacco‐specific N‐nitrosamines in urine by liquid chromatography–atmospheric pressure ionization tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC/MS/MS) method was developed and validated for the determination of five total tobacco‐specific N‐nitrosamines (TSNA), including free and conjugated forms in urine. The limits of detection for 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol, N′‐nitrosonornicotine, 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone, N′‐nitrosoanatabine and N′‐nitrosoanabasine were 0.6, 0.6, 10.0, 0.4 and 0.4 pg/mL, respectively, with a linear calibration range of up to 20,000 pg/mL. Intra‐ and inter‐day precision for TSNA measurements ranged from 0.82 to 3.67% and from 2.04 to 7.73% respectively. For total TSNAs, the β‐glucuronidase amount was optimized for hydrolysis time and yield. Different liquid chromatography columns and mobile phases with different pH conditions were evaluated. The validated method was then applied to 50 smoker and 30 nonsmoker urine samples. Our results suggest that this sensitive and relatively simple analytical method is suitable for application to epidemiological investigations of health risks associated with the exposure to tobacco smoke or secondhand smoke in both smokers and nonsmokers. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Tertiary aromatic amide for memory of chirality: access to enantioenriched alpha-substituted valine

A new methodology for the asymmetric synthesis of quaternary alpha-substituted amino acids using memory of chirality has been developed. This strategy employs dynamic axial chirality of tertiary aromatic amides to memorize the initial chirality of an alpha-amino acid during the enolization step. Starting from L-valine, an oxazolidin-5-one containing a tertiary aromatic amide was synthesized in one step and then alkylated with various electrophiles with good yield and enantioselectivity (up to 96%). Quaternary products can be obtained enantiomerically pure by recrystallization. One-step deprotection affords enantioenriched (S)-alpha-methyl valine (ee = 94%) or enantiopure (S)-alpha-isopropyl aspartic acid (ee >99%) in only three steps starting from L-valine.     

Some recent advances in the design and the use of miniaturized droplet-based continuous process: applications in chemistry and high-pressure microflows

This mini-review focuses on two different miniaturizing approaches: the first one describes the generation and use of droplets flowing within a millifluidic tool as individual batch microreactors. The second one reports the use of high pressure microflows in chemistry. Millifluidics is an inexpensive, versatile and easy to use approach which is upscaled from microfluidics. It enables one to produce hierarchically organized multiple emulsions or particles with a good control over sizes and shapes, as well as to provide a convenient data acquisition platform dedicated to slow or rather fast chemical reactions, i.e., from hours to a few minutes. High-pressure resistant devices were recently fabricated and used to generate stable droplets from pressurized fluids such as supercritical fluid-liquid systems. We believe that supercritical microfluidics is a promising tool to develop sustainable processes in chemistry.     

Isospectral sets for akns systems on the unit interval with generalized periodic boundary conditions

We analyze isospectral sets of potentials associated with generalized periodic boundary conditionsB inSL (2, ) for the 2 ×2AKNS systems on the unit interval. WhenB is a rotation we get the usual periodic case. WhenB is not a rotation isospectral sets are cylindrical real analytic submanifolds ofL ² ([0, 1])² ×SL(2, ) and their sections for fixed boundary conditions are real analytic submanifolds ofL ² ([0, 1])².     

Efficiency of mercaptan chain transfer agents in emulsion copolymerizations. I. Influence on kinetics and microstructure. Modeling of radical desorption

The effect of chain transfer agents (CTA) on the emulsion copolymerization of styrene and butyl acrylate was studied in a bench scale 7 L reactor. On-line estimates of conversion were obtained through the joint use of calorimetric measurements and fast gravimetric data. Off-line measurements of partial conversions, molecular weight distribution (MWD), glass transition temperature (T_g), and particle diameter were also performed in order to investigate the effect of two mercaptans (tert-butanethiol and n-dodecanethiol) on both the kinetics of the polymerization process and the microstructure-dependent properties of the copolymer. The obtained experimental results were interpreted in terms of radical desorption and diffusive limitations of the CTA between the oil droplets and the particles. A model has been derived to compute the kinetic constants, the number of radicals per particle, and both the GPC/SEC diagrams and DSC thermograms related to MWD and T_g measurements, respectively. Several batch and semibatch examples are proposed to show that these important variables are satisfactorily fit by the model. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 157–168, 1998