Development of a carbohydrate silylation method in ionic liquids for their gas chromatographic analysis

This paper reports on the feasibility of silylation of low molecular weight carbohydrates dissolved in different ionic liquids (ILs) for their further analysis by gas chromatography (GC). Derivatization reagents (nature and amounts), temperature and time of reaction and stirring conditions were evaluated for different carbohydrates (i.e., glucose, mannose, fructose and lactose) dissolved in 1-ethyl-3-methylimidazolium dicyanamide [EMIM][DCA]. Evaluation of conformational isomerism of glucose dissolved in [EMIM][DCA] revealed the effect of the time of dissolution in the equilibration of α- and β-furanoses (up to 3% and 6%, respectively, after 70 h of incubation) and that 21 h sufficed to obtain results similar to those provided by the reference method involving pyridine. Once optimized, the proposed derivatization procedure provided satisfactory yields (i.e., close to 100%) using 100 μL of trimethylsilylimidazole (TMSI) at mild conditions (25 °C) for a relatively short time (1 h) for most of the investigated carbohydrates. Under these experimental conditions, linear responses (i.e., R² better than 0.974) were obtained in the tested range of 0.25–1 mg of the derivatized target compounds. Other reagents, such as N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) + 1% trimethylchlorosilane (TMCS), were successfully used under ultrasonic conditions for aldose monosaccharides and disaccharides derivatization, while BSTFA was useful for ketose monosaccharides. The possibility of using the proposed method for the derivatization of selected carbohydrates dissolved in different ILs and the efficiency of the method applied to the analysis of carbohydrates present in real samples (fruit juices) have also been investigated.     

Synthesis and dynamic study of new ortho-(alkylchalcogen)acetanilide atropisomers. A second look at the hydrolysis of quaternary 2-methylbenzazol-3-ium salts

The base-catalysed hydrolysis of N-ethyl-2-methylbenzazol-3-ium iodides was re-examined performing the reaction in boiling 96% ethanol, in the presence of triethylamine. The resulting unstable intermediates were isolated as the corresponding ether, thioether or selenoether derivatives, depending on the starting benzazole salt, by trapping via alkylation with ethyl and hexyl iodides, in moderate to good yields. Reduction of the o-(alkylchalcogen)acetanilides so obtained afforded the corresponding o-(alkylchalcogen)anilines. This methodology provides potential access to o-(alkylchalcogen)anilines bearing up to three different N-alkyl groups introduced in an unambiguous and regioselective way.     

Self-assembled liquid crystals by hydrogen bonding between bipyridyl and alkylbenzoic acids: solvent-free synthesis by mechanochemistry

A series of thermotropic hydrogen-bonded liquid crystalline structures based on 4,4′-bipyridyl and aliphatic carboxylic acids was prepared by a mechanosynthesis technique. This series was characterised by polarising optical microscope, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray powder diffraction and ¹H NMR relaxometry experimental techniques. In these complexes, the bipyridyl component, a non-mesogenic substance by itself, acts as a double H-bond acceptor, whereas the alkylbenzoic acid acts as a H-bond donor, in a 1:2 proportion. The so-formed complexes exhibit mesophases that are not observed by the single components. A characteristic phase (smectic A) is identified and shown to be affected by the alkyl chain length. The isotropisation temperature is increased by the supramolecular aggregation through the H-bonds.     

Intermolecular interactions on amine‐cured epoxy matrices with different crosslink densities. Influence on the hole and specific volumes and the mechanical behavior

The architecture of an epoxy matrix was modified by curing the resin with mono‐/diamine mixtures having identical chemical structures. Both hole volume and specific volume variations were studied by positron annihilation lifetime spectroscopy and pressure‐volume‐temperature/density measurements, respectively. The average hole volume of the networks at room temperature slightly increased when the monoaminic chain extender content increased. The increment in the intermolecular interactions between functional groups of the networks chains, due to the less hindered nitrogen introduced by the monoamine, appears to be the responsible for the observed behavior. Besides, only small variations on the specific volume were observed on increasing the monoamine content, which points out that for a cured epoxy system, the chemical structure of the curing agent is mainly responsible for chain packing in the networks. On the other hand, intermolecular interactions between chains were considered as the key factor for fixing stiffness and strength. Thus, it was observed that the increase of the intermolecular interactions with the monoamine content produced a decrease in the sub‐T_g small‐range cooperative motions, which increased the low‐deformation mechanical properties at temperatures between β and α relaxations. This conclusion could be applied to previous investigations with epoxy matrices not fully crosslinked (nonstoichiometric or noncompletely cured formulations). Finally, it was found that fracture properties do not significantly depend either on the hole volume or on the intermolecular interactions. Fracture properties are more dependent on the crosslink density and the glass transition temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1240–1252, 2009     

Cu, Zn Superoxide dismutase: distorted active site binds substrate without significant energetic cost

Copper, Zinc superoxide dismutase (CuZnSOD) catalyzes the dismutation of the toxic superoxide radical into molecular oxygen and hydrogen peroxide. Dismutation is achieved by reduction and re-oxidation of the active site copper ion, where the superoxide substrate binds. This enzyme is considered to be a perfect enzyme, as the catalytic rate is very high and diffusion controlled. The redox active copper ion is coordinated by four histidine residues in a distorted square planar geometry. Much has been written about the biological significance of the geometry distortion. It is sometimes considered that it should help to tune the redox potential of the copper ion in order to efficiently reduce the first superoxide molecule and oxidize the second one. In this work we present a series of high level theoretical calculations using realistic models, which demonstrate that the distorted geometry is fundamental for the catalytic efficiency of the enzyme by allowing substrate binding without extensive geometric reorganization of the copper complex, upon changing from four to five ligands. A lower limit for the reorganization energy is calculated here in 22 kcal/mol, which would slow down the reaction kinetics by more than 13 orders of magnitude, transforming a perfect enzyme into an inefficient one.     

On the microbial reduction of ethyl α-methylacetoacetate

In the present work several microorganisms were screened in the reduction of methyl and ethyl acetoacetates. Good to excellent ees were obtained with up to quantitative substrate conversions. These microorganisms were also tested in the reduction of ethyl α-methylacetoacetate with good des and excellent ees. It was noticed that Kluyveromyces marxianus and Trichoderma harzianum were found to lead to products of opposite configuration with the use of methyl or ethyl acetoacetates, which is a very unusual finding.     

Determination of Caffeic Acid in Red Wine by Voltammetric Method

The electrochemical oxidation of 3,4‐dihydroxycinnamic acid, caffeic acid, leads to a stable electroactive poly(caffeic acid) thin film containing quinone moiety on a preactivated glassy polymeric carbon electrode. The properties of the deposited films as well as the stability study under different experimental conditions were investigated. Taking advantage of the electrochemical behavior, an analytical method based on differential pulse voltammetry for determination of caffeic acid in red wine was proposed.     

Optimization strategies in credit portfolio management

This paper focuses on the application of an original global optimization algorithm, based on the hybridization between a genetic algorithm and a semi-deterministic algorithm, for the resolution of various constrained optimization problems for realistic credit portfolios. Results are analyzed from a financial point of view in order to confirm their relevance.