Recovery and purification of lactic acid from fermentation broth by adsorption

Applied Biochemistry and Biotechnology - Riedel-de-Haen VI-15, Dowex MWA-1 and Amberlite IRA-35 were employed for lactic acid recovery using model fermentation broth. The broth was first acidified...     

Kinetics of metal ion complex formation in micellar media. A comparison between normal and polymerized micelles

Micellar media can be used to investigate the rate of complex formation between hydrophobic extractants and metal ions. Acceleration or retardation effects may be obtained, depending on factors such as the nature of the surfactant, the hydrophilic/lipophilic character and ionization state of the extractant, etc. The present work was aimed at studying the influence of some specific parameters in producing retardation effects, which have potential application for performing separation of metal ions on a kinetic basis. The stopped-flow technique was used to measure the rate of complex formation between Cu²⁺ and complexing agents with varying alkyl chain length. Micelles made of the nonionic surfactants C₁₂EO₆, Triton X-100 and Brij 35 were first considered, which did not show any direct correlation between the rate of complex formation and the thickness of the hydrophilic layer constituted by the polar heads of the surfactant molecules.In a second approach, we have used polymerized micelles obtained from undec-10-enyltrimethyl ammonium bromide, which we assumed to be more rigid than normal micelles. Although the absence of CMC was confirmed, the rates measured in these polymerized micelles were larger than those obtained in micellar solutions of CTAB and DTAB. The results are discussed in relation with the nature of the hydrophobic domains in the different situations.Institut Nancéien de Chimie Moléculaire (I.N.C.M.), FU CNRS n=8     

Colloidal Interaction at the Air-Liquid Interface

In this paper, we propose a model to analyze the stability of colloidal particles at the air-liquid interface. The proposed model for the colloidal particle interaction considers DLVO interactions and capillary, hydrophobic, and dipolar interactions between the particles. Typical values from the literature were assigned to most parameters included in the model. Numerical computation revealed the most important parameter in determining the total interaction is the density of dipoles at the external surface of the particles. We have found significant differences for the pair potential between hydrophobic and hydrophilic particles. Hydrophobic particles must aggregate in a principal minimum of the interaction potential curve while hydrophilic particles aggregate in a secondary minimum. Copyright 2000 Academic Press.     

Charge reversal in real colloids: Experiments, theory and simulations

In the last years, the inclusion of ionic short-range correlations in the study of colloidal stability has led to significant disagreements with the predictions obtained from classical treatments. An example of these discrepancies is the occurrence of charge reversal of charged particles. In order to shed light on this issue, the charge reversal of latex particles in the presence of asymmetric electrolytes has been investigated through Monte Carlo (MC) simulations. In particular, experimental results concerning electrophoretic mobility reversals and the Hyper-Netted-Chain/Mean-Spherical-Approximation (HNC/MSA) predictions have been compared with simulations in which two alternative methods for evaluating energies have been applied. A realistic hydrated ion size is used in the HNC/MSA calculations and simulations. In this way, the existence of a reversal in the electrophoretic mobility due to ion size correlations and without requiring specific counterion adsorption is probed. Moreover, the simulations appears as a useful tool for explaining those results in which the HNC/MSA does not reproduce the experimental trends.     

Chiral N,N Ligands Enabling Palladium‐Catalyzed Enantioselective Intramolecular Heck–Matsuda Carbonylation Reactions by Sequential Migratory and CO Insertions

Unprecedented enantioselective intramolecular Heck carbonylation reactions of arenediazonium salts were enabled by a chiral N,N ligand. This reaction constitutes the first enantioselective Heck carbonylation that proceeds through migratory insertion followed by CO insertion. The enantioenriched functionalized dihydrobenzofurans were obtained in good to high yields and enantiomeric ratios of up to 98:2 under mild and operationally simple reaction conditions.     

A reliable analytical approach based on gas chromatography coupled to triple quadrupole and time‐of‐flight mass analyzers for the determination and confirmation of polycyclic aromatic hydrocarbons in complex matrices from aquaculture activities

The potential of gas chromatography coupled to tandem mass spectrometry (GC/MS/MS) with a triple quadrupole analyzer (QqQ) has been investigated for the quantification and reliable identification of sixteen polycyclic aromatic hydrocarbons (PAHs) from the EPA priority list in animal and vegetable samples from aquaculture activities, whose fat content ranged from 5 to 100%. Matrices analyzed included fish fillet, fish feed, fish oil and linseed oil. Combining optimized saponification and solid‐phase extraction led to high efficiency in the elimination of interfering compounds, mainly fat, from the extracts. The developed procedure minimized the presence of these interfering compounds in the extracts and provided satisfactory recoveries of PAHs. The excellent sensitivity and selectivity of GC/(QqQ)MS/MS in selected reaction monitoring (SRM) allowed to reach limits of detection at pg/g levels. Two SRM transitions were acquired for each analyte to ensure reliable identification of compounds detected in samples. Confirmation of positive findings was performed by GC coupled to high‐resolution time‐of‐flight mass spectrometry (GC/TOFMS). The accurate mass information provided by GC/TOFMS in full acquisition mode together with its high mass resolution makes it a powerful analytical tool for the unequivocal confirmation of PAHs in the matrices tested. The method developed was applied to the analysis of real‐world samples of each matrix studied with the result of detecting and confirming the majority of analytes at the µg/kg level by both QqQ and TOF mass spectrometers. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of alexine-like compounds from chiral five-membered endocyclic enecarbamates

Stereoselective syntheses of enantiomerically enriched trihydroxy pyrrolizidine and indolizidines were accomplished from a common chiral endocyclic enecarbamate. The synthetic strategy features an efficient [2+2] cycloaddition of ketenes to the endocyclic enecarbamate and a highly regioselective Baeyer-Villiger oxidation of the intermediate azabicyclic-cyclobutanones. These new heterocycles are compounds structurally related to the alexines.     

Polyol Additives Modulate the In Vitro Stability and Activity of Recombinant Human Phenylalanine Hydroxylase

Phenylketonuria (PKU; OMIM 261600), the most common disorder of amino acid metabolism, is caused by a deficient activity of human phenylalanine hydroxylase (hPAH). Although the dietetic treatment has proven to be effective in preventing the psycho-motor impairment, much effort has been made to develop new therapeutic approaches. Enzyme replacement therapy with hPAH could be regarded as a potential form of PKU treatment if the reported in vitro hPAH instability could be overcome. In this study, we investigated the effect of different polyol compounds, e.g. glycerol, mannitol and PEG-6000 on the in vitro stability of purified hPAH produced in a heterologous prokaryotic expression system. The recombinant human enzyme was stored in the presence of the studied stabilizing agents at different temperatures (4 and −20 °C) during a 1-month period. Protein content, degradation products, specific activity, oligomeric profile and conformational characteristics were assessed during storage. The obtained results showed that the use of 50% glycerol or 10% mannitol, at −20 °C, protected the enzyme from loss of its enzymatic activity. The determined ΔG ⁰ and quenching parameters indicate the occurrence of conformational changes, which may be responsible for the observed increase in catalytic efficiency.     

Colloidal stability of IgG- and IgY-coated latex microspheres

The stabilization of antibody-latex complexes at high salt concentration is an event that cannot be explained by the widespread DLVO theory. Adsorption of antibodies on polystyrene latex usually leads to a loss in colloidal stability. However, after the expected particle aggregation induced by an increase in ionic strength, an 'anomalous' restabilization occurs when the electrolyte concentration increases even more. This non-DLVO behaviour can be explained taking into account the hydration forces, which become significant in hydrophilic surfaces. This restabilization has already been observed in different protein latex complexes. In the present work, a study on the stability patterns of polystyrene particles covered independently by mammalian and chicken antibodies has been performed. This study reveals that avian antibodies present a more hydrophobic surface than that of mammalian antibodies. In addition, it has been possible to obtain some information about the molecular orientation of the adsorbed antibodies from the stability experiments. This information has been corroborated by an immunoreactivity study.