Affiche presentee dans le cadre du Colloque de l'ARC, «La recherche collegiale et son milieu : enracinement, deploiement et interdependance», dans le cadre du 83e Congres de l'Acfas, Universite du Quebec a Rimouski (UQAR), Rimouski, le 27 mai 2015.

Metal-ions removal from large volumes of waste water from dilute solutions is an important environmental problem. Traditional separation techniques such as membrane filtration and/or liquid-liquid extraction are not efficient enough and evaporation is too expensive. Therefore, an alternative is to use water-soluble polymers that selectively bind, by complexation, with the metal ion in combination with ultrafiltration. The bound metals have such a large molecular weight that they cannot cross the membrane and are concentrated by simple size exclusion. Once performed, the polymer-metal ions must be split apart and the polymer is recycled using simple ultra-filtration. The polymer molecules are retained and the unbound ions are able to flow through the membrane. The concentration and Zinc removal from aqueous solutions with Polyacrylic Acid (PAA) will be used as an example and examined as a function of ultra-filtration parameters such as temperature, pH and the initial concentrations of metallic ions and polymer.

Reactive solvent extraction is commonly used in industries to extract organic and inorganic products. In such a process, the solute present in an aqueous solution is extracted into an immiscible solvent containing a specific extracting agent. These experiments are usually carried out in conventional dispersion-based contacting devices such as colunm or mixer-settlers. Under this configuration, two problems arise: the extracting agent (usually a toxic or environmentally harmful compound) is dispersed into the medium and later in the environment and/or permanent emulsions are formed. To overcome these drawbacks, the introduction of a solid membrane between the two fluid phases using a hollow fibre liquidliquid contactor in order to keep a large surface of contact between the two media represents a good alternative. Two selected examples will be shortly presented in this article to illustrate the interest of this technology that uses the same membrane for the extraction of organic and inorganic compounds from aqueous solutions.

A new strategy is proposed to optimize the design of solvent blends without using complex mathematical models and (or) graphical representations. All calculations are made with standard electronic programs, such as Excel, Lotus, etc. This approach was developed for the cleaning and degreasing industry, which has to find new recipes of solvent blends on a regular basis. The process relies on a visual analysis of the sum of normalized rotating vectors associated with the chemical composition and the physical properties of the individual components. This approach allows for representation of all parameters on a two-dimensional plot, including information about chemical composition, as well as the physical properties to be optimized. The research of a new mixture of halogenated solvents will be used as an example to illustrate the various steps of this technique. This method is not limited to solvent applications; it also applies to all problems that involve comparisons of physical and chemical properties of blends.Key words: solvents, mixtures, components, optimization, cleaning.

Far cross-linked amylose (CLA) tablets prepared by direct compression, a Linear increase in cross-linking degree (cld) defined as percentage of epichlorohydrin cross-linker/polymer, generates non-monotonous variation of drug release time. Controlled release (up to 20-24 h) properties were obtained only for tablets from CLA (Contramid(TM)) with relatively low cld (CLA-2 up to CLA-6). Moderate increase in cld (CLA-15) generates a sharp decrease in the release time (2-6 h). This is a particular characteristic of the CLA matrix. The controlled release properties were related to the X-ray pattern of the dry CLA network. The increase in dd induces a transition from B-type (double helix) to a predominat V-type (single helix) and to more amorphous conformation of CLA powders. Furthermore, FT-IR data indicated low free water content at low cld. For low cross-linked CLA, chains are closely located and stabilized by HO groups involved in hydrogen bonding and thus more resistant to hydration and more appropriate for the control of drug release. (C) 1998 Elsevier Science Ltd. AU rights reserved.

Countercurrent chromatography (CCC) is a separation technique in which the stationary phase is a liquid. Diethylhexyl phosphoric acid (DEHPA) forms reverse micelles in heptane. Metallic ions, located in an aqueous phase, can be extracted into the aqueous core of the reverse micelles in the heptane phase. A CCC apparatus can be considered as a powerful mixing and extracting machine with efficiency above several hundreds of theoretical plates. La3+, Ce3+, Pr3+, and Nd3+ lanthanide cations were separated using CCC with a DEHPA-containing heptane stationary phase. Studying the retention variations with aqueous mobile phase pH, it was possible to determine the lanthanide extraction constants and separation coefficients. Overloading conditions are described. Frontal chromatography was performed using a Co2+ and Ni2+ solution. The Co2+ ions were concentrated in the heptane + DEHPA stationary phase, a part of the solution was deionized, and another part was enriched in only Ni2+ ions. This method also produced the extraction constants and separation coefficients. The use of CCC with a complexing stationary phase can be applied to any cation for ion filtering and concentration, or for deionization of aqueous phases. Key words: countercurrent chromatography, CCC; ion extraction, ion filtering, deionization, lanthanides, transition metals.

The binding of the methylmercury cation CH 3 Hg + by poly( L -glutamic acid) (PGA) and by poly( L -lysine) (PLL) has been investigated by Raman spectroscopy. Coordination on the side-chain COO − and NH groups of these polypeptides gave characteristic ligand–Hg stretching modes at ca. 505 and 450 cm −1 , respectively. Precipitation generally occurred upon formation of the complexes and changes of conformation were common. The solid complex obtained from PGA at pH 4.6 was found to have a mostly disordered conformation, which differed from the respective α-helical and β-sheet structures of the dissolved and precipitated uncomplexed polypeptide in the same conditions. An α-helical structure was generally adopted by the complex formed with PLL, even in pH and temperature conditions where the free polypeptide normally exists in another conformation. The addition of a stronger complexing agent, glutathione, to the PLL/CH 3 Hg + complex caused a migration of the bound cations and a restoration of the polypeptide to its original state.

A systematic Raman spectroscopic investigation of the complexation of CH3Hg+ by the standard amino acids is reported. It is shown that the vibrational bands due to the ligand—Hg and Hg—CH3 stretching modes and to the symmetric —CH3 bending mode of the —HgCH3 unit are well suited to characterize the extent of complexation and the sites of attachment of the cation. Coordination, which occurs mostly on sulfur and nitrogen atoms by substitution of a proton on the thiol group of cysteine or on amino groups in general, is best identified by the frequency of the ligand—Hg stretching vibration in the 250–550 cm−1 region of the spectrum.

Two different crystalline complexes have been obtained from aqueous mixtures of glycylglycine (GlyGly) and methylmercury(II), and they were studied by vibrational spectroscopy and X-ray diffraction. In the first compound, a hydrogen atom of the protonated amino group of GlyGly is substituted by the CH3Hg+ cation, giving (CH3Hg)GlyGly: orthorhombic, Pna21, a = 7.920(6) Å, b = 13.473(5) Å, c = 8.059(3) Å, and Z = 4. Further complexation on the carboxylate group yielded the complex [(CH3Hg)2GlyGly]ClO4: monoclinic, P21/c, a = 6.407(4) Å, b = 24.439(6) Å, c = 8.461(2) Å, β = 93.82(4)°, and Z = 4. The sites of complexation and the conformations of these solid complexes are well reflected in their vibrational spectra. Raman spectra indicate that complexation in aqueous solutions is limited to substitution on the —NH3+ group of GlyGly.

A new type of sample holder suitable for Raman difference spectroscopy is described. It can accommodate up to six different samples (∼10 μL) contained in capillary cells such as those commonly used in conventional Raman spectroscopy. This system can be readily incorporated in an instrument equipped with a conventional computerized control system and it provides a differential frequency accuracy (±0.03 cm−1) which is comparable to that of other existing devices.

The complexes (CH3Hg)Gly, (CH3Hg)(L-Ala), and (CH3Hg)(DL-Ala) were prepared by reacting CH3HgOH with glycine (HGly) and alanine (HAla). Crystals of (CH3Hg)(DL-Ala) are monoclinic, space group P21/c, a = 9.460(2), b = 8.794(2), c = 8.723(2) Å, β = 97.49(2)°, Z = 4. The structure was refined on 935 MoKα reflections to R = 0.042. The complex results from displacement of an alanine NH3+ proton by the CH3Hg+ ion, which is linearly bonded to the —NH2 group. An intramolecular Hg … O contact of 2.63 Å is also formed with a carboxylate oxygen. The Raman and infrared spectra of solid (CH3Hg)Gly and (CH3Hg)(L-Ala) are compared with those of the ligands. Raman spectra of aqueous solutions at different pH indicate that the NH2-bonded structure is retained in solution, although no complexation via the carboxylate occurs.