Capillary electrophoretic analysis of sulfur and cyanicides speciation during cyanidation of gold complex sulfidic ores

A capillary electrophoretic protocol for the separation and quantification of the most important species potentially liberated during the cyanidation of gold sulfide‐rich ores was accomplished in this study. The separation of 11 ions: S₂O₃^2–, Cu(CN)₃^2–, Fe(CN)₆^4–, Fe(CN)₆^3–, SCN^–, Au(CN)₂^–, Ag(CN)₂^–, SO₄^2–, OCN^–, SO₃^2–, and HS^– was achieved using an indirect UV detection method. The robustness of the analytical protocol was tested by analyzing ions speciation during the cyanidation of two gold sulfide‐rich ores. The 1‐h cyanidation of the two ores released up to six complexes into solution: S₂O₃^2–, Cu(CN)₃^2–, SCN^–, Fe(CN)₆^4–, OCN^–, and SO₄^2–. The mineralogy of the ore was found to influence directly the nature and the amount of the dissolved species. Conserving the cyanidation solution for 72 h after sampling resulted in 96% total sulfur recovery. These results allow us to conclude that the analytical protocol developed in this study can become very useful for the optimization of precious‐metals cyanidation plants.     

Electrical conductivity and complex impedance analysis of 20% Ti-doped La0.7Sr0.3MnO3 perovskite

The electrical conductance of 20% Ti-doped La_0.7Sr_0.3MnO₃ (LSMO) was measured using admittance spectroscopy over a wide temperature and frequency ranges. The impedance plane plot shows semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. Activation energy inferred from conductance spectrum matches very well with the value estimated from relaxation time indicating that relaxation process and conductivity have the same origin. The electrical conductance of La_0.7Sr_0.3Mn_0.8Ti_0.2O₃ is found to be dependent on temperature and frequency. Also, the electronic conduction appears to be dominated by thermally activated hopping of small polaron (SPH) at high temperatures and by variable range hopping (VRH) at low temperatures.     

Regioselective bond cleavage in the dissociative electron transfer to benzyl thiocyanates

The electrochemical reduction of benzyl thiocyanate and p-nitrobenzyl thiocyanate was investigated in acetonitrile at an inert electrode. These two compounds reveal a change in the reductive cleavage mechanism, and more interestingly, they show a clear-cut example of a regioselective bond dissociation. Both phenomena may be understood on the basis of the dissociative ET theory and its extension to the formation/dissociation reactions of radical ions. While the effect of the standard oxidation potential of the leaving group seems to be predominant in understanding the change in the ET mechanism by changing the driving force, the regioselective cleavage is dictated by changes in the intrinsic barrier related to the nature of the substituent on the aryl moiety.     

Torquoselectivity induced by lone-pair conjugation in the electrocyclic reactions of 1-azapolyenes

Torquoselectivity in the electrocyclic interconversions of 1-azapolyenes and their heterocyclic isomers was investigated theoretically. The ring openings of 1,2-dihydroazete, 1,2-dihydropyridine, and 1,2-dihydroazocine were examined using HF, MP2, and B3LYP calculations. A large preference for inward rotation of the nitrogen lone pair and outward rotation of the N-H group was found for the four- and six-electron systems. No strong preference was observed for the eight-electron system.     

Multi-shock structure of roll wavesStructure multi-chocs d'ondes à rouleaux

The special class of periodic travelling waves which is known as roll waves is investigated for nonhomogeneous hyperbolic equations of gas dynamics type. In this Note these equations are applied to shallow water flows in inclined open channels, but the results obtained are more general and far-reaching. The necessary conditions for the existence of a roll wave are derived. It is shown that for a nonconvex pressure term, multi-shock configurations of roll waves of finite amplitude exist. A new type of periodic travelling wave, which corresponds to the slug flow regime in two-layer flows, is found. To cite this article: A. Boudlal, V.Yu. Liapidevskii, C. R. Mecanique 332 (2004).     

Development of an In Situ Detachment Protocol of Vero Cells Grown on Cytodex1 Microcarriers Under Animal Component-Free Conditions in Stirred Bioreactor

Subcultivation of Vero cells grown in a proprietary animal component-free medium named IPT-AFM, on microcarriers, was studied. TrypLE Select, a non-animal-derived protease, was used as an alternative to trypsin for cell passaging. We first studied the effect of increasing concentrations of TrypLE Select toward cell growth and then studied the inactivation of the protease using either soybean trypsin inhibitor (STI) or the soy hydrolysate Hypep 1510, in six-well plates. Data showed that cell growth was impaired by residual level of TrypLE Select; STI was identified as an efficient agent to neutralize this effect. To restore cell growth and inactivate TrypLE Select, STI should be added to the medium at least at 0.2 g L^?1. Cells were also grown in spinner flask on 2 g L^?1 Cytodex1 in IPT-AFM. In these conditions, the cell detachment yield was equal to 78?±?8 %. Furthermore, cells exhibited a typical growth profile when using the dislodged cells to seed a new culture. A cell detachment yield of 70?±?19 % was also achieved when the cells were grown in a 2-L stirred bioreactor in IPT-AFM, on 3 g L^?1 Cytodex1. This protocol can be of great interest to scale-up the process of Vero cells cultivation in IPT-AFM on Cytodex1 from one stirred bioreactor culture to another.     

Thermodynamics and molecular bases of the interaction of ampicillin and streptomycin at their binding sites of bovine serum albumin

Among the biological parameters of chemotherapeutics, serum albumin binding is a critical factor in determining drug distribution and bioavailability. In this study, the binding properties as well as the interaction of ampicillin and streptomycin at their binding sites of bovine serum albumin (BSA) were investigated. The binding constant varied from 3.2 × 10³ M^?1 at 298 K to 37.5 × 10³ M^?1 at 313 K for ampicillin, and from 10.7 × 10³ M^?1 at 298 K to 3.5 × 10³ M^?1 at 313 K for streptomycin. By increasing the temperature, from 298 to 313 K, the binding affinity decreased by about 11-fold for ampicillin. Conversely, streptomycin showed stronger binding at higher temperature, which is decreased by threefold at 298 K. Interestingly, the affinity of ampicillin with the free BSA was ~4-fold higher than the binding with BSA/streptomycin complex. In contrast, the affinity of streptomycin with the free BSA was ~6-fold lower than the binding with BSA/ampicillin complex. Mutual binding experiments indicate that ampicillin and streptomycin are sharing both of common and different binding sites on BSA. Dissection of the forces of interactions indicated that rigid-body binding was the mode of binding of ampicillin and streptomycin with BSA with minor degree of conformational changes. Both of ampicillin and streptomycin can bind with free BSA. Furthermore, the binding of ampicillin with BSA improves the binding of streptomycin, while the binding of streptomycin with BSA adversely affect the binding of ampicillin.     

Vibrational Study of Dipotassium Zinc Bis(Dihydrogendiphosphate) Dihydrate,K2ZN(H2P2O7)2·2H2O

Abstract

Infrared and Raman spectra of dipotassium zinc bis(dihydrogendiphosphate) dihydrate, K₂Zn(H₂P₂O₇)₂ .2H₂O have been collected and interpreted using factor group analysis. Noncoincidence of the Raman and infrared spectra bands confirms a centrosymmetric structure for K₂Zn(H₂P₂O₇)₂ .2H₂O previously investigated by X-ray structural study, as well as the joint appearance of ν_as POP and ν_s POP point to a bent POP configuration.