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The biological technologies application in sulfide minerals leaching to the recovery of valuables metal is a very important technological advance. They are environmental friendly and favor the sustainability of metals production in the mining and metals industry. Nowadays there is not enough basic information on molybdenite bioleaching, as well as there isn`t equip capable to obtain efficient molybdenum extractions. The difficulty depends in part on microorganisms tolerance to the molybdenum. An 85% molybdenum extraction in 6 months has been reported. This work assesses the molybdenite bioleaching from a concentrate (MoS2) with thermophilic microorganisms, at a temperature of 65 °C, on a new reactor designed at the Faculty of Chemistry of the Universidad Nacional Autónoma de México, to obtain higher extractions of molybdenum. Since bioleaching an aerobic process, the oxygen transference is a difficult condition to achieve because its solubility in water is very low and in the air 20.9 %. In addition to homogenize and maintain constant the nutrients concentration, in this new bioreactor could be established the physical, chemical and biological conditions that lead to the microorganisms optimal growth, due to these are environmental sensitive. This new equip allows us mix the nutrients in a homogeneous way. Also is able maintain constant the nutrients concentration, and all controlled physical, biological and chemical parameters. Finally does not cause any microorganisms damage. The RELVA-ARBP bioreactor allows us the control of necessary conditions for a growth more efficient of the bacterial strains. This will allow leach more rapidly the ore, increasing the molybdenum extraction kinetics. The tests results of bioleaching molybdenite with a mixed strain of extreme thermophiles carried out at 65 °C in an orbital incubator and in the RELVA-ARBP bioreactor, show a better efficiency of the bioreactor used. more...

Although the biological techniques application into sulfide minerals leaching to obtain valuable metals ​​is an important technological advance, the disadvantage of relatively slow kinetics bio-oxidation still limits its commercial application. However, it stimulates the research for constant improvement. Microorganisms are capable of performing their intended role with great efficiency under optimal conditions. Bioreactor design seeks to maintain certain environmental conditions that favour efficient microbial growth as pH, temperature, oxygen and carbon dioxide dissolution, stirring speed, etc. In an aerobic process such as bioleaching the optimum oxygen transference is extremely difficult to be achieved, because little oxygen dissolves in water. Furthermore the oxygen transference usually is facilitated by agitation, which is also required to mix the nutrients and maintain homogeneous solution, this transference is limited by the agitation speed because of the high power consumption, and the damage that undergoes the microorganisms submitted to excessive shear. In order to improve bio oxidation kinetics, in this paper we designed a new bioreactor, which combines elements of the stirred tank and airlift reactor, and introduces new elements, to their effective use in biohydrometallurgy. A new bio-reactor called RELBA was designed and build-up in the UNAM laboratories. It controls dissolved O2 among other parameters and it prevents shear. Bioleaching tests of the ore, containing 0.135% Cu and 3.07% Fe, were performed in the orbital incubator and in the RELBA bio-reactor to 35oC using a mixed strain of Acidithiobacillus caldus, Acidihiobacillus thiooxidans and Leptospirillum ferriphilum, which confirm the advantages of the new bioleaching reactor. more...

Some new 16β-acetoxy-22,26-epoxy-23-vinylcholest-22-ene steroid derivatives have been synthesized from sapogenins via a two-step sequence involving the reduction of a vinylogous ester moiety by 9-BBN, a reaction with few precedents and for which a coherent mechanistic interpretation has not been given before now. Some mechanistic insight into this reaction was gained from NMR spectroscopic evidence. A plausible general mechanistic interpretation of the action of 9-BBN on vinylogous esters is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) more...

The compounds (4R, 5R)-3,4-dimethyl-5-phenyl-1,3-oxazolidine (OXA1), (4S, 5R)-3,4-dimethyl-5-phenyl-1,3-oxazolidine (OXA2) [Chemical Abstracts registry number 123618-06-4], and (4R, 5R)-2,2,3,4-tetramethyl-5-phenyl-oxazolidine (OXA3) [Chemical Abstracts registry number 141271-51-4] have been studied by oxygen bomb combustion calorimetry, and the vapor pressures were measured at different temperatures by a static method. On the basis of the experimental results, the standard molar enthalpies of formation of the liquid and gaseous compounds were determined. A summary of experimental and derived results at the temperatureT=298.15 K is shown below; where ΔcUm°(l), ΔcHm°(l), ΔfHm°(l), ΔlgHm°(l), and ΔfHm°(g) denote the standard molar energy of combustion, the standard molar enthalpy of combustion, the standard molar enthalpy of formation of the liquid compound, the standard molar enthalpy of vaporization, and the standard molar enthalpy of formation of the gaseous compound, respectively. more...

The compoundscis-5a,6,11a,12-tetrahydro[1,4]benzothiazino[3,2-b][1,4]benzothiazine(BTB) and 5a,6,11a,12-tetrahydro[1,4]benzoxazino[3,2-b][1,4]benzoxazine(BOB) have been studied by oxygen bomb combustion calorimetry and by the Knudsen effusion method using a quartz-crystal microbalance. Based on the experimental results, the standard molar enthalpies of formation of the solid and gaseous compounds were determined. A summary of experimental and derived results at the temperatureT=298.15 K is shown below: [Table] From a group-contribution scheme and from the experimental results, the group-contribution terms to the standard molar enthalpies of formation of the gaseous compounds for the molecular groups {C–(S)(N)(C)(H)} and {C–(O)(N)(C)(H)} were calculated as –76.1 kJ·mol−1and –42.7 kJ·mol−1, respectively. It is concluded that the standard molar enthalpy of formation in the gas phase is decreased by (340.4±9.0) kJ·mol−1when two Cb–S bonds and two C–S bonds are substituted by two Cb–O bonds and two C–O bonds in the compound BTB to obtain BOB; here Cbrefers to a carbon atom in the benzene ring. more...

The one step conversion of the side chain in sapogenins into the 22,26-epoxycholest-22-ene framework was achieved in yields >85% using BF 3·OEt 2. The new structures maintain the natural chirality at C20 and C25, as shown by X-ray diffraction analyses. more...

In this paper, we report the synthesis and characterization of new boron compounds derived from dithiooxamides. The compounds were characterized by NMR (1H and 13C), UV-vis, fluorescence spectroscopy, and high resolution mass spectrometry. The crystal structure of the mononuclear boron compound was determined by single-crystal X-ray diffraction analysis. The photophysical properties of the boron compounds were investigated, and we found moderate fluorescence emission (compound 2 ΦF: 4.07% and compound 4 ΦF: 2.89%). We also observed that the mononuclear complex presented greater stability. Compound 4 showed interesting luminescent properties; in solid state, it exhibited an increase in fluorescence by mechanostimuli by changing to a bright red color, and also in solution, it showed a decrease in fluorescence intensity when oxygen and air were supplied to the solution. more...