Greener reactants, renewable energies and environmental impact mitigation strategies in pyrometallurgical processes: A review.

Abstract: Metals and alloys are among the most technologically important materials for our industrialized societies. They are the most common structural materials used in cars, airplanes and buildings, and constitute the technological core of most electronic devices. They allow the transportation of energy over great distances and are exploited in critical parts of renewable energy technologies. Even though primary metal production industries are mature and operate optimized pyrometallurgical processes, they extensively rely on cheap and abundant carbonaceous reactants (fossil fuels, coke), require high power heating units (which are also typically powered by fossil fuels) to calcine, roast, smelt and refine, and they generate many output streams with high residual energy content. Many unit operations also generate hazardous gaseous species on top of large CO2 emissions which require gas-scrubbing and capture strategies for the future. Therefore, there are still many opportunities to lower the environmental footprint of key pyrometallurgical operations. This paper explores the possibility to use greener reactants such as bio-fuels, bio-char, hydrogen and ammonia in different pyrometallurgical units. It also identifies all recycled streams that are available (such as steel and aluminum scraps, electronic waste and Li-ion batteries) as well as the technological challenges associated with their integration in primary metal processes. A complete discussion about the alternatives to carbon-based reduction is constructed around the use of hydrogen, metallo-reduction as well as inert anode electrometallurgy. The review work is completed with an overview of the different approaches to use renewable energies and valorize residual heat in pyrometallurgical units. Finally, strategies to mitigate environmental impacts of pyrometallurgical operations such as CO2 capture utilization and storage as well as gas scrubbing technologies are detailed. This original review paper brings together for the first time all potential strategies and efforts that could be deployed in the future to decrease the environmental footprint of the pyrometallurgical industry. It is primarily intended to favour collaborative work and establish synergies between academia, the pyrometallurgical industry, decision-makers and equipment providers. Highlights: A more sustainable production of metals using greener reactants, green electricity or carbon capture is possible and sometimes already underway. More investments and pressure are required to hasten change. Discussion: Is there enough pressure on the aluminum and steel industries to meet the set climate targets?The greenhouse gas emissions of existing facilities can often be partly mitigated by retrofitting them with green technologies, should we close plants prematurely to build new plants using greener technologies?Since green or renewable resources presently have limited availability, in which sector should we use them to maximize their benefits?

Functions of Saccharomyces cerevisiae Ecm27p, a putative Na(+)/Ca(2+) exchanger, in calcium homeostasis, carbohydrate storage and cell cycle reentry from the quiescent phase.

The quiescent phase of the cell cycle is of fundamental importance for fungi, yet our understanding of this phase of the cycle is much less well understood than the mitotic cell cycle. We found that the ECM27 gene, which encodes a Na(+)/Ca(2+) exchanger, is responsible for influx of calcium from the extracellular space and release from intracellular stores during membrane stress. Wild type cells increase total Ca(2+) in quiescence but cells lacking ECM27 gene fail to do so and are defective in cell cycle reentry from the quiescent phase. ecm27Δ cells are also defective in maintaining trehalose levels throughout this phase. Addition of high levels of CaCl2 to the growth medium can increase total cellular calcium in ecm27Δ cells during quiescence and can also restore trehalose levels as well as partially restore ability of cells to reenter the mitotic cell cycle. ecm27Δ cells also have altered glycogen levels in exponentially growing cells. Our results show that Ecm27p and Ca(2+) play roles in maintaining a high level of trehalose in quiescent cells, which in turn is important in the ability of cells to rapidly return to proliferation.

Synthesis and antifungal activity of derivatives of 2- and 3-benzofurancarboxylic acids.

We found that amiodarone has potent antifungal activity against a broad range of fungi, potentially defining a new class of antimycotics. Investigations into its molecular mechanisms showed amiodarone mobilized intracellular Ca2+, which is thought to be an important antifungal characteristic of its fungicidal activity. Amiodarone is a synthetic drug based on the benzofuran ring system, which is contained in numerous compounds that are both synthetic and isolated from natural sources with antifungal activity. To define the structural components responsible for antifungal activity, we synthesized a series of benzofuran derivatives and tested them for the inhibition of growth of two pathogenic fungi, Cryptococcus neoformans and Aspergillus fumigatus, to find new compounds with antifungal activity. We found several derivatives that inhibited fungal growth, two of which had significant antifungal activity. We were surprised to find that calcium fluxes in cells treated with these derivatives did not correlate directly with their antifungal effects; however, the derivatives did augment the amiodarone-elicited calcium flux into the cytoplasm. We conclude that antifungal activity of these new compounds includes changes in cytoplasmic calcium concentration. Analyses of these benzofuran derivatives suggest that certain structural features are important for antifungal activity. Antifungal activity drastically increased on converting methyl 7-acetyl-6-hydroxy-3-methyl-2-benzofurancarboxylate (2b) into its dibromo derivative, methyl 7-acetyl-5-bromo-6-hydroxy-3-bromomethyl-2-benzofurancarboxylate (4).

Ethanol induces calcium influx via the Cch1-Mid1 transporter in Saccharomyces cerevisiae.

Yeast suffers from a variety of environmental stresses, such as osmotic pressure and ethanol produced during fermentation. Since calcium ions are protective for high concentrations of ethanol, we investigated whether Ca(2+) flux occurs in response to ethanol stress. We find that exposure of yeast to ethanol induces a rise in the cytoplasmic concentration of Ca(2+). The response is enhanced in cells shifted to high-osmotic media containing proline, galactose, sorbitol, or mannitol. Suspension of cells in proline and galactose-containing media increases the Ca(2+) levels in the cytoplasm independent of ethanol exposure. The enhanced ability for ethanol to induce Ca(2+) flux after the hypertonic shift is transient, decreasing rapidly over a period of seconds to minutes. There is partial recovery of the response after zymolyase treatment, suggesting that cell wall integrity affects the ethanol-induced Ca(2+) flux. Acetate inhibits the Ca(2+) accumulation elicited by the ethanol/osmotic stress. The Ca(2+) flux is primarily via the Cch1 Ca(2+) influx channel because strains carrying deletions of the cch1 and mid1 genes show greater than 90% reduction in Ca(2+) flux. Furthermore, a functional Cch1 channel reduced growth inhibition by ethanol.

Amiodarone induces stress responses and calcium flux mediated by the cell wall in Saccharomyces cerevisiae.

We used a proteomic approach to study effects of amiodarone on cells of the yeast Saccharomyces cerevisiae. Amiodarone has been shown to have antifungal activity in vitro and causes a massive increase in cytoplasmic calcium levels ([Ca2+]cyt). Proteomic analysis of cells exposed to amiodarone show that this drug elicits stress responses and points to involvement of proteins associated with the cell wall. We tested several of those proteins for involvement in the Ca2+ flux. In particular, the amiodarone-induced Ca2+ flux was decreased in bgl2Delta cells, which have altered levels of beta-glucan and chitin. The involvement of the cell wall in the Ca2+ flux induced by amiodarone treatment was tested by addition of yeast cell-wall components. While mannan inhibited the rise in [Ca2+]cyt, beta-glucan potentiated the Ca2+ flux by 4.5-fold, providing evidence that the cell wall is directly involved in controlling this Ca2+ flux. This conclusion is corroborated by the inhibition of the Ca2+ flux by calcofluor, which is known to bind to cell-wall chitin and inhibit cell growth. Zymolyase treatment altered the kinetics of amiodarone-induced calcium flux and uncoupled the inhibitory effect of calcofluor. These effects demonstrate that the cell-wall beta-glucan regulates calcium flux elicited by amiodarone.

Amiodarone induces a caffeine-inhibited, MID1-depedent rise in free cytoplasmic calcium in Saccharomyces cerevisiae.

Calcium signalling is involved in myriad cellular processes such as mating morphogenesis. Mating in yeast induces changes in cell morphology with a concomitant increase in calcium uptake that is dependent on the MID1 and CCH1 genes. Mid1p and Cch1p are believed to function in a capacitive calcium entry (CCE)-like process. Amiodarone alters mammalian calcium channel activity but, despite its clinical importance, its molecular mechanisms are not clearly defined. We have shown previously that amiodarone has fungicidal activity against a broad array of fungi. We show here that amiodarone causes a dramatic increase in cytoplasmic calcium ([Ca2+]cyt) in Saccharomyces cerevisiae. The majority of this increase is dependent on extracellular Ca2+ nonetheless, a significant increase in [Ca2+]cyt is still induced by amiodarone when no uptake of extracellular Ca2+ can occur. The influx of extracellular Ca2+ may be a direct effect of amiodarone on a membrane transporter or may be by a CCE mechanism. Uptake of the extracellular Ca2+ is inhibited by caffeine and reduced in strains deleted for the mid1 gene, but not in cells deleted for cch1. Our data are the first demonstrating control of yeast calcium channels by amiodarone and caffeine.

A phosphotyrosine-dependent protein interaction screen reveals a role for phosphorylation of caveolin-1 on tyrosine 14: recruitment of C-terminal Src kinase.

Caveolin-1 is a substrate for nonreceptor tyrosine kinases including Src, Fyn, and Abl. To investigate the function of caveolin-1 phosphorylation, we modified the Gal4-based yeast two-hybrid system to screen for phosphorylation-dependent protein interactions. A cDNA library was screened using the N terminus of caveolin-1 as bait in a yeast strain expressing the catalytic domain of Abl. We identified two proteins in this screen that interact with caveolin-1 in a phosphorylation-dependent manner: tumor necrosis factor-alpha receptor-associated factor 2 (TRAF2) and C-terminal Src kinase (Csk). TRAF2 bound to nonphosphorylated caveolin-1, but this association was increased 3-fold by phosphorylation. In contrast, association of Csk with caveolin-1 was completely dependent on phosphorylation of caveolin-1, both for fusion proteins in yeast (>35-fold difference in affinity) and for endogenous proteins in tissue culture cells. Our data suggest that phosphorylation of caveolin-1 leads to Csk translocation into caveolae. This may induce a feedback loop that leads to inactivation of the Src family kinases that are highly enriched in caveolae.

Characterization of a novel, broad-based fungicidal activity for the antiarrhythmic drug amiodarone.

Fungal infections are common in patients with acquired immunodeficiency syndrome and pose a major health management problem. There is a need for identification of new antifungals to complement the limited current repertoire and to combat newly arising resistant fungal strains. We have identified a novel antifungal activity for the antiarrhythmic drug amiodarone. Extensive characterization of this activity shows that amiodarone exhibits a growth inhibition for several diverse fungi, including species of Cryptococcus, Saccharomyces, Aspergillus, Candida, and Fusarium. The antifungal activity was shown to be fungicidal; Cryptococcus neoformans treated with amiodarone lost viability within hours of drug exposure. Growth inhibition could be suppressed by addition of very high concentrations (10 mM) of calcium to the medium, suggesting that disruption of calcium homeostasis was involved in the antifungal activity. Direct measurement of radiolabeled calcium efflux showed that addition of amiodarone resulted in an immediate efflux of cellular calcium. In conclusion, amiodarone displays broad-based fungicidal activity and may be acting in part by perturbing the calcium balance.

A novel quantitative mating assay for the fungal pathogen Cryptococcus neoformans provides insight into signalling pathways responding to nutrients and temperature.

Cryptococcus neoformans is a fungal pathogen that causes a lethal meningitis in immunocompromised individuals. Several factors are associated with virulence of this fungus, including its mating type; however, the mechanism by which mating type affects virulence is unknown. C. neoformans is a basidiomycete that exists in two mating types called a and alpha that can fuse to form an a/alpha dikaryon. A mating assay was developed that allowed a quantitative analysis of cryptococcal mating physiology. Interestingly, the efficiency of mating appeared to be dependent on temperature, being highest at 30 degrees C and almost completely absent at 37 degrees C. Thus, while mating type itself may be associated with virulence (which must occur at 37 degrees C), the ability to mate is probably not a virulence factor. Mating efficiency was increased by altering the carbon or nitrogen sources to give so-called starvation media. The addition of various drugs also seemed to alter the frequency of mating, depending on the composition of mating medium. The data suggested that cAMP, 8-bromo-cAMP and caffeine increased mating on starvation medium but only cAMP and 8-bromo-cAMP stimulated mating on rich medium; caffeine was unable to stimulate mating on rich medium. Aluminium fluoride, an activator of heterotrimeric GTP-binding proteins (G-proteins), was also found to stimulate mating, suggesting the involvement of a G-protein that may regulate the level of cAMP.