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Abstract
Metal sulfide minerals are assumed to form naturally at ambient conditions via reaction of a metallic element with (poly)sulfide ions, usually produced by microbes in oxygen-depleted environments. Recently, the formation of mercury sulfide (β-HgS) directly from linear Hg(II)-thiolate complexes (Hg(SR)2) in natural organic matter and in cysteine solutions was demonstrated under aerated conditions. Here, a detailed description of this non-sulfidic reaction is provided by computations at a high level of molecular-orbital theory. The HgS stoichiometry is obtained through the cleavage of the S-C bond in one thiolate, transfer of the resulting alkyl group (R') to another thiolate, and subsequent elimination of a sulfur atom from the second thiolate as a thioether (RSR'). Repetition of this mechanism leads to the formation of RS-(HgS)n-R chains which may self-assemble in parallel arrays to form cinnabar (α-HgS), or more commonly, quickly condense to four-coordinate metacinnabar (β-HgS). The mechanistic pathway is thermodynamically favorable and its predicted kinetics agrees with experiment. The results provide robust theoretical support for the abiotic natural formation of nanoparticulate HgS under oxic conditions and in the absence of a catalyst, and suggest a new route for the (bio)synthesis of HgS nanoparticles with improved technological properties.
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Manceau A, Lemouchi C, Enescu M, Gaillot AC, Lanson M, Magnin V, Glatzel P, Poulin BA, Ryan JN, Aiken GR, Gautier-Luneau I, Nagy KL. Formation of Mercury Sulfide from Hg(II)-Thiolate Complexes in Natural Organic Matter. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:9787-9796. [PMID: 26168020 DOI: 10.1021/acs.est.5b02522] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Methylmercury is the environmental form of neurotoxic mercury that is biomagnified in the food chain. Methylation rates are reduced when the metal is sequestered in crystalline mercury sulfides or bound to thiol groups in macromolecular natural organic matter. Mercury sulfide minerals are known to nucleate in anoxic zones, by reaction of the thiol-bound mercury with biogenic sulfide, but not in oxic environments. We present experimental evidence that mercury sulfide forms from thiol-bound mercury alone in aqueous dark systems in contact with air. The maximum amount of nanoparticulate mercury sulfide relative to thiol-bound mercury obtained by reacting dissolved mercury and soil organic matter matches that detected in the organic horizon of a contaminated soil situated downstream from Oak Ridge, TN, in the United States. The nearly identical ratios of the two forms of mercury in field and experimental systems suggest a common reaction mechanism for nucleating the mineral. We identified a chemical reaction mechanism that is thermodynamically favorable in which thiol-bound mercury polymerizes to mercury-sulfur clusters. The clusters form by elimination of sulfur from the thiol complexes via breaking of mercury-sulfur bonds as in an alkylation reaction. Addition of sulfide is not required. This nucleation mechanism provides one explanation for how mercury may be immobilized, and eventually sequestered, in oxygenated surface environments.
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Affiliation(s)
- Alain Manceau
- †ISTerre, Université Grenoble Alpes, CNRS, 38000 Grenoble, France
| | - Cyprien Lemouchi
- †ISTerre, Université Grenoble Alpes, CNRS, 38000 Grenoble, France
- ‡Institut Néel, Université Grenoble Alpes, CNRS, 38000 Grenoble, France
| | - Mironel Enescu
- §Laboratoire Chrono Environnement, Université de Franche-Comté, CNRS, 25030 Besançon, France
| | - Anne-Claire Gaillot
- ∥Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2 Rue de la Houssinière, 44322 Nantes, France
| | - Martine Lanson
- †ISTerre, Université Grenoble Alpes, CNRS, 38000 Grenoble, France
| | - Valérie Magnin
- †ISTerre, Université Grenoble Alpes, CNRS, 38000 Grenoble, France
| | - Pieter Glatzel
- ⊥European Synchrotron Radiation Facility (ESRF), 71 Rue des Martyrs, 38000 Grenoble, France
| | - Brett A Poulin
- #Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, 428 UCB, Boulder, Colorado 80309-0428, United States
- ∇U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303, United States
| | - Joseph N Ryan
- #Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, 428 UCB, Boulder, Colorado 80309-0428, United States
| | - George R Aiken
- ∇U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303, United States
| | | | - Kathryn L Nagy
- @Department of Earth and Environmental Sciences, University of Illinois at Chicago, MC-186, 845 West Taylor Street, Chicago, Illinois 60607, United States
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Wang Y, Rischer H, Eriksen NT, Wiebe MG. Mixotrophic continuous flow cultivation of Chlorella protothecoides for lipids. BIORESOURCE TECHNOLOGY 2013; 144:608-614. [PMID: 23907064 DOI: 10.1016/j.biortech.2013.07.027] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Revised: 07/03/2013] [Accepted: 07/06/2013] [Indexed: 06/02/2023]
Abstract
The oleaginous alga Chlorella protothecoides accumulates lipid in its biomass when grown in nitrogen-restricted conditions. To assess the relationship between nitrogen provision and lipid accumulation and to determine the contribution of photosynthesis in mixotrophic growth, C. protothecoides was grown in mixo- and heterotrophic nitrogen-limited continuous flow cultures. Lipid content increased with decreasing C/N, while biomass yield on glucose was not affected. Continuous production of high lipid levels (57% of biomass) was possible at high C/N (87-94). However, the lipid production rate (2.48 g L(-1) d(-1)) was higher at D=0.84 d(-1) with C/N 37 than at D=0.44 d(-1) and C/N 87 even though the lipid content of the biomass was lower (38%). Photosynthesis contributed to biomass and lipid production in mixotrophic conditions, resulting in 13-38% reduction in CO2 production compared with heterotrophic cultures, demonstrating that photo- and heterotrophic growth occurred simultaneously in the same population.
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Affiliation(s)
- Yanming Wang
- VTT Technical Research Centre of Finland, VTT, Espoo, Finland
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