Mercury‐dependent artisanal and small‐scale gold mining (ASGM) is the largest source of mercury pollution on Earth. In this practice, elemental mercury is used to extract gold from ore as an amalgam. ...The amalgam is typically isolated by hand and then heated—often with a torch or over a stove—to distill the mercury and isolate the gold. Mercury release from tailings and vaporized mercury exceed 1000 tonnes each year from ASGM. The health effects on the miners are dire, with inhaled mercury leading to neurological damage and other health issues. The communities near these mines are also affected due to mercury contamination of water and soil and subsequent accumulation in food staples, such as fish—a major source of dietary protein in many ASGM regions. The risks to children are also substantial, with mercury emissions from ASGM resulting in both physical and mental disabilities and compromised development. Between 10 and 19 million people use mercury to mine for gold in more than 70 countries, making mercury pollution from ASGM a global issue. With the Minamata Convention on Mercury entering force this year, there is political motivation to help overcome the problem of mercury in ASGM. In this effort, chemists can play a central role. Here, the problem of mercury in ASGM is reviewed with a discussion on how the chemistry community can contribute solutions. Introducing portable and low‐cost mercury sensors, inexpensive and scalable remediation technologies, novel methods to prevent mercury uptake in fish and food crops, and efficient and easy‐to‐use mercury‐free mining techniques are all ways in which the chemistry community can help. To meet these challenges, it is critical that new technologies or techniques are low‐cost and adaptable to the remote and under‐resourced areas in which ASGM is most common. The problem of mercury pollution in ASGM is inherently a chemistry problem. We therefore encourage the chemistry community to consider and address this issue that affects the health of millions of people.
Mercury rising: The intentional use of mercury in artisanal and small‐scale gold mining directly impacts the health of millions of people globally. Collaborative input from the chemistry community is required to help end this threat to the environmental and human well‐being. The image was used with permission from Yayasan Tambuhak Sinta (YTS) and Pure Earth.
Inverse vulcanization is a copolymerization of elemental sulfur and alkenes that provides unique materials with high sulfur content (typically ≥50% sulfur by mass). These polymers contain a dynamic ...and reactive polysulfide network that creates many opportunities for processing, assembly, and repair that are not possible with traditional plastics, rubbers and thermosets. In this study, we demonstrate that two surfaces of these sulfur polymers can be chemically joined at room temperature through a phosphine or amine-catalyzed exchange of the S-S bonds in the polymer. When the nucleophile is pyridine or triethylamine, we show that S-S metathesis only occurs at room temperature for a sulfur rank > 2-an important discovery for the design of polymers made by inverse vulcanization. This mechanistic understanding of the S-S metathesis was further supported with small molecule crossover experiments in addition to computational studies. Applications of this chemistry in latent adhesives, additive manufacturing, polymer repair, and recycling are also presented.
Polymers made by inverse vulcanization can be assembled, repaired, and recycled at room temperature through nucleophile-catalyzed S-S metathesis.
Chemical modification of proteins is a rapidly expanding area in chemical biology. Selective installation of biochemical probes has led to a better understanding of natural protein modification and ...macromolecular function. In other cases such chemical alterations have changed the protein function entirely. Additionally, tethering therapeutic cargo to proteins has proven invaluable in campaigns against disease. For controlled, selective access to such modified proteins, a unique chemical handle is required. Cysteine, with its unique reactivity, has long been used for such modifications. Cysteine has enjoyed widespread use in selective protein modification, yet new applications and even new reactions continue to emerge. This Focus Review highlights the enduring utility of cysteine in protein modification with special focus on recent innovations in chemistry and biology associated with such modifications.
Inverse vulcanization provides dynamic and responsive materials made from elemental sulfur and unsaturated cross‐linkers. These polymers have been used in a variety of applications such as energy ...storage, infrared optics, repairable materials, environmental remediation, and precision fertilizers. In spite of these advances, there is a need for methods to recycle and reprocess these polymers. In this study, polymers prepared by inverse vulcanization are shown to undergo reactive compression molding. In this process, the reactive interfaces of sulfur polymers are brought into contact by mechanical compression. Upon heating these molds at relatively low temperatures (≈100 °C), chemical bonding occurs at the polymer interfaces by S−S metathesis. This method of processing is distinct from previous studies on inverse vulcanization because the polymers examined in this study do not form a liquid phase when heated. Neither compression nor heating alone was sufficient to mold these polymers into new architectures, so this is a new concept in the manipulation of sulfur polymers. Additionally, high‐level ab initio calculations revealed that the weakest S−S bond in organic polysulfides decreases linearly in strength from a sulfur rank of 2 to 4, but then remains constant at about 100 kJ mol−1 for higher sulfur rank. This is critical information in engineering these polymers for S−S metathesis. Guided by this insight, polymer repair, recycling, and repurposing into new composites was demonstrated.
Under pressure: The reactive interfaces of rubber polysulfides made by inverse vulcanization bond together when heated with compression. The S−S metathesis reaction occurs at relatively low temperature and allows additive assembly, recycling, and repurposing of these materials, as well as the preparation of composites.
Site-selective chemical conjugation of synthetic molecules to proteins expands their functional and therapeutic capacity. Current protein modification methods, based on synthetic and biochemical ...technologies, can achieve site selectivity, but these techniques often require extensive sequence engineering or are restricted to the N- or C-terminus. Here we show the computer-assisted design of sulfonyl acrylate reagents for the modification of a single lysine residue on native protein sequences. This feature of the designed sulfonyl acrylates, together with the innate and subtle reactivity differences conferred by the unique local microenvironment surrounding each lysine, contribute to the observed regioselectivity of the reaction. Moreover, this site selectivity was predicted computationally, where the lysine with the lowest pK a was the kinetically favored residue at slightly basic pH. Chemoselectivity was also observed as the reagent reacted preferentially at lysine, even in those cases when other nucleophilic residues such as cysteine were present. The reaction is fast and proceeds using a single molar equivalent of the sulfonyl acrylate reagent under biocompatible conditions (37 °C, pH 8.0). This technology was demonstrated by the quantitative and irreversible modification of five different proteins including the clinically used therapeutic antibody Trastuzumab without prior sequence engineering. Importantly, their native secondary structure and functionality is retained after the modification. This regioselective lysine modification method allows for further bioconjugation through aza-Michael addition to the acrylate electrophile that is generated by spontaneous elimination of methanesulfinic acid upon lysine labeling. We showed that a protein–antibody conjugate bearing a site-specifically installed fluorophore at lysine could be used for selective imaging of apoptotic cells and detection of Her2+ cells, respectively. This simple, robust method does not require genetic engineering and may be generally used for accessing diverse, well-defined protein conjugates for basic biology and therapeutic studies.
A polysulfide material was synthesized by the direct reaction of sulfur and d‐limonene, by‐products of the petroleum and citrus industries, respectively. The resulting material was processed into ...functional coatings or molded into solid devices for the removal of palladium and mercury salts from water and soil. The binding of mercury(II) to the sulfur‐limonene polysulfide resulted in a color change. These properties motivate application in next‐generation environmental remediation and mercury sensing.
Waste not: A polysulfide has been synthesized from the industrial by‐products sulfur and limonene. The material can be processed into coatings or molded into objects and responds selectively to mercury(II), producing a bright yellow deposit that adheres to the material (see picture). The use of the polysulfide in water and soil remediation is demonstrated.
Cysteine oxidation is important in cellular redox regulation, signaling, and biocatalysis. To understand the biological relevance of cysteine oxidation, it is desirable to identify the proteins ...involved, the site of the oxidized cysteine, and the relevant oxidation states. Because the thiol of cysteine can be converted to a wide range of oxidation states, mapping these oxidative modifications is challenging. The dynamic and reversible nature of many cysteine oxidation states compounds the difficulty in such proteomic analyses. In this review, we examine methods to detect cysteine sulfenic acid — a particularly challenging functional group to analyze because of its reactive nature. We focus on the selectivity of recently reported probes and discuss some challenges and opportunities in this field.
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•Probes for detecting cysteine sulfenic acid are important for understanding signaling, enzyme catalysis, and responses to oxidative stress.•Probes such as dimedone and related nucleophiles may react with off-target groups such the cyclic sulfenamide form of cysteine.•Strained alkenes and alkynes can react with cysteine sulfenic acid, but off-target reactions with cysteine are known.•There is substantial opportunity for the development of new probes that are selective for specific oxidation states of cysteine.
Inverse vulcanized polymer materials have received considerable attention as a way to use sulfur, an industrial byproduct, as a starting material for synthesis. The resulting high-sulfur content ...polymers have also been investigated because their properties give rise to promising applications such as infrared imaging, energy storage, and heavy metal capture due to their unique structure. However, synthesis of a flexible sulfur polymer network which shows good mechanical properties combining high strength, high elongation, and high toughness is still a significant challenge. Moreover, further exploration of the properties of sulfur polymers to better understand the relationship between the polymers’ structure with their performance is still needed. Here, a range of cross-linked sulfur polymers with high tensile elongation and toughness and without losing high strength were successfully synthesized. The obtained cross-linked sulfur polymers show high solvent tolerance in most organic solvents but are demonstrated to be chemically de-cross-linked in polar solvents dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone and can be re-cross-linked after removing the solvent due to the high sulfur ranks present in the polymer network. Despite the significantly improved mechanical properties, highly efficient thermal recycling performance typical of inverse vulcanized polymers was retained. Flexibility and durability, combined with chemical and thermal recycling, could open a new door for wider applications of inverse vulcanized polymers.
An electrochemical synthesis of gold(I)‐N‐heterocyclic carbene (Au‐NHC) complexes has been developed. The electrochemical methodology uses only imidazolium salts, gold metal electrodes, and ...electricity to produce these complexes with hydrogen gas as the only by‐product. This high‐yielding and operationally simple procedure has been used to produce eight mononuclear and three dinuclear Au‐NHC complexes. The electrochemical procedure facilitates a clean reaction with no by‐products. As such, Au‐NHC complexes can be directly transferred to catalytic reactions without work‐up or purification. The Au‐NHC complexes were produced on‐demand and tested as catalysts in a vinylcyclopropanation reaction. All mononuclear Au‐NHC complexes performed similarly to or better than the isolated complexes.
An electrochemical synthesis of gold(I)‐N‐heterocyclic carbene (Au‐NHC) complexes has been developed in which the only by‐product is hydrogen gas. This enables the clean Au‐NHC complexes to be transferred directly to subsequent catalytic reactions without extra work‐up. This telescoped methodology has been showcased for several mononuclear and dinuclear Au‐NHC complexes in a catalytic vinylcyclopropanation reaction, delivering high yields and demonstrating procedural simplicity.
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