Constructing protein polyhedra via orthogonal chemical interactions.

Many proteins exist naturally as symmetrical homooligomers or homopolymers1. The emergent structural and functional properties of such protein assemblies have inspired extensive efforts in biomolecular design2-5. As synthesized by ribosomes, proteins are inherently asymmetric. Thus, they must acquire multiple surface patches that selectively associate to generate the different symmetry elements needed to form higher-order architectures1,6-a daunting task for protein design. Here we address this problem using an inorganic chemical approach, whereby multiple modes of protein-protein interactions and symmetry are simultaneously achieved by selective, 'one-pot' coordination of soft and hard metal ions. We show that a monomeric protein (protomer) appropriately modified with biologically inspired hydroxamate groups and zinc-binding motifs assembles through concurrent Fe3+ and Zn2+ coordination into discrete dodecameric and hexameric cages. Our cages closely resemble natural polyhedral protein architectures7,8 and are, to our knowledge, unique among designed systems9-13 in that they possess tightly packed shells devoid of large apertures. At the same time, they can assemble and disassemble in response to diverse stimuli, owing to their heterobimetallic construction on minimal interprotein-bonding footprints. With stoichiometries ranging from [2 Fe:9 Zn:6 protomers] to [8 Fe:21 Zn:12 protomers], these protein cages represent some of the compositionally most complex protein assemblies-or inorganic coordination complexes-obtained by design.

Author Correction: Hyperexpandable, self-healing macromolecular crystals with integrated polymer networks.

Change history: In this Letter, Alexander Groisman should have been listed as an author. This error has been corrected online.

Hyperexpandable, self-healing macromolecular crystals with integrated polymer networks.

The formation of condensed matter typically involves a trade-off between structural order and flexibility. As the extent and directionality of interactions between atomic or molecular components increase, materials generally become more ordered but less compliant, and vice versa. Nevertheless, high levels of structural order and flexibility are not necessarily mutually exclusive; there are many biological (such as microtubules1,2, flagella 3 , viruses4,5) and synthetic assemblies (for example, dynamic molecular crystals6-9 and frameworks10-13) that can undergo considerable structural transformations without losing their crystalline order and that have remarkable mechanical properties8,14,15 that are useful in diverse applications, such as selective sorption 16 , separation 17 , sensing 18 and mechanoactuation 19 . However, the extent of structural changes and the elasticity of such flexible crystals are constrained by the necessity to maintain a continuous network of bonding interactions between the constituents of the lattice. Consequently, even the most dynamic porous materials tend to be brittle and isolated as microcrystalline powders 14 , whereas flexible organic or inorganic molecular crystals cannot expand without fracturing. Owing to their rigidity, crystalline materials rarely display self-healing behaviour 20 . Here we report that macromolecular ferritin crystals with integrated hydrogel polymers can isotropically expand to 180 per cent of their original dimensions and more than 500 per cent of their original volume while retaining periodic order and faceted Wulff morphologies. Even after the separation of neighbouring ferritin molecules by 50 ångströms upon lattice expansion, specific molecular contacts between them can be reformed upon lattice contraction, resulting in the recovery of atomic-level periodicity and the highest-resolution ferritin structure reported so far. Dynamic bonding interactions between the hydrogel network and the ferritin molecules endow the crystals with the ability to resist fragmentation and self-heal efficiently, whereas the chemical tailorability of the ferritin molecules enables the creation of chemically and mechanically differentiated domains within single crystals.

Microbial communities from weathered outcrops of a sulfide-rich ultramafic intrusion, and implications for mine waste management.

The Duluth Complex (DC) contains sulfide-rich magmatic intrusions that represent one of the largest known economic deposits of copper, nickel, and platinum group elements. Previous work showed that microbial communities associated with experimentally-weathered DC waste rock and tailings were dominated by uncultivated taxa and organisms not typically associated with mine waste. However, those experiments were designed for kinetic testing and do not necessarily represent the conditions expected for long-term environmental weathering. We used 16S rRNA gene methods to characterize the microbial communities present on the surfaces of naturally-weathered and historically disturbed outcrops of DC material. Rock surfaces were dominated by diverse uncultured Ktedonobacteria, Acetobacteria, and Actinobacteria, with abundant algae and other phototrophs. These communities were distinct from microbial assemblages from experimentally-weathered DC rocks, suggesting different energy and nutrient resources in environmental samples. Sulfide mineral incubations performed with and without algae showed that photosynthetic microorganisms could have an inhibitory effect on autotrophic populations, resulting in slightly lower sulfate release and differences in dominant microorganisms. The microbial assemblages from these weathered outcrops show how communities develop during weathering of sulfide-rich DC rocks and represent baseline data that could evaluate the effectiveness of future reclamation of waste produced by large-scale mining operations.

Fluoride and gallein inhibit polyphosphate accumulation by oral pathogen Rothia dentocariosa.

The uptake and storage of extracellular orthophosphate (Pi) by polyphosphate (polyP) accumulating bacteria may contribute to mineral dissolution in the oral cavity. To test the effect of potential inhibitors of polyP kinases on Rothia dentocariosa, gallein (0, 25, 50, and 100 µM) and fluoride (0, 50, and 100 ppm) were added to R. dentocariosa cultures grown in brain-heart infusion broth. At a late log growth phase (8 h), extracellular Pi was measured using an ascorbic acid assay, and polyP was isolated from bacterial cells treated with RNA/DNAases using a neutral phenol/chloroform extraction. Extracts were hydrolyzed and quantified as above. Gallein and fluoride had minor effects on bacterial growth with NaF having a direct effect on media pH. Gallein (≥25 µM) and fluoride (≥50 ppm) attenuated the bacterial drawdown of extracellular Pi by 56.7% (P < 0.05) and 37.3% (P < 0.01). There was a corresponding polyP synthesis decrease of 73.2% (P < 0.0001) from gallein and 83.1% (P < 0.0001) from fluoride. Attenuated total reflectance-Fourier-transform infrared spectroscopy validated the presence of polyP and its reduced concentration in R. dentocariosa bacterial cells following gallein and fluoride treatment. Rothia dentocariosa can directly change extracellular Pi and accumulate intracellular polyP, but the mechanism is attenuated by gallein and NaF.

Structurally Diverse Bench-Stable Nickel(0) Pre-Catalysts: A Practical Toolkit for In Situ Ligation Protocols.

A flurry of recent research has centered on harnessing the power of nickel catalysis in organic synthesis. These efforts have been bolstered by contemporaneous development of well-defined nickel (pre)catalysts with diverse structure and reactivity. In this report, we present ten different bench-stable, 18-electron, formally zero-valent nickel-olefin complexes that are competent pre-catalysts in various reactions. Our investigation includes preparations of novel, bench-stable Ni(COD)(L) complexes (COD=1,5-cyclooctadiene), in which L=quinone, cyclopentadienone, thiophene-S-oxide, and fulvene. Characterization by NMR, IR, single-crystal X-ray diffraction, cyclic voltammetry, thermogravimetric analysis, and natural bond orbital analysis sheds light on the structure, bonding, and properties of these complexes. Applications in an assortment of nickel-catalyzed reactions underscore the complementary nature of the different pre-catalysts within this toolkit.

Planar chromatography and immunodetection of hydrocarbons on polyvinylidene difluoride membranes.

Fast, cheap, and simple separation of lipids and hydrocarbons can currently be achieved using thin-layer chromatography. Here, we describe an alternative planar chromatographic method using polyvinylidene difluoride membranes as the stationary phase. The procedure has the same advantages of thin-layer chromatography over other expensive and time-consuming techniques, such as high-performance liquid chromatography or gas chromatography. Polyvinylidene difluoride membranes, however, also provide an immediate support for analyte development via immunodetection, are easy to manipulate, and potentially increase the performance of other detection methods. We show that polyvinylidene difluoride membranes are compatible with a variety of solvents that can migrate by capillarity and redistribute analytes between the membrane and the solvent according to their relative affinities, providing a chromatographic separation. We directly test the developed membranes by immunoblotting using anti-squalene antibodies that cross-react with acyclic isoprenoids. Separations of crude oils and plant extracts under different solvent conditions show the potential to resolve hydrocarbon group types and also to provide characteristic fingerprints of plant pigments and squalene degradation products. Polyvinylidene difluoride membranes prove useful as a stationary phase for planar chromatography and for the subsequent immunodetection of the separated compounds, providing a new and simple chromatographic technique to analyze lipids and hydrocarbons.

Tunable and Cooperative Thermomechanical Properties of Protein-Metal-Organic Frameworks.

We recently introduced protein-metal-organic frameworks (protein-MOFs) as chemically designed protein crystals, composed of ferritin nodes that predictably assemble into 3D lattices upon coordination of various metal ions and ditopic, hydroxamate-based linkers. Owing to their unique tripartite construction, protein-MOFs possess extremely sparse lattice connectivity, suggesting that they might display unusual thermomechanical properties. Leveraging the synthetic modularity of ferritin-MOFs, we investigated the temperature-dependent structural dynamics of six distinct frameworks. Our results show that the thermostabilities of ferritin-MOFs can be tuned through the metal component or the presence of crowding agents. Our studies also reveal a framework that undergoes a reversible and isotropic first-order phase transition near-room temperature, corresponding to a 4% volumetric change within 1 °C and a hysteresis window of ∼10 °C. This highly cooperative crystal-to-crystal transformation, which stems from the soft crystallinity of ferritin-MOFs, illustrates the advantage of modular construction strategies in discovering tunable-and unpredictable-material properties.

Anisotropic Dynamics and Mechanics of Macromolecular Crystals Containing Lattice-Patterned Polymer Networks.

The mechanical and functional properties of many crystalline materials depend on cooperative changes in lattice arrangements in response to external perturbations. However, the flexibility and adaptiveness of crystalline materials are limited. Additionally, the bottom-up, molecular-level design of crystals with desired dynamic and mechanical properties at the macroscopic level remains a considerable challenge. To address these challenges, we had previously integrated mesoporous, cubic ferritin crystals with hydrogel networks, resulting in hybrid materials (polymer-integrated crystals or PIX) which could undergo dramatic structural changes while maintaining crystalline periodicity and display efficient self-healing. The dynamics and mechanics of these ferritin-PIX were devoid of directionality, which is an important attribute of many molecular and macroscopic materials/devices. In this study, we report that such directionality can be achieved through the use of ferritin crystals with anisotropic symmetries (rhombohedral or trigonal), which enable the templated formation of patterned hydrogel networks in crystallo. The resulting PIX expand and contract anisotropically without losing crystallinity, undergo prompt bending motions in response to stimuli, and self-heal efficiently, capturing some of the essential features of sophisticated biological devices like skeletal muscles.

An Exceptionally Stable Metal-Organic Framework Constructed from Chelate-Based Metal-Organic Polyhedra.

We report the rational design and synthesis of a water-stable metal-organic framework (MOF), Fe-HAF-1, constructed from supramolecular, Fe3+-hydroxamate-based polyhedra with mononuclear metal nodes. Owing to its chelate-based construction, Fe-HAF-1 displays exceptional chemical stability in organic and aqueous solvents over a wide pH range (pH 1-14), including in the presence of 5 M NaOH. Despite the charge neutrality of the Fe3+-tris(hydroxamate) centers, Fe-HAF-1 crystals are negatively charged above pH 4. This unexpected property is attributed to the formation of defects during crystallization that results in uncoordinated hydroxamate ligands or hydroxide-coordinated Fe centers. The anionic nature of Fe-HAF-1 crystals enables selective adsorption of positively charged ions in aqueous solution, resulting in efficient separation of organic dyes and other charged species in a size-selective fashion. Fe-HAF-1 presents a new addition to a small group of chelate-based MOFs and provides a rare framework whose 3D connectivity is exclusively formed by metal-hydroxamate coordination.

Diverse Communities of hgcAB+ Microorganisms Methylate Mercury in Freshwater Sediments Subjected to Experimental Sulfate Loading.

Methylmercury (MeHg) is a bioaccumulative neurotoxin produced by certain sulfate-reducing bacteria and other anaerobic microorganisms. Because microorganisms differ in their capacity to methylate mercury, the abundance and distribution of methylating populations may determine MeHg production in the environment. We compared rates of MeHg production and the distribution of hgcAB genes in epilimnetic sediments from a freshwater lake that were experimentally amended with sulfate levels from 7 to 300 mg L-1. The most abundant hgcAB sequences were associated with clades of Methanomicrobia, sulfate-reducing Deltaproteobacteria, Spirochaetes, and unknown environmental sequences. The hgcAB+ communities from higher sulfate amendments were less diverse and had relatively more Deltaproteobacteria, whereas the communities from lower amendments were more diverse with a larger proportion of hgcAB sequences affiliated with other clades. Potential methylation rate constants varied 52-fold across the experiment. Both potential methylation rate constants and % MeHg were the highest in sediments from the lowest sulfate amendments, which had the most diverse hgcAB+ communities and relatively fewer hgcAB genes from clades associated with sulfate reduction. Although pore water sulfide concentration covaried with hgcAB diversity across our experimental sulfate gradient, major changes in the community of hgcAB+ organisms occurred prior to a significant buildup of sulfide in pore waters. Our results indicate that methylating communities dominated by diverse anaerobic microorganisms that do not reduce sulfate can produce MeHg as effectively as communities dominated by sulfate-reducing populations.

Polyphosphate-Accumulating Bacteria: Potential Contributors to Mineral Dissolution in the Oral Cavity.

Bacteria that accumulate polyphosphates have previously been shown to dynamically influence the solubility of phosphatic minerals in marine settings and wastewater. Here, we show that dental plaque, saliva, and carious lesions all contain abundant polyphosphate-accumulating bacteria. Saturation state modeling results, informed by phosphate uptake experiments using the model organism Lactobacillus rhamnosus, which is known to inhabit advanced carious lesions, suggest that polyphosphate accumulation can lead to undersaturated conditions with respect to hydroxyapatite under some oral cavity conditions. The cell densities of polyphosphate-accumulating bacteria we observed in some regions of oral biofilms are comparable to those that produce undersaturated conditions (i.e., those that thermodynamically favor mineral dissolution) in our phosphate uptake experiments with L. rhamnosus These results suggest that the localized generation of undersaturated conditions by polyphosphate-accumulating bacteria constitutes a new potential mechanism of tooth dissolution that may augment the effects of metabolic acid production.IMPORTANCE Dental caries is a serious public health issue that can have negative impacts on overall quality of life and oral health. The role of oral bacteria in the dissolution of dental enamel and dentin that can result in carious lesions has long been solely ascribed to metabolic acid production. Here, we show that certain oral bacteria may act as a dynamic shunt for phosphate in dental biofilms via the accumulation of a polymer known as polyphosphate-potentially mediating phosphate-dependent conditions such as caries (dental decay).

First biochemical and crystallographic characterization of a fast-performing ferritin from a marine invertebrate.

Ferritin, a multimeric cage-like enzyme, is integral to iron metabolism across all phyla through the sequestration and storage of iron through efficient ferroxidase activity. While ferritin sequences from ∼900 species have been identified, crystal structures from only 50 species have been reported, the majority from bacterial origin. We recently isolated a secreted ferritin from the marine invertebrate Chaetopterus sp. (parchment tube worm), which resides in muddy coastal seafloors. Here, we present the first ferritin from a marine invertebrate to be crystallized and its biochemical characterization. The initial ferroxidase reaction rate of recombinant Chaetopterus ferritin (ChF) is 8-fold faster than that of recombinant human heavy-chain ferritin (HuHF). To our knowledge, this protein exhibits the fastest catalytic performance ever described for a ferritin variant. In addition to the high-velocity ferroxidase activity, ChF is unique in that it is secreted by Chaetopterus in a bioluminescent mucus. Previous work has linked the availability of Fe2+ to this long-lived bioluminescence, suggesting a potential function for the secreted ferritin. Comparative biochemical analyses indicated that both ChF and HuHF showed similar behavior toward changes in pH, temperature, and salt concentration. Comparison of their crystal structures shows no significant differences in the catalytic sites. Notable differences were found in the residues that line both 3-fold and 4-fold pores, potentially leading to increased flexibility, reduced steric hindrance, or a more efficient pathway for Fe2+ transportation to the ferroxidase site. These suggested residues could contribute to the understanding of iron translocation through the ferritin shell to the ferroxidase site.

Synthetic Modularity of Protein-Metal-Organic Frameworks.

Previously, we adopted the construction principles of metal-organic frameworks (MOFs) to design a 3D crystalline protein lattice in which pseudospherical ferritin nodes decorated on their C3 symmetric vertices with Zn coordination sites were connected via a ditopic benzene-dihydroxamate linker. In this work, we have systematically varied both the metal ions presented at the vertices of the ferritin nodes (Zn(II), Ni(II), and Co(II)) and the synthetic dihydroxamate linkers, which yielded an expanded library of 15 ferritin-MOFs with the expected body-centered (cubic or tetragonal) lattice arrangements. Crystallographic and small-angle X-ray scattering (SAXS) analyses indicate that lattice symmetries and dimensions of ferritin-MOFs can be dictated by both the metal and linker components. SAXS measurements on bulk crystalline samples reveal that some ferritin-MOFs can adopt multiple lattice conformations, suggesting dynamic behavior. This work establishes that the self-assembly of ferritin-MOFs is highly robust and that the synthetic modularity that underlies the structural diversity of conventional MOFs can also be applied to the self-assembly of protein-based crystalline materials.

Novel Microbial Assemblages Dominate Weathered Sulfide-Bearing Rock from Copper-Nickel Deposits in the Duluth Complex, Minnesota, USA.

The Duluth Complex in northeastern Minnesota hosts economically significant deposits of copper, nickel, and platinum group elements (PGEs). The primary sulfide mineralogy of these deposits includes the minerals pyrrhotite, chalcopyrite, pentlandite, and cubanite, and weathering experiments show that most sulfide-bearing rock from the Duluth Complex generates moderately acidic leachate (pH 4 to 6). Microorganisms are important catalysts for metal sulfide oxidation and could influence the quality of water from mines in the Duluth Complex. Nevertheless, compared with that of extremely acidic environments, much less is known about the microbial ecology of moderately acidic sulfide-bearing mine waste, and so existing information may have little relevance to those microorganisms catalyzing oxidation reactions in the Duluth Complex. Here, we characterized the microbial communities in decade-long weathering experiments (kinetic tests) conducted on crushed rock and tailings from the Duluth Complex. Analyses of 16S rRNA genes and transcripts showed that differences among microbial communities correspond to pH, rock type, and experimental treatment. Moreover, microbial communities from the weathered Duluth Complex rock were dominated by taxa that are not typically associated with acidic mine waste. The most abundant operational taxonomic units (OTUs) were from the genera Meiothermus and Sulfuriferula, as well as from diverse clades of uncultivated Chloroflexi, Acidobacteria, and Betaproteobacteria Specific taxa, including putative sulfur-oxidizing Sulfuriferula spp., appeared to be primarily associated with Duluth Complex rock, but not pyrite-bearing rocks subjected to the same experimental treatment. We discuss the implications of these results for the microbial ecology of moderately acidic mine waste with low sulfide content, as well as for kinetic testing of mine waste.IMPORTANCE Economic sulfide mineral deposits in the Duluth Complex may represent the largest undeveloped source of copper and nickel on Earth. Microorganisms are important catalysts for sulfide mineral oxidation, and research on extreme acidophiles has improved our ability to manage and remediate mine wastes. We found that the microbial assemblages associated with weathered rock from the Duluth Complex are dominated by organisms not widely associated with mine waste or mining-impacted environments, and we describe geochemical and experimental influences on community composition. This report will be a useful foundation for understanding the microbial biogeochemistry of moderately acidic mine waste from these and similar deposits.

A Metal Organic Framework with Spherical Protein Nodes: Rational Chemical Design of 3D Protein Crystals.

We describe here the construction of a three-dimensional, porous, crystalline framework formed by spherical protein nodes that assemble into a prescribed lattice arrangement through metal-organic linker-directed interactions. The octahedral iron storage enzyme, ferritin, was engineered in its C3 symmetric pores with tripodal Zn coordination sites. Dynamic light scattering and crystallographic studies established that this Zn-ferritin construct could robustly self-assemble into the desired bcc-type crystals upon coordination of a ditopic linker bearing hydroxamic acid functional groups. This system represents the first example of a ternary protein-metal-organic crystalline framework whose formation is fully dependent on each of its three components.

Metatranscriptomic analysis of diminutive Thiomargarita-like bacteria ("Candidatus Thiopilula" spp.) from abyssal cold seeps of the Barbados Accretionary Prism.

Large sulfur-oxidizing bacteria in the family Beggiatoaceae are important players in the global sulfur cycle. This group contains members of the well-known genera Beggiatoa, Thioploca, and Thiomargarita but also recently identified and relatively unknown candidate taxa, including "Candidatus Thiopilula" spp. and "Ca. Thiophysa" spp. We discovered a population of "Ca. Thiopilula" spp. colonizing cold seeps near Barbados at a ∼4.7-km water depth. The Barbados population consists of spherical cells that are morphologically similar to Thiomargarita spp., with elemental sulfur inclusions and a central vacuole, but have much smaller cell diameters (5 to 40 µm). Metatranscriptomic analysis revealed that when exposed to anoxic sulfidic conditions, Barbados "Ca. Thiopilula" organisms expressed genes for the oxidation of elemental sulfur and the reduction of nitrogenous compounds, consistent with their vacuolated morphology and intracellular sulfur storage capability. Metatranscriptomic analysis further revealed that anaerobic methane-oxidizing and sulfate-reducing organisms were active in the sediment, which likely provided reduced sulfur substrates for "Ca. Thiopilula" and other sulfur-oxidizing microorganisms in the community. The novel observations of "Ca. Thiopilula" and associated organisms reported here expand our knowledge of the globally distributed and ecologically successful Beggiatoaceae group and thus offer insight into the composition and ecology of deep cold seep microbial communities.

Sedimenticola thiotaurini sp. nov., a sulfur-oxidizing bacterium isolated from salt marsh sediments, and emended descriptions of the genus Sedimenticola and Sedimenticola selenatireducens.

A marine facultative anaerobe, strain SIP-G1T, was isolated from salt marsh sediments, Falmouth, MA, USA. Phylogenetic analysis of its 16S rRNA gene sequence indicated that it belongs to an unclassified clade of Gammaproteobacteria that includes numerous sulfur-oxidizing bacteria that are endosymbionts of marine invertebrates endemic to sulfidic habitats. Strain SIP-G1T is a member of the genus Sedimenticola, of which there is one previously described isolate, Sedimenticola selenatireducens AK4OH1T. S. selenatireducens AK4OH1T was obtained for further characterization and comparison with strain SIP-G1T. The two strains were capable of coupling the oxidation of thiosulfate, tetrathionate, elemental sulfur and sulfide to autotrophic growth and they produced sulfur inclusions as metabolic intermediates. They showed varying degrees of O2 sensitivity, but when provided amino acids or peptides as a source of energy, they appeared more tolerant of O2 and exhibited concomitant production of elemental sulfur inclusions. The organic substrate preferences and limitations of these two organisms suggest that they possess an oxygen-sensitive carbon fixation pathway(s). Organic acids may be used to produce NADPH through the TCA cycle and are used in the formation of polyhydroxyalkanoates. Cell-wall-deficient morphotypes appeared when organic compounds (especially acetate) were present in excess and reduced sulfur was absent. Levels of DNA-DNA hybridization (∼47%) and phenotypic characterization indicate that strain SIP-G1T represents a separate species within the genus Sedimenticola, for which the name Sedimenticola thiotaurini sp. nov. is proposed. The type strain is SIP-G1T ( = ATCC BAA-2640T = DSM 28581T). The results also justify emended descriptions of the genus Sedimenticola and of S. selenatireducens.

Comparison of Archaeal and Bacterial Diversity in Methane Seep Carbonate Nodules and Host Sediments, Eel River Basin and Hydrate Ridge, USA.

Anaerobic oxidation of methane (AOM) impacts carbon cycling by acting as a methane sink and by sequestering inorganic carbon via AOM-induced carbonate precipitation. These precipitates commonly take the form of carbonate nodules that form within methane seep sediments. The timing and sequence of nodule formation within methane seep sediments are not well understood. Further, the microbial diversity associated with sediment-hosted nodules has not been well characterized and the degree to which nodules reflect the microbial assemblage in surrounding sediments is unknown. Here, we conducted a comparative study of microbial assemblages in methane-derived authigenic carbonate nodules and their host sediments using molecular, mineralogical, and geochemical methods. Analysis of 16S rRNA gene diversity from paired carbonate nodules and sediments revealed that both sample types contained methanotrophic archaea (ANME-1 and ANME-2) and syntrophic sulfate-reducing bacteria (Desulfobacteraceae and Desulfobulbaceae), as well as other microbial community members. The combination of geochemical and molecular data from Eel River Basin and Hydrate Ridge suggested that some nodules formed in situ and captured the local sediment-hosted microbial community, while other nodules may have been translocated or may represent a record of conditions prior to the contemporary environment. Taken together, this comparative analysis offers clues to the formation regimes and mechanisms of sediment-hosted carbonate nodules.

Discovery of N-X anomeric amides as electrophilic halogenation reagents.

Electrophilic halogenation is a widely used tool employed by medicinal chemists to either pre-functionalize molecules for further diversity or incorporate a halogen atom into drugs or drug-like compounds to solve metabolic problems or modulate off-target effects. Current methods to increase the power of halogenation rely on either the invention of new reagents or activating commercially available reagents with various additives such as Lewis or Brønsted acids, Lewis bases and hydrogen-bonding activators. There is a high demand for new reagents that can halogenate otherwise unreactive compounds under mild conditions. Here we report the invention of a class of halogenating reagents based on anomeric amides, taking advantage of the energy stored in the pyramidalized nitrogen of N-X anomeric amides as a driving force. These robust halogenating methods are compatible with a variety of functional groups and heterocycles, as exemplified on over 50 compounds (including 13 gram-scale examples and 1 flow chemistry scale-up).