Abiotic Reactions Research Articles

Mapping the Photochemistry of European Mid-Latitudes Rivers: An Assessment of Their Ability to Photodegrade Contaminants.

The abiotic photochemical reactions that take place naturally in sunlit surface waters can degrade many contaminants that pose concern to water bodies for their potentially toxic and long-term effects. This works aims at assessing the ability of European rivers to photoproduce reactive transient intermediates, such as HO• radicals and the excited triplet states of chromophoric dissolved organic matter (3CDOM*), involved in pollutant degradation. A photochemical mapping of the steady-state concentrations of these transients was carried out by means of a suitable modeling tool, in the latitude belt between 40 and 50°N. Such a map allowed for the prediction of the photochemical lifetimes of the phenylurea herbicide isoproturon (mostly undergoing photodegradation upon reaction with HO• and especially 3CDOM*) across different European countries. For some rivers, a more extensive dataset was available spanning the years 1990–2002, which allowed for the computation of the steady-state concentration of the carbonate radicals (CO3•−). With these data, it was possible to assess the time trends of the photochemical half-lives of further contaminants (atrazine, ibuprofen, carbamazepine, and clofibric acid). The calculated lifetimes were in the range of days to weeks, which might or might not allow for efficient depollution depending on the river-water flow velocity.

Conductive Magnetite Nanoparticles Enhance the Microbial Electrosynthesis of Acetate from CO2 while Diverting Electrons away from Methanogenesis

AbstractMicrobial electrosynthesis (MES) is an emerging technology which exploits microbial cells to convert CO2 into fuels, and value‐added chemicals using electrons supplied by a solid‐state cathode. Methane and acetic acid are typically the main CO2‐reduction products attained in microbial electrosynthesis studies, although the production of other more valuable products has also been reported. So far, however, practical strategies to manipulate and steer the distribution of CO2 reduction products during microbial electrosynthesis, particularly when mixed microbial cultures are employed as catalysts, are lacking.To specifically address this issue, here we investigated the influence of magnetite nanoparticles (NPs) supplementation (to a final concentration of 300 mg Fe L−1) on the microbial electrosynthesis process. Results demonstrated, that cells supplemented with magnetite NPs, exhibited a substantially higher yield of acetate production relative to unamended controls (up to 8.5 times higher, during the run with the cathode set at a potential of −700 mV vs. SHE, with a corresponding cathode capture efficiency of 17%) and, correspondingly, a lower yield of methane production (52% in the magnetite‐supplemented cell vs. 74% in the unamended control cell). Abiotic experiments indicated that the observed effects derived from magnetite catalyzing the biotic and abiotic hydrogen evolution reaction.

Redox Cycling Driven Transformation of Layered Manganese Oxides to Tunnel Structures.

Mn oxides are among the most ubiquitous minerals on Earth and play critical roles in numerous elemental cycles in biotic/abiotic loops as the key redox center. Yet, it has long puzzled geochemists why the laboratory synthesis of todorokite, a tunnel-structured Mn oxide, is extremely difficult while it is the dominant form over other tunneled phases in low-temperature natural environments. This study employs a novel electrochemical method to mimic the cyclic redox reactions occurring over long geological time scales in an accelerated manner. The results revealed that the kinetics and electron flux of the cyclic redox reaction are key to the layer-to-tunnel structure transformation of Mn oxides, provided new insights for natural biotic and abiotic redox reactions, and explained the dominance of todorokite in nature.

FIELD APPLICATION OF A REAGENT FOR IN SITU CHEMICAL REDUCTION AND ENHANCED REDUCTIVE DICHLORINATION TREATMENT OF AN AQUIFER CONTAMINATED WITH TETRACHLOROETHYLENE (PCE), TRICHLOROETHYLENE, 1,1-DICHLOROETHYLENE, DICHLOROPROPANE AND 1,1,2,2-TETRACHLOROETHANE (R-130)

Groundwater at an abandoned industrial area near Bergamo, Italy, was historically contaminated by tetrachloroethylene (PCE) (>100 g/L) and, to a lesser extent, by trichlorethylene (TCE), dichloropropane (DP) and 1,1,2,2-tetrachloroethane (R-130). A liquid reagent (EHC Liquid) was selected for remediation of groundwater at the site. The reagent is provided in two parts: EHC Liquid Mix (a soluble organo-iron salt), and ELS Microemulsion (a lecithin-based carbon substrate), and is designed to promote both in situ chemical reduction (ISCR) and enhanced reductive dechlorination (ERD) to destroy chlorinated organic compounds. The two components are mixed with water and injected into the subsurface. Once in groundwater, EHC Liquid rapidly generates highly reduced conditions, favouring both biotic and abiotic dechlorination reactions. Less than 6 months after the injection of EHC Liquid in the main source area, concentrations of the target contaminants had reached the site-specific remediation target values (CSC Legislative Decree 152/06) in the main monitoring piezometers present in the area, thus demonstrating the effective establishment of enhanced biotic and abiotic reducing conditions and degradation of the target compounds.

СЕРПЕНТИНИЗАЦИЯ МАНТИЙНЫХ ПЕРИДОТИТОВ КАК ОСНОВНОЙ ИСТОЧНИК ГЛУБИННЫХ УГЛЕВОДОРОДОВ ЗАПАДНО-СИБИРСКОГО НЕФТЕГАЗОНОСНОГО БАССЕЙНА

The authors have proposed a scheme for the formation of the hydrocarbon capacity of the West Siberian oil and gas basin in a paleosubduction geodynamic setting and continue developing the idea concerning the abiogenic deep genesis of hydrocarbons due to the low-temperature serpentinization of mantle peridotites during spreading in the Ordovician back-arc basin, which occupied at that time within the area of the future West Siberian basin, and the high-temperature hydration of peridotites in the mantle wedges above the subduction zones during the Selurian and Devonian. Another source of abyssal hydrocarbons is the serpentinization of mantle peridotites fragments in water saturated basement. A major role is being established in the formation of hydrocarbon deposits in the sedimentary cover of Western Siberia in the vertical migration of deep hydrocarbon fluids through degassing pipes, including anomalous annular zones, through deep thrusts, which are active gas-oil supply channels and along a large zone of Neogene-Quaternary low-amplitude horizontal shifts in the basement thickness. Deep-seated faults that comprise triassic rift system of West Siberian play a major role in water removal from deep sources. The feeding with new portions of oil and gas in hydrocarbon fields of West Siberian basin continues in present time, which provides renewability of regional hydrocarbons. The total volume of methane generated in the serpentinization zones of mantle peridotites is formed from two sources — abiotic (reaction of hydrogen with carbon dioxide dissolved in seawater) and biotic (methanogens). The origin of hydrocarbons is considered in the context of a new polygenetic scheme of oil and gas formation in the process of «abiogenic-biogenic» synthesis.

Effects of sterilization techniques on chemodenitrification and N<sub>2</sub>O production in tropical peat soil microcosms

Abstract. Chemodenitrification – the non-enzymatic process of nitrite reduction – may be an important sink for fixed nitrogen in tropical peatlands. Rates and products of chemodenitrification are dependent on O2, pH, Fe2+ concentration, and organic matter composition, which are variable across peat soils. Assessing abiotic reaction pathways is difficult because sterilization and inhibition agents can alter the availability of reactants by changing iron speciation and organic matter composition. We compared six commonly used soil sterilization techniques – γ irradiation, chloroform, autoclaving, and the use of three different chemical inhibitors (mercury, zinc, and azide) – for their compatibility with chemodenitrification assays for tropical peatland soils (organic-rich, low-pH soil from the eastern Amazon). Out of the six techniques, γ irradiation resulted in soil treatments with the lowest cell viability and denitrification activity and the least effect on pH, iron speciation, and organic matter composition. Nitrite depletion rates in γ-irradiated soils were highly similar to untreated (live) soils, whereas other sterilization techniques showed deviations. Chemodenitrification was a dominant process of nitrite consumption in tropical peatland soils assayed in this study. Nitrous oxide (N2O) is one possible product of chemodenitrification reactions. Abiotic N2O production was low to moderate (3 %–16 % of converted nitrite), and different sterilization techniques lead to significant variations on production rates due to inherent processes or potential artifacts. Our work represents the first methodological basis for testing the abiotic denitrification and N2O production potential in tropical peatland soil.

Nitrous oxide production by ammonia oxidizers: Physiological diversity, niche differentiation and potential mitigation strategies

Oxidation of ammonia to nitrite by bacteria and archaea is responsible for global emissions of nitrous oxide directly and indirectly through provision of nitrite and, after further oxidation, nitrate to denitrifiers. Their contributions to increasing N2 O emissions are greatest in terrestrial environments, due to the dramatic and continuing increases in use of ammonia-based fertilizers, which have been driven by requirement for increased food production, but which also provide a source of energy for ammonia oxidizers (AO), leading to an imbalance in the terrestrial nitrogen cycle. Direct N2 O production by AO results from several metabolic processes, sometimes combined with abiotic reactions. Physiological characteristics, including mechanisms for N2 O production, vary within and between ammonia-oxidizing archaea (AOA) and bacteria (AOB) and comammox bacteria and N2 O yield of AOB is higher than in the other two groups. There is also strong evidence for niche differentiation between AOA and AOB with respect to environmental conditions in natural and engineered environments. In particular, AOA are favored by low soil pH and AOA and AOB are, respectively, favored by low rates of ammonium supply, equivalent to application of slow-release fertilizer, or high rates of supply, equivalent to addition of high concentrations of inorganic ammonium or urea. These differences between AOA and AOB provide the potential for better fertilization strategies that could both increase fertilizer use efficiency and reduce N2 O emissions from agricultural soils. This article reviews research on the biochemistry, physiology and ecology of AO and discusses the consequences for AO communities subjected to different agricultural practices and the ways in which this knowledge, coupled with improved methods for characterizing communities, might lead to improved fertilizer use efficiency and mitigation of N2 O emissions.

Elucidation of the nitrogen-transformation mechanism for nitrite removal using a microbial-mediated iron redox cycling system

Given the abundance of iron on the Earth, nitrogen-contaminated water is a key region for the biogeochemical cycling of N and Fe under anaerobic conditions. However, the biogeochemical processes between N and Fe remain uncertain, as do the understanding of nitrogen-transformation pathways. In this study, the nitrogen balance for the nitrite removal process in the system containing Shewanella oneidensis MR-1 and the iron oxide of either ferrihydrite or magnetite was elucidated by microbially mediated biotic and abiotic reactions with the participation of Fe. Gas chromatography results showed that during the subsequent operation phase with the re-addition of nitrite, nitrite reduction by biogenic Fe(II) was the sole process to produce gaseous nitrogen (N2O), and yields of which were achieved to 65.56 % and 23.13 % with the ferrihydrite and magnetite systems, respectively. Meanwhile, both ferrihydrite and magnetite remained relatively stable with a small amount of phosphosiderite. Accompanied with biogenic Fe(II) formation in the start-up phase, reduction of nitrite to ammonia coupled with lactate oxidation could be driven by Shewanella oneidensis MR-1. Thus, in order to remediate nitrogen pollution in aquatic environment, given the intimate association between the microbial-mediated Fe mineralization process and the biogeochemical cycling of N, it is essential to truly understand the nitrogen-transformation mechanism under the coexistence of both processes.

Evaluation of abiotic stress reaction on Lophantus anisatus

Plantago australis is a perennial plant widely distributed in Latin America, and its seeds and leaves are used in folk medicine to treat many diseases and conditions. Among its various chemical compounds, verbascoside is one of the most present, and has several pharmacological activities described, but there is not much information about its toxicity.The aims of this study were to optimize the extraction of verbascoside from P. australis leaves with ultrasound methods, to develop a validated HPLC method to quantify verbascoside, and to evaluate the toxicological safety of the extract and verbascoside using in vitro and in vivo assays.Dried leaves of P. australis were submitted to different extraction methods (percolation and ultrasound). The optimization of the ultrasound extraction was carried out by complete factorial design (22) and response surface methodology (RSM), followed by HPLC analysis for marker compounds. HPLC analysis was performed to verify the presence of the marker compounds aucubin, baicalein, oleanolic acid, ursolic acid and verbascoside. Mutagenicity was assessed by Salmonella/microsome mutagenicity assay. Cytotoxicity and genotoxicity were evaluated in V79 cells by reduction of tetrazolium salt (MTT) and neutral red uptake (NRU) assays, and alkaline comet assay, respectively. Verbascoside phototoxicity was assessed in 3T3 cells by the NRU phototoxicity assay. Wistar rats were used to perform the acute and sub-chronic toxicity tests.Among the marker compounds, only verbascoside was found in the hydroethanolic extract of P. australis leaves (PAHE); its highest concentration was obtained with the ultrasound-assisted extraction (UAE) method, optimized in 40 min and 25 °C, and the method validation was successfully applied. Neither PAHE nor verbascoside showed mutagenic or genotoxic activities. Cytotoxicity assays demonstrated that both PAHE and verbascoside reduced cell viability only at the highest concentrations, and verbascoside had no phototoxic properties. The in vivo toxicity evaluation of PAHE suggested that the LD50 is higher than 5000 mg/Kg, indicating that this extract is safe for use. In addition, no signs of toxicity were found in subchronic exposure.The HPLC method to quantify verbascoside was validated, and the extraction of verbascoside from P. australis leaves through ultrasound method was optimized, yielding an extract with 6% verbascoside. Our results suggest the toxicological safety of PAHE and verbascoside, corroborating the use of P. australis in folk medicine, and also indicate verbascoside as a potential ingredient in topical formulations.

Peptide Synthesis under the Alkaline Hydrothermal Conditions on Enceladus

Chemical evolution is an abiotic reaction process in which complex organic molecules arise from a combination of simple inorganic and organic chemical compounds. To assess the possible ongoing chem...

Characterization of Bone Char and Carbon Xerogel as Sustainable Alternative Bioelectrodes for Bioelectrochemical Systems

Bioelectrochemical systems (BES) are growing future sustainable energy and chemical production technologies that combine biological catalytic redox activity with classic abiotic electrochemical reactions and physics. Several aspects of these systems, such as cell configuration, applied voltage, electrode materials, inoculum/substrate, and low-cost electrodes to facilitate scaling, have been studied and reported. This work focuses on the development of inexpensive materials with desirable characteristics for use as electrodes for BES. The two selected carbon-based anode materials were carbon xerogels and bone char; both have different surface morphologies and are carbonaceous materials with precursors that allow control of their porosity. Industrial-grade raw material and cattle bone waste were used to fabricate the anodes. The electrochemical properties of the bone char and carbon xerogel electrodes were characterized by the open circuit voltage (OCV), electrochemical impedance spectroscopy, and cyclic voltammetry. Chronoamperometry was recorded for 25 days to follow the setup bioanodes. When the microbial bioanode process was completed, the bioelectrodes were immersed into fresh inoculum/substrate, and BES were operated for 10 days at the OCV until a relatively constant cell voltage output was achieved. The results show that the carbon xerogel surface area (468 m2/g) is 5 times higher than bone char, but the xerogel surface roughness is lower than that of the char. Similar to the electrochemical properties, the current density of the xerogel (25 mA/cm2) is 4 times less than that of the bone; therefore, the biofilm growth is promoted on the bone char surface. Our findings show that the bone char bioanode has a capacitance feature of 1.65 F/m2, which is even higher than the double layer capacitances of carbon-based materials reported in the literature. Hence, it is possible to use BES for simultaneous production and storage of renewable electricity.

Transcription factor genes involved in plant response to abiotic stress factors

Hypothermia, drought, salinity and heavy metals are the most widespread stress factors negatively affecting plant growth and development. Plants respond to these stress factors on molecular, cellular, and physiological levels through the complicated mechanisms of signal perception and transduction, subsequently inducing various defense mechanisms. Transcription factors controlling the expression of numerous defense proteins are the most significant abiotic stress reaction regulators. Mainly, the negative environmental influence activates the AP2/ERF, WRKY, MYB, NAC, bZIP transcription factors. The numerous transcription factors genes can be used in genetic engineering of agricultural crops resistant to abiotic stress. These genes are also of great interest in marker assisted selection of cultivated plants. This review is dedicated to description of transcription factors and their genes, involved in plant response to hypothermia, drought, salinity and heavy metals.

Enhanced hydrolysis of 1,1,2,2-tetrachloroethane by multi-walled carbon nanotube/TiO2 nanocomposites: The synergistic effect

Once released into the environment, engineered nanomaterials can significantly influence the transformation and fate of organic contaminants. To date, the abilities of composite nanomaterials to catalyze environmentally relevant abiotic transformation reactions of organic contaminants are largely unknown. Herein, we investigated the effects of two nanocomposites – consisting of anatase titanium dioxide (TiO2) with different predominantly exposed crystal facets (i.e., {101} or {001} facets) anchored to hydroxylated multi-walled carbon nanotubes (OH-MWCNT) – on the hydrolysis of 1,1,2,2-tetrachloroethane (TeCA), a common groundwater contaminant, at ambient pH (6, 7 and 8). Both OH-MWCNT/TiO2 nanocomposites were more effective in catalyzing the dehydrochlorination of TeCA than the respective component materials (i.e., bare OH-MWCNT and bare TiO2). Moreover, the synergistic effect of the two components was evident, in that the incorporation of OH-MWCNT increased the TeCA adsorption capacity of the nanocomposites, significantly enhancing the catalytic effect of the deprotonated hydroxyl and carboxyl groups on nanocomposite surfaces, which served as the main catalytic sites for TeCA hydrolysis. The findings may have important implications for the understanding of the environmental implications of composite nanomaterials and may shed light on the design of high-performance nanocomposites for enhanced contaminant removal.

Community structure of microaerophilic iron-oxidizing bacteria in Japanese paddy field soils

ABSTRACT Redox cycle of iron (Fe) is the central process in the biogeochemistry of paddy field soil. Although Fe(II)-oxidizing process is mediated by both abiotic and biotic reactions, microorganisms involved in the process have not been well studied in paddy field soil. The present study investigated the community structure of microaerophilic Fe(II)-oxidizing bacteria (FeOB) in the family Gallionellaceae in the plow layer of paddy fields located in the central (Anjo) and northeastern (Omagari) Japan since the members in the family are the typical FeOB in circumneutral freshwater environments and possibly have the significant role for Fe(II) oxidation in paddy field soils. A primer set targeting 16S rRNA gene of Gallionella-related FeOB was newly designed for the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and quantitative PCR (qPCR) analyses. DGGE analysis showed significant differences in the band patterns between the field sites. Besides, minor differences were observed in the patterns between the soil depths (0–1 cm and below 1 cm) in the Anjo field, while the patterns were relatively stable in the Omagari field during the annual rice cultivation practices. In total 54 bands were sequenced and clustered into 20 operational taxonomic units (OTUs) on the basis of the 97% similarity. Eighteen out of twenty OTUs (50 of 54 bands) were affiliated within the FeOB cluster of Gallionellaceae, some of which were clustered with known microaerophilic FeOB, Ferrigenium kumadai, Ferriphaselus amnicola, ‘Sideroxydans lithotrophicus’ and ‘S. paludicola’. The number of the 16S rRNA gene copies was 105–107 and 106–108 copies g−1 dried soil in the two paddy fields and negatively correlated to the contents of acetate-extractable Fe(II) in the soils during the rice cultivation period. These results suggested inhabitance of considerable number of diverse Gallionella-related FeOB and their potential involvement in the Fe(II)-oxidizing process of soil, especially during the rice cultivation period in the paddy field soils.

Site‐Selective Functionalization of (sp3)C−H Bonds Catalyzed by Artificial Metalloenzymes Containing an Iridium‐Porphyrin Cofactor

AbstractThe selective functionalization of one C−H bond over others in nearly identical steric and electronic environments can facilitate the construction of complex molecules. We report site‐selective functionalizations of C−H bonds, differentiated solely by remote substituents, catalyzed by artificial metalloenzymes (ArMs) that are generated from the combination of an evolvable P450 scaffold and an iridium‐porphyrin cofactor. The generated systems catalyze the insertion of carbenes into the C−H bonds of a range of phthalan derivatives containing substituents that render the two methylene positions in each phthalan inequivalent. These reactions occur with site‐selectivity ratios of up to 17.8:1 and, in most cases, with pairs of enzyme mutants that preferentially form each of the two constitutional isomers. This study demonstrates the potential of abiotic reactions catalyzed by metalloenzymes to functionalize C−H bonds with site selectivity that is difficult to achieve with small‐molecule catalysts.

Site-Selective Functionalization of (sp3 )C-H Bonds Catalyzed by Artificial Metalloenzymes Containing an Iridium-Porphyrin Cofactor.

The selective functionalization of one C-H bond over others in nearly identical steric and electronic environments can facilitate the construction of complex molecules. We report site-selective functionalizations of C-H bonds, differentiated solely by remote substituents, catalyzed by artificial metalloenzymes (ArMs) that are generated from the combination of an evolvable P450 scaffold and an iridium-porphyrin cofactor. The generated systems catalyze the insertion of carbenes into the C-H bonds of a range of phthalan derivatives containing substituents that render the two methylene positions in each phthalan inequivalent. These reactions occur with site-selectivity ratios of up to 17.8:1 and, in most cases, with pairs of enzyme mutants that preferentially form each of the two constitutional isomers. This study demonstrates the potential of abiotic reactions catalyzed by metalloenzymes to functionalize C-H bonds with site selectivity that is difficult to achieve with small-molecule catalysts.

Solving a shuttle mystery.

Shewanella oneidensis bacteria use an abiotic reaction to help shuttle electrons outside of the cell.

Abiotic Methylation of Tetrabromobisphenol A (TBBPA) with the Occurrence of Methyl Iodide in Aqueous Environments

Tetrabromobisphenol A (TBBPA) is the most widely used brominated flame retardant in the world. Its biotic methylation products, tetrabromobisphenol A mono- and dimethyl ether (TBBPA MME and TBBPA DME, respectively), are frequently detected in the environment, but the importance of abiotic methylation reactions of TBBPA in the environment is not known. In this study, the methylation of TBBPA mediated by methyl iodide (CH3I), a ubiquitous compound in aqueous environments, was investigated in simulated waters in the laboratory. It was found that abiotic methylation occurred under both light and dark conditions and was strongly affected by the pH, temperature, and natural organic matter concentration of the water. Abiotic methylation was further verified in natural river water, and the yield of TBBPA MME mediated abiotically by CH3I was much greater than that of biotic methylation. According to our calculations and by comparison of the activation energies (E a) for the abiotic methylation of TBBPA and the other four typical phenolic contaminants and/or metabolites (bisphenol A, triclosan, 5-OH-BDE-47, and 4'-OH-CB-61) mediated by CH3I, those phenolic compounds all show great methylation potentials. The results indicate a new abiotic pathway for generating TBBPA MME and TBBPA DME from TBBPA, and they also confirm the potentials for abiotic methylation of other phenolic contaminants in aqueous environments.

Nitrate transformation and immobilization in particulate organic matter incubations: Influence of redox, iron and (a)biotic conditions.

Nitrate can be reduced to other N inorganic species via denitrification and incorporated into organic matter by immobilization; however, the effect of biotic/abiotic and redox condition on immobilization and denitrification processes from a single system are not well documented. We hypothesize nitrate (NO3-) transformation pathways leading to the formation of dissolved- and solid-phase organic N are predominantly controlled by abiotic reactions, but the formation of soluble inorganic N species is controlled by redox condition. In this study, organic matter in the form of leaf compost (LC) was spiked with 15NO3- and incubated under oxic/anoxic and biotic/abiotic conditions at pH 6.5. We seek to understand how variations in environmental conditions impact NO3- transformation pathways through laboratory incubations. We find production of NH4+ is predominantly controlled by redox whereas NO3- conversion to dissolved organic nitrogen (DON) and immobilization in solid-phase N are predominantly controlled by abiotic processes. Twenty % of added 15N-NO3- was incorporated into DON under oxic conditions, with abiotic processes accounting for 85% of the overall incorporation. Nitrogen immobilization processes resulted in N concentrations of 4.1–6.6 μg N (g leaf compost)-1, with abiotic processes accounting for 100% and 66% of the overall (biotic+abiotic) N immobilization under anoxic and oxic conditions, respectively. 15N-NMR spectroscopy suggests 15NO3- was immobilized into amide/aminoquinones and nitro/oxime under anoxic conditions. A fraction of the NH4+ was produced abiotically under anoxic conditions (~10% of the total NH4+ production) although biotic organic N mineralization contributed to most of NH4+ production. Our results also indicate Fe(II) did not act as an electron source in biotic-oxic incubations; however, Fe(II) provided electrons for NO3- reduction in biotic-anoxic incubations although it was not the sole electron source. It is clear that, under the experimental conditions of this investigation, abiotic and redox processes play important roles in NO3- transformations. As climatic conditions change (e.g., frequency/intensity of rainfall), abiotic reactions that shift transformation pathways and N species concentrations from those controlled by biota might become more prevalent.

Biocatalytic Strategy for Highly Diastereo- and Enantioselective Synthesis of 2,3-Dihydrobenzofuran-Based Tricyclic Scaffolds.

2,3-Dihydrobenzofurans are key pharmacophores in many natural and synthetic bioactive molecules. A biocatalytic strategy is reported here for the highly diastereo- and enantioselective construction of stereochemically rich 2,3-dihydrobenzofurans in high enantiopurity (>99.9% de and ee), high yields, and on a preparative scale via benzofuran cyclopropanation with engineered myoglobins. Computational and structure-reactivity studies provide insights into the mechanism of this reaction, enabling the elaboration of a stereochemical model that can rationalize the high stereoselectivity of the biocatalyst. This information was leveraged to implement a highly stereoselective route to a drug molecule and a tricyclic scaffold featuring five stereogenic centers via a single-enzyme transformation. This work expands the biocatalytic toolbox for asymmetric C-C bond transformations and should prove useful for further development of metalloprotein catalysts for abiotic carbene transfer reactions.