Bacterial cysteate dissimilatory pathway involves a racemase and d-cysteate sulfo-lyase.

The sulfite-reducing bacterium Bilophila wadsworthia, a common human intestinal pathobiont, is unique in its ability to metabolize a wide variety of sulfonates to generate sulfite as a terminal electron acceptor (TEA). The resulting formation of H2S is implicated in inflammation and colon cancer. l-cysteate, an oxidation product of l-cysteine, is among the sulfonates metabolized by B. wadsworthia, although the enzymes involved remain unknown. Here we report a pathway for l-cysteate dissimilation in B. wadsworthia RZATAU, involving isomerization of l-cysteate to d-cysteate by a cysteate racemase (BwCuyB), followed by cleavage into pyruvate, ammonia and sulfite by a d-cysteate sulfo-lyase (BwCuyA). The strong selectivity of BwCuyA for d-cysteate over l-cysteate was rationalized by protein structural modeling. A homolog of BwCuyA in the marine bacterium Silicibacter pomeroyi (SpCuyA) was previously reported to be a l-cysteate sulfo-lyase, but our experiments confirm that SpCuyA too displays a strong selectivity for d-cysteate. Growth of B. wadsworthia with cysteate as the electron acceptor is accompanied by production of H2S and induction of BwCuyA. Close homologs of BwCuyA and BwCuyB are present in diverse bacteria, including many sulfate- and sulfite-reducing bacteria, suggesting their involvement in cysteate degradation in different biological environments.

Dimerized Nonfused Electron Acceptor Based on a Thieno[3,4-c]pyrrole-4,6-dione Core for Organic Solar Cells.

In this work, the first dimerized nonfused electron acceptor (NFEA), based on thieno[3,4-c]pyrrole-4,6-dione as the core, has been designed and synthesized. The dimerized acceptor and its single counterpart exhibit similar energy levels but different absorption spectra due to their distinct aggregation behavior. The dimerized acceptor-based organic solar cells (OSCs) demonstrate a higher power conversion efficiency of 11.05%, accompanied by enhanced thermal stability. This improvement is attributed to the enhancement of the short-circuit current density and fill factor, along with an increase in the glass transition temperature. Characterizations of exciton dynamics and film morphology reveal that a dimerized acceptor-based device possesses an enhanced exciton dissociation efficiency and a well-established charge transport pathway, explaining its improved photovoltaic performance. All these results indicate that the dimerized NFEA as a promising candidate can achieve efficiency-stability-cost balance in OSCs.

The correlation between electron exchange capacity of Fenton-like heterogeneous catalyst and catalytic activity.

Electron transfer played key role in peroxymonosulfate (PMS) activation for heterogeneous Fenton-like catalysts (HFCs). However, the relationship between electron exchange capacity (EEC) and catalytic activity of HFCs has not been elucidated. Herein, thirteen HFCs reported in our previous studies were selected to measure their EEC via electrochemical methods and to investigate the correlation between EEC and catalytic activity for PMS. The results show that nitrogen-doped graphene oxide had much higher EEC (5.299 mM(e) g-1), followed by reduced graphene oxide (3.23 mM(e) g-1), nitrogen-doped biochar-700 (2.032 mM(e) g-1), graphene oxdie (1.789 mM(e) g-1), nitrogen-doped biochar-300 (1.15 mM(e) g-1), g-C3N4 (0.752 mM(e) g-1) and biochar (0.351 mM(e) g-1). For carbon materials, their catalytic activity was not determined by electron donor capacity (EDC), electron acceptor capacity (EAC) and EEC (EDC + EAC), but was linear correlation with |EDC-EAC| that can characterize the extent of HFCs reacting with PMS. The higher the |EDC-EAC| is, the higher the catalytic activity of HFCs is. For carbonaceous materials, their catalytic activity was not proportional to EAC, but had good linear correlation with EDC and |EDC-EAC|. The discrepancy between carbon materials and carbonaceous materials could be due to the different activation mechanisms. Further analysis found that there was no correlation between EEC and the reactive species derived from PMS, indicating that the produced reactive species was not only controlled by EEC. This study firstly elucidated the correlation between EEC and catalytic activity of HFCs, and |EDC-EAC| could be used as an index for evaluating the catalytic activity of HFCs.

Enigmatic persistence of aerobic methanotrophs in oxygen-limiting freshwater habitats.

Methanotrophic bacteria mitigate emissions of the potent greenhouse gas methane (CH4) from a variety of anthropogenic and natural sources, including freshwater lakes, which are large sources of CH4 on a global scale. Despite a dependence on dioxygen (O2) for CH4 oxidation, abundant populations of putatively aerobic methanotrophs have been detected within microoxic and anoxic waters and sediments of lakes. Experimental work has demonstrated active aerobic methanotrophs under those conditions, but how they are able to persist and oxidize CH4 under O2 deficiency remains enigmatic. In this review, we discuss possible mechanisms that underpin the persistence and activity of aerobic methanotrophs under O2-limiting conditions in freshwater habitats, particularly lakes, summarize experimental evidence for microbial oxidation of CH4 by aerobic bacteria under low or no O2, and suggest future research directions to further explore the ecology and metabolism of aerobic methanotrophs in O2-limiting environments.

An A-D-A'-D-A-Type Narrow Bandgap Electron Acceptor Based on Selenophene-Flanked Diketopyrrolopyrrole for Sensitive Near-Infrared Photodetection.

Near-infrared organic photodetectors possess great application potential in night vision, optical communication, and image sensing, but their development is limited by the lack of narrow bandgap organic semiconductors. A-D-A'-D-A-type molecules, featuring multiple intramolecular charge transfer effects, offer a robust framework for achieving near-infrared light absorption. Herein, we report a novel A-D-A'-D-A-type narrow bandgap electron acceptor named DPPSe-4Cl, which incorporates a selenophene-flanked diketopyrrolopyrrole (Se-DPP) unit as its central A' component. This molecule demonstrates exceptional near-infrared absorption properties with an absorption onset reaching 1120 nm and a low optical bandgap of 1.11 eV, owing to the strong electron-withdrawing ability and quinoidal resonance effect induced by the Se-DPP unit. By implementing a doping compensation strategy assisted by Y6 to reduce the trap density in the photoactive layer, the optimized organic photodetector based on DPPSe-4Cl exhibited efficient spectral response and remarkable sensitivity in the range of 300-1100 nm. Particularly, a specific detectivity surpassing 1012 Jones in the wavelength range of 410-1030 nm is achieved. This work offers a promising approach for developing highly sensitive visible to near-infrared broadband photodetection technology using organic semiconductors.

Simple-Structured Acceptor with Highly Interconnected Electron-Transport Pathway Enables High-Efficiency Organic Solar Cells.

Achieving desirable charge-transport highway is of vital importance for high-performance organic solar cells (OSCs). Here, it is shown how molecular packing arrangements can be regulated via tuning the alkyl-chain topology, thus resulting in a 3D network stacking and highly interconnected pathway for electron transport in a simple-structured nonfused-ring electron acceptor (NFREA) with branched alkyl side-chains. As a result, a record-breaking power conversion efficiency of 17.38% (certificated 16.59%) is achieved for NFREA-based devices, thus providing an opportunity for constructing low-cost and high-efficiency OSCs.

Influence of acetate-to-butyrate ratio on carbon chain elongation in anaerobic fermentation.

This study investigated the effect of electron acceptor (EA) distribution (acetate to butyrate ratio) on the carbon chain elongation (CCE) process. The results showed that the higher content of butyrate in the initial material led to the higher production of caproate. The maximum production of caproate was 3.74 ± 0.30 g·L-1, which was obtained when only butyrate was added as EA. Little caproate but much butyrate was produced where only acetate was added as EA. This indicated that CCE bacteria preferentially selected acetate as the EA to produce butyrate, and butyrate could be selected as EA to produce caproate only when the acetate content was much lower than butyrate. Unclassified_f_Dysgonomonadaceae, Massilibacterium, and Seramator were the predominant bacteria. Functional enzyme analysis showed that high butyrate content strengthened the fatty acid biosynthesis pathway and reverse ß-oxidization pathway. The findings showed the importance of butyrate in CCE for caproate production.

NO3- as an electron acceptor elevates antibiotic resistance gene and human bacterial pathogen risks in managed aquifer recharge (MAR): A comparison with O2.

Managed aquifer recharge (MAR) stands out as a promising strategy for ensuring water resource sustainability. This study delves into the comparative impact of nitrate (NO3-) and oxygen (O2) as electron acceptors in MAR on water quality and safety. Notably, NO3-, acting as an electron acceptor, has the potential to enrich denitrifying bacteria, serving as hosts for antibiotic resistance genes (ARGs) and enriching human bacterial pathogens (HBPs) compared to O2. However, a direct comparison between NO3- and O2 remains unexplored. This study assessed risks in MAR effluent induced by NO3- and O2, alongside the presence of the typical refractory antibiotic sulfamethoxazole. Key findings reveal that NO3- as an electron acceptor resulted in a 2 times reduction in dissolved organic carbon content compared to O2, primarily due to a decrease in soluble microbial product production. Furthermore, NO3- significantly enriched denitrifying bacteria, the primary hosts of major ARGs, by 747%, resulting in a 66% increase in the overall abundance of ARGs in the effluent of NO3- MAR compared to O2. This escalation was predominantly attributed to horizontal gene transfer mechanisms, as evidenced by a notable 78% increase in the relative abundance of mobile ARGs, alongside a minor 27% rise in chromosomal ARGs. Additionally, the numerous denitrifying bacteria enriched under NO3- influence also belong to the HBP category, resulting in a significant 114% increase in the abundance of all HBPs. The co-occurrence of ARGs and HBPs was also observed to intensify under NO3- influence. Thus, NO3- as an electron acceptor in MAR elevates ARG and HBP risks compared to O2, potentially compromising groundwater quality and safety.

Mechanism of Cr(VI) bioreduction by Clostridium sp. LQ25 under Fe(III) reducing conditions.

The Cr(VI) bioreduction has attracted widespread attention in the field of Cr(VI) pollution remediation due to its environmental friendliness. Further in-depth research on the reduction mechanisms is necessary to enhance the efficiency of Cr(VI) bioreduction. However, the limited research on Cr(VI) bioreduction mechanisms remains a bottleneck for the practical application of Cr(VI) reduction. In this study, The Cr(VI) reduction of strain LQ25 was significantly improved when Fe(III) was used as an electron acceptor, which increased by 1.6-fold maximum within the set Cr(VI) concentration range. Based on this, the electron transfer process of Cr(VI) reduction was analyzed using strain LQ25. Based on genomic data, flavin proteins were found to interact closely with electron transfer-related proteins using protein-protein interaction (PPi) analysis. Transcriptome analysis revealed that flavin synthesis genes (ribE, ribBA, and ribH) and electron transfer flavoprotein genes (fixA, etfA, fixB, and etfB) were significantly upregulated when Fe(III) was used as the electron acceptor. These results indicate that the fermentative dissimilatory Fe(III)-reducing bacterial strain LQ25 mainly uses flavin as an electron shuttle for electron transfer, which differs from the common use of cytochrome c in respiratory bacteria. These findings on the mechanism of Cr(VI) bioreduction provide technical support for improving the efficiency of Cr(VI) reduction which promote the practical application of Cr(VI) bioreduction in the field of Cr(VI) pollution remediation.

Morphology Control for Efficient Nonfused Acceptor-Based Organic Photovoltaic Cells.

Non-fused electron acceptors have huge advantages in fabricating low-cost organic photovoltaic (OPV) cells. However, morphology control is a challenge as non-fused C─C single bonds bring more molecular conformations. Here, by selecting two typical polymer donors, PBDB-TF and PBQx-TF, the blend morphologies and its impacts on the power conversion efficiencies (PCEs) of non-fused acceptor-based OPV cells are studied. A selenium-containing non-fused acceptor named ASe-5 is designed. The results suggest that PBQx-TF has a lower miscibility with ASe-5 when compared with PBDB-TF. Additionally, the polymer networks may form earlier in the PBQx-TF:ASe-5 blend film due to stronger preaggregation performance, leading to a more obvious phase separation. The PBQx-TF:ASe-5 blend film shows faster charge transfer and suppressed charge recombination. As a result, the PBQx-TF:ASe-5-based device records a good PCE of 14.7% with a higher fill factor (FF) of 0.744, while the PBDB-TF:ASe-5-based device only obtains a moderate PCE of 12.3% with a relatively low FF of 0.662. The work demonstrates that the selection of donors plays a crucial role in controlling the blend morphology and thus improving the PCEs of non-fused acceptor-based OPV cells.

A Pyrene-Fused Dimerized Acceptor for Ternary Organic Solar Cells with 19% Efficiency and High Thermal Stability.

A pyrene-fused dimerized electron acceptor has been successfully synthesized and subsequently incorporated as the third component in ternary organic solar cells (OSCs). Diverging from the traditional dimerized acceptors with a linear configuration, this novel electron acceptor displays a distinctive "butterfly-like" structure, comprising two Y-acceptors as wings fused with a pyrene-based backbone. The extended π-conjugated backbone and the electron-donating nature of pyrene enable the new acceptor to show low solubility, elevated glass transition temperature (Tg ), and low-lying frontier energy levels. Consequently, the new dimerized acceptor seamlessly integrates as the third component into ternary OSCs, enhancing electron transporting properties, reducing non-radiative voltage loss, and elevating open-circuit voltage. These merits have enabled the ternary OSCs to show an exceptional efficiency of 19.07%, a marked improvement compared to the 17.6% attained in binary OSCs. More importantly, the high Tg exhibited by the pyrene-fused electron acceptor helps to stabilize the morphology of the photoactive layer thermal-treated at 70 °C, retaining 88.7% efficiency over 600 hours. For comparison, binary OSCs experience a decline to 73.7% efficiency after the same duration. These results indicate that the "butterfly-like" design and the incorporation of a pyrene unit is a promising strategy in the development of dimerized electron acceptors for OSCs.

Synthesis and Characterization of Ionic Li+ @C70 Endohedral Fullerene.

Ion-endohedral-fullerene has attracted growing interest due to the unique electronic and structural characteristics arising from its distinctive ionic nature. Although there has been only one reported ion-encapsulated fullerene, Li+ @C60 , a significant number of fundamental and applied studies have been conducted, making a substantial impact not only in chemistry and physics but also across various interdisciplinary research fields. Nevertheless, studies on ion-endohedral fullerenes are still in their infancy due to the limitations in variety, and hence, it remains an open question how the size and symmetry of fullerene, as well as the motion and position of the encapsulated ion, affect their physical/chemical properties. Herein, we report the synthesis of lithium-ion-endohedral [70]fullerene (Li+ @C70 X- , X=PF6 - and TFSI- ), a novel ionic endohedral fullerene. X-ray crystallography confirmed the encapsulation of Li+ by C70 cage as well as its ion-pair structure stabilized by external TFSI- counter anion. The encapsulated Li+ drastically lowered the orbital energy of the C70 cage by Coulomb interactions but did not affect the orbital energy gap and degeneracy. DFT studies were also performed, which supported the experimentally observed electronic effects caused by the encapsulated Li+ .

Molecular insight into the vertical migration and degradation of dissolved organic matter in riparian soil profiles.

Due to the molecular complexity of dissolving organic matter (DOM), the vertical molecular distribution of riparian soil DOM (especially dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP)) in different land use types and their relationship with the bacterial community is still unclear. This study analyzed the spectral characteristics of riparian soil DOM from 0 to 100 cm in wild grassland, agricultural land, and bare land. The molecular distribution of DOM was revealed through Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and the specific relationship between DOM and bacterial community composition (BCC) was evaluated. The results showed that the DOM in the upper soil layer (0-40 cm) was mainly composed of recalcitrant macromolecular organics, while that in the lower layer (40-100 cm) was labile small molecular organics. In agricultural land, the total storage of DOM was lower than that in wild grassland, but with a higher abundance of recalcitrant organic carbon (lignin, etc.). At the same time, the bacterial community in agricultural land is shifting towards copiotrophs. In addition, the abundance of labile C degrading genes increases with nitrate as the main electron acceptor. However, sulfates are mainly used as electron acceptors in wild grasslands. Both DOP and DON were dominated by lignin and displayed higher chemical diversity in the upper soil. The bioavailability of DOP in three types of soil is higher than that of DON. DOM-BCC network analysis shows that the recalcitrant DON and DOP molecules in soil are positively correlated with phylum Actinobacteriota in agricultural land. These results emphasize that the DOM molecular characteristics were closely related to the function of the soil bacterial community.

Effect of electron acceptors on product selectivity and carbon flux in carbon chain elongation with Megasphaera hexanoica.

Megasphaera hexanoica is a bacterial strain following the reverse ß-oxidation pathway to synthesize caproate (CA) using lactate (LA) as an electron donor (ED) and acetate (AA) or butyrate (BA) as electron acceptors (EA). Differences in the type and concentration of EA lead to distinctions in product distribution and energy bifurcation of carbon fluxes in ED pathways, thereby affecting CA production. In this study, the effect of various ratios of AA, BA, and AA+BA as EA on carbon flux and CA specific titer during the carbon chain elongation in M. hexanoica was explored. The results indicated that the maximum levels of CA were 18.81 mM and 31.48 mM when the molar ratios of LA/AA and LA/BA were 10:1 and 3:1, respectively. Meanwhile, when AA and BA were used as combined EA (LA, AA, and BA molar amounts of 100, 23, and 77 mM), a maximum CA production of 39.45 mM was obtained. Further analysis revealed that the combined EA exhibited a CA production carbon flux of 49 % (4.3 % and 19.5 % higher compared to AA or BA, respectively) and a CA production specific titer of 45.24 mol (80.89 % and 58.51 % higher compared to AA or BA, respectively), indicating that the effective carbon utilization rate and CA production efficiency were greatly improved. Finally, a scaled-up experiment was conducted in a 1.2 L (working volume) automated bioreactor, implying high biomass (optical density at 600 nm or OD600 = 1.809) and a slight decrease in CA production (28.45 mM). A decrease in H2 production (4.11 g/m3) and an increase in CO2 production (0.632 g/m3) demonstrated the appropriate metabolic adaptation of M. hexanoica to environmental changes such as stirring shear.

Effects of electron acceptors and donors on anaerobic biodegradation of PAHs in marine sediments.

Polycyclic aromatic hydrocarbons (PAHs) are typical organic pollutants accumulated in the environment. PAHs' bioremediation in sediments can be promoted by adding electron acceptor (EA) and electron donor (ED). Bicarbonate and sulfate were chosen as two EAs, and acetate and lactate were selected as two EDs. Six groups of amendments were added into the sediments to access their role in the anaerobic biodegradation of five PAHs, containing phenanthrene, anthracene, fluoranthene, pyrene, and benzo[a]pyrene. The concentrations of PAHs, EAs and EDs, electron transport system activity, and microbial diversity were analyzed during 126-day biodegradation in serum bottles. The HA group (bicarbonate and acetate) achieved the maximum PAH degradation efficiency of 89.67 %, followed by the SL group (sulfate and lactate) with 87.10 %. As the main PAHs degrading bacteria, the abundance of Marinobacter in H group was 8.62 %, and the addition of acetate significantly increased the abundance of Marinobacter in the HA group by 75.65 %.

Study on the accelerated biodegradation of PAHs in subsurface soil via coupled low-temperature thermally treatment and electron acceptor stimulation based on metagenomic sequencing.

In situ anoxic bioremediation is a sustainable technology to remediate PAHs contaminated soils. However, the limited degradation rate of PAHs under anoxic conditions has become the primary bottleneck hindering the application of this technology. In this study, coupled low-temperature thermally treatment (<50 °C) and EA biostimulation was used to enhance PAH removal. Anoxic biodegradation of PAHs in soil was explored in microcosms in the absence and presence of added EAs at 3 temperatures (15 °C, 30 °C, and 45 °C). The influence of temperature, EA, and their interaction on the removal of PAHs were identified. A PAH degradation model based on PLSR analysis identified the importance and the positive/negative role of parameters on PAH removal. Soil archaeal and bacterial communities showed similar succession patterns, the impact of temperature was greater than that of EA. Soil microbial community and function were more influenced by temperature than EAs. Close and frequent interactions were observed among soil bacteria, archaea, PAH-degrading genes and methanogenic genes. A total of 15 bacterial OTUs, 1 PAH-degrading gene and 2 methanogenic genes were identified as keystones in the network. Coupled low-temperature thermally treatment and EA stimulation resulted in higher PAH removal efficiencies than EA stimulation alone and low-temperature thermally treatment alone.

Tuning the Nucleophilicity and Electrophilicity of Group 10 Elements through Substituent Effects: A DFT Study.

In this study, a series of electron donor (-NH2, -NMe2 and -tBu) and electron-withdrawing substituents (-F, -CN and -NO2) were used to tune the nucleophilicity or electrophilicity of a series of square planar Ni2+, Pd2+ and Pt2+ malonate coordination complexes towards a pentafluoroiodobenzene and a pyridine molecule. In addition, Bader's theory of atoms in molecules (AIM), noncovalent interaction plot (NCIplot), molecular electrostatic potential (MEP) surface and natural bond orbital (NBO) analyses at the PBE0-D3/def2-TZVP level of theory were carried out to characterize and discriminate the role of the metal atom in the noncovalent complexes studied herein. We hope that the results reported herein may serve to expand the current knowledge regarding these metals in the fields of crystal engineering and supramolecular chemistry.

Effect of electron acceptor addition on the temperature sensitivity of soil anaerobic carbon mineralization in the Yellow River Estuary wetland, China.

The temperature sensitivity of soil carbon mineralization (Q10) is an important index to evaluate the responses of ecosystem carbon cycling to climate change. We examined the effects of three electron acceptors [SO42-, NO3- and Fe(Ⅲ)] addition on the Q10 value of anaerobic carbon mineralization of Phragmites australis community soil (0-10 cm) in the Yellow River Estuary wetland with the closed culture-gas chromatography method. The results showed that the three electron acceptors addition inhibited the production of CO2 and CH4 during the 48-day culture period, with a decrease of 17.3%-20.8% for CO2 and 29.2%-36.2% for CH4. Generally, the CO2 production differed with the concentrations of electron acceptors, while CH4 production differed with the type of electron acceptors. The CO2:CH4 ratios were significantly different with temperature, indicating an obvious temperature dependence for the anaerobic carbon mineralization pathway. The Q10 values of CO2 and CH4 production under three electron acceptor additions ranged from 1.08 to 1.11 and from 1.19 to 1.37, respectively, showing an increasing trend compared with the control. The type and concentration of electron acceptors affected the temperature dependence of CO2 production, while electron acceptors affected that of CH4 production. It is suggested that the input of reducing salts would retard the mineralization loss of organic carbon in estuary freshwater wetlands under the background of climate change, but enhance the sensitivity of carbon mineralization to increasing temperature.

A Negatively Curved π-Expanded Pyracylene Comprising a Tropylium Cation.

We disclose π-expanded pyracylenes and their cationic species comprising 7-membered rings. The compounds were synthesized by stepwise oxidative cyclodehydrogenation to monitor the effect of successive cyclization on the structural and optoelectronic properties. As shown by X-ray crystallography, the complete cyclization leads to a boat-shaped scaffold featuring negative curvature provided by the 7-membered ring. The embedded tropone unit enabled the convenient generation of a stabilized tropylium cation, showing bathochromically shifted absorption bands reaching into the near-infrared region beyond 1000 nm. The altered structural features, supported by theoretical calculations, point towards the positively charged 7-membered ring having aromatic character.

Anaerobic oxidation of methane in terrestrial wetlands: The rate, identity and metabolism.

The recent discovery of anaerobic oxidation of methane (AOM) in freshwater ecosystems has caused a great interest in "cryptic methane cycle" in terrestrial ecosystems. Anaerobic methanotrophs appears widespread in wetland ecosystems, yet, the scope and mechanism of AOM in natural wetlands remain poorly understood. In this paper, we review the recent progress regarding the potential of AOM, the diversity and distribution, and the metabolism of anaerobic methanotrophs in wetland ecosystems. The potential of AOM determined through laboratory incubation or in situ isotopic labeling ranges from 1.4 to 704.0 nmol CH4·g-1 dry soil·d-1. It appears that the availability of electron acceptors is critical in driving different AOM in wetland soils. The environmental temperature and salinity exert a significant influence on AOM activity. Reversal methanogenesis and extracellular electron transfer are likely involved in the AOM process. In addition to anaerobic methanotrophic archaea, the direct involvement of methanogens in AOM is also probable. This review presented an overview of the rate, identity, and metabolisms to unravel the biogeochemical puzzle of AOM in wetland soils.