Natural Rubrolides and Their Synthetic Congeners as Inhibitors of the Photosynthetic Electron Transport Chain.

Rubrolides are a family of naturally occurring 5-benzylidenebutenolides, which generally contain brominated phenol groups, and nearly half of them also present a chlorine attached to the butenolide core. Seven natural rubrolides were previously synthesized. When these compounds were tested against the model plant Raphanus sativus, six were found to exert a slight inhibition on plant growth. Aiming to exploit their scaffold as a model for the synthesis of new compounds targeting photosynthesis, nine new rubrolide analogues were prepared. The synthesis was accomplished in 2-4 steps with a 10-39% overall yield from 3,4-dichlorofuran-2(5H)-one. All compounds were evaluated for their ability to inhibit the whole Hill reaction or excluding photosystem I (PSI). Several natural rubrolides and their analogues displayed good inhibitory potential (IC50 = 2-8 µM). Molecular docking studies on the photosystem II-light harvesting complex II (PSII-LHCII supercomplex) binding site were also performed. Overall, data support the use of rubrolides as a model for the development of new active principles targeting the photosynthetic electron transport chain to be used as herbicides.

The alternative enzymes-bearing tunicates lack multiple widely distributed genes coding for peripheral OXPHOS subunits.

The respiratory chain alternative enzymes (AEs) NDX and AOX from the tunicate Ciona intestinalis (Ascidiacea) have been xenotopically expressed and characterized in human cells in culture and in the model organisms Drosophila melanogaster and mouse, with the purpose of developing bypass therapies to combat mitochondrial diseases in human patients with defective complexes I and III/IV, respectively. The fact that the genes coding for NDX and AOX have been lost from genomes of evolutionarily successful animal groups, such as vertebrates and insects, led us to investigate if the composition of the respiratory chain of Ciona and other tunicates differs significantly from that of humans and Drosophila, to accommodate the natural presence of AEs. We have failed to identify in tunicate genomes fifteen orthologous genes that code for subunits of the respiratory chain complexes; all of these putatively missing subunits are peripheral to complexes I, III and IV in mammals, and many are important for complex-complex interaction in supercomplexes (SCs), such as NDUFA11, UQCR11 and COX7A. Modeling of all respiratory chain subunit polypeptides of Ciona indicates significant structural divergence that is consistent with the lack of these fifteen clear orthologous subunits. We also provide evidence using Ciona AOX expressed in Drosophila that this AE cannot access the coenzyme Q pool reduced by complex I, but it is readily available to oxidize coenzyme Q molecules reduced by glycerophosphate oxidase, a mitochondrial inner membrane-bound dehydrogenase that is not involved in SCs. Altogether, our results suggest that Ciona AEs might have evolved in a mitochondrial inner membrane environment much different from that of mammals and insects, possibly without SCs; this correlates with the preferential functional interaction between these AEs and non-SC dehydrogenases in heterologous mammalian and insect systems. We discuss the implications of these findings for the applicability of Ciona AEs in human bypass therapies and for our understanding of the evolution of animal respiratory chain.

Calorie restriction anti-hypertrophic effects are associated with improved mitochondrial content, blockage of Ca2+-induced mitochondrial damage, and lower reverse electron transport-mediated oxidative stress.

Calorie restriction is a nutritional intervention that reproducibly protects against the maladaptive consequences of cardiovascular diseases. Pathological cardiac hypertrophy leads to cellular growth, dysfunction (with mitochondrial dysregulation), and oxidative stress. The mechanisms behind the cardiovascular protective effects of calorie restriction are still under investigation. In this study, we show that this dietetic intervention prevents cardiac protein elevation, avoids fetal gene reprogramming (atrial natriuretic peptide), and blocks the increase in heart weight per tibia length index (HW/TL) seen in isoproterenol-induced cardiac hypertrophy. Our findings suggest that calorie restriction inhibits cardiac pathological growth while also lowering mitochondrial reverse electron transport-induced hydrogen peroxide formation and improving mitochondrial content. Calorie restriction also attenuated the opening of the Ca2+-induced mitochondrial permeability transition pore. We also found that calorie restriction blocked the negative correlation of antioxidant enzymes (superoxide dimutase and glutatione peroxidase activity) and HW/TL, leading to the maintenance of protein sulphydryls and glutathione levels. Given the nature of isoproterenol-induced cardiac hypertrophy, we investigated whether calorie restriction could alter cardiac beta-adrenergic sensitivity. Using isolated rat hearts in a Langendorff system, we found that calorie restricted hearts have preserved beta-adrenergic signaling. In contrast, hypertrophic hearts (treated for seven days with isoproterenol) were insensitive to beta-adrenergic activation using isoproterenol (50 nM). Despite protecting against cardiac hypertrophy, calorie restriction did not alter the lack of responsiveness to isoproterenol in isolated hearts harvested from isoproterenol-treated rats. These results suggest (through a series of mitochondrial, oxidative stress, and cardiac hemodynamic studies) that calorie restriction possesses beneficial effects against hypertrophic cardiomyopathy.

Short-term hyperoxia induced mitochondrial respiratory chain complexes dysfunction and oxidative stress in lung of rats.

BACKGROUND: Oxygen therapy is an alternative for many patients with hypoxemia. However, this practice can be dangerous as oxygen is closely associated with the development of oxidative stress. METHODS: Male Wistar rats were exposed to hyperoxia with a 40% fraction of inspired oxygen (FIO2) and hyperoxia (FIO2 = 60%) for 120 min. Blood and lung tissue samples were collected for gas, oxidative stress, and inflammatory analyses. RESULTS: Hyperoxia (FIO2 = 60%) increased PaCO2 and PaO2, decreased blood pH and caused thrombocytopenia and lymphocytosis. In lung tissue, neutrophil infiltration, nitric oxide concentration, carbonyl protein formation and the activity of complexes I and II of the mitochondrial respiratory chain increased. FIO2 = 60% decreased SOD activity and caused several histologic changes. CONCLUSION: In conclusion, we have experimentally demonstrated that short-term exposure to high FIO2 can cause oxidative stress in the lung.

Differential photosynthetic plasticity of Amazonian tree species in response to light environments.

To investigate how and to what extent there are differences in the photosynthetic plasticity of trees in response to different light environments, six species from three successional groups (late successional, mid-successional, and pioneers) were exposed to three different light environments [deep shade - DS (5% full sunlight - FS), moderate shade - MS (35% FS) and full sunlight - FS]. Maximum net photosynthesis (Amax), leaf N partitioning, stomatal, mesophile, and biochemical limitations (SL, ML, and BL, respectively), carboxylation velocity (Vcmax), and electron transport (Jmax) rates, and the state of photosynthetic induction (IS) were evaluated. Higher values of Amax, Vcmax, and Jmax in FS were observed for pioneer species, which invested the largest amount of leaf N in Rubisco. The lower IS for pioneer species reveals its reduced ability to take advantage of sunflecks. In general, the main photosynthetic limitations are diffusive, with SL and ML having equal importance under FS, and ML decreasing along with irradiance. The leaf traits, which are more determinant of the photosynthetic process, respond independently in relation to the successional group, especially with low light availability. An effective partitioning of leaf N between photosynthetic and structural components played a crucial role in the acclimation process and determined the increase or decrease of photosynthesis in response to the light conditions.

In situ short-term responses of Amazonian understory plants to elevated CO2.

The response of plants to increasing atmospheric CO2 depends on the ecological context where the plants are found. Several experiments with elevated CO2 (eCO2) have been done worldwide, but the Amazonian forest understory has been neglected. As the central Amazon is limited by light and phosphorus, understanding how understory responds to eCO2 is important for foreseeing how the forest will function in the future. In the understory of a natural forest in the Central Amazon, we installed four open-top chambers as control replicates and another four under eCO2 (+250 ppm above ambient levels). Under eCO2, we observed increases in carbon assimilation rate (67%), maximum electron transport rate (19%), quantum yield (56%), and water use efficiency (78%). We also detected an increase in leaf area (51%) and stem diameter increment (65%). Central Amazon understory responded positively to eCO2 by increasing their ability to capture and use light and the extra primary productivity was allocated to supporting more leaf and conducting tissues. The increment in leaf area while maintaining transpiration rates suggests that the understory will increase its contribution to evapotranspiration. Therefore, this forest might be less resistant in the future to extreme drought, as no reduction in transpiration rates were detected.

The mitochondrial respiratory chain from Rhodotorula mucilaginosa, an extremophile yeast.

Rhodotorula mucilaginosa survives extreme conditions through several mechanisms, among them its carotenoid production and its branched mitochondrial respiratory chain (RC). Here, the branched RC composition was analyzed by biochemical and complexome profiling approaches. Expression of the different RC components varied depending on the growth phase and the carbon source present in the medium. R. mucilaginosa RC is constituted by all four orthodox respiratory complexes (CI to CIV) plus several alternative oxidoreductases, in particular two type-II NADH dehydrogenases (NDH2) and one alternative oxidase (AOX). Unlike others, in this yeast the activities of the orthodox and alternative respiratory complexes decreased in the stationary phase. We propose that the branched RC adaptability is an important factor for survival in extreme environmental conditions; thus, contributing to the exceptional resilience of R. mucilaginosa.

Introduction of a terminal electron sink in chloroplasts decreases leaf cell expansion associated with higher proteasome activity and lower endoreduplication.

Foliar development involves successive phases of cell proliferation and expansion that determine the final leaf size, and is characterized by an early burst of reactive oxygen species generated in the photosynthetic electron transport chain (PETC). Introduction of the alternative PETC acceptor flavodoxin in tobacco chloroplasts led to a reduction in leaf size associated to lower cell expansion, without affecting cell number per leaf. Proteomic analysis showed that the biogenesis of the PETC proceeded stepwise in wild-type leaves, with accumulation of light-harvesting proteins preceding that of electron transport components, which might explain the increased energy and electron transfer to oxygen and reactive oxygen species build-up at this stage. Flavodoxin expression did not affect biogenesis of the PETC but prevented hydroperoxide formation through its function as electron sink. Mature leaves from flavodoxin-expressing plants were shown to contain higher levels of transcripts encoding components of the proteasome, a key negative modulator of organ size. Proteome profiling revealed that this differential accumulation was initiated during expansion and led to increased proteasomal activity, whereas a proteasome inhibitor reverted the flavodoxin-dependent size phenotype. Cells expressing plastid-targeted flavodoxin displayed lower endoreduplication, also associated to decreased organ size. These results provide novel insights into the regulation of leaf growth by chloroplast-generated redox signals, and highlight the potential of alternative electron shuttles to investigate the link(s) between photosynthesis and plant development.

The branched mitochondrial respiratory chain from the jellyfish Stomolophus sp2 as a probable adaptive response to environmental changes.

During their long evolutionary history, jellyfish have faced changes in multiple environmental factors, to which they may selectively fix adaptations, allowing some species to survive and inhabit diverse environments. Previous findings have confirmed the jellyfish's ability to synthesize large ATP amounts, mainly produced by mitochondria, in response to environmental challenges. This study characterized the respiratory chain from the mitochondria of the jellyfish Stomolophus sp2 (previously misidentified as Stomolophus meleagris). The in-gel activity from isolated jellyfish mitochondria confirmed that the mitochondrial respiratory chain contains the four canonical complexes I to IV and F0F1-ATP synthase. Specific additional activity bands, immunodetection, and mass spectrometry identification confirmed the occurrence of four alternative enzymes integrated into a branched mitochondrial respiratory chain of Stomolophus sp2: an alternative oxidase and three dehydrogenases (two NADH type II enzymes and a mitochondrial glycerol-3-phosphate dehydrogenase). The analysis of each transcript sequence, their phylogenetic relationships, and each protein's predicted models confirmed the mitochondrial alternative enzymes' identity and specific characteristics. Although no statistical differences were found among the mean values of transcript abundance of each enzyme in the transcriptomes of jellyfish exposed to three different temperatures, it was confirmed that each gene was expressed at all tested conditions. These first-time reported enzymes in cnidarians suggest the adaptative ability of jellyfish's mitochondria to display rapid metabolic responses, as previously described, to maintain energetic homeostasis and face temperature variations due to climate change.

Designing Quantum Capacitive Peptide Interfaces for Electroanalytical Applications.

Redox-active moieties assembled on metallic interfaces have been shown to follow quantum mechanical rules, where the quantum capacitance of the interface (directly associated with the electronic structure of the redox-active moieties) plays a key role in the electron transfer dynamics of the interface. Modifying these interfaces with biological receptors has significant advantages (simplifying molecular diagnostics methods, reducing size, time, and cost while maintaining high sensitivity), enabling the fabrication of miniaturized electroanalytical devices that can compete with traditional ELISA and RT-PCR benchtop assay methods. Owing to their intrinsic characteristics, the use of peptide-based redox-active moieties is a promising chemical route for modifying metallic surfaces, resulting in a high quantum capacitive signal sensitivity. In the present work, different ferrocene-tagged peptides with a structure of Fc-Glu-XX-XX-Cys-NH2 (XX = serine, phenylalanine, glycine) were used to form self-assembled monolayers on gold. The feasibility of using these interfaces in an electroanalytical assay was verified by detecting the NS1 DENV (Dengue Virus) biomarker to compare the efficiency of peptide structures for biosensing purposes. Parameters such as the formal potential of the interface, normalized electronic density of states (DOS), quantum capacitance, and electron transfer rate constants were obtained for Ser-, Phe-, and Gly-peptides. The Gly-peptide structure presented the highest analytical performance for sensing NS1 with a sensitivity of 5.6% per decade and the lowest LOD (1.4 ng mL-1) and LOQ (2.6 ng mL-1), followed by Phe-peptide, whereas Ser-peptide had the lowest performance. This work demonstrates that the use of peptides to fabricate a self-assembled monolayer as a biosensor component has advantages for low-cost point-of-care diagnostics. It also shows that the performance of the sensing interface depends strongly on how the chemistry of the surface is designed as a whole, not only on the redox-active group.

Molecular Recognition Study toward the Mitochondrial Electron Transport Chain Inhibitor Mubritinib and Human Serum Albumin.

The ability to bind plasma proteins helps in comprehending relevant aspects related to the pharmacological properties of many drugs. Despite the vital role of the drug mubritinib (MUB) in the prophylaxis of various diseases, its interaction with carrier proteins still needs to be clarified. The present work focuses on the interaction between MUB and Human serum albumin (HSA), investigated by employing multispectroscopic, biochemical, and molecular docking approaches. The results reveal that MUB has quenched HSA intrinsic fluorescence (following a static mechanism) by attaching very close (r = 6.76 Å) and with moderate affinity (Kb ≈ 104 M-1) to the protein site I (mainly by H-bonds, hydrophobic and Van der Waals forces). On one side, the HSA-MUB interaction has been accompanied by a slight disturbance in the HSA chemical environment (around the Trp residue) and protein secondary structure modifications. On another side, MUB competitively inhibits HSA esterase-like activity, which is very similar to other Tyrosine kinase inhibitors, and evidence that protein functional alterations have been triggered by MUB interaction. In summary, all of the presented observations can shed light on diverse pharmacological factors associated with drug administration.

The Molecular Basis of Organic Chemiluminescence.

Bioluminescence (BL) and chemiluminescence (CL) are interesting and intriguing phenomena that involve the emission of visible light as a consequence of chemical reactions. The mechanistic basis of BL and CL has been investigated in detail since the 1960s, when the synthesis of several models of cyclic peroxides enabled mechanistic studies on the CL transformations, which led to the formulation of general chemiexcitation mechanisms operating in BL and CL. This review describes these general chemiexcitation mechanisms-the unimolecular decomposition of cyclic peroxides and peroxide decomposition catalyzed by electron/charge transfer from an external (intermolecular) or an internal (intramolecular) electron donor-and discusses recent insights from experimental and theoretical investigation. Additionally, some recent representative examples of chemiluminescence assays are given.

Antioxidant activity and enzymatic of lichen substances: A study based on cyclic voltammetry and theoretical.

The antioxidant activity of nine lichen substances, including methylatrarate (1), methyl haematommate (2), lobaric acid (3), fumarprotocetraric acid (4), sphaerophorin (5), subsphaeric acid (6), diffractaic acid (7), barbatolic acid (8) and salazinic acid (9) has been determined through cyclic voltammetry. The compounds 1-4 presented slopes close to the Nernst constant of 0.059 V, indicating a 2H+/2e- relation between protons and electrons, as long as the compounds 5, 6, 7, 8, and 9 present slopes between 0.037 V and 0.032 V, indicating a 1H+/2e- relation between protons and electrons. These results show a high free radical scavenging activity by means of the release of H+, suggesting an important antioxidant capacity of these molecules. Theoretical calculations of hydrogen bond dissociation enthalpies (BDE), proton affinities (PA), and Proton Transfer (PT) mechanisms, at M06-2x/6-311+G(d,p) level complement the experimental results. Computations support that the best antioxidant activity is obtained for the molecules (3, 4, 5, 6, 7 and 8), that have a carboxylic acid group close to a phenolic hydroxyl group, through hydrogen atomic transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanisms. Additional computations were performed for modelling binding affinity of the lichen substances with CYPs enzymes, mainly CYP1A2, CYP51, and CYP2C9*2 isoforms, showing strong affinity for all the compounds described in this study.

Correlating Coffea canephora 3D architecture to plant photosynthesis at a daily scale and vegetative biomass allocation.

Coffea canephora (C. canephora) has two botanical varieties, Robusta and Conilon. Intraspecific variability was hypothesized and projected for the selection of C. canephora plants able to maintain production in the context of global climate changes. For that, architectural, C-assimilation and biomass analyses were performed on 17-month-old Robusta (clones 'A1' and '3 V') and Conilon (clones '14' and '19') varieties grown in non-limiting soil, water and mineral nutrient conditions. Nondestructive coffee plant architecture coding, reconstruction and plant photosynthesis estimations were performed using a functional-structural plant modeling platform OpenAlea. 3D reconstructions and inclusion of parameters calculated and estimated from light response curves, such as dark respiration (Rd), maximum rate of carboxylation of RuBisCO and photosynthetic electron transport allowed the estimation of instantaneous and daily plant photosynthesis. The virtual orchard leaf area index was low, and light was not a limiting factor in early C. canephora development stages. Under such conditions, Robusta assimilated more CO2 at the plant and orchard scale and produced higher total biomass than Conilon. Lower plant daily photosynthesis and total biomass were correlated to higher Rd in Conilon than in Robusta. Among the architectural traits, leaf inclination, size and allometry were most highly correlated with plant assimilation and biomass. Relative allocation in leaf biomass was higher in '19' Conilon than in young Robusta plants, indicating intraspecific biomass partitioning. Similarly, variation in relative distribution of the root biomass and the root volume reflected clonal variation in soil occupation, indicating intraspecific variability in space occupation competitiveness. Coffea canephora denoted high root allocation in both Conilon and Robusta clones. However, relevant differences at subspecific levels were found, indicating the high potential of C. canephora to cope with drought events, which are expected to occur more frequently in the future, because of climate changes. The methodology developed here has the potential to be used for other crops and tree species. Highlights Functional-structural plant model was used to estimate photosynthesis on a plant and daily scales in Coffea canephora (C. canephora). Among the architectural traits, leaf shape and inclination had the most impact on photosynthesis and biomass. Under non-limiting conditions, Robusta had higher plant photosynthesis and biomass than Conilon. A higher leaf biomass allocation in Conilon clone '19' than in Robusta suggested variety-specific partitioning. Variation in the relative distribution of the root biomass indicated C. canephora intraspecific soil occupation variability.

Environmentally relevant copper concentrations stimulate photosynthesis in Monoraphidium sp.

Microalgae require copper (Cu) in trace levels for their growth and metabolism, it is a vital component of certain metalloproteins. Although this element has been widely studied concerning microalgae physiology, the effects of environmentally relevant levels have been less studied. We studied the photosynthesis and growth of the Chlorophyte Monoraphidium sp. exposed to Cu ranging from low (1.7 nM) to high (589.0 nM) free Cu ions (Cu2+) concentrations. The growth rate was unaffected by Cu concentrations in the range of 1.7-7.4 nM Cu2+, but decreased beyond it. The relative maximum electron transport rate (rETRm), saturation irradiance (Ek), photochemical quenching (qP and qL), and PSII operating efficiency [Formula: see text] were stimulated in the 3.4-7.4 nM Cu2+ range, concentrations slightly higher than the control, whereas non-photochemical quenching (NPQ) gradually increased with increasing Cu2+. The photosystem II antenna size [Sigma (II)440] increased under high Cu (589.0 nM), which resulted in a decrease in the quinone A (QA) reduction time (tau). In contrast, the QA re-oxidation time was unaffected by Cu exposure. These findings show that a slight increase in Cu stimulated photosynthesis in Monoraphidium sp., whereas high Cu reduced photosynthesis and increased the dissipation of captured light energy. This research is a contribution to the understanding of the dynamic photo-physiological responses of Monoraphidium sp. to Cu ions.

Study of the Electrochemical Behavior of N-Substituted-4-Piperidones Curcumin Analogs: A Combined Experimental and Theoretical Approach.

The electrochemical behavior of N-methyl- and N-benzyl-4-piperidone curcumin analogs were studied experimentally and theoretically. The studied compounds present different substituents at the para position in the phenyl rings (-H, -Br, -Cl, -CF3, and -OCH3). We assessed their electrochemical behavior by differential pulse and cyclic voltammetry, while we employed density functional theory (DFT) M06 and M06-2x functionals along with 6-311+G(d,p) basis set calculations to study them theoretically. The results showed that compounds suffer a two-electron irreversible oxidation in the range of 0.72 to 0.86 V, with surface concentrations ranging from 1.72 × 10-7 to 5.01 × 10-7 mol/cm2. The results also suggested that the process is diffusion-controlled for all compounds. M06 DFT calculations showed a better performance than M06-2x to obtain oxidation potentials. We found a good correlation between the experimental and theoretical oxidation potential for N-benzyl-4-piperidones (R2 = 0.9846), while the correlation was poor for N-methyl-4-piperidones (R2 = 0.3786), suggesting that the latter suffer a more complex oxidation process. Calculations of the BDEs for labile C-H bonds in the compounds suggested that neither of the two series of compounds has a different tendency for a proton-coupled electron transfer (PCET) oxidation process. It is proposed that irreversible behavior is due to possible dimerization of the compounds by Shono-type oxidation.

Photosynthetic electron transport rate and root dynamics of finger millet in response to Trichoderma harzianum.

Finger millet (ragi) is the main food grain for many people, especially in the arid and semiarid regions of developing countries in Asia and Africa. The grains contain an exceptionally higher amount of Ca (>300 mg/100 g) when compared to other major cereals. For sustainable production of ragi in the current scenario of climate change, this study aimed to evaluate the impact of Trichoderma harzianum (TRI) on ragi performance. The performance of photosynthetic pigment pool, photosynthetic apparatus, and root dynamics of three varieties of ragi (PRM-1, PRM-701, and PRM-801) in response to four treatments viz., C (soil), S+ TRI (soil + Trichoderma), farmyard manure (soil+ FYM), and FYM+TRI (Soil + FYM + Trichoderma) were studied. Results have shown a significant increase in the photosynthetic pigment pool and optimized functional and structural integrity of the photosynthetic apparatus in response to the combination of farmyard manure (FYM) with TRI. Higher yield parameters viz., φ(Po) and φ(Eo), δ(Ro), efficiency ψ(Eo), performance indices - PIabs and PItotal, and enhanced root canopy and biomass were observed in all three varieties. Improved electron transport from PSII to PSI, root canopy and biomass, may also suitably favor biological carbon sequestration to retain soil health and plant productivity in case grown in association with FYM and TRI.

Separation and analysis of Bacillus subtilis respiratory chain complexes.

Bacillus subtilis is a Gram-positive bacterium with a respiratory chain embedded in the cytoplasmic membrane. The respiratory chain is bifurcated after menaquinol into a cytochrome b6c + caa3 branch and a branch with up to three quinol oxidases. The complexes that generate the proton gradient are b6c, associated with caa3 and aa3 oxidase. The b6c and caa3 complexes form a supercomplex, and it is proposed to form respiratory strings in the membrane. There is still information missing about the quinol branch and if the primary oxidase quinol aa3 is associated with the electron donor complexes. It is unclear whether succinate quinone reductase (SQR) can form associations with the quinol branch or the cytochrome branch. In this paper, we show the separation of an almost pure b6c complex associated with cytochromes c550 and c551. We obtained a b6c + caa3 supercomplex of 600 kDa and SQR, aa3, and NADH dehydrogenase by dodecyl maltoside solubilization and separation of the respiratory chain components by ionic exchange chromatography. We found that aa3 does not associate with other complexes. SQR was associated with the b6c complex in a mutant lacking aa3. This association could facilitate electron transfer from SQR to menaquinone-7. The lack of associations between the abundant quinol oxidase aa3 and other complexes is a feature we cannot explain yet.

The role of iron nanoparticles on anaerobic digestion: mechanisms, limitations, and perspectives.

Anaerobic digestion (AD) is the most widely used technology for organic matter treatment. However, multiple types of research have reported on improving the process because different operation inhibition factors and limitations affect the performance of AD process. Owing to the increasing use of iron-nanoparticles (Fe-NP) on AD, this review addresses the knowledge gaps and summarizes the finding from academic articles based on (i) the AD upgrading operations: limitations and upgrade techniques, (ii) Fe-NPs mechanisms on AD, (iii) Fe-NP effect on microbial communities associated to AD systems, and (iv) perspectives. The selected topics give the Fe-NP positive effects on the AD methane-production process in terms of gas production, effluent quality, and process optimization. The main results of this work indicate that (i) Fe-NP addition can be adapted among different feedstocks and complement other pretreatments, (ii) Fe-NP physicochemical characteristics enhance biogas production via direct interspecies electron transfer (DIET) mechanisms, and Fe-ion release due to their structure and their conductivity capability, and (iii) syntrophic bacteria and acetoclastic methanogens have been reported as the communities that better uptake Fe-NPs on their metabolisms. Finally, our research perspectives and gaps will be discussed to contribute to our knowledge of using Fe-NPs on AD systems.

Chalcogen Atoms as Electron Donors in Proton-Coupled Electron Transfer Reactions.

Proton-coupled electron transfer (PCET) reactions are crucial for the optimal functioning of a broad scope of chemical and biological processes. In this report, we present an unprecedented type of concerted PCET (cPCET), in which a chalcogen atom acts as the electron donor. The nature of this mechanism is key for understanding the reactivity of different radical-trapping antioxidants having heavy chalcogens (S, Se, or Te) in their structures. Moreover, this chalcogen-assisted cPCET is likely to be occurring in multiple systems of biological interest.