Chain Elongation Research Articles

Impact of cell voltage on synthesis of caproic acid from carbon dioxide and ethanol in direct current powered microbial electrosynthesis cell

Production of medium chain fatty acids (MCFAs) from CO2 through microbial electrosynthesis (MES) holds great potential. The present study investigated the effect of cathode voltages of − 0.8 V (MES-1), −1.0 V (MES-2) and −1.2 V vs Ag/AgCl (MES-3), on the production of MCFAs from CO2 and ethanol using an enriched culture. Direct current (DC) power supply was used to maintain constant cathode voltages. The highest amounts of caproic acid were produced in MES-2 at an average concentration of 1.51 ± 0.14 g/L with a maximum selectivity of 68 ± 7 %. Microbial diversity analysis showed abundance of the Clostridiaceae family that allowed chain elongation in all MES reactors. This study shows that potentiostatic control approach for MCFA synthesis, can be replaced by DC power supply in future MES setups. Using selective culture enrichment, MES efficiently produces MCFAs from CO2 and ethanol, with −1.0 V yielding the highest caproic acid.

Advanced Statistical Optimization for Enhanced Medium-Chain Fatty Acid Production

In recent years, the development of feed ingredients with natural additives has gained significant importance in increasing the health and quality of animal products, as well as in promoting weight gain in animals. Since Salmonella infection is a significant disease that transmits from animals to humans, the inhibition of Salmonella species can be achieved particularly through the improvement of gastrointestinal metabolism in chickens. At this point, the effectiveness of using MCFA (Medium Chain Fatty Acids) as a feed additive has been proven. MCFA are composed of a mixture of various fatty acids, including acetic acid, butyric acid, hexanoic acid, etc. Highest portion of MCFA are hexanoic acid. Besides feed additives hexanoic acid play a crucial role as primary resources in various industries, including the chemical, food, agricultural, and biofuel sectors. It is typically obtained from petrochemical-based solutions but there has been a growing focus on biotechnological production and natural sources in recent years. One of the mostly known bioprocess to produce MCFA is chain elongation (conversion of acetate and ethanol into MCFA by β oxidation reaction) by Clostridium kluyveri. However, as in most biotechnological processes, there are low yields and high costs in these reactions as well. In this study, Box-Behnken Design, a statistical experimental design method, was used to optimize the concentrations of acetate, ethanol (the two primary components of chain elongation reactions) and pH for MCFA production via chain elongation reactions with Clostridium kluyveri. Batch experiments were performed at 30°C and 37°C to also see the effect of temperature. Higher values of hexanoic acid and bacterial growth were observed at 37°C. From an economic perspective, a 14% reduction in costs has been observed with optimized components.

Caproate production from the mixture of corn straw and food waste via chain elongation with reinforcement of biofilm

As a precursor, caproate is widely used in food and medicine for production of various valuable products. From an environmental point of view, caproate production by anaerobic fermentation is a sustainable way. The cost of caproate could be reduced if the wasted biomass is used as substrate. In this study, the caproate production from corn straw and food waste was investigated. Results showed that the sulfuric acid – enzyme method was the optimum approach for hydrolysis of corn straw, and the corresponding glucose concentration was 24.3 g/L. At the optimum condition, the 5-hydroxymethyl furfural (HMF) was found to be the main inhibitor of the hydrolysate, which exhibited inhibitory effect to ethanol and caproate fermentation. Further analysis showed that the inhibition threshold of HMF to Clostridium kluyveri was 1.2 g/L. The formation of biofilm in the fermentation system was found to be an effective way for improving the robustness of cells to inhibitors. The caproate production of 13.5 g/L was obtained when the ethanol and acetate derived from corn straw and food waste was used as substrates. This study cast an insight that it was a promising way for caproate production from the corn straw and food waste.

The role of human papillomavirus in laryngeal carcinoma using PCR

<b>Introduction:</b> The etiology of laryngeal carcinoma is multifactorial. Smoking and alcoholism are well-known risk factors; however, recently oncogenic human papillomavirus has been suggested to promote carcinogenesis. PCR has had the most dramatic impact on molecular biology, enabling the amplification of specific regions of interest and detection of gene sequences.<b>Aim:</b> The aims are to evaluate the possible relationship between laryngeal carcinoma and human papillomavirus and its impact on the socio-demographic findings and the clinicopathological presentation.<b>Material and method:</b> Twenty-five patients with laryngeal carcinoma were included. Two biopsies were taken from every patient, the first from the main bulk of the tumor, the second from the normal surrounding mucosal tissues and considered as a control group. Virus detection was done by PCR test. The HPV screen test is an <i>in vitro</i> nucleic acid amplification test for qualitative detection of HPV type (16, 18, 31, 33, 35, 39, 45, 52, 53, 56, 58, 59, 66, and 70) and β-globin gene used as internal control. Samples were transferred into the thermal cycler, in which denaturation, annealing, and chain elongation occurred. Specific bands of HPV were detected using a high-resolution Cannon camera.<b>Results:</b> The average age of the patients was 60.8 years. Twenty-three patients (92%) were males. Viral DNA was detected in 8% of patients, representing genotypes (16, 18, 31, 33, 35, 39, 45, 52, 53, 56, 58, 59, 66, and 70). There is no statistically significant relationship between the presence of the virus and epidemiological and clinic-pathological features except for female gender distribution (P-value = 0.022).<b>Conclusions:</b> There is no significant relationship between laryngeal carcinoma and human papillomavirus, nor a significant impact on socio-demographic findings and clinicopathological presentation.

Variability in n-caprylate and n-caproate producing microbiomes in reactors with in-line product extraction.

Medium-chain carboxylates (MCCs) are used in various industrial applications. These chemicals are typically extracted from palm oil, which is deemed not sustainable. Recent research has focused on microbial chain elongation using reactors to produce MCCs, such as n-caproate (C6) and n-caprylate (C8), from organic substrates such as wastes. Even though the production of n-caproate is relatively well-characterized, bacteria and metabolic pathways that are responsible for n-caprylate production are not. Here, three 5 L reactors with continuous membrane-based liquid-liquid extraction (i.e., pertraction) were fed ethanol and acetate and operated for an operating period of 234 days with different operating conditions. Metagenomic and metaproteomic analyses were employed. n-Caprylate production rates and reactor microbiomes differed between reactors even when operated similarly due to differences in H2 and O2 between the reactors. The complete reverse β-oxidation (RBOX) pathway was present and expressed by several bacterial species in the Clostridia class. Several Oscillibacter spp., including Oscillibacter valericigenes, were positively correlated with n-caprylate production rates, while Clostridium kluyveri was positively correlated with n-caproate production. Pseudoclavibacter caeni, which is a strictly aerobic bacterium, was abundant across all the operating periods, regardless of n-caprylate production rates. This study provides insight into microbiota that are associated with n-caprylate production in open-culture reactors and provides ideas for further work.IMPORTANCEMicrobial chain elongation pathways in open-culture biotechnology systems can be utilized to convert organic waste and industrial side streams into valuable industrial chemicals. Here, we investigated the microbiota and metabolic pathways that produce medium-chain carboxylates (MCCs), including n-caproate (C6) and n-caprylate (C8), in reactors with in-line product extraction. Although the reactors in this study were operated similarly, different microbial communities dominated and were responsible for chain elongation. We found that different microbiota were responsible for n-caproate or n-caprylate production, and this can inform engineers on how to operate the systems better. We also observed which changes in operating conditions steered the production toward and away from n-caprylate, but more work is necessary to ascertain a mechanistic understanding that could be predictive. This study provides pertinent research questions for future work.

Temperature is an underestimated parameter to regulate the start-up of enhanced carbon chain elongation

Temperature is an important environmental factor for optimized bioreactions. In this study, seven temperatures between 25 and 55 °C were undertaken to explore the product spectrums of carbon chain elongation in a mixed culture. Temperature was manifested to significantly affect the production rate, productivity, and selectivity of carbon chain elongation. 40 °C resulted in the highest caproate concentration (138.94 mmol-C/L) and the highest caproate selectivity up to 84.5 %. Combining microbial quantitative and diversity analysis, it was identified that the optimized temperature was owing to the competitive abilities of metabolically different species. The dominant bio-elongation Clostridium kluyveri preferred 35–45 °C. The competitive fermentative bacteria Clostridium magnum and Clostridium butyricum for acetate and butyrate anabolism preferred 25–35 °C, therefore, excluding lower temperature bio-elongation because of more acetate and butyrate conversion but not caproate. Metabolically diverse Pseudomonas sp was abundant at higher temperatures (50–55 °C) and longer duration, therefore, excluding thermophilic bio-elongation because of reduced caproate productivity.

Proton-Coupled Electron Transfer on Cu2O/Ti3C2Tx MXene for Propane (C3H8) Synthesis from Electrochemical CO2 Reduction.

Electrochemical CO2 reduction reaction (CO2RR) to produce value-added multi-carbon chemicals has been an appealing approach to achieving environmentally friendly carbon neutrality in recent years. Despite extensive research focusing on the use of CO2 to produce high-value chemicals like high-energy-density hydrocarbons, there have been few reports on the production of propane (C3H8), which requires carbon chain elongation and protonation. A rationally designed 0D/2D hybrid Cu2O anchored-Ti3C2Tx MXene catalyst (Cu2O/MXene) is demonstrated with efficient CO2RR activity in an aqueous electrolyte to produce C3H8. As a result, a significantly high Faradaic efficiency (FE) of 3.3% is achieved for the synthesis of C3H8 via the CO2RR with Cu2O/MXene, which is ≈26 times higher than that of Cu/MXene prepared by the same hydrothermal process without NH4OH solution. Based on in-situ attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and density functional theory (DFT) calculations, it is proposed that the significant electrocatalytic conversion originated from the synergistic behavior of the Cu2O nanoparticles, which bound the *C2 intermediates, and the MXene that bound the *CO coupling to the C3 intermediate. The results disclose that the rationally designed MXene-based hybrid catalyst facilitates multi-carbon coupling as well as protonation, thereby manipulating the CO2RR pathway.

New insight into process pH regulation on caproate production from waste activated sludge acidogenic fermentation liquid by cathodic electro-fermentation

Cathodic electro-fermentation (CEF) has been proven to enhance the production of caproate from biowaste by improving chain elongation metabolism. However, the impact of process pH control in catholyte to avoid pH changes caused by redox reactions under polarized cathode on chain elongation has been rarely reported. Here the caproate production performances from waste activated sludge acidogenic fermentation liquid were evaluated and compared between different process pHs of 5.5, 6.0, and 6.5 with control group at 0.9 V. Results demonstrated the maximum caproate concentration was reached 4.1 g/L at pH 6.0, which was significantly higher than the 2.7 g/L of the control group, indicating the benefits of pH control on chain elongation metabolism in CEF. Mechanisms analysis revealed that the enhancement of pH regulation was attributed to the enrichment of organic degraders (Pseudomonas) in catholyte and the increased metabolic activity (like acetyl-CoA carboxylase) of chain elongator (Clostridium_sensus_stricto_12) on biofilm. These results were evidenced by the improved release and conversion performance of substrates (especially the amino acids) in catholyte and the enhanced biofilm activity. Hence, this study contributes novel insights to the pH regulation of chain elongation for enhancing caproate production from biowaste by electro-fermentation.

Molecular Identification and Functional Characterization of LC-PUFA Biosynthesis Elongase (elovl2) Gene in Chinese Sturgeon (Acipenser sinensis).

Elongases of very-long-chain fatty acids (Elovls) are critical rate-limiting enzymes that are involved in LC-PUFA biosynthesis through catalyzing the two-carbon elongation of a pre-existing fatty acyl chain. Thus far, several Elovls have been extensively studied in teleost. However, the functional and physiological roles of Elovls in chondrichthyans have rarely been reported. In this study, we identified and characterized elovl2 from the endangered Chinese sturgeon (Acipenser sinensis) by whole genome scanning. The results show that the coding sequence of elovl2 was 894 bp in length, for a putative protein of 297 amnio acids. Comparative genomic analyses indicated that Chinese sturgeon elovl2 was evolutionarily conserved. Functional characterization in yeast demonstrated that the Chinese sturgeon Elovl2 could efficiently elongate C20 (ARA and EPA) and C22 (22:4n-6 and 22:5n-3) substrates, confirming its critical roles in LC-PUFA biosynthesis. Spatial and temporal expression analyses showed high elovl2 mRNA levels were detected in the liver and brain and showed an increase trend both in embryonic and post-hatching stages. Interestingly, diets with vegetable oils as lipid sources could significantly induce the high expression of elovl2 in Chinese sturgeon, implying that the endogenous LC-PUFA biosynthesis pathway was stimulated by lack of LC-PUFA in their diets. Our findings will enhance our understanding about the evolutionary and functional roles of elovl2 and provide novel insights into the LC-PUFA biosynthesis mechanism in vertebrates.

Continuous Liquid-Liquid Extraction of Medium-Chain Fatty Acids from Fermentation Broth Using Hollow-Fiber Membranes.

Medium-chain fatty acids (MCFAs; carbon-lengths: C6-C12) are high-value platform chemicals that serve a variety of industrial applications, including green antimicrobials, food ingredients, animal feed additives, cosmetics, fragrances, pharmaceuticals, and structured lipids. Currently, most MCFAs are produced from palm and coconut oil originating from Southeast Asia and South America. The conventional approach to harvesting palm and coconut fruits causes considerable ecological damage in these regions. Therefore, researchers are developing biological approaches (e.g., precision and open-culture fermentations) to generate MCFAs more sustainably using low-value substrates (e.g., methanol, ethanol, lactate) or organic wastes as feedstock. Microbial chain-elongation (CE) is a rapidly maturing open-culture fermentation platform that converts short-chain fatty acids (SCFAs; carbon lengths: C1-C5) into a subset of these MCFAs at industrially relevant rates. However, continuous in situ extraction of MCFA products is necessary not only to avoid product inhibition but also to facilitate the recovery of MCFAs in a pure and usable form.Liquid-liquid extraction (LLE) using hollow-fiber membranes and targeted extractant mixtures has proven a robust approach to selectively extract MCFA products from fermentation broths containing SCFAs. Here, the application of LLE for continuous MCFA removal is demonstrated using CE as the reference fermentation system and 3% (w/v) trioctylphosphine oxide in mineral oil as the extractant system. Fatty acids ranging from valeric acid (C5) to caprylic acid (C8) are selectively removed from SCFA-containing broths and concentrated to high titers in a semi-batch alkaline stripping solution for downstream processing.

Membrane-based fermentation enables highly selective caproic acid production from wine lees

Chain elongation is a green chemistry approach to convert organic waste or agro-industrial side-products into caproic acid. Nonetheless, such feedstocks may contain microorganisms and chemical pollutants that could deteriorate the product yield and purity. This study introduces a membrane-based fermentation process designed to isolate the caproic acid producing bacteria from these contaminants. A tubular polysiloxane (silicone) membrane submerged into a fermentor allowed the selective diffusion of ethanol and acetic acid while preventing the cross-over of bacteria and contaminants such as ions. Abiotic tests confirmed that membrane thickness, feedstock pH and flow velocity can be adjusted to independently control the diffusion of ethanol and acetic acid. Thereof, optimal ethanol:acetic acid ratios for chain elongation (6:1) were obtained from a feedstock solution with equimolar (1 M) concentrations of both. In the biotic tests, this resulted in a highly selective (>90 %) caproic acid production at a highest rate of 3.1 g/(L·d). Maintaining the pH above 6.8, thereby keeping most caproic acid in its dissociated form, prevented its back-diffusion through the membrane. Similar caproic acid productivity was achieved from diluted wine lees (1 M ethanol), amended with 1 M acetic acid. In contrast, unamended wine lees resulted in three times lower caproic acid production rate, although the product selectivity remained high (94 %). Downstream processing by acidification and phase separation yielded 6–13 mL/Lfeedstock of an oily product containing up to 784 g/L caproic acid (84.3 % purity). In conclusion, membrane-based fermentation enables highly selective caproic acid production from highly concentrated and unbalanced substrates.

Microbiota modulatory properties of novel non-digestible xylitol-derived galacto-oligosaccharides and non-digestible lactulose derived carbohydrate mixtures

This study describes the microbiota modulatory properties of novel non-digestible galacto-oligosaccharides derived from xylitol and lactulose, through in vitro fecal batch fermentations. Differential analysis of microbiota profiles revealed the enhanced capacity to promote Bifidobacterium and Lactobacillus of the new galacto-oligosaccharides compared to commercial xylitol, among other genera. These novel galacto-oligosaccharides, especially those derived from the transgalactosylation of xylitol, led also to a high production of SCFAs, concretely in acetic acid, which were correlated with the promotion of several bacterial taxa. The reported fermentation patterns of these oligosaccharide structures could be of special interest to design novel prebiotic mixtures. Likewise, both xylitol and lactulose-derived galacto-oligosaccharides might exhibit slower fermentation rates compared to xylitol and lactulose controls due to the elongation of the carbohydrate chain, according to previous evidence. Therefore, novel prebiotic formulations based on xylitol and lactulose-derived galacto-oligosaccharides could promote the growth of beneficial gut commensals in the distal regions of the colon.

Elucidating Microglial Heterogeneity and Functions in Alzheimer’s Disease Using Single-cell Analysis and Convolutional Neural Network Disease Model Construction

In this study, we conducted an in-depth exploration of Alzheimer's Disease (AD) by integrating state-of-the-art methodologies, including single-cell RNA sequencing (scRNA-seq), weighted gene co-expression network analysis (WGCNA), and a convolutional neural network (CNN) model. Focusing on the pivotal role of microglia in AD pathology, our analysis revealed 11 distinct microglial subclusters, with 4 exhibiting obviously alterations in AD and HC groups. The investigation of cell–cell communication networks unveiled intricate interactions between AD-related microglia and various cell types within the central nervous system (CNS). Integration of WGCNA and scRNA-seq facilitated the identification of critical genes associated with AD-related microglia, providing insights into their involvement in processes such as peptide chain elongation, synapse-related functions, and cell adhesion. The identification of 9 hub genes, including USP3, through the least absolute shrinkage and selection operator (LASSO) and COX regression analyses, presents potential therapeutic targets. Furthermore, the development of a CNN-based model showcases the application of deep learning in enhancing diagnostic accuracy for AD. Overall, our findings significantly contribute to unraveling the molecular intricacies of microglial responses in AD, offering promising avenues for targeted therapeutic interventions and improved diagnostic precision.

LSPR anisotropy minimization by sequential growth of Ag nanoparticles on nanoripple patterned Si surface for SERS Application

The present work describes the formation of low-aspect-ratio Ag nanoparticles (NPs) arrays by sequential deposition of Ag from different growth directions on a nanoripple-patterned Si substrate, produced by low-energy ion beam irradiation. It is observed that the growth of Ag-NPs on ripple surfaces is direction-dependent due to the asymmetric ridge of the ripple pattern. This asymmetric ridge can be utilized to tune the shape of NP from elongated to spherical and in turn, assists in minimizing the LSPR anisotropy. The Finite-Difference-Time-Domain (FDTD) simulations demonstrate that the interparticle gap, major, and minor axis combinations of a NP are crucial in minimizing anisotropic near-field interaction. NPs grown perpendicular to the ripple from either direction lead to an elongated chain of nanoparticles; however, if a proper combination of sequential growth times is chosen then the aspect ratio of NPs can be tuned from elongation to spherical ones. Interestingly, a LSPR shift of 209 nm was observed when NPs are grown for 60 min on ripple patterns from one direction only. On the other hand, it reduces to 54 nm when NPs are sequentially grown for 30 min from each of directions, perpendicular to the ripples. SERS measurements also evidence a minimized anisotropic nature in sequentially grown NP arrays; hence, the growth direction as well as optimized growth times together can be used to control the LSPR anisotropy of NP arrays which can be used to fabricate such isotropic SERS substrates.

Synthesis and antiproliferative activity of (−)-cleistenolide, (6S)-cleistenolide and 4-substituted cleistenolide analogues

A new total synthesis of the natural δ-lactone cleistenolide (1) and its (6S)-stereoisomer 2 was achieved starting from d-glucose. Key steps in the synthesis of 1 involved: oxidative cleavage of the C1–C2 bond in partially protected d-glucose derivative (20), and chain extension of resulting aldehyde 20a with a single C2 fragment using (Z)-selective Wittig olefination. Synthesis of 2 involves the following key steps: periodate cleavage of the C5–C6 bond in the commercially available monoacetone d-glucose (24), followed by C2 chain elongation by using the (Z)-selective Wittig olefination. This new approach is also applied to prepare a few new 4-substituted cleistenolide analogues (3 – 18). Compounds 3 – 7 were designed using molecular hybridization, while the remaining eleven analogues were designed using the bioisosterism method. MTT assay showed that most analogues were more active than lead 1 against several malignant cells, but were completely inactive in the culture of normal foetal lung fibroblasts (MRC-5). The K562 cells appeared to be the most sensitive to the synthesized analogues. The strongest antiproliferative activity against this cell line was shown by 4-O-cinnamoyl derivative 3 and 4,6-di-O-benzyl derivative 17, with submicromolar IC50 values (0.76 and 0.67 μM, respectively). Structural features important for the activity of this class of compounds were identified by SAR analysis.

Comprehensive comparative study on n-caproate production by Clostridium kluyveri: batch vs. continuous operation modes

Recently, there has been notable interest in researching and industrially producing medium-chain carboxylic acids (MCCAs) like n-caproate and n-caprylate via chain elongation process. This study presents a comprehensive assessment of the behavior and MCCA production profiles of Clostridium kluyveri in batch and continuous modes, at different ethanol:acetate molar ratios (1.5:1, 3.5:1 and 5.5:1). The highest n-caproate concentration, 12.9 ± 0.67 g/L (92.9 ± 1.39 % MCCA selectivity), was achieved in batch mode at a 3.5:1 ratio. Interestingly, higher ratios favored batch mode selectivity over continuous mode when this was equal or higher to 3.5:1. Steady state operation yielded the highest n-caproate (9.5 ± 0.13 g/L) and n-caprylate (0.35 ± 0.020 g/L) concentrations at the 3.5:1 ratio. Increased ethanol:acetate ratios led to a higher excessive ethanol oxidation (EEO) in both operational modes, potentially limiting n-caproate production and selectivity, especially at the 5.5:1 ratio. Overall, this study reports the efficient MCCA production of both batch and continuous modes by C. kluyveri.

Asymmetrical Elongation of Branched Alkyl Chains in Non‐Fullerene Acceptors for Large‐Area Organic Solar Modules

AbstractWith the drive toward the development of large‐area organic solar cells (OSCs), there is a critical need for advanced fabrication techniques that ensure both their efficiency and scalability. In particular, a shift from toxic halogenated solvents to safer non‐halogenated alternatives such as o‐xylene, which have lower environmental and health impacts, is required. However, transitioning to non‐halogenated solvents can lead to serious problems, including aggregation within the active layer, which compromises film morphology and the resulting efficiency of OSCs. To address this aggregation, in the present study, the 2‐ethylhexyl (EH) groups in L8‐BO(EH‐EH) are replaced with longer chains (2‐heptylundecyl [HU], 2‐decyltetradecyl [DT], and 2‐dodecylhexadecyl [DH] groups) to synthesize the non‐fullerene acceptors (NFAs) of L8‐BO(HU‐HU), L8‐BO(HU‐DT), and L8‐BO(HU‐DH). The NFAs with the longer alkyl chains are highly soluble in o‐xylene and produce highly uniform films, making them more suitable for use in large‐area OSCs. Using the NFAs, slot‐die‐coated organic solar modules with an active area of 200 cm2 are fabricated; the L8‐BO(HU‐DT)‐based module exhibits an impressive power conversion efficiency of 11.44%. This work thus underscores the asymmetrical elongation of alkyl chains in the NFAs to mitigate severe NFA phase separation and improve film printability in the practical production of organic solar modules.

Conversion of wine lees and waste activated sludge into caproate and heptanoate: Thermodynamic and microbiological insights

In this study, wine lees and waste activated sludge (WAS) were co-fermented for the first time in a 4:1 ratio (COD basis) at 20, 40, 70 and 100 gCOD/L, in batch at 37 °C and pH 7.0. The substrates were successfully converted to caproate (C6) and heptanoate (C7) with a high selectivity (40.2 % at 40 gCOD/L). The rapidly-growing chain-elongating microbiome was enriched inClostridiaceaeandOscillospiraceae, representing together 3.4–8.8 % of the community. Substrate concentrations higher than 40 gCOD/L negatively affected C6 and C7 selectivities and yields, probably due to microbial inhibition by high ethanol concentrations (15.82–22.93 g/L). At 70 and 100 gCOD/L, chain elongation shifted from ethanol-based to lactate-based, with a microbiome enriched in the lactic acid bacteriaRoseburia intestinalis(27.3 %) andEnterococcus hirae(13.8 %). The partial pressure of H2(pH2) was identified by thermodynamic analysis as a fundamental parameter for controlling ethanol oxidation and improving C6 and C7 selectivities.

Nano zero valent iron stimulated acetaldehyde oxidation, electron transfer, and RBO pathway for enhanced medium-chain carboxylic acids production

Nano zero-valent iron (NZVI) has been shown to effectively enhance the chain elongation (CE) process, addressing the issue of limited yield of medium-chain carboxylic acids (MCCA) from organic wastewater. However, the specific impact of NZVI on the metabolism of CE bacteria (CEB) is not well understood. In this study, it was aimed to investigate the mechanism by which an optimal concentration of NZVI influences CE metabolism, particularly in relation to ethanol oxidation, electron transfer, and MCCA synthesis. This was achieved through single-factor influence experiments and metagenomic analysis. The results showed that the addition of 1 g/gVSS NZVI achieved the highest MCCA yield (n-caproic acid + n-octanoic acid) at 2.02 g COD/L, which was 4.9 times higher than the control. This improvement in MCCA production induced by NZVI was attributed to several factors. Firstly, NZVI facilitated the oxidation of acetaldehyde, leading to its reduced accumulation in the system (from 18.4 % to 5.8 %), due to the optimized chemical environment created by NZVI corrosion, including near-neutral pH and a more reductive oxidation–reduction potential (ORP). Additionally, the inherent conductivity property of NZVI and the additional Fe ions released during corrosion improved the electron transfer efficiency between CEB. Lastly, both the composition of microbial communities and the abundance of unique enzyme genes confirmed the selective stimulation of NZVI on the reverse β-oxidation (RBO) pathway. These findings provide valuable insights into the role of NZVI in CEB metabolism and its potential application for enhancing MCCA production in CE bioreactors.

Demethylation C–C coupling reaction facilitated by the repulsive Coulomb force between two cations

Carbon chain elongation (CCE) is normally carried out using either chemical catalysts or bioenzymes. Herein we demonstrate a catalyst-free approach to promote demethylation C–C coupling reactions for advanced CCE constructed with functional groups under ambient conditions. Accelerated by the electric field, two organic cations containing a methyl group (e.g., ketones, acids, and aldehydes) approach each other with such proximity that the energy of the repulsive Coulomb interaction between these two cations exceeds the bond energy of the methyl group. This results in the elimination of a methyl cation and the coupling of the residual carbonyl carbon groups. As confirmed by high-resolution mass spectrometry and isotope-labeling experiments, the C–C coupling reactions (yields up to 76.5%) were commonly observed in the gas phase or liquid phase, for which the mechanism was further studied using molecular dynamics simulations and stationary-point calculations, revealing deep insights and perspectives of chemistry.