Mechanistic Insights into the Biodegradation of Carbon Dots by Fungal Laccase

The Use of Carbon Dots for Food Packaging and Preservation: Toxic or Beneficial?

Carbon dots (CDs), which are emerging as versatile nanomaterials, have gained interest in food packaging and preservation due to their sustainable origin and multifunctional characteristics, such as antimicrobial, antioxidant, and UV-protective properties. CDs can be synthesized from biomass and have been proposed as functional additives to packaging material to improve the safety and shelf life of the packaged food. Despite these benefits, concerns are raised about their potential toxicity when leached into foods, especially since they belong to the nanomaterial category. Interestingly, foodborne CDs, which are naturally formed in heat-processed foods and have been consumed by humans for centuries, add a new complexity to the debate. Although there is no definitive evidence linking these endogenous CDs to adverse health effects, some studies suggest their potential to interfere with metabolism in animal models. In addition, the presence of hazardous substances in thermally processed foods, such as polycyclic aromatic hydrocarbons (PAHs), may further complicate safety assessment. This review addresses the paradox of CD from food and packaging sources, highlighting its dual role as both a potentially toxic agent and a beneficial functional material. More extensive research is essential to fully understand the long-term effects of CD on human health and to determine whether its use in food packaging is truly safe or beneficial.

Laccase Functional Analysis: Substrates, Activity Assays, Challenges, and Prospects

Enzyme functional analysis is a multifaceted process that can be used for various purposes, such as screening for specific activities, as well as developing, optimising, and validating processes or final products. Functional analysis methods are crucial for assessing enzyme performance and catalytic properties. Laccase, a well-known blue multi-copper oxidase, holds immense potential in diverse industries such as pharmaceuticals, paper and pulp, food and beverages, textiles, and biorefineries due to its clean oxidation process and versatility in handling a wide range of substrates. Despite its prominence, the use of laccase encounters challenges in selecting appropriate functional analysis substrates and methods. This review delves into the substrates utilised in qualitative and quantitative techniques for laccase activity analysis. Although laccase catalyses mono-electron oxidation of aromatic hydroxyl, amine, and thiol compounds efficiently, using molecular oxygen as an electron acceptor, the review identifies limitations in the specificity of the commonly employed substrates, concerns regarding the stability of certain compounds and highlights potential strategies.

Advanced enzyme-assembled hydrogels for the remediation of contaminated water

Enzyme-catalyzed biodegradation is an emerging green strategy for environmental remediation, although challenged by high cost and poor robustness. Herein, natural biopolymer (cellulose)-derived hydrogels concurrently doped with β-cyclodextrin and montmorillonite nanosheets that are synthesized in one-step demonstrate exceptional pollutant affinity and mechanical strength. Laccase is then stably and effectively assembled onto the hydrogels by a facile strategy based on charge-assisted H-bonding, which can be extended to other enzymes. The advanced laccase-assembled hydrogels display excellent stability and increased degradation activity achieved by strong substrate capture and rapid electron transfer. The laccase-assembled hydrogels exhibit significantly improved removal (62-fold) and degradation (52-fold) performance compared to free laccase for diverse organic pollutants (e.g., polycyclic aromatic hydrocarbons) in real wastewater. This enhanced performance is maintained despite the presence of heavy metals, other organic chemicals or dissolved organic matter. This work provides a practical strategy for designing an advanced and sustainable biodegradation tool for environmental remediation.

Theoretical Insights into the Catalytic Oxidation of Phenols and Arylamines by Laccases via the Proton-Coupled Electron Transfer Mechanism

Laccases play a vital role in the degradation of toxic phenolic and aromatic amine compounds, generating considerable attention in ecological pollution remediation. However, the distinct mechanism of the laccase-catalyzed oxidation of phenols and arylamines remains unclear. Here, we examined the catalytic oxidation mechanisms of phenols and arylamines by Trametes versicolor (TvL) and Melanocarpus albomyces (MaL) laccases using molecular docking, quantum mechanics (QM), and QM/molecular mechanics (QM/MM) calculations. We docked four phenolic substrates, including 1,2-benzenediol, 2-propenylphenol, 2-methoxyhydroquinone, and 2-aminophenol, to TvL and identified their favorable reaction conformations, in which Asp206 of TvL plays an important role in binding substrates to promote the catalytic reactions. Based on the docking conformations, the QM and QM/MM calculations revealed that the oxidation reactions take place via a proton-coupled electron transfer mechanism, with proton transfer (PT) from the hydroxyl groups of substrates to the side chain of Asp206 and synchronous electron hopping from the aromatic ring of substrates to the type one copper (T1Cu) of TvL. For the MaL and 2,6-dimethoxyphenol interacting system, the oxidation reactions occur through a concerted double-proton-coupled electron transfer mechanism with a water-mediated indirect PT from the hydroxyl group of substrates to the conserved Glu235 and electron hopping from the substrate to T1Cu at the same time. The corresponding energy barriers change from 0.7 to 18.4 kcal/mol, indicating the different degradation rates of the phenols and arylamines by laccases. These findings provide insights into the oxidation mechanism of phenols and arylamines by laccases and may extend the applications of laccases.

Unraveling the Distribution, Metabolization, and Catabolism of Foliar Sprayed Carbon Dots in Maize and Effect on Soil Environment

The enormous potential of carbon dots (CDs) in agriculture has been widely reported, whereas their accurate distribution, transformation, and metabolic fate and potential soil health effects are not clearly understood. Herein, 13C-labeled CDs (13C-CDs) were sprayed on maize leaf, accumulated in all tissues, and promoted photosynthesis. Specifically, 13C-CDs were internalized to participate in the synthesis of glucose, sucrose, citric acid, glyoxylate, and chlorogenic acid, promoting tricarboxylic acid cycle (TCA) and phenylalanine metabolism. Additionally, the catabolism of 13C-CDs in vivo was mainly mediated by O2•- produced by oxidative stress. 13C-CDs did not have an obvious impact on the soil environment at the overall level. The detection of 13C signals in soil fauna suggested 13C-CDs in soil food chain transmission. This study systematically described the exact fate of CDs in plants and potential soil ecological risks and provided a more comprehensive analysis and support for the potential advantages of CDs in agricultural application.

Synergistic Mitochondrial Genotoxicity of Carbon Dots and Arsenate in Earthworms Eisenia fetida across Generations: The Critical Role of Binding

The escalating utilization of carbon dots (CDs) in agriculture raises ecological concerns. However, their combined toxicity with arsenic remains poorly understood. Herein, we investigated the combined mitochondrial genotoxicity of CDs and arsenate at environmentally relevant concentrations across successive earthworm generations. Iron-doped CDs (CDs-Fe) strongly bound to arsenate and arsenite, while nitrogen-doped CDs (CDs-N) exhibited weaker binding. Both CDs enhanced arsenate bioaccumulation without affecting its biotransformation, with most arsenate being reduced to arsenite. CDs-Fe generated significantly more reactive oxygen species than did CDs-N, causing stronger mitochondrial DNA (mtDNA) damage. Arsenate further exacerbated the oxidative mtDNA damage induced by CDs-N, as evidenced by increased reactive oxygen species, elevated 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-OHdG) levels, and a higher correlation between 8-OHdG and mtDNA damage. This was due to arsenic inhibiting the antioxidant enzyme catalase. This exacerbation was negligible with CDs-Fe because their strong binding with arsenic prevented catalase inhibition. Maternal mitochondrial DNA damage was inherited by filial earthworms, which experienced significant weight loss in coexposure groups coupled with mtDNA toxicity. This study reveals the synergistic genotoxicity of CDs and arsenate, suggesting that CDs could disrupt the arsenic biogeochemical cycle, increase arsenate risk to terrestrial animals, and influence ecosystem stability and health through multigenerational impacts.

From Bulk to Nano: Formation, Features, and Functions of Nano-Black Carbon in Biogeochemical Processes

Globally increasing wildfires and widespread applications of biochar have led to a growing amount of black carbon (BC) entering terrestrial ecosystems. The significance of BC in carbon sequestration, environmental remediation, and the agricultural industry has long been recognized. However, the formation, features, and environmental functions of nanosized BC, which is one of the most active fractions in the BC continuum during global climate change, are poorly understood. This review highlights the formation, surface reactivity (sorption, redox, and heteroaggregation), biotic, and abiotic transformations of nano-BC, and its major differences compared to other fractions of BC and engineered carbon nanomaterials. Potential applications of nano-BC including suspending agent, soil amendment, and nanofertilizer are elucidated based on its unique properties and functions. Future studies are suggested to develop more reliable detection techniques to provide multidimensional information on nano-BC in environmental samples, explore the critical role of nano-BC in promoting soil and planetary health from a one health perspective, and extend the multifield applications of nano-BC with a lower environmental footprint but higher efficiency.

Aquatic photolysis of high-risk fluorinated liquid crystal monomers: Kinetics, toxicity evaluation, and mechanisms

Despite the frequent detection of fluorinated liquid-crystal monomers (FLCMs) in the environment, the level of understanding of their fate, toxicity, and transformation remains insufficient. Herein, we investigated the degradation kinetics and mechanism of an FLCM (4-cyano-3-fluorophenyl 4-ethylbenzoate, CEB-F) under ultraviolet (UV) photolysis in aquatic environment. Our findings demonstrated that the UV photolysis of CEB-F followed first-order kinetics. Photodegradation products were identified using liquid chromatography with mass spectrometry, and detailed reaction pathways were proposed. It is postulated that through the attack of reactive oxygen species, hydroxylation, and CO/C-F bond cleavage, CEB-F gradually degraded into small molecular compounds, releasing fluorine ions. Acute immobilization tests with Daphnia magna (D. magna) revealed significant acute toxicity of CEB-F, with LC50 values ranging from 1.023 to 0.0536 μM over 24 to 96 h, emphasizing the potential high risk of FLCMs in aquatic ecosystems if inadvertently discharged. Interestingly, we found that the toxicity of CEB-F photolysis reaction solutions was effectively reduced. Through catalase and acetylcholinesterase activities analysis along with molecular docking simulation, we proposed differences in the underlying toxicity mechanisms of CEB-F and its photolysis products to D. magna. These findings highlight the potential harmful effects of FLCMs on aquatic ecosystems and enrich our understanding of the photolysis behavior of FLCMs.