Decoding the key compounds responsible for the empty cup aroma of soy sauce aroma type baijiu

The empty cup aroma in soy sauce aroma type baijiu (SSB) is distinct, but the specific compounds responsible for its unique aroma remain unknown. The aroma characteristics of SSB and the empty cup were investigated using molecular sensory science. Fifty-three and 27 aroma active compounds were identified in SSB and empty cup aroma, respectively. AEDA of the empty cup showed ethyl 3-phenylpropanoate, phenylethyl alcohol, sotolon, p-cresol, and 2,3-dimethyl-5-ethyl pyrazine could be the most important aroma contributors to the empty cup aroma due to their high FD values. Sotolon, characterized by its seasoning-like and herbal aroma, was identified as a crucial aroma compound for the empty cup aroma for the first time. Lactic acid was found to decrease the olfactory threshold of sotolon markedly in both 53% ethanol water solution and empty cup, promoting the contribution of sotolon to the empty cup aroma.

Tracking the binding site of anticancer drug fluxoridin with Fe-related proteins to achieve intelligent drug delivery

In cancer cells that need a lot of iron for growth and metastasis, halo-transferrin (TF-containing iron) enters the cell with the help of the transferrin receptor 1 (TFR1) protein. If the anticancer drug can bind to the iron site by interacting with apo-transferrin (iron-free FT), it can enter the cancer cell by the same mechanism. Two iron-related proteins, Bovine liver catalase (BLC) and apo-Transferrin (TF), that are important in cancer patients were selected and their interaction with the anti-cancer drug Floxuridine (FUDR) was investigated. Here, the protective role of FUDR was evaluated by several variables such as drug concentration, interaction time, and temperature-induced degradation of enzyme function. The results showed that the protective effect of the FUDR is greater in high concentrations (in 5 × 10-5 M:1.78 % and 2.59 % after 24 and 48 h). The interaction of the FUDR with both proteins can reduce the intensity of the fluorescence emission by a static mechanism. The binding strength of the FUDR with both proteins was almost similar and with the order of 104 M-1 (Kb = 3.90 ± 0.41 × 104 M-1 for BLC-FUDR and 5.01 ± 0.36 × 104 M-1 for TF-FUDR at 310 K). The thermodynamic calculations (in agreement with the docking results) indicated that FUDR-protein complex formation was exothermic and the main binding forces in the binding process were van der Waals interactions and hydrogen bonds. Both fluorophores tryptophan (Trp) and tyrosine (Tyr) of both proteins had significant roles in fluorescence quenching and the interaction process, the polarity of their microenvironment changed. CD results showed that the secondary structure changes of TF are slightly more than BLC. Molecular docking showed that the binding of the FUDR to TF is very close to the Fe-specific site and is placed in the cavity among the wrapping domain, N-Terminal arm, and β-barrel in BLC.

Interaction mechanism between surface layer protein and yeast mannan: Insights from multi-spectroscopic and molecular dynamics simulation analyses

Tibet kefir grain (TKG) formation is mainly dependent on the aggregation of lactobacillus and yeasts. The interaction of surface layer protein (SLP) and yeast mannan plays an important role in mediating the co-aggregation of Lactobacillus kefiri with Saccharomyces cerevisiae. The interaction mechanism of the two was researched through multispectral spectroscopy, morphology observation and silico approaches. Fluorescence spectra data revealed that mannan was bound to SLP through a spontaneous binding process. The particle size of the binding complex increased as the mannan concentration increased. Synchronous fluorescence spectroscopy and circular dichroism (CD) spectra showed the conformational and microenvironment alteration of SLP treated with mannan. Molecular docking results indicated that hydrophobic interactions played major roles in the formation of SLP-mannan complexes. These findings provide a deeper insight into the interactions of protein and polysaccharide, and this knowledge is valuable in the application of SLP and mannan in co-fermentation systems.

Identification of natural xanthine oxidase inhibitors: Virtual screening, anti-xanthine oxidase activity, and interaction mechanism

Xanthine oxidase (XO) is a crucial target for hyperuricemia treatment(s). Naturally occurred XO inhibitors with minimal toxicity and high efficacy have attracted researchers' attention. With the goal of quickly identifying natural XO inhibitors, an integrated computational screening strategy was constructed by molecular docking and calculating the free energy of binding. Twenty-seven hits were achieved from a database containing 19,377 natural molecules. This includes fourteen known XO inhibitors and four firstly-reported inhibitors (isolicoflavonol, 5,7-dihydroxycoumarin, parvifolol D and clauszoline M, IC50 < 40 μM). Iolicoflavonol (hit 8, IC50 = 8.45 ± 0.68 μM) and 5,7-dihydroxycoumarin (hit 25, IC50 = 10.91 ± 0.71 μM) displayed the great potency as mixed-type inhibitors. Docking study and molecular dynamics simulation revealed that both hits could interact with XO's primarily active site residues ARG880, MOS1328, and ASN768 of XO. Fluorescence spectroscopy studies showed that hit 8 bound to the active cavity region of XO, causing changes in XO's conformation and hydrophobicity. Hits 8 and 25 exhibit favorable Absorption, Distribution, Metabolism, and Excretion (ADME) properties. Additionally, no cytotoxicity against human liver cells was observed at their median inhibition concentrations against XO. Therefore, the present study offers isolicoflavonol and 5,7-dihydroxycoumarin with the potential to be disease-modifying agents for hyperuricemia.

High capacity and selective adsorption of Congo red by cellulose-based aerogel with mesoporous structure: Adsorption properties and statistical data simulation

Large quantities of organic dyes are discharged into the environment, causing serious damage to the ecosystem. Therefore, it is urgent to develop inexpensive adsorbents to remove organic dyes. A novel cellulose-based aerogel (MPPA) with 3D porous structure was prepared by using cassava residue (cellulose) as basic construction blocks, doping ferroferric oxide (Fe3O4) for magnetic separation, and applying polyethyleneimine (PEI) as functional material for highly efficient and selective capture of Congo red (CR). MPPA exhibited porous network structure, numerous active capture sites, nontoxicity, high hydrophilicity, and excellent thermal stability. MPPA showed superior adsorption property for CR, with an equilibrium adsorption capacity of 2018.14 mg/g, and still had an adsorption property of 1189.31 mg/g after five recycling procedures. In addition, MPPA has excellent selectivity for CR in four binary dye systems. The adsorption behavior of MPPA on CR was further explored using a multilayer adsorption model, EDR-IDR hybrid model and AOAS model. Electrostatic potential and independent gradient models were used to further verify the possible interaction between MPPA and CR molecules. In conclusion, MPPA is a promising adsorbent in the field of treating anionic dyes.

The adsorption and release mechanism of different aged microplastics toward Hg(II) via batch experiment and the deep learning method

Aged microplastics are ubiquitous in the aquatic environment, which inevitably accumulate metals, and then alter their migration. Whereas, the synergistic behavior and effect of microplastics and Hg(II) were rarely reported. In this context, the adsorptive behavior of Hg(II) by pristine/aged microplastics involving polystyrene, polyethylene, polylactic acid, and tire microplastics were investigated via kinetic (pseudo-first and second-order dynamics, the internal diffusion model), Langmuir, and Freundlich isothermal models; the adsorption and desorption behavior was also explored under different conditions. Microplastics aged by ozone exhibited a rougher surface attached with abundant oxygen-containing groups to enhance hydrophilicity and negative surface charge, those promoted adsorption capacity of 4-20 times increment compared with the pristine microplastics. The process (except for aged tire microplastics) was dominated by a monolayer chemical reaction, which was significantly impacted by pH, salinity, fulvic acid, and co-existing ions. Furthermore, the adsorbed Hg(II) could be effectively eluted in 0.04% HCl, simulated gastric liquids, and seawater with a maximum desorption amount of 23.26 mg/g. An artificial neural network model was used to predict the performance of microplastics in complex media and accurately capture the main influencing factors and their contributions. This finding revealed that aged microplastics had the affinity to trap Hg(II) from freshwater, whereafter it released the Hg(II) once transported into the acidic medium, the organism's gastrointestinal system, or the estuary area. These indicated that aged microplastics could be the sink or the source of Hg(II) depending on the surrounding environment, meaning that aged microplastics could be the vital carrier to Hg(II).

Simultaneous catalytic oxidation of toluene and CO over Cu-V/Al-Ce catalysts: Physicochemical properties-activity relationship and simultaneous oxidation mechanism

Cu-V/Al-Ce with varying ratios of Al2O3/CeO2 were prepared to study the simultaneous catalytic oxidation of toluene and CO. Experimental results show that Cu-V/20Al-80Ce exhibits optimal simultaneous oxidation activity and good durability. This superior performance is related to Cu-Ce, V-Ce, and Al-Ce interactions, which facilitate the exposure of active centers, the creation of oxygen vacanicies, and efficient electron transfer. The mutual influence between toluene and CO during the simultaneous oxidation is then demonstrated. Toluene hinders CO oxidation through the competitive adsorption and the consumption of reactive oxygen species. CO enhances toluene oxidation, which is comprehensively explained by affecting the competition between the desorption and oxidation of benzaldehyde. Despite the mutual influence between toluene and CO, the pathways of CO and toluene oxidation are mutually independent. Toluene oxidation proceeds sequentially from toluene to benzyl alcohol, benzaldehyde, benzoate, and finally to CO2. Before being completely oxidized to CO2, CO is initially converted to carboxylic acid, hydrogen carbonate, free carbonate ion, bidentate formate, and monodentate carbonate.

The interaction of perfluorooctane sulfonate with hemoproteins and its relevance to molecular toxicology

Perfluorooctane sulfonate (PFOS), a representative of perfluorinated compounds in industrial and commercial products, has posed a great threat to animals and humans via environmental exposure and dietary consumption. Herein, we investigated the effects of PFOS binding on the redox state and stability of two hemoproteins (hemoglobin (Hb) and myoglobin (Mb)). Fluorescence spectroscopy, circular dichroism and UV-vis absorption spectroscopy demonstrated that PFOS could induce the conformational changes of proteins along with the exposure of heme cavity and generation of hemichrome, which resulted in the increased release of free hemin. After that, free hemin liberated from hemoproteins led to reactive oxygen species formation, lipid peroxidation, cell membrane damage and loss of cell viability in vascular endothelial cells, while neither Hb nor Mb did show cytotoxicity. Chemical inhibitors of ferroptosis effectively mitigated hemin-caused toxicity, identifying the hemin-dependent ferroptotic cell death mechanisms. These data demonstrated that PFOS posed a potential threat of toxicity through a mechanism which involved its binding to hemoproteins, decreased oxygen transporting capacity, and increased hemin release. Altogether, our findings elucidate the binding mechanisms of PFOS with two hemoproteins, as well as possible risks on vascular endothelial cells, which would have important implications for the human and environmental toxicity of PFOS.

Activated biochar derived from Enteromorpha with high specific surface area for efficient removal of phenanthrene: Experiments, mechanism and DFT calculations

Conversion of solid marine waste into innovative nanomaterials has been successfully developed for removing organic pollutants from aqueous solutions. In this study, activated biochar (HTST) was successfully synthesized using a straightforward three-step method involving pretreatment, carbonization, and chemical regulation. Multiple characterization techniques revealed the presence of abundant three-dimensional hierarchical porous structures in the samples, along with amorphous and active functional group structures such as -COOH, -OH, -NHR, -CC, and C-O. Notably, the prepared sample exhibited a remarkable specific surface area (SBET) of 3284.52 m2/g, which was close to 1700 times larger than that of the raw biomass. Additionally, the highest removal efficiency could reach approximately 100% under neutral condition, while the adsorption capacity even achieved up to 782.37 mg/g within 2 h at room temperature. Calculations simulation not only highlighted the significance of the π-π conjugation between sample and pollutant molecules, but deeply explored the bonding interaction of active functional groups on the surface, whereas adsorption energies of different configurations had the following order: ΔE(-NHR) = 0.75194674 eV > ΔE(-OH) = 0.72502369 > ΔE(-COOH) = 0.71488135 > ΔE(-CC-) = 0.53852269 eV. Moreover, the adsorption activities for the optimized configuration were further analyzed based on the LUMO-HOMO energy gap and electric distribution. This work presents a viable synthesis method for low-cost nanomaterials and offers new insights into the exceptional adsorption properties of advanced adsorbents for wastewater treatment.

The improved bioavailability of zein/soybean protein isolate by puerarin in vitro

As the largest emitter of greenhouse gases, the livestock and poultry industry is facing the challenge of increasing production to meet global demand while reducing environmental impacts. Improving feed digestibility by optimizing feed structure (e.g., exogenous additive) is one of the green breeding measures to alleviate carbon pressure. In this study, the interaction mechanism and in vitro digestibility properties of puerarin (PUE) with feed proteins (zein and soy protein isolate (SPI)) to form Zein-PUE and SPI-PUE complexes were investigated mainly by multispectral and molecular docking techniques. Results indicated that the addition of PUE improved the physicochemical properties of proteins (e.g., solubility and disulfide bond contents). Then, the spectral results showed that the binding processes were spontaneous, and the protein structure tended to loose and disordered after binding, and more hydrophobic residues were exposed to the hydrophilic microenvironment. Moreover, on the basis of molecular docking revealed that PUE bound to zein by hydrogen bond, electrostatic and hydrophobic interactions, while with SPI by hydrogen bond and hydrophobic interaction. Finally, in vitro digestion experiments demonstrated that the bioavailability of Zein-PUE and SPI-PUE complexes increased by 1.15 % and 2.11 %, respectively. Overall, PUE is a promising feed additive beneficial for enhancing protein digestibility and bioavailability.

Unravelling the interaction between α-SOH and myofibrillar protein based on spectroscopy and molecular dynamics simulation

This work systematically investigated the dose-response interaction between hydroxy-α-sanshool (α-SOH) and pork myofibrillar proteins (MPs) via spectroscopy, molecular docking, and molecular dynamics simulation methods. Results showed that MPs bound with low α-SOH can enhance the surface hydrophobicity and particle size of MPs, whereas high concentrations were exactly the opposite. The main interaction force in α-SOH/MPs complex changed from hydrophobic to hydrogen bonding with increased α-SOH. α-SOH causes tryptophan quenching and bring about a red shift at low concentration, as well as to promote α-helix conversion into β-sheet in MPs. Simultaneously, molecular docking and dynamics simulations verified that hydrogen bonding and hydrophobic forces were the main contributors to α-SOH/MPs complex, indicating that the binding of α-SOH with MPs proceeded spontaneously with high intensity, in which TYR286 contributed the most significant energy. Therefore, revealing the binding mechanism of α-SOH and MPs can contribute to the deep processing of numbing meat products.

Effect of microplastics on the adherence of coexisting background organic contaminants to natural organic matter in water

Microplastics (MPs) may interact with background organic substances (including natural organic matter and organic pollutants) after entering the aquatic environment and affect their original binding. Thus, the interaction of MPs with background organic substances (i.e., humic acid (HA), polychlorinated biphenyls (PCBs), and hydroxy PCBs) were elucidated. According to the results, PCB and hydroxy PCB displayed a strong propensity to adhere to HAs in the absence of MPs. However, the PCBs and hydroxy PCBs that were initially bound to HAs shifted from HAs to MPs in the presence of MPs. Further analysis demonstrated that this transfer was dominated by van der Waals interactions, with hydrogen bond interactions as an additional driving force. Upon the interaction, large MPs-HA-PCB/ hydroxy PCB aggregates with MPs as the core and HAs as the outermost layer were formed. Significant changes in the properties of background organic matter, including the distribution of PCB/hydroxy PCB around HA, diffusion coefficient, and hydrogen bond networks in the HA-PCB/ hydroxy PCB domains, occurred during the MP-HA-PCB/hydroxy PCB interaction. These results provide molecular-level evidence that the intrusion of MPs changes the binding preference of background organic pollutants and can lead to a redistribution of background organic pollutants.

Deciphering the interaction mechanism and binding mode between chickpea protein isolate and flavonoids based on experimental studies and molecular simulation

Chickpea protein isolate (CPI) is a promising novel plant protein, and protein-flavonoid system has also been applied in various food products. However, the interaction mechanism between CPI and flavonoids remains to be elucidated. In this paper, the affinity behavior between flavonoids and CPI was explained by constructing the three-dimensional quantitative structure-activity relationship (R2 = 0.988, Q2 = 0.777). Subsequently, four representative flavonoids were selected for further study. Multi-spectroscopy analysis showed that the sequence of affinity for CPI was puerarin > apigenin > naringenin > epigallocatechin gallate. Meanwhile, flavonoids altered the secondary structure and spatial conformation of CPI, leading to the static quenching of CPI. Additionally, thermodynamic analysis indicated that hydrogen bonding and van der Waals forces were the main driving forces for complex binding. Molecular docking and molecular dynamics simulations further explored the binding sites and conformations of complexes. This study provides theoretical guidance for in-depth research on the interaction patterns between biomacromolecules and small molecules in food matrices.

Binding divergence of polystyrene nanoparticles with serum albumin caused by surface functionalization

Using a combination of spectroscopy, we devised an integrated structural strategy to comprehensively profile the molecular details of the impact of differently functionalized (plain, aminated, and carboxylated) polystyrene nanoparticles (PSNPs) on human serum albumin (HSA). The binding isotherms obtained from fluorescence and UV-vis absorption measurements demonstrate that surface functionalization can distinguish the interaction of PSNPs with HSA. Three-dimensional fluorescence and circular dichroism analysis of the effect of interaction with PSNPs on the native conformation and secondary structures of the protein reveals a diminution in the skeleton structure of HSA induced by the PSNPs. In accordance with this, it is discovered that the esterase activity of protein-PSNPs aggregates is diminished compared to that of the native protein. The carboxylated PSNPs exhibited the strongest protein binding and perturbation effects compared to other particles. Plain PSNPs exhibited significant hydrophobic interaction properties, as evidenced by spectral blue shifts and a diminished Stokes shift in the three-dimensional fluorescence assay. Our results exclusively highlight that the hydrophobic and surface charge characteristics of PSNPs govern the extent of interaction with the protein, which is beneficial to understanding microplastic toxicology.

Exploring the effect of a series of flavonoids on tyrosinase using integrated enzyme kinetics, multispectroscopic, and molecular modelling analyses

The control of food browning can be achieved by inhibiting tyrosinase (TY) activity, but current studies on the interaction of flavonoids as potent inhibitors with TY are inadequate. Herein, the effect of a library of flavonoids on TY was investigated using enzyme kinetics, multispectroscopic methods, and molecular modelling. Some flavonoids including 4, 8, 10, 17, 18, 28, 30, 33, and 34 exhibited potent TY inhibitory activity, with compound 10 demonstrating reversible inhibition in a mixed-competitive manner. Ultraviolet-visible spectral changes confirmed the formation of flavonoid-TY complexes. Fluorescence quenching analysis suggested effective intrinsic fluorescence quenching by flavonoids through static quenching with the ground-state complex formation. Synchronous fluorescence spectra showed the microenvironment change around the fluorophores induced by flavonoids. ANS-binding fluorescence assay indicated TY's surface hydrophobicity change by flavonoids and highlighted the change in secondary structure conformation, which was further confirmed by Fourier-transform infrared spectra. Molecular modelling results helped visualize the preferred binding conformation at the active site of TY, and demonstrated the important role of hydrophobic interaction and hydrogen bonding in stabilizing the flavonoid-TY complexes. These findings prove that diverse flavonoid structures distinctly impact their binding behavior on TY and contribute to understanding flavonoids' potential as TY inhibitors in controlling food browning.

Release of dissolved organic matter from wetland plants and its interaction with polycyclic aromatic hydrocarbons

Dissolved organic matter (DOM) derived from wetland plants played a critical role in CWs pollutant migration. This study investigated the character and release pattern of DOM derived from two wetland plants, Phragmites australis and Cladophora sp., and the interaction between DOM with phenanthrene (PHE), benzo(a)pyrene (Bap), and benzo [k]fluoranthene (BkF) under different physical conditions were also studied using spectroscopic techniques. DOM release was related to plant species and withering stage. Humic acid (HA)-like fractions (C3 and C5) were dominated in P. australis (52%) and completely withered Cladophora sp. groups (55%), while protein-like fractions (C1 and C2) dominated in early withered Cladophora sp. groups (52%). Due to the cell and tissue structure difference among plants and their withering stage, DOM derived from early withered P. australis revealed a two-stage slow-fast phase, while other groups were linearly released (R2 0.87207-0.97091). A strong correlation existed between HA-like fractions and water quality index, reflecting the critical influence of plant decay in CWs operation performance. The analysis with Stern-Volmer equation indicated that plant-based DOM interacted with PAHs to form ground state complexes with possible involvement of π-π interaction, hydrogen bonding and cation bridging effect. Aromatic, molecular weight, and hydrophilicity of both DOM and PAHs affected their binding with the interaction capability in the order of BKF > Bap > PHE and C3 > C5 > C2 > C1 > C4. Besides, alkaline environment and high DO condition was highly unsuitable for the combination. Scientific management and appropriate operating condition were important in optimizing operation performance and controlling pollutant migration in CWs.

Mechanisms of ssDNA aptamer binding to Cd2+ in aqueous solution: A molecular dynamics study

ssDNA aptamers have been increasingly used to detect heavy metal ions as recognition elements due to their high affinity and specificity. However, the specific recognition and binding mechanisms between aptamers and most heavy metals were still unclear, which limits the development of aptamer-based detection methods. In this work, the interaction mechanisms of CD-2-1 aptamers with Cd2+ in aqueous solutions were investigated using molecular dynamic simulations. The most stable complex was found where Cd2+ binding at aptamer's stem-loop junction and preferred at the phosphate backbone or bases. Noteworthily, two binding modes of Cd2+ combining aptamer in aqueous solution were discovered: direct and indirect. In the former mode, Cd2+ directly coordinated O atoms of bases. For the latter, Cd2+ connected to bases with coordinated water molecules as bridges. Electrostatic interaction was found to be the main driving force, and differences of residues role between two binding modes were elucidated. Buffer molecules in aqueous solutions can stabilize aptamer-Cd2+ complex by hydrogen bonds. This study revealed the specific interaction mechanisms of aptamer with Cd2+ at an atomic level, which provided theoretical references for aptamer-based Cd2+ detection methods establishment as well as an efficient technical route of screening potential aptamers for heavy metal ions.

Adsorption-desorption behaviors of ciprofloxacin onto aged polystyrene fragments in aquatic environments

As two emerging pollutants of great concern, microplastics (MPs) and antibiotics inevitably cooccur in various aquatic environments and interact with each other, impacting the fate and ecological risks. Aging obviously complicates their interaction and deserves further study. Therefore, the adsorption-desorption behaviors of ciprofloxacin (CIP) onto polystyrene (PS) fragments with various aging extent were investigated, and the key physiochemical properties influencing the interaction and the interaction mechanisms were clarified by redundancy analysis, FTIR and XPS spectra. The physicochemical properties of PS MPs were significantly changed with aging time, and the morphological and chemical changes seemed to occur asynchronously. The adsorption of CIP onto the pristine PS MPs relied on physisorption, especially the ion-involving electrostatic and cation-π interaction. Due to the hydrogen bonding formed by the C-OH, CO, and O-CO groups of PS and CIP, the adsorption capacities of the aged PS MPs were greatly increased. The desorption efficiency of CIP from MPs in the gastric fluid was closely related to the solution ionic strengths, C-OH and CO groups of MPs, while that in the intestinal fluid was associated with O-CO groups of MPs. The different impact factors could be well described by the differences in the chemical components and pHs of the simulated gastric and intestinal fluids. This study gives a comprehensive understanding of the adsorption-desorption behaviors of antibiotics onto MPs at a molecular level and indicates that MPs could act as Trojan horses to transport antibiotics into aquatic organisms.

Interaction mechanism and spatial effect of cross-regional haze pollution based on a multisectoral economy-energy-environment (3E) model and the evidence from China

The transboundary characteristics and multisectoral factor interaction mechanism of haze pollution have aroused widespread attention but remain understudied. This article proposes a comprehensive conceptual model that clarifies regional haze pollution, further establishes a theoretical framework on a cross-regional, multisectoral economy-energy-environment (3E) system, and attempts to empirically investigate the spatial effect and interaction mechanism employing a spatial-econometrics model based on China's province-level regions. The results demonstrate that (1) regional haze pollution is a transboundary atmospheric state formed by the accumulation and agglomeration of various emission pollutants; moreover, there is a "snowball" effect and a spatial spillover effect. (2) The formation and evolution of haze pollution are driven by the multisectoral factors of 3E system interaction, and the findings still hold after theoretical and empirical analysis and robustness tests. (3) Significant spatial autocorrelation exists for the 3E factors, presenting different clustering modes with a dynamic spatiotemporal evolution, particularly in the high-high (H-H) mode and low-low (L-L) mode. (4) Significant heterogeneous impacts of economic and energy factors on haze pollution are identified, namely, an inverted "U-shaped" relationship and a positive linear association, respectively. Further spatial analysis demonstrates a strong spatial spillover and obvious path dependence among local and neighboring regions. Policymakers are advised to consider multisectoral 3E system interaction and cross-regional collaboration. Integr Environ Assess Manag 2023;19:1525-1543. © 2023 SETAC.

Intrinsic mechanism for the removal of antibiotic pollution by a dual coagulation process from the perspective of the interaction between NOM and antibiotic

Antibiotics bring potential risks to human health and ecosystem, and their coexistence with natural organic matters (NOMs) could have harmful impacts on the environment. Herein, a polyaluminium chloride (PAC)-polydimethyl diallyl ammonium chloride (PDMDAAC) dual coagulation process was designed to remove the co-pollutants of chlortetracycline (CTC) and humic acid (HA), representing antibiotics and NOMs, respectively. The main research strength was given to understand molecular interactions and their mechanisms associated with the coagulation and flocculation. We found that the co-existing HA and CTC increased the hydrophily and stability of contaminants, and generated HA@CTC complexes with large particles size. The interaction mechanism between CTC and HA was mainly hydrogen bonding, hydrophobic association action, n-π* electron donor-acceptor interaction, and π-π* conjugation. Lewis acid-base interaction was the main force between HA and CTC. The bonding energies of OH…N, OH…O, and hydrophobic association were -12.2 kcal/mol, -13.1 kcal/mol, and -11.4 kcal/mol, respectively, indicating that hydrogen bonding was stronger than hydrophobic association. The interactions between HA and CTC could improve their removal efficiency in the coagulation process. This is due to that the functional groups (COOH and OH) in the HA@CTC could be adsorbed by Al based hydrolysates. Polar interaction dominated the CTC and HA removal, and PAC was more efficient than PDMDAAC to remove HA@CTC complexes due to its higher complexing capacity. Thanks to the low concentration of residual contaminants and the formation of large and loose flocs, the interaction of HA and CTC could alleviate membrane fouling during ultrafiltration process. This study will provide new insight into the efficient removal of combined pollution and membrane fouling control.

Elucidation of interactions between myofibrillar proteins and κ-carrageenan as mediated by NaCl level: Perspectives on multiple spectroscopy and molecular docking

The present study was aimed to investigate the intermolecular interaction between myofibrillar proteins (MP) and κ-carrageenan (KC) as mediated by KC concentration (0.1, 0.2, 0.3, and 0.4 %, w/w) and NaCl levels (0.3 and 0.6 M) based on the multiple spectroscopy and molecular docking. The results showed that the incorporation of KC increased the turbidity, zeta-potential, and surface hydrophobicity of MP-KC mixed sols with a dose-dependent manner, as well as significantly decreasing the protein solubility (P < 0.05), which indicated that the interaction between KC and MP promoted the expansion of protein structure and exposed more hydrophobic groups. Fluorescence spectra result revealed that the interaction between MP and KC was a static quenching in the fluorescence quenching process, which affected the aromatic amino acids residue microenvironment of MP. Moreover, the existence of KC decreased the α-helix contents of MP (P < 0.05), contributing to the transformation from random structure to organized configuration of MP. In addition, molecular forces, the molecular docking and thermodynamic parameters indicated that hydrophobic interactions, van der Waals force, and hydrogen bonding were considered as the main interaction forces between MP and KC. Furthermore, 0.6 M NaCl level rendered higher solubility and particle size, as well as lower turbidity and the surface hydrophobicity of MP-KC mixed sols than those with 0.3 M NaCl level (P < 0.05), which promoted the unfolding of MP molecule and subsequently increased the numbers of binding sites between MP and KC, facilitating the intermolecular interactions between MP and KC in mixed sols.

Probing the molecular mechanism of interaction between polystyrene nanoplastics and catalase by multispectroscopic techniques

Nanoplastics are emerging pollutants that pose a potential threat to the environment and organisms and are widely distributed in environmental samples and food chains. The accumulation of polystyrene nanoplastics (PS-NPs) in an organism can cause oxidative stress. Currently, toxicity studies of PS-NPs mainly focus on the individual and cellular levels, whereas few studies have been conducted on the molecular mechanisms of the interaction between PS-NPs and catalase (CAT). Based on this, CAT was chosen as the target receptor for molecular toxicity research to reveal the interaction mechanism at the molecular level between PS-NPs and CAT by using various spectroscopic means and enzyme activity detection methods. The results indicated that PS-NPs destroyed the secondary structure of CAT, causing its protein skeleton to loosen and unfold, increasing the content of α-helices, decreasing the content of β-sheets, and exposing the position of the heme group. After exposure to PS-NPs, the internal fluorophore of CAT underwent fluorescence sensitization, resulting in a micelle-like structure, which enhanced the hydrophobicity of aromatic amino acids but did not change their polarity. In addition, the aggregation state of CAT was altered upon binding to PS-NPs, and the volume was further increased. Finally, these structural changes led to a gradual decrease in CAT activity. This study presents a comprehensive assessment of the toxicity of PS-NPs at the molecular level, which can provide more experimental support for the study of the biotoxicological efficacy of PS-NPs.

Slice-layer COFs-aerogel: a regenerative dispersive solid-phase extraction adsorbent for determination of ultra-trace quinolone antibiotics

A novel type of three-dimensional network structure, covalent organic frameworks (COFs) aerogel, was fabricated and applied to dispersive solid-phase extraction (dSPE) of quinolone antibiotics (QAs). Density functional theory (DFT) was applied to investigate the possible interaction mechanism and results confirmed that the strong adsorption affinity is attributed to the intralayer hydrogen bonds and π-π interaction. Furthermore, a sensitive analytical method based on COFs-aerogel for determining quinolone antibiotics residues in water and honey samples was developed and HPLC-MS/MS was used for sample detection and quantification. Under the optimal conditions, COFs-aerogel exhibited a wide linearity (0.1-500 ng∙L-1), low limits of detection (0.02-0.06 ng∙L-1), and good precision (RSD ˂ 10%) for selected QAs. A preliminary practical application of the developed method was proved by the efficient detection of quinolone antibiotics in water and food samples with good recoveries (68.2-104% and 64.0-100% for water and honey samples, respectively). Combining the experimental data with theoretical calculation, results illustrated that COFs-aerogel holds a great potential to capture contaminants and address environmental and food safety issues.

An integrated method for studying the biodegradation of benzo[a]pyrene by Citrobacter sp. HJS-1 and interaction mechanism based on the structural model of the initial dioxygenase

A bacterial strain Citrobacter sp. HJS-1 was discovered from the sludge in a drainage canal of a coal mine. Firstly, its biodegradation capacity for benzo[a]pyrene (BaP) was detected under different concentrations. The results proved that the strain possessed excellent biodegradation capacity for BaP with high-efficiency degradation rates ranging from 78.9 to 86.8%. The highest degradation rate was observed in the low-concentration sample, and the high-concentration BaP had a slight influence on the biodegradation capacity due to the potential toxicity of BaP and its oxygen-containing derivatives. Meanwhile, the degradation test for the other five aromatic hydrocarbons (2- to 4-ring) proved that the strain had a comprehensive degradation potential. To clarify the biodegradation mechanism of BaP, a dioxygenase structure was constructed by homology modeling. Then, the interactions between dioxygenase and BaP were researched by molecular simulation. Combined with the identification of the vital BaP-cis-7,8-dihydrodiol intermediate and the interaction analysis, the initial oxidation mode and the binding site of BaP were revealed in the dioxygenase. Taken together, this study has offered a way to understand the biodegradation process of BaP and its interaction mechanism based on experimental and theoretical analysis.

Substrate-enzyme interactions and catalytic mechanism in a novel family VI esterase with dibutyl phthalate-hydrolyzing activity

Microbial degradation has been confirmed as effective and environmentally friendly approach to remediate phthalates from the environment, and hydrolase is an effective element for contaminant degradation. In the present study, a novel dibutyl phthalate (DBP)-hydrolyzing carboxylesterase (named PS06828) from Pseudomonas sp. PS1 was heterogeneously expressed in E. coli, which was identified as a new member of the lipolytic family VI. Purified PS06828 could efficiently degrade DBP with a wide range of temperature (25-37 °C) and pH (6.5-9.0). Multi-spectroscopy methods combined with molecular docking were employed to study the interaction of PS06828 with DBP. Fluorescence and UV-visible absorption spectra revealed the simultaneous presence of static and dynamic component in the fluorescence quenching of PS06828 by DBP. Synchronous fluorescence and circular dichroism spectra showed inconspicuous alteration in micro-environmental polarity around amino acid residues but obvious increasing of α-helix and reducing of β-sheet and random coil in protein conformation. Based on the information on exact binding sites of DBP on PS06828 provided by molecular docking, the catalytic mechanism mediated by key residues (Ser113, Asp166, and His197) was proposed and subsequently confirmed by site-directed mutagenesis. The results can strengthen our mechanistic understanding of family VI esterase involved in hydrolysis of phthalic acid esters, and provide a solid foundation for further enzymatic modification.