New insights into the interaction between dissolved organic matter and different types of antibiotics, oxytetracycline and sulfadiazine: Multi-spectroscopic methods and density functional theory calculations

Distribution characteristics of sulfonamide antibiotics between water and extracellular polymeric substances in municipal sludge

The interaction between extracellular polymeric substances (EPS) in municipal sludge and antibiotics in wastewater is critical in wastewater treatment, resource recovery, and sludge management. Therefore, it is increasingly urgent to investigate the distribution coefficient (Log K) of sulfonamide antibiotics (SAs) in EPS, particularly in sludge-derived dissolved organic carbon (DOC) and aqueous phase systems. Herein, through balance experiments, the concentrations of SAs were determined using alkaline extraction EPS (AEPS) and alginate-like extracellular polymer (ALE) systems, and the Log KDOC values were determined. The results showed that the Log KDOC of AEPS was higher than that of ALE, which exhibited a negative KDOC value, indicating an inhibitory effect on dissolution. For the three SAs studied, the Log KDOC values were in the following order: sulfamethoxazole > sulfapyridine > sulfadiazine. This order can be attributed to the differing physicochemical properties, such as polarity, of the SAs. Three-dimensional excitation-emission matrix fluorescence spectra and fitting results indicated a lack of aromatic proteins dominated by tryptophan and humus-like substances in ALE. Meanwhile, the hydrophobic interaction of aromatic proteins dominated by tryptophan was the main driving force in the binding process between AEPS and SAs.

Molecular insights into linkages among free-floating macrophyte-derived organic matter, the fate of antibiotic residues, and antibiotic resistance genes

Macrophyte rhizospheric dissolved organic matter (ROM) served as widespread abiotic components in aquatic ecosystems, and its effects on antibiotic residues and antibiotic resistance genes (ARGs) could not be ignored. However, specific influencing mechanisms for ROM on the fate of antibiotic residues and expression of ARGs still remained unclear. Herein, laboratory hydroponic experiments for water lettuce (Pistia stratiotes) were carried out to explore mutual interactions among ROM, sulfamethoxazole (SMX), bacterial community, and ARGs expression. Results showed ROM directly affect SMX concentrations through the binding process, while CO and N-H groups were main binding sites for ROM. Dynamic changes of ROM molecular composition diversified the DOM pool due to microbe-mediated oxidoreduction, with enrichment of heteroatoms (N, S, P) and decreased aromaticity. Microbial community analysis showed SMX pressure significantly stimulated the succession of bacterial structure in both bulk water and rhizospheric biofilms. Furthermore, network analysis further confirmed ROM bio-labile compositions as energy sources and electron shuttles directly influenced microbial structure, thereby facilitating proliferation of antibiotic resistant bacteria (Methylotenera, Sphingobium, Az spirillum) and ARGs (sul1, sul2, intl1). This investigation will provide scientific supports for the control of antibiotic residues and corresponding ARGs in aquatic ecosystems.

Diverse Applications of Two-Dimensional Correlation Spectroscopy (2D-COS)

This second of the two-part series of a comprehensive survey review provides the diverse applications of two-dimensional correlation spectroscopy (2D-COS) covering different probes, perturbations, and systems in the last two years. Infrared spectroscopy has maintained its top popularity in 2D-COS over the past two years. Fluorescence spectroscopy is the second most frequently used analytical method, which has been heavily applied to the analysis of heavy metal binding, environmental, and solution systems. Various other analytical methods including laser-induced breakdown spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, capillary electrophoresis, seismologic, and so on, have also been reported. In the last two years, concentration, composition, and pH are the main effects of perturbation used in the 2D-COS fields, as well as temperature. Environmental science is especially heavily studied using 2D-COS. This comprehensive survey review shows that 2D-COS undergoes continuous evolution and growth, marked by novel developments and successful applications across diverse scientific fields.

Biochar-derived dissolved organic matter enhanced the release of residual ciprofloxacin from the soil solid phase

Biochar has been utilized to reduce ciprofloxacin (CIP) residues in soil. However, little is known about the effect of biochar-derived dissolved organic matter (DOM) on residual CIP transformation. Thus, we analyzed the residual soil CIP as influenced by biochar generated from rice straw (RS3 and RS6), pig manure (PM3 and PM6), and cockroach shell (CS3 and CS6) at 300 °C and 600 °C. The three-dimensional excitation-emission matrix (3D-EEM), parallel factor analysis (PARAFAC) and two-dimensional correlation spectral analysis (2D-COS) were used to describe the potential variation in the DOM-CIP interaction. Compared with CK, biochar amendment increased the water-soluble CIP content by 160.7% (RS3), 55.2% (RS6), 534.1% (PM3), 277.5% (PM6), 1160.6% (CS3) and 703.9% (CS6), indicating that the biochar feedstock controlled the soil CIP release. The content of water-soluble CIP was positively correlated with the content of dissolved organic carbon (r = 0.922, p < 0.01) and dissolved organic nitrogen (r = 0.898, p < 0.01), suggesting that the major influence of the water-soluble CIP increase was DOM. The fluorescence quenching experiment showed that the interaction between DOM and CIP triggered static quenching and the creation of a DOM complex. The mean log K of protein-like material (4.977) was higher than that of terrestrial humus-like material (3.491), suggesting that the protein-like material complexed CIP was more stable than the humus-like material. Compared with pyrolysis at 300 °C, pyrolysis at 600 °C decreased the stability of the complex of protein-like material and CIP by 0.44 (RS), 1.689 (PM) and 0.548 (CS). This result suggested that the influence of temperature change was more profound on PM biochar-derived DOM than on RS and CS. These insights are essential for understanding CIP transportation in soil and controlling CIP contamination with biochar.

Recent advances in the role of dissolved organic matter during antibiotics photodegradation in the aquatic environment

The presence of residual antibiotics in the environment is a prominent issue. Photodegradation behavior is an important way of antibiotics reduction, which is closely related to dissolved organic matter (DOM) in water. The review provides an overview of the latest advancements in the field. Classification, characterization of DOM, and the dominant mechanisms for antibiotic photodegradation were discussed. Furthermore, it summarized and compared the effects of DOM on different antibiotics photodegradation. Moreover, the review comprehensively considered the factors influencing the photodegradation of antibiotics in the aquatic environment, including the characteristics of light, temperature, dosage of DOM, concentration of antibiotics, solution pH, and the presence of coexisting ions. Finally, potential directions were proposed for the development of predictive models for the photodegradation of antibiotics. Based on the review of existing literature, this paper also considered several pathways for the future study of antibiotic photodegradation. This study allows for a better understanding of the DOM's environmental role and provides important new insights into the photochemical fate of antibiotics in the aquatic environment.

The structural transformation reversibility of biogas slurry derived dissolved organic matter and its binding properties with norfloxacin under temperature fluctuation

The widespread use of biogas slurry could potentially raise the environmental risk of antibiotics. Dissolved organic matter (DOM), as the most active part of biogas slurry, was able to interact with antibiotics and play a crucial role in the structure and function of soil and aquatic ecosystems. The recent shifts in global climate patterns have garnered significant attention due to their substantial impact on temperature, thereby exerting a direct influence on the characteristics of DOM and subsequently on the environmental behavior of antibiotics. However, there is limited research concerning the impact of temperature on the binding of DOM and antibiotics. Thus, this study aimed to explore the temperature-dependent structural transformation and driving factors of biogas slurry-derived DOM (BSDOM). Additionally, the binding characteristics between BSDOM and the commonly used antibiotic norfloxacin (NOR) at different temperatures were studied by using multi spectroscopic methods and two-dimensional correlation spectroscopy (2D-COS) analysis. The results suggested that the temperature-dependent structural transformation of BSDOM was reversible, with a slight lag in the transition temperature under cooling (13 °C for heating and 17 °C for cooling). Heating promoted the conversion of protein-like to humic-like substances while cooling favored the decomposition of humic-like substances. BSDOM and NOR were static quenching, with oxygen-containing functional groups such as C-O and -OH playing an important role. Temperature influenced the order of binding, the activity of the protein fraction, and its associated functional groups. At temperatures of 25 °C and 40 °C, the fluorescent components were observed to exhibit consistent binding preferences, whereby the humic-like component demonstrated a greater affinity for NOR compared to the protein-like component. However, the functional group binding order exhibited an opposite trend. At 10 °C, a new protein-like component appeared and bound preferentially to NOR, when no C-O stretch corresponding to the amide was observed. The finding will contribute to a comprehensive understanding of the interaction mechanisms between DOM and antibiotics under climate change, as well as providing a theoretical basis to reduce the environmental risks of biogas slurry and antibiotics.

Field migration of veterinary antibiotics via surface runoff from chicken-raising orchard in responding to natural rainfalls

Knowledge on runoff transport of manure-sourced antibiotics from farmland soil to aquatic environment is limited due to complexity of hydrological regime and pathways. This study monitored natural rainfalls in sloping orchard plots with free-range chickens, with an attempt to investigate the migration characteristics of typical antibiotics via surface runoff as well as the impact of manure presence. Results showed that rainstorms continuously carried away antibiotics in surface runoff and all target antibiotics including those with high affinities to soil were detected at the beginning of runoff production. Concentration of antibiotics was found to respond strongly to the instantaneous rainfall intensity, showing consistent fluctuations during rainfalls. Concentrations of sulfonamides and florfenicol were two orders of magnitude higher than that of tetracyclines and fluoroquinolones. Compared to the control without raising chickens, antibiotics migration was considerably increased with the increased runoff production due to soil surface changes caused by chicken activities. Additionally, dynamics of antibiotic concentration significantly correlated with variations of fluorescent DOM components. Chicken manure-derived DOM mainly contained tryptophan moiety, and laboratory fluorescence quenching test with 2D-COS analysis indicated that all antibiotics interacted more strongly and preferentially with tryptophan than humic-like species. Antibiotics bonded to manure DOM with an affinity corresponding to the significance level of their correlations. In this light, potential use of fluorescence indices based on the established correlations may provide a convenient tool for tracing runoff migration of antibiotics during rainfalls.

Water-soluble organic carbon (WSOC) from vegetation fire and its differences from WSOC in natural media: Spectral comparison and self-organizing maps (SOM) classification

Vegetation fire frequently occurs globally and produces two types of water-soluble organic carbon (WSOC) including black carbon WSOC (BC-WSOC) and smoke-WSOC, they will eventually enter the surface environment (soil and water) and participate in the eco-environmental processes on the earth surface. Exploring the unique features of BC-WSOC and smoke-WSOC is critical and fundamental for understanding their eco-environmental effects. Presently, their differences from the natural WSOC of soil and water remain unknown. This study produced various BC-WSOC and smoke-WSOC by simulating vegetation fire and used UV-vis, fluorescent EEM-PARAFAC, and fluorescent EEM-SOM to analyze their different features from natural WSOC of soil and water. The results showed that the maximum yield of smoke-WSOC reached about 6600 folds that of BC-WSOC after a vegetation fire event. The increasing burning temperature decreased the yield, molecular weight, polarity, and protein-like matters abundance of BC-WSOC and increased the aromaticity of BC-WSOC, but presented a negligible effect on the features of smoke-WSOC. Furthermore, compared with natural WSOC, BC-WSOC had a greater aromaticity, smaller molecular weight, and more humic-like matters, while smoke-WSOC had a lower aromaticity, smaller molecular size, higher polarity, and more protein-like matters. EEM-SOM analysis indicated that the ratio between the fluorescence intensity at Ex/Em: 275 nm/320 nm and the sum fluorescence intensity at Ex/Em: 275 nm/412 nm and Ex/Em: 310 nm/420 nm could effectively differentiate WSOC of different sources, following the order of smoke-WSOC (0.64-11.38) > water-WSOC and soil-WSOC (0.06-0.76) > BC-WSOC (0.0016-0.04). Hence, BC-WSOC and smoke-WSOC possibly directly alter the quantity, properties, and organic compositions of WSOC in soil and water. Owing to smoke-WSOC having far greater yield and bigger difference from natural WSOC than BC-WSOC, the eco-environmental effect of smoke-WSOC deposition should be given more attention after a vegetation fire.

The investigation of interaction and chaperon-like activity of α-synuclein as a protein in pathophysiology of Parkinson's disease upon direct interaction with tectorigenin

Analyzing the therapeutic potential of a therapeutic biomolecule requires an understanding of how it may interact with proteins and modify their corresponding functions. α-Synuclein is a protein which is widely involved in the pathogenesis of Parkinson's disease (PD) and shows chaperon-like activity. We have selected tectorigenin, a most common methoxyisoflavone extracted from plants, among therapeutic bioactive molecules that are documented to have different therapeutic effects. Herein, we aimed to explore how tectorigenin interacts with α-synuclein in vitro by mimicking the physiological environment. Spectroscopic as well as theoretical studies including molecular docking simulation, were used to examine the effects of tectorigenin on the conformation and dynamics of α-synuclein. It was shown that tectorigenin is able to quench the protein emission spectra relied on a mixed static-dynamic quenching mechanism. Furthermore, it was displayed that tectorigenin binding to α-synuclein leads to microenvironmental changes in the tertiary structure of protein, however the protein's secondary structure was almost unchanged. It was also deduced that tectorigenin results in thermal stability of α-synuclein structure, evidenced by less perturbation of α-synuclein secondary structure following elevation of temperature in the presence of tectorigenin relative to that of free form. Molecular docking simulation demonstrated that non-covalent reactions, mainly hydrogen bonds, had a key role in the interaction and stabilization of α-synuclein in the presence of tectorigenin. Moreover, chaperon-like activity of α-synuclein was improved in the presence of tectorigenin against two model proteins, βL-crystallin and catalase. The findings showed that tectorigenin can lead to stabilization of α-synuclein, which may be used as a therapeutic agent in prevention of neurodegenerative diseases.

Multiple spectroscopic insights into the interaction mechanisms between proteins and humic acid

Proteins are important constituents of dissolved organic matter (DOM) in aqueous environments, and their interaction with humic acid (HA), another key component of DOM, substantially affects the environmental behaviors of DOM. In this work, the interaction mechanisms between tryptophan-containing proteins and HA were systematically investigated using multiple molecular spectroscopic approaches. The fluorescence quenching tests indicate that bovine serum albumin (BSA) was more readily quenched by HA and the coexisting phenolic, carboxyl, and quinone groups in HA contributed to this process significantly. By comparison, the fluorescence of L-tryptophan (L-Trp) was more stable under the same conditions. Furthermore, with multiple groups in HA, static quenching with the binding constants and the number of sites were calculated in the protein-HA and L-Trp-HA mixtures. In addition, the differential fluorescence spectra, UV‒Vis spectra, and two-dimensional correlation spectroscopy results confirmed that L-tryptophan amino acid could indeed form a complex with HA, while did not lead to fluorescence quenching. Finally, the molecular docking and density functional theory (DFT) simulations highlighted the contribution of multiple residues surrounding the HA groups to their interactions. The direct interaction between the tryptophan residue and HA might not be the prerequisite for the fluorescence response. Therefore, our work provides further insights into protein-HA interactions and implies other reasonable elucidations for further explanation.

Detection and binding interactions of pharmaceutical contaminants using quartz crystal microbalance - Role of adsorbate structure and surface functional group on adsorption

HYPOTHESIS

Emerging contaminants (ECs) can interact with soft solid/aqueous interfaces of particulate organic matter and microplastics in the aquatic environment but to what extent? It is hypothesized that EC adsorption can be detected using quartz crystal microbalance (QCM), a sensitive gravimetric tool, and their adsorption energetics and uptake capacity can be measured for various substrates of distinct functional group. This in turn reveals the specific vs. nonspecific interactions.

EXPERIMENTS

QCM has been used to detect and measure the adsorption of selected pharmaceuticals, amlodipine (AMP) and carbamazepine (CBZ), onto butyl, carboxyl, amine, and phenyl functionalized self-assembled monolayers (SAMs), mapping out the hydrophobic effect, H-bonding capability, and π- interactions. Adsorption free energy (ΔGads) and maximum interfacial concentration (cmax) for these surfaces are compared. Solvatochromic studies to elucidate the likelihood of H-bonding interactions for CBZ and AMP have been conducted using UV-Vis absorption spectroscopy.

FINDINGS

Amlodipine and carbamazepine adsorb onto butyl/aqueous interface with respective ΔGads values of -35.8 ± 1.1 and -37.7 ± 0.1 kJ/mol. Nonspecific interaction allows a greater extent of cmax on the hydrophobic/aqueous interface. CBZ does not bind to the phenyl surface. AMP and CBZ exhibit H-bonding and show proclivity for the amine and carboxyl SAMs. Interfacial chemical environment and adsorbate structural properties play a significant role on EC adsorption.

Effects of dissolved organic matter on the adsorption of norfloxacin on a sandy soil (fraction) from the Yellow River of Northern China

Dissolved organic matter (DOM), which exists widely in the environment, coming from different sources, may greatly affect the adsorption of antibiotics. However, the adsorption mechanisms of antibiotics in a sandy soil and the effects of DOM from different sources on the adsorption remain poorly understood. This study systematically investigated the adsorption characteristics of norfloxacin (NOR) onto a sandy soil obtained from the banks of Xi'an in Yellow River and in the presence of three DOM including HDOM (commercially available humic acids), LDOM (derived from fallen leaves) and MDOM (derived from cattle manure). Elemental analysis, UV-vis spectroscopy, 3D-EEM, XPS, TOC, SEM, and FTIR were used to analyze the adsorption mechanism. It was found that all the DOM sources we used could reduce the adsorption of NOR on sandy soil and prolong the reaction time to reach adsorption equilibrium. The decreasing adsorption capacities of NOR by the three types of DOM (10 mg/L) followed the order as: HDOM < LDOM < MDOM, which was related to their aromaticity, polarity and hydrophobicity. These adsorption processes of NOR on sandy soil in the presence of DOM were well fitted by Double-chamber first-order kinetics, Linear model and Freundlich models. Besides, the adsorption reaction was endothermic and spontaneous. Adsorption competition of DOM molecules with NOR, or formation of DOM-NOR complexes in solution resulted in a decrease of sandy soil adsorption capacity. Correspondingly, co-adsorption and cumulative adsorption were also considered to be the key processes that determined NOR adsorption towards sandy soil after adding DOM. Moreover, the adsorption of NOR onto sandy soil exhibited strong pH-dependent characteristic and NOR might be more easily leached from sandy soil in the aquifer at an alkaline pH. High-ion strength suppressed the adsorption. These results would help to understand the fate and risk of NOR under the action of different DOM.