Mechanical Properties of Low-Molecular-Weight Peptide Hydrogels Improved by Thiol-Ene Click Chemistry.

Low-molecular-weight peptide hydrogels can be formed by self-assembly through weak interactions, but the application of the hydrogel is influenced by its weak mechanical properties. Therefore, it is important to construct low-molecular-weight peptide hydrogels with excellent mechanical properties. In this work, we designed the pentapeptide molecule Fmoc-FFCKK-OH (abbreviated as FFCKK) with a sulfhydryl group, and another low-molecular-weight cross-linker N,N'-methylenebis(acrylamide) (MBA) was introduced to construct a hydrogel with excellent mechanical properties. The secondary structure change process of FFCKK and the assembly mechanism of hydrogel were analyzed using theoretical calculations and experimental characterizations. The occurrence of thiol-ene click chemistry provides covalent interaction in the hydrogel, and the synergistic effect ofcovalent interaction and hydrogen bonding improves the mechanical properties of the hydrogel by nearly 10-fold. The hydrogel was observed to be able to withstand a stress of 368 Pa and to break in a layer-by-layer manner by compression testing. The micromechanics of the hydrogels were characterized, and the excellent mechanical properties of the hydrogels were confirmed. The synergistic approach provides a new idea for the preparation of low-molecular-weight peptide hydrogels and facilitates the expansion of their potential applications in biomedical fields.

Isolation and thermo-acclimation of thermophilic bacteria in hyperthermophilic fermentation system.

Hyperthermophilic microorganisms play a key role in the hyper-thermophilic composting (HTC) technique. However, little information is available about the hyperthermophilic microorganisms prevalent in HTC systems, except for the Calditerricola satsumensis, Calditerricola yamamurae, and Thermaerobacter. To obtain effective hyper-thermophilic microorganisms, a continuous thermo-acclimation of the suitable thermophilic microorganisms was demonstrated in this study. Bacillus thermoamylovorans with high-temperature endurance (70 °C) were newly isolated from sludge composting, and an adequate slow heating rate (2 °C per cycle) was applied to further improve its thermostability. Finally, a strain with a maximum growth temperature of 80 °C was obtained. Moreover, structural and hydrophobic changes in cell proteins, the special amino acid content ratio, and the membrane permeability of the thermophilic bacterium after thermo-acclimation were evaluated for improved thermostability. In addition, the acclimated hyperthermophilic bacterium was further inoculated into the HTC system, and an excellent performance with a maximum operating temperature of 82 °C was observed.

Study on the Release Potential of BPA and Steroid Estrogens in the Sediments of Erhai Lake, a Typical Plateau Lake of China.

On-site sampling analysis and laboratory-scale experiments were conducted to study the pollution status and release potential of EDCs in Erhai Lake. We found that nitrogen and phosphorus pollution in Erhai Lake sediment were both at a high level, as well as EDCs pollution. The concentrations of BPA, E2α, E1, E2ß, EE2, and E3 were 36.84 ng/g(DW), 13.04 ng/g(DW), 128.97 ng/g(DW), 52.57 ng/g(DW), 18.48 ng/g(DW) and 5.36 ng/g(DW), respectively. The concentrations of E2α, E1, E2ß and EE2 in the bottom water were higher than the surface water due to the impact of sediment release. The results of the 20 days release test indicated that BPA release from the sediment had a greater correlation with the original concentration and the particle size of sediment, while the steroid EDCs had no obvious correlation with these two factors, probably due to the difference in hydrophobicity between them. Under hydraulic disturbance and aerobic conditions, the release process of EDCs was accompanied by a large amount of microbial degradation, and degradation amount > released amount. BPA was released quickly, 9.56% was released in 20 days, but only 3.37% of steroid EDCs released. In comparison, the release process of steroids was longer and posed a greater threat to aquatic ecology.

Trend analysis and modeling of nutrient concentrations in a preliminary eutrophic lake in China.

Accurately measuring and estimating trends and variations in nutrient levels is a significant part of managing emerging eutrophic lakes in developing countries. This study developed an integrated approach containing Seasonal Trend Decomposition using Loess (STL) and a dynamic nonlinear autoregressive model with exogenous input (NARX) network to decompose and estimate the nutrient concentrations in Lake Erhai, a preliminary eutrophic lake in China. The STL decomposition results indicated that total nitrogen (TN) concentration of Lake Erhai progressively descended from 2006 to 2014, except for some agriculture area. The total phosphorus (TP) concentration showed an increasing trend from 2006 to 2013 and then decreased in 2014, but in the area near the tourist attractions, TP increased continuously from 2011 to 2014. Seasonal variations in TN and TP indicated that the lowest water quality of Lake Erhai occurred from July to October. Based on results obtained with STL, TP was selected as the sensitive parameter, as it showed a significant deterioration trend, and the area near the tourist attractions was selected as the sensitive area. Three variables (DO, pH, and water temperature) were selected as input parameters to estimate TP using the dynamic NARX model. The NARX modeling results demonstrated that it can accurately estimate TP concentrations with low root-mean-square error (0.0071 mg/L). The study establishes a new approach to better understand trends and variations in nutrient levels and to better refine estimates by identifying more easily accessible physical parameters in a preliminary eutrophic lake.

Green Upconversion Emissions in Er³âº/Yb³âº Co-Doped CaMoO4Prepared by Microwave-Assisted Metathetic Method.

In this study Er³âº doped CaMoO4 (CaMoO4:Er³âº), and Er³âº/Yb³âº-co-doped CaMoO4 (CaMoO4:Er³âºYb³âº) nanoparticles have been synthesized by the microwave-assisted metathetic method. Er³âº/Yb³âº co-doped CaMoO4 nanoparticles sintered at 600 °C showed the strongest photoluminescence intensity, and crystallized well. At the excitation of 980 nm, the CaMoO4 nanoparticles show the strongest green emission at the 520 nm and 550 nm emission bands. Moreover, the green light produced has a better color purity.

Principles, applications, and limitations of diffusive gradients in thin films induced fluxed in soils and sediments.

The diffusive gradients in thin films (DGT) technique serves as a passive sampling method, inducing analyte transport and concentration. Its application is widespread in assessing labile components of metals, organic matter, and nutrients across various environmental media such as water, sediments, and saturated soils. The DGT devices effectively reduce the porewater concentration through irreversible binding of solutes, consequently promoting the release of labile species from the soil/sediment solid phase. However, the precise quantification of simultaneous adsorption and desorption of labile species using DGT devices alone remains a challenge. To address this challenge, the DGT-Induced Fluxes in Soils and Sediments (DIFS) model was developed. This model simulates analyte kinetics in solid phases, solutions, and binding resins by incorporating factors such as soil properties, resupply parameters, and kinetic principles. While the DIFS model has been iteratively improved to increase its accuracy in portraying kinetic behavior in soil/sediment, researchers' incomplete comprehension of it still results in unrealistic fitting outcomes and an oversight of the profound implications posed by kinetic parameters during implementation. This review provides a comprehensive overview of the optimization and utilization of DIFS models, encompassing fundamental concepts behind DGT devices and DIFS models, the kinetic interpretation of DIFS parameters, and instances where the model has been applied to study soils and sediments. It also highlights preexisting limitations of the DIFS model and offers suggestions for more precise modeling in real-world environments.

Responses to phytoplankton community succession and expression of key functional genes in plateau lakes under 17ß-estradiol interference.

Steroid estrogens (SEs) have garnered global attention because of their potential hazards to human health and aquatic organisms at low concentrations (ng/L). The ecosystems of plateau freshwater lakes are fragile, the water lag time is long, and pollutants easily accumulate, making them more vulnerable to the impact of SEs. However, the knowledge of the impact of SEs on the growth and decomposition of phytoplankton communities in plateau lakes and the eutrophication process is limited. This study investigated the effects and mechanisms of SEs exposure on dominant algal communities and the expression of typical algal functional genes in Erhai Lake using indoor simulations and molecular biological methods. The results showed that phytoplankton were sensitive to 17ß-estradiol (E2ß) pollution, with a concentration of 50, and 100 ng/L E2ß exposure promoting the growth of cyanophyta and chlorophyta in the short term; this poses an ecological risk of inducing algal blooms. E2ß of 1000 ng/L exposure led to cross-effects of estrogenic effects and toxicity, with most phytoplankton being inhibited. However, small filamentous cyanobacteria and diatoms exhibited greater tolerance; Melosira sp. even exhibited "low inhibition, high promotion" behavior. Exposure to E2ß reduced the Shannon-Wiener diversity index (H'), Pielou index (J), and the number of dominant algal species (S) in phytoplankton communities, leading to instability in community succession. E2ß of 50 ng/L enhanced the expression levels of relevant functional genes, such as ftsH, psaB, atpB, and prx, related to Microcystis aeruginosa. E2ß of 50 ng/L and 5 mg/L can promote the transcription of Microcystis toxins (MC) related genes (mcyA), leading to more MC production by algal cells.

Change of physiochemical characteristics, nutritional quality, and volatile compounds of Chenopodium quinoa Willd. during germination.

The impacts of varying germination periods (0-72 h) on morphological properties, proximate composition, amino acid profile, GABA levels, antioxidant attributes, polyphenol content (both free and bound), and volatile compounds of quinoa were evaluated. Germination significantly increased the content of fiber, amino acids, GABA, polyphenols, and in-vitro antioxidant activities in quinoa. The optimal nutritional quality and antioxidant capacity of quinoa were observed during the 36-72 h germination period. We examined the dynamics of 47 phenolic compounds in quinoa during germination and noted a substantial rise in free phenolic acids and bound flavonoids post-germination. A total of 53 and 84 volatile compounds were respectively identified in ungerminated quinoa and germinated quinoa. It was found that the germination period of 24-48 h contributed to reducing the presence of undesirable flavors. TEM analysis revealed significant structural damage to the ultrastructure and relaxation of the cell wall in germinated quinoa grains.

Pollution Characteristics and Risk Assessment of Heavy Metals in the Sediments of the Inflow Rivers of Dianchi Lake, China.

To explore the contamination status and identify the source of the heavy metals in the sediments in the major inflow rivers of Dianchi Lake in China, sediment samples were collected and analyzed. Specifically, the distribution, source, water quality, and health risk assessment of the heavy metals were analyzed using correlation analysis (CA), principal component analysis (PCA), the heavy metal contamination factor (Cf), the pollution load index (PLI), and the potential ecological risk index (PERI). Additionally, the chemical fractions were analyzed for mobility characteristics. The results indicate that the average concentration of the heavy metals in the sediment ranked in the descending order of Zn > Cr > Cu > Pb > As > Ni > Cd > Hg, and most of the elements existed in less-mobile forms. The Cfwas in the order of Hg > Zn > Cd > As > Pb > Cr > Ni; the accumulation of Hg, Zn, Cd, and As was obvious. Although the spatial variability of the heavy metal contents was pronounced, the synthetical evaluation index of the PLI and PERI both reached a high pollution level. The PCA and CA results indicate that industrial, transportation, and agricultural emissions were the dominant factors causing heavy metal pollution. These results provide important data for improving water resource management efficiency and heavy metal pollution prevention in Dianchi Lake.

Composition, distribution, and source of organic carbon in surface sediments of Erhai Lake, China.

Lake sediment is an important organic carbon (OC) sink. Nevertheless, few studies have been conducted on sediment organic carbon (SOC) in lakes, and the effects of environmental variables on SOC pools remain poorly understood. We combined physicochemical and spectroscopic analyses to investigate the composition, distribution, and source of OC in surface sediments of Erhai Lake, southwest China, and explored the relationships between environmental variables and its SOC pool. The SOC pool consists of relatively high proportions of labile organic carbon fractions, mainly from algal production, which are rapidly decomposed and exhibit high turnover rates. The relative content of humus carbon ranges from 13.5 % to 20.5 %, with fulvic acid carbon predominating (average 52.95 %), indicating weak humification and a relatively active humus carbon pool. The dissolved organic matter in water column and sediments of Erhai Lake is largely influenced by endogenous production, with a great contribution from phytoplankton. Surface sediments contained more protein-like components than overlying waters (80.0 % vs. 63.0 %), attributed mainly to abundant algal deposition and intense bacterial metabolism. Among environmental variables, sediment chlorophyll a showed the strongest relationship with the SOC pool, and was associated with rapid decomposition and promotion of the humification process, which supported the conclusion that algae had an important influence on the SOC pool. The SOC pool in the southern region of the lake is mainly contributed by algae, other microorganisms, and sewage, exhibiting a greater potential to release organic matters into the water column. The center and northern SOC pools show relatively stable characteristics and stronger OC sink capacity, mainly because of the input of terrestrial refractory organic matters from runoff. Our data shed light on the OC storage mechanisms in the surface sediments of Erhai Lake and provide theoretical bases for enhancing the OC sink of sediments in the lake.

Oxidized sodium alginate/polyacrylamide hydrogels adhesive for promoting wheat growth.

Chemical modification of sodium alginate (SA) polymer chains can increase its functional group species. Sodium periodate (SP) was usually used to oxidize the hydroxyl groups on the chain of SA to aldehyde groups, the preparation of oxidized sodium alginate (OSA) using SP is not only complicated, also limits the variety of functional groups on the chain of OSA. By contrast, we have developed an innovative strategy for OSA, in which ammonium persulfate (APS) was used to oxidize SA, providing a clear elucidation of the oxidizing process and mechanism. OSA/PAM hydrogels were synthesized using OSA, the hydrogels possess excellent adhesion properties to various non-metallic and metallic substrates. Tensile and compression tests show that the cross-linked OSA/PAM hydrogels have superior mechanical properties. We exploit OSA/PAM hydrogels as soil adhesive and water-retaining agents for wheat growth. OSA/PAM hydrogels significantly improve the survival time of wheat grown in brown loam soil under a water-shortage environment, and slow down the wilting of wheat in a water-shortage environment and prolong the survival time of wheat in sandy soils. Our trials should make hydrogels important for wheat cultivation in brown loam soils and the development of desert areas.

Relative contributions of different sources to DOM in Erhai Lake as revealed by PLS-PM.

Dissolved organic matter (DOM) is a complex mixture of organic molecules that plays an important role in freshwater lake ecosystems. Excitation emission matrix-parallel factor analysis (EEM-PARAFAC) is an important tool for the identification and source analysis of DOM but is still inadequate for studying the differences and quantifying the contributions of different sources. Here, based on the maximum fluorescence intensities (Fmax) of the four fluorescent components (e.g., protein-like component C1, and the humic-like components C2, C3, C4) identified by EEM-PARAFAC, combined with large-scale data obtained from observations at Erhai Lake, we used partial least squares path modeling (PLS-PM) to improve the understanding of the migration and transformation mechanisms of DOM. The results showed that the phytoplankton and trophic state had greater impacts on DOM, while the impacts of sediment and inflow rivers were less significant. The results of the models that used nitrogen nutrients (N) and phosphorus nutrients (P) to separately indicate the trophic state suggested that the driving force of P on DOM was stronger than that of N in Erhai Lake. Among the four fluorescent components, the protein-like component with the largest relative proportion (41.98%) was mainly affected by phytoplankton, which was consistent with the autogenic characteristics obtained through spontaneous source index (BIX). The duality of the humic-like components was consistent with the duality of DOM through fluorescent index (FI). C3 had a higher sensitivity to the trophic state than the other components, and C2 received the greatest positive contribution from the rivers entering the lake. These results provide an improved insight into the influence of different sources on the behavior of DOM and demonstrate the potential of using PLS-PM to study the complex driving mechanism of aquatic biogeochemical parameters.

Synthesis of 3D graphene-based materials and their applications for removing dyes and heavy metals.

Contamination of water streams by dyes and heavy metals has become a major problem due to their persistence, accumulation, and toxicity. Therefore, it is essential to eliminate and/or reduce these contaminants before discharge into the natural environment. In recent years, 3D graphene has drawn intense research interests owing to its large surface area, superior charge conductivity, and thermal conductivity properties. Due to their unique surface and structural properties, 3D graphene-based materials (3D GBMs) are regarded as ideal adsorbents for decontamination and show great potential in wastewater or exhaust gas treatment. Here, this minireview summarizes the recent progress on 3D GBMs synthesis and their applications for adsorbing dyes and heavy metals from wastewater based on the structures and properties of 3D GBMs, which provides valuable insights into 3D GBMs' application in the environmental field.

Optimisation of enzymatic saccharification of wheat straw pre-treated with sodium hydroxide.

To enhance the reducing sugar yield in enzymatic hydrolysis, various factors (NaOH concentration, solid content and pre-treatment time) that affect the pre-treatment process were investigated and evaluated based on the reducing sugar yield of the subsequent enzymatic hydrolysis. The enzymatic hydrolysis was based on the cellulase from Trichoderma reesi ATCC 26921, the optimum NaOH pre-treatment conditions were an NaOH concentration of 1.0% (w/w), a solid content of 5.0% (w/v) and a pre-treatment time of 60 min. Various parameters that affect the enzymatic hydrolysis of wheat straw, including the solid content, enzyme loading, pH and hydrolysis time, were investigated and optimized through a Box-Behnken design and response surface methodology. The predicted optimum conditions for enzymatic hydrolysis were a solid content of 8.0% (w/v), an enzyme loading of 35 FPU/g substrate, a temperature of 50 °C, a pH of 5.3 and a hydrolysis time of 96 h. The experimental result showed that the maximum reducing sugar yield was 60.73% (53.35% higher than the wheat straw without NaOH pre-treatment), which is in accordance with the predicted conditions.

Natural Products Self-Assembled Nanozyme for Cascade Detection of Glucose and Bacterial Viability in Food.

Sugar content and bacterial contamination levels are important indicators for the health and safety of food, respectively. Therefore, it is important to construct a method that can detect both glucose and bacterial activity. Herein, natural compounds (gallic acid and glucose oxidase) were assembled into nanozyme (GOx@GA-Fe (ii)) for mild cascade detection. The nanozyme catalyzes glucose to produce hydrogen peroxide, which is then converted to ·OH and oxidized colorless TMB from blue oxidized TMB. Under the optimal conditions, the method has a good linear relationship in the glucose concentration range of 1-500 µM (R2 = 0.993) with minimum detection concentration of 0.43 µM. Based on the glucose consumption of bacteria metabolism, the cascade reaction was then applied to detect the viability of 5 common bacteria. As such, a cascade method based on a natural self-assembled nanozyme was fabricated to monitor the quality of food.

Effects of iron on growth and intracellular chemical contents of Microcystis aeruginosa.

OBJECTIVE: To investigate the effect of iron on the growth, physiology and photosynthesis of cyanobacteria. METHODS: A gradient of iron concentrations was employed to investigate the growth, photo-pigments (chlorophyll A and phycocyanin), and cell chemical contents (C, N, P) of Microcystis aeruginosa in response to different iron additions. RESULTS: The specific growth rate during the exponential growth phase, as well as the cell chlorophyll A and the phycocyanin content, was limited by iron below 12.3 tmol Fe x L(-1). The growth was inhibited when the iron concentration was at 24.6 micromol Fe x L(-1). The cell chlorophyll A and the phycocyanin content were saturated when the iron concentration was above 12.3 micromol Fe x L(-1) and declined slightly at 24.6 micromol Fe x L(-1). At a low iron concentration (about 6.15 micromol Fe x L(-1) and less), the cell nitrogen and carbohydrate content were iron limited, and the variation of the cell phosphorus content was similar to that of the nitrogen and carbohydrate, with a transition point of 12.3 micromol Fe x L(-1). CONCLUSION: The variation of cynobacteria growth is synchronous with that of the photo-pigments or the cell chemical content, and there exist relationships among photosynthesis, growth and internal chemical content, which could be useful for the growth estimation from the cell characteristics.

MOFs-derived conductive structure for high-performance removal/release of phosphate as electrode material.

Porous metal-organic frameworks (MOFs) have drawn increasing attention as promising phosphate adsorbents. Yet the potential agglomeration of MOFs particles and the difficult collection process largely thwarted their application. Meanwhile, adsorbents regeneration might destroy MOFs structures due to the use of strong alkaline solution. In this work, we reported a strategy for designing and fabricating an electrode to remove phosphate based on MIL-101 derived metal/carbon via a two-step carbonization step, which not only introduced C doping but also created a stable structure. With the assistance of electric field, the migration and capture of phosphate anions were greatly enhanced. Under 1 V condition, the material exhibited a high maximum removal capacity of 97.73 mg P/g. Adsorption kinetics and parameters for phosphate at different conditions were analyzed. Langmuir and Freundlich isotherms were employed to validate the adsorption data. More importantly, the regeneration of electrode was achieved in a more facile and efficient way than micro/ nanoparticles adsorbents by simple voltage control. Such an intriguing approach may provide a new platform to further expand the use of MOFs for adsorption process.

Effects of antibiotics on microbial community structure and microbial functions in constructed wetlands treated with artificial root exudates.

In the rhizosphere, plant root exudates can mediate the toxicity of antibiotics on microorganisms, yet the mechanisms are poorly understood. To simulate the antibiotic contamination of global rivers and lakes, the current study investigated the effects of two antibiotics (ofloxacin at 8.69 × 104 ng L-1 and tetracycline at 8.62 × 104 ng L-1) and their binary combination (8.24 × 104 ng L-1 ofloxacin and 7.11 × 104 ng L-1 tetracycline) on bacterial communities in micro-polluted constructed wetlands with and without artificial root exudates. The two antibiotics had no significant effects on the removal of excess carbon and nitrogen from the microcosms treated with and without exudates. Furthermore, with regard to bacterial community structure, antibiotic exposure increased the bacterial richness of bulk and exudate treated microcosms (P < 0.05). However, a significant increase (P < 0.05) in bacterial diversity elicited by ofloxacin and antibiotic mixture exposure was only observed in microcosms with exudates. In exudate treated microcosms, ofloxacin promoted the relative abundance of Arthrobacter spp., which are ofloxacin-resistant bacterial species, which significantly varied from what was observed in microcosms free of exudates. Moreover, tetracycline, ofloxacin and their combination all significantly increased the relative abundance of nitrogen cycling bacteria Rhizobacter spp. and Rhizobium spp., and decreased the relative abundance of antibiotic-resistant bacteria Pseudomonas spp. Simultaneously, with regard to bacterial community functions, the functional profiles (Kyoto Encyclopedia of Genes and Genomes) showed that the pathways of amino acid and carbohydrate metabolism were enhanced by antibiotics in microcosms with exudates. The findings illustrate that antibiotics not only alter the bacterial structure and composition but also change their functional properties in constructed wetlands, and these interruption effects could be affected by root exudates of plants, which may further reveal the ecological implication of plants in constructed wetlands.

Phosphate removal and recovery through crystallization of hydroxyapatite using xonotlite as seed crystal.

Xonotlite was synthesized and tested for phosphate removal and recovery from synthetic solution in a batch mode. The effects of pH, initial calcium concentration, bicarbonate concentration on phosphate removal through crystallization were examined. The morphology and X-ray diffraction (XRD) pattern of xonotlite before and after crystallization confirmed the formation of crystalline hydroxyapatite. The results indicated that the crystallization product had a very high P content (> 10%), which is comparable to phosphate rock at the dosage of 50-200 mg xonotlite per liter, with a maximum P content of 16.7%. The kinetics of phosphate removal followed the second-order reaction equation. The phosphate removal ability increased with increasing pH. The precipitation of calcium phosphate took place when pH was higher than 7.2, whereas the crystallization occurred at pH 6.0. A high calcium concentration could promote the removal of phosphate via crystallization, while a high bicarbonate concentration also enhanced phosphate removal, through that the pH was increased and thus induced the precipitation process. When xonotlite was used to remove phosphate from wastewater, the removal efficiency could reach 91.3% after 24 h reaction, with removal capacity 137 mg/g. The results indicated that xonotlite might be used as an effective crystal seed for the removal and recovery of phosphate from aqueous solution.

Variation of phytoplankton community before an induced cyanobacterial (Arthrospira platensis) bloom.

A cyanobacterial (Arthrospira platensis) bloom was induced in situ by nutrient manipulation in an enclosure. The succession of the phytoplankton community and the water chemistry variations before the appearance of bloom, as well as their relationship, were investigated. The cell pigment variations were studied simultaneously. The Pearson's correlation analysis showed that there was no significant correlation between water chemistry and green algal or cyanobacterial composition, indicating that water chemistry variations were not suitable to be used as indicators for cyanobacterial-bloom early-warning. However, the diversity index of the phytoplankton community decreased sharply before the bloom appeared. Therefore, the dynamics of phytoplankton community was put forward to be an indicator for cyanobacterial-bloom early-warning. In addition, the cell pigment variations represented the changes of community structure, which should be useful for studying the dynamics of phytoplankton community.