Deamination Reaction Research Articles

Facilely tuning the triazine-heptazine ratios in crystalline g-C3N4 for efficient photo-degradation of tylosin

Intrinsically, g-C3N4 has high-density defects, insufficient efficiencies of photogenerated charge carrier separation and transfer, and inadequate photocatalytic ability against antibiotics. A facile crystallinity engineering on g-C3N4 assisted by molten-salts and simultaneously fine-tuning the triazine-heptazine ratio led to forming type-II homojunctions, without introducing foreign atoms and being metal-free. It was successfully achieved through modulating the calcination temperatures and using KCl-LiCl. The salts accelerated deamination reaction kinetics, tuned the unit ratio, and improved the degree of carbon nitride polymerization. At a triazine-heptazine ratio of 74:26 obtained at 450 °C, 10 mg/L of tylosin was completely mitigated within 9 min by the catalyst. Active radicals including O2− and OH were boosted from charge carriers under visible light, and the recombination of photogenerated excitons was relieved on the interfaces of the homojunctions. Breaking glycosidic bonds and dropping off deoxyglycosyl moieties are considered the main degradation mechanism. The cytotoxicity and acute toxicity of the degradation product are classified as harmless. In addition, 3D-molecular docking between the transformation products and target proteins (L4 and L22) in ribosome confirms toxicity reduction. This work paves a way for efficient and harmless photocatalytic degradation of tylosin by facilely modulating the unit ratio and enhancing the crystallinity of carbon nitride without introducing foreign atoms.

Pre-Coordination Induced Further Deamination to Create Inter-Chain Cross-Linking in Carbon Nitride for Enhanced Photocatalytic H2O2 Production.

Creating cross-linking to establish efficient inter-chain charge-transfer channels in carbon nitride represents a promising strategy for enhancing its photocatalytic capabilities. Molten salt-assisted calcining has emerged as a method for preparing cross-linked carbon nitrides. However, the precise influence of molten salts on the molecular structure of carbon nitride remains to be fully elucidated. Herein, we develop a KCl guided cross-linking reaction to preliminarily reveal the formation mechanism of cross-linking. The cross-linking reaction is initiated by the pre-coordination of amino groups with K+. Subsequent heating at high temperature converts the amino groups into chlorines. Then, dechlorination leads to the formation of cross-linking. Thus, this cross-linking reaction can be accurately described as a pre-coordination-induced, two-step deamination reaction. The pre-coordination step plays a pivotal role in the cross-linking process. Sufficient pre-coordination results in a relatively high cross-linking degree of the as-prepared CNK-2. Consequently, CNK-2 demonstrates a significantly enhanced photocatalytic H2O2 production, with a generation rate of 682 μmol L-1 h-1, about 59 times that of traditional carbon nitride.

Effects of atmosphere and stepwise pyrolysis on the pyrolysis behavior, product characteristics, and N/S migration mechanism of vancomycin fermentation residue

Vancomycin fermentation residue (VFR) urgently needs proper treatment due to its complex and hazardous nature. Pyrolysis is a promising treatment method, while the product characteristics of VFR pyrolysis remain unclear. Therefore, the influence of different atmospheres and stepwise pyrolysis (including one-stage reaction in N2 or CO2 and two-stage reaction in N2) on pyrolysis behavior, product characteristics, and N/S migration mechanism during VFR pyrolysis were investigated for the first time in this work. The results showed that VFR mainly decomposed at 180–600 °C, forming non-condensable gas, bio-oil, and biochar. The main released gases included CO2, H2O, NH3, HCN, SO2, and H2S, whereas the N-containing pollutant gas, notably NH3, should be focused due to its high emission (>10 %). Bio-oil was rich in N-containing compounds with a content exceeding 46 %, mainly consisting of Indolizne (9.2–11.5 %), 5H-1-Pyrindine (5.0–9.9 %), and Indole (8.4–9.0 %), and 9-Octadecenamide, (Z)- (1.8–10.1 %). Moreover, the effects of different conditions on the product characteristics were as follows: For the one-stage reaction, compared to N2, the CO2 atmosphere promoted the formation of alcohols (intended product, increasing 2.2–14.6 %), whereas the two-stage reaction in N2 inhibited alcohol production (decreasing 1.1–2.5 %). At CO2 condition, the harmless temperature of VFR reduced from 600 °C (pyrolysis in N2) to 400 °C. Both CO2 (increasing 0.6–1.5 %) and the two-stage reaction in N2 (increasing 0.4–1.0 %) retained more N in the solid. Kinetics showed that the pyrolysis process of VFR conformed to diffusion models and reaction order models (F2/D1/F3/D1 for N2 and F2/D2/F3/D1 for CO2). The VFR transformed to the chemicals and fuels mainly through the deamination, desulfurization, dehydration, decarboxylation, and dehydrogenation reactions. This work provides guidance for harmless disposal and resource utilization during VFR pyrolysis.

Constructing p-n heterojunctions of Cl-Cu2O and PANI on three-dimensional nanofiber networks for enhanced photocatalytic degradation of oxytetracycline

A p-n heterojunction was constructed on a bacterial cellulose (BC) film by combining n-type semiconductor chlorine-doped Cu2O (Cl-Cu2O) and p-type semiconductor polyaniline (PANI), creating a ternary composite flexible film of Cl-Cu2O/PANI/BC. The chemical structure, microscopic morphology, and photoelectrochemical properties of Cl-Cu2O/PANI/BC were characterized and analyzed. Compared with pure Cl-Cu2O, the Cl-Cu2O/PANI/BC composite flexible film exhibited a broader response range to visible and near-infrared light, higher carrier concentration, lower impedance value, and substantial reduction in the recombination probability of photogenerated carriers. The process conditions for the photocatalytic degradation of oxytetracycline (OTC) were optimized using the response surface method, and the degradation rate of OTC caused by the Cl-Cu2O/PANI/BC was 96.3 %. In the degradation process of OTC, superoxide radical is the main active species. It was found that OTC molecules degraded via demethylation, secondary alcohol oxidation, decarboxylation, and deamination reactions, finally being degraded into H2O, CO2, and other small organic molecules. Thirteen major intermediates and possible degradation pathways were speculated. The photocatalytic performance of the Cl-Cu2O/PANI/BC was improved owing to the successful construction of the p-n heterojunction. The built-in electric field generated at the interface between the two semiconductors promoted the diffusion of photogenerated holes from the n-type Cl-Cu2O particles to the PANI coating layer on the BC chain, whereas the photogenerated electrons from PANI diffused toward Cl-Cu2O, accelerating the separation efficiency of photoinduced electrons and holes in the two semiconductors and thereby improving the efficiency of photocatalytic degradation. In addition, the three-dimensional network structure of a composite flexible film can help recover the photocatalyst. After performing seven experiments for recovery and reuse, the photocatalytic degradation rate of OTC still remained above 90 %.

Enhancing the amination activity of meso-diaminopimelate dehydrogenase from Symbiobacterium thermophilum by modifying the crucial residue His154 for deamination

During the deamination and amination processes of meso-diaminopimelate dehydrogenase (meso-DAPDH) from Symbiobacterium thermophilum (StDAPDH), residue R71 was observed to display distinct functions. H154 has been proposed as a basic residue that facilitates water molecules to attack the D-chiral carbon of meso-DAP during deamination. Inspired by the phenomenon of R71, the effects of H154 during deamination and amination were investigated in this study with the goal of enhancing the amination activities of StDAPDH. Single site saturation mutagenesis indicated that almost all of the H154 mutants completely lost their deamination activity towards meso-DAP. However, some H154 variants showed enhanced kcat/Km values towards pyruvic acid and other bulky 2-keto acids, such as 2-oxovaleric acid, 4-methyl-2-oxopentanoic acid, 2-ketobutyric acid, and 3-methyl-2-oxobutanoic acid. When combined with the previously reported W121L/H227I mutant, triple mutants with significantly improved kcat/Km values (2.4-, 2.5-, 2.5-, and 4.0-fold) towards these 2-keto acids were obtained. Despite previous attempts, mutations at the H154 site did not yield the desired results. Moreover, this study not only recognizes the distinctive impact of H154 on both the deamination and amination reactions, but also provides guidance for further high-throughput screening in protein engineering and understanding the catalytic mechanism of StDAPDH.

Biodegradation characteristics of p-Chloroaniline and the mechanism of co-metabolism with aniline by Pseudomonas sp. CA-1

Co-metabolism is a promising method to optimize the biodegradation of p-Chloroaniline (PCA). In this study, Pseudomonas sp. CA-1 could reduce 76.57 % of PCA (pH = 8, 70 mg/L), and 20 mg/L aniline as the co-substrate improved the degradation efficiency by 12.50 %. Further, the response and co-metabolism mechanism of CA-1 to PCA were elucidated. The results revealed that PCA caused deformation and damage on the surface of CA-1, and the –OH belonging to polysaccharides and proteins offered adsorption sites for the contact between CA-1 and PCA. Subsequently, PCA entered the cell through transporters and was degraded by various oxidoreductases accompanied by deamination, hydroxylation, and ring-cleavage reactions. Thus, the key metabolite 4-chlorocatechol was identified and two PCA degradation pathways were proposed. Besides, aniline further enhanced the antioxidant capacity of CA-1, stimulated the expression of catechol 2,3-dioxygenase and promoted meta-cleavage efficiency of PCA. The findings provide new insights into the treatment of PCA-aniline co-pollution.

Molecular-level insights into dissolved organic matter and its variations of the full-scale processes in a typical petrochemical wastewater treatment plant

Petrochemical wastewater (PCWW) treatment poses challenges due to its unique and complex dissolved organic matter (DOM) composition, originating from various industrial processes. Despite the addition of advanced treatment units in PCWW treatment plants to meet discharge standards, the mechanisms of molecular-level sights into DOM reactivity of the upgraded full-scale processes including multiple biological treatments and advanced treatment remain unclear. Herein, we employ water quality indexes, spectra, molecular weight (MW) distribution, and Fourier transform ion cyclotron resonance mass spectrometry to systematically characterize DOM in a typical PCWW treatment plant including influent, micro-oxygen hydrolysis acidification (MOHA), anaerobic/oxic (AO), and micro-flocculation sand filtration–catalytic ozonation (MFSF–CO). Influent DOM is dominated by tryptophan-like and soluble microbial products with MW fractions 〈 1 kDa and 〉 100 kDa, and CHO with lignin and aliphatic/protein structures. MOHA effectively degrades macromolecular CHO (10.86 %) and CHON (5.24 %) compounds via deamination and nitrogen reduction, while AO removes CHOS compounds with MW < 10 kDa by desulfurization, revealing distinct DOM conversion mechanisms. MFSF–CO transforms unsaturated components to less aromatic and more saturated DOM through oxygen addition reactions and shows high CHOS and CHONS reactivity via desulfurization and deamination reactions, respectively. Moreover, the correlation among multiple parameters suggests UV254 combined with AImod as a simple monitoring indicator of DOM to access the chemical composition. The study provides molecular-level insights into DOM for the contribution to the improvement and optimization of the upgraded processes in PCWW.

Conversion mechanism of pyrolysis humic substances of cotton stalks and carbide slag and its excellent repair performance in Cd-contaminated soil

Unlike traditional biomass composting humification, pyrolysis humification can rapidly convert waste biomass into humic substances (HSs) at lower temperatures and in an alkaline environment for soil remediation. This study utilized the strong alkaline solid waste carbide slag (CARBIDE) and cotton stalk (CS) for pyrolysis humification. The pyrolysis humification mechanism and effect of CARBIDE and CS were investigated using FT-IR, NMR, and Py-GC/MS. Furthermore, the ability of HSs to remediate cadmium-contaminated soil (Cd-soil) was assessed through soil property analysis, pot tests, and microbial diversity studies. The results showed that humic acid (HA) and fulvic acid (FA) had the highest yield of 19 % and 5 %, respectively, among the humic substances (HS-CS&CA) produced under the conditions of 250 ℃, reaction time of 2 h and mass ratio of CS to CARBIDE of 5: 1. At 250 ℃, CARBIDE changed the heat transfer mechanism of biomass, promoted the decomposition of more hemicellulose and protein, promoted the Deamination, Ketonization and Maillard reaction, and synthesized more HAs. HS-CS&CA had a significant remediation effect on Cd-soil. The immobilization rate of Cd was as high as 23 %, and the accumulation of Cd in maize was reduced by 65 %. At the same time, the relative abundance of beneficial bacteria such as Xanthomonadaceae and Bacillaceae for immobilizing Cd was increased, and the cycling effect of N and P was also enhanced. This study provides an innovative technical route for the rapid humification of CARBIDE and CS and its application in Cd-soil remediation.

Efficient removal of heavy metals from sewage sludge using a low-cost protic ionic liquid: Investigation of mechanism and ecological risk

Land utilization for the disposal of sewage sludge (SS) is an effective strategy, yet the existence of heavy metals (HMs) in the SS represents critical constraints to its implementation on a larger scale. By the principles of simple synthesis steps and low synthesis cost, a low-cost double cationic protic ionic liquid was produced in this study for HMs removal from SS. The influence of reaction time, protic ionic liquid to SS mass ratio, and reaction temperature on HM removal were thoroughly investigated. This result indicated that the integration of protic ionic liquid and heat treatment was efficacious in the efficient elimination of HMs. Under 60°C, 15 min, and protic ionic liquid: SS of 0.5, the removal efficiency of Zn, Fe, Ni, and Cd exceeded 80%, and Cr achieved a removal efficiency of up to 93%. The BCR sequential extraction procedure and calculation of the potential ecological risk index revealed a significant reduction in the ecological risk associated with the treated SS, transitioning from a high to a low-risk level. The alterations in elemental and chemical bonding within the solid phase of SS and changes in polysaccharide and fluorescence properties within the liquid phase of SS were investigated using redundancy analysis, two-dimensional correlation analysis, and parallel factor analysis. These findings suggest that dehydration, deamination, and decarboxylation reactions may be responsible for removing HMs within SS. These findings have a positive impact on further elucidating the effects of protic ionic liquid in SS pretreatment, thereby facilitating the efficient utilization of municipal SS resources.

Construction of a Zero-gap Flow-Through Microfluidic Reactor with Porous RuO2-IrO2@Pt Anode for Electrocatalytic Oxidation of Antibiotics in Water.

In this study, a zero-gap flow-through microfluidic reactor was constructed for the degradation of tetracycline and norfloxacin in water using a porous Ti/RuO2-IrO2@Pt electrode as the anode and porous titanium plate as the cathode. The operation parameters included electrolyte type, electrolyte concentration, current density, initial concentration of pollutants and pH, were investigated. The degradation efficiency and energy consumption were calculated and compared with traditional electrolyzer. In the zero-gap flow-through microfluidic reactor, 100 % of both tetracycline and norfloxacin can be decomposed in 15 min, and high mineralization rate were achieved under the optimized reaction condition. And the reaction was consistent with pseudo-first-order kinetics with k value of 0.492 cm-1 and 1.010 cm-1, for tetracycline and norfloxacin, respectively. In addition, the energy consumption was 28.33 kWh ⋅ kg-1 TC and 8.36 kWh ⋅ kg-1 NOR, for tetracycline and norfloxacin, respectively, which was much lower than that of traditional electrolyzer. The LC-MS results showed that tetracycline underwent a series of demethylation, dehydration and deamination reactions, and the norfloxacin went through ring opening reaction, decarboxylation and hydroxylation reaction, and finally both produced CO2 and H2O.

Fast pyrolysis of Enteromorpha prolifera model compounds for syngas: A simulated and experimental study

The large-scale blooming of Enteromorpha prolifera (EP) results in "green tide," triggering significant environmental issues. However, EP as algal biomass can be converted to syngas through fast pyrolysis. This research investigates the fast pyrolysis of modeled compounds of EP for syngas production. Rhamnose (Rha), glucuronic acid (GlcA), aspartic acid (Asp), glutamic acid (Glu), and alanine (Ala) are used as the model compounds. This study employs experiments and simulations on fast pyrolysis processes. The results reveal that polysaccharide sulfate (PS) undergoes various reactions, including glycosidic bond cleavage, pyran ring opening, dehydration, and C-C bond cleavage. Simultaneously, amino acids experience dehydration, deamination, decarboxylation, and decarboxylation reactions. Fast co-pyrolysis of modeled compounds of EP, the monosaccharides and uronic acid molecules produced by PS pyrolysis also attack each other with amino acid molecules to produce other substances. The pyrolysis gas obtained from the model compounds of PS exhibits the highest CO content. Notably, amino acids possess a superior capability to produce H2 compared with PS. With the fast co-pyrolysis of EP model compounds, the CO2 content increases while the CO content decreases. This study provides a theoretical basis for the fast pyrolysis of EP to produce syngas.

Tracking of the conversion and transformation pathways of dissolved organic matter in sludge hydrothermal liquids during Cr(VI) reduction using FT-ICR MS

In this study, the remediation effects of two types of sludge (ferric-based flocculant and non-ferric-based flocculant) on Cr(VI)-polluted wastewater were evaluated to clarify the key components in sludge hydrothermal solutions responsible for reducing Cr(VI) and understand the underlying molecular-level transformation mechanisms. The results revealed that the primary reactions during the hydrothermal processes were deamination and decarboxylation reactions. Correlation analysis highlighted proteins, reducing sugars, amino groups, and phenolic hydroxyl groups as the major contributors. In-depth analysis of the transformation process of functional groups within dissolved organic matter (DOM) and synergistic redox process between Cr(VI) and DOM in hydrothermal solutions demonstrated that phenolic hydroxyl and amino groups gradually underwent oxidation during reduction of Cr(VI) by DOM, forming aldehyde and carboxyl groups, among the others. Time-dependent density functional theory calculations revealed notable shift of reducing functional groups from ground state to excited state following iron complexation, ultimately facilitating reduction reaction. Subsequent investigations, including soil column leaching and seed germination rate tests, indicated that synergistic redox interaction between Cr(VI) and DOM significantly reduced waterborne heavy metal and toxic organic pollution. These findings carry substantial implications for sludge treatment and remediation of heavy metal pollution in wastewater, offering valuable insights into effective environmental remediation strategies.

Dipeptides Containing Pyrene and Modified Photochemically Reactive Tyrosine: Noncovalent and Covalent Binding to Polynucleotides.

Dipeptides 1 and 2 were synthesized from unnatural amino acids containing pyrene as a fluorescent label and polynucleotide binding unit, and modified tyrosine as a photochemically reactive unit. Photophysical properties of the peptides were investigated by steady-state and time-resolved fluorescence. Both peptides are fluorescent (Φf = 0.3-0.4) and do not show a tendency to form pyrene excimers in the concentration range < 10-5 M, which is important for their application in the fluorescent labeling of polynucleotides. Furthermore, both peptides are photochemically reactive and undergo deamination delivering quinone methides (QMs) (ΦR = 0.01-0.02), as indicated from the preparative photomethanolysis study of the corresponding N-Boc protected derivatives 7 and 8. Both peptides form stable complexes with polynucleotides (log Ka > 6) by noncovalent interactions and similar affinities, binding to minor grooves, preferably to the AT reach regions. Peptide 2 with a longer spacer between the fluorophore and the photo-activable unit undergoes a more efficient deamination reaction, based on the comparison with the N-Boc protected derivatives. Upon light excitation of the complex 2·oligoAT10, the photo-generation of QM initiates the alkylation, which results in the fluorescent labeling of the oligonucleotide. This study demonstrated, as a proof of principle, that small molecules can combine dual forms of fluorescent labeling of polynucleotides, whereby initial addition of the dye rapidly forms a reversible high-affinity noncovalent complex with ds-DNA/RNA, which can be, upon irradiation by light, converted to the irreversible (covalent) form. Such a dual labeling ability of a dye could have many applications in biomedicinal sciences.

The impact of H-ZSM-5 catalyst on the mechanism of fuel-N conversion during glutamic acid pyrolysis

During the pyrolysis of biomass, Fuel-bound Nitrogen (Fuel-N) is converted into N-containing compounds present in bio-oil and biochar. These compounds are easily oxidized into NOx during subsequent utilization, causing ecological damage. Catalytic fast pyrolysis has emerged as a promising method for denitrogenation in recent years, but the underlying catalyst mechanism still needs to be determined. This study analyzed the impact of catalyst H-ZSM-5 on the mechanism of Fuel-N conversion during the pyrolysis of glutamic acid, a model compound for nitrogenous biomass, through experimental studies and theoretical calculations. According to literature data, the pyrolysis of glutamic acid predominantly yielded the N-containing products pyrrole, glutarimide, and pyrrolidone. The H-ZSM-5 catalyst showed optimum denitrification at 600 ℃, resulting in a 49.62% reduction in the proportion of N-containing compounds. In the catalytic pyrolysis products, the generation of toluene and naphthalene increased. In-situ DRIFTS experiments were consistent with the results of Py-GC-MS experiments, with catalytic pyrolysis promoting deaminations and decarboxylations, decreased imines and nitriles, and increased aromatic hydrocarbons. Additionally, the energy barrier changes of each pyrolysis pathway were calculated based on Density Functional Theory (DFT). The results showed that the H-ZSM-5 catalyst primarily promoted the deamination reaction, followed by the decarboxylation and dehydration condensation reactions, while inhibiting the dehydrogenation reaction. Moreover, the energy barrier for unsaturated hydrocarbon addition reactions was reduced, facilitating the formation of aromatic compounds. The acid sites inside the H-ZSM-5 catalyst weakly interacted with the reactants, making it easier to detach the amino group during catalytic pyrolysis. This study provides a reference for the denitrification of bio-oil and biochar. Subsequent work can realize the regulation of nitrogen conversion by changing the acidity and concentration of catalyst acid sites.

Hydrothermal carbonization of coking sludge: Formation mechanism and fuel characteristic of hydrochar

In this study, the chemical structures, fuel characteristic, and formation mechanism of hydrochar during hydrothermal carbonization (HTC) at 150–270 °C for 0–120 min were investigated using coking sludge (CS) as the feedstock. The results showed that the yield decreased from 96.86 to 60.98%, whereas the carbonization rate increased from 6.74 to 93.41% at 270 °C. More stable structures with aromatic and N-heterocycles rings were formed through hydrolysis and polymerization. The H/C and O/C ratio decreased from 1.75 to 0.60 to 1.04 and 0.09, and the combustion stability index (Hf) decreased from 0.86 to 0.60 °C.103, and the flammability index (S) increased from 24.16 to 26.42 %/(min2 °C3) 10−8, indicating an improvement of fuel performance. A kinetic model to describe the conversion of organic components of CS was developed to elucidate the formation mechanism of hydrochar combined with the change of water-soluble intermediates (SM). The solid-solid conversion reaction of protein and humus components was the predominant hydrochar formation pathway, with an activation energy (Ea) of 26.06 kJ/mol. The polymerization of aromatic compounds slightly participated in the hydrochar formation, with an Ea of 86.12 kJ/mol. The water-soluble intermediates mostly transformed into inorganic substances (IS) through decarboxylation, deamination, or decomposition reaction, with an Ea of 5.73 kJ/mol. This study provided insights for understanding the formation of hydrochar from CS through HTC, which is vital for controlling the polymerization of intermediates and solid-solid conversion to enhance the carbonization efficiency.

Ultrasonic degradation of tetracycline combining peroxymonosulfate and BiVO4 microspheres

Tetracycline (TC) has received widespread attention due to the negative impacts of the drug abuse on ecological system and human health. Sonodegradation coupled with catalyst has proven to be an efficient method to treating TC. In this paper, BiVO4 microspheres synthesized by hydrothermal method and peroxymonosulfate (PMS) were used as sonocatalysts. Comparison of the degradation experiments revealed that combination of BiVO4/PMS with ultrasound (US) resulted in the highest degradation rate of TC, and the synergistic factor was calculated to be 6.17, which indicates a very significant synergistic effect. Effects of many factors, such as US power, BiVO4 concentration, dosage of PMS, initial TC concentration and matrix ion, on tetracycline degradation were investigated, and the operating parameters were optimized by response surface methodology, which predicted that TC degradation rate could reach 91.4 % after 60 min by setting initial TC concentration of 20 mg/L, BiVO4 concentration of 1.156 g/L, PMS dosage of 2.331 mM, and US power of 419 W. Active species analysis verified that radicals, such as OH, SO˙4−, h+ and O˙2−, were the primary contributors to TC removal, and ultrasonic cavitation plays a key role in sonocatalysis. The TC degradation rate only decreased by 1.6 % after four reuses of BiVO4. Moreover, the intermediate of TC degradation was detected using a liquid chromatograph-mass spectrometer (LC-MS), and the degradation pathway revealed that deamination, decarbonization and ring-opening reaction eventually result in the decomposition of TC. This work proposes a method for an efficient degradation of TC in waste water.

Microbial transglutaminase promotes cross-linking for enhancing gelation of myofibrillar protein in frozen Litopenaeus vannamei through deamination reaction

In this paper, the effects of different microbial transglutaminase (mTGase) treatments (0–0.5% w/w) on the structural and functional characteristics of frozen shrimp (Litopenaeus vannamei) were investigated to explore the changes in myofibrillar protein (MP) during the catalytic process of mTGase, and further enhance the gel properties of shrimp surimi products. Fourier transform infrared spectroscopy showed that mTGase treatment caused a shift from α-helix to β-turn and β-sheet in the secondary structure of the protein, while chemical force results indicated that moderate addition of enzyme could promote the formation of disulfide bonds in the gel system, contributing to the formation of a stable three-dimensional spatial structure. These structural changes led to a significant increase in gel strength, WHC and storage modulus (G′) after mTGase-induced protein gelation, resulting in an increase in the solid properties of the gel; and the relaxation time T22 was significantly shortened, indicating a gradual decrease in water freedom in the protein gel network. In addition, scanning electron microscopy results showed that the gel with 0.4% mTGase had a denser network structure and more uniform pores. Simultaneously, mTGase facilitated the reduction of free amino groups through deamination reaction, resulting in an elevated cross-linking degree and a reduced hydrolysis rate of pepsin. The above results indicated that appropriate mTGase treatment could improve the structure and functional properties of shrimp, benefit the quality of shrimp surimi products, and provide some references for the highly processed frozen Litopenaeus vannamei.

Pyrolysis mechanisms of the main model compounds of enteromorpha prolifera to produce syngas

The large-scale flooding of Enteromorpha prolifera (EP) forms “green tide”, which causes severe environmental problems. However, EP, an algal biomass, can be converted into syngas via pyrolysis. In this study, the pyrolysis mechanisms of the main compositional models of EP used to produce syngas are investigated using a combination of molecular dynamics simulations and fixed-bed experiments. Rhamnose (Rha), glucuronic acid (GlcA), aspartic acid (Asp), glutamic acid (Glu), and alanine (Ala) are used as the model compounds. The results indicate that H2 is primarily produced by Glu (reached 24.68 vol%), followed by Asp and Ala, and CO is produced by Ala (reached 44.94 vol%), Glu, and Asp. The molecular dynamics simulation results indicate that the energy barriers for the pyrolysis of Glu and Ala to produce H2 and CO, respectively, are the lowest. Three amino acids undergo dehydration, deamination, and decarboxylation. Moreover, the synergistic effect of the three amino acids in co-pyrolysis is reflected in the production of hydrogen groups from Asp; and the hydrogen group then attacks Glu to seize the hydrogen group on it to produce hydrogen. In addition, the H2 content in the syngas produced by the separate pyrolysis of Rha (17.75 vol%) and GlcA (17.35 vol%) are similar and lower than those of the Rha and GlcA mixtures (19.12 vol%). The CO content in the pyrolysis gas of GlcA is higher than that of Rha. The simulation results prove that the amino acids undergo dicarboxylic and deamination reactions to produce amino acids and CO2. Meanwhile, polysaccharide sulfate breaks glycosidic bonds, producing free radicals such as hydrogen and hydroxyl groups at 700 K. When the temperature rises to 1900 K, the products of the previous stage further break the bond, producing small-molecule gases. However, the addition of polysaccharide model compounds promotes the production of CO2 and CO groups and inhibits the formation of CO. Co-pyrolysis cannot increase H2, and the synergistic effect is not significant. Moreover, Ni and SAPO-34 exhibited good catalytic activities, which could increase syngas production. A raw materials to catalyst ratio of 5:1 is a good choice because it improves the H2 and CO contents and makes economical use of Ni. With the increase of Ni catalyst cycles, H2 content also shows a decreasing trend, from 22.86 vol% to 16.27 vol% (third cycle). With the number of SAPO-34 cycles, the increase of CO content, from 28.66 vol% to 32.67 vol% is explained by the increase in the specific surface area of the catalyst caused by repeated use, which increases the selectivity of C2 and enhances the ability of decarbonylation. This study focuses on the syngas reaction paths and pyrolysis reactions of different EP model compounds. The pyrolysis mechanism of EP to produce syngas is determined using a combination of experiments and simulations, providing a method for the energy utilization of EP.

Photocatalytic degradation of antibiotic sulfamethizole by visible light activated perovskite LaZnO3

In this work, the perovskite LaZnO3 was synthesized via sol-gel method and applied for photocatalytic treatment of sulfamethizole (SMZ) antibiotics under visible light activation. SMZ was almost completely degraded (99.2% ± 0.3%) within 4 hr by photocatalyst LaZnO3 at the optimal dosage of 1.1 g/L, with a mineralization proportion of 58.7% ± 0.4%. The efficient performance of LaZnO3 can be attributed to its wide-range light absorption and the appropriate energy band edge levels, which facilitate the formation of active agents such as ·O2−, h+, and ·OH. The integration of RP-HPLC/Q-TOF-MS and DFT-based computational techniques revealed three degradation pathways of SMZ, which were initiated by the deamination reaction at the aniline ring, the breakdown of the sulfonamide moieties, and a process known as Smile-type rearrangement and SO2 intrusion. Corresponding toxicity of SMZ and the intermediates were analyzed by quantitative structure activity relationship (QSAR), indicating the effectiveness of LaZnO3-based photocatalysis in preventing secondary pollution of the intermediates to the ecosystem during the degradation process. The visible-light-activated photocatalyst LaZnO3 exhibited efficient performance in the occurrence of inorganic anions and maintained high durability across multiple recycling tests, making it a promising candidate for practical antibiotic treatment.

Pyrolysis of food waste digestate residues for biochar: Pyrolytic properties, biochar characterization, and heavy metal behaviours

The current work has examined the pyrolytic properties, product formation mechanisms, biochar properties, and heavy metal (HMs) safety of biochar during food waste digestate residue (DR) pyrolysis. The results have shown that DR pyrolysis proceeded in five stages. The kinetic model for Stages 1, 3 and 4 was the simple reaction order model, the one-dimensional diffusion model for Stage 2, and the three-dimensional (Jander) diffusion model for Stage 5. Based on thermogravimetric-Fourier transform infrared spectrometry (TG-FTIR) and pyrolysis–gas chromatography-mass spectrometry (Py-GCMS) analysis, the volatile components of the DR pyrolysis were mainly produced by the Maillard, decarboxylation, and deamination reactions as H2O, CH4, CO2, CO, phenol, CO (anhydride/ketone/aldehyde), C-O and NH3. While there were six main components of the pyrolysis oil, that is, amines and amides, nitriles, N-hybrid compounds, oxides, and sulfides. Appropriate aromatic properties were observed in the prepared biochar, and the biochar obtained at a pyrolysis temperature of 700 °C had a relatively high specific surface area. The HMs results showed that the HMs in biochar obtained from DR pyrolysis at 400, 500, 600, 700, and 800 °C were predominantly in the oxidizable and residual fractions. The toxicity characteristic leaching procedure (TCLP) tests and the potential ecological risk indices for HMs have indicated a high safety profile for biochar. This work has elucidated the formation process of DR pyrolysis products and the physicochemical properties and safety of biochar. It has also provided an outlet for the application of biochar, which provides a strong contribution to promoting resource use of DR.