Catalytic Hydrogenolysis Lignin to Obtain Phenols: A Review of Selective Cleavage of Ether Bonds

Lignin depolymerized phenolic compounds and biofuel precursors are ideal value-added products for lignin residues generated in biorefineries and modern paper pulp facilities. Hydrogenolysis of lignin is an efficient depolymerization method for the production of carbon-neutral sustainable fuels and platform chemicals. Lignin is underutilized due to its complex structure, mainly because of its complex interunit linkage crosslinks such as α-O-4, β-O-4, 4-O-5, and β-5. This paper centers on the hydrolysis reaction of three major ether bonds (α-O-4, β-O-4, 4-O-5) in lignin and lignin model compounds based on different catalysts for hydrogenative degradation and catalytic systems. The methods and strategies to inhibit the condensation reactions are summarized. In particular, density functional theory calculation of the reaction pathways are combined with isotopically labeled reaction pathways to deeply analyze the hydrogenation degradation mechanism of biomass and further improve the yield of monophenols during the hydrogenation degradation of lignin. Finally, a brief summary of the challenges and prospects of lignin hydrogenation degradation is proposed

Transformation and products of captopril with humic constituents during laccase-catalyzed oxidation: Role of reactive intermediates

The transformation of captopril (CAP), a widely-used thiol drug, was studied with the presence of dissolved model humic constituents (HCs) in a laccase-catalyzed system. Reaction products were analyzed by ultra-performance liquid chromatography coupled to time-of-flight mass spectrometry and condensed fukui function computation. CAP reacted with different model HCs in the enzymatic system for 1 h, ranging from 75% (syringic acid) to 96% (p-coumaric acid). In the absence of HCs, only 15% of CAP was removed through self-coupling. The presence of HCs apparently changed the transformation of CAP in aqueous environment, and the HC reactive intermediates played an important role. First, during laccase catalysis, HCs with different structures were oxidized to produce reactive intermediates, including phenoxyl radical cation, ortho-, and pars-quinone intermediates. Second, these intermediates were readily attacked by CAP via nucleophilic reactions, forming C-S-C covalent conjugates. More importantly, the standard reduction potential of these intermediates is a critical parameter, as PCA showed the highest reactivity to the nucleophilic addition reaction with CAP by forming phenoxy radical cations. While SYR showed the least reactivity due to the formation of pars-quinone intermediates. Therefore, the functional groups on HCs could greatly influence the cross-coupling with CAP, as well as the type and stability of the coupling products. This work clearly demonstrated the transformation of CAP and other thiol drugs with the presence of HCs in aqueous environment, which is similar to the natural humification process. (C) 2016 Elsevier Ltd. All rights reserved.</p

Oxidation of amino acids by peracetic acid: Reaction kinetics, pathways and theoretical calculations

Peracetic acid (PAA) is a sanitizer with increasing use in food, medical and water treatment industries. Amino acids are important components in targeted foods for PAA treatment and ubiquitous in natural waterbodies and wastewater effluents as the primary form of dissolved organic nitrogen. To better understand the possible reactions, this work investigated the reaction kinetics and transformation pathways of selected amino acids towards PAA. Experimental results demonstrated that most amino acids showed sluggish reactivity to PAA except cysteine (CYS), methionine (MET), and histidine (HIS). CYS showed the highest reactivity with a very rapid reaction rate. Reactions of MET and HIS with PAA followed second-order kinetics with rate constants of 4.6 ± 0.2, and 1.8 ± 0.1 M−1⋅s−1 at pH 7, respectively. The reactions were faster at pH 5 and 7 than at pH 9 due to PAA speciation. Low concentrations of H2O2 coexistent with PAA contributed little to the oxidation of amino acids. The primary oxidation products of amino acids with PAA were [O] addition compounds on the reactive sites at thiol, thioether and imidazole groups. Theoretical calculations were applied to predict the reactivity and regioselectivity of PAA electrophilic attacks on amino acids and improved mechanistic understanding. As an oxidative disinfectant, the reaction of PAA with organics to form byproducts is inevitable; however, this study shows that PAA exhibits lower and more selective reactivity towards biomolecules such as amino acids than other common disinfectants, causing less concern of toxic disinfection byproducts. This attribute may allow greater stability and more targeted actions of PAA in various applications. Keywords: Peracetic acid, Amino acids, Water treatment, Food sanitization, Disinfection, Oxidatio

Photo-transformation of wastewater effluent organic matter reduces the formation potential and toxicity of chlorinated disinfection byproducts

Sunlight exposure can degrade and transform discharged wastewater effluent organic matter (EfOM) in aquatic systems, potentially enhancing the feasibility of reusing wastewater for drinking purposes. However, there remains a lack of comprehensive understanding regarding the sunlight-induced changes in the molecular-level composition, characteristics, and chlorine reactivity of EfOM. Herein, we investigated the impact of sunlight on the optical properties, chemical composition, and formation of disinfection byproducts of EfOM using multiple spectroscopic analyses, high-resolution mass spectrometry, chlorination experiments, and in vitro bioassays. Upon natural sunlight exposure, we observed significant decreases in ultraviolet–visible absorbance and fluorescence intensity of EfOM, indicating the destruction of chromophores and fluorophores. Photolysis generally yields products with lower molecular weight and aromaticity, and with higher saturation and oxidation levels. Moreover, a shift within the EfOM from condensed aromatic-like compounds to tannin-like components was observed. Furthermore, sunlight exposure reduced the reactivity of EfOM toward the formation of trihalomethanes and haloacetonitriles during chlorination, while there was a slight increase in the specific formation potential of haloketones. Importantly, the disinfection byproducts resulting from chlorination of the irradiated EfOM exhibited reduced microtoxicity. Overall, this study provides new insights into alterations in EfOM under sunlight exposure and aids in predicting the health risks of effluent discharge in water environments

Enhanced formation of trihalomethane disinfection byproducts from halobenzoquinones under combined UV/chlorine conditions

Halobenzoquinones (HBQs) are highly toxic disinfection byproducts (DBPs) and are also precursors of other DBPs such as trihalomethanes (THMs). The formation of THMs from HBQs during chlorine-only and UV/chlorine processes with or without bromide was investigated experimentally. Density functional theory (DFT) reactivity descriptors were also applied to predict the nucleophilic/electrophilic reactive sites on HBQs and intermediates. The results were combined to explain the different behaviors of 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) and tetrachloro-1,4-benzoquinone (TCBQ) and to propose mechanism for the promoting roles of UV and hydroxylation of HBQs in THMs formation. Under UV/chlorine, UV significantly enhanced THMs formation from 2,6-DCBQ compared to chlorine-only, mainly due to the production of OH-DCBQ*. Excited 2,6-DCBQ* by UV benefited nucleophilic hydrolysis to produce OH-DCBQ*, which favored electrophilic attack by chlorine, thereby inducing more THMs formation. UV/chlorine modestly promoted THMs formation from TCBQ compared to chlorine-only. Hydroxylation of TCBQ and UV irradiation were both important in promoting THMs formation due to the high electrophilic property of OH-TCBQ and TCBQ*. Meanwhile, hydroxylation of HBQs and CHCl3 formation were enhanced at higher pH. This work suggested that enhanced formation of THMs from HBQs should be considered in the application of combined UV and chlorine processes

Dissipation, Bioconcentration and Dietary Risk Assessment of Thiamethoxam and Its Metabolites in <i>Agaricus bisporus</i> and Substrates under Different Application Methods

In order to acquire scientific evidence for the application of thiamethoxam (TMX) in Agaricus bisporus cultivation, residue and dissipation experiments for field trials were performed with the application of TMX in compost and casing soil, respectively. An effective QuEChERS method was established to analyze TMX and its two metabolites, clothianidin (CLO) and thiamethoxam-urea (TMX-urea), in compost, casing soil, and fruiting bodies. The results indicated that the TMX dissipation half-lives (t1/2) at dosages of 10 and 50 mg kg−1 were 19.74 d (day) and 28.87 d in compost and 33.54 d and 42.59 d in casing soil, individually. TMX, CLO, and TMX-urea were observed after TMX application in compost and casing soil. For TMX applied to the casing soil, only TMX residues were detected in fruiting bodies with bioconcentration factors (BCFs) of 0.0003~0.0009. In addition, both the chronic risk quotient (RQ) and acute risk quotient (HQ) values of TMX in fruiting bodies were far less than 1, which means the dietary health risks to humans were acceptable. However, in the TMX application to the compost, these analytes were not detected in the fruiting bodies. This suggested that the application of TMX in compost was safer than in casing soil during A. bisporus cultivation

Transfer learning to decode brain states reflecting the relationship between cognitive tasks

Transfer learning improves the performance of the target task by leveraging the data of a specific source task: the closer the relationship between the source and the target tasks, the greater the performance improvement by transfer learning. In neuroscience, the relationship between cognitive tasks is usually represented by similarity of activated brain regions or neural representation. However, no study has linked transfer learning and neuroscience to reveal the relationship between cognitive tasks. In this study, we propose a transfer learning framework to reflect the relationship between cognitive tasks, and compare the task relations reflected by transfer learning and by the overlaps of brain regions (e.g., neurosynth). Our results of transfer learning create cognitive taskonomy to reflect the relationship between cognitive tasks which is well in line with the task relations derived from neurosynth. Transfer learning performs better in task decoding with fMRI data if the source and target cognitive tasks activate similar brain regions. Our study uncovers the relationship of multiple cognitive tasks and provides guidance for source task selection in transfer learning for neural decoding based on small-sample data

Dramatic coupling of visible light with ozone on honeycomb-like porous g-C3N4 towards superior oxidation of water pollutants

Porous g-C3N4 (PGCN) has attracted enormous attention due to its accessible nanoporous framework benefiting photocatalytic reactions. Here, we reported a one-pot template-free method to fabricate honeycomb-like PGCN by simply mixing ammonia chloride with the precursor of g-C3N4 before calcination. The resulting PGCN exhibited obviously improved photocatalytic activity for p-hydroxybenzoic acid (PHBA) degradation under visible light due to its high surface area and enlarged band gap, but PHBA can hardly be mineralized in this process. Hence, for the first time, Vis/PGCN was coupled with ozone in this paper and the results showed that PGCN could trigger a vigorous synergy between photocatalysis and ozonation. Vis/O-3/PGCN led to almost complete mineralization of PHBA with an ozone dosage of 1.5 mg/min, and the process could be further accelerated by increasing the ozone dosage. Such a remarkable mineralization enhancement was mainly attributed to the systematically promoted generation of non-selective hydroxyl radicals ((OH)-O-center dot). The high CB level of PGCN benefited electron capture by ozone molecules, thus significantly enhanced charge separation and the decay of ozone into abundant (OH)-O-center dot. (OH)-O-center dot could vigorously react with PHBA and its ozone-recalcitrant intermediates such as the identified carboxylic acids, finally leading to thorough mineralization. Electrospray ionization-mass spectrometry was adopted to detect the evolution of degradation intermediates in ozonation and Vis/O-3/PGCN, and the mineralization procedure from the original PHBA to CO2 and H2O was comprehensively proposed. This study contributes to the integration of sunlight/PGCN with ozone as an efficient metal-free advanced oxidation process for water treatment. (C) 2015 Elsevier B.V. All rights reserved

Transformation of halobenzoquinones with the presence of amino acids in water: Products, pathways and toxicity

The transformation and detoxification of halobenzoquinones (HBQs), a class of emerging disinfection byproducts (DBPs), was studied in the presence of amino acids (AAs). The reaction activity of three HBQs with Ms generally ranked as 2-chlorobenzoquinone (CBQ) &lt; 2,6-dichlorobezoquinone (DCBQ) &lt; tetrachloroquinone (TCBQ), consistent with their halogenation degree and the calculated electron affinity (EA) results. According to mass spectrometry and density functional theory (DFT) calculations, Ms can easily covalently incorporate into HBQs via nucleophilic addition (CBQ and DCBQ) or substitution (TCBQ) through C-N-C or C-S-C linkages. Hydroxylation, nucleophilic reaction and decarboxylation were proposed to be the three major reaction pathways for HBQs transformation with AAs. HBQs firstly underwent the spontaneous hydrolysis, resulting in OH-HBQs formation. Then, nucleophilic addition/substitution of AAs occurred on HBQs and OH-HBQs to produce AA-HBQs/AA-HBQs-OH adducts. These adducts were subsequently oxidized into their corresponding decarboxylated forms. Based on the results of Luminous bacterium Q67 acute toxicity test, the toxicity of HBQs solution greatly decreased with Ms presented. The toxicity change was well explained by the lowest unoccupied molecular orbital energy (E-LUMO) of formed products. Notably, the step that AAs nucleophilic bonded with HBQs led to the highest rise of k(LUMO), which should be the most effective pathway for HBQs detoxification. This study shows that binding with amino nitrogen compounds should be an important process for HBQs transformation and detoxification, which helps to better understand the fate of this typical DBP in surface water. (C) 2017 Elsevier Ltd. All rights reserved.</p