N-heterocyclic Aromatic Compounds Research Articles

Rational design of titanium-doped Y zeolite for hydrodenitrogenation of aromatic N-heterocyclic compounds

Ti modified Y zeolites with different Ti content were synthesized by in-situ hydrothermal crystallization method and used as the support of hydrodenitrogenation (HDN) catalyst. The forms of Ti species in the zeolites and the effect of Ti incorporation on the active metal states of the corresponding catalysts were investigated by XRD, UV–Vis DRS, XPS, HAADF-STEM, ICP-OES, Py-FTIR, H2-TPR, HRTEM, and DFT calculation. The results show that the incorporation of in-situ Ti species into Y zeolite led to a decrease in the Brønsted acid sites (BAS) /Lewis acid sites (LAS) value of the corresponding catalyst, but effectively enhanced the stacking layer number of the WS2 active phase by weakening the interaction between the active metals and the supports, which is manifested in the improvement of the hydrogenolysis activity and the decrease of the hydrogenation activity of the catalyst. When the hydrogenolysis activity and hydrogenation activity in the catalyst match to a certain extent, that is, the BAS/LAS value and the stacking layer number of the active phase reach an appropriate value, the HDN catalyst exhibited the highest catalytic activity. The NiW/Y-0.1Ti catalyst with suitable amount of BAS and stacking layer number of active phase showed the maximum kHDN values (11.7 × 10-4 mol·g−1·h−1 and 3.9 × 10-4 mol·g−1·h−1) and TOFs (1.91 h−1 and 1.04 h−1) of quinoline and indole HDN.

Gold catalysis in quinoline synthesis.

Quinolines are biologically and pharmaceutically important N-heterocyclic aromatic compounds, which have broad applications in medicinal chemistry. Thus, their efficient synthesis has attracted extensive attention, and a broad range of synthetic strategies have been established. Of note, gold-catalyzed methodologies for the synthesis of quinolines have greatly advanced this field. Various gold-catalyzed intermolecular annulation reactions, such as annulations of aniline derivatives with carbonyl compounds or alkynes, annulations of anthranils with alkynes, and annulations based on A3-coupling reactions, as well as intramolecular cyclization reactions of azide-tethered alkynes, 1,2-diphenylethynes, and 2-ethynyl N-aryl indoles, have been developed. This review provides an overview of this exciting research area. Typical achievements in reaction methodologies and plausible reaction mechanisms are summarized.

Peatland Wildfires Enhance Nitrogen-Containing Organic Compounds in Marine Aerosols over the Western Pacific.

Peatland wildfires contribute significantly to the atmospheric release of light-absorbing organic carbon, often referred to as brown carbon. In this study, we examine the presence of nitrogen-containing organic compounds (NOCs) within marine aerosols across the Western Pacific Ocean, which are influenced by peatland fires from Southeast Asia. Employing ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in electrospray ionization (ESI) positive mode, we discovered that NOCs are predominantly composed of reduced nitrogenous bases, including CHN+ and CHON+ groups. Notably, the count of NOC formulas experiences a marked increase within plumes from peatland wildfires compared to those found in typical marine air masses. These NOCs, often identified as N-heterocyclic alkaloids, serve as potential light-absorbing chromophores. Furthermore, many NOCs demonstrate pyrolytic stability, engage in a variety of substitution reactions, and display enhanced hydrophilic properties, attributed to chemical processes such as methoxylation, hydroxylation, methylation, and hydrogenation that occur during emission and subsequent atmospheric aging. During the daytime atmospheric transport, aging of aromatic N-heterocyclic compounds, particularly in aliphatic amines prone to oxidation and reactions with amine, was observed. The findings underscore the critical role of peatland wildfires in augmenting nitrogen-containing organics in marine aerosols, underscoring the need for in-depth research into their effects on marine ecosystems and regional climatic conditions.

Progress in Asymmetric Hydrogenation of Aromatic N-Heterocyclic Compounds

Progress in Asymmetric Hydrogenation of Aromatic N-Heterocyclic Compounds

Hydrothermally synthesized mesoporous titanium-containing Y zeolites with different titanium contents and their high activity for hydrodenitrogenation of quinoline and indole

Herein, the effect of in-situ Ti modification on the physicochemical properties of the TixY zeolites and the corresponding NiW supported TixY-A catalysts, as well as on the catalytic performances for aromatic N-heterocyclic compounds hydrodenitrogenation (HDN) was investigated. The existing forms of Ti atoms in the Y zeolites and the active metal states of the corresponding catalysts were investigated by XRD, ICP-OES, SEM, FTIR, UV–Vis DRS, CP-MAS NMR, N2 physical adsorption–desorption, Py-FTIR, H2-TPR, HRTEM, XPS and DFT calculation. The results show that the Ti atoms can be effectively introduced into the Y zeolite framework by the in-situ hydrothermal crystallization method. With the increase of TiO2/Al2O3 molar ratio in the Y zeolite, the amount of Brønsted acid sites of the zeolite tended to decrease constantly, but the reducibility of the catalyst and the stacking layer number as well as the sulfidation degree of the NiWS active phase continued to be enhanced. The highest quinoline and indole conversions of 86.5 % and 46.9 % at 320 °C, 4.0 MPa, 300 H2/oil (v/v), and 10 h−1 LHSV, as well as the highest TOFs of 2.24 h−1 and 1.04 h−1, the highest kHDN values of 12.4 × 10−4 mol·g−1·h−1 and 3.6 × 10−4 mol·g−1·h−1, and the highest denitrogenated product selectivities of 46.1 % and 66.2 % under quinoline and indole conversions of about 15 % and 50 % respectively have been achieved in catalyst NiW/Ti0.1Y-A due to the perfect matching of its hydrogenation and hydrogenolysis performance, which was mainly derived from the remarkable synergistic effect between the Brønsted acid sites of the Y zeolite and the NiWS active phase of the catalyst.

N-N self-inhibition effect of aromatic N-heterocyclic compounds on NiWS supported γ-Al2O3 hydrotreating catalyst

The reason for high-difficulty nitrogen removal of aromatic N-heterocyclic compounds in petroleum fractions was investigated from the main thought of “NiWS property - Reaction behavior - DFT calculation”. The properties of the used catalyst were characterized by a series of techniques with the aim of providing the basis for model construction in the DFT calculations. The kinetic experiments in fixed-bed reactor revealed that although 1,2,3,4-tetrahydroquinoline (THQ1) and decahydroquinoline (DHQ), o-ethylaniline (OEA) exhibited relatively high yields in the HDN reaction of quinoline and indole respectively, they were all able to show high conversions and HDN rates when reacted as feedstocks alone. The study of product normalizations in the reaction system of the mixed feedstocks demonstrated that the difficulty of conversion of THQ1 and DHQ in quinoline HDN was mainly due to the inhibition effect of quinoline feedstock. While in the HDN of indole, the presence of the intermediate product OEA was the main factor for the low conversion of indole. This phenomenon of inhibition originating from within the molecular reaction network was proposed as N-N self-inhibition effect for the first time. The DFT calculations suggested that the inhibition of quinoline on THQ1 could be attributed to the adsorption advantage of quinoline, while the inhibition on DHQ was mainly due to the steric hindrance effect of DHQ itself. And the inhibition effect of OEA on indole can be mainly attributed to its greater nucleophilicity and stronger adsorption ability on the active sites compared with IND.

Genomic potential for inorganic carbon sequestration and xenobiotic degradation in marine bacterium Youngimonas vesicularis CC-AMW-ET affiliated to family Paracoccaceae.

Ecological studies on marine microbial communities largely focus on fundamental biogeochemical processes or the most abundant constituents, while minor biological fractions are frequently neglected. Youngimonas vesicularis CC-AMW-ET, isolated from coastal surface seawater in Taiwan, is an under-represented marine Paracoccaceae (earlier Rhodobacteraceae) member. The CC-AMW-ET genome was sequenced to gain deeper insights into its role in marine carbon and sulfur cycles. The draft genome (3.7Mb) contained 63.6% GC, 3773 coding sequences and 51 RNAs, and displayed maximum relatedness (79.06%) to Thalassobius litoralis KU5D5T, a Roseobacteraceae member. While phototrophic genes were absent, genes encoding two distinct subunits of carbon monoxide dehydrogenases (CoxL, BMS/Form II and a novel form III; CoxM and CoxS), and proteins involved in HCO3- uptake and interconversion, and anaplerotic HCO3- fixation were found. In addition, a gene coding for ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO, form II), which fixes atmospheric CO2 was found in CC-AMW-ET. Genes for complete assimilatory sulfate reduction, sulfide oxidation (sulfide:quinone oxidoreductase, SqrA type) and dimethylsulfoniopropionate (DMSP) cleavage (DMSP lyase, DddL) were also identified. Furthermore, genes that degrade aromatic hydrocarbons such as quinate, salicylate, salicylate ester, p-hydroxybenzoate, catechol, gentisate, homogentisate, protocatechuate, 4-hydroxyphenylacetic acid, N-heterocyclic aromatic compounds and aromatic amines were present. Thus, Youngimonas vesicularis CC-AMW-ET is a potential chemolithoautotroph equipped with genetic machinery for the metabolism of aromatics, and predicted to play crucial roles in the biogeochemical cycling of marine carbon and sulfur.

Impact of fossil and non-fossil fuel sources on the molecular compositions of water-soluble humic-like substances in PM2.5 at a suburban site of Yangtze River Delta, China

Abstract. Atmospheric humic-like substances (HULIS) affect the global radiation balance due to their strong light absorption at the ultraviolet wavelength. The potential sources and molecular compositions of water-soluble HULIS at a suburban site in the Yangtze River Delta from 2017 to 2018 were discussed, based on the results of the radiocarbon (14C) analysis and combining the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) technique in this study. The 14C results showed that the averaged non-fossil-fuel source contributions to HULIS were 39 ± 8 % and 36 ± 6 % in summer and winter, respectively, indicating significant contributions from fossil fuel sources to HULIS. The Van Krevelen diagrams obtained from the FT-ICR-MS results showed that the proportions of tannin-like and carbohydrate-like groups were higher in summer, suggesting significant contribution of HULIS from biogenic secondary organic aerosols (SOAs). The higher proportions of condensed aromatic structures in winter suggested increasing anthropogenic emissions. Molecular composition analysis on the CHO, CHON, CHOS, and CHONS subgroups showed relatively higher intensities of high O-containing macromolecular oligomers in the CHO compounds in summer, further indicating stronger biogenic SOA formation in summer. High-intensity phenolic substances and flavonoids, which were related to biomass burning and polycyclic aromatic hydrocarbon (PAH) derivatives indicating fossil fuel combustion emissions, were found in winter CHO compounds. Besides, two high-intensity CHO compounds containing condensed aromatic ring structures (C9H6O7 and C10H5O8) identified in the summer and winter samples were similar to those from off-road engine samples, indicating that traffic emissions were one of the important fossil fuel sources of HULIS at the study site. The CHON compounds were mainly composed of nitro compounds or organonitrates with significantly higher intensities in winter, which were associated with biomass burning emissions, in addition to the enhanced formation of organonitrates due to high NOx in winter. However, the high-intensity CHON molecular formulas in summer were referring to N-heterocyclic aromatic compounds, which were produced from the atmospheric secondary processes involving reduced N species (e.g., ammonium). The S-containing compounds were mainly composed of organosulfates (OSs) derived from biogenic precursors, namely long-chain alkane and aromatic hydrocarbon, which illustrate the mixed sources of HULIS. Generally, different policies need to be considered for each season due to the different seasonal sources (i.e., biogenic emissions in summer and biomass burning in winter for non-fossil-fuel sources, traffic emissions and anthropogenic SOA formation in both seasons, and additional coal combustion in winter). Measures to control emissions from motor vehicles and industrial processes need to be considered in summer. Additional control measures on coal power plants and biomass burning should be applied in winter. These findings add to our understanding of the interaction between the sources and the molecular compositions of atmospheric HULIS.

Mechanism of the Multistep Catalytic Cycle of 6-Hydroxynicotinate 3-Monooxygenase Revealed by Global Kinetic Analysis

The class A flavoenzyme 6-hydroxynicotinate 3-monooxygenase (NicC) catalyzes a rare decarboxylative hydroxylation reaction in the degradation of nicotinate by aerobic bacteria. While the structure and critical residues involved in catalysis have been reported, the mechanism of this multistep enzyme has yet to be determined. A kinetic understanding of the NicC mechanism would enable comparison to other phenolic hydroxylases and illuminate its bioengineering potential for remediation of N-heterocyclic aromatic compounds. Toward these goals, transient state kinetic analyses by stopped-flow spectrophotometry were utilized to follow rapid changes in flavoenzyme absorbance spectra during all three stages of NicC catalysis: (1) 6-HNA binding; (2) NADH binding and FAD reduction; and (3) O2 binding with C4a-adduct formation, substrate hydroxylation, and FAD regeneration. Global kinetic simulations by numeric integration were used to supplement analytical fitting of time-resolved data and establish a kinetic mechanism. Results indicate that 6-HNA binding is a two-step process that substantially increases the affinity of NicC for NADH and enables the formation of a charge-transfer-complex intermediate to enhance the rate of flavin reduction. Singular value decomposition of the time-resolved spectra during the reaction of the substrate-bound, reduced enzyme with dioxygen provides evidence for the involvement of C4a-hydroperoxy-flavin and C4a-hydroxy-flavin intermediates in NicC catalysis. Global analysis of the full kinetic mechanism suggests that steady-state catalytic turnover is partially limited by substrate hydroxylation and C4a-hydroxy-flavin dehydration to regenerate the flavoenzyme. Insights gleaned from the kinetic model and determined microscopic rate constants provide a fundamental basis for understanding NicC's substrate specificity and reactivity.

Determination and Characterization of Genes that Encode the Nicotinate Dehydrogenase and 6‐Hydroxynicotinate Dehydrogenase Complexes within the Nicotinic Acid Degradation Pathway by Bacillus Niacini

N‐Heterocyclic aromatic compounds (NHACs) are constituents of many manufactured products such as pharmaceuticals, vitamins, and personal care products. Their widespread use has led to contamination of groundwater and soils, posing environmental concerns. Therefore, mechanisms of how NHACs are catabolized by bacteria have been studied to develop bioremediation strategies. Nicotinic acid (NA) is an example of an NHAC where its catabolism has been studied in a variety of microorganisms, such as Pseudomonas, Eubacterium,and Bacillus. While NA degradation has been elucidated in microorganisms such as P. putidaand E. barkeri,the majority of B. niacini’sNA catabolism pathway is relatively uncharacterized. Previous work identified a nicgene cluster that had been found to be upregulated in the presence of NA and 6‐hydroxynicotinic acid (6‐HNA), leading to the hypothesis that the set of protein subunits NicA1, NicA2, NicB1, NicB2 and CoxG are involved in the first two hydroxylation steps of B. niacini’sNA degradation pathway. These proteins are thought to form distinct multi‐subunit protein complexes with nicotinate dehydrogenase (NDH) and 6‐hydroxynicotinate dehydrogenase (6‐HNDH) activities. Due to the involvement of the molybdopterin cofactor present in the B subunits, recombinant forms of these enzymes have not shown activity when expressed and purified from E. coli. A vector specific for expressing the genes in Pseudomonas (pBBr) was engineered to contain the set of five B. niacini genes hypothesized to code for NA hydroxylating enzymes and was transformed into Pseudomonas fluorescens 1f2,a strain shown to be unable to degrade nicotinic acid naturally. Analysis of the media upon incubation of the Pf‐1f2 transformants with NA or 6‐HNA in minimal media by C‐18 chromatography (HPLC) showed rapid and complete hydroxylation of NA to 6‐HNA, as well as the hydroxylation of 6‐HNA to 2,6‐dihydroxynicotinic acid (2,6‐DHNA). This is the first evidence of activity observed from recombinant B. niacini“NicAB” protein complexes. However, the combination of gene‐encoded subunits that compose the NDH and 6‐HNDH complexes is currently unknown. Using deletion mutagenesis, specific genes cloned into the pBBr vector will be removed to recombinantly express variant complexes that lack a specific subunit to determine the substrate specificity and oligomeric structure of the complexes.

Exploring The Promiscuity Potential Of 6‐Hydroxynicotinate‐3‐Monooxygenase: Consequences To Catalysis Of Adding A Nitrogen At C5 Within The Substrate’s Aromatic Ring

Bacterial degradation of nicotinic acid is a model for exploring the bioremediation potential of soil bacteria. One enzyme within this catabolic pathway is 6‐hydroxynicotinate‐3‐monooxygenase (NicC), a group A flavoenzyme that catalyzes the conversion of 6‐hydroxynicotinate (6HNA) to 2,5‐dihydroxypyridine. This decarboxylative hydroxylation reaction is relatively unique in biology. We recently published a study highlighting NicC’s ability to catalyze the decarboxylation and hydroxylation reaction with alternative substrates including 4‐hydroxybenzoate (4HBA) and 5‐chloro‐6‐hydroxynicotinate (5‐Cl‐6HNA). To further explore the structural basis of a substrate that enables tight binding and catalysis with NicC, 2‐hydroxypyrimidine‐5‐caboxylate (2HM5A) was characterized. This 6‐HNA analogue with an extra N atom at C5 was chosen due to its fundamental symmetry and comparable electron distribution as 5‐Cl‐6HNA. Analyses of NicC with 2HM5A show that the expected product, 2,5‐dihydroxypyrimidine (isouracil), is generated, with H2O2 occurring at a mol fraction of about 0.07, indicating that uncoupling between NADH oxidation and substrate hydroxylation is minimal. Equilibrium titration of NicC with 2HM5A by changes in A‐450 nm measure the Kd = 39 ± 6 µM, indicating that this substrate is bound more tightly than 6‐HNA (Kd= 58 ± 12 µM) but less tightly than 5‐Cl‐6‐HNA (Kd= 7 ± 2 µM). Interestingly, the overall ΔA450 elicited by the binding of 2HM5A (0.018) was smaller in comparison to the ΔA450 observed for the binding of 5‐Cl‐6HNA (0.07) or 6‐HNA (0.05). Attenuated flavin movement due the extra nitrogen of the pyrimidine ring in 2HM5A H‐bonding to the isoalloxazine ring may explain this observation. The kinetics of binding 2HM5A by NicC measured by stopped flow spectrophotometry shows that this analogue binds by a two‐step mechanism, with a nearly ten‐fold higher initial affinity for NicC prior to isomerization (ionization) than 6‐HNA. This added affinity may again be explainable by the added H‐bonding potential of this analogue. In the second step of binding, 2HM5A was observed to have a rate constant similar to 5‐Cl‐6HNA (k2= 220 s‐1), possibly indicating that increased electron density at/near the C5 position accelerates this phase of the binding mechanism. How 2HM5A affects NicC’s mechanism of flavin reduction and oxidation will also be presented. These findings provide further evidence of this monooxygenase’s potential to be engineered to hydroxylate other N‐heterocyclic aromatic compounds in bioremediation.

Elucidating The Nicotinic Acid Degradation Pathway In Bacillus niacini: Identification and Biochemical Characterization Of Proteins Of Unknown Function

N‐Heterocyclic aromatic compounds (NHACs) are abundant in the manufacturing of solvents, pesticides, and dyes; however, accumulation of these compounds can lead to detrimental environmental impacts. To alleviate these impacts, it is critical to understand the mechanisms microbial species use to catabolize these types of molecules so that bioremediation techniques can be implemented. Nicotinic acid is commonly used as a model system for NHAC degradation because it is environmentally safe and can be degraded by a variety of bacterial species. Bacillus niacini is a soil‐dwelling bacterium that has been identified to degrade NA through an uncharacterized pathway. This makes B. niacini an organism of interest, as elucidation of the mechanism by which it catabolizes NA will reveal differences between these pathways that can be exploited to optimize bioremediation efforts. Bioinformatic analyses of genomic and transcriptomic data revealed a potential operon responsible for NA degradation in B. niacini. This operon contains 15 genes that encode for 7 enzymes that are necessary for NA degradation as well as three genes that have not yet been elucidated: a domain of unknown function (DUF), a flavin monooxygenase (FMO), and a hypothetical protein (HP). NA degradation in B. niacini is unique in that it involves two ring hydroxylating steps, forming the intermediate 2,6‐dihydroxynicotinic acid (DHNA). After decarboxylation of DHNA to 2,6‐dihydroxypridine (DHP), we show that the DUF hydroxylates DHP to 2,3,6‐trihydroxypyridine (THP). Separation of the DUF‐catalyzed reaction products by C‐18 chromatography (HPLC) and detection by UV‐Vis at pH 3 shows a new species with an Absmaxat 320 nm and 590 nm. Mass spectrometry (Q‐TOF) analysis of the reaction identifies the products as DHP‐ and THP‐ oxidized dimers (nicotine blue). Formation of these products are observed to be O2 dependent. When the DUF, FMO and HP genes are recombinantly expressed together in E. coli, the cell extract is able to degrade DHP without forming the DHP‐oxidized dimer. That observation suggests the possible roles of FMO and/or HP in catalyzing the conversion of the DHP‐dimer back to DHP. This study is the first to characterize the genes responsible for NA degradation by B. niacini and further establishes the NA degradation pathway.

A Facile Synthesis of Bioactive Five- and Six-membered N-heterocyclic Aromatic Compounds Using AlCoFe2O4 as a Green Catalyst.

Nitrogen-containing heterocycles have been extensively studied due to their broad biological and pharmaceutical applications. In this study, we synthesized five- and six-membered nitrogen-containing rings through one-pot multicomponent reaction using an aluminium-doped cobalt ferrite nano-catalyst. The nano-catalyst was prepared by the co-precipitation method from the corresponding metal salts. The obtained results show that the proposed catalyst has a high efficiency and has enabled the formation of the desired products with high efficiency and purity. In addition, simplicity of operation, facile purification of products, shorter reaction times, mild reaction conditions, easy separation and recyclability of the catalyst, are the main advantages of this catalyst.

Bidirectional Cell-Cell Communication via Indole and Cyclo(Pro-Tyr) Modulates Interspecies Biofilm Formation.

The extracellular signaling molecule indole plays a pivotal role in biofilm formation by the enteric gammaproteobacterium Escherichia coli; this process is particularly correlated with the extracellular indole concentration. Using the indole-biodegrading betaproteobacterium Burkholderia unamae, we examined the mechanism by which these two bacteria modulate biofilm formation in an indole-dependent manner. We quantified the spatial organization of cocultured microbial communities at the micrometer scale through computational image analysis, ultimately identifying how bidirectional cell-to-cell communication modulated the physical relationships between them. Further analysis allowed us to determine the mechanism by which the B. unamae-derived signaling diketopiperazine cyclo(Pro-Tyr) considerably upregulated indole biosynthesis and enhanced E. coli biofilm formation. We also determined that the presence of unmetabolized indole enhanced the production of cyclo(Pro-Tyr). Thus, bidirectional cell-to-cell communication that occurred via interspecies signaling molecules modulated the formation of a mixed-species biofilm between indole-producing and indole-consuming species. IMPORTANCE Indole is a relatively stable N-heterocyclic aromatic compound that is widely found in nature. To date, the correlations between indole-related bidirectional cell-to-cell communications and interspecies communal organization remain poorly understood. In this study, we used an experimental model, which consisted of indole-producing and indole-degrading bacteria, to evaluate how bidirectional cell-to-cell communication modulated interspecies biofilm formation via intrinsic and environmental cues. We identified a unique spatial patterning of indole-producing and indole-degrading bacteria within mixed-species biofilms. This spatial patterning was an active process mediated by bidirectional physicochemical interactions. Our findings represent an important step in gaining a more thorough understanding of the process of polymicrobial biofilm formation and advance the possibility of using indole-degrading bacteria to address biofilm-related health and industry issues.

Synthesis of Anilines and N-Heterocyclic Aromatic Compounds Catalyzed by Ni/C Nanocomposites

Key words nickel catalysis - anilines - nitrobenzenes - N-heterocycles - hydrogen transfer

Superhydrophobic nickel/carbon core–shell nanocomposites for the hydrogen transfer reactions of nitrobenzene and N-heterocycles

In this work, catalytic hydrogen transfer as an effective, green, convenient and economical strategy is for the first time used to synthesize anilines and N-heterocyclic aromatic compounds from nitrobenzene and N-heterocycles in one step.

A new interspecies and interkingdom signaling molecule-Indole

Indole, as a typical N-heterocyclic aromatic compound, is widespread in natural environment. A growing number of researches have proved that indole is a new interspecies and interkingdom signal molecule with certain biological activities. Indole could regulate virulence, biofilm formation, antibiotic tolerance and quorum sensing of bacteria. Indole not only modulates plant growth and defense system, but also affects intestinal inflammation, oxidative stress and hormone secretion in animals. Hence indole plays important roles in diverse aspects such as microbial metabolism, human health and plant growth, holding important significance both in biology and ecology. This review presents the history of indole from biological metabolism to signal transmission, the current knowledge on indole as an intercellular and interspecies signal of microorganisms, and interkingdom signal between bacteria and plants or animals. This review will help to explore the biological significant and ecological mechanism of indole metabolic and signal regulation in complex environment.

Synthesis of an aromatic N-heterocycle derived from biomass and its use as a polymer feedstock

Aromatic N-heterocyclic compounds are very important chemicals, which are currently produced mostly from petroleum. Here we report that a pyridazine-based compound 6-(4-hydroxy-3-methoxyphenyl)pyridazin-3(2H)-one (GSPZ) can be efficiently synthesized by the Friedel-Crafts reaction of guaiacol and succinic anhydride, both of which can be derived from biomass. GSPZ is then treated with bio-based epichlorohydrin to prepare the epoxy resin precursor GSPZ-EP. With 4,4'-diaminodiphenylmethane as curing agent, GSPZ-EP possesses higher glass transition temperature (187 oC vs. 173 oC) and shows a 140%, 70 and 93% increase in char yield (in N2), storage modulus (30 oC) and Young’s modulus, respectively when compared with a standard petroleum-based bisphenol A epoxy resin. Moreover, the cured GSPZ-EP shows good intrinsic flame retardancy properties and is very close to the V-0 rating of UL-94 test. This work opens the door for production of aromatic N-heterocyclic compounds, which can be derived from biomass and employed to construct high performance polymers.

Speciation and transformation of nitrogen for spirulina hydrothermal carbonization

Nitrogen conversion (N-conversion) mechanism of spirulina (SP) in hydrothermal carbonization (HTC) was investigated under medium-low temperature (180–280 °C). N-conversion in bio-char, liquid and bio-oil were studied by FTIR, XPS, GC–MS and other analytical methods. Results indicated that the temperature could significantly affect the evolution of nitrogen. At 180–200 °C, the content of protein-N and pyridine-N in bio-char fell 23.01% and 9.51% respectively. In contrast, the contents of inorganic-N and quaternary-N increased by 16.99% and 16% respectively. Protein-N hydrolysis and Maillard reaction produced the key intermediate compounds, including amines, amides and N-heterocyclic compounds during the HTC. At 200–280 °C, the inorganic-N was obviously converted from solid to liquid. With the increased of temperature, it would enhance the polymerization of pyrrole-N and pyridine-N, which could cause the significant increase of aromatic N-heterocyclic compounds (e.g., nitriles and indole derivatives) in bio-oil. A N-conversion mechanism of SP HTC was proposed in this study.

Alicycliphilus: current knowledge and potential for bioremediation of xenobiotics.

Alicycliphilus is a promising candidate for participating in the development of novel xenobiotics bioremediation processes. Members of the Alicycliphilus genus are environmental bacteria mostly found in polluted sites such as landfills and contaminated watercourses, and in sewage sludges from wastewater treatment plants. They exhibit a versatile metabolism and the ability to use oxygen, nitrate and chlorate as terminal electron acceptors, which allow them to biodegrade xenobiotics under oxic or anoxic conditions. Pure cultures of Alicycliphilus strains are able to biodegrade some pollutants such as industrial solvents (acetone, cyclohexanol and N-methylpyrrolidone), aromatic hydrocarbons (benzene, toluene and anthracene), as well as polyurethane varnishes and foams, and they can even transform Cr(VI) to Cr(III). In addition, Alicycliphilus has also been identified in bacterial communities involved in wastewater treatment plants for denitrification, and the degradation of emerging pollutants such as triclosan, nonylphenol, N-heterocyclic aromatic compounds (indole and quinoline), and antibiotics (tetracycline and oxytetracycline). This work summarizes the current knowledge on the Alicycliphilus genus, describing its different metabolic characteristics, focusing on its xenobiotic biodegradation abilities and examining the distinct pathways and molecular bases that sustain them. We also discuss the progress made in genetic manipulation and 'omics' analyses, as well as Alicycliphilus participation in novel bioremediation strategies.