Bridge Cleavage Research Articles

Comprehensive toxicological, metabolomic, and transcriptomic analysis of the biodegradation and adaptation mechanism by Achromobacter xylosoxidans SL-6 to diuron.

Biodegradation was considered a promising and environmentally friendly method for treating environmental pollution caused by diuron. However, the mechanisms of biodegradation of diuron required further research. In this study, the degradation process of diuron by Achromobacter xylosoxidans SL-6 was systematically investigated. The results suggested that the antioxidant system of strain SL-6 was activated by adding diuron, thereby alleviating their oxidative stress response. In addition, degradation product analysis showed that diuron in strain SL-6 was mainly degraded by urea bridge cleavage, dehalogenation, deamination, and ring opening, and finally cis, cis-muconic acid was generated. The combined analysis of metabolomics and transcriptomics revealed the biodegradation and adaptation mechanism of strain SL-6 to diuron. Metabolomics analysis showed that after the strain SL-6 was exposed to diuron, metabolic pathways such as tricarboxylic acid cycle (cis, cis-muconic acid), glutathione metabolism (oxidized glutathione), and urea cycle (arginine) were reprogrammed in the cells. Furthermore, diuron could induce the production of membrane transport proteins in strain SL-6 cells and overexpress antioxidant enzyme genes, finally ultimately promoting the up-regulation of genes encoding amide hydrolases and dioxygenases, which was revealed by transcriptomics studies. This work enriched the biodegradation mechanism of phenylurea herbicides and provided guidance for the removal of diuron residues in the environment and promoting agriculture sustainable development.

Kinetic Insights into Bridge Cleavage Pathways in Periodic Mesoporous Organosilicas.

Bridging functionalities in periodic mesoporous organosilicas (PMOs) enable new functionalities for a wide range of applications. Bridge cleavage is frequently observed during anneals required to form porous structures, yet the mechanism of these bridge cleavages has not been completely resolved. Here, these chemical transformations and their kinetic pathways on sub-millisecond timescales induced by laser heating are revealed. By varying anneal times and temperatures, the transformation dynamics of bridge cleavage and structural transformations and their activation energies are determined. The structural relaxation time for individual reactions and their effective local heating time are determined and compared, and the results directly demonstrate the manipulation of different molecules through kinetic control of the sequence of reactions. By isolating and understanding the earliest stage of structural transformations, this study identifies the kinetic principles for new synthesis and post-processing routes to control individual molecules and reactions in PMOs and other material systems withmulti-functionalities.

Application of pesticide application measures to reduce residue based on the metabolic transfer law of imidacloprid in banana leaves and soil

An investigation of the metabolism and transfer of imidacloprid (IMI) in banana plants and soil was performed using high-resolution mass spectrometry. Results indicated the presence of eight IMI metabolites in soil and leaves that resulted from hydroxylation of the imidazolidine ring, the reduction and loss of nitro groups, and oxidative cleavage of methylene bridges. Six metabolites, including 4/5-hydroxy IMI (4/5-hydroxy), IMI olefin (olefin), and 6-chloronicotinic acid (6-CNA), were detected in the fruits following leaf treatment, while only three were detected after soil treatment. Quantitative analysis showed that the total amount of imidacloprid and its metabolites transferred from leaves to fruits was higher than that transferred from soil to fruits. Therefore, leaf transfer was considered the main means by which IMI and its metabolites transferred to banana fruits. We found that adjuvants tank-mixed with IMI could reduce the total concentration of pesticide transfer from leaves to fruits, especially reducing the amount of metabolites transformed from the reduction and loss of nitro groups and oxidative cleavage of methylene bridges, thus reducing the pesticide residue in fruits and achieving the purpose of reducing the safety risk.

Effect of solvent quality on covalent bonds cleavage behaviors of lignite during pyrolysis/liquefaction processes

Effect of solvent quality on coal conversion and product distribution during lignite pyrolysis/liquefaction were investigated at the temperatures ranging from 180 to 460 °C, and the covalent bond cleavage behaviors in different solvents were comparatively elucidated. Results showed that at the temperatures below 280 °C, weak covalent bonds, such as methoxy and carboxyl groups, are cleaved to generate a small amount of gaseous products (mainly CO2) and liquefied oil. At the temperatures of 330–380 °C, ether bridges that connecting the aromatic clusters are cleaved and contributed significantly to the production of preasphaltene (PA). Meanwhile, oil yield and coal conversion increased to 27.50% and 64.58% in tetralin. At the temperatures of 430–460 °C, the cleavage of CH2 bridges, alkyl substituent groups and aromatic heterocyclic structures proceeded markedly, and the scission of CH2 bridges and some naphthenic CH2 bonds significantly contributed to oil production. Consequently, oil yield and coal conversion greatly increased to 43.90% and 84.13% in tetralin. Hydrogen donor solvent is conducive to the cleavage of strong covalent bonds, such as Car–O–Car and Car-Cal bonds, to realize the efficient liquefaction of coal.

Remediation of polychlorinated biphenyls (PCBs) polluted soil using dielectric barrier discharge (DBD) plasma: Reactive nitrogen species (RNS) and produced dioxins

Soil contaminated by PCBs from the electronic processing industries has attracted global concern because of their potentially persistent risks to human and ecological health. In this study, remediation of PCBs polluted soil using dielectric barrier discharge plasma (DBD) focused on 3,3′,4,4′-tetrachlorobiphenyl (PCB77) and 2,2′-dichlorobiphenyl (PCB4). About 90 % of PCB77 and PCB4 were degraded under input power of 120 W within 30 min. The carbon dioxide mineralization of PCB77 achieved at 18.2 % in 10 min treatment. Greater PCBs degradation was obtained with higher input power, lower moisture content, weaker acidity and presence of oxygenated gas. Increasing initial concentration of PCBs had no significant effect on PCB77 degradation, but contributed to PCB4 removal. PCBs degradation reactions were initiated by high-energy electrons. Reactive oxygen species (ROS) played major roles in PCBs degradation, which was also promoted by reactive nitrogen species (RNS) such as peroxynitrous radicals (HOONO). Multiple spectroscopies showed that chlorine radicals participated in PCBs degradation reactions. Chlorine substitution, ring-opening and bridge cleavage reactions were the main degradation pathways for PCB77. The production and re-degradation of trace dioxin-like substances ensured the safety of DBD use in the remediation of PCBs-contaminated soils.

Laser desorption ionization and collision induced dissociastion as powerful tools for FT-ICR mass spectrometric characterization of asphaltene fractions enriched in island and archipelago motifs

Due to advances in mass spectrometry, it is widely accepted that asphaltenes molecules from the island and archipelago motifs coexist in the samples. However, analyzing asphaltenes remains a challenging task mostly due to these species' high complexity and self-association tendencies. Herein we introduce laser laser desorption ionization (LDI) as an adequate tool to ionize even the most unstable samples. In addition, we demonstrate collision-induced dissociation (CID) experiments as a powerful tool to perform structural characterization of asphaltenes. Using these tools, it was possible to characterize asphaltene samples enriched in island and archipelago-type structures in a much easier way without any capillary obstructions and damages to the equipment. Also, it was possible to perform an in-depth analysis of asphaltene and propose structures to asphaltene detected in the most abundance in the selected samples. Finally, the relative percentages of product ions derived from the cleavage of alkyl bridges between aromatic nuclei in archipelago-type molecules were calculated, and we tried to establish correlations with the asphaltene structures with their stability.

NIR-responsive polydopamine-based calcium carbonate hybrid nanoparticles delivering artesunate for cancer chemo-photothermal therapy

Artesunate (AS), the first-line treatment of malaria with a satisfactory safety profile, has been repurposed as a potential anticancer candidate as it mainly generates reactive oxygen species (ROS) through its intrinsic endoperoxide bridge reacting with ferrous-based catalysts to suppress cancer cell growth. However, further clinical translation of AS is hindered by the attenuated anticancer efficacy due to insufficient ROS generation. Herein, we rationally integrated hydrophobic-modified AS (hAS) with biomimetic polydopamine (PDA) and biomineral calcium carbonate to fabricate high AS-loaded nanomedicine (Ca-PDA/hAS@PEG) for cancer chemo-photothermal therapy, which exerted anticancer effects in the following ways: (1) the heat was generated when PDA was irradiated by near-infrared (NIR) light for photothermal therapy. Meanwhile, the increased temperature accelerated the production of ROS from hAS, thus enhancing the anticancer efficacy of hAS-based chemotherapy; (2) hAS-mediated chemotherapy boosted the cancer inhibition effect of photothermal therapy by arousing the intracellular ROS levels in the presence of endogenous ferrous ions and sensitizing cancer cells to thermal ablation; (3) the integration of calcium carbonate into the nanoparticle facilitated the pH-responsive drug release for precise treatment. Such hybrid nanoparticles exhibited a combinational antitumor effect of photothermal therapy and chemotherapy in vivo with no systemic toxicity. Taken together, our work presents a facile strategy to improve the anticancer efficacy of AS by combining chemical modification and photothermal therapy-assisted endoperoxide bridge cleavage, which may offer opportunities to pave the way for clinical translation of AS-based nanomedicines. Statement of significanceThe clinical translation of artesunate (AS) is hindered by the attenuated anticancer efficacy due to insufficient ROS generation. Herein, we rationally integrated hydrophobic-modified AS (hAS) with biomimetic polydopamine (PDA) and biomineral calcium carbonate to fabricate high AS-loaded nanomedicine (Ca-PDA/hAS@PEG) for improved cancer chemo-photothermal therapy. The heat generated from PDA in response to near-infrared light irradiation could locally ablate tumor as well as accelerate the production of ROS by hAS, thus enhancing the anticancer efficacy of hAS-based chemotherapy. On the other hand, hAS-based chemotherapy amplified the intracellular oxidative stress, sensitizing cancer cells to thermal ablation. Our work presents a facile strategy to improve the anticancer efficacy of AS by combining chemical modification and photothermal therapy-assisted endoperoxide bridge cleavage.

Persistence and transformation of flucetosulfuron herbicide in soil as affected by biotic and abiotic factors

Effect of biotic and abiotic factors of soil on persistence and transformation of flucetosulfuron was studied in three soils from paddy growing zones of India. Herbicide residues in three soils dissipated with half-life ranging from 1.41 to 8.38 and 0.58 to 1.14 days under sterile and non-sterile conditions, respectively. Acidic pH and soil microbial activity contributed more toward the degradation of flucetosulfuron in soil. Under flooded soils, dissipation was bit slower than under field capacity moisture level. Five transformation products were identified with LC-MS/MS analysis. Ester hydrolysis and sulfonyl urea bridge cleavage seems to be the major transformation pathways for flucetosulfuron in soil.

Synthesis and Characterisation of Transition Metal Complexes of a Novel 1,5‐benzodiazepine‐Functionalised Tertiary Phosphine

AbstractThe one‐step synthesis (44 % isolated yield) of the 1,5‐benzodiazapine functionalised phosphine 1, C31H31N2OP, is reported. Bridge cleavage of {MCl(μ‐Cl)(η5‐Cp*)}2 (M=Ir, Rh) with 2 equiv. of 1 in CH2Cl2 gave the mononuclear compounds [MCl2(η5‐Cp*)(P‐1)] (M=Ir, 2 a; M=Rh, 2 b) in which 1 functions as a P‐monodentate ligand. Rapid C(sp3)−H bond activation, at room temperature, is observed for 2 a leading to the unusual cyclometallated complex [Ir(η5‐Cp*)(P,N,C‐1)]Cl2 3 (or 3‘) bearing an anionic P/Namine/C‐terdentate ligand. Reaction of [Pt(CH3)Cl(η4‐cod)] with one equiv. of 1 led to [Pt(CH3)Cl(P,N‐1)] 4, suggesting that 3 may form via an intermediate IrIII cationic species in which the ligand is P,N‐bound. The IrI complex [IrCl(η4‐cod)(P‐1)] 5 does not, under similar conditions, show any evidence for C−H activation. Single crystal X‐ray studies on 1, 2 a, 2 b, 3, 3‘, 4, and 5 reveal intramolecular N ⋅⋅⋅ H−O H‐bonding in all cases.

Stabilisation of sheep wool fibres under air atmosphere: Study of physicochemical changes

Natural fibres constitute interesting, low cost and environmentally friendly precursors of carbon fibres. However, they are prone to fuse and degrade upon thermal treatment, affecting the properties of the products unless a stabilization step was included. Aiming to reach a better understanding of the stabilization mechanism of wool as a potential precursor for the preparation of carbon fibres, in this study we have analysed the chemical, structural and morphological transformations during its oxidative stabilization in air. Below 400 °C, both the structure and morphology of the fibres were preserved. The chemical composition changed with the stabilization temperature; main changes include the loss of secondary protein structure, cleavage of sulphur bridges, dehydration, oxidative crosslinking and rearrangements of N-groups through the formation of carbodiimides. Oxidation of the wool at 300 °C rendered materials with a fibrous morphology and high carbon yield (ca. 36 wt%), yielding carbon fibres upon carbonization at high temperatures.

Theoretical insights into the dimerization mechanism of aluminum species at two different pH conditions

Dimerization mechanism of aluminum species is investigated in weakly acidic solutions and in strongly alkaline solutions using density functional theory, respectively. The results indicate the dimerization is controlled by dehydration of monomeric aluminum and the dissolution of dimer is controlled by the hydroxyl bridge cleavage in weakly acidic solutions. The two processes are enhanced by the rising pH. In addition, the main pathway generating the fluorine bridge is not the direct polymerization, but the terminal substitution of F− into polymeric aluminum followed by the transition of terminal F to bridging F. The formation of fluorine bridge promotes dissolution and di-fluorine-bridged dimer should be excluded. In strongly alkaline solutions, the formation processes of three dimers were speculated, and the existence of mono-hydroxyl-bridged dimer is denied due to the extraordinary instability and high formation energy barriers. It is possible that mono-oxygen-bridged and di-hydroxyl-bridged dimers coexist in highly alkaline solutions. However, the salts of mono-oxygen-bridged anion are much more stable than salts of di-hydroxyl-bridged anion due to the effect of counter cations and the removal of ambient water molecules.

Reversible Redox Crosslinking of Thiopropylsilicones.

Most silicone elastomers are thermosets. As a response to the new paradigm of polymer recyclability, the development of silicone elastomers that can be reversibly and repeatedly cured and uncrosslinked using redox conditions is reported. Thiopropyl-modified silicones are oxidized to elastomers with disulfide crosslinks using the organosoluble oxidant PhI(OAc)2 . As with any elastomer, mechanical properties can be tuned by varying crosslink density. Thermal stabilities in air show that the products are comparable to traditional silicone thermosets, with degradation only starting over 300°C. Uncrosslinking back to the same thiopropyl-modified silicones involves reductive S-S bridge cleavage using a Piers-Rubinsztajn reaction with hydrosilanes catalyzed by B(C6 F5 )3 ; HSiMe2 OSiMe3 is identified as a convenient reducing agent. The initially formed silicone-(CH2 )3 S-SiMe2 OSiMe3 products need deprotection with water in isopropanol/water to completely regenerate the thiopropylsilicones. This oxidation/reduction crosslinking/uncrosslinking cycle is practiced thrice, with a yield of 89% per cycle, with essentially no change in the Young's moduli of the elastomers, or 1 H NMR spectra of the uncrosslinked fluids after reduction. Further oxidation of disulfide groups on the elastomer surface permanently and significantly improved water wettability.

A DFT study on the cleavage of dichalcogenide bridges in cystines and selenocystines: Effect of hydrogen bonding

Density functional theory calculations were employed to quantify the effect of hydrogen bonding interactions in the reactions involving cleavage of dichalcogenides in cystines and selenocystines. The computed gas phase reaction has a multistep mechanism involving hydrogen bond transfers from one heteroatom to another across the reaction coordinate along with the anionic charge transfer from the nucleophile to the product. The solution phase mechanism, however, is simple SN2 irrespective of the nature of the reaction centre or hydrogen bonding interaction at the reaction site, or the nucleophile. When compared to similar reactions without any hydrogen bonding interactions at the reaction centre, these were found to be very facile both in gas phase as well as in aqueous solution.

Cytokinetic bridge triggers de novo lumen formation in vivo

Multicellular rosettes are transient epithelial structures that serve as intermediates during diverse organ formation. We have identified a unique contributor to rosette formation in zebrafish Kupffer’s vesicle (KV) that requires cell division, specifically the final stage of mitosis termed abscission. KV utilizes a rosette as a prerequisite before forming a lumen surrounded by ciliated epithelial cells. Our studies identify that KV-destined cells remain interconnected by cytokinetic bridges that position at the rosette’s center. These bridges act as a landmark for directed Rab11 vesicle motility to deliver an essential cargo for lumen formation, CFTR (cystic fibrosis transmembrane conductance regulator). Here we report that premature bridge cleavage through laser ablation or inhibiting abscission using optogenetic clustering of Rab11 result in disrupted lumen formation. We present a model in which KV mitotic cells strategically place their cytokinetic bridges at the rosette center, where Rab11-associated vesicles transport CFTR to aid in lumen establishment.

Ruthenium(II) complexes of the tetradentate polypyridyl thioether 1,2-bis[3′-(2″-pyridyl)-1′-thiapropyl]benzene

Several new Ru(II) polypyridyl complexes of the novel tetradentate thioether 1,2-bis[3′-(2″-pyridyl)-1′-thiapropyl]benzene (Ppes) form from the dinuclear ruthenium(II) complex [{Ru(Ppes)}2(µ-Cl)2]2+via reaction with various bidentate diimines. Facile symmetrical bridge cleavage occurs, producing mononuclear complexes of the form [Ru(Ppes)(L)]2+, where L is the bidentate diimine. Redox chemistry shows single-electron Ru(II) → Ru(III) oxidations over a wide range of potentials.

Synthesis of mono/dinuclear rhenium(i) tricarbonyl substituted with 4-mercaptopyridine related ligands: spectral and theoretical evidence of thiolate/thione interconversion

κ1-S complexes show solvent-mediated tautomerism. The S–S bridge cleavage in κ1-N derivatives is attributed to the presence of a proton source.

Fully amino acid-based hydrogel as potential scaffold for cell culturing and drug delivery.

Polymer hydrogels are ideal scaffolds for both tissue engineering and drug delivery. A great advantage of poly(amino acid)-based hydrogels is their high similarity to natural proteins. However, their expensive and complicated synthesis often limits their application. The use of poly(aspartic acid) (PASP) seems an appropriate solution for this problem due to the relatively cheap and simple synthesis of PASP. Using amino acids not only as building blocks in the polymer backbone but also as cross-linkers can improve the biocompatibility and the biodegradability of the hydrogel. In this paper, PASP cross-linked with cystamine (CYS) and lysine-methylester (LYS) was introduced as fully amino acid-based polymer hydrogel. Gels were synthesized employing six different ratios of CYS and LYS. The pH dependent swelling degree and the concentration of the elastically active chain were determined. After reduction of the disulfide bonds of CYS, the presence of thiol side groups was also detected. To determine the concentration of the reactive cross-linkers in the hydrogels, a new method based on the examination of the swelling behavior was established. Using metoprolol as a model drug, cell proliferation and drug release kinetics were studied at different LYS contents and in the presence of thiol groups. The optimal ratio of cross-linkers for the proliferation of periodontal ligament cells was found to be 60−80% LYS and 20−40% CYS. The reductive conditions resulted in an increased drug release due to the cleavage of disulfide bridges in the hydrogels. Consequently, these hydrogels provide new possibilities in the fields of both tissue engineering and controlled drug delivery.

Catalytic degradation of organic pollutants in Fe(III)/peroxymonosulfate (PMS) system: performance, influencing factors, and pathway.

This study demonstrated, for the first time, Fe(III)/peroximonosulphate (PMS) could be an efficient advanced oxidation process (AOP) for wastewater treatment. Bisphenol A (BPA) was chosen as a model pollutant in the present study. Fe(III)-activated PMS system proved very effective to eliminate 92.18% of BPA (20 mg/L) for 30-min reaction time at 0.50 mM PMS, 1.5 g/L Fe(III), pH 7.0. The maximum degradation of BPA occurred at neutral pH, while it was suppressed at both strongly acidic and alkaline conditions. Organic and inorganic ions can interfere with system efficiency either positively or negatively, so their interaction was thoroughly investigated. Furthermore, the presence of organic acids also affected BPA degradation rate, especially the addition of 10 mM citric acid decreased the degradation rate from 92.18 to 66.08%. Radical scavenging experiments showed that SO4•- was the dominant reactive species in Fe(III)/PMS system. A total of 5 BPA intermediates were found by using LC/MS. A possible degradation pathway was proposed which underwent through bridge cleavage and hydroxylation processes. Acute toxicity of the BPA degradation products was assessed using Escherichia coli growth inhibition test. These findings proved to be promising and economical to deal with wastewater using iron mineral for the elimination of organic pollutants. Graphical abstract.

Total Synthesis of (±)-Prostratin

Summary Prostratin, a highly complex diterpene natural product, is a pre-clinical candidate in developing a cure for HIV-1 infection and also a potent and selective inhibitor of several tumors. Despite nearly 40 years of progress, prostratin and related natural products still present formidable challenges for synthetic chemists. Here, we report a total synthesis of (±)-prostratin that proceeds in 23 steps from cyclopentadiene. The synthetic strategy includes rapid assembly of the tricyclic core and highly controlled establishment of the densely functionalized C ring, featuring an array of stereoselective transformations including alkoxide-guided 1,4-additions and cyclopropane formation. This work should enable further explorations of chemical and biological spaces based on prostratin and related natural products.

New phosphorus ylide palladacyclic: Synthesis, characterization, X-Ray crystal structure, biomolecular interaction studies, molecular docking and in vitro cytotoxicity evaluations

The ylide-phosphonium salt [PPh3CH2C(O)CH2Cl]+Cl− was reacted with Pd(OAc)2 to give the chloro-bridged dinuclear complex [Pd{C(H)PPh3C(O)CH2Cl}(μ-Cl)(OAc)]2, which experienced bridge cleavage reactions with triphenylphosphine (PPh3) and pyridine (Py), and to prepare the new orthometallated complexes [Pd{(C,C)C6H4PPh2C(H)C(O)CH2Cl}L]Cl, [L = PPh3 (1) and Py (2)]. The complexes were identified and characterized using various techniques. X-ray crystallography was used to determine the crystal structure of 1, which revealed the presence of an orthometallated C6H4-PPh2 unit. CT-DNA binding interaction of the synthesis compounds was tested by fluorescence spectroscopy, UV–Vis absorption spectroscopy, and the viscometric titration method. The analysis of the obtained data indicated that the Pd complexes could bind to DNA via groove binding by the partial intercalation mode. The emission titration of bovine serum albumin (BSA) with two Pd complexes showed a static process for the fluorescence quenching mechanism of BSA. In addition, the results of competitive binding by Eosin-Y, Ibuprofen and Digoxin site markers revealed that the complexes were bound to the site I of BSA. The donor (BSA) - acceptor (Pd complexes) distance was calculated using fluorescence resonance energy transfer (FRET). Notably, molecular docking studies were used for the determination of DNA and BSA-Pd (II) complexes binding. Finally, the two complexes exhibited significant in vitro cytotoxicity against human leukemic T cell (Jurkat) and chronic myelogenous leukemia (K562) cancer cell lines using MTT([3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide] colorimetric. In cell cycle analysis conducted on Jurkat and K562 cells treated with ligand and Pd complexes, a decrease in DNA cell content and shift in the main population of cells toward the subG1 phase were observed.