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Laccase-Assisted Biocatalytic Removal of Lignin from Lignocellulosic Biomass
Published in Pankaj Bhatt, Industrial Applications of Microbial Enzymes, 2023
Sadia Noreen, Sara Rehman, Memoona Asif, Muhammad Bilal, Hafiz M. N. Iqbal
Nonphenolic (like β-O-4 linked) oxidation by the laccase HBT opens aromatic ring (oxidation of π electron), oxidizes Cα and cleaves the Cα-Cß and β-ether bonds for producing the carboxylic acids and aromatic carbonyl compounds. The beta-aryl radical (cation) or the Cα (benzylic) radical intermediates generates oxidation reactions of the substrate through an electron transfer mechanism. Beta-ether cleavage of β-O-4 lignin substructure results from the reaction with Cα-peroxy intermediate radical (formed by benzylic radical). If the reaction involves cleavage of the aromatic ring, aryl cation radicals are formed from the degraded products. The typical products of lignin degradation are 4-ethyl-2,6-dimethoxybenzaldehyde, 2,6-dimethoxy-4-((E)-prop-1-enyl) benzaldehyde, and 2, 6-dimethoxy-4-methylbenzaldehyde. Lignin molecular weight and the phenolic content influence pathways catalyzed by laccases (Christopher et al., 2014).
Functionalization of Graphite and Graphene
Published in Titash Mondal, Anil K. Bhowmick, Graphene-Rubber Nanocomposites, 2023
Akash Ghosh, Simran Sharma, Anil K. Bhowmick, Titash Mondal
Diazonium chemistry has a significant contribution in the covalent functionalization of material. It emphasizes the carbon-carbon bond formation using diazonium salt for the tuning of graphitic-like materials—the functionalization reaction is believed to be governed by the free radical mechanism. The generic functionalization of graphene via the diazonium chemistry is shown in Figure 4.4. Liu et al. reported that aniline was functionalized on graphene nanosheet using diazonium coupling, further reduced by hydrazine. The functional attachment was confirmed by X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared (FTIR) Spectroscopy, and Raman Spectroscopy. The diazonium salt releases a molecule of nitrogen gas and produces a highly reactive aryl radical using any thermal, photochemical, or electrochemical stimuli. As the radical gets covalently attached with the graphitic material, the hybridization of graphitic carbon changes from sp2 to sp3. Consequently, the aromatic system will get disrupted, and a change is observed in the electronic behavior (Liu et al. 2014).
Role of Macrocyclic Receptors in Surface Self-assembly
Published in Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney, Macrocyclic Receptors for Environmental and Biosensing Applications, 2022
Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney
The photocleavage ability was attributed to the cucurbit[8]uril induced inhibition of intramolecular backward electron transfer in aromatic donor-viologen acceptor compounds that increased the lifetime of the charge-separated excited state. The *Aryl, HO•, and 1O2 were found to be responsible for the photo-cleavage of DNA. The light exposure caused an electron transfer from the excited state of the aromatic ring-like anthracene, pyrene or benzene to the viologen fragment to produce a charge-separated *Aryl-CH2-EV+• species as the excited state (Sun et al. 2010). The EV+• reduced the oxygen dissolved in the aqueous solution to the reactive singlet oxygen that oxidizes the DNA with *Aryl radical species. The system demonstrated its utility in the development of a system to cleave DNA using light through the exploitation of host-guest macrocyclic chemistry. However, the EV+• species lifetime is very short due to the backward intermolecular electron transfer. The cucurbit[8]uril inhibits this intermolecular electron transfer and thereby increases the lifetime of EV+•, which in turn improves its DNA photo-cleavage efficiency.
Evaluation of catalytic deoxygenation of soluble species from a coal using mass spectrometers
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Chi Zhang, Guo-Sheng Li, Xing Fan, Jing Jiang, Feng-Yun Ma, Yun-Peng Zhao, Xian-Yong Wei, Wen-Long Mo, Wei Zhao
As shown in Figure 2, the relative abundance of phenols obviously increases after the catalytic process. FTIR spectra in Figure 1 also indicate the enrichment of phenols. Phenols were partially derived from alcoholysis reactions or the cleavage of aralkyl ether bridge bonds (Wang et al. 2018a). Although Car-O bonds are broken easier compared with Calk-O under pyrolysis (Siskin and Aczel 1983), the break of C-O bonds via catalysis is different from those resulting from the pyrolysis (Yang et al. 2018). In coals, aromatic rings are linked by Car-Calk, Car-O, Car-N and/or Car-S bonds to compose macromolecules (Mathews and Chaffee 2012). The cleavage of Car-Calk bond is difficult because of the extreme stable aryl radical. Hydrogen transfer from H• (or from H+) is crucial for the Car-Calk bond cleavage because the addition of H• or H+ to the ipso-position of an aryl group affords a stable aromatic molecule rather than a labile aryl radical (Ni et al. 2003). Calk-O bond is more likely to be broken under the attack of H+ owing to the high dissociation energy of Car-O, inducing the generation of phenols.
Carob extract attenuates brain and lung injury in rats exposed to waterpipe smoke
Published in Egyptian Journal of Basic and Applied Sciences, 2018
Mona Abdel-Rahman, Amira A. Bauomy, Fatma Elzahraa H. Salem, Mona Ahmed Khalifa
Previous studies revealed that amiodarone is metabolized to an aryl radical that may give rise to other reactive oxygen species (ROS) [61,62] which cause endothelial injury leading to oedema, thrombosis and inflammation contributing to morbidity and mortality in acute lung injury [63]. The activation of macrophages and release of inflammatory and cytotoxic mediators drive amiodarone-induced lung fibrosis [64]. In vitro studies have shown that alveolar leucocytes and macrophages from cigarette smokers spontaneously increase the release of oxidants amounts such as O2− and hydrogen peroxide (H2O2) compared with non-smokers [65]. Neutrophils sequestered in the pulmonary circulation following cigarette smoke inhalation in the rabbit [66]. Also, in hamsters; the cigarette smoke inhalation activates neutrophils, increasing their adhesion to the endothelium of both arterioles and venules which is mediated by superoxide anion [67]. Thus, by several mechanisms involving oxidants, cigarette smoke causes neutrophil sequestration in the pulmonary microcirculation [68].
Expedient synthesis of 2-alkylthio-N6-aryladenosines from guanosine
Published in Journal of Sulfur Chemistry, 2018
Miao Tian, Ning Chen, Fangming Xu, Xiuxiu Li, Shunlai Li, Hongguang Du
In order to afford 2-alkylthio-N6-arylpurine riboside 5 (Scheme 2), two possible ways were designed: C6-amination first (route 1) or C2-arylthio-substitution first (route 2). Both approaches were examined, but only the latter one produced the target molecule. Take 2-ethylthio-N6-phenylamino-purine acetyl nucleoside 5′a as an example; in route 1, amination of 3a from aniline gave corresponding 6-arylaminopurine riboside 4a in 44% yield, but only trace yields of the target 5′a was detected from thin-layer chromatography (TLC) in the followed diazotization-alkylthionation process with iso-amylnitrite and diethyl disulfide [17]. The result demonstrates that electron-donating group (alkylamino) on purine motif makes the purine too electron-rich to stabilize the followed aryl radical [19], thus inhibiting the further radical alkylthio coupling. We thus switched the sequences of the reactions. First, the diazotization-alkylthionation approach of 3 was carried out with 65% yield of isolated 4′a, which further demonstrated that electron-withdrawing group C6-position facilitated the radical coupling. To our gratification, the subsequent amination of 4′a with aniline in the presence of triethylamine afforded the substitution product 5′a in 81% yield.