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Environmental Applications of Carbon Nanotubes
Published in Ann Rose Abraham, Soney C. George, A. K. Haghi, Carbon Nanotubes, 2023
I. S. Vidyalakshmi, Aparna Raj, S. Neelima, L. Vidya, Riju K. Thomas
Catalyst is important for accelerating chemical reaction by reducing activation energy. Catalysts can be homogeneous or heterogeneous. An optimal catalyst shows superior performance in mainly four areas: selectivity, activity, durability, and recoverability.63 The activity of a catalyst expresses the number of molecules converted to product molecules by catalyst per unit time. Turn over frequency (TOF) is used to measure the activity of catalyst. Homogeneous catalysts show high TOF of 0.3 s−1 or higher, while heterogeneous catalyst in the range of 0.03 s−1 or even lower. The lifetime of a catalyst is a measure of a number of cycles it can undergo without replacement. The turnover number (TON) is the number of products that can be formed by a given amount of catalyst. The recoverability of catalytic active substance is important, in the commercial point of view. It should be able to separate from the reaction mixture and reuse after the termination of reaction. The selectivity, activity, durability, and recover-ability are mainly influenced by catalyst size, shape, and surface composition. When the catalyst size comes in nano range, the more active sites are accessible to the substrate. Graphene oxides can be dispersed in CNT and Pt nanocatalyst. The resulting GOCNT-Pt nano composites show greatly enhanced electrocatalysis and power density.64 This so prepared enzyme mimic exhibit catalytic performance comparable to protein peroxidase, with higher catalytic efficiency, environmental robustness, stability, and cost-effectiveness.
Organic Polymers, Oligomers, and Catalysis
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Oxidation reactions with core-functionalized dendrimer-supported organocatalysts were catalyzed in presence of O2 and peroxides. By using flavin as a core of a poly(benzylether) dendrimer, a mimic of flavoenzymes was created. In presence of O2, this catalyst could outperform riboflavin for N-benzyl-1,4-dihydronicotinamide oxidation [55]. Singlet oxygen could also be generated by engineering dendrimers with photosensitizing cores such as tetraalkoxybenzophenone derivatives [56]. This strategy could be improved further by using porphyrin photosensitizers for both the core and the branches of the dendrimer. The corresponding photocatalyst could be recycled three times for converting 1-methyl-1-cyclohexene into a mixture of three peroxides [57]. Peptide derivatives incorporated on dendrimers exhibits also interesting catalytic properties for bonds cleavage. In that sense, they are promising enzyme mimic platforms. Several esters could be hydrolyzed by using multifunctional dendrimers almost entirely composed of aspartate, histidine and serine derivatives [58, 59]. Histidine derivatives were found to play a critical role in such a catalysis system. For instance, when a dendrimer constituted of only histidine-serine was assembled from generation 1 to 4, the catalysis efficiently increased 140,000-fold compared to the 4-methylimidazole catalyst [60].
Organic and Inorganic Supramolecular Catalysts
Published in Jubaraj Bikash Baruah, Principles and Advances in Supramolecular Catalysis, 2019
Cyt P450 enzymes cause oxidation of different organic substrates; they have active prosthetic groups of iron porphyrin complexes. In these enzymes, the porphyrin holds a Fe(III) metal ion whose fifth coordination site is occupied by a cysteine residue (Cys 400) of the peptide chain. The iron sites are coordinatively unsaturated; the sixth coordination site in each case is vacant. Oxygen is activated at this vacant site, and the catalytic oxidation processes involve the tetravalent intermediate Fe(IV)═O radical cation. The radical cation binds the organic substrate. Two strategies are adopted to prepare the metal organic framework as a Cyt P450 enzyme mimic. Functionalised porphyrins such as 2.76a and 2.76b form different MOFs in the reaction with cobalt (II) and iron (II) complexes. These MOFs are biological mimics of CytP450 (Figure 2.77). They catalytically convert (E)-1,2-diphenylethene to 2,3-diphenyloxirane in the presence of oxygen. The rates are much slower than those of the natural enzymes; the constraints are on the necessity of diffusing a reactant into the interiors of the pores and the discharge of the product. In principle, in an MOF, the number of active sites increases due to the surface of the voids as catalytic sites and multiple metal ions, but the synergic constraints of diffusion reduce the extent of activation one would have anticipated.
Targeted co-delivery of methotrexate and chloroquine via a pH/enzyme-responsive biocompatible polymeric nanohydrogel for colorectal cancer treatment
Published in Journal of Biomaterials Science, Polymer Edition, 2023
Hamid Rashidzadeh, Ali Ramazani, Seyed Jamal Tabatabaei Rezaei, Hossein Danafar, Shayan Rahmani, Hassan Veisi, Mohsen Rajaeinejad, Zahra Jamalpoor, Zahra Hami
MTX was covalently attached to the PMMA surface through amide linkages. To assess the release profile of MTX from PMAA nanohydrogels proteinase K enzyme (mimic the lysosomal condition), was used to dissociate the amide bonds between MTX and PMAA according to a previously published study [11]. Moreover, the MTX release study was carried out at the pH values of acidic and normal physiological 5.5 and 7.4 irrespectively with and without the proteinase K enzyme. Briefly, PMAA-MTX (2 mg) along with a PBS solution containing proteinase K enzyme (1 mg/mL) was added to a dialysis bag (Mw 12 kDa) and immersed in 35 mL of PBS solution with different pH of 5.5 and 7.4 and shaken (100 rpm) at 37 °C. Finally, the amount of released MTX at different time intervals was determined at a wavelength of 304 nm using a spectrophotometer. In order to determine the CQ content similar procedure was performed except using the proteinase K enzyme.
Fabrication of peroxidase-mimic iron oxide/carbon nanocomposite for highly sensitive colorimetric detection
Published in Journal of Experimental Nanoscience, 2022
Xinhua Liu, Tian Gao, Hailong Liu, Yinchun Fang, Liping Wang
Enzymes with the characteristic of high specificity and highly catalytic efficiency are considered as green catalysts which are widely used in many fields[1,2]. However, the limitations of stringent using conditions, high cost and hard to storage restrict their applications[3,4]. In recent years, artificial enzymes have received more and more attentions which were used to mimic the catalytic properties of natural enzymes[5,6]. Among the artificial enzymes, nanozymes which are prepared by nanomaterials with enzyme-mimic activity has been one of the most promising substitutes of natural enzymes since the unexpected discovery of peroxidase-like activities of magnetic Fe3O4 nanoparticles[7]. In recent years, nanozyme has been a focus of research in the field of high-performance enzyme mimic catalysts due to its simpler structure than natural enzymes, stronger environmental tolerance, lower cost in preparation, preservation and use, and easier recovery[8,9]. Until now, four types of redox enzymes including peroxidase, oxidase, catalase, and superoxide dismutase have been reported to be mimicked by nanomaterials[10–13].
Assembly of polyoxometalate-templated metal-organic framework with effective peroxidase-like catalytic activity
Published in Journal of Coordination Chemistry, 2019
Fei Xie, Xiao Li, Yujing Li, Xusheng Jiang, Qi Rui, Jingquan Sha
Catalytic activities of HRP and most reported enzyme mimics are dependent on pH, temperature, and H2O2 dosage. Therefore, the effects of these factors on the catalytic activity of Cu10PW12 were also explored. As shown in Figure 5a and Supporting Information Figure S4a, the absorbance of solution decreases gradually with increasing pH values; above 35% relative activity could be maintained in the pH range from 3.5 to 7.0. So Cu10PW12 as enzyme mimic can extend its application around the physiological condition. The reaction temperature-dependent response curves are shown in Figure 5b and Supporting Information Figure S4b, and the highest catalytic activity could be observed at 40 °C from 25 to 60 °C; 40 °C was selected as the optimal reaction temperature for subsequent activity analysis, since it is closer to physiological temperature.