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491.
This work uses density functional calculations to design a new high-valent Fe(V)=O catalyst [Mo5O18Fe=O]3-, which is based on the Lindqvist polyoxometalate (Mo6O19(2-)). Because the parent species is stable to oxidative conditions, one may assume that the newly proposed iron-oxo species will be stable, too. The calculated M?ssbauer spectroscopic data may be helpful toward an eventual identification of the species. The calculations of C-H hydroxylation and C=C epoxidation of propene show that, if made, [Mo5O18Fe=O]3- should be a potent oxidant that will be subject to strong solvent effect. Moreover, the Lindqvist catalyst leads to an intriguing result; the reaction that starts along an epoxidation pathway with C=C activation ends with a C-H hydroxylation product ((4)6) due to rearrangement on the catalyst. The origins of this result are analyzed in terms of the structure of the catalyst and the electronic requirements for conversion of an epoxidation intermediate to a hydroxylation product. Thus, if made, the [Mo5O18Fe=O]3 will be a selective C-H hydroxylation reagent. 相似文献
492.
Quantum mechanics/molecular mechanics calculations were utilized to study the process of oxidation of a native substrate (ferulic acid) by the active species of horseradish peroxidase (Dunford, H. B. Heme Peroxidases; Wiley-VCH: New York, 1999), Compound I and Compound II, and the manner by which the enzyme returns to its resting state. The results match experimental findings and reveal additional novel features. The calculations demonstrate that both oxidation processes are initiated by a proton-coupled electron-transfer (PCET) step, in which the active species of the enzyme participate only as electron-transfer partners, while the entire proton-transfer event is being relayed from the substrate to and from the His42 residue by a water molecule (W402). The reason for the observed (Henriksen, A; Smith, A. T.; Gajhede, M. J. Biol. Chem. 1999, 274, 35005-35011) similar reactivities of Compound I and Compound II toward ferulic acid is that the reactive isomer of Compound II is the, hitherto unobserved, Por(*)(+)Fe(III)OH isomer that resembles Compound I. The PCET mechanism reveals that His42 and W402 are crucial moieties and they determine the function of the HRP enzyme and account for its ability to perform substrate oxidation (Poulos, T. L. Peroxidases and Cytochrome P450. In The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 4, pp 189). In view of the results, the possibility of manipulating substrate oxidation by magnetic fields is an intriguing possibility. 相似文献
493.
Deyu Wang Sule Erten Ela Shaik M. Zakeeruddin Peter Pechy Ivan Exnar Qing Wang Michael Grätzel 《Electrochemistry communications》2009,11(7):1350-1352
The poor electronic conductivity of LiFePO4 has been one of the major issues impeding it from achieving high power and energy density lithium-ion batteries. In this communication, a novel polymer-wiring concept was proposed to improve the conduction of the insulating electrode material. By using a polymer with tethered “swing” redox active molecules (S) attached on a polymer chain, as the standard redox potential of S matches closely the Fermi level of LiFePO4, electronic communication between the redox molecule and LiFePO4 is established. Upon charging, S is oxidized at the current collector to S+, which then delivers the charge (holes) to the LiFePO4 particles by intermolecular hopping assisted by a “swing” – type motion of the shuttle molecule. And Li+ is extracted. Upon discharging, the above process is just reversed. Preliminary studies with redox polymer consisting of poly (4-vinylpyridine) and phenoxazine moiety tethered with a C12 alkyl chain have shown promising result with carbon-free LiFePO4, where effective electron exchange between the shuttle molecule and LiFePO4 has been observed. In addition, as the redox polymer itself could act as binder, we anticipate that the polymer-wiring concept would provide a viable approach to conducting-additive and binder free electrode for high energy density batteries. 相似文献
494.
This paper, introduces the nearest weighted interval and point approximations of a fuzzy number, and then suggests weighted possibilistic moments about these points of fuzzy numbers. The possibilistic moments play an important role in fuzzy sets and systems, specifically in physics, mathematics and statistics. We provide the definition of the moments of fuzzy numbers as well as the definition of moments in probability theory; some of their applications are mentioned. 相似文献
495.
We consider a two-dimensional electron gas (2DEG) with the Rashba spin-orbit interaction (SOI) in the presence of a perpendicular magnetic field. We derive analytical expressions of the density of states (DOS) of a 2DEG with the Rashba SOI in the presence of a magnetic field by using the Green's function technique. The DOS allows us to obtain the analytical expressions of the magnetoconductivities for spin-up and spin-down electrons. The conductivities for spin-up and spin-down electrons oscillate with different frequencies and give rise to the beating patterns in the amplitude of the Shubnikov-de Haas (SdH) oscillations. We find a simple equation which determines the zero-field spin splitting energy if the magnetic field corresponding to any beat node is known from the experiment. Our analytical results reproduce well the experimentally observed non-periodic beating patterns, number of oscillations between two successive nodes and the measured zero-field spin splitting energy. 相似文献
496.
Shaik Inayath Basha Atta Ur Rehman Md. Abdul Aziz Jung-Hoon Kim 《Chemical record (New York, N.Y.)》2023,23(4):e202200293
3D concrete printing (3DCP) is an emerging additive manufacturing technology in the construction industry. Its challenges lie in the development of high-performance printable materials and printing processes. Recently developed carbon-based nanomaterials (CBNs) such as graphene, graphene oxide, graphene nanoplatelets, and carbon nanotubes, have various applications due to their exceptional mechanical, chemical, thermal, and electrical characteristics. CBNs also have found potential applications as a concrete ingredient as they enhance the microstructure and modify concrete properties at the molecular level. This paper focuses on state-of-the-art studies on CBNs, 3DCP technology, and CBNs in conventional and 3D printable cement-based composites including CBN dispersion techniques, concrete mixing methods, and fresh and hardened properties of concrete. Furthermore, the current limitations and future perspectives of 3DCP using CBNs to produce high-quality composite mixtures are discussed. 相似文献
497.
An efficient acid-catalyzed synthesis of 1,5-diaryl-3-(arylamino)-1H-pyrrol-2(5H)-ones is reported using novel N-sulfonic acid modified poly (styrene-diethylenetriamine) through three-component reaction between aldehyde, amine, and ethyl pyruvate in high yields and short times. This heterogeneous solid catalyst is produced by reacting amine-modified chloromethyl polystyrene with neat chlorosulfonic acid. The structure of the synthesized catalyst was examined with Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron micrograph (SEM), Brunauer–Emmett–Teller (BET), energy dispersive spectroscopy (EDS), and elemental analyses. The heterogeneous catalyst has many advantages, including an easy work-up procedure, a high product yield, and the capability to be easily regenerated and reused for at least five cycles without losing its activity. 相似文献
498.
Shaik Sultana Dr. Godugu Kumar Dr. Loka Subramanyam Sarma Prof. Dr. Vemula Venkatramu Prof. Dr. Nallagondu Chinna Gangi Reddy 《European journal of organic chemistry》2023,26(10):e202300032
For the first time, interstitial nitrogen-doped TiO2 nanotubes (INDTNTs) have been utilized as heterogeneous green catalysts for the synthesis of D-π-A-type Knoevenagel adducts ( 3 ) and β-enaminones ( 6 ). Notable advantages of the present method include its wide substrate scope, low catalyst loading, avoiding the use of hazardous bases and solvents, products do not require chromatographic purification, high yields, catalyst reusability, etc. The optimized catalyst, INDTNTs-4 has been characterized by XRD, HRTEM, and XPS techniques. The photophysical and electrochemical properties of D-π-A-type 3 and 6 have been evaluated. The study revealed that the colour tunability (cold white light to orange light) and the HOMO/LUMO levels depend mainly on the presence of various electron donating and withdrawing groups on the aromatic/heteroaromatic rings of 3 and 6 . The results indicate that the D-π-A-type 3 and 6 could be promising materials for the fabrication of optoelectronic devices. 相似文献
499.
Amin Al-Fakih Zakaria Mohamed Nor Shaik Inayath Basha M. Nasiruzzaman Shaikh Shamsad Ahmad Mohammed A. Al-Osta Md. Abdul Aziz 《Chemical record (New York, N.Y.)》2023,23(5):e202300039
The disposal of red mud (RM), a waste material generated by the aluminum industry, remains a global environmental concern because of its high alkalinity and smaller particle size, which have the potential to pollute air, soil, and water. Recently, efforts have been made to develop a strategy for reusing industrial byproducts, such as RM, and turning waste into value-added products. The use of RM as (i) a supplementary cementitious material for construction and building materials, such as cement, concrete, bricks, ceramics, and geopolymers, and (ii) a catalyst is discussed in this review. Furthermore, the physical, chemical, mineralogical, structural, and thermal properties of RM, as well as its environmental impact, are also discussed in this review. It is possible to conclude that using RM in catalysis, cement, and construction industries is the most efficient way to recycle this byproduct on a large scale. However, the low cementitious properties of RM can be attributed to a reduction in the fresh and mechanical properties of composites incorporating RM. On the other hand, RM can be used as an efficient active catalyst to synthesize organic molecules and reduce air pollution, which not only makes use of solid waste but also lowers the price of the catalyst. The review provides basic information on the characterization of RM and its suitability in various applications, paving the way for more advanced research on the sustainable disposal of RM waste. Future research perspectives on the utilization of RM are also addressed. 相似文献