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Fundamentals of Atomically Dispersed Metallic Materials
Published in Wei Yan, Xifei Li, Shuhui Sun, Xueliang Sun, Jiujun Zhang, Atomically Dispersed Metallic Materials for Electrochemical Energy Technologies, 2023
Rongbo Sun, Xiao Han, Xun Hong
Deep understanding of the structure-performance relationship between metal monatomic coordination environment and catalytic performance would be conducive to the development and application of advanced ADMM [147]. The coordination environments of single-site metal atoms can significantly alter the adsorption affinity of the metal centers and, in turn, the catalytic performances. Furthermore, heteroatoms adjacent to metal atom center particularly affect the catalytic properties. In general, coordination engineering can be achieved by precisely adjusting individual metal active centers and coordination atoms. It should be pointed out that precise control of the coordination environment of a single metal active center in the M–Nx–C (M = transition metal, N = non-metal) catalyst can effectively improve the catalytic activity and selectivity, but it is extremely challenging [148].
Molecular Design of Organic Conductors
Published in Jean-Pierre Farges, Organic Conductors, 2022
Vladimir Khodorkovsky, James Y. Becker
Cyclic voltammograms of unsubstituted arenes usually exhibit irreversible oxidation waves. Often, the introduction of heteroatoms enhances both donor ability and stability (due to better charge delocalization) of the corresponding cation radicals. The electrochemical behavior of aminosubstituted derivatives 15 [41], 16 [42], and 17 [43] can serve as representative examples. Thus compound 15 oxidizes extremely easily at a potential as low as —0.2 V (two-electron process), whereas compound 16 oxidizes at higher potentials, but in two one-electron steps: E1 = 0.29 V, E2 = 0.37 V (data for 15 and 16 in MeCN, recalculated for Ag/AgCl). Hexaazaoctadecahydrocoronene 17, one of the strongest known donors, exhibits four reversible one-electron redox couples at -0.44, 0.06, 0.52, 0.92 V (versus SCE, in MeCN) [43].
Synthesis of Bioactive Heterocyclic Compounds
Published in Ahindra Nag, Greener Synthesis of Organic Compounds, Drugs and Natural Products, 2022
Heteroatoms in cyclic organic compounds are an important fragment of a number of biologically active compounds. Recent estimates indicate that more than 85% of all biologically active chemical entities contain a heterocycle ring [1]. For instance, penicillin (1), a currently used antibiotic, contains β-lactam as an important bioactive part of this compound. Taxol (2), the most widely used anticancer pharmaceutical, contains oxetane ring in its structure [2]. This ring is considered a required pharmacophore for the expression of its anticancer activity. Similarly, other anticancer compounds, zanthosimuline (3), huajiasimuline (4) and pyrazolo [4,3-c]quinoline-3-one (5) contain heterocyclic rings incorporated into their structures [3–5]. Heterocycles play an important role in enhancing the physical and chemical properties of biologically active compounds such as solubility, lipophilicity, polarity, hydrogen bonding, etc. These properties make them excellent candidates for the drug-discovery process.
Designed new mesogens via Vilsmeier–Haack reagent: synthesis and phase transition study
Published in Phase Transitions, 2022
Nisreen H. Karam, Alaa N. Kurdi, Ammar H. Al-Dujaili
The enantiotropic smectic C (SmC) and smectic A (SmA) phases, which accompanied the nematic phase, were detected when the length of the alkoxy chain increased from [IX]a,b to [XI]a,b. The nematic phase begins with [V]a,b and continues until both series’ last member. The persistence of the N phase implies that the net effect given by the end-to-end cohesive forces in this series is similar to that of all other molecular forces. It has been reported that the inclusion of heteroatoms can significantly change the polarity, polarizability and occasionally the geometric shape of the molecule, thus influencing the type of mesophase, phase transition temperatures, dielectric and other properties of the mesogens [33]. This could be explained why the liquid crystalline character was absent in [XII-XV]a, but was present in the compounds [XIII-XV]b containing the heterocyclic unit in the main-chain structure of the later compounds. Furthermore, the linking group is one of the determining factors that influence whether the target compound will exhibit a mesogenic phase instead of a nonmesogenic. Biphenyl linking group generally favors rigidity, which ultimately generates the mesogenic phase [34]. This explained the occurrence of mesogenic phases in [XIII-XV]b rather than in [XII-XV]a.
Sorption of pharmaceuticals and personal care products (PPCPs) from water and wastewater by carbonaceous materials: A review
Published in Critical Reviews in Environmental Science and Technology, 2022
Ming Zhang, Jialing Shen, Yuchi Zhong, Tao Ding, Pavani Dulanja Dissanayake, Yi Yang, Yiu Fai Tsang, Yong Sik Ok
In addition to the morphological structure of carbonaceous adsorbents, the surface chemical functional groups are also a key factor affecting the sorption of PPCPs. The type and number of surface functional groups of carbonaceous materials are related to the nature of the raw materials, the modification or activation methods, and the carbonization temperature (Ahmed, Zhou, Ngo, Guo, & Chen, 2016). Heteroatoms (such as hydrogen, oxygen, nitrogen and halogen atoms) on the periphery of a carbon material control the surface chemistry. Among the organic functional groups composed of these heteroatoms, oxygen-containing groups are the most common and important species (Liu et al., 2008), which can be introduced by mechanical (Boudou et al., 2003), chemical (Pittman et al., 1997) and electrochemical pathways (Hu & Wang, 2004) and have different acidity, alkalinity and neutrality (Liu et al., 2008). The acid-modified biochar has more acidic functional groups, such as carboxyl groups, hydroxyl groups, and ketones, while amination can introduce basic groups such as C-H, C = N groups, cyclic amides, amino, and pyrrole-like structure (Li et al., 2014;Masahiko et al., 2000).
Rhodium catalysis in the synthesis of fused five-membered N-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Neha Ahlawat, Yamini Verma, Pranshu Bhardwaj, Pooja Grewal, Nirmala Kumari Jangid
Recent research has led to the development of mild, efficient and selective catalytic systems based on Rh(I) complexes. Rhodium catalysis plays a key role in the development of efficient methods for the selective functionalization of C-H bonds. Therefore, it is not surprising that rhodium-based catalysts are capable of promoting C-N bond formation via C-H bond activation [16j]. In a survey of examples of heteroatom-directed Rh catalysis, two mechanistically distinct reaction pathways are revealed. In one case, the heteroatom acts as a chelator to bind the Rh catalyst, facilitating reactivity at a proximal site. In this case, the formation of a five-membered metallacycle provides a favorable driving force in inducing reactivity at the desired location. In the other case, the heteroatom initially coordinates the Rh catalyst and then acts to stabilize the formation of a metal-carbon bond at a proximal site [16k]. This review has the demonstration of rhodium-catalyzed formation of fused five-membered nitrogen bearing heterocycles.