Synthesis of cubic mesoporous silica and carbon using fly ash

A supernatant solution of silicate species extracted from coal fly ash in a power plant by alkali fusion was used under acidic conditions to prepare a mesoporous silica, SBA-16. SBA-16 was used as a template for the synthesis of a mesoporous carbon using sucrose as a carbon source. These mesoporous silica and carbon materials were characterized by XRD, N₂ adsorption-desorption, SEM, and TEM. Textural properties of the silica and carbon samples prepared using fly ash were found to be comparable to those prepared by pure chemicals, successfully demonstrating the feasibility of recycling fly ash for the synthesis of high quality porous materials.     

The Remarkable Effect of Halogen Substitution on the Membrane Transport of Fluorescent Molecules in Living Cells

Small‐molecule‐based fluorescent probes have become important tools in biology for sensing and imaging applications. However, the biological applications of many of the fluorescent molecules are hampered by low cellular uptake and high toxicity. In this paper, we show for the first time that the introduction of halogen atoms enhances the cellular uptake of fluorescent molecules and the nature of halogen atoms plays a crucial role in the plasma membrane transport in mammalian cells. The remarkably higher uptake of iodinated compounds compared to that of their chloro or bromo analogues suggests that the strong halogen bonding ability of iodine atoms may play an important role in the membrane transport. This study provides a novel strategy for the transport of fluorescent molecules across the plasma membrane in living cells.     

Antioxidant and Prooxidant Nanozymes: From Cellular Redox Regulation to Next-Generation Therapeutics

Nanozymes, nanomaterials with enzyme-mimicking activity, have attracted tremendous interest in recent years owing to their ability to replace natural enzymes in various biomedical applications, such as biosensing, therapeutics, drug delivery, and bioimaging. In particular, the nanozymes capable of regulating the cellular redox status by mimicking the antioxidant enzymes in mammalian cells are of great therapeutic significance in oxidative-stress-mediated disorders. As the distinction of physiological oxidative stress (oxidative eustress) and pathological oxidative stress (oxidative distress) occurs at a fine borderline, it is a great challenge to design nanozymes that can differentially sense the two extremes in cells, tissues and organs and mediate appropriate redox chemical reactions. In this Review, we summarize the advances in the development of redox-active nanozymes and their biomedical applications. We primarily highlight the therapeutic significance of the antioxidant and prooxidant nanozymes in various disease model systems, such as cancer, neurodegeneration, and cardiovascular diseases. The future perspectives of this emerging area of research and the challenges associated with the biomedical applications of nanozymes are described.     

Kinetics and mechanism of oxidation of N,α-diphenylnitrones by 4-(dimethylamino)pyridinium chlorochromate (DMAPCC) in aqueous DMF medium

The kinetics of oxidation of aldonitrones by 4-(dimethylamino)pyridinium chlorochromate (DMAPCC) has been studied in aqueous N,N-dimethylformamide in the presence of perchloric acid. The reaction follows first-order kinetics with respect to each of DMAPCC and nitrone. The order with respect to [H⁺] was found to be close to zero. The rate of oxidation was unaltered by the variation of [NaClO₄] but addition of MnSO₄ decreased the rate. The reaction rate was found to decrease with a decrease in dielectric constant of the medium. Electron-releasing and electron-withdrawing groups perturb the reaction rate with a good Hammett correlation. The oxidation products were found to be benzaldehyde and nitrosobenzene. The reaction was carried out at four different temperatures and the activation parameters have been calculated. On the basis of the experimental findings, a suitable mechanism has been proposed.     

Heme peroxidase-catalyzed iodination of human angiotensins and the effect of iodination on angiotensin converting enzyme activity

The heme peroxidase-catalyzed iodination of human angiotensins I and II is described. It is observed that lactoperoxidase (LPO) can effectively and selectively iodinate the tyrosyl residues in angiotensin peptides. The thiourea/thiouracil-based peroxidase inhibitors effectively inhibit the iodination reactions, indicating that iodination is an enzymatic reaction and the mechanism of iodination is similar to that of peroxidase-catalyzed iodination of thyroglobulin. This study also shows that the monoiodo Ang I is a better substrate for the angiotensin converting enzyme than the native peptide.     

Vacancy‐Engineered Nanoceria: Enzyme Mimetic Hotspots for the Degradation of Nerve Agents

Organophosphorus‐based nerve agents, such as paraoxon, parathion, and malathion, inhibit acetylcholinesterase, which results in paralysis, respiratory failure, and death. Bacteria are known to use the enzyme phosphotriesterase (PTE) to break down these compounds. In this work, we designed vacancy‐engineered nanoceria (VE CeO₂ NPs) as PTE mimetic hotspots for the rapid degradation of nerve agents. We observed that the hydrolytic effect of the nanomaterial is due to the synergistic activity between both Ce³⁺ and Ce⁴⁺ ions located in the active site‐like hotspots. Furthermore, the catalysis by nanoceria overcomes the product inhibition generally observed for PTE and small molecule‐based PTE mimetics.     

Total synthesis and structural elucidation of azaspiracid-1. Synthesis-based analysis of originally proposed structures and indication of their non-identity to the natural product

The key building blocks (6, 7, and 8) for the intended construction of the originally proposed structures of azaspiracid-1, a potent marine-derived neurotoxin, were coupled and the products elaborated to the targeted compounds (1a,b) and their C-20 epimers (2 and 3). The assembly of the three intermediates was accomplished by a dithiane-based coupling reaction that united the C(1)-C(20) (7) and C(21)-C(27) (8) fragments, followed by a Stille-type coupling which allowed the incorporation of the C(28)-C(40) fragment (6) into the growing substrate. Neither of the final products (1a,b) matched the natural substance by TLC or (1)H NMR spectroscopic analysis, suggesting one or more errors in the originally proposed structure for this notorious biotoxin.