Chemistry - An Asian Journal

The utilization of hydrogen bonding as an activation force has become a powerful tool in asymmetric organocatalysis. Significant advances have been made in the recent past in this emerging field. Due to space constraints, this Focus Review summarizes only the key aspects with an emphasis on catalysis based on chiral ureas and thioureas, diols, and phosphoric acids. The examples provided neatly demonstrate that chiral ureas and thioureas, diols, and phosphoric acids display effective and unique activation modes of catalysis for a broad spectrum of asymmetric organic transformations, including single‐step and multiple‐step cascade reactions. These functionalities, which have the ability to afford efficient H‐bond activation of electrophiles including CO, CN, aziridines, and epoxides, have established their status as “privileged” functional groups in the design of organocatalysts.

As a newly developed technique, photoelectrochemical (PEC) immunoassays have attracted great attention in recent years because of their low cost and desirable sensitivity. Because the detection signal originates from the photoelectric conversion of photoelectric materials, the appearance and application of quantum dots (QDs), which possess unique photophysical properties and regulated optoelectronic characteristics, has taken the development of PEC immunoassays to new heights. This review concisely introduces the general mechanism of QDs‐based photoelectric conversion for immunoassays and summarizes the current advances in QD applications in immunoassays. Given that signal strategies and photoactive materials are the key elements in PEC biosensor systems, we comprehensively highlight the state‐of‐the‐art signaling strategies and various applications of QDs in PEC immunoassays to introduce advances in QDs‐based PEC immunoassays. Finally, challenges and future developmental trends are briefly discussed

In the past few years, highly luminescent noble metal nanoclusters (e.g., Au and Ag NCs or Au/Ag NCs in short) have emerged as a class of promising optical probes for the construction of high‐performance optical sensors because of their ultrasmall size (<2 nm), strong luminescence, good photostability, excellent biocompatibility, and unique metal‐core@ligand‐shell structure. In this Focus Review, we briefly summarize the common syntheses for water‐soluble highly‐luminescent thiolate‐ and protein‐protected Au/Ag NCs and their interesting luminescence properties, highlight recent progress in their use as optical sensors with an emphasis on the mechanisms underlying their selectivity, and finally discuss approaches to improving their sensitivity. The scope of the works surveyed is confined to highly luminescent thiolate‐ and protein‐protected Au/Ag NCs.

The Mitsunobu reaction is a widely used and versatile method for the dehydrative oxidation–reduction condensation of an acid/pronucleophile usually with a primary or secondary alcohol that requires the combination of a reducing phosphine reagent together with an oxidizing azo reagent. The utility of this reaction stems from the fact that it is generally highly stereoselective and occurs with inversion of the stereochemical configuration of the alcohol starting material. Furthermore, as carboxylic acids, phenols, imides, sulfonamides, and other compounds can be used as the acid/pronucleophile, this reaction is useful for the preparation of a wide variety of functional groups. This Focus Review of the Mitsunobu reaction summarizes its origins, the current understanding of its mechanism, and recent improvements and applications.

The copper(I)‐catalyzed modern version of the Huisgen‐type azide–alkyne cycloaddition to give a 1,4‐disubstituted 1,2,3‐triazole unit is introduced as a powerful ligation method for glycoconjugation. Owing to its high chemoselectivity and tolerance of a variety of reaction conditions, this highly atom‐economic and efficient coupling reaction is especially useful for the effective construction of complex glycosylated structures such as clusters, dendrimers, polymers, peptides, and macrocycles. In all cases the triazole ring plays a key role by locking into position the various parts of these molecular architectures. The examples reported and briefly discussed in this short review highlight the use of this reaction in carbohydrate chemistry and pave the way to further developments and applications.

Layered double hydroxides (LDHs) are biocompatible materials which can be used as drug‐delivery nanovehicles. In order to define the optimum size of LDH nanoparticles for efficient cellular uptake and drug‐delivery pathway, we prepared different sized LDH nanoparticles with narrow size distribution by modulating the crystal growth rate, and labelled each LDH particle with a fluorophore using a silane coupling reaction. The cellular uptake rate of LDHs was found to be highly dependent on particle size (50>200≥100>350 nm), whose range of 50 to 200 nm was selectively internalized into cells through clathrin‐mediated endocytosis with enhanced permeability and retention. Our study clearly shows that not only the particle size plays an important role in the endocytic pathway and processing, but also the size control of LDH nanoparticles results in their targeted uptake to site‐specific clathrin‐mediated endocytosis. This result provides a new perspective for the design of LDH nanoparticles with maximum ability towards targeted drug delivery.

Effective detection of organic/inorganic pollutants, such as antibiotics, nitro‐compounds, excessive Fe³⁺ and MnO₄⁻, is crucial for human health and environmental protection. Here, a new terbium(III)–organic framework, namely [Tb(TATAB)(H₂O)]⋅2H₂O (Tb‐MOF, H₃TATAB=4,4′,4′′‐s‐triazine‐1,3,5‐triyltri‐m‐aminobenzoic acid), was assembled and characterized. The Tb‐MOF exhibits a water‐stable 3D bnn framework. Due to the existence of competitive absorption, Tb‐MOF has a high selectivity for detecting Fe³⁺, MnO₄⁻, 4‐nirophenol and nitroimidazole (ronidazole, metronidazole, dimetridazole, ornidazole) in aqueous through luminescent quenching. The results suggest that Tb‐MOF is a simple and reliable reagent with multiple sensor responses in practical applications. To the best of our knowledge, this work represents the first Tb^III‐based MOF as an efficient fluorescent sensor for detecting metal ions, inorganic anions, nitro‐compounds, and antibiotics simultaneously.

Carbon quantum dots (CQDs) were synthesized by heating various carbon sources in HNO₃ solution at reflux, and the effects of HNO₃ concentration on the size of the CQDs were investigated. Furthermore, the oxygen‐containing surface groups of as‐prepared CQDs were selectively reduced by NaBH₄, leading to new surface states. The experimental results show that the sizes of CQDs can be tuned by HNO₃ concentration and then influence their photoluminescent behaviors; the photoluminescent properties are related to both the size and surface state of the CQDs, but the photocatalytic activities are determined by surface states alone. The different oxygen‐containing groups on the surface of the CQDs can induce different degrees of the band bending upward, which determine the separation and combination of the electron–hole pairs. The high upward band bending, which is induced by CO and COOH groups, facilitates separation of the electron–hole pairs and then enhances high photocatalytic activity. In contrast, the low upward band bending induced by COH groups hardly prevents the electron–hole pairs from surface recombination and then exhibits strong photoluminescence. Therefore, both the photocatalytic activities and optical properties of CQDs can be tuned by their surface states.

The photoelectrochemical production and degradation properties of hydrogen peroxide (H₂O₂) were investigated on a WO₃/BiVO₄ photoanode in an aqueous electrolyte of hydrogen carbonate (HCO₃⁻). High concentrations of HCO₃⁻ species rather than CO₃²⁻ species inhibited the oxidative degradation of H₂O₂ on the WO₃/BiVO₄ photoanode, resulting in effective oxidative H₂O₂ generation and accumulation from water (H₂O). Moreover, the Au cathode facilitated two‐electron reduction of oxygen (O₂), resulting in reductive H₂O₂ production with high current efficiency. Combining the WO₃/BiVO₄ photoanode with a HCO₃⁻ electrolyte and an Au cathode also produced a clean and promising design for a photoelectrode system specializing in H₂O₂ production (η_anode(H₂O₂)≈50 %, η_cathode(H₂O₂)≈90 %) even without applied voltage between the photoanode and cathode under simulated solar light through a two‐photon process; this achieved effective H₂O₂ production when using an Au‐supported porous BiVO₄ photocatalyst sheet.