Accounts of Chemical Research最新文献

Next-generation cost-effective anion exchange membrane (AEM) fuel cells (AEMFCs) and AEM water electrolyzers (AEMWEs) have emerged as promising alternatives to costly proton exchange membrane (PEM) fuel cells and water electrolyzers due to the possibility of utilizing platinum-group-metal (PGM)-free catalysts and phasing out unsustainable perfluorosulfonic acid polymers. Anion exchange polyelectrolytes (AEPs), which can be utilized as AEMs or ionomers, are pivotal materials in AEM devices. Despite extensive exploration in the past decade, the application of AEPs has been significantly impeded by their poor ionic conductivity, insufficient alkaline stability, and unfavorable mechanical properties. Therefore, developing highly conductive and robust AEPs is critical to the success of AEMFCs and AEMWEs. (i) Our group has developed a series of highly conductive and durable poly(aryl-co-aryl piperidinium) (c-PAP) AEPs to address the aforementioned issues. c-PAP AEMs and ionomers enable outstanding OH^- conductivity (>160 mS cm^-1 at 80 °C), alkaline stability (1 M NaOH at 80 °C > 2000 h), dimensional stability, and mechanical properties (tensile strength > 80 MPa), giving them all the properties required for applications in AEM devices. (ii) Based on c-PAP AEMs and ionomers, we have developed high-performance AEMFCs and AEMWEs, as well as provided insights into the ionomer research and the design of membrane electrode assemblies. Typically, c-PAP AEMFCs reached the topmost peak power densities (PPDs) of 2.7 W cm^-2 at 80 °C in H₂-O₂ along with 1000 h cell durability. Moreover, cathode-dried AEMWEs achieved a record-breaking current density of 17 A cm^-2 in 1 M KOH, and the cell can be run stably at a 1.5 A cm^-2 current density for over 2000 h. The remarkable performances achieved by this new class of c-PAP AEPs identify them as the most promising candidates for practical applications in AEMFCs and AEMWEs. In this account, we will elaborate on our strategies and methodologies associated with c-PAP AEPs and AEM devices, covering the screening and identification of highly durable cation head groups and molecular-engineering approaches to design c-PAP AEMs and ionomers. Moreover, we underscore our strategy in terms of developing highly efficient and durable AEMFCs and AEMWEs. We also elucidate different approaches for further enhancing the ion conductivity and mechanical stability of c-PAP AEMs, including the design of backbones and side chains, cross-linking, and reinforcement. We firmly believe that our series of studies has made substantial contributions to the fields of AEM, ionomers, AEMFCs, and AEMWEs, which have advanced AEM technology to be on par with PEM technology, opening a new avenue for commercialization of AEMFCs and AEMWEs.

ConspectusBoronic acids (BAs) are one of the most important classes of reagents in modern synthesis, enabling a wide range of powerful transformations that facilitate the formation of key carbon-carbon and carbon-heteroatom bonds. While their success as reagents is well-known, their remarkable potential as building blocks for creating functional molecules is often overlooked.At the core of BAs' uniqueness is their ability to form reversible covalent bonds, thanks to the interconversion of the boron atom between its uncharged trigonal planar structure and an anionic sp³-hybridized form. This coordination chemistry has paved the way for exciting developments in fields such as medicinal chemistry and chemical biology. In recent years, BAs have been used to create a wide variety of materials, including small-molecule drugs, bioconjugates, drug delivery vehicles, polymeric nanomaterials, sensors, and even photosensitizers. What makes this strategy particularly unique is the structural diversity that can be achieved by functionalizing the BA coordination sphere, along with the possibility of incorporating stimuli-responsive mechanisms. This reactivity is further enhanced by the well-known oxidation of BAs in the presence of reactive oxygen species (ROS).A detailed understanding of the mechanisms governing the dynamic nature of BAs enables the engineering of sophisticated materials that can respond to specific molecular stimuli, such as changes in pH, carbohydrate or glutathione concentrations, and hydrogen peroxide. These stimuli are often key indicators of diseases such as cancer, inflammation, and neurodegeneration, placing BAs at the forefront of tools for designing materials that can potentially influence the mechanisms behind these diseases.In this Account, we draw on our group's expertise to explore the exciting potential of BAs in the design of functional materials. The focus is on the response of different boron complexes to biologically relevant stimuli. We describe the preparation of boronated esters (BEs), BA-salicylhydroxamic acid (BA-SHA) complexes, iminoboronates, diazaborines, and boronated thiazolidines and discuss how these chemotypes respond to disease-relevant triggers. Given the growing importance of using external stimuli to control the efficacy of modern drugs, we also explore how some of these compounds respond to specific chemicals. While this Account is not meant to be an exhaustive survey of every example of BA stimulus-responsiveness, we aim to integrate existing chemotypes and their chemical triggers. Our goal is to provide an overview of the mechanisms enabled by BAs for designing functional materials that could one day lead to innovative therapeutic options for human diseases.

ConspectusSelective oxidation with molecular oxygen is one of the most appealing approaches to functionalization of organic molecules and, yet at the same time, one of the most challenging reactions facing organic synthesis due to poor selectivity control. Molecular oxygen is a green and inexpensive oxidant, producing water as the only byproduct in oxidation. Not surprisingly, it has been used in the manufacturing of many commodity chemicals in the industry. It is also nature's choice of oxidant and drives a variety of oxidation reactions critical to life and various other biologic processes. While the past decades have witnessed great progress in understanding, both structurally and mechanistically, how nature exploits metalloenzymes, i.e., monooxygenases and dioxygenases, to tackle some of the most challenging oxidation reactions, e.g., methane oxidation to methanol, there are only a small number of well-defined, man-made metal complexes that have been reported to enable selective oxidation with molecular oxygen of compounds more relevant to fine chemical and pharmaceutical synthesis.In the past 10 years or so, our laboratories have developed several transition metal complexes and shown that they are capable of catalyzing selective oxidation under 1 atm of O₂. Thus, we have shown that an Fe(II)-bisimidazolidinyl-pyridine complex catalyzes selective oxygenation of C-H bonds in ethers with concomitant release of hydrogen gas instead of water, and when the iron center is replaced with Fe(III), selective oxidative cleavage of C═C bonds of olefins becomes feasible. To address the low activity of the iron complex in oxidizing less active olefins, we have developed a Mn(II)-bipyridine complex, which catalyzes oxidative cleavage of C═C bonds in aliphatic olefins, C-C bonds in diols, and carboxyl units in carboxylic acids under visible light irradiation. Light is necessary in the oxidation to cleave an off-cycle, inactive manganese dimer into a catalytically active Mn═O oxo species. Furthermore, we have found that a binuclear salicylate-bridged Cu(II) complex enables the C-H oxidation of tetrahydroisoquinolines as well as C═C bond cleavage, and when a catalytic vitamin B1 analogue is brought in, oxygenation of tetrahydroisoquinolines to lactams takes place via carbene catalysis. Still further, we have found that a readily accessible binuclear Rh(II)-terpyridine complex catalyzes the oxidation of alcohols, and being water-soluble, the catalyst can be easily separated and reused multiple times. In addition, we recently unearthed a simple protocol that allows waste polystyrene to be depolymerized to isolable, valuable chemicals. A cheap Brønsted acid acts as the catalyst, activating molecular oxygen to a singlet state through complexation with the polymer under light irradiation, thereby depolymerizing the polymer.

This study aimed to review epidemiology of diabetic foot (DF) amputation and provide a pooled estimation of DF amputation rate in the region. A comprehensive search was performed in Web of Science, PubMed, Scopus and EMBASE databases using appropriate search term. Obtained records were entered endnote software and after removing duplicats were screened by title, abstract and full text. Data was extracted from the remained documents. Random effect meta-analysis was used to pool the estimated prevalence rate due to sever heterogeneity between studies. Finally 17 articles in diabetes, 20 in patients with DFU (diabetic foot ulcer) and two in both remained after screening and included in meta-analysis. Overall pooled amputation rate in diabetes was 2% (95% CI: 1%-3%) which was not significantly different between countries. The pooled prevalence of amputation rate in DFU patients was 33% (24%-43%) and the pooled prevalence in Saudi Arabia was significantly higher than in other countries. The estimated rate of foot amputation in diabetes patients and those with DFUs in the Middle East region is approximately high, which may indicate low quality of preventive foot care, low socioeconomics and low patients awareness or education in countries with high amputation rate.