Carbohydrate-based nanostructured catalysts: applications in organic transformations

The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well.     

γ-Valerolactone (GVL) as a green and efficient dipolar aprotic reaction medium

The great challenge for modern research is to define the most efficient tools to make more sustainable the industrial production and manufacturing. Among the different aspects that require attention the replacement of toxic and/or non-renewable solvents it is certainly playing a crucial role. Dealing with widely used dipolar aprotic solvents, among the different alternatives proposed in the literature γ-valerolactone (GVL) plays a pivotal role covering different application area. In this contribution, the benefits derived from the use of GVL as a circular, safe, biomass-derived reaction medium are highlighted covering most recent publications (2021). The presentation has been divided into three major sections: (i) biomass valorization, (ii) materials synthesis, manufacturing and recycle and (iii) new synthetic methodologies.     

Fast Cysteine Bioconjugation Chemistry

Cysteine bioconjugation serves as a powerful tool in biological research and has been widely used for chemical modification of proteins, constructing antibody-drug conjugates, and enabling cell imaging studies. Cysteine conjugation reactions with fast kinetics and exquisite selectivity have been under heavy pursuit as they would allow clean protein modification with just stoichiometric amounts of reagents, which minimizes side reactions, simplifies purification and broadens functional group tolerance. In this concept, we summarize the recent advances in fast cysteine bioconjugation, and discuss the mechanism and chemical principles that underlie the high efficiencies of the newly developed cysteine reactive reagents.     

Electro-assisted Molecular Assembly Giving Atomic-Scale Catalytic Active-Site Detection

The artificially accurate design of nonmetal electrocatalysts’ active site has been a huge challenge because no pure active species with the specific structure could be strictly controlled by traditional synthetic methods. Species with a multiconfiguration in the catalyst hinder identification of the active site and the subsequent comprehension of the reaction mechanism. We have developed a novel electro-assisted molecular assembly strategy to obtain a pure pentagon ring on perfect graphene avoiding other reconstructed structures. More importantly, the active atom was confirmed by the subtle passivation process as the topmost carbon atom. Recognition of the carbon-defect electrocatalysis reaction mechanism was first downsized to the single-atom scale from the experimental perspective. It is expected that this innovative electro-assisted molecular assembly strategy could be extensively applied in the active structure-controlled synthesis of nonmetal electrocatalysts and verification of the exact active atom.     

Self-oscillating gels based on novel catalyst for the Belousov–Zhabotinsky reaction

We report on the synthesis of new Ru(bpy)₂(phen) catalyst for the oscillatory Belousov–Zhabotinsky chemical reaction and on the preparation of novel Ru(bpy)₂(phen)-based self-oscillating gels. The synthesized gels exhibit high-amplitude autonomous mechanical oscillations when the Belousov–Zhabotinsky reaction proceeds inside these gels     

室温铁磁性Sr3YCo4O10.5+δ多晶有序化的烧结工艺及电磁性能

采用固相反应法制备了不同烧结温度(950~1 180 ℃)、烧结时间、烧结次数共7种工艺的Sr₃YCo₄O_10.5+δ多晶块材,通过热分析、XRD、SEM确定了有序化相变和最佳烧结工艺(1 180 ℃/24 h+1 180 ℃/24 h),并研究了多晶的电磁性能。结果表明,964 ℃完全晶化的四方相Sr₃YCo₄O_10.5在1 042 ℃吸氧(δ)完成有序化,生成Sr₃YCo₄O_10.5+δ,而1 100 ℃和1 180 ℃烧结的样品均出现(103)、(215)超结构峰,验证了其结构的有序性。块材均呈半导体电输运行为,二次烧结晶格完整性提高,晶粒长大,300 K时电阻率仅为0.06 Ω·cm,居里温度(T_c)~335 K,零场冷曲线(ZFC)上的Hopkinson峰源于低温时被冻结的磁矩随温度升高转向磁场方向,磁化强度在298 K达到最大,随后受热扰动的影响减小。室温铁磁性源于有序结构导致的中自旋或高自旋态Co³⁺的e_g轨道有序。     

Single-atom Fe Embedded Co3S4 for Efficient Electrocatalytic Oxygen Evolution Reaction

Constructing atomically dispersed active sites with densely exposed and dispersed double metal-S_x catalytic sites for favorable OER catalytic activity remains rare and challenging. Herein, we design and construct a Fe₁S_x@Co₃S₄ electrocatalyst with Fe single atoms epitaxially confined in Co₃S₄ nanosheets for catalyzing the sluggish alkaline oxygen evolution reaction(OER). Consequently, in ultralow concentration alkaline solutions(0.1 mol/L KOH), such a catalyst is highly active and robust for OER with low overpotentials of 300 and 333 mV at current densities of 10 and 30 mA/cm², respectively, accompanying long-term stability without significant degradation even for 350 h. In addition, Fe₁S_x@Co₃S₄ shows a turnover frequency(TOF) value of 0.18 s⁻¹, nearly three times that of Co₃S₄(0.07 s⁻¹), suggesting the higher atomic utilization of Fe single atoms. Mössbauer and in-situ Raman spectra confirm that the OER activity of Fe₁S_x@Co₃S₄ origins from a thin catalytic layer of Co(Fe)OOH that interacts with trace-level Fe species in the electrolyte, creating dynamically stable active sites. Combined with experimental characterizations, it suggests that the most active S-coordinated dual-metal site configurations are 2S-bridged (Fe-Co)S₄, in which Co-S and Fe-S moieties are shared with two S atoms, which can strongly regulate the adsorption energy of reaction intermediates, accelerating the OER reaction kinetics.     

Electrochemical dehydrogenative N–H/N–H coupling reactions

The N–N bond is present in many important organic compounds, such as hydrazines, pyrazoles, azos, etc. Many methods based on transition metal catalyzed N–N coupling or functionalization of hydrazine have been reported for the synthesis of N–N containing organic compounds. In recent years, electrochemical dehydrogenative N–H/N–H coupling has become a powerful tool for the construction of N–N bearing organic compounds. The electrochemical methods employ electrons as traceless redox reagents instead of chemicals and produce hydrogen as the only byproduct. In this review, we summarize the recent advances in the electrochemical dehydrogenative N–H/N–H coupling reactions with focus on the mechanistic insights and synthetic applications of these transformations.     

环加成反应、环合反应、电环化反应与环化反应的区别*

环加成反应、环合反应、电环化反应与环化反应都是合成有机环状化合物的成环反应,它们描述的反应类型完全不同。但是,它们却经常被误用或者混用。阐述了这4类反应的区别,希望能够从教学上明确这4类反应,从源头为将来的有机化学工作者建立起准确的概念。