Simultaneous enantioseparation of three commonly used chiral antifungal pesticides (diniconazole, hexaconazole, and imazalil) was first studied based on micellar electrokinetic chromatography (MEKC) ...with hydroxypropyl-γ-CD (HP-γ-CD) as chiral selector. In this study, the importance of experimental parameters such as chiral selector type and concentration, sodium dodecyl sulfate (SDS) concentration, the ratio of methanol, and separation voltage in optimizing were investigated. The simultaneous enantioseparation of diniconazole, hexaconazole, and imazalil was successfully achieved in 30 mM borate buffer (pH 9.0) containing 10 mM HP-γ-CD and 20 mM SDS with methanol (8%) added as organic modifiers. The resolution of diniconazole, hexaconazole, and imazalil was 15.2, 2.12, and 2.78, respectively, and the peak efficiency (N) was over 566,825 plates/m. This study provides an alternative way to systematically separate chiral antifungal pesticides with high efficiency.
Recent advances related to catalytic enantioselectice fluorination are examined. Catalytic enantioselective monofluoromethylation and catalytic enantioselective difluoromethylation are among the ...topics discussed.
A versatile kinetic resolution of protecting‐group‐free BINAMs and NOBINs has been realized through chiral phosphoric acid catalyzed triazane formation with azodicarboxylates. A series of ...mono‐N‐protected and unprotected BINAMs, diphenyl diamines and NOBIN derivatives could be kinetically resolved with excellent performances (with s factor up to 420). The gram‐scale reactions and facile derivatizations of the chiral products demonstrate the potential of these methods in the asymmetric synthesis of chiral catalysts and ligands.
A highly efficient and versatile method for kinetic resolution of protecting‐group‐free BINAMs and NOBINs has been developed through chiral phosphoric acid catalyzed triazane formation with azodicarboxylates. Broad substrate scope, excellent kinetic performance, and facile transformation of the triazane products into axially chiral biaryl diamines and amino alcohols was observed.
Metal halide perovskites have aroused burgeoning interest in the field of photovoltaics owing to their versatile optoelectronic properties. The outstanding power conversion efficiency, high specific ...power (i.e., power to weight ratio), compatibility with flexible substrates, and excellent radiation resistance of perovskite solar cells (PSCs) enable them to be a promising candidate for next‐generation space photovoltaic technology. Nevertheless, compared with other practical space photovoltaics, such as silicon and III‐V multi‐junction compound solar cells, the research on PSCs for space applications is just in the infancy stage. Therefore, there are considerable interests in further strengthening relevant research from the perspective of both mechanism and technology. Consequently, the approaches used for and the consequences of PSCs for space applications are reviewed. This review provides an overview of recent progress in PSCs for space applications in terms of performance evolution and mechanism exploration of perovskite films and devices under space extreme environments.
Perovskite solar cells (PSCs) are considered as promising candidates for next‐generation space photovoltaic technology. Key space environments and specific requirements for space photovoltaics are outlined. Some recent advances in terms of performance evolution and mechanism exploration of perovskite films and devices under space extreme environments are summarized. Progress and challenges associated with space applications of PSCs are highlighted.
Evidence for metastable dynamics and its role in brain function is emerging at a fast pace and is changing our understanding of neural coding by putting an emphasis on hidden states of transient ...activity. Clustered networks of spiking neurons have enhanced synaptic connections among groups of neurons forming structures called cell assemblies; such networks are capable of producing metastable dynamics that is in agreement with many experimental results. However, it is unclear how a clustered network structure producing metastable dynamics may emerge from a fully local plasticity rule, i.e., a plasticity rule where each synapse has only access to the activity of the neurons it connects (as opposed to the activity of other neurons or other synapses). Here, we propose a local plasticity rule producing ongoing metastable dynamics in a deterministic, recurrent network of spiking neurons. The metastable dynamics co-exists with ongoing plasticity and is the consequence of a self-tuning mechanism that keeps the synaptic weights close to the instability line where memories are spontaneously reactivated. In turn, the synaptic structure is stable to ongoing dynamics and random perturbations, yet it remains sufficiently plastic to remap sensory representations to encode new sets of stimuli. Both the plasticity rule and the metastable dynamics scale well with network size, with synaptic stability increasing with the number of neurons. Overall, our results show that it is possible to generate metastable dynamics over meaningful hidden states using a simple but biologically plausible plasticity rule which co-exists with ongoing neural dynamics.
Helicenes and helicene‐like molecules, usually containing multiple ortho‐fused aromatic rings, possess unique helical chirality. These compounds have found a wide range of important applications in ...many research fields, such as asymmetric catalysis, molecular recognition, sensors and responsive switches, circularly polarized luminescence materials and others. However, the catalytic enantioselective synthesis of helicenes was largely underexplored, when compared with the enantioselective synthesis of molecules bearing other stereogenic elements (e.g. central chirality and axial chirality). Since the pioneer work of asymmetric synthesis of helicenes via enantioselective 2+2+2 cycloaddition of triynes by Stará and Starý, last two decades have witnessed the tremendous development in the catalytic enantioselective synthesis of helicenes. In this review, we comprehensively summarized the advances in this field, which include methods enabled by both transition metal catalysis and organocatalysis, and provide our perspective on its future development.
Helicenes and helicene‐like molecules have found a plethora of important applications in many research fields. Consequently, the catalytic enantioselective synthesis of these unique skeletons have drawn a lot of research interests and achieved notable advances in the last two decades. In this review, we comprehensively summarized the progresses in this field, including methods enabled by both asymmetric transition metal catalysis and organocatalysis.
An efficient method for the asymmetric synthesis of 4H‐3,1‐benzoxazines was developed by kinetic resolution of 2‐amido benzyl alcohols using chiral phosphoric acid catalyzed intramolecular ...cyclizations. A broad range of benzyl alcohols (both secondary and tertiary alcohols) were kinetically resolved with high selectivities, with an s factor of up to 94. Mechanistic studies were performed to elucidate the mechanism of these reactions, wherein the amide moieties reacted as the electrophiles. Gram‐scale reaction and facile transformations of the chiral products demonstrate the potential of this method in asymmetric synthesis of biologically active chiral heterocycles.
A practical approach for the asymmetric synthesis of 4H‐3,1‐benzoxazines was achieved by the kinetic resolution of 2‐amido benzyl alcohols in the presence of a chiral phosphoric acid (CPA). The method demonstrates broad substrate scope and excellent kinetic resolution (with an s factor of up to 94).
Abstract
Planar chiral 2.2paracyclophane derivatives are a type of structurally intriguing and practically useful chiral molecules, which have found a range of important applications in the field of ...asymmetric catalysis and material science. However, access to enantioenriched 2.2paracyclophanes represents a longstanding challenge in organic synthesis due to their unique structures, which are still highly dependent on the chiral chromatography separation technique and classical chemical resolution strategy to date. In this work, we report on an efficient and versatile kinetic resolution protocol for various substituted amido2.2paracyclophanes, including those with
pseudo-geminal
,
pseudo-ortho
,
pseudo-meta
and
pseudo-para
disubstitutions, using chiral phosphoric acid (CPA)-catalyzed asymmetric amination reaction, which was also applicable to the enantioselective desymmetrization of an achiral diamido2.2paracyclophane. Detailed experimental studies shed light on a new reaction mechanism for the electrophilic aromatic C-H amination, which proceeded through sequential triazane formation and N1,5-rearrangement. The facile large-scale kinetic resolution reaction and diverse derivatizations of both the recovered chiral starting materials and the C-H amination products showcased the potential of this method.
Lead halide perovskite films have witnessed rapid progress in optoelectronic devices, whereas polycrystalline heterogeneities and serious native defects in films are still responsible for undesired ...recombination pathways, causing insufficient utilization of photon‐generated charge carriers. Here, radiation‐enhanced polycrystalline perovskite films with ultralong carrier lifetimes exceeding 6 μs and single‐crystal‐like electron–hole diffusion lengths of more than 5 μm are achieved. Prolongation of charge‐carrier activities is attributed to the electronic structure regulation and the defect elimination at crystal boundaries in the perovskite with the introduction of phenylmethylammonium iodide. The introduced electron‐rich anchor molecules around the host crystals prefer to fill the halide/organic vacancies at the boundaries, rather than form low‐dimensional phases or be inserted into the original lattice. The weakening of the electron‐phonon coupling and the excitonic features of the photogenerated carriers in the optimized films, which together contribute to the enhancement of carrier separation and transportation, are further confirmed. Finally the resultant perovskite films in fully operating solar cells with champion efficiency of 23.32% are validated and a minimum voltage deficit of 0.39 V is realized.
Ultralong charge‐carrier lifetimes >6 μs are achieved in polycrystalline halide perovskites by decorating the grain boundaries with a trace amount of electron‐rich anchors, which benefits from weak excitonic effects and the weakening of electron–phonon couplings in passivated films, fulfilling reduced voltage deficits and enhanced efficiencies in perovskite photovoltaics. This finding provides a new insight into realizing superior carrier properties of polycrystalline perovskite films and high‐performance perovskite optoelectronics.
Glycosylation of proteins and lipids is critical to many life processes. Secondary metabolites (or natural products), such as flavonoids, steroids, triterpenes, and antibiotics, are also frequently ...modified with saccharides. The resulting glycosides include diverse structures and functions, and some of them have pharmacological significance. The saccharide portions of the glycosides often have specific structural characteristics that depend on the aglycones. These molecules also form heterogeneous “glycoform” mixtures where molecules have similar glycosidic linkages but the saccharides vary in the length and type of monosaccharide unit. Thus, it is difficult to purify homogeneous glycosides in appreciable amounts from natural sources. Chemical synthesis provides a feasible access to the homogeneous glycosides and their congeners. Synthesis of a glycoside involves the synthesis of the aglycone, the saccharide, the connection of these two parts, and the overall manipulation of protecting groups. However, most synthetic efforts to date have focused on the aglycones, treating the attachment of saccharides onto the aglycones as a dispensable topic. The synthesis of the aglycone and the synthesis of the saccharide belong to two independent categories of chemistry, and different types of the aglycones and saccharides pose as specific synthetic subjects in their own disciplines. The only reaction that integrates the broad chemistry of glycoside synthesis is the glycosidic bond formation between the saccharide and the aglycone. Focusing on this glycosylation reaction in this Account, we string together our experience with the synthesis of the naturally occurring glycosides. We briefly describe the synthesis of 18 glycosides, including glycolipids, phenolic glycosides, steroid glycosides, and triterpene glycosides. Each molecule represents a prototypical structure of a family of the natural glycosides with interesting biological activities, and we emphasize the general tactics for the synthesis of these diverse structures. We provide a rationale for four tactics for the synthesis of glycosides, based on the stage at which the glycosidic bond is formed between the saccharide and the aglycone. This choice of tactic determines the success or failure of a synthesis, and the flexibility and the overall efficiency of the synthesis as well. Toward the synthesis of heterogeneous glycoform mixtures, we discuss successive and random glycosylation reactions. Finally, we have developed two new glycosylation protocols that address the challenges in the glycosylation of aglycones that are poorly nucleophilic, extremely acid labile, or extremely electrophilic. One of these new protocols takes advantage of glycosyl trifluoroacetimidate donors, and a second protocol uses gold(I)-catalyzed glycosylation with glycosyl ortho-alkynylbenzoate donors.
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