Chemistry - A European Journal最新文献

Pillar[n]arenes are a class of special macrocyclic compounds with rigid and porous structures, representing an important branch of host macrocycles in the field of supramolecular chemistry. Since their discovery in 2008, pillar[n]arenes have been in-depth applied in the field of biomedicine, such as molecular recognition, bio-imaging, and tumor detection, due to the enhancement of fluorescent signal when combining with chromophores. Over the past decade, many pillar[n]arene units-incorporated polymers have been synthesized and served as ideal polymer hosts for the enhancement of luminescent performance of applied to enhance aggregation-induced emission (AIE) performance. Driven by researchers' keen exploration of pillararene polymers for AIE enhancement, this review will elaborate on the AIE-enhancing effects of pillararenes from two aspects: pillararene-containing monomers and pillararene-containing linear polymers. It also introduces the synthesis methods of pillararenes and the principles underlying their AIE-enhancing effects. Additionally, their applications in areas such as fluorescent sensing and artificial light-harvesting systems are presented. Finally, the current challenges and prospects of pillararenes are discussed.

More than 3,000 natural products have been identified from cyanobacteria. These natural products often displayed antiparasitic, anti-inflammatory, antimicrobial, and anticancer activities. Cyanobacterial cyclic natural products are ribosomal or nonribosomal peptides, typically containing one or more proline residues. However, the presence and population of the cis-Pro conformation are not always explicitly stated in the literature. The two proline isomers can affect protein function and interactions. This review focuses on the NMR characteristics and biosynthetic logic of cyanobacterial cyclic peptides containing cis-Pro dominant conformations, aiming to provide an overview of the cis-Pro conformations in cyanobacterial cyclic peptides. We manually reviewed the chemical structures and NMR chemical shifts of 150 cyanobacterial cyclic peptides containing proline residues, of which 51 cyclic peptides possessed cis-prolyl amide bonds. Furthermore, we explained the Pro cis/trans isomerism in cyclic peptides and discussed methods for better studying these Pro cis/trans conformations in the future.

Metal oxoanions present significant challenges because of their high solubility in water and their charge characteristics. Among these, carcinogenic chromate and radioactive pertechnetate are particularly concerning. Conventional adsorbents often suffer from low recyclability and reduced selectivity to remove oxoanionic pollutants. Herein, we report a guanidinium-based porous organic polymer (POF-3) that selectively adsorbs CrO₄ ^2-and TcO₄ ^- from real-life water samples. POF-3 displays maximum adsorption capacities of 123 mg g^-1 for chromate and 177 mg g^-1 for perrhenate at pH = 6. The removal efficiency of POF-3 at low concentrations of chromate and pertechnetate is very far below the corresponding EPA limit. The adsorption mechanism mainly follows electrostatic interaction and the ion exchange mechanism. Reducing carcinogenic Cr(VI) to Cr(III) is a crucial step; introducing thiophene in the structural backbone of POF-3 facilitates the redox properties. Morphological transformation into a sheet-like structure confirms the effective sorption of chromate and perrhenate. In this context, NMR titration of monomeric compound also suggests interaction of POF-3(M) with guanidium sites of material towards chromate and perrhenate effectively, as proven by solid phase study. These effective adsorption capacities, faster kinetics, and ion exchange ability make it a promising solution for environmental remediation.

The chemical system Li/Ti/P has previously been subject to intensive investigation. However, reliable structural data for the reported phases have remained elusive. Motivated by the growing interest in phosphorus-based lithium-ion conductors, we have reinvestigated the synthesis, crystal structure, and physical properties of Li₈TiP₄. Phase pure Li₈TiP₄ was obtained, which crystallizes in the tetragonal space group P4₂mc (no. 105) with a = 8.37581(2) Å and c = 5.90489(2) Å. According to a structure determination from X-ray diffraction powder data, Li₈TiP₄ is closely related to known Li₈TtP₄ with Tt = Si, Ge, and Sn, but adapts a different structure type. Basic structural findings are confirmed by solid state ⁶Li and ³¹P NMR spectroscopy. DFT calculations reveal a band gap of 2.5 eV and a good correlation between theoretical and experimental Raman spectra. From potentiostatic impedance spectroscopy an ion conductivity of (4.3 ± 0.6) × 10^-6 S∙cm^-1 at 298 K was found. In addition to the investigation of ternary Li₈TiP₄, an isotypic quaternary Ta-containing phase is observed and studied by single crystal structure determination. Special emphasis in this study is placed on the role of Li occupancy in the voids of the cubic close-packed (ccp) P atom arrangement and its impact on the ionic conductivity, in comparison to the known compounds Li_{7+5 x}Ta_xP₄ and Li_{8- x}Ti_{1- x}Ta_xP₄ and traced back to the difference in crystal symmetry. Possible diffusion pathways of the Li⁺ ions were approached by BVSE calculations.

Solid-state nuclear magnetic resonance spectroscopy under Magic Angle Spinning (MAS) is one of the most powerful analytic techniques and in principle the method of choice to elucidate with molecular detail all components of complex solid or solid-liquid samples. MAS NMR under light irradiation is yet little developed, with technical solutions and first applications just emerging. We present the first operando observation of photoreforming of methanol to formaldehyde in a transparent rotor, irradiated at 365 nm by four LEDs, at spinning rates up to 11.5 kHz. The photon flux inside the rotor is quantified by an actinometric reaction. Efficient light penetration into the entire rotor volume is crucial. Therefore, we introduce silica monoliths with a continuous network of macropores, coated with TiO₂ (anatase) as supported heterogeneous catalyst. These monoliths provide a large pore volume to accommodate the liquid substrate and a high surface area. Centrally, the network of pores larger than the visible light enhances light penetration into the material by a factor of two compared to a powder. Silica monoliths may be easily decorated with various photocatalysts and thus provide a versatile platform for observing in real time photocatalytic reactions by solid-state NMR.

DNA, traditionally regarded as genetic material, has emerged as a versatile building block in molecular technology. Catalytic DNA oligomers known as DNAzymes, especially those capable of cleaving target RNA at specific sites, have shown great potential in DNA-based diagnostics, therapeutics, and dynamic DNA nanotechnology. For advanced applications, stimuli-responsive DNAzymes, which are activated only under specific conditions or by specific chemical stimuli, have attracted particular attention. Although such DNAzymes can be obtained by in vitro selection under strictly controlled conditions, more general strategies for their rational design are strongly needed. In this approach, stimuli-responsiveness is introduced into existing DNAzymes by sequence engineering or chemical modification. This review focuses on the rational design of stimuli-responsive RNA-cleaving DNAzymes using modified and artificial nucleotides. Here, we discuss representative strategies, including recent examples: (i) stimulus-induced reconstitution of split DNAzymes, (ii) activity control by strand cleavage or ligation, (iii) blocking of the catalytic core with removable oligonucleotides, (iv) caging with labile protecting groups, and (v) stimuli-induced conformational switching between inactive and active structures. These approaches enable externally controllable activation mechanisms, while maintaining the intrinsic catalytic activity of DNAzymes, providing a valuable toolkit for molecular sensing and DNA nanotechnology.

Copper- and silver-catalyzed reactions of active methylene isocyanides provide powerful and versatile strategies for the construction of heterocyclic architectures relevant to pharmaceutical and materials science. Owing to their unique ambiphilic reactivity, active methylene isocyanides serve as key building blocks for the synthesis of fused, bicyclic, polycyclic, and spirocyclic heterocycles under mild catalytic conditions. This review summarizes recent advances in the copper- and silver-catalyzed transformation of functionalized isocyanides toward multi-substituted five- and six-membered heterocyclic frameworks. Particular emphasis is placed on [3+n] cycloaddition reactions, as well as tandem processes involving cycloaddition, annulation, alkylation, and insertion pathways. In addition, emerging strategies that exploit nonfunctionalized isocyanides, strained alkene surrogates, and multi-isocyanide reaction manifolds are discussed, highlighting new opportunities for complexity generation and asymmetric heterocycle synthesis.

A molecular-level understanding of supramolecular chirality amplification and attenuation is established through the coordination-driven self-assembly of a 'nano-size' achiral Zn(II)porphyrin trimer (host) and a series of chiral diamino esters (substrates). The processes occur through the stepwise formation of polymer and dimer via intermolecular assembling and disassembling processes, respectively. Crystallographic characterizations of both the polymer and dimer allow systematic scrutiny of their structural changes, elucidating their chiroptical properties. The electronic circular dichroism (CD) spectra display opposite signs for the R and S substrates in both the polymer and dimer, indicating that the chirality of the complexes are dictated solely by the absolute configuration of the substrate. In the dimer, both intra- and intermolecular couplings were identified while in the polymer, CD signals were significantly amplified, owing to cumulative intermolecular couplings. DFT and TDDFT studies corroborate these experimental findings and provide valuable insights into the origin of the chiroptical responses, amplification and reduction in these systems.

Reproducibility is the main weak point of most of the currently available synthetic strategies for metal nanostructures, and this issue is hampering both production and research on such materials. While several synthetic strategies can be found in literature, most of them are fundamentally based on strict protocols consisting of lists of subsequential predefined operations to be executed in a time-defined manner. Such protocols are designed and optimized on the basis of pilot runs and are intrinsically affected by noncontrollable fluctuations in the experimental conditions. In this work an innovative, intrinsically flexible, automatized, and self-correcting strategy is proposed, which, in combination with real-time monitoring of the optical properties of the reaction mixture, allows to synthesize precisely tuned gold nanorods. This strategy is based on the fast and precisely controlled oxidation of precursor AuNRs. The fast reaction allows the selective and predictable etching of the nanorods by online-controlled subsequential additions of small amounts of oxidants, which are also able to remove undesirably shaped byproducts possibly present in the sample. Due to these features, this process can be automated and allows starting from nonpurified nanorod dispersions with variable aspect-ratio. Furthermore, the reaction can be stopped by oxidizer quenching, providing stable dispersions.

The intricate structures of RNA molecules facilitate their diverse cellular functions. These structures are shaped by the cellular environment, a context that in silico and in vitro methods typically cannot reconstitute, making it more difficult to study the structure of RNA in cells. In response to these challenges, RNA structure probing using cell-permeable chemicals has emerged as an effective method to capture the RNA structural landscape in its native environment. The integration of these probes with advanced adduct detection techniques, particularly second- and third-generation sequencing, has propelled the field forward, facilitating a deeper understanding of the RNA structurome within its precise functional context, including the examination of RNA structure at the single-molecule and single-cell levels, within specific subcellular compartments, and across various stages of RNA biogenesis and regulation. This Review summarizes the significant advances in the field of RNA structure probing, focusing on the development of novel structural probes, strategies for RNA structure reconstruction, innovative methodologies that offer extended applicability to address unique biological questions, and concludes with an outlook on future directions in the field.