Chimia最新文献

Often the synthesis of catalysts can be time-consuming, multistep tasks, but sometimes they can turn up fortuitously, hidden treasure finds in essence. The alkali metal dihydropyridinate complexes discussed here fit the latter scenario. First reported simply as in situ intermediates by reaction of two commercially available reagents, an alkyllithium and pyridine, a whole class of such compounds, isolated and structurally characterised are now known where M = Li, Na, K, Rb and Cs. Here, some of their recent applications in homogeneous catalysis are outlined, including dehydrocoupling of aminoboranes, hydroboration of aldehydes and ketones, dehydrocyclization of diamine boranes, and transfer hydrogenation of alkenes to alkanes.

Deep Eutectic Solvents (DESs) based on abundant and non-toxic first-row metals have emerged as versatile and sustainable alternatives to conventional solvents/promoters in a variety of synthetic organic protocols under greener and milder reaction conditions. In particular, Fe(III)-based Lewis Acidic DESs (LADESs) have recently shown great potential as dual solvent/promoter systems enabling efficient transformations under air and recyclable conditions without requiring toxic volatile organic compound (VOC) solvents at any stage in the protocol (synthesis, isolation or purification). Specifically, in this short review, we summarize our recent progress in the application of FeCl3-based DESs as sustainable and efficient promoters/solvents in organic synthesis by presenting two representative examples: i) the hydration and hydration/oxidation of terminal or internal alkynes to yield methyl ketones or 1,2-diketones, respectively; and ii) the Friedel-Crafts benzylation reaction. The performance, recyclability, mechanistic features and green metrics for these processes are discussed, highlighting the promise of this approach for sustainable synthesis.

Transition metal complexes with N-heterocyclic vinylidene ligands can be obtained by combining N-heterocyclic diazoolefins with suitable metal precursors. The vinylidene ligands can act as potent C-donor ligands, allowing for the stabilization of electron-deficient and low-coordinate metal complexes.

Nickel olefin complexes have served as ubiquitous precursors in nickel chemistry ever since their discovery. One class of compounds derived from these precursors is low valent nickelate complexes. While their role as key intermediates in challenging cross-coupling reactions has recently been confirmed, knowledge regarding the coordination preferences of these complexes, in particular when extended to π-systems, is still very limited. Herein we present a summary of our most important findings from the investigation of the coordination of a series of organic π-acceptors to low valent alkali-metal nickelate complexes. This includes the coordination of polyaromatic molecules such as anthracene or coronene. Extending these studies to biphenylene has uncovered the ability of these heterobimetallic complexes to mediate C-C bond oxidative addition processes, where the nature of the alkali-metal plays an important role in influencing the rate of these activations.

Polylactide (PLA) is one of the most prominent bioplastics, derived from renewable feedstocks and noted for its biocompatibility. Yet, the full potential of PLA has not been fulfilled due to limitations in its production processes, especially the dependence on traditional toxic catalysts such as tin(II) octanoate. Recent studies have highlighted the advantages of alkali metal complexes as efficient, non-toxic, and versatile catalysts for the ring-opening polymerization (ROP) of lactide. Historically, alkali metals were considered too reactive or poorly controlled to be effective in ROP catalysis. However, recently it has been demonstrated that this limitation can be overcome through judicious ligand design and reaction engineering, transforming alkali metals into powerful tools for sustainable polymer chemistry. As such, the use of bulky ligands can tune the metal environment and assert a better control over the polymerization. As well, depending on the presence or not of the co-initiator, the polymerization mechanism varies significantly which influences the control of the stereoregularity of the polymers obtained, and poly-L-lactide (PLLA) with different D-lactide units can be obtained. This stereoregularity determines the thermal and mechanical properties and hence the applications of the PLLA. Furthermore, using chiral alkali compounds and controlling the aggregation, isoselective rac-lactide polymerization can be achieved. Hence, catalyst design and reaction conditions can be combined to tune polymer microstructure, molecular weight, and tacticity, advancing PLA toward a sustainable and circular material future. Furthermore, the alkali metal compounds described herein not only enable rapid lactide polymerization, but also promote PLA depolymerization under mild conditions, thereby connecting synthesis with chemical recycling.

Photodynamic therapy (PDT) is a clinically proven, non-invasive cancer treatment that enables precise spatial and temporal control of cytotoxicity. Yet, many current photosensitisers (PSs) suffer from poor tumour specificity, limiting their effectiveness. Targeted photodynamic therapy (tPDT) addresses this by directing PSs to selectively accumulate in tumour tissue. Among the emerging strategies, enzyme targeting stands out as a powerful approach. This review explores enzyme-targeted PDT using metal-based PSs conjugated to small-molecule enzyme inhibitors - a dual-action design that enables tumour destruction while blocking key pro-tumour signalling pathways. Five distinct proteins with enzymatic activity such as carbonic anhydrase (CA), cathepsin B, cyclooxygenase (COX), epidermal growth factor receptor (EGFR), and heat shock protein 90 (Hsp90) are presented through selected conjugates. These cases underscore the versatility of tPDT in achieving precise tumour targeting. By enhancing therapeutic efficacy, minimising off-target toxicity and collateral damage, and ultimately improving patient safety, enzyme-directed tPDT bridges targeted therapy, photomedicine, and precision oncology - setting the stage for next-generation cancer treatments.

Building on the success of N-heterocyclic carbenes, extended versions comprised of an exocyclic metal bonding site have become increasingly popular. Pyridinium amidates (PYAs) belong to these ligand systems, as they contain a N-donor site that is formally stabilized by a pyridine-derived carbene. These PYAs are characterized by a unique donor flexibility, which imparts in some settings extraordinarily high catalytic activity, and in other settings remarkable stability of (catalytic) intermediates, which allows for deciphering mechanistic pathways.

Nanoscale confinement strongly alters the behavior of soft matter, from polymer crystallization to lipid self-assembly. In this mini review, we summarize recent progress on how confinement impacts molecular transport, crystallization, dynamics, and phase behavior in two distinct media: hard confinement in inorganic nanopores and soft confinement in lipidic mesophases. In the first part, we highlight polymer transport and dynamics in rigid nanopores, emphasizing how chain topology (linear, star-shaped, hyperbranched) governs confined crystallization and relaxation dynamics. In the second part, we turn to lipidic mesophases as biomimetic soft confining media, where phase transitions and molecular transport are intricately coupled to hydration and interfacial interactions. Together, these studies reveal that confinement effects arise not only from geometry but also from surface interactions, and that their interplay determines the structure and dynamics of confined matter. Understanding these principles opens avenues for applications in drug delivery, cryo-enzymology, and nanofabrication of functional materials and devices.

Biological systems rely on a complex and precisely controlled mix of biomolecules to sustain life as we know it. In addition to their compositional heterogeneity, individual biomolecules undergo dynamic rearrangements to fulfil their cellular function: they move, reversibly interact, and alternate between multiple conformations. Disentangling these compositional and dynamic complexities of biological systems poses a formidable challenge to established ensemble techniques. In this review, we discuss two single-molecule techniques - nanopore recordings and single-molecule Förster Resonance Energy Transfer (smFRET) measurements - and highlight their powerful abilities to unravel mixtures and resolve biomolecular dynamics with the ultimate resolution of single molecules. Applications range from identifying the vast sequence space populated by nucleic acids and stoichiometries observed in small messenger molecules, to detecting time-varying conformations and interactions of large multi-domain proteins. This non-exhaustive review aims to introduce non-expert readers to the unique benefits of single-molecule experiments, which can overcome ensemble and time averaging as well as dynamic range limitations, and therefore offer unique, quantitative descriptions of the intriguingly complex biomolecular mechanisms found within and around us.