Chimia最新文献

Cellulose nanofiber (CNF) sponges or CNF aerogels are promising biocompatible materials with applications ranging from biomedicine to environmental remediation. The highly porous architecture of these sponges - which is crucial for their functionality - is significantly influenced by the freezing step during fabrication. This review explores the critical role of freezing techniques in tailoring pore geometry and, consequently, the macroscopic properties of CNF sponges. We discuss conventional directional freezing methods and their limitations, highlighting the advantages of dynamic freezing for achieving isotropic pore structures. Furthermore, we examine various crosslinking strategies to enhance the stability and mechanical properties of CNF sponges. Finally, we present recent findings from our laboratory demonstrating the successful fabrication of biocompatible and crosslinked CNF sponges with tailored pore geometries using a dynamic freezing approach.

Large scale exploitation of shale gas has stimulated the developments of on-purpose propane dehydrogenation (PDH) technologies. Pt-based PDH catalysts have been utilized in industry, e.g. Pt-Sn/Al2O3 and Pt-Ga/ Al2O3, where the actual role of metal dopants is not fully understood. In this regard, the development of model systems possessing tailored surface sites is necessary in order to look into the structure-activity relationships. In that context, the surface organometallic chemistry (SOMC) approach has emerged as a powerful tool to yield PDH model catalysts, revealing that the formation of alloyed particles and residual unreduced metal sites are important for high productivity and stability.

The temperature-dependent reactivity of three triplet carbenes (denoted as C1, C2 and C3) were investigated using instanton theory. Experiments showed that C1undergoes an intramolecular reaction at very low temperatures, while C2 requires heating, and C3 remains stable despite heating. The reactions studied involved both hydrogen transfer and intersystem crossing, and therefore we considered sequential and concerted processes as possible candidates for the reaction mechanism. Calculations of instanton tunnelling pathways in conjunction with double-hybrid density functional theory showed that the sequential mechanism dominates the reaction at high temperatures while the concerted mechanism is the predominant channel at low temperatures. The observed temperature-dependent reactivity can thus be explained in terms of a crossover temperature where the mechanism switches. This study suggests a powerful way to control the reactivity of triplet carbenes solely by tuning temperature.

Water-soluble polymers (WSPs) are widely used in industrial and agricultural applications, as well as in consumer products. After use, they may be released into both engineered and natural environments, where their fate is governed by transfer and transformation processes which are strongly influenced by their molecular weight distribution (MWD). Unlike traditional low molecular weight organic chemicals, WSPs are ensembles of molecules with varying chain lengths. This work suggests the use of Monte Carlo (MC) simulations to model shifts in MWDs resulting from abiotic and biotic chain scission reactions in receiving environments. We specify key factors influencing chain-scission selectivity, including chain-end scissions, molecular weight-dependent scissions, and site-specific scissions. Experimental validation of MC simulation predictions presents analytical challenges, requiring high-resolution MWD characterization of WSPs and reliable extraction techniques from complex environmental matrices. MC simulations may play a pivotal role not only in identifying the most relevant molecular weight (MW) ranges for targeted analysis but also in predicting and elucidating environmental chain scission processes.

Metal oxide nanocrystals, like ZrO2 and HfO2, serve as hosts for optically active lanthanide ions. However, synthesizing colloidally stable nanocrystals with complex architectures remains challenging. We have pioneered the synthesis of metal oxide core/shell nanocrystals, where HfO2 epitaxially grows onto ZrO2. The beneficial effect of the shell on the optical properties is demonstrated by investigating the photoluminescence of ZrO2:Eu and of ZrO2:Eu/ZrO2 after growing a protective zirconia shell on it.[1].

Symmetry-breaking charge separation (SB-CS) is a photoinduced electron transfer reaction in which the chromophore acts as both the acceptor and the donor. This reaction which is still poorly understood may enable long-lived charge separation interesting for many applications. Here we show that SB-CS can be realised bimolecularly with perylene and discuss the factors favouring it. Furthermore, using a pyrene bichromophoric system, we discuss the influence of interchromophore coupling and how the photophysics can be fine-tuned to yield SB-CS over other processes such as excimer formation.

Over the past decades, s-block metal amides including LiTMP and TMPMgCl.LiCl (TMP = 2,2,6,6-tetramethylpiperidide) have found widespread applications in the deprotonative metalation of aromatic compounds. In contrast, transition metal amides usually exhibit diminished basicity to metalate these substrates. Here we present an overview of the synthesis of a highly reactive TMP-based cobalt(II) bis(amide) complex Co(TMP)2 and its relevance in the direct Co-H exchange processes with fluoroarenes. This deprotonative metalation reactivity can be further extended to cyclopentadiene to generate cobaltocene. Exhibiting an unusual reactivity, Co(TMP)2 has also been found to be highly nucleophilic, as evidenced by the insertion of CO2 molecules into both of its Co-NTMP bonds.

Many anticancer drugs are ineffective in tumors that have functional DNA repair mechanisms. In contrast, trabectedin, a tetrahydroisoquinoline alkaloid marine natural product, stands out as it is more lethal to cancer cells with active DNA repair, particularly transcription-coupled nucleotide excision repair (TC-NER), making it an intriguing alternative to standard chemotherapeutic agents. To optimize trabectedin's use in precision oncology, it is essential to understand how its toxicity depends on TC-NER. In this study, we reveal that incomplete TC-NER of trabectedin-DNA adducts generates persistent single-strand breaks (SSBs). These adducts are found to obstruct the second of two sequential NER-mediated DNA incisions. By mapping the 3'-hydroxyl groups of SSBs resulting from the first NER incision at trabectedin-DNA adducts, we achieve genome-wide visualization of TC-NER. Our findings show that trabectedin-induced SSBs predominantly occur in the transcribed strands of active genes, accumulating near transcription start sites. This work provides new insights into how trabectedin can be leveraged for targeted cancer therapies and for studying TC-NER and transcription.

The low-temperature reverse water-gas shift (LT-RWGS) is a critical and energy effective technology for syngas production and the mitigation of anthropogenic carbon emissions. Developing efficient and well-defined catalysts for the LT-RWGS, from which structure-activity relationships can be drawn, is a significant challenge. Herein we describe how the identification of the grafting properties of tetramesityldiiron (Fe2Mes4) helps with designing tailored and highly efficient catalysts of PtFe@SiO2 composition. To that end, a molecular analogue, Fe2Mes3OSi(OtBu)3, was synthesized and characterized by X-ray diffraction, 57Fe-Mössbauer and 1H-NMR spectroscopy. The results confirmed that tetramesityldiiron grafts onto silica via selective displacement of a single mesityl ligand, forming Fe2Mes3@SiO2, while steric hindrance likely prevents secondary interactions with surface siloxide bridges. This work highlights the potential of tetramesityldiiron as a versatile precursor for synthesizing bimetallic MFe@SiO2 systems, enabling the rational development of highly efficient LT-RWGS and CO2 hydrogenation catalysts.

Nanopore sensing is an emerging technology that can distinguish subtle differences in molecules and allows the observation of molecular processes. The technique has revolutionized DNA sequencing through long reads of single molecules. Following this success, nanopores are now increasingly applied to protein analysis. Proteins play central roles in cellular function and major diseases, however their analysis using established methods is complicated by the lack of protein-amplification methods. Here, two examples of nanopore-based protein analysis are described: the identification of biomarkers, and the analysis of protein function.