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Facet {100} Fosters Resonance Energy Transfer in Ni/Co-doped CsPbBr3 Nanocrystals
No full textThe design of an effective light harvester with metal-doped perovskite nanocrystals (M:PNCs) aims at achieving directional energy flow. The potential of crystal facets needs to be assessed for dictating energy transfer dynamics of M:PNCs. Herein we have engineered facets of amine-capped CsPbBr3 perovskite nanocrystals by doping with a trace amount of Ni and Co ions. Ni-doped CsPbBr3 (Ni:PNC) showcases structural heterogeneity with regular cubic and rod shapes whereas bimetallic-doped CsPbBr3 (Ni:Co:PNC) evolves to an elongated dodecahedron structure. Structural analysis using Rietveld Refinement strongly corroborates the construction of dodecahedron structure for Ni:Co:PNC through systematic displacement of Cs ions. Energy transfer from doped nanocrystals to Rhodamine B (RhB) occurs through dipole-dipole interaction, known as Fluorescence Resonance Energy Transfer (FRET). The emergence of isoemissive point, and rise-time of RhB conclusively establish Resonance Energy Transfer mechanism. Energy transfer in thin films occurs at much faster rate than in toluene medium. {100} facet-dominated Ni:PNC registers a FRET efficiency of 94% whereas {111}, {002} facet-dominated Ni:Co:PNC restricts at 21% FRET efficiency. The distance between donor and acceptor, RDA dictates the dynamics of energy transfer, rather than spectral overlap, and photoluminescence quantum yield of these doped-nanocrystals. Surface composition of facets, typically Cs ions perhaps plays a decisive role in regulating the binding constant of donor and acceptor. Our study demonstrates the importance of facets of nanocrystals in tuning the desired energy transfer processes for photocatalytic applications
A Versatile and Fast Photocatalyzed Deoxygenation of Organic N-oxides with a Rhenium Complex in the Presence of H2O
No full textThe oxidation of N-heterocycles is key to their functionalization since it enhances their reactivity in the ortho position. How-ever, an efficient post-reduction is often required to access the targeted compound. Here, a rhenium-based photocatalyst enables the versatile and fast deoxygenation of N-heterocyclic and alkyl N-oxides, avoiding sacrificial oxophilic reagents. The strong influence of the reaction conditions (solvent, H2O as additive, irradiation set-up) is demonstrated. The system shows a high functional group tolerance towards other reducible functions (free alcohol, carboxylic acid, ester, nitrile, halo-gen,…) and light-sensitive N-heterocycles
Photochemical C3-Amidation of Pyridines via Zincke Imine Intermediates
No full textSelective skeletal and peripheral editing of the pyridine moiety broadly expanded the chemical space. While CH functionalizations at the positions C2 and C4 are enabled by the inherent reactivity of this heteroarene, selective derivatization at C3 has long posed a significant challenge. Recently, based on dearomatization-rearomatization sequence, involving Zincke imine intermediates, selective halogenation (-Br, -Cl, -I) and isotopic labelling was accomplished. Here, we report a mild and regioselective method for C3 amination that relies on the photochemical reaction of Zincke imine with an amidyl radical generated from N-aminopyridinium salts. Mechanistic and theoretical studies confirmed radical intermediates involved and explains C-3 regioselectivity of the reaction
Fuzz testing molecular representation using deep variational anomaly generation
No full textAs efforts to improve the robustness of molecular representations advance, so does the need for methods to test and validate them. We use a Variational Auto-Encoder (VAE), an unsupervised deep learning model, to generate anomalous samples of a well-known molecular string format called SELF-referencIng Embedded Strings (SELFIES). This exercise questions a fundamental SELFIES assumption -- that they are always valid when converted to another string representation, SMILES. Interestingly, we discover that specific regions in the VAE\u27s latent space are particularly effective at generating SELFIES that defy this assumption. This organization of validity in the latent space, which proceeds continuously and radially, helps us better understand the factors affecting the molecular representation\u27s reliability. We propose that the VAE and associated anomaly generation approach offer an effective tool for assessing the robustness of molecular representations. We also explore why some SELFIES strings (version 2.1.1) might be invalid and suggest changes to improve them, aiming to spark further discussion on molecular string representations
Synergetic Hybridization Strategy to Enhance the Dynamicity of Poorly Dynamic CO2-derived Vitrimers achieved by a Simple Copolymerization Approach
No full textCopolymerization allows tuning polymer’s properties and a synergetic effect may be achieved for the resulting hybrid, i.e., outperforming the properties of its parents as often observed in natural materials. This synergetic concept is herein applied to enhance both dynamicity and properties of vitrimeric materials using poorly dynamic hydroxyurethane and non-dynamic epoxy thermosets. The latter generates activated hydroxyl, promoting exchange reactions 15 times faster than pure polyhydroxyurethanes. This strategy allows obtaining catalyst-free high-performance vitrimers from conventional epoxy-amine formulations and an easily scalable (bio-)CO2-based yet poorly efficient dynamic network. The resulting hybrid network exhibits modulus retention superior to 95% with fast relaxation (<10 min). The hydroxyurethane moieties actively participate in the network to enhance the properties of the hybrid. The material can be manufactured as any conventional epoxy formulation. This new strategy to design dynamic networks opens the door to large-scale circular high-performance structural carbon fiber composites (CFRP). The CFRP can be easily reshaped and welded from flat plates to complex geometries. The network is degradable under mild conditions, facilitating the recovery and re-use of high-added-value fibers. This accessible and cost-effective approach provides a versatile range of tunable dynamic epoxides, applicable across various industries with minimal adjustments to existing marketed products
PolyUniverse: Generation of a Large-scale Polymer Library Using Rule-Based Polymerization Reactions for Polymer Informatics
No full textRecent advancements in machine learning have revolutionized polymer research, leading to the swift integration of diverse computational techniques for de novo molecular design. A crucial aspect of these processes is to expand the number of candidate polymer structures, as the currently known real polymer structures are very limited. In contrast, small molecule databases are vast, offering extensive opportunities for the design of new molecules, such as drug discovery. In this study, we collected extensive small molecule compounds from GDB-17, GDB-13, and PubChem, and selected polymerization reaction pathways for eight types of polymers, including polyimide, polyolefin, polyester, polyamide, polyurethane, epoxy, polybenzimidazole (PBI), and vitrimer. These small molecule datasets and polymerization reactions enabled us to generate hundreds of quadrillions of hypothetical polymer structures. For each of the eight polymers, along with one promising copolymer, poly(imide-imine), we randomly generated over one million hypothetical structures, except for PBI, for which we created 10,000 structures. Chemical space visualization using t-distributed stochastic neighbor embedding and synthetic accessibility scores were employed to assess the feasibility of synthesizing these new polymers. Customized feedforward neural network models predicted thermal, mechanical, and gas permeation properties for both real and hypothetical polymers. Results show that many hypothetical polymers, especially polyimides, exhibit significant potential, often surpassing real polymers in performance, particularly for high-temperature applications and gas separation. Our findings highlight the immense potential of large-scale hypothetical polymer libraries for materials discovery and design. These libraries not only aid in identifying promising polymer materials through high-throughput screening but also provide valuable datasets for training advanced machine learning models, such as large language models. This research also demonstrates the power of data-driven approaches in polymer science, paving the way for the development of next-generation polymeric materials with superior properties for diverse industrial applications
Nickel-Catalyzed Arylative Telomerization of Isoprene
No full textDeveloping new transformations of bulk chemicals is an important approach to expand the reaction boundary of current chemistry. Instead of traditional hydroarylation of dienes, we herein demonstrated a nickel-catalyzed arylative telomerization of isoprene with high chemo- and regioselectivities. By utilizing a bulky mono-phosphine ligand, a range of structurally diverse aryl substituted
terpenes was created efficiently under redox-neutral conditions. Preliminary mechanistic studies suggest this telomerization proceeds through an oxidative cyclometallation of isoprene with Ni(0) species followed by arylation with organoboron reagents. This work not only
offers a new transformation of isoprene, but also provides a complementary approach for the creation of unnatural monoterpenoids
Guest-directed synthesis reveals vast family of robust polyphenolic metal-organic frameworks
No full textStructure directing agents (SDAs) are widely used in the synthesis of ubiquitous porous materials, such as zeolites, but their application and role in the synthesis of metal-organic frameworks (MOFs) has been comparatively understudied. Here we report a diverse family of anionic MOFs with all frameworks constructed exclusively from the same metal cation and plant-based organic linker—Zr(IV) cations and ellagate anions. Applying the same synthesis conditions but only changing the species of the SDA resulted in 10 novel zirconium ellagate MOFs (denoted SU-103 – SU-112) with varying dimensionality, topologies, Zr(IV) coordination geometries, intermolecular framework interactions, and framework interpenetration. Modern electron diffraction and electron microscopy techniques revealed the location of the SDA molecules in the pores of all MOFs, enabling a detailed study of their interactions. Despite having similar framework compositions, the properties of these MOFs noticeably differ due to the different ammonium SDAs and the unique framework structures obtained. The MOFs demonstrate chemical stability in aqueous media, basic conditions, and concentrated salt solutions, which is attributed to the strong Zr-catecholate chelating interactions consolidating the frameworks. We anticipate these 10 MOFs are only a small portion of a potential plethora of MOFs that could be discovered within this system. This lays the groundwork for the discovery of many other chemically robust structure-directed MOFs made with different cationic SDAs, framework metal cations, as well as other organic linkers with polyanionic functional groups
Ice templating water-stable macroporous polysaccharide hydrogels to mimic plant stems
No full textWater-stable macroporous hydrogels, inspired by the structural and chemical characteristics of plant stems are expected to open a wide range of possibilities in soft materials for passive liquid transport. However, obtaining efficient materials for these applications still poses a major challenge due to the complexity of shaping hydrogels at the relevant scale-length. Here, water-stable macroporous hydrogels were fabricated using alginate and TEMPO-oxidized cellulose via a new approach involving ice templating and topotactic ion-crosslinking with Ca2+. This approach allows to fully avoid the energy-intensive lyophilization process and results in composite hydrogels with pore sizes akin to those found in celery xylem, a model we chose for plant stems. Importantly, the pore size could be tailored by adjusting both the ice-growth velocities and the ratios of alginate to oxidized cellulose. The resulting hydrogels displayed remarkable water stability along with viscoelastic properties and wettability that depend on the alginate and oxidized cellulose ratios. Mechanical properties, such as compression stress and toughness, consistently increased with higher alginate contents. In addition, liquid transport measurements on crosslinked hydrogels with varying compositions and ice growth velocities revealed comparable rising speeds to those observed in celery, confirming the ability of polysaccharide-based hydrogels obtained by ice templating and topotactic crosslinking as relevant materials to mimic the function of plant stems
Raw Data and Noise in Spectrophotometry
No full textSpectrophotometers are ubiquitous in chemical and biological science; however, their precision limits are under-appreciated. Rules-of-thumb and IUPAC referenced guidance restricting the range of absorbance to minimize uncertainty are based on historically important instruments which are no longer as widely used. Instrumentation advances over the last half-century have changed the nature of spectrophotometric “raw” data while enabling opportunities to better evaluate their performance. Current IUPAC refenced guidance indicates that absorbance be limited to between 0.1 and 1.0 a.u. and that optimal performance (minimum relative standard deviation (RSD)) will be obtained at 0.43 a.u. or 0.86 a.u. depending on the type of limiting noise. We characterised noise in UV-Vis spectrophotometers across the spectrum and found wavelength-dependent variation in optimal performance. Optimal RSD approached neither extreme with minima varying depending on wavelength. We could find no evidence justifying guidance restricting absorbance to between 0.1 and 1.0 a.u. Measured RSD and light intensity are more important than absorbance values for assuring good quality measurements. Recovering light intensity estimates is a difficult inverse problem when I and I0 are not available, and the modern commercial instruments tested did not provide these. Based on this work, we recommend IUPAC modernise the references in its Gold Book with up-to-date articles and press instrument makers to provide access to instrument raw data