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Uranium(III) and uranium(IV) meta-terphenyl thiolate complexes
No full textWe report the synthesis and characterization of crystalline uranium(IV) and uranium(III) complexes supported by the bulky hexa-iso-propyl-m-terphenylthiolate ligand system, SAriPr6 (SAriPr6 = {SC6H3-2,6-(Tripp)2}; Tripp = 2,4,6-iPr-C6H2). These constitute the first examples of m-terphenylthiolate complexes of uranium in any oxidation state and highlight the supporting role of U···arene interactions in the isolation of heteroleptic complexes with this ligand set, and demonstrate the diverse reactivity of [UIV(BH4)4]. Treatment of UIVCl4 with two equivalents of KSAriPr6 in Et2O afforded [UIV(SAriPr6)2(Cl)2] (1) in poor yield along with several crystals of the Et2O adduct, [UIV(SAriPr6)2(Cl)2(Et2O)2] (1·Et2O). While the reaction between [UIV(BH4)4] and one equivalent of KSAriPr6 in toluene gave several crystals of the poorly soluble double salt, [UIV(μ-SAriPr6)(BH4)2(μ-BH4)(μ3-BH4)K]2 (2), exposing the crude reaction mixture to Et2O gave the oxidized disulfide ligand dimer, (SAriPr6)2 as the sole identifiable product. The reaction between [UIV(BH4)4] and one equivalent of HSAriPr6 in hot toluene gave [UIII(H3B·SAriPr6 κS,H,H)(BH4)2] (3) – the net product of thermolytic reduction of the uranium and deprotonation of the arylthiol. Complex 3 proved resistant to further substitution using either HSAriPr6 or KSAriPr6. Both U(III) mono-arylthiolates, [UIII(SAriPr6)(BH4)2] (4a) and [{UIII(SAriPr6)(BH4)}2{μ-B2H6}] (4b) were isolated as a mixture from the reaction between [UIII(BH3)3(toluene)] and one equivalent of KSAriPr6. Complex 4b is a rare example of a nido-mettaloborane. When two equivalents of KSAriPr6 were reacted with [UIII(BH3)3(toluene)], the bis-arylthiolate complex [UIII(SAriPr6)2(BH4)] (5) was isolated in good yield. Complexes 1–5 have been characterized variously by single-crystal X-ray diffraction, multi-nuclear NMR spectroscopy, infra-red spectroscopy, UV-Vis-NIR spectroscopy, SQUID magnetometry, elemental analyses as appropriate. Quantum chemical calculations have been employed to interpret the nature of the U–S bonding interactions across these U(III) and U(IV) complexes
Photothermal Conversion Recycling of Commercial Polystyrene Plastic
No full textPhotothermal conversion can promote plastic depolymerization (chemical recycling)
through light-to-heat conversion. The highly localized temperature gradient on
photothermal agent surface allows selective heating with spatial controls not observed
with bulk heating. However, identifying practical photothermal agents that are easily
incorporated and reusable can be challenging. Interestingly, the rarely recycled black
plastics containing carbon black is a potential candidate for photothermal conversion
recycling. Herein, we use photothermal conversion to depolymerize commercial
polystyrene plastics back into styrene monomers using the pigment in black plastics.
Synthesized polystyrene-carbon black composites were depolymerized under white LED
light irradiation, producing styrene monomer in up to 60 % yield. We demonstrate the
recyclability of monomer and carbon black for a fully circular plastics economy.
Ultimately, commercial black polystyrene samples are successfully converted to styrene
through photothermal depolymerization without additional additives, with yields up to
70 % under focused solar irradiation in just 5 minutes. Broadly, this sustainable method
holds the potential to actualize a closed-loop economy of black plastics
Chain-Growth Synthesis of Extensively Cross-Conjugated Polyenes via Strained [3]Cumulenes
No full textFor years, polyenes with an extensively cross-conjugated backbone have fascinated chemists by their unique opto-electronic properties and reactivities, but so far only short oligomers (≤ 12 vinylene units) are available through multi-step assembly of vinylic building blocks. Here, we report a single-step chain-growth approach that streamlines the synthesis of cross-conjugated polyenes with up to 86 consecutive vinylene units averaged per chain and well-defined end groups. This method highlights a key interaction between an organocopper species with a strained [3]cumulene, unlocking a previously unknown 2,3-polymerization pathway. The resulting polyenes display decent two-photon-absorption capacity without compromising visible transparency, facilitating visible range two-photon lithography with sub-diffraction-limit resolution
Teaching Softness of Polymer Microgels Employing Atomic Force Microscopy
No full textStudying the properties of soft nanoparticles exposes students to emerging trends in materials science, fosters interdisciplinary knowledge, and prepares them for their own contributions in both academic and industrial settings. We developed a laboratory atomic force microscopy (AFM) experiment using poly-N -isopropylacrylamide (PNI- PAM) microgels and investigated single nanogels as well as monolayers by AFM and quantitative image analysis. The experiments show how soft nanogels are deformed at interfaces and the students learn to quantify the deformation by quantitative analysis of height and phase images. The deformation is related to a core-corona type of crosslinker distribution inside the microgel. Further experiments address the structure of microgel monolayers and demonstrate structural transitions from a hexagonal phase of microgels in corona-corona contact toward a different regime at higher interfacial concentrations in which microgels form a second hexagonal phase in core-core contact. A quantitative analysis of height images provides the distribution of nearest-neighbor distances. The students use dip-coating to prepare the samples and learn how to correlate AFM exper- iments in the dry state, i.e., at the solid/air interface after evaporation of the solvent, with properties of the microgel in bulk solution, and at the water/air interface
Thermal Fluctuations and Framework Flexibility of IRMOF-1 upon CH4 and CO2 Adsorption
No full textFlexibility of metal-organic frameworks (MOFs) plays an important role in their applications for adsorption separations, energy and gas storage, and drug delivery. Here, we demonstrate that thermal fluctuations and flexibility of the host framework affect adsorption of guest molecules, which in turn exert a significant adsorption stress, up to 0.1 GPa, on the framework causing its deformation. We find that in contrast with expected gradual swelling during adsorption, framework deformation is non-monotonic with sharp contraction during the pore filling followed by partial expansion. As an important example, we study adsorption of CH4, and CO2 on iso-reticular IRMOF-1 crystal at different temperatures using an original computational scheme of iterative grand canonical Monte Carlo (GCMC) and isothermal-isobaric ensemble molecular dynamics (NPT-MD) simulations. The effects or non-monotonic framework flexibility are confirmed by quantitative agreement with adsorption experiments and are expected to be characteristic to different degrees to other MOFs
Chiral Symmetry Breaking in Colloidal Metal Nanoparticle Solutions by Circularly Polarized Light
No full textShape symmetry breaking in the formation of inorganic nanostructures is of large current interest. It was typically achieved through growth of colloidal nanoparticles with adsorbed chiral molecules. Photochemical processes induced through asymmetric plasmon excitation by circularly polarized light in surface immobilized nanostructures also led to symmetry breaking. Here we show that chiral symmetry breaking can be achieved on randomly rotating gold@silver core-shell nanobars in colloidal solution, by means of circularly polarized illumination, where orientational averaging does not eliminate the symmetry breaking of an asymmetric plasmon-induced galvanic replacement reaction. Different morphological effects that are produced by circularly vs. linearly polarized light illumination demonstrate the intricate effect of light polarization on the localized plasmonic-induced photochemical response. The symmetry breaking becomes smaller in more symmetric geometrical shapes such as triangular nanoprisms and nanocubes, down to zero in spherical ones. The symmetry breaking rises when the nanobars are immobilized on a substrate and illuminated from a single direction
Fluorogenic detection of cyanide ions in pure aqueous media through intramolecular crossed-benzoin reaction: limitations unveiled and possible solutions
No full textReaction-based fluorogenic sensing of lethal cyanide anion in aqueous matrices remains a big challenge. We have revisited the approach proposed by the Kim group (Chem. Commun. 2015, 51, 7709-7712) and highlighted its limitations related to poor aqueous stability of probes and impossibility to achieve molecular amplification despite the assumed catalytic activation mechanism. Self-immolative linker strategies were considered to obtain usable cyanide-responsive chemodosimeters and statistical analyses of fluorescence data have been deepened to accurately delineate their sensing performances, especially limit of detection (LOD)
How Hot Plasmonic Heating Can Be: Phase Transition and Melting of P25 TiO2 from Plasmonic Heating of Au Nanoparticles
No full textPlasmonic heating has been utilized in many applications, including photocatalysis, photothermal therapy, and photocuring. However, the heat dissipation process of the plasmonic nanoparticles (NPs) and the surrounding matrix is complex. How high the temperature of the matrix that surrounds the plasmonic NPs, such as the catalyst and substrate, can be reached is unclear. Herein, we study the dissipation of plasmonic heat generated by resonantly excited gold (Au) NPs dispersed on P25 TiO2 NP porous film in air. Under resonant 532 nm continuous wave (CW) laser irradiation at the surface of the Au-TiO2, the surface evaporation and the aggregation of Au NPs were observed at moderate laser power (10 mW/um2). This process is accompanied by the phase transition of TiO2. More importantly, the TiO2 nanoparticle film melted, forming melt pools and molten TiO2 matrix. This indicates that the temperature of the TiO2 reached as high as its melting point of 1830 °C. When Au/TiO2 was irradiated with an off-resonance laser at 638 nm, no phase transformation or melting of TiO2 was observed. The temperature calculation showed that the heating generated by Au NPs is not localized. The collective heating from an ensemble of Au NPs in the irradiated area produced a global temperature rise that melted TiO2. Our results suggest that the photothermal effect could be a significant mechanism in the plasmon-assisted photocatalytic reactions. The melting of the supporting metal oxide film by plasmonic heating at relatively low laser power suggests new applications for utilizing plasmonic heating, such as additive manufacturing
Chiral N-Hydroxyalkyl Pyrid-2-ylidenes: a new class of ligand for Copper-Catalyzed Asymmetric Allylic Alkylation
No full textA new class of chiral N-Heterocyclic Carbenes derived from pyridine, namely N-hydroxyalkyl pyrid-2-ylidenes, was developed. Capitalizing the exceptional steric and electronic features of pyrid-2-ylidene core with the presence of the chiral hydroxyalkyl-chelating arm on the nitrogen-atom, these ligands demonstrated high performances in copper-catalyzed asymmetric allylic alkylation of dialkylzincs to various allylic or dienic phosphates with excellent gamma-selectivity (>98%) and enantioselectivity (up to 95% ee). Importantly, the catalyst loading can be decreased below to 0.5 mol% without any loss of catalyst efficiency, thus outperforming N-hydroxyalkyl imidazoline-2-ylidene congeners. Moreover, thanks to the versatile post-transformation of resulting enantioenriched skipped 1,4-dienes, various relevant building blocks were synthesized, notably a key intermediate in the total synthesis of (+) Phorbasin C. Furthermore, by involving a transient oxazolidine, which acts as a masked carbene before the insertion of the metal center, a well-defined but air-sensitive N-hydroxyalkyl pyrid-2-ylidene copper(I) chloride complex was isolated. Deuteration experiments and computational studies provided valuable insights about the formation of the oxazolidine and the corresponding copper complex
A water playground for re-assembly from fibrils to plates
No full textShort-peptide amyloid assembly and disassembly play crucial roles in various research fields, which range from addressing pathologies that lack therapeutic solutions to the development of innovative soft (bio)materials. Hydrogels from short peptides typically show thermo-reversible gel-to-sol transition, whereby fibrils disassemble upon heating, and re-assemble upon cooling down to room temperature (rt). Despite ongoing intense research studies in this area, the majority focus on peptide-peptide interaction and neglect the structuring role of water in peptide supramolecular behavior. This study describes an unprotected tetrapeptide gelator that forms highly stable fibrils which, upon heating, re-organize into plates that persist upon cooling to rt. All-atom molecular dynamics (MD) simulations and experimental methods reveal water as a key player in the thermodynamics that accompany this irreversible morphological transition, and advance our understanding of supramolecular structures