Synthesis and Reactivity of a Cyclooctatetraene-Like Polyphosphorus Ligand Complex [Cyclo-P8]

The thermolysis of Cp′′′Ta(CO)₄ with white phosphorus (P₄) gives access to [{Cp′′′Ta}₂(μ,η^{2 : 2 : 2 : 2 : 1 : 1}-P₈)] ( A ), representing the first complex containing a cyclooctatetraene-like (COT) cyclo-P₈ ligand. While ring sizes of n >6 have remained elusive for cyclo-P_n structural motifs, the choice of the transition metal, co-ligand and reaction conditions allowed the isolation of A . Reactivity investigations reveal its versatile coordination behaviour as well as its redox properties. Oxidation leads to dimerization to afford [{Cp′′′Ta}₄(μ₄,η^{2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1}-P₁₆)][TEF]₂ ( 4 , TEF=[Al(OC{CF₃}₃)₄]⁻). Reduction, however, leads to the fission of one P−P bond in A followed by rapid dimerization to form [K@[2.2.2]cryptand]₂[{Cp′′′Ta}₄(μ₄,η^{2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1}-P₁₆)] ( 5 ), which features an unprecedented chain-type P₁₆ ligand. Lastly, A serves as a P₂ synthon, via ring contraction to the triple-decker complex [{Cp′′′Ta}₂(μ,η^{6 : 6}-P₆)] ( B ).     

Upcycling of Polybutadiene Facilitated by Selenium-Mediated Allylic Amination

Accumulation of end-of-life plastics presents ongoing environmental concerns. One strategy to solve this grand challenge is to invent new techniques that modify post-consumer waste and impart new functionality. While promising approaches for the chemical upcycling of commodity polyolefins and polyaromatics exist, analogous approaches to repurpose unsaturated polymers (e.g., polybutadiene) are scarce. In this work, we propose a method to upcycle polybutadiene, one of the most widely used commercial rubbers, via a mild, metal-free allylic amination reaction. The resulting materials have tunable thermal and surface wetting properties as a function of both sulfonamide identity and grafting density. Importantly, this approach maintains the parent alkene microstructure without evidence of olefin reduction, olefin transposition, and/or chain scission. Based on these findings, we anticipate future applications in the remediation of complex elastomers and vulcanized rubbers.     

Differentiating between Acidic and Basic Surface Hydroxyls on Metal Oxides by Fluoride Substitution: A Case Study on Blue TiO2 from Laser Defect Engineering

Both oxygen vacancies and surface hydroxyls play a crucial role in catalysis. Yet, their relationship is not often explored. Herein, we prepare two series of TiO₂ (rutile and P25) with increasing oxygen deficiency and Ti³⁺ concentration by pulsed laser defect engineering in liquid (PUDEL), and selectively quantify the acidic and basic surface OH by fluoride substitution. As indicated by EPR spectroscopy, the laser-generated Ti³⁺ exist near the surface of rutile, but appear to be deeper in the bulk for P25. Fluoride substitution shows that extra acidic bridging OH are selectively created on rutile, while the surface OH density remains constant for P25. These observations suggest near-surface Ti³⁺ are highly related to surface bridging OH, presumably the former increasing the electron density of the bridging oxygen to form more of the latter. We anticipate that fluoride substitution will enable better characterization of surface OH and its correlation with defects in metal oxides.     

The Highly Controlled and Efficient Polymerization of Ethylene

The highly controlled and efficient polymerization of ethylene is a very attractive but challenging target. Herein we report on a Coordinative Chain Transfer Polymerization catalyst, which combines a high degree of control and very high activity in ethylene oligo- or polymerization with extremely high chain transfer agent (triethylaluminum) to catalyst ratios (catalyst economy). Our Zr catalyst is long living and temperature stable. The chain length of the polyethylene products increases over time under constant ethylene feed or until a certain volume of ethylene is completely consumed to reach the expected molecular weight. Very high activities are observed if the catalyst elongates 60 000 or more alkyl chains and the polydispersity of the strictly linear polyethylene materials obtained are very low. The key for the combination of high control and efficiency seems to be a catalyst stabilized by only one strongly bound monoanionic N-ligand.     

Nanostructure-Driven Indocyanine Green Dimerization Generates Ultra-Stable Phototheranostics Nanoparticles

Indocyanine green (ICG) is the only near-infrared (NIR) dye approved for clinical use. Despite its versatility in photonic applications and potential for photothermal therapy, its photobleaching hinders its application. Here we discovered a nanostructure of dimeric ICG (Nano-dICG) generated by using ICG to stabilize nanoemulsions, after which ICG enabled complete dimerization on the nanoemulsion shell, followed by J-aggregation of ICG-dimer, resulting in a narrow, red-shifted (780 nm→894 nm) and intense (≈2-fold) absorbance. Compared to ICG, Nano-dICG demonstrated superior photothermal conversion (2-fold higher), significantly reduced photodegradation (−9.6 % vs. −46.3 %), and undiminished photothermal effect (7 vs. 2 cycles) under repeated irradiations, in addition to excellent colloidal and structural stabilities. Following intravenous injection, Nano-dICG enabled real-time tracking of its delivery to mouse tumors within 24 h by photoacoustic imaging at NIR wavelength (890 nm) distinct from the endogenous signal to guide effective photothermal therapy. The unprecedented finding of nanostructure-driven ICG dimerization leads to an ultra-stable phototheranostic platform.     

Neutralizing the Impact of the Virulence Factor LecA from Pseudomonas aeruginosa on Human Cells with New Glycomimetic Inhibitors

Bacterial adhesion, biofilm formation and host cell invasion of the ESKAPE pathogen Pseudomonas aeruginosa require the tetravalent lectins LecA and LecB, which are therefore drug targets to fight these infections. Recently, we have reported highly potent divalent galactosides as specific LecA inhibitors. However, they suffered from very low solubility and an intrinsic chemical instability due to two acylhydrazone motifs, which precluded further biological evaluation. Here, we isosterically substituted the acylhydrazones and systematically varied linker identity and length between the two galactosides necessary for LecA binding. The optimized divalent LecA ligands showed improved stability and were up to 1000-fold more soluble. Importantly, these properties now enabled their biological characterization. The lead compound L2 potently inhibited LecA binding to lung epithelial cells, restored wound closure in a scratch assay and reduced the invasiveness of P. aeruginosa into host cells.     

Facile Synthesis of an Octagermacubane with Two Three-Coordinate Germanium(0) Atoms and its Unique Radical Anion

Thermolysis of a 1 : 1 mixture of tris(di-tert-butylmethylsilyl)germane 9 and bis(di-tert-butylmethylsilyl)germane 17 at 100 °C produces unexpectedly octagermacubane 18 , having two 3-coordinate Ge⁰ atoms (40 % yield). 18 was characterized by X-ray crystallography and it is a singlet biradical (according to DFT quantum mechanical calculations and the absence of an EPR signal). Reactions of 18 with CH₂Cl₂ and H₂O yield the novel dichloro-octagermacubane 24 and hydroxy-octagermacubane 25 , respectively. Reduction of 18 with tBuMe₂SiNa in THF produces an isolable octagermacubane radical anion 26-Na . Based on X-ray crystallography, EPR spectroscopy and DFT quantum mechanical calculations, 26-Na is classified as a Ge-centered radical anion.     

Molecular versus Silica-Supported Iridium Water Oxidation Catalysts

A stringent comparison between two pairs of molecular/immobilized water oxidation catalysts ([Cp^*Ir(Me-pica)Cl], 1 , versus 1_SiO₂ , Me-pica=κ²-N-methyl-picolinamide; [Cp^*Ir(pysa)NO₃], 2 , versus 2_SiO₂ , pysa=κ²-pyridine-2-sulfonamide]) reveals distinctive catalytic trends. While the molecular compound 1 exhibits a substantial higher activity than the analogous immobilized system 1_SiO₂ , under all the experimental conditions explored, the contrary is found with 2 that is far less active than its immobilized counterpart 2_SiO₂ . This is explained by the unique tendency of 2 to form dimeric complexes [Cp^*Ir-(κ²-μ₂-Hpysa)(κ²-μ₂-pysa)IrCp^*], 2 a , in phosphate buffered solution at pH 7, and [Cp^*Ir-(κ²-μ₂-Hpysa)₂IrCp^*], 2 b , in water. 2 a and 2 b have been completely characterized in solution by multinuclear and multidimensional NMR spectroscopy. They have been also isolated as single crystals and their structure in solid state determined by X-Ray diffractometry. 2 a and 2 b appear to be off-cycle species, whose formation is detrimental for water oxidation activity, as indicated by the observation of a long induction period when 2 a is used as catalytic precursor. In addition, TOF versus ΔE (E−E⁰=−RT/nF ln([IO₄⁻]/[IO₃⁻]) trends for the first two runs do not overlap for catalyst 2 and TOF_max is remarkably higher in the second run upon the addition of fresh NaIO₄. In the immobilized system 2_SiO₂ the detrimental associative processes are likely inhibited leading to an activity higher than that of 2 .     

Nitraza-/Oxa-Propylene- and Hydrazonemethylene-Bridged 1,2,4-Nitraminotriazoles and Selected Salts

Two new bridged nitraminotriazoles with bridging oxapropylene and nitrazapropylene moieties were synthesized, and converted into several salts, as well as from the hydrazonemethylene bridged nitraminotriazole. All compounds were fully characterized by NMR and IR spectroscopy, elemental analysis as well as differential thermal analysis. The sensitivity towards friction and impact were determined according to BAM standard technics and the energetic properties were calculated by using the EXPLO5 computer code. The neutral compounds as well as the various salts were examined in terms of their physicochemical properties and detonation performance to each other and compared to the commonly used secondary explosive RDX.     

Ternary eluent compositions in supercritical fluid chromatography improved fingerprinting of therapeutic peptides

Currently, little information has been published on the application of ternary eluent compositions in supercritical fluid chromatography for separating peptides. This work investigates the benefits of adding acetonitrile to methanol as the modifier. Three cyclic antibiotic peptides (bacitracin, colistin, and daptomycin) ranging between 1000 and 2000 Da were chosen as model substances. The ternary mixture of carbon dioxide, methanol, and acetonitrile is optimized to increase the resolution of the peptide's fingerprint. In addition, varying compositions of methanol and acetonitrile were found to change the elution order of the analytes, which is a valuable tool during method development. An individual gradient method using two Torus 2-PIC columns (each 100 × 3.0 mm, 1.7 μm), carbon dioxide, and a modifier consisting of acetonitrile/methanol/water/methanesulfonic acid (60:40:2:0.1, v:v:v:v) was optimized for each of the peptides. Subsequently, a generic method development protocol applicable to polypeptides is proposed.