Formation of Tc metal in 12 M HCl using Zn as a reductant

Amorphous TcO₂ and NH₄TcO₄ solubilized into 12 M HCl will spontaneously convert to hexachlorotechnetate (TcCl₆ ^2?). This process is accelerated upon heating but species lower than Tc(IV) are not generated by this action. TcCl₆ ^2? is kinetically unstable with regards to formation in solutions of low concentrations of HCl and will spontaneously convert back to soluble and insoluble forms of Tc(IV) in water. TcCl₆ ^2? in 12 M HCl placed in contact with the reducing metal Zn at elevated temperatures (90 °C) forms a black precipitate that contains amorphous Tc metal, TcO₂, and oxy-chlorides of Tc. Powder X-ray diffraction indicates the presence of Tc metal after thermal treatment where X-ray absorption fine structure spectroscopy indicates the presence of hexagonal Tc metal and amorphous TcO₂ in the precipitate after rinsing with 12 HCl but before thermal treatment. The resulting solution contains a mixture of Tc chlorides and oxy-chlorides following reduction where TcCl₆ ^2? is completely consumed resulting primarily in Tc₂OCl₁₀ ^4? dominating the UV–visible spectra. Reducing the solution volume and reconstituting the products into 12 M HCl while boiling the mixed solution (>24 h) will slowly convert all soluble Tc back to TcCl₆ ^2?. Expanding on previous efforts made in this laboratory to recover Tc metal from aqueous solution, we investigate its synthesis when Tc(IV) and Tc(VII) in 12 M HCl is placed in contact with the reducing metal (i.e., Zn) at elevated temperatures.     

Tetronic Acids and Derivatives Part VIII (1) o-Alkylation of 3-Unsubstituted Tetronic Acids

4-methoxy-(5H)-furan-2-ones 1 are useful starting materials for the synthesis of naturally occuring lactones². In a previous communication we have described an efficient entry to 4-alkoxy-(5H)-furan-2-ones 1–3 (alkyl tetronates) by lactonization of ethyl 4-acetoxy 3-ketoesters 4 using hydrochloric acid in several alcohols¹. The detection of 4-hydroxy-(5H)-furan-2-ones 5 (tetronic acids) during the reaction course³ allowed us to postulate them as intermediates which were subsequently etherified to the products 1–3. In a very recent communication⁴, it was claimed that attempted alkylation of tetronic acids 5 using HC1 in an alcohol or alkyl halides on tetronic acids sodium salts are unsuccessful; moreover, the structure of our compounds 1–3 was questionned by arguing that isomeric 2-alkylated materials     

Technique for characterization of dimensional changes in slanted holographic gratings by monitoring the angular selectivity profile

A method has been developed for retrieving the complete angular selectivity profile of transmission holographic gratings in one step. The method is applied to study in real time the shrinkage and changes in the effective optical thickness of a slanted holographic grating recorded in an acrylamide-based photopolymer. It can form the basis of a holographic sensor of analytes that cause a thickness change in the holographic medium. It can also be useful for the study and optimization of holographic recording materials and for quality control during production of holographic optical elements.     

Internal representation of hierarchical sequences involves the default network

Background  

The default network is a set of brain regions that exhibit a reduction in BOLD response during attention-demanding cognitive tasks, and distinctive patterns of functional connectivity that typically include anti-correlations with a fronto-parietal network involved in attention, working memory, and executive control. The function of the default network regions has been attributed to introspection, self-awareness, and theory of mind judgments, and some of its regions are involved in episodic memory processes.     

Photodynamic Priming Overcomes Per- and Polyfluoroalkyl Substance (PFAS)-Induced Platinum Resistance in Ovarian Cancer†

Per- and polyfluoroalkyl substances (PFAS) are widespread environmental contaminants linked to adverse outcomes, including for female reproductive biology and related cancers. We recently reported, for the first time, that PFAS induce platinum resistance in ovarian cancer, potentially through altered mitochondrial function. Platinum resistance is a major barrier in the management of ovarian cancer, necessitating complementary therapeutic approaches. Photodynamic therapy (PDT) is a light-based treatment modality that reverses platinum resistance and synergizes with platinum-based chemotherapy. The present study is the first to demonstrate the ability of photodynamic priming (PDP), a low-dose, sub-cytotoxic variant of PDT, to overcome PFAS-induced platinum resistance. Comparative studies of PDP efficacy using either benzoporphyrin derivative (BPD) or 5-aminolevulinic acid-induced protoporphyrin IX (PpIX) were conducted in two human ovarian cancer cell lines (NIH:OVCAR-3 and Caov-3). BPD and PpIX are clinically approved photosensitizers that preferentially localize to, or are partly synthesized in, mitochondria. PDP overcomes carboplatin resistance in PFAS-exposed ovarian cancer cells, demonstrating the feasibility of this approach to target the deleterious effects of environmental contaminants. Decreased survival fraction in PDP + carboplatin treated cells was accompanied by decreased mitochondrial membrane potential, suggesting that PDP modulates the mitochondrial membrane, reducing membrane potential and re-sensitizing ovarian cancer cells to carboplatin.     

Trimethylsilyl Chloride Aids in Solubilization of Oxidative Addition Intermediates from Zinc Metal

Trimethylsilyl chloride (TMSCl) is commonly used to “activate” metal(0) powders toward oxidative addition of organohalides, but knowledge of its mechanism remains limited by the inability to characterize chemical intermediates under reaction conditions. Here, fluorescence lifetime imaging microscopy (FLIM) overcomes these prior limitations and shows that TMSCl aids in solubilization of the organozinc intermediate from zinc(0) metal after oxidative addition, a previously unknown mechanistic role. This mechanistic role is in contrast to previously known roles for TMSCl before the oxidative addition step. To achieve this understanding, FLIM, a tool traditionally used in biology, is developed to characterize intermediates during a chemical reaction—thus revealing mechanistic steps that are unobservable without fluorescence lifetime data. These findings impact organometallic reagent synthesis and catalysis by providing a previously uncharacterized mechanistic role for a widely used activating agent, an understanding of which is suitable for revising activation models and for developing strategies to activate currently unreactive metals.