New Polyoxometalates Containing Hybrid Polymers and Their Potential for Nano‐Patterning

Two new polyoxometalate (POM)‐based hybrid monomers (Bu₄N)₅(H)[P₂V₃W₁₅O₅₉{(OCH₂)₃CNHCO(CH₃)C?CH₂}] ( 2 ) and (S(CH₃)₂C₆H₄OCOC(CH₃)=CH₂)₆[PVMo₁₀O₄₀] ( 5 ) were developed by grafting polymerizable organic units covalently or electrostatically onto Wells–Dawson and Keggin‐type clusters and were characterized by analytical and spectroscopic techniques including ESI‐MS and/or single‐crystal X‐ray diffraction analyses. Radical initiated polymerization of 2 and 5 with organic monomers (methacryloyloxy)phenyldimethylsulfonium triflate (MAPDST) and/or methylmethacrylate (MMA) yielded a new series of POM/polymer hybrids that were characterized by ¹H, ³¹P NMR and IR spectroscopic techniques, gel‐permeation chromatography as well as thermal analyses. Preliminary tests were conducted on these POM/polymer hybrids to evaluate their properties as photoresists using electron beam (E‐beam)/extreme ultraviolet (EUV) lithographic techniques. It was observed that the POM/polymer hybrid of 2 with MAPDST exhibited improved sensitivity under EUV lithographic conditions in comparison to the MAPDST homopolymer resist possibly due to the efficient photon harvesting by the POM clusters from the EUV source.     

Chemoselective and Site‐Selective Lysine‐Directed Lysine Modification Enables Single‐Site Labeling of Native Proteins

The necessity for precision labeling of proteins emerged during the efforts to understand and regulate their structure and function. It demands selective attachment of tags such as affinity probes, fluorophores, and potent cytotoxins. Here, we report a method that enables single‐site labeling of a high‐frequency Lys residue in the native proteins. At first, the enabling reagent forms stabilized imines with multiple solvent‐accessible Lys residues chemoselectively. These linchpins create the opportunity to regulate the position of a second Lys‐selective electrophile connected by a spacer. Consequently, it enables the irreversible single‐site labeling of a Lys residue independent of its place in the reactivity order. The user‐friendly protocol involves a series of steps to deconvolute and address chemoselectivity, site‐selectivity, and modularity. Also, it delivers ordered immobilization and analytically pure probe‐tagged proteins. Besides, the methodology provides access to antibody‐drug conjugate (ADC), which exhibits highly selective anti‐proliferative activity towards HER‐2 expressing SKBR‐3 breast cancer cells.     

Molecular‐Recognition‐Assisted pKa Shifts and Metal‐Ion‐Induced Fluorescence Regeneration in p‐Sulfonatocalix[6]arene‐Encapsulated Acridine

The host–guest interactions of cationic (AcH⁺) and neutral (Ac) forms of the dye acridine with the macrocyclic host p‐sulfonatocalix[6]arene (SCX6) were investigated by using ground‐state absorption, steady‐state and time‐resolved fluorescence, and NMR measurements. The cationic form undergoes significant complexation with SCX6 (K_eq=2.5×10⁴ M ^?1), causing a sharp decrease in the fluorescence intensity and severe quenching in the excited‐state lifetime of the dye. The strong binding of the AcH⁺ form of the dye with SCX6 is attributed to ion–ion interactions involving the sulfonato groups (SO₃^?) of SCX6 and the positively charged AcH⁺ at pH of approximately 4.3. Whereas, the neutral Ac form of the dye undergoes weak complexation with SCX6 (K_eq=0.9×10³ M ^?1) and the binding constant is lowered by one order of magnitude compared with that of the SCX6–AcH⁺ system. The strong affinity of SCX6 to the protonated form leads to a large upward pK_a shift (≈2 units) in the dye. In contrast, strong emission quenching upon SCX6 interaction and the regeneration of fluorescence intensity of the dye in the presence of Gd³⁺ through competitive binding have also been demonstrated.     

A macrocyclic piperazine linked extremely Zn selective fluorescent chemosensor with bio-imaging and for H2PO4 sensing

A new macrocyclic fluorescent chemosensor piperazine coupled diimine phenol (PCDP) which forms extremely selective Zn(II) complex and thus builds up the platform for H₂PO₄⁻ (DHP) sensing in mixed aqueous medium, has been designed and synthesized. The binding of PCDP with Zn²⁺ and its displacement by DHP have been supported by DFT studies. The blue fluorescence in the PCDP–Zn complex is useful for bio-imaging. The fluorescence enhancement of PCDP on association with Zn²⁺ ion is quenched sharply in the presence of intracellular DHP.     

Gap modes due to impurity pairs in ki

The pair modes due to Cl^?, Br^?, Na⁺W and Rb^v impurities in KI have been investigated using the Greens function technique. Group theory is used to put the final results as solutions of (2 × 2) determinants which could be tried by a hand calculator. Even a mass defect approximation reproduced the gap modes due to chlorine pairs, but in all cases a small change in the force constant, deduced from fitting single impurity gap modes, was used. The Raman active modes in all these cases were also computed.     

Enantioselective H-atom transfer reaction: a strategy to synthesize formaldehyde aldol products

[reaction: see text] Enantioselective radical alkylation of Baylis-Hillman adducts furnished aldol products in good yield and selectivity. The results illustrate that the selectivity in the hydrogen atom transfer is dependent on the size of the ester substituent, with smaller substituents providing better enantioselectivity.     

Oxidative C-H activation/C-C bond forming reactions: synthetic scope and mechanistic insights

This paper describes a new palladium-catalyzed method for C-H activation/carbon-carbon bond formation with hypervalent iodine arylating agents. This transformation has been applied to a variety of arene and benzylic substrates containing different directing groups (pyridines, quinolines, oxazolidinones, and amides) and proceeds with high levels of regiocontrol. Mechanistic experiments provide preliminary evidence in support of an unusual mechanism for this transformation involving a Pd(II)/Pd(IV) catalytic cycle.     

Structural evidence for the radical scavenging mechanism of some aminothiol group of radioprotectants

Aminothiols constitute an important group of radioprotectants. The structures of a few well-known compounds belonging to the family of radioprotectants have been determined by single crystal x-ray diffraction methods. The sulphur and the amino nitrogen atoms are separated by two tetrahedral carbon atoms in these compounds. Thegauche conformation of the sulphur and the nitrogen atoms and the consequent non-bonded intramolecular S … N interaction observed in some of the crystal structures appear to favour the hypothesis that the protective mechanism of these compounds is by free radical scavenging.