Effect of Ligand Fields on the Reactivity of O2‐Activating Iron(II)‐Benzilate Complexes of Neutral N5 Donor Ligands

Three new iron(II)‐benzilate complexes [(N4Py)Fe^II(benzilate)]ClO₄ ( 1 ), [(N4Py^Me2)Fe^II(benzilate)]ClO₄ ( 2 ) and [(N4Py^Me4)Fe^II(benzilate)]ClO₄ ( 3 ) of neutral pentadentate nitrogen donor ligands have been isolated and characterized to study their dioxygen reactivity. Single‐crystal X‐ray structures reveal a mononuclear six‐coordinate iron(II) center in each case, where benzilate binds to the iron center in monodentate mode via one carboxylate oxygen. Introduction of methyl groups in the 6‐positions of the pyridine rings makes the N4Py^Me2 and N4Py^Me4 ligand fields weaker compared to that of the parent N4Py ligand. All the complexes ( 1 – 3 ) react with dioxygen to decarboxylate the coordinated benzilate to benzophenone quantitatively. The decarboxylation is faster for the complex of the more sterically hindered ligand and follows the order 3 > 2 > 1 . The complexes display oxygen atom transfer reactivity to thioanisole and also exhibit hydrogen atom transfer reactions with substrates containing weak C?H bonds. Based on interception studies with external substrates, labelling experiments and Hammett analysis, a nucleophilic iron(II)‐hydroperoxo species is proposed to form upon two‐electron reductive activation of dioxygen by each iron(II)‐benzilate complex. The nucleophilic oxidants are converted to the corresponding electrophilic iron(IV)‐oxo oxidant upon treatment with a protic acid. The high‐spin iron(II)‐benzilate complex with the weakest ligand field results in the formation of a more reactive iron‐oxygen oxidant.     

Time resolved fluorescence and anisotropy of 1-pyrene butyric acid and pyranine as probes of solvent organization in sucrose solutions

The microenvironment of solute-solvent interactions in aqueous sucrose solutions, ranging from 0 to 80 wt% in concentration, was investigated using time resolved fluorescence techniques. The fluorescence lifetimes and rotational correlation times of the trace fluorescent probes, PBA (1-pyrene butyric acid) and pyranine (trisodium 8-hydroxy-1,3,6-pyrenetrisulfonate), were measured in sucrose solutions. The behavior of the fluorescence lifetimes and the increase in the rotational correlation times with increasing sucrose concentration provided no evidence for the formation of water exclusive solute clusters in the metastable solutions. Instead, the results indicated the formation of a network of hydrogen bonding interactions between dispersed sucrose molecules.     

Arginyltransferase is an ATP-independent self-regulating enzyme that forms distinct functional complexes in vivo

Posttranslational arginylation mediated by arginyl transferase (ATE1) plays an important role in cardiovascular development, cell motility, and regulation of cytoskeleton and metabolic enzymes. This protein modification was discovered decades ago, however, the arginylation reaction and the functioning of ATE1 remained poorly understood because of the lack of good biochemical models. Here, we report the development of an in vitro arginylation system, in which ATE1 function and molecular requirements can be tested using purified recombinant ATE1 isoforms supplemented with a controlled number of components. Our results show that arginylation reaction is a self-sufficient, ATP-independent process that can affect different sites in a polypeptide and that arginyl transferases form different molecular complexes in vivo, associate with components of the translation machinery, and have distinct, partially overlapping subsets of substrates, suggesting that these enzymes play different physiological functions.     

Ionic liquid integrated polyethylene glycol (PEG)-based quasi-solid electrolyte for efficiency enhancement of dye-sensitized solar cell

Journal of Solid State Electrochemistry - We are presenting herein the effect of using three different cell electrolytes namely: (a) propylene carbonate containing 0.2 M LiI and...     

Efficient enantioselective synthesis of (+)-sclareolide and (+)-tetrahydroactinidiolide: chiral LBA-induced biomimetic cyclization

An efficient enantioselective synthesis of the lactones (+)-sclareolide and (+)-tetrahydroactinidiolide has been achieved through Lewis acid-assisted chiral Brønsted acid-induced enantioselective cyclization of terpenic carboxylic acids. The reaction sequence involved the [2,3] sigmatropic rearrangement of an allylic alcohol and biomimetic cyclization of terpenic acid in the presence of (R)-2-benzyloxy-2′-hydroxy-1,1′-binaphthyl and tin tetrachloride as key steps. The cyclization gave lactones in good yield and with high enantiomeric excess.     

Rational Syntheses of CdII and PbII Metal‐Organic Frameworks for Luminescence Sensing of Nitroaromatics,Ferric and Chromate Ions

The metal‐organic frameworks (MOFs), {[Cd(L)(H₂O)] · CH₃OH · DMF} ( 1 ) and [Pb(L)(DMF)] ( 2 ) (L = 2,4‐dihydroxybenzaldehyde nicotinoylhydrazone), were synthesized and characterized using microanalyses, IR spectroscopy, and single‐crystal X‐ray diffraction. Single crystal X‐ray analyses revealed that both 1 and 2 exhibit 2D grid networks. The photoluminescence investigation indicates that 1 and 2 could be a prospective candidate for developing luminescencent sensors for the selective sensing of nitrobenzene, which is used as a precursor for explosives. The luminescent properties of 1 and 2 in different solvents were investigated and corroborated by theoretical calculations. Additionally compounds 1 and 2 also show selective sensing ability for Fe³⁺ as well as for CrO₄^2– ions.     

A Self-Replicating Peptide under Ionic Control

The chemical coupling of two peptide fragments to give the peptide K1 K2 (shown in the helical wheel diagram on the right) is autocatalytic at high NaClO₄ concentrations (1 M ). Under these conditions K1 K2 assumes a coiled-coil conformation, which can function as a template for the coupling. Autocatalysis is not observed under conditions that prevent formation of the coiled-coil conformation.     

Zinc(II) complexes derived from di-2-pyridyl ketone N-phenyl-3-semicarbazone: Crystal structures and spectral studies

Six zinc(II) complexes, Zn(HL)Br₂ (1), Zn(HL)Cl₂ (2), ZnL(OAc) (3), ZnLN₃ (4), ZnL₂ (5) and ZnL₂ · H₂O (6), have been synthesized and characterized by different physicochemical techniques. Complex 1 is five coordinated and has a distorted square pyramidal geometry. Complexes 5 and 6 are six coordinated and have distorted octahedral geometries. In complexes 1 and 2, the ligand moieties are coordinated in the neutral form (HL), and in the other complexes they are monoanionic (L⁻).