Probing the Nature of Zinc in Copper-Zinc-Zirconium Catalysts by Operando Spectroscopies for CO2 Hydrogenation to Methanol

Active Zn species in Cu-based methanol synthesis catalysts have not been clearly identified yet due to their complex nature and dynamic structural changes during reactions. Herein, atomically dispersed Zn on ZrO₂ support is established in Cu-based catalysts by separating Zn and Zr components from Cu (Cu−ZnZr) via the double-nozzle flame spray pyrolysis (DFSP) method. It exhibits superiority in methanol selectivity and yield compared to those with Cu−ZnO interface and isolated ZnO nanoparticles. Operando X-ray absorption spectroscopy (XAS) reveals that the atomically dispersed Zn species are induced during the reaction due to the strengthened Zn−Zr interaction. They can suppress formate decomposition to CO and decrease the H₂ dissociation energy, shifting the reaction to methanol production. This work enlightens the rational design of unique Zn species by regulating coordination environments and offers a new perspective for exploring complex interactions in multi-component catalysts.     

Selective Deletion of the Internal Lysine Residue from the Peptide Sequence by Collisional Activation

The gas-phase peptide ion fragmentation chemistry is always the center of attraction in proteomics to analyze the amino acid sequence of peptides and proteins. In this work, we describe the formation of an anomalous fragment ion, which corresponds to the selective deletion of the internal lysine residue from a series of lysine containing peptides upon collisional activation in the ion trap. We detected several water-loss fragment ions and the maximum number of water molecules lost from a particular fragment ion was equal to the number of lysine residues in that fragment. As a consequence of this water-loss phenomenon, internal lysine residues were found to be deleted from the peptide ion. The N,N-dimethylation of all the amine functional groups of the peptide stopped the internal lysine deletion reaction, but selective N-terminal ??-amino acetylation had no effect on this process indicating involvement of the side chains of the lysine residues. The detailed mechanism of the lysine deletion was investigated by multistage CID of the modified and unmodified peptides, by isotope labeling and by energy resolved CID studies. The results suggest that the lysine deletion might occur through a unimolecular multistep mechanism involving a seven-membered cyclic imine intermediate formed by the loss of water from a lysine residue in the protonated peptide. This intermediate subsequently undergoes degradation reaction to deplete the interior imine ring from the peptide backbone leading to the deletion of an internal lysine residue.     

Anionic [4+3] heteroannulation of 2-azidoacrylates: a modular synthesis of 2-benzazepin-1-ones

2-Azidoacrylates undergo [4+3] annulation with phthalides under anionic conditions at low temperatures to furnish 5-hydroxy-2-benzazepinones, the formation of which represents a new concept for the construction of azepines as well as a new reactivity of 2-azidoacrylates.     

A Series of Amino Acid Functionalized Tripodal Hexaamide Anion Receptors: Ion‐Pair‐Assisted Capped‐Cleft Formation by a Pentafluorophenyl‐Functionalized Amide

A new series of tris(2‐aminoethyl)amine (tren)‐based L ‐alanine amino acid backboned tripodal hexaamide receptors (L1–L5) with various attached moieties based on electron‐withdrawing fluoro groups and lipophilicity have been synthesized and characterized. Detailed binding studies of L1–L5 with different anions, such as halides (F^?, Cl^?, Br^?, and I^?) and oxyanions (AcO^?, BzO^? (Bz=benzoyl), NO₃^?, H₂PO₄^?, and HSO₄^?), have been carried out by isothermal titration calorimetric (ITC) experiments in acetonitrile/dimethylsulfoxide (99.5:0.5 v/v) at 298 K. ITC titration experiments have clearly shown that receptors L1–L4 invariably form 1:1 complexes with Cl^?, AcO^?, BzO^?, and HSO₄^?, whereas L5 forms a 1:1 complex only with AcO^?. In the case of Br^?, I^?, and NO₃^?, no appreciable heat change is observed owing to weak interactions between these anions and receptors; this is further confirmed by ¹H NMR spectroscopy. The ITC binding studies of F^? and H₂PO₄^? do not fit well for a 1:1 binding model. Furthermore, ITC binding studies also revealed slightly higher selectivity of this series of receptors towards AcO^? over Cl^?, BzO^?, and HSO₄^?. Solid‐state structural evidence for the recognition of Cl^? by this new category of receptor was confirmed by single‐crystal X‐ray structural analysis of the complex of tetrabutylammonium chloride (TBACl) and L1. Single‐crystal X‐ray diffraction clearly showed that the pentafluorophenyl‐functionalized amide receptor (L1) encapsulated Cl^? in its cavity by hydrogen bonds from amides, and the cavity of L1 was capped with a TBA cation through hydrogen bonding and ion‐pair interactions to form a capped‐cleft orientation. To understand the role of the cationic counterpart in solution‐state Cl^? binding processes with this series of receptors (L1–L4), a detailed Cl^? binding study was carried out with three different tetraalkylammonium (Me₄N⁺, Et₄N⁺, and Bu₄N⁺) salts of Cl^?. The binding affinities of these receptors with different tetralkylammonium salts of Cl^? gave binding constants with the TBA cation in the following order: butyl>ethyl>methyl. This study further supports the role of the TBA countercation in ion‐pair recognition by this series of receptors.     

The synthesis of heliannuol C, an allelochemical from Helianthus annuus

The synthesis of the allelochemical heliannuol C 1 is described by employing a Bargellini condensation and a Claisen rearrangement to install the gem-dimethyl and vinyl functionalities, respectively. A Dieckmann cyclisation of diester 11 enabled the generation of the benzoxepane ring system enshrined in 1.     

Coordination chemistry of Group 12 metals with phosphorodiselenoates: syntheses, structures and VT 31P NMR study of monomer-dimer exchange equilibrium

The reactions of diselenophosphates, [dsep, (RO)2PSe2-; R = Et, (n)Pr and (i)Pr] with cadmium(II) and mercury(II) perchlorates in a 2 : 1 molar ratio formed compounds of stoichiometry M[Se2P(OR)2]2{M = Cd, R = Et (1), (n)Pr (2), (i)Pr (3); Hg, Et(4), (n)Pr (5), (i)Pr (6)}, and with zinc(II) perchlorates, chalcogen centered tetranuclear clusters, [Zn4(micro4-E){Se2P(OR)2}6]{E = Se, R = Et (7), (n)Pr (8), (i)Pr (9); E = O, R = Et (10), (n)Pr (11), (i)Pr (12)} were formed. All these complexes have been characterized with the help of analytical data, X-ray crystallography (1, 3, 6, 10, 11 and 12), and FAB-mass spectrometry (7-12). Compound 1 is a linear double-chain polymer, in which each pair of Cd atoms is bridged by two dsep ligands; the mercury 6 polymer has a helical chain structure, in which two Hg atoms are bridged by one dsep ligand, and the other ligand chelates the Hg atom. The chelating dsep ligands lie on either side of the helical chain. Compound 3 exists as a dimer in which two cadmium atoms are connected by two bridging dsep ligands, and each cadmium atom is further chelated by a dsep ligand. The metal atoms in 1, 3 and 6 are each coordinated by four selenium atoms in a distorted tetrahedral geometry. Clusters 10-12 have tetrahedral array of zinc atoms with an oxygen atom in the center with edge-bridging dsep ligands. Positive FAB-mass spectra support the formation of selenium-centered clusters,7-9, of which the cluster 8 was structurally confirmed earlier. The solution state behavior of compounds 1-12 has been studied by using multinuclear NMR spectroscopy. Dimer 3 in CD2Cl2 showed monomer-dimer exchange equilibrium in the temperature range 20 to -90 degrees C and the free energy of activation is calculated from the coalescence temperature as DeltaG++(223 K)= 38.5 kJ mol(-1). Polymer undergoes depolymerization in CDCl3 and exhibits monomer-dimer exchange equilibrium in the temperature range 20 to -60 degrees C.     

Saradaferin, a new sesquiterpenoid coumarin from Ferula assafoetida

Phytochemical investigation of the gum resin of Ferula assafoetida resulted in the isolation and characterization of a new sesquiterpenoid coumarin, Saradaferin (1) named as [Decahydro-(3-alpha-hydroxy-4,4,10-trimethyl-8-methylene-9-naphthenyl)-alpha-hydroxymethyl] ether of umbelliferone.     

Percolation phenomenon in mixed reverse micelles: the effect of additives

The conductivity of AOT/IPM/water reverse micellar systems as a function of temperature, has been found to be non-percolating at three different concentrations (100, 175 and 250 mM), while the addition of nonionic surfactants [polyoxyethylene(10) cetyl ether (Brij-56) and polyoxyethylene(20) cetyl ether (Brij-58)] to these systems exhibits temperature-induced percolation in conductance in non-percolating AOT/isopropyl myristate (IPM)/water system at constant compositions (i.e., at fixed total surfactant concentration, omega and X(nonionic)). The influence of total surfactant concentration (micellar concentration) on the temperature-induced percolation behaviors of these systems has been investigated. The effect of Brij-58 is more pronounced than that of Brij-56 in inducing percolation. The threshold percolation temperature, Tp has been determined for these systems in presence of additives of different molecular structures, physical parameters and/or interfacial properties. The additives have shown both assisting and resisting effects on the percolation threshold. The additives, bile salt (sodium cholate), urea, formamide, cholesteryl acetate, cholesteryl benzoate, toluene, a triblock copolymer [(EO)13(PO)30(EO)13, Pluronic, PL64], polybutadiene, sucrose esters (sucrose dodecanoates, L-1695 and sucrose monostearate S-1670), formamide distinctively fall in the former category, whereas sodium chloride, cholesteryl palmitate, crown ether, ethylene glycol constitute the latter for both systems. Sucrose dodecanoates (L-595) had almost marginal effect on the process. The observed behavior of these additives on the percolation phenomenon has been explained in terms of critical packing parameter and/or other factors, which influence the texture of the interface and solution properties of the mixed reverse micellar systems. The activation energy, Ep for the percolation process has been evaluated. Ep values for the AOT/Brij-56 systems have been found to be lower than those of AOT/Brij-58 systems. The concentration of additives influence the parameters Tp and Ep for both systems. A preliminary report for the first time on the percolation phenomenon in mixed reverse micelles in presence of additives has been suggested on the basis of these parameters (Tp and Ep).