Search

A series of remarkable crystalline compounds [Cu2(BTC)4/3(H2O)2]6[HnXM12O40]·(C4H12N)2 (X = Si, Ge, P, As; M = W, Mo) were obtained from the simple one-step hydrothermal reaction of copper nitrate, benzentricaboxylate (BTC), and different Keggin polyoxometalates (POMs). In these compounds, the catalytically active Keggiri polyanions were alternately arrayed as noncoordinating guests in the cuboctahedral cages of a Cu-BTC-based metal-organic framework (MOF) host matrix. X-ray crystallographic analyses, TG, FT-IR, UV-vis, N2 adsorption studies, and acid-base titration demonstrated their high stability and toleration for thermal and acid-base conditions. No POM leaching or framework decomposition was observed in our study. The representative acid catalytic performance of a compound containing PW12 species was assessed through the hydrolysis of esters in excess water, which showed. high catalytic activity and can be used repeatedly without activity loss. Moreover, catalytic selectivity, which is dependent on the molecular size of substrates, and substrate accessibility for the pore surface were observed, It is the first time that the well-defined, crystalline, MOF-supported POM compound has behaved as a true heterogeneous acid catalyst. The unique attributes of MOF and well-dispersed level of POMs prohibited the conglomeration and deactivation of POMs, which allowed for the enhancement of their catalytic properties. [ABSTRACT FROM AUTHOR]

With limited reductant and nitrite under anaerobic conditions, copper-containing nitrite reductase (NiR) of Rhodobacter sphaeroides yielded endogenous NO and the Cu(l)NO derivative of NiR. 14N- and 15N-nitrite substrates gave rise to characteristic 14NO and 15NO EPA hyperfine features indicating NO involvement, and enrichment of NiR with 63Cu isotope caused an EPA line shape change showing copper involvement. A markedly similar Cu(l)NONiR complex was made by anaerobically adding a little endogenous NO gas to reduced protein and immediately freezing. The Cu(l)NONiR signal accounted for 60-90% of the integrated EPR intensity formerly associated with the Type 2 catalytic copper. Analysis of NO and Cu hyperfine couplings and comparison to couplings of inorganic Cu(l)NO model systems indicated ~50% spin on the N of NO and ~17% spin on Cu. ENDOR revealed weak nitrogen hyperfine coupling to one or more likely histidine ligands of copper. Although previous crystallography of the conservative 1289V mutant had shown no structural change beyond the 289 position, this mutation, which eliminates the Cδ1 methyl of 1289, caused the Cu(l)NONiR EPA spectrum to change and proton ENDOR features to be significantly altered. The proton hyperfine coupling that was significantly altered was consistent with a dipolar interaction between the Cδ1 protons of 289 and electron spin on the NO, where the NO would be located 3.0-3.7 Å from these protons. Such a distance positions the NO of Cu(l)NO as an axial ligand to Type 2 Cu(l). [ABSTRACT FROM AUTHOR]

The article discusses the study which probes on the conformation of the putative turn region in membrane-associated influenza fusion peptide (IFP) via nuclear magnetic resonance (NMR) spectroscopy. In this study, IFP has been sequenced and synthesized. It signifies that a helix-turn-helix motif for the membrane-associated IFP at both pH 5.0 and pH 7.4 and a second turn conformation at pH 5.0 in line with the protonation of the Glu-11 side chain is supported by solid-state NMR spectra.

A sodalite-type porous metal-organic framework with polyoxometalate templates, H3[(Cu4Cl)3(BTC)8]2[PW12O40]·(C4H12N)6·3H2O (NENU-11; BTC = 1,3,5-benzenetricarboxylate), was obtained by a hydrothermal reaction. As a reasonable candidate for eliminating nerve gas, NENU-11 displays good adsorption behavior for dimethyl methylphosphonate (15.5 molecules per formula unit). In virtue of the catalytic activity of polyoxometalate guests, this nerve gas mimic could be facilely decomposed by a hydrolysis reaction. [ABSTRACT FROM AUTHOR]

A combination of spectroscopy and DFT calculations has been used to define the geometric and electronic structure of the nitrite bound type 2 (T2) copper site at high and low pH in nitrite reductase from Rhodobacter sphaeroides. At high pH there is no electron transfer from reduced type 1 (T1) to the nitrite bound T2 copper, while protonation triggers T1 - T2 electron transfer and generation of NO. The DFT calculated reaction coordinate for the N-O bond cleavage in nitrite reduction by the reduced 12 copper suggests that the process is best described as proton transfer triggering electron transfer. Bidentate nitrite binding to copper is calculated to play a major role in activating the reductive cleavage of the nitrite bond through backbonding combined with stabilization of the OH product by coordination to the Cu2+. [ABSTRACT FROM AUTHOR]

Reversible lysine acetylation and methylation regulate the function of a wide variety of proteins, including histones. Here, we have synthesized azalysine-containing peptides in acetylated and unacetylated forms as chemical probes of the histone deacetylases (HDAC8, Sir2Tm, and SIRT1) and the histone demethylase, LSD1. We have shown that the acetyl-azalysine modification is a fairly efficient substrate for the sirtuins, but a weaker substrate for HDAC8, a classical HDAC. In addition to deacetylation by sirtuins, the acetyl-azalysine analogue generates a novel ADP-ribose adduct that was characterized by mass spectrometry, Western blot analysis, and nuclear magnetic resonance spectroscopy. This peptide-ADP-ribose adduct is proposed to correspond to a derailed reaction intermediate, providing unique evidence for the direct 2′-hydroxyl attack on the O-alkylimidate intermediate that is formed in the course of sirtuin catalyzed deacetylation. An unacetylated azalysine-containing H3 peptide proved to be a potent inhibitor of the LSD1 demethylase, forming an FAD adduct characteristic of previously reported related structures, providing a new chemical probe for mechanistic analysis. [ABSTRACT FROM AUTHOR]

Palladium-catalyzed direct arylation reactions are described with a broad range of azine and azole N-oxides. In addition to aspects of functional group compatibility, issues of regioselectivity have been explored when nonsymmetrical azine N-oxides are used. In these cases, both the choice of ligand and the nature of the azine substituents play important roles in determining the regioisomeric distribution. When azole N-oxides are employed, preferential reaction is observed for arylation at C2 which occurs under very mild conditions. Subsequent reactions are observed to occur at C5 followed by arylation at C4. The potential utility of this methodology is illustrated by its use in the synthesis of a potent sodium channel inhibitor 1 and a Tie2 Tyrosine Kinase inhibitor 2. [ABSTRACT FROM AUTHOR]

The article presents the study regarding the spectroscopy and crystallography solution using copper nitrate reductase (NiR). NiR is a homotrimeric enzyme from Rhodobacter sphaerides with T1 copper site. The mechanism for the reaction of NiR reductase containing excess nobelium (NO) includes two electron oxidation.