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c-h bond activation

Simon Sung, Qingyang Wang, Tobias Krämer, Rowan D Young
We report the first example of a cobalt PCcarbene P pincer complex ( 1 ) featuring a central alkylidene carbon donor accessed through the dehydration of an alcoholic POP proligand. Complex 1 shares bonding similarities with cobalt PBP and PNP pincer complexes where the donor atom engages in π-bonding with the cobalt centre, and thus completes the PXP (X = B, C, N) pincer ligand series for cobalt (for X donors that partake in M-L π-bonding). As compared to PBP and PNP pincer complexes, which are known to be good hydride and proton acceptors (respectively), complex 1 is found to be an effective hydrogen atom acceptor...
November 21, 2018: Chemical Science
Saba Atefyekta, Maria Pihl, Chris Lindsay, Sarah C Heilshorn, Martin Andersson
Antimicrobial peptides (AMPs) are currently receiving interest as an alternative to conventional antibiotics to treat biomaterial-associated infection. However, the inherent instability of such peptides often limits their efficacy in intended clinical applications. Covalent immobilization of AMPs to surfaces is one strategy to increase the long-term stability and minimize the toxicity. In this work, an antimicrobial peptide, RRPRPRPRPWWWW-NH2 (RRP9W4N), was used to modify elastin-like polypeptide (ELP) surface coatings containing cell-adhesive peptide domains (RGD) using covalent chemistry...
January 1, 2019: Acta Biomaterialia
Simran Kaur, Arpita Devi, Bhaskarjyoti Saikia, Robin Doley
Trancriptomic analysis of the venom gland cDNA library of Bungarus flaviceps revealed Kunitz-type serine protease inhibitor as one of the major venom protein families with three groups A, B, C. One of the group B isoforms named Flavikunin, which lacked an extra cysteine residue involved in disulfide bond formation in β-bungarotoxin, was synthesized, cloned, and overexpressed in Escherichia coli. To decipher the structure-function relationship, the P1 residue of Flavikunin, histidine, was mutated to alanine and arginine...
December 10, 2018: Journal of Biochemical and Molecular Toxicology
Benjamin Schweitzer, Stephan N Steinmann, Carine Michel
Converting biomass into sustainable chemicals and energy feed-stocks requires innovative heterogeneous catalysts, which are able to efficiently work under aqueous conditions. Computational chemistry is a key asset in the design of these novel catalysts, but it has to face two challenges: the large reaction networks and the potential role of hydration. They can be addressed using scaling relations such as Brønsted-Evans-Polanyi (BEP) and solvation models, respectively. In this study, we show that typical reaction and activation energies of alcohol decomposition on Pt(111) are not strongly modified by the inclusion of the water solvent as a continuum model...
December 10, 2018: Physical Chemistry Chemical Physics: PCCP
Pavlo Bielytskyi, Daniel Gräsing, Stefan Zahn, Kaustubh R Mote, A Alia, P K Madhu, Jörg Matysik
Modified versions of through-bond heteronuclear correlation (HETCOR) experiments are presented to take advantage of the light-induced hyperpolarization that occurs on 13 C nuclei due to the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect. Such 13 C-1 H photo-CIDNP MAS-J-HMQC and photo-CIDNP MAS-J-HSQC experiments are applied to acquire the 2D 13 C-1 H correlation spectra of selectively 13 C-labeled photochemically active cofactors in the frozen quinone-blocked photosynthetic reaction center (RC) of the purple bacterium Rhodobacter (R...
November 29, 2018: Journal of Magnetic Resonance
Christopher P Gordon, Damien B Culver, Matthew P Conley, Odile Eisenstein, Richard A Andersen, Christophe Copéret
C-H bond activation via π-bond metathesis is typically observed with transition-metal alkyl compounds in d0 or d0fn electron configurations, e.g. biscyclopentadienyl metal alkyls. Related C-H activation processes are also observed for transition-metal alkyls with higher d-electron counts, such as W(II), Fe(II) or Ir(III). A σ-bond metathesis mechanism has been proposed in all cases with a preference for oxidative addition - reductive elimination pathway for Ir(III). Herein we show that, regardless of the exact mechanism, C-H activation with all of these compounds is associated with π-character of the M-C bond, according to a detailed analysis of the 13C NMR chemical shift tensor of the α-carbon...
December 10, 2018: Journal of the American Chemical Society
Eric Steffensmeier, Matthew T Swann, Kenneth M Nicholas
The oxo-vanadium-catalyzed redox disproportionation of activated alcohols (oxidation-reductive coupling, Ox-RC) produces carbonyl compounds and hydrocarbon dimers. A mechanistic study of this novel reaction is reported herein. Following our initial disclosure, new findings include the following: (1) The [(salimin)VO2 ]- -catalyzed Ox-RC of Ph2 CHOH in the presence of fluorene affords the products of H-atom abstraction and all possible hydrocarbon dimers. (2) Electronic substituent effects on the relative rates of Ox-RC with respect to 4-X-BnOH reactants and Bu4 N[(Y-salimin)VO2 ] catalysts (1a-c) reveal (a) a correlation of the oxidation rate of X-BnOH reactants with the radical σ parameter and (b) correlation of the oxidation rate for (Y-salimin)VO2 - with the standard Hammett σ parameter...
December 7, 2018: Inorganic Chemistry
Lingqia Su, Shixiong Wu, Jinyun Feng, Jing Wu
Maltooligosyl trehalose trehalohydrolase (MTHase, EC catalyzes the release of trehalose, a novel food ingredient, by splitting the α-1,4-glucosidic linkage adjacent to the α-1,1-glucosidic linkage of maltooligosyl trehalose. However, the high-yield preparation of recombinant MTHase has not yet been reported. In this study, a codon-optimized synthetic gene encoding Sulfolobus acidocaldarius MTHase was expressed in Escherichia coli. In initial expression experiments conducted using pET-24a (+) and E...
December 6, 2018: Bioprocess and Biosystems Engineering
Jirapat Santatiwongchai, Duangkamol Gleeson, Matthew Paul Gleeson
Serine hydroxymethyltransferase (SHMT) is a pyridoxal phosphate (PLP) dependent enzyme that catalyzes the reversible conversion of serine and tetrahydrofolate (THF) to glycine and 5,10-methylene THF. SHMT is a folate pathway enzyme and is therefore of considerable medical interest since this is an important intervention point for anti-malarial, anti-cancer and anti-bacterial treatments. Despite considerable experimental effort the precise reaction mechanism of SHMT remains unclear. In this study we explore the reaction mechanism of SHMT with its natural substrates to determine the roles of each active site residue and the nature and the sequence of chemical steps...
December 6, 2018: Journal of Physical Chemistry. B
Vanesa Salamanca, Alberto Toledo, Ana C Albeniz
The ligand [2, 2'-bipyridin]-6(1H)-one (bipy-6-OH) has a strong accelerating effect in the Pd-catalyzed direct arylation of pyridine or arenes. The isolation of relevant intermediates and the study of their decomposition unequivocally show that the deprotonated coordinated ligand acts as a base and assists the cleavage of the C-H bond. Mechanistic work indicates that the direct arylation of pyridine with this ligand occurs through a Pd(0)/Pd(II) cycle. Because of this dual ligand-intramolecular base role, there is no need of an available coordination site on the metal for an external base, a difficulty encountered when chelating ligands are used in coupling reactions that involve a C-H cleavage step...
December 6, 2018: Journal of the American Chemical Society
Xiao Shang, Zi-Zhang Liu, Shan-Shan Lu, Bin Dong, Jing-Qi Chi, Jun-Feng Qin, Xien Liu, Yong-Ming Chai, Chen-Guang Liu
The hydrogen evolution reaction activity of carbon-supported Pt catalyst is highly dependent on Pt-C interfaces. Herein, we focus on the relationships between Pt activity and N/O-functionalized hollow carbon sphere (HCS) substrate in acidic media. The electrochemical dissolution of Pt counter electrode is performed to prepare Pt nanoparticles in low loading. The N groups are beneficial for homogeneously sized Pt nanoparticles, whereas the O groups lead to aggregated nanoparticles. Moreover, the proper electronegativity of the N groups may enable capturing of protons to create proton-rich Pt-C interfaces and transfer them onto the Pt sites...
December 6, 2018: ACS Applied Materials & Interfaces
Chao Deng, Yingxin Sun, Yi Ren, Weihua Zhang
Density functional theory calculations were carried out to study the reaction mechanism of the Rh(iii)-catalyzed regioselective C-H cyanation of indole and indoline with N-cyano-N-phenyl-para-methylbenzenesulfonamide (NCTS). This mechanism involves four major steps: C-H activation, cyano group insertion, β-N elimination, and regeneration of active species. How different indole and indoline substrates affect the regioselectivity of C-H bond cyanation has been examined and analyzed in detail. Our calculation results indicate that the regioselectivity of C-H bond cyanation of indole depends on the nucleophilicity of carbon atoms in C-Rh(iii) bonds to the cyano group...
December 5, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Ning Ning Chen, Jian Ning Ni, Jun Wang
A novel two-dimensional CdII coordination framework, poly[[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene-κ2 N:N'](μ-1,3-phenylenediacetato-κ4 O,O':O'',O''')cadmium(II)] dihydrate], {[Cd(C10 H8 O4 )(C14 H14 N4 )]·2H2 O}n or {[Cd(PDA)(1,3-BMIB)]·2H2 O}n [1,3-BMIB is 1,3-bis(2-methyl-1H-imidazol-1-yl)benzene and H2 PDA is 1,3-phenylenediacetic acid], has been prepared and characterized using IR, elemental analysis, thermal analysis and single-crystal X-ray diffraction, the latter revealing that the compound is a (4,4) grid coordination polymer with layers oriented parallel to the bc crystal planes...
December 1, 2018: Acta Crystallographica. Section C, Structural Chemistry
Silja Kuusk, Riin Kont, Piret Kuusk, Agnes Heering, Morten Sørlie, Bastien Bissaro, Vincent G H Eijsink, Priit Väljamäe
Lytic polysaccharide monooxygenases (LPMOs) are mono-copper enzymes that catalyze oxidative cleavage of glycosidic bonds in polysaccharides in the presence of an external electron donor (reductant). In the classical O2 -driven monooxygenase reaction, the reductant is needed in stoichiometric amounts. In a recently discovered, more efficient H2 O2 -driven reaction, the reductant would be needed only for the initial reduction (priming) of the LPMO to its catalytically active Cu(I) form. However, the influence of the reductant on reducing the LPMO or on H2 O2 production in the reaction remains undefined...
December 4, 2018: Journal of Biological Chemistry
Junbo He, Hao Shi, Shuangshuang Huang, Lijuan Han, Weinong Zhang, Qixin Zhong
Nanoencapsulation of α-tocopherol (α-TOC) by blending sodium oleate (NaOl) and rebaudioside A (RebA) was successfully prepared by self-assembly method under mild conditions. The optimized nanoemulsion showed the loading capacity of α-TOC was 30 wt% of sodium oleate. FTIR analysis suggested that hydrogen bonds and hydrophobic interactions were the major forces in α-TOC-NaOl/RebA complexes that were spherical and possessed well-distinguishable core-shell structures. The freeze-dried α-TOC-NaOl/RebA complexes had great stability under ambient conditions...
December 3, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Shuo Wu, Xinxin Wu, Dongping Wang, Chen Zhu
Regioselective incorporation of a particular functional group into aliphatic sites by direct activation of unreactive C-H bonds is of great synthetic value. Despite advances in radical-mediated functionalization of C(sp3)-H bonds via HAT process, the site-selective vinylation of remote C(sp3)-H bonds still remains underexplored. Herein we report a new protocol for the regioselective vinylation of unactivated C(sp3)-H bonds. The remote C(sp3)-H activation is promoted by C-centered radical instead of the commonly used N- and O-radicals...
December 4, 2018: Angewandte Chemie
Patrick E Konold, Ivo H M van Stokkum, Fernando Muzzopappa, Adjélé Wilson, Marie Louise Groot, Diana Kirilovsky, John T M Kennis
The Orange Carotenoid Protein (OCP) is a two-domain photoactive protein that noncovalently binds an echinenone (ECN) carotenoid and mediates photoprotection in cyanobacteria. In the dark, OCP assumes an orange, inactive state known as OCPO; blue light illumination results in the red active state, known as OCPR. The OCPR state is characterized by large-scale structural changes that involve dissociation and separation of C-terminal and N-terminal domains accompanied by carotenoid translocation into the N-terminal domain...
December 4, 2018: Journal of the American Chemical Society
Houhua Li, Rajesh Gontla, Jana Flegel, Christian Merten, Slava Ziegler, Andrey P Antonchick, Herbert Waldmann
Herein, we report the first enantioselective annulation of α-arylidene pyrazolones through a formal C(sp3 )-H activation under mild conditions enabled by highly variable RhIII -Cpx catalysts. The method has a wide substrate scope and proceeds with good to excellent yields and enantioselectivities. Its synthetic utility was demonstrated by the late-stage functionalization of drugs and natural products as well as the preparation of enantioenriched [3]dendralenes. Preliminary biological investigations also identified the spiropyrazolones as a novel class of Hedgehog pathway inhibitors...
October 17, 2018: Angewandte Chemie
Steve Peigneur, Olivier Cheneval, Mohitosh Maiti, Enrico Leipold, Stefan H Heinemann, Eveline Lescrinier, Piet Herdewijn, Maria Elena De Lima, David J Craik, Christina I Schroeder, Jan Tytgat
A 13 aa residue voltage-gated sodium channel (NaV ) inhibitor peptide, Pn, containing 2 disulfide bridges was designed by using a chimeric approach. This approach was based on a common pharmacophore deduced from sequence and secondary structural homology of 2 NaV inhibitors: Conus kinoshitai toxin IIIA, a 14 residue cone snail peptide with 3 disulfide bonds, and Phoneutria nigriventer toxin 1, a 78 residue spider toxin with 7 disulfide bonds. As with the parent peptides, this novel NaV channel inhibitor was active on NaV 1...
December 3, 2018: FASEB Journal: Official Publication of the Federation of American Societies for Experimental Biology
Erika Rocha-Del Castillo, Omar Gómez-García, Dulce Andrade-Pavón, Lourdes Villa-Tanaca, Teresa Ramírez-Apan, Antonio Nieto-Camacho, Elizabeth Gómez
A series of organotin(IV) complexes was herein prepared and characterized. A one-pot synthetic strategy afforded reasonable to high yields, depending on the nature of the ligand. All new complexes were fully characterized by spectroscopic techniques, consisting of IR, MS and NMR (1 H, 13 C and 119 Sn). The in vitro cytotoxicity tests demonstrated that the organotin complexes produced a greater inhibition, versus cisplatin (the positive control), of the growth of six human cancer cell lines: U-251 (glioblastoma), K-562 (chronic myelogenous leukemia), HCT-15 (colorectal), MCF-7 (breast), MDA-MB-231 (breast) and SKLU-1 (non-small cell lung)...
2018: Chemical & Pharmaceutical Bulletin
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