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Cooper EPR

Margarethe van der Meer, Yvonne Rechkemmer, Uta Frank, Frauke D Breitgoff, Stephan Hohloch, Cheng-Yong Su, Petr Neugebauer, Raphael Marx, María Dörfel, Joris van Slageren, Biprajit Sarkar
Quinonoid ligands are excellent bridges for generating redox-rich dinuclear assemblies. A large majority of these bridges are symmetrically substituted, with examples of unsymmetrically substituted quinonoid bridges being extremely rare. We present here a dicobalt complex in its various redox states with an unsymmetrically substituted quinonoid bridging ligand. Two homovalent forms and one mixed-valent form have been isolated and characterized by single crystal X-ray diffraction. The complex displays a large comproportionation constant for the mixed-valent state which is three orders of magnitude higher than that observed for the analogous complex with a symmetrically substituted bridge...
September 19, 2016: Chemistry: a European Journal
Feng-Chun Lo, Chang-Chih Hsieh, Manuel Maestre-Reyna, Chin-Yu Chen, Tzu-Ping Ko, Yih-Chern Horng, Yei-Chen Lai, Yun-Wei Chiang, Chih-Mao Chou, Cheng-Hung Chiang, Wei-Ning Huang, Yi-Hung Lin, D Scott Bohle, Wen-Feng Liaw
Molecular mechanisms underlying the repair of nitrosylated [Fe-S] clusters by the microbial protein YtfE remain poorly understood. The X-ray crystal structure of YtfE, in combination with EPR, magnetic circular dichroism (MCD), UV, and (17) O-labeling electron spin echo envelope modulation measurements, show that each iron of the oxo-bridged Fe(II) -Fe(III) diiron core is coordinatively unsaturated with each iron bound to two bridging carboxylates and two terminal histidines in addition to an oxo-bridge. Structural analysis reveals that there are two solvent-accessible tunnels, both of which converge to the diiron center and are critical for capturing substrates...
July 4, 2016: Chemistry: a European Journal
Simon Duval, Joanne M Santini, David Lemaire, Florence Chaspoul, Michael J Russell, Stephane Grimaldi, Wolfgang Nitschke, Barbara Schoepp-Cothenet
While the molybdenum cofactor in the majority of bisPGD enzymes goes through two consecutive 1-electron redox transitions, previous protein-film voltammetric results indicated the possibility of cooperative (n=2) redox behavior in the bioenergetic enzyme arsenite oxidase (Aio). Combining equilibrium redox titrations, optical and EPR spectroscopies on concentrated samples obtained via heterologous expression, we unambiguously confirm this claim and quantify Aio's redox cooperativity. The stability constant, Ks, of the Mo(V) semi-reduced intermediate is found to be lower than 10(-3)...
September 2016: Biochimica et Biophysica Acta
Jian-Zhen Liao, Chen Wu, Xiao-Yuan Wu, Shui-Quan Deng, Can-Zhong Lu
An unusual room-temperature light sensitivity was realized in a polyoxometalate-based hybrid material due to cooperative multicomponent molecular charge-transfer interactions taking place in this material, mainly among POMs, NDIs, and other molecules. The functional π-acidic NDI linkers and POM clusters in the discussed hybrid material were individually designed as photosensors and electron reservoirs. To propose a photo-induced charge-transfer mechanism, EPR, XPS, UV-Vis and computational studies were carried out, and indicated the presence of active charge-transfer interactions among several of the components...
May 31, 2016: Chemical Communications: Chem Comm
Yuri Kutin, Vivek Srinivas, Matthieu Fritz, Ramona Kositzki, Hannah S Shafaat, James Birrell, Eckhard Bill, Michael Haumann, Wolfgang Lubitz, Martin Högbom, Julia J Griese, Nicholas Cox
A manganese/iron cofactor which performs multi-electron oxidative chemistry is found in two classes of ferritin-like proteins, the small subunit (R2) of class Ic ribonucleotide reductase (R2c) and the R2-like ligand-binding oxidase (R2lox). It is unclear how a heterodimeric Mn/Fe metallocofactor is assembled in these two related proteins as opposed to a homodimeric Fe/Fe cofactor, especially considering the structural similarity and proximity of the two metal-binding sites in both protein scaffolds and the similar first coordination sphere ligand preferences of Mn(II) and Fe(II)...
April 16, 2016: Journal of Inorganic Biochemistry
Elisenda Lopez-Manzano, Andrea A Cronican, Kristin L Frawley, Jim Peterson, Linda L Pearce
The complex of cobalt(II) with the ligand 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]heptadeca-1(17)2,11,13,15-pentaene (CoN4[11.3.1]) has been shown to bind two molecules of cyanide in a cooperative fashion with an association constant of 2.7 (±0.2) × 10(5). In vivo, irrespective of whether it is initially administered as the Co(II) or Co(III) cation, EPR spectroscopic measurements on blood samples show that at physiological levels of reductant (principally ascorbate) CoN4[11.3.1] becomes quantitatively reduced to the Co(II) form...
June 20, 2016: Chemical Research in Toxicology
Hong-Xing Zheng, Zu-Feng Xiao, Chuan-Zhi Yao, Qiang-Qiang Li, Xiao-Shan Ning, Yan-Biao Kang, Yong Tang
Phenanthroline and tert-butoxide have been established as powerful radical initiators in reactions such as the SRN1-type coupling reactions due to the cooperation of large heteroarenes and a special feature of tert-butoxide. The first phenanthroline-tert-butoxide-catalyzed transition-metal-free allylic isomerization is described. The resulting ketones are key intermediates for indenes. The control experiments rule out the base-promoted allylic anion pathway. The radical pathway is supported by experimental evidence that includes kinetic study, kinetic isotope effect, isotope-labeling experiments, trapping experiments, and EPR experiments...
December 18, 2015: Organic Letters
Ahmed Farouk, Magdy Zakaria, Adel Megahed, Fatma A Omara
In this paper, we generalize a secured direct communication process between N users with partial and full cooperation of quantum server. So, N - 1 disjointed users u1, u2, …, uN-1 can transmit a secret message of classical bits to a remote user uN by utilizing the property of dense coding and Pauli unitary transformations. The authentication process between the quantum server and the users are validated by EPR entangled pair and CNOT gate. Afterwards, the remained EPR will generate shared GHZ states which are used for directly transmitting the secret message...
2015: Scientific Reports
Huafei Li, Yun Sun, Di Chen, He Zhao, Mengxin Zhao, Xiandi Zhu, Changhong Ke, Ge Zhang, Cheng Jiang, Li Zhang, Fulei Zhang, Huafeng Wei, Wei Li
Simultaneously blocking multiple mediators offers new hope for the treatment of complex diseases. However, the curative potential of current combination therapy by chronological administration of separate monoclonal antibodies (mAbs) or multi-specific mAbs is still moderate due to inconvenient manipulation, low cooperative effectors, poor pharmacokinetics and insufficient tumor accumulation. Here, we describe a facile strategy that arms distinct mAbs with cooperative effectors onto a long chain to form a multicomponent comb-like nano mAb...
2015: Scientific Reports
K Ackermann, A Giannoulis, D B Cordes, A M Z Slawin, B E Bode
Correction for 'Assessing dimerisation degree and cooperativity in a biomimetic small-molecule model by pulsed EPR' by K. Ackermann et al., Chem. Commun., 2015, 51, 5257-5260.
October 28, 2015: Chemical Communications: Chem Comm
Denan Wang, Sergey V Lindeman, Adam T Fiedler
The remarkable chemistry of mononuclear complexes featuring tridentate, meridionally chelating "pincer" ligands has stimulated the development of ligand frameworks containing multiple pincer sites. Here, the coordination chemistry of a novel pentadentate ligand (L(N3O2)) that provides two closely spaced NNO pincer-type compartments fused together at a central diarylamido unit is described. The trianionic L(N3O2) chelate supports homobimetallic structures in which each M(II) ion (M = Co, Cu, Zn) is bound in a meridional fashion by the bridging diarylamido N atom and O,N-donors of the salicyaldimine arms...
September 8, 2015: Inorganic Chemistry
Yongming Deng, Chamini V Karunaratne, Erika Csatary, David L Tierney, Kraig Wheeler, Hong Wang
A new type of chiral bimetallic catalyst is disclosed. These chiral bimetallic catalysts are easily formed through mixing a metal Lewis acid and a metal binaphthyl phosphate (MLA/M[P]3) in solution. (1)H and (31)P NMR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and X-ray crystallographic analysis reveal a bimetallic structure of the Y(Yb)(III)/Y[P]3 complexes with bridging binaphthyl phosphate ligands...
August 21, 2015: Journal of Organic Chemistry
Valerie A Schmidt, Jordan M Hoyt, Grant W Margulieux, Paul J Chirik
Aryl-substituted bis(imino)pyridine cobalt dinitrogen compounds, ((R)PDI)CoN2, are effective precatalysts for the intramolecular [2π + 2π] cycloaddition of α,ω-dienes to yield the corresponding bicyclo[3.2.0]heptane derivatives. The reactions proceed under mild thermal conditions with unactivated alkenes, tolerating both amine and ether functional groups. The overall second order rate law for the reaction, first order with respect to both the cobalt precatalyst and the substrate, in combination with electron paramagnetic resonance (EPR) spectroscopic studies established the catalyst resting state as dependent on the identity of the precatalyst and diene substrate...
June 24, 2015: Journal of the American Chemical Society
Mursaleem Ansari, Nidhi Vyas, Azaj Ansari, Gopalan Rajaraman
High-valent iron-oxo species are key intermediates in C-H bond activation of several substrates including alkanes. The biomimic heme and non-heme mononuclear Fe(IV)=O complexes are very popular in this area and have been thoroughly studied over the years. These species despite possessing aggressive catalytic ability, cannot easily activate inert C-H bonds such as those of methane. In this context dinuclear complexes have gained attention, particularly μ-nitrido dinuclear iron species [(TPP)(m-CBA)Fe(IV)(μ-N)Fe(IV)(O)(TPP(˙+))](-) reported lately exhibits remarkable catalytic abilities towards substrates such as methane...
September 14, 2015: Dalton Transactions: An International Journal of Inorganic Chemistry
Sansa Dutta, Lev Weiner, Mordechai Sheves
A member of the retinal protein family, halorhodopsin, acts as an inward light-driven Cl(-) pump. It was recently demonstrated that the Natronomonas pharaonis halorhodopsin-overproducing mutant strain KM-1 contains, in addition to the retinal chromophore, a lipid soluble chromophore, bacterioruberin, which binds to crevices between adjacent protein subunits. It is established that halorhodopsin has several chloride binding sites, with binding site I, located in the retinal protonated Schiff base vicinity, affecting retinal absorption...
May 26, 2015: Biochemistry
Moran Feller, Eyal Ben-Ari, Yael Diskin-Posner, Raanan Carmieli, Lev Weiner, David Milstein
A unique mode of molecular oxygen activation, involving metal-ligand cooperation, is described. Ir pincer complexes [((t)BuPNP)Ir(R)] (R = C6H5 (1), CH2COCH3 (2)) react with O2 to form the dearomatized hydroxo complexes [((t)BuPNP*)Ir(R)(OH)] ((t)BuPNP* = deprotonated (t)BuPNP ligand), in a process which utilizes both O-atoms. Experimental evidence, including NMR, EPR, and mass analyses, indicates a binuclear mechanism involving an O-atom transfer by a peroxo intermediate.
April 15, 2015: Journal of the American Chemical Society
K Ackermann, A Giannoulis, D B Cordes, A M Z Slawin, B E Bode
Pulsed electron paramagnetic resonance (EPR) spectroscopy is gaining increasing importance as a complementary biophysical technique in structural biology. Here, we describe the synthesis, optimisation, and EPR titration studies of a spin-labelled terpyridine Zn(II) complex serving as a small-molecule model system for tuneable dimerisation.
March 28, 2015: Chemical Communications: Chem Comm
Iftikhar Ali Khawar, Jung Ho Kim, Hyo-Jeong Kuh
Malignant transformation and growth of the tumor mass tend to induce changes in the surrounding microenvironment. Abnormality of the tumor microenvironment provides a driving force leading not only to tumor progression, including invasion and metastasis, but also to acquisition of drug resistance, including pharmacokinetic (drug delivery-related) and pharmacodynamic (sensitivity-related) resistance. Drug delivery systems exploiting the enhanced permeability and retention (EPR) effect and active targeting moieties were expected to be able to cope with delivery-related drug resistance...
March 10, 2015: Journal of Controlled Release: Official Journal of the Controlled Release Society
Jagadeesan Lakshmipraba, Sankaralingam Arunachalam, Anvarbatcha Riyasdeen, Rajakumar Dhivya, Mohammad Abdulkader Akbarsha
The water soluble polyethyleneimine-copper(II) complexes, [Cu(phen)(L-tyr)BPEI]ClO4 (where phen=1,10-phenanthroline, L-tyr=L-tyrosine and BPEI=branched polyethyleneimine) with various degree of copper(II) complex units in the polymer chain were synthesized and characterized by elemental analysis and electronic, FT-IR, EPR spectroscopic techniques. The binding of these complexes with CT-DNA was studied using UV-visible absorption titration, thermal denaturation, emission, circular dichroism spectroscopy and cyclic voltammetric methods...
January 2015: Journal of Photochemistry and Photobiology. B, Biology
David Bardelang, Gilles Casano, Florent Poulhès, Hakim Karoui, Jessica Filippini, Antal Rockenbauer, Roselyne Rosas, Valérie Monnier, Didier Siri, Anouk Gaudel-Siri, Olivier Ouari, Paul Tordo
The flexible tetranitroxide 4T has been prepared and was shown to exhibit a nine line EPR spectrum in water, characteristic of significant through space spin exchange (J(ij)) between four electron spins interacting with four nitrogen nuclei (J(ij) ≫ a(N)). Addition of CB[8] to 4T decreases dramatically all the Jij couplings, and the nine line spectrum is replaced by the characteristic three line spectrum of a mononitroxide. The supramolecular association between 4T and CB[8] involves a highly cooperative asymmetric complexation by two CB[8] (K1 = 4027 M(-1); K2 = 202,800 M(-1); α = 201) leading to a rigid complex with remote nitroxide moieties...
December 17, 2014: Journal of the American Chemical Society
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