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https://www.readbyqxmd.com/read/28640584/spectroscopic-evidence-for-a-h-bond-network-at-y356-located-at-the-subunit-interface-of-active-e-coli-ribonucleotide-reductase
#1
Thomas U Nick, Kanchana R Ravichandran, JoAnne Stubbe, Müge Kasanmascheff, Marina Bennati
The reaction catalyzed by E. coli ribonucleotide reductase (RNR) composed of α and β subunits that form an active α2β2 complex is a paradigm for proton-coupled electron transfer (PCET) processes in biological transformations. β2 contains the diferric tyrosyl radical (Y122•) cofactor that initiates a radical transfer (RT) over 35 Å via a specific pathway of amino acids (Y122• ↔ [W48] ↔ Y356 in β2 to Y731 ↔Y730↔ C439 in α2). Experimental evidence exists for co-linear and orthogonal PCET in α2 and β2 respectively...
June 22, 2017: Biochemistry
https://www.readbyqxmd.com/read/28636907/epr-spectroscopy-targets-structural-changes-in-the-e-%C3%A2-coli-membrane-fusion-cusb-upon-cu-i-binding
#2
Aviv Meir, Ahmad Abdelhai, Yoni Moskovitz, Sharon Ruthstein
Bacterial cells have developed sophisticated systems to deal with the toxicity of metal ions. Escherichia coli CusCFBA is a complex efflux system, responsible for transferring Cu(I) and Ag(I) ions; this system, located in the periplasm, involves four proteins, CusA, CusB, CusC, and CusF. CusA, CusB, and CusC are connected to one another in an oligomerization ratio of 3:6:3 CusA/CusB/CusC to form the CusCBA periplasm membrane transporter. CusB is an adaptor protein that connects the two membrane proteins CusA (inner membrane) and CusC (outer membrane)...
June 20, 2017: Biophysical Journal
https://www.readbyqxmd.com/read/28636384/role-of-crystal-structure-and-chalcogenide-redox-properties-on-the-oxidative-assembly-of-cadmium-chalcogenide-nanocrystals
#3
Jessica Davis, Aaron M Chalifoux, Stephanie L Brock
Oxidative assembly of metal chalcogenide nanocrystals (NCs) enables formation of 2-D (dense) and 3-D porous structures without the presence of intervening ligands between particles that can moderate transport properties. This route has been demonstrated successful for a range of single component structures including CdQ, PbQ and ZnQ (Q = S, Se, Te). En route to controllable assembly of multicomponent nanostructures, the roles of Q redox properties (2Q2-  Q22- + 2e), responsible for particle crosslinking, and the native structure (cubic zinc blende vs...
June 21, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28636006/copper-ion-interaction-with-the-rnase-catalytic-site-fragment-of-the-angiogenin-protein-an-experimental-and-theoretical-investigation
#4
Antonio Magrì, Giovanni Tabbì, Raffaella Breglia, Luca De Gioia, Piercarlo Fantucci, Maurizio Bruschi, Raffaele P Bonomo, Diego La Mendola
The angiogenin protein (Ang) is a member of the vertebrate-specific secreted ribonucleases and one of the most potent angiogenic factors known. Ang is a normal constituent of human plasma and its concentration increases under some physiological and pathological conditions to promote neovascularization. Ang was originally identified as an angiogenic tumour factor, but its biological activity has been found to extend from inducing angiogenesis to promoting cell survival in different neurodegenerative diseases...
June 21, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28635269/the-reduction-potentials-of-fefe-hydrogenase-accessory-iron-sulfur-clusters-provide-insights-into-the-energetics-of-proton-reduction-catalysis
#5
Jacob H Artz, David W Mulder, Michael W Ratzloff, Carolyn E Lubner, Oleg A Zadvornyy, Axl X LeVan, S Garrett Williams, Michael W W Adams, Anne K Jones, Paul W King, John W Peters
An [FeFe]-hydrogenase from Clostridium pasteurianum, CpI, is a model system for biological H2 activation. In addition to the catalytic H-cluster, CpI contains four accessory iron-sulfur [FeS] clusters in a branched series that transfer electrons to and from the active site. In this work, potentiometric titrations have been employed in combination with electron paramagnetic resonance (EPR) spectroscopy at defined electrochemical potentials to gain insights into the role of the accessory clusters in catalysis...
June 21, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28631929/-13-c-dynamic-nuclear-polarization-using-a-trimeric-gd-3-complex-as-an-additive
#6
Peter Niedbalski, Christopher Parish, Qing Wang, Andhika Kiswandhi, Zahra Hayati, Likai Song, Lloyd Laporca Lumata
Dissolution dynamic nuclear polarization (DNP) is one of the most successful techniques that resolves the insensitivity problem in liquid-state nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) by amplifying the signal by several thousand-fold. One way to further improve the DNP signal is the inclusion of trace amounts of lanthanides in DNP samples doped with trityl OX063 free radical as the polarizing agent. In practice, stable monomeric gadolinium complexes such as Gd-DOTA or Gd-HP-DO3A are used as beneficial additives in DNP samples, further boosting the DNP-enhanced solid-state 13C polarization by a factor of 2 or 3...
June 20, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28631900/-experimental-development-and-rationale-for-a-renal-decellularization-protocol-with-subsequent-comprehensive-assessment-of-the-biological-scaffold
#7
P V Glybochko, S N Alekseenko, E A Gubareva, E V Kuevda, A A Basov, A S Sotnichenko, S S Dzhimak, I S Gumenyuk, I Kh Egiev, V N Chechelyan, R Z Nakokhov, O M Lyasota, Yu V Teterin
Chronic renal failure (CRF) is one of the most challenging problems of contemporary medicine. Patients with chronic renal failure usually need renal replacement therapy as either hemodialysis, peritoneal dialysis or a kidney transplant. The latter is the most promising option for end-stage kidney disease. However, the shortage of donor organs, the complexity of their delivery, the difficulty in finding an immunologically compatible donor and the need for lifelong immunosuppression triggered advances in modern tissue engineering...
June 2017: Urologii︠a︡
https://www.readbyqxmd.com/read/28630436/a-novel-gd-dtpa-conjugated-poly-l-%C3%AE-glutamyl-glutamine-paclitaxel-polymeric-delivery-system-for-tumor-theranostics
#8
Lipeng Gao, Jinge Zhou, Jing Yu, Qilong Li, Xueying Liu, Lei Sun, Ting Peng, Jing Wang, Jianzhong Zhu, Jihong Sun, Weiyue Lu, Lei Yu, Zhiqiang Yan, Yiting Wang
The conventional chemotherapeutics could not be traced in vivo and provide timely feedback on the clinical effectiveness of drugs. In this study, poly(L-γ-glutamyl-glutamine)-paclitaxel (PGG-PTX), as a model polymer, was chemically conjugated with Gd-DTPA (Gd-diethylenetriaminepentaacetic acid), a T1-contrast agent of MRI, to prepare a Gd-DTPA-conjugated PGG-PTX (PGG-PTX-DTPA-Gd) delivery system used for tumor theranostics. PGG-PTX-DTPA-Gd can be self-assembled to NPs in water with a z-average hydrodynamic diameter about 35...
June 19, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28628743/preparation-of-blatter-radicals-via-aza-wittig-chemistry-the-reaction-of-n-aryliminophosphoranes-with-1-het-aroyl-2-aryldiazenes
#9
Anastasia C Savva, Styliana I Mirallai, Georgia A Zissimou, Andrey A Berezin, Marina Demetriades, Andreas Kourtellaris, Christos P Constantinides, Constantinos Nicolaides, Theodossis Trypiniotis, Panayiotis A Koutentis
Reacting N-aryliminophosphoranes with 1-(het)aroyl-2-aryldiazenes in preheated diphenyl ether at ca. 150-250 °C for 5-25 min, affords in most cases the 1,3-diaryl-1,4-dihydro-1,2,4-benzotriazin-4-yls (aka Blatter radicals) in moderate to good yields. All new compounds are fully characterized, including for the radicals EPR and CV studies. Single crystal x-ray structures of 1-benzoyl-2-(perfluorophenyl)diazene and 1-(perfluorophenyl)-3-phenyl-1,4-dihydro-1,2,4-benzotriazinyl are also presented.
June 19, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28628261/studying-the-conformation-of-a-receptor-tyrosine-kinase-in-solution-by-inhibitor-based-spin-labeling
#10
Dongsheng M Yin, Jeffrey S Hannam, Anton Schmitz, Olav Schiemann, Gregor Hagelueken, Michael Famulok
The synthesis of a spin label based on PD168393, a covalent inhibitor of a major anticancer drug target, the epidermal growth factor receptor (EGFR), is reported. The label facilitates the analysis of the EGFR structure in solution by pulsed electron paramagnetic resonance (EPR) spectroscopy. For various EGFR constructs, including near-full-length EGFR, we determined defined distance distributions between the two spin labels bound to the ATP binding sites of the EGFR dimer. The distances are in excellent agreement with an asymmetric dimer of the EGFR...
June 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28627547/probing-the-electronic-structure-of-a-copper-ii-complex-by-cw-and-pulse-epr-spectroscopy
#11
Zoi G Lada, Yiannis Sanakis, Catherine P Raptopoulou, Vassilis Psycharis, Spyros P Perlepes, George Mitrikas
Nucleophilic attack by the carbanion (-):CH2COCH3 at the carbonyl group of di-2-pyridyl ketone, (py)2CO, in the presence of Cu(II) under moderately basic conditions has yielded the cationic mononuclear complex [Cu{(py)2C(CH2COCH3)(OH)}2](NO3)2·2H2O (1·2H2O) in ∼40% yield, where (py)2C(CH2COCH3)(OH) is the ligand bis(2-pyridine-2-yl)butane-1-ol-3-one. The Cu(II) atom of the cation sits on a crystallographically imposed inversion center. The neutral molecule is coordinated to the metal ion as a tridentate fac chelating ligand through the hydroxyl oxygen atom and two 2-pyridyl nitrogen atoms...
June 19, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28627400/improved-tacrolimus-skin-permeation-by-co-encapsulation-with-clobetasol-in-lipid-nanoparticles-study-of-drug-effects-in-lipid-matrix-by-electron-paramagnetic-resonance
#12
Lígia Marquez Andrade, Luis Antônio Dantas Silva, Anna Paula Krawczyk-Santos, Isabella Cristina de S M Amorim, Priscila Bianca Rodrigues da Rocha, Eliana Martins Lima, Jorge Luiz V Anjos, Antonio Alonso, Ricardo Neves Marreto, Stephânia Fleury Taveira
Combined therapy with corticosteroids and immunosuppressant-loaded nanostructured lipid carriers (NLC) could be useful in the treatment of skin diseases. To circumvent NLC loading capacity problems, loaded drugs should have different physicochemical characteristics, such as tacrolimus (TAC) and clobetasol (CLO). Therefore, in the present study, TAC and CLO were encapsulated in NLC (TAC-NLC, CLO-NLC and TAC+CLO-NLC), coated or otherwise with chitosan. Electron paramagnetic resonance (EPR) spectroscopy of different spin labels was used to investigate the impact of drug and oil incorporation on the lipid dynamic behavior of the lipid matrices...
June 13, 2017: European Journal of Pharmaceutics and Biopharmaceutics
https://www.readbyqxmd.com/read/28627073/determination-of-radical-radical-distances-in-light-active-proteins-and-their-implication-for-biological-magnetoreception
#13
Daniel Nohr, Bernd Paulus, Ryan Rodriguez, Asako Okafuji, Robert Bittl, Erik Schleicher, Stefan Weber
Light-generated short-lived radial pairs have been suggested to play pivotal roles in cryptochromes and photolyases. Chryptochromes are very probably involved in magnetic compass sensing in migratory birds and the magnetic-field-dependent behavior of insects. We examined photo-generated transient states in the cryptochrome of Drosophila melanogaster and in the structurally related DNA-repair enzyme Escherichia coli DNA photolyase. Using pulsed EPR spectroscopy, the exchange and dipolar contributions to the electron spin-spin interaction were determined in a straightforward and direct way...
June 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28624739/degradation-of-1-4-dioxane-by-biochar-supported-nano-magnetite-particles-activating-persulfate
#14
Da Ouyang, Jingchun Yan, Linbo Qian, Yun Chen, Lu Han, Anqi Su, Wenying Zhang, Hao Ni, Mengfang Chen
Nano magnetite biochar composite (nFe3O4/biochar) was synthesized and used to activate persulfate for the degradation of 1,4-dioxane. Analytical techniques using X-ray diffraction (XRD), fourier transform infrared analysis (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated that nFe3O4 was spherical and successfully loaded onto the surface of biochar. The results of batch-scale experiments illustrated that the 1,4-dioxane degradation efficiency in aqueous phase was 98...
May 30, 2017: Chemosphere
https://www.readbyqxmd.com/read/28621917/molecules-designed-to-contain-two-weakly-coupled-spins-with-a-photo-switchable-spacer
#15
Guillem Aromi, Jorge Salinas-Uber, Marta Estrader, Jordi Garcia, Paul Lloyd-Williams, Anna Sadurní, Dominik Dengler, Joris van Slageren, Nicholas Chilton, Olivier Roubeau, Simon Teat, Jordi Ribas-Ariño
Controlling the charges and spins of molecules lyes at the heart of spintronics. We report the design of a photoswitchable molecule consisting of two independent spins separated by a photo-switchable moiety contained within a new ligand, H4L, that features a dithienylethene photochromic unit and two lateral coordinating moieties, yielding molecules with the [MM···MM] topology. Compounds [M4L2(py)6] (M = Cu, 1; Co, 2; Ni, 3; Zn, 4) have been prepared and described by single crystal X-ray diffraction (SCXRD)...
June 16, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28621522/formation-and-structure-of-wild-type-huntingtin-exon-1-fibrils
#16
J Mario Isas, Andreas Langen, Myles C Isas, Nitin Kumar Pandey, Ansgar B Siemer
The fact that the heritable neurodegenerative disorder Huntington's Disease (HD) is autosomal dominant means that there is one wild type and one mutant allele in most HD patients. The CAG repeat expansion in the exon 1 of the protein huntingtin (HTTex1) that causes the disease, leads to the formation of HTT fibrils in vitro and vivo. An important question for understanding the molecular mechanism of HD is which role wild type HTT plays for the formation, propagation, and structure of these HTT fibrils. Here we report that fibrils of mutant HTTex1 are able to seed the aggregation of wild type HTTex1 into amyloid fibrils which in turn can seed the fibril formation of mutant HTTex1...
June 16, 2017: Biochemistry
https://www.readbyqxmd.com/read/28620695/liposomes-modified-by-mono-and-bis-phthalocyanines-a-comprehensive-epr-study
#17
Dariusz Man, Rudolf Słota, Anna Kawecka, Grzegorz Engel, Gabriela Dyrda
The impact of selected metallophthalocyanines, featuring diverse molecular structure, upon the fluidity of liposome membranes was studied using the spin label EPR technique. The "mono"-type MPc's (M = Zn, Sn; Pc = C32H16N8 is the phthalocyanine ligand) and sandwich LnPc2 complexes (Ln = Nd, Sm, Gd) were explored. Liposomes were obtained in a sonication process, from egg yolk lecithin (EYL) in water. TEMPO and 16-DOXYL spin labels were used to monitor the peripheral and central part of the lipid double layer, respectively, which allowed to localize the phthalocyanine additive within the bilayer, as well as to perform independent measurements of changes in fluidity upon addition thereof...
June 2017: European Physical Journal. E, Soft Matter
https://www.readbyqxmd.com/read/28618363/simultaneous-sorption-and-catalytic-oxidation-of-trivalent-antimony-by-canna-indica-derived-biochars
#18
Xiaoqiang Cui, Qijun Ni, Qiang Lin, Kiran Yasmin Khan, Tingqiang Li, Muhammad Bilal Khan, Zhenli He, Xiaoe Yang
The simultaneous sorption and oxidation of Sb(III) on biochars were investigated using batch experiments. The biochars were derived from Canna indica at different pyrolysis temperatures (300-600 °C, referred as CIB300-CIB600), and characterized by FTIR, BET, XRD, SEM-EDS, EPR and Boehm titration. The Sb(III) sorption data could be well fitted by both the Langmuir and Freundlich models, and the pseudo-second order model is best for describing the kinetic data. The maximum Sb(III) sorption capacity of CIB300 was 16...
June 12, 2017: Environmental Pollution
https://www.readbyqxmd.com/read/28613896/catalytic-n2-reduction-into-silylamines-and-thermodynamics-of-n2-binding-at-square-planar-fe
#19
Demyan E Prokopchuk, Eric S Wiedner, Eric D Walter, Codrina V Popescu, Nicholas A Piro, W Scott Kassel, R Morris Bullock, Michael T Mock
The geometric constraints imposed by a tetradentate P4N2 ligand play an essential role in stabilizing square planar Fe complexes with changes in metal oxidation state. A combination of high-pressure electrochemistry and variable temperature UV-vis spectroscopy were used to obtain thermodynamic measurements of N2 binding. In addition, X-ray crystallography, 57Fe Mössbauer spectroscopy, and EPR spectroscopy were used to fully characterize these new compounds. Analysis of Fe0, FeI, and FeII complexes reveals that the free energy of N2 binding across three oxidation states spans more than 37 kcal mol-1...
June 14, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28613843/highly-elevated-levels-and-particle-size-distributions-of-environmentally-persistent-free-radicals-in-haze-associated-atmosphere
#20
Li Li Yang, Guorui Liu, Minghui Zheng, Rong Jin, Qingqing Zhu, Yuyang Zhao, Xiaolin Wu, Yang Xu
Levels and particle-size distributions of environmentally persistent free radicals (EPFRs) in haze-associated atmospheric particulate matter (PM) have not been highlighted, even though they may enter the human body along with PM and adversely affect human health. This study quantified the levels of EPFRs in airborne PM with different aerodynamic diameters (dae) using electron paramagnetic resonance (EPR) spectroscopy. EPR spectra showed a single, unstructured signal from persistent semiquinone radicals. The average concentration of EPFRs in the airborne PM during haze events was 2...
June 14, 2017: Environmental Science & Technology
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