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Israel Journal of Chemistry

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https://www.readbyqxmd.com/read/29335656/hydrogen-atom-transfer-oxidation-with-h2o2-catalyzed-by-feii-1-2-bis-2-2-bipyridyl-6-yl-ethane-h2o-2-2-likely-involvement-of-a-%C3%AE-hydroxo-%C3%AE-1-2-peroxo-diiron-iii-intermediate
#1
Alexander M Khenkin, Madhu Vedichi, Linda J W Shimon, Matthew A Cranswick, Johannes E M N Klein, Lawrence Que, Ronny Neumann
The iron(II) triflate complex (1) of 1,2-bis(2,2'-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30% H2O2 to an acetonitrile solution of 1 yielded 2, a green compound with λmax=710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (ΔEQ) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm-1 that downshifted to 832, 540 and 441 cm-1 when 1 was treated with H218O2...
November 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/29332949/convergent-synthesis-of-%C3%AE-branched-amines-by-transition-metal-catalyzed-c-h-bond-additions-to-imines
#2
Joshua R Hummel, Jonathan A Ellman
α-Branched amines are ubiquitous in drugs and natural products, and consequently, synthetic methods that provide convergent and efficient entry to these structures are of considerable value. Transition-metal-catalyzed C-H bond additions to imines have the potential to be highly practical and atom-economic approaches for the synthesis of a diverse and complex array of α-branched amine products. These strategies typically employ readily available starting inputs, display high functional group compatibility, and often avoid the production of stoichiometric waste byproducts...
November 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/29129937/cerebrospinal-fluid-proteins-as-regulators-of-beta-amyloid-aggregation-and-toxicity
#3
Kayla M Pate, Regina M Murphy
Amyloid disorders, such as Alzheimer's, are almost invariably late-onset diseases. One defining diagnostic feature of Alzheimer's disease is the deposition of beta-amyloid as extracellular plaques, primarily in the hippocampus. This raises the question: are there natural protective agents that prevent beta-amyloid from depositing, and is it loss of this protection that leads to onset of disease? Proteins in cerebrospinal fluid (CSF) have been suggested to act as just such natural protective agents. Here, we describe some of the early evidence that led to this suggestion, and we discuss, in greater detail, two CSF proteins that have garnered the bulk of the attention...
July 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28993712/reversing-the-amyloid-trend-mechanism-of-fibril-assembly-and-dissolution-of-the-repeat-domain-from-a-human-functional-amyloid
#4
Ryan P McGlinchey, Jennifer C Lee
Amyloids are traditionally observed in the context of disease. However, there is growing momentum that these structures can serve a beneficial role where the amyloid carries out a specific function. These so called 'functional amyloids' have all the structural hallmarks of disease-associated amyloids, raising the question as to what differentiates a well-behaved benign amyloid from a lethally destructive one. Here, we review our work on the repeat domain (RPT) from Pmel17, an important functional amyloid involved in melanin biosynthesis...
July 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28935998/theory-of-amyloid-fibril-nucleation-from-folded-proteins
#5
Lingyun Zhang, Jeremy D Schmit
We present a theoretical model for the nucleation of amyloid fibrils. In our model we use helix-coil theory to describe the equilibrium between a soluble native state and an aggregation-prone unfolded state. We then extend the theory to include oligomers with β-sheet cores and calculate the free energy of these states using estimates for the energies of H-bonds, steric zipper interactions, and the conformational entropy cost of forming secondary structure. We find that states with fewer than ~10 β-strands are unstable relative to the dissociated state and three β-strands is the highest free energy state...
July 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28919642/membrane-binding-of-parkinson-s-protein-%C3%AE-synuclein-effect-of-phosphorylation-at-positions-87-and-129-by-the-s-to-d-mutation-approach
#6
Pravin Kumar, Nathalie Schilderink, Vinod Subramaniam, Martina Huber
Human α-synuclein, a protein relevant in the brain with so-far unknown function, plays an important role in Parkinson's disease. The phosphorylation state of αS was related to the disease, prompting interest in this process. The presumed physiological function and the disease action of αS involves membrane interaction. Here, we study the effect of phosphorylation at positions 87 and 129, mimicked by the mutations S87A, S129A (nonphosphorylated) and S87D, S129D (phosphorylated) on membrane binding. Local binding is detected by spin-label continuous-wave electron paramagnetic resonance...
July 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/29104308/stereocontrolled-synthesis-of-spiroketals-an-engine-for-chemical-and-biological-discovery
#7
Alyssa L Verano, Derek S Tan
Spiroketals are key structural motifs found in diverse natural products with compelling biological activities. However, stereocontrolled synthetic access to spiroketals, independent of their inherent thermodynamic preferences, is a classical challenge in organic synthesis that has limited in-depth biological exploration of this intriguing class. Herein, we review our laboratory's efforts to advance the glycal epoxide approach to the stereocontrolled synthesis of spiroketals via kinetically controlled spirocyclization reactions...
April 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28659646/synthesis-of-the-right-side-structure-of-type-b-physalins
#8
Masaki Morita, Shuntaro Kojima, Megumi Ohkubo, Hiroyuki Koshino, Daisuke Hashizume, Go Hirai, Keiji Maruoka, Mikiko Sodeoka
We present a full account of our synthetic studies on the racemic DEFGH-ring moiety of physalins, featuring domino ring transformation of a tricyclic key intermediate. We also report the results of a detailed mechanistic examination of the domino ring transformation, as well as a reoptimization of the 2,3-Wittig rearrangement and methylation steps. Furthermore, we have newly established a method for the preparation of an optically active synthetic intermediate by enzymatic kinetic resolution. Our work provides access to both natural and nonnatural right-side physalin structures...
April 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28652644/the-development-of-alkoxide-directed-metallacycle-mediated-annulative-cross-coupling-chemistry
#9
Glenn C Micalizio, Haruki Mizoguchi
Alkoxide-directed metallacycle-mediated cross-coupling is a rapidly growing area of reaction methodology in organic chemistry. Over the last decade, developments have resulted in > thirty new and highly selective intermolecular (or "convergent") C-C bond-forming reactions that have established powerful retrosynthetic relationships in stereoselective synthesis. While early studies were focused on developing transformations that forge a single C-C bond by way of a functionalized and unsaturated metallacyclopentane intermediate, recent advances mark the ability to employ this organometallic intermediate in additional stereoselective transformations...
April 2017: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/29081538/mean-first-passage-times-in-biology
#10
Nicholas F Polizzi, Michael J Therien, David N Beratan
Many biochemical processes, such as charge hopping or protein folding, can be described by an average timescale to reach a final state, starting from an initial state. Here, we provide a pedagogical treatment of the mean first-passage time (MFPT) of a physical process, which depends on the number of intervening states between the initial state and the target state. Our aim in this tutorial review is to provide a clear development of the mean first-passage time formalism and to show some of its practical utility...
November 2016: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28736456/activating-metal-sites-for-biological-electron-transfer
#11
Edward I Solomon, Ryan G Hadt, Benjamin E R Snyder
This review focuses on the unique spectroscopic features of the blue copper active sites. These reflect a novel electronic structure that activates the site for rapid long-range electron transfer in its biological function. The role of the protein in determining the geometric and electronic structure of this site is defined, as is its contribution to function. This has been referred to as the entatic/rack-induced state. These concepts are then extended to cytochrome c, which is also determined to be in an entatic state...
October 2016: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28239191/the-rise-of-radicals-in-bioinorganic-chemistry
#12
Harry B Gray, Jay R Winkler
Prior to 1950, the consensus was that biological transformations occurred in two-electron steps, thereby avoiding the generation of free radicals. Dramatic advances in spectroscopy, biochemistry, and molecular biology have led to the realization that protein-based radicals participate in a vast array of vital biological mechanisms. Redox processes involving high-potential intermediates formed in reactions with O2 are particularly susceptible to radical formation. Clusters of tyrosine (Tyr) and tryptophan (Trp) residues have been found in many O2-reactive enzymes, raising the possibility that they play an antioxidant protective role...
October 2016: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28190893/metalloneurochemistry-and-the-pierian-spring-shallow-draughts-intoxicate-the-brain
#13
Jacob M Goldberg, Andrei Loas, Stephen J Lippard
Metal ions perform critical and diverse functions in nervous system physiology and pathology. The field of metalloneurochemistry aims to understand the mechanistic bases for these varied roles at the molecular level. Here, we review several areas of research that illustrate progress toward achieving this ambitious goal and identify key challenges for the future. We examine the use of lithium as a mood stabilizer, the roles of mobile zinc and copper in the synapse, the interplay of nitric oxide and metals in retrograde signaling, and the regulation of iron homeostasis in the brain...
October 2016: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/28090121/redox-signaling-through-dna
#14
Elizabeth O'Brien, Rebekah M B Silva, Jacqueline K Barton
Biological electron transfer reactions between metal cofactors are critical to many essential processes within the cell. Duplex DNA is, moreover, capable of mediating the transport of charge through its π-stacked nitrogenous bases. Increasingly, [4Fe4S] clusters, generally redox-active cofactors, have been found to be associated with enzymes involved in DNA processing. DNA-binding enzymes containing [4Fe4S] clusters can thus utilize DNA charge transport (DNA CT) for redox signaling to coordinate reactions over long molecular distances...
October 2016: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/27994254/using-biosynthetic-models-of-heme-copper-oxidase-and-nitric-oxide-reductase-in-myoglobin-to-elucidate-structural-features-responsible-for-enzymatic-activities
#15
Ambika Bhagi-Damodaran, Igor Petrik, Yi Lu
In biology, a heme-Cu center in heme-copper oxidases (HCOs) is used to catalyze the four-electron reduction of oxygen to water, while a heme-nonheme diiron center in nitric oxide reductases (NORs) is employed to catalyze the two-electron reduction of nitric oxide to nitrous oxide. Although much progress has been made in biochemical and biophysical studies of HCOs and NORs, structural features responsible for similarities and differences within the two enzymatic systems remain to be understood. Here, we discuss the progress made in the design and characterization of myoglobin-based enzyme models of HCOs and NORs...
October 2016: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/27909346/copper-i-dioxygen-adducts-and-copper-enzyme-mechanisms
#16
Jeffrey J Liu, Daniel E Diaz, David A Quist, Kenneth D Karlin
Primary copper(I)-dioxygen (O2) adducts, cupric-superoxide complexes, have been proposed intermediates in copper-containing dioxygen-activating monooxygenase and oxidase enzymes. Here, mechanisms of C-H activation by reactive copper-(di)oxygen intermediates are discussed, with an emphasis on cupric-superoxide species. Over the past 25 years, many synthetically derived cupric-superoxide model complexes have been reported. Due to the thermal instability of these intermediates, early studies focused on increasing their stability and obtaining physical characterization...
October 2016: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/27777444/exploring-electron-proton-transfer-and-conformational-changes-in-the-nitrogenase-mofe-protein-and-femo-cofactor-through-cryoreduction-epr-measurements
#17
Roman Davydov, Nimesh Khadka, Zhi-Yong Yang, Andrew J Fielding, Dmitriy Lukoyanov, Dennis R Dean, Lance C Seefeldt, Brian M Hoffman
We combine cryoreduction/annealing/EPR measurements of nitrogenase MoFe protein with results of earlier investigations to provide a detailed view of the electron/proton transfer events and conformational changes that occur during early stages of [e(-)/H(+)] accumulation by the MoFe protein. This includes reduction of (i) the non-catalytic state of the iron-molybdenum cofactor (FeMo-co) active site that is generated by chemical oxidation of the resting-state cofactor (S = 3/2)) within resting MoFe (E0), and (ii) the catalytic state that has accumulated n =1 [e(-)/H(+)] above the resting-state level, denoted E1(1H) (S ≥ 1) in the Lowe-Thorneley kinetic scheme...
October 2016: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/26213415/a-newcomer-s-guide-to-peptide-crystallography
#18
Ryan K Spencer, James S Nowick
Here we provide a guide for adapting the tools developed for protein X-ray crystallography to study the structures and supramolecular assembly of peptides. Peptide crystallography involves selecting a suitable peptide, crystallizing the peptide, collecting X-ray diffraction data, processing the diffraction data, determining the crystallographic phases and generating an electron density map, building and refining models, and depositing the crystallographic structure in the Protein Data Bank (PDB). Advances in technology make this process easy for a newcomer to adopt...
June 1, 2015: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/27635101/mechanistic-enzymology-of-the-radical-sam-enzyme-desii
#19
Mark W Ruszczycky, Hung-Wen Liu
DesII is a member of the radical SAM family of enzymes that catalyzes radical-mediated transformations of TDP-4-amino-4,6-didexoy-D-glucose as well as other sugar nucleotide diphosphates. Like nearly all radical SAM enzymes, the reactions begin with the reductive homolysis of SAM to produce a 5'-deoxyadenosyl radical which is followed by regiospecific hydrogen atom abstraction from the substrate. What happens next, however, depends on the nature of the substrate radical so produced. In the case of the biosynthetically relevant substrate, a radical-mediated deamination ensues; however, when this amino group is replaced with a hydroxyl, one instead observes dehydrogenation...
April 2015: Israel Journal of Chemistry
https://www.readbyqxmd.com/read/27110035/identification-of-lectins-from-metastatic-cancer-cells-through-magnetic-glyconanoparticles
#20
Herbert W Kavunja, Patricia G Voss, John L Wang, Xuefei Huang
Cancer cells can have characteristic carbohydrate binding properties. Previously, it was shown that a highly metastatic melanoma cell line B16F10 bound to galacto-side-functionalized nanoparticles much stronger than the corresponding less metastatic B16F1 cells. To better understand the carbohydrate binding properties of cancer cells, herein, we report the isolation and characterization of endogenous galactose binding proteins from B16F10 cells using magnetic glyconanoparticles. The galactose-coated magnetic glyconanoparticles could bind with lectins present in the cells and be isolated through magnet-mediated separation...
March 1, 2015: Israel Journal of Chemistry
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