On Generalized Pseudostandard Words Over Binary Alphabets

International audienceIn this paper, we study generalized pseudostandard words over a two-letter alpha- bet, which extend the classes of standard Sturmian, standard episturmian and pseu- dostandard words, allowing different involutory antimorphisms instead of the usual palindromic closure or a fixed involutory antimorphism. We first discuss about pseu- doperiods, a useful tool for describing words obtained by iterated pseudopalindromic closure. Then, we introduce the concept of normalized directive bi-sequence (Θ,w) of a generalized pseudostandard word, that is the one that exactly describes all the pseudopalindromic prefixes of it. We show that a directive bi-sequence is normalized if and only if its set of factors does not intersect a finite set of forbidden ones. Moreover, we provide a construction to normalize any directive bi-sequence. Next, we present an explicit formula, generalizing the one for the standard episturmian words introduced by Justin, that computes recursively the next prefix of a generalized pseudostandard word in term of the previous one. Finally, we focus on generalized pseudostandard words having complexity 2n, also called Rote words. More precisely, we prove that the normalized bi-sequences describing Rote words are completely characterized by their factors of length 2

Hydrogen bonding to the cysteine ligand of superoxide reductase: acid–base control of the reaction intermediates

International audienceSuperoxide reductase SOR is a non-heme iron metalloenzyme that detoxifies superoxide radical in microorganisms. Its active site consists of an unusual non-heme Fe2+ center in a [His4 Cys1] square pyramidal pentacoordination, with the axial cysteine ligand proposed to be an essential feature in catalysis. Two NH peptide groups from isoleucine 118 and histidine 119 establish H-bondings with the sulfur ligand (Desulfoarculus baarsii SOR numbering). In order to investigate the catalytic role of these H-bonds, the isoleucine 118 residue of the SOR from Desulfoarculus baarsii was mutated into alanine, aspartate or serine residues. Resonance Raman spectroscopy showed that the mutations specifically induced an increase of the strength of the Fe3+-S(Cys) and S-Cβ(Cys) bonds as well as a change in conformation of the cysteinyl side chain, which was associated with the alteration of the NH hydrogen bonding to the sulfur ligand. The effects of the isoleucine mutations on the reactivity of SOR with O2●- were investigated by pulse radiolysis. These studies showed that the mutations induced a specific increase of the pKa of the first reaction intermediate, recently proposed to be an Fe2+-O2●- species. These data were supported by DFT calculations carried out on three models of the Fe2+-O2●- intermediate, with one, two or no H-bonds on the sulfur ligand. Our results demonstrated that the hydrogen bonds between the NH (peptide) and the cysteine ligand tightly control the rate of protonation of the Fe2+-O2●- reaction intermediate to form an Fe3+-OOH species

Elucidating dramatic ligand effects on SET processes: iron hydride versus Iron borohydride catalyzed reductive radical cyclization of unsaturated organic halides

An iron(II) borohydride complex ([(η1-H3BH)FeCl(NCCH3)4]) is employed as the precatalyst in iron-catalyzed radical cyclizations of unsaturated organic halides in the presence of NaBH4. Mechanistic investigations have established that the ligand bound to the metal center (acetonitrile versus ethylenebis(diphenylphosphine) (dppe)) plays a crucial role in the structure and reactivity of the active anionic iron(I) hydride ([HFeCl(dppe)2]−) and borohydride ([(η1-H3BH)FeCl(NCCH3)4]−) with unsaturated haloacetals. This work provides new insights into iron(I) hydride and borohydride species and their potential implication in single-electron processes

Iron oxidation in Escherichia coli bacterioferritin ferroxidase centre, a site designed to react rapidly with H2O2 but slowly with O2

Both O2 and H2O2 can oxidize iron at the ferroxidase center (FC) of Escherichia coli bacterioferritin (EcBfr) but mechanistic details of the two reactions need clarification. UV/Vis, EPR, and Mössbauer spectroscopies have been used to follow the reactions when apo‐EcBfr, pre‐loaded anaerobically with Fe2+, was exposed to O2 or H2O2. We show that O2 binds di‐Fe2+ FC reversibly, two Fe2+ ions are oxidized in concert and a H2O2 molecule is formed and released to the solution. This peroxide molecule further oxidizes another di‐Fe2+ FC, at a rate circa 1000 faster than O2, ensuring an overall 1:4 stoichiometry of iron oxidation by O2. Initially formed Fe3+ can further react with H2O2 (producing protein bound radicals) but relaxes within seconds to an H2O2‐unreactive di‐Fe3+ form. The data obtained suggest that the primary role of EcBfr in vivo may be to detoxify H2O2 rather than sequester iron

The Ruthenium Nitrosyl Moiety in Clusters: Trinuclear Linear μ-Hydroxido Magnesium(II)-Diruthenium(II), μ3-Oxido Trinuclear Diiron(III)–Ruthenium(II), and Tetranuclear μ4-Oxido Trigallium(III)-Ruthenium(II) Complexes

The ruthenium nitrosyl moiety, {RuNO}6, is important as a potential releasing agent of nitric oxide and is of inherent interest in coordination chemistry. Typically, {RuNO}6 is found in mononuclear complexes. Herein we describe the synthesis and characterization of several multimetal cluster complexes that contain this unit. Specifically, the heterotrinuclear μ3-oxido clusters [Fe2RuCl4(μ3-O)(μ-OMe)(μ-pz)2(NO)(Hpz)2] (6) and [Fe2RuCl3(μ3-O)(μ-OMe)(μ-pz)3(MeOH)(NO)(Hpz)][Fe2RuCl3(μ3-O)(μ-OMe)(μ-pz)3(DMF)(NO)(Hpz)] (7·MeOH·2H2O) and the heterotetranuclear μ4-oxido complex [Ga3RuCl3(μ4-O)(μ-OMe)3(μ-pz)4(NO)] (8) were prepared from trans-[Ru(OH)(NO)(Hpz)4]Cl2 (5), which itself was prepared via acidic hydrolysis of the linear heterotrinuclear complex {[Ru(μ-OH)(μ-pz)2(pz)(NO)(Hpz)]2Mg} (4). Complex 4 was synthesized from the mononuclear Ru complexes (H2pz)[trans-RuCl4(Hpz)2] (1), trans-[RuCl2(Hpz)4]Cl (2), and trans-[RuCl2(Hpz)4] (3). The new compounds 4-8 were all characterized by elemental analysis, ESI mass spectrometry, IR, UV-vis, and 1H NMR spectroscopy, and single-crystal X-ray diffraction, with complexes 6 and 7 being characterized also by temperature-dependent magnetic susceptibility measurements and Mössbauer spectroscopy. Magnetometry indicated a strong antiferromagnetic interaction between paramagnetic centers in 6 and 7. The ability of 4 and 6-8 to form linkage isomers and release NO upon irradiation in the solid state was investigated by IR spectroscopy. A theoretical investigation of the electronic structure of 6 by DFT and ab initio CASSCF/NEVPT2 calculations indicated a redox-noninnocent behavior of the NO ancillary ligand in 6, which was also manifested in TD-DFT calculations of its electronic absorption spectrum. The electronic structure of 6 was also studied by an X-ray charge density analysis

GDF15 promotes weight loss by enhancing energy expenditure in muscle

Funding Information: We thank R. Seeley for sharing GFRAL-null mice; B. Lowell for sharing β-less mice; and J. Wu for shipping β-less mice to us. G.R.S. was supported by a Diabetes Canada Investigator Award (DI-5-17-5302-GS), a Canadian Institutes of Health Research Foundation Grant (201709FDN-CEBA-116200), a Tier 1 Canada Research Chair in Metabolic Diseases and a J. Bruce Duncan Endowed Chair in Metabolic Diseases; D.W. by Fellowship Grants from the McMaster Institute for Research on Aging (MIRA) at McMaster University; S.R. by a postdoctoral fellowship supported by MITACS and Novo Nordisk; L.K.T. by a CIHR Post-Doctoral Fellowship Award and Michael DeGroote Fellowship Award in Basic Biomedical Science; E.M.D. by a Vanier Canada Graduate Scholarship; G.P.H. by the Natural Sciences and Engineering Research Council of Canada (NSERC: 400362); G.J.D. and S.M.F. by NSERC-CGSM scholarships; L.D. by the Fonds de Recherche du Québec-Santé doctoral training award; D.P.B. by the GSK Chair in Diabetes of Université de Sherbrooke and a FRQS J1 salary award. The Genotype-Tissue Expression (GTEx) Project was supported by the Common Fund of the Office of the Director of the National Institutes of Health, and by the NCI, NHGRI, NHLBI, NIDA, NIMH and NINDS. Funding Information: S.B.J. and R.E.K. are employees of Novo Nordisk, a pharmaceutical company producing and selling medicine for the treatment of diabetes and obesity. G.R.S. is a co-founder and shareholder of Espervita Therapeutics. McMaster University has received funding from Espervita Therapeutics, Esperion Therapeutics, Poxel Pharmaceuticals and Nestle for research conducted in the laboratory of G.R.S. S.R. is supported by a MITACS postdoctoral fellowship sponsored by Novo Nordisk. H.C.G. holds the McMaster-Sanofi Population Health Institute Chair in Diabetes Research and Care. G.R.S., G.P. and H.C.G. are inventors listed on a patent for identifying GDF15 as a biomarker for metformin. G.R.S. has received consulting/speaking fees from Astra Zeneca, Eli Lilly, Esperion Therapeutics, Merck, Poxel Pharmaceuticals and Cambrian Biosciences. The other authors declare no competing interests. Publisher Copyright: © 2023, The Author(s).Peer reviewedPublisher PD

Mixed valence (μ-phenoxido) FeII^{II}FeIII^{III} and FeIII^{III}FeIV^{IV} compounds: Electron and proton transfers

International audienceMixed-valence non-heme diiron centers are present at the active sites of a few enzymes and confer them interesting reactivities with the two ions acting in concert. Related (μ-phenoxido)diiron complexes have been developed as enzyme mimics. They exhibit very rich spectroscopic properties enabling independent monitoring of each individual ion, which proved useful for mechanistic studies of catalytic hydrolysis and oxidation reactions. In our studies of such complexes, we observed that these compounds give rise to a wide variety of electron transfers (intervalence charge transfer), proton transfers (tautomerism), coupled electron and proton transfers (H. abstraction and PCET). In this minireview, we present and analyze the main results illustrating the latter aspects

Towards a spin coupling model for the Mn4 cluster in Photosystem II

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