Search results for "PROTON"
showing 10 items of 5886 documents
Cyclopentadienylmolybdenum(II) and -(III) complexes containing diene and allyl ligands. Part 4. Reactivity studies of the bisallyl complex CpMo(supin…
1998
Abstract Compound CpMo( η 3 -C 3 H 5 ) 2 , 3, has been synthesized from CpMoCl 4 and four equivalents of allylmagnesium bromide. While the compound is stable in donor solvents at room temperature, warming in refluxing MeCN induces the formation of 1,5-hexadiene by a metal-mediated allyl-allyl coupling process. Treatment of 3 with Bu t NC at room temperature affords CpMo( η 3 -C 3 H 5 )(Bu t NC) 2 , 4. A similar reduction with presumed allyl radical loss occurs for [CpMo( η 3 -C 3 H 5 )( η 4 -C 4 H 6 )] + , [1c] + , to afford [CpMo( η 4 -C 4 H 6 )(Bu t NC) 2 ] + , 5. Treatment of [1c] + with methyllithium affords two products, the major one (1c) corresponding to the one-electron reduction pa…
From C–S–H to C–A–S–H: Experimental study and thermodynamic modelling
2015
Abstract It has long been known that the stoichiometry of C–S–H varies with the calcium hydroxide concentration in solution. However, this issue is still far from understood. We revisit it in both experimental and modelling aspects. A careful analysis of the solubility confirms the existence of three different C–S–H phases, defined as Ca 4 H 4 Si 5 O 16 , Ca 2 H 2 Si 2 O 7 and Ca 6 (HSi 2 O 7 ) 2 (OH) 2 , respectively. The variation of the Ca/Si ratio of the three phases has been described by surface reactions: the increase of the Si content is accounted for by silicate bridging, the increase of calcium content and the surface charge are accounted for by reactions involving silanol groups v…
Paramagnetic NMR investigations of Co(II) and Ni(II) amicyanin.
1999
The paramagnetic 1H NMR spectra of the Co(II) and Ni(II) substituted forms of the type 1 blue copper protein (cupredoxin) amicyanin have been assigned. This is the first such analysis of a cupredoxin, which has a distorted tetrahedral active site with the ligands provided by two histidines, a cysteine and a methionine. The isotropic shifts of the resonances in these spectra are compared with those of Co(II) and Ni(II) azurin. A number of interesting similarities and differences are found. The coordination of the metal by the two equatorial histidine ligands is very similar in both proteins. The interaction between the introduced metal and the thiolate sulfur of the equatorial cysteine ligan…
NMR and homology modeling studies of copper(II)-halocyanin from Natronobacterium pharaonis bacteria
2004
Abstract Halocyanin from the haloalkaliphilic archaean Natronobacterium pharaonis is a peripheral membrane type 1 blue copper protein with a single polypeptide chain of 163 amino acid residues. Halocyanin participates as putative electron carrier protein associated to an electron acceptor role for a terminal oxidase and has the lowest redox potential value reported to date for a BCP. NMR studies and homology modeling calculations were performed to evaluate the electronic properties of Cu(II)-halocyanin from Natronobacterium pharaonis . The copper coordination site properties of Cu(II)-halocyanin are discussed. The 1 H NMR spectra, isotropic chemical shifts and relaxation times for halocyani…
Amino-phosphanes in Rh(I)-catalyzed hydroformylation: new mechanistic insights using D2O as deuterium-labeling agent
2005
International audience; In previous work, we have demonstrated that the dangling amino group in amino-phosphane ligands increases the rate of Rh-catalyzed styrene hydroformylation as a function of the amino group basicity and of the distance between the P and N functions. We now report additional stereochemical and mechanistic insights resulting from new catalytic experiments performed with Rh-α-P,N catalytic systems in the presence of D2O. In addition to the expected D0 product, the formation of the β-D1 aldehyde, PhCH(CH2D)CHO was observed in all cases by 1H and 13C NMR spectroscopy, indicating that H/D exchange occurs for the rhodium-hydride complex. Minor amounts of a β-D2 product, PhCH…
Thioflavin T Hydroxylation at Basic pH and Its Effect on Amyloid Fibril Detection
2008
The fluorescent dye thioflavin T (ThT) is commonly used for in situ amyloid fibril detection. In this work, we focused on the spectroscopic properties and chemical stability of ThT in aqueous solution as a function of pH, temperature, and dye concentration. A reversible hydroxylation process occurs in alkaline solutions, which was characterized using a combination of UV-vis absorption spectroscopy, proton NMR, and density functional theory (DFT). On the basis of these studies, we propose a chemical structure for the hydroxylated form. Finally, by means of fluorescence spectroscopy, ThT hydroxylation effects on in situ amyloid detection have been investigated, providing new insights on the e…
Requirement for the Proton-Pumping NADH Dehydrogenase I of Escherichia Coli in Respiration of NADH to Fumarate and Its Bioenergetic Implications
1997
In Escherichia coli the expression of the nuo genes encoding the proton pumping NADH dehydrogenase I is stimulated by the presence of fumarate during anaerobic respiration. The regulatory sites required for the induction by fumarate, nitrate and O2 are located at positions around –309, –277, and downstream of –231 bp, respectively, relative to the transcriptional-start site. The fumarate regulator has to be different from the O2 and nitrate regulators ArcA and NarL. For growth by fumarate respiration, the presence of NADH dehydrogenase I was essential, in contrast to aerobic or nitrate respiration which used preferentially NADH dehydrogenase II. The electron transport from NADH to fumarate …
“AND” luminescent “reactive” molecular logic gates: a gateway to multi-analyte bioimaging and biosensing
2014
This review outlines examples that illustrate a recent and highly innovative concept in the field of (bio)molecular sensing, namely the simultaneous multi-analyte detection using "reactive" luminescent probes that are able to produce an optical signal only in response to multiple (bio)chemical inputs and through covalent chemical reactions with target (bio)analytes. Unlike conventional "AND" molecular logic gates based on supramolecular photochemical mechanisms, these unusual "smart" optical (bio)probes are suitable tools to track the rise and fall of a wider range of biologically relevant analytes, in complex media and with higher selectivity. The potential utility of this concept for in v…
Investigation into the reaction of (t-BuC5H4)2Nb(η2-Te2)H with CH3Li: Hydride abstraction versus telluride methylation
2007
Abstract The reaction of [ Cp 2 ′ Nb ( Te 2 ) H ] ( 1 ) (Cp′ = t -BuC 5 H 4 ) with CH 3 Li in THF was examined by variable temperature 1 H NMR, ESR and mass spectroscopic means. From these methods it is evident that the diamagnetic compounds [ Cp 2 ′ NbH 2 ( TeCH 3 ) ] ( 2 ) and [ Cp 2 ′ Nb ( Te ) CH 3 ] ( 3 ) as well as the paramagnetic compound [ Cp 2 ′ Nb ( TeCH 3 ) 2 ] ( 4 ) form simultaneously. In the subsequent reaction of the intermediate solution with [Co 2 (CO) 8 ] compound 4 was consumed and the compound [ Cp 2 ′ Nb ( μ - TeCH 3 ) 2 Co(CO) 2 ] ( 5 ) formed in good yield. Complex 5 was characterized by IR and variable temperature 1 H NMR spectroscopies. Electrochemical two-electro…
Influence of Proton Conducting Cations on the Structure and Properties of 2D Anilate-Based Magnets
2017
The syntheses, structures, magnetic, and proton conductivity properties of a family of bimetallic anilate-based compounds with inserted alkylammonium cations are presented. The structures of (Me2NH2)[MnIICrIII(Br2An)3]·2H2O (1), (Et2NH2)[MnIICrIII(Br2An)3] (2), (Et3NH)[MnIICrIII(Cl2An)3] (3), and [(Et)(i-Pr)2NH]-[MnIICrIII(Br2An)3]·(CHCl3)0.5·(H2O) (4) contain a 2D anionic network formed by Mn(II) and Cr(III) ions linked through anilate ligands. In 1, 2, and 3, the hexagonal holes of this network are occupied by Me2NH2+, Et2NH2+, or Et3NH+ cations. Interestingly, the small increase of size of the templating cation in 4 ([(Et)(i-Pr)2NH]+ in the place of Me2NH2+, Et2NH2+ or Et3NH+), gives ris…