Search results for "Protonation"
showing 10 items of 583 documents
Theoretical insights into inorganic-organic intercalation products of the layered perovskite HLaNb2O7: perspectives for hybrid proton conductors
2019
The modification of metal oxide surfaces with organic moieties has been widely studied as a method of preparing organic-inorganic hybrid materials for various applications. Among the inorganic oxides, ion-exchangeable layered perovskites are particularly interesting, because of their appealing electronic and reactive properties. In particular, their protonated interlayer surface can be easily functionalized with organic groups allowing the production of stable hybrid materials. As a further step in the design of new inorganic-organic hybrid proton conductors, a combined experimental and theoretical study of two intercalated compounds (propanol and imidazole) in HLaNb2O7 is presented here. A…
Adducts of free-base meso-tetraarylporphyrins with trihaloacetic acids: Structure and photostability
2020
Abstract Four diverse meso-tetraarylporphyrins in the form of diprotonated adducts with trifluoro-, trichloro-, tribromoacetic acids and acetic acid were investigated in benzene solution. Despite similar structural distortion of the chromophore system due to protonation, the respective adducts demonstrated different photostability when exposed to UV irradiation. The trifluoro- and trichloroacetic adducts, and the acetic acid one, showed some common features both molecular and in the mechanism of photodegradation. However, the tribromo-derivative decayed according to a different kinetic scheme, revealing a considerable impact of the bromine atoms upon the pyrrole units of the porphyrin macro…
Assignment of complex species by affinity capillary electrophoresis: The case of Th(IV)‐desferrioxamine B
2020
International audience; The electrophoretic mobility change of desferrioxamine B (DFO) was monitored by UV absorption spectrophotometry upon increasing the thorium(IV) concentration in the background electrolyte at two acidities ([HClO4]Tot = 0.0316 and 0.0100 M). These data enabled to assess the speciation model and to determine the equilibrium constant of [Th(DFO)H2]3+ at fixed ionic strength (I = 0.1 M (H,Na)ClO4). Affinity capillary electrophoresis (ACE) turned out to be most helpful in identifying the complexed species by ascertaining its charge and protonation state. The assignment of the correct stoichiometry relied on the reliable estimation of the electrophoretic mobility by assumi…
Quantitative parameters for the sequestering capacity of polyacrilates towards alkaline earth metal ions
2002
The complex formation constants of polyacrylic (PAA) ligands (1.4</=logN</=2.4, N=number of monomer units) with calcium and magnesium ions were determined in different ionic media at different ionic strengths, 0</=I</=1 mol l(-1), at t=25 degrees C. Experimental pH-metric data in the presence of Ca(2+) or Mg(2+) were firstly analysed in terms of apparent protonation constants, logK(H*), using the "three parameter model" proposed by Hogfeldt; differences in logK(H*), determined in different ionic media, were interpreted in terms of complex species formation. The only species present in the system M-PAA (M=Ca(2+) or Mg(2+)) is ML(2): attempts to find species of different stoichiometry were un…
CO2fixation and activation by metal complexes of small polyazacyclophanes
2001
The interaction of the cyclophanes 2,6,9,13-tetraaza[14]paracyclophane (L1) and 2,6,9,13-tetraaza[14]metacyclophane (L2) and of their Zn2+ and Cu2+ complexes with CO32− and its protonated forms is described. The actuation of the Cu2+–L2 system as an electrocatalyst for the reduction of CO2 to CO in water is advanced. Copyright © 2001 John Wiley & Sons, Ltd.
Diammine{N-[2-(hydroxyimino)propionyl]-N′-[2-(oxidoimino)propionyl]propane-1,3-diaminido-κ4N,N′,N′′,N′′′}iron(III)
2012
In the title compound, [Fe(C9H13N4O4)(NH3)2], the Fe(III) atom, lying on a mirror plane, is coordinated by four N atoms of a triply deprotonated tetra-dentate N-[2-(hy-droxy-imino)-propion-yl]-N'-[2-(oxidoimino)-propion-yl]propane-1,3-diaminide ligand in the equatorial plane and two N atoms of two ammonia mol-ecules at the axial positions in a distorted octa-hedral geometry. A short intra-molecular O-H⋯O hydrogen bond between the cis-disposed oxime O atoms stabilizes the pseudo-macrocyclic configuration of the ligand. In the crystal, mol-ecules are linked by N-H⋯O hydrogen bonds into a three-dimensional network. The ligand has a mirror-plane symmetry. One of the methyl-ene groups of the pro…
Diaqua[5,10,15,20-tetrakis(4-chlorophenyl)porphyrinato-κ4N]iron(III) trifluoromethanesulfonate–4-hydroxy-3-methoxybenzaldehyde–water (1/1/2)
2014
In the title compound, [Fe(C44H24Cl4N4)(H2O)2](SO3CF3)·C8H8O3·2H2O, the FeIIIcation is chelated by the four N atoms of the deprotonated tetrakis(4-chlorotetraphenyl)porphyrin (TClPP) and further coordinated by two water molecules in a distorted octahedral geometry. In the crystal, the cations, anions, 4-hydroxy-3-methoxybenzaldehyde and water molecules of crystallization are linked by classical O—H...O hydrogen bonds and weak C—H...O and C—H...Cl hydrogen bonds into a three-dimensional supramolecular architecture. The crystal packing is further stabilized by weak C—H...π interactions involving pyrrole and benzene rings. π–π stacking between parallel benzene rings of adjacent 4-hydroxy-3-met…
Cover Picture: Direct CH Metalation with Chromium(II) and Iron(II): Transition-Metal Host / Benzenediide Guest Magnetic Inverse-Crown Complexes (Ang…
2009
Chromation and ferration are the latest additions to the concept of alkali-metal-mediated metalation, as described by J. Klett, R. E. Mulvey, and co-workers in their Communication on page 3317 ff. While the more electropositive sodium is essential for the reaction, it is the less electropositive chromium or iron that actually performs deprotonation of benzene. This novel reactivity can be likened to a game of chess in which the queen (Na) holds the king in check, while the knight (Cr, Fe) scores checkm(etal)ate.
Substrate promiscuity in DNA methyltransferase M.PvuII. A mechanistic insight
2012
M.PvuII is a DNA methyltransferase from the bacterium Proteus vulgaris that catalyzes methylation of cytosine at the N4 position. This enzyme also displays promiscuous activity catalyzing methylation of adenine at the N6 position. In this work we use QM/MM methods to investigate the reaction mechanism of this promiscuous activity. We found that N6 methylation in M.PvuII takes place by means of a stepwise mechanism in which deprotonation of the exocyclic amino group is followed by the methyl transfer. Deprotonation involves two residues of the active site, Ser53 and Asp96, while methylation takes place directly from the AdoMet cofactor to the target nitrogen atom. The same reaction mechanism…
UV‐Vis Spectroscopy Reveals a Correlation Between Y263 and BV Protonation States in Bacteriophytochromes
2019
Red-light photosensory proteins, phytochromes, link light activation to biological functions by interconverting between two conformational states. For this, they undergo large-scale secondary and tertiary changes which follow small-scale Z to E bond photoisomerization of the covalently bound bilin chromophore. The complex network of amino acid interactions in the chromophore-binding pocket plays a central role in this process. Highly conserved Y263 and H290 have been found to be important for the photoconversion yield, while H260 has been identified as important for bilin protonation and proton transfer steps. Here, we focus on the roles these amino acids are playing in preserving the chemi…