Search results for "Protonation"
showing 10 items of 583 documents
A comparative study of the application of the method of least-squares in the potentiometric determination of protonation constants.
1982
Methods of simple and multiple linear regression applied to the potentiometric determination of protonation constants of diprotic and triprotic acids are studied critically. The best way of fitting the data, according to the order of magnitude of the constants, is established. The conclusions are checked by calculating the protonation constants of succinic and citric acids.
Theoretical study on hydration of symmetrically different diazanaphthalenes
2005
Abstract Quinazoline (symmetrical) and quinoxaline (unsymmetrical), diazanaphthalenes involved in certain biological reactions, have been studied computational with the purpose of comparing their protonation and covalent hydration mechanisms. Geometry optimizations of neutral, mono and diprotonated cations and hydrated products have been carried out at three levels of theory. Geometry optimizations were performed at HF, DFT/B3LYP levels of theory using 6-311G* basis set and single point energies were calculated at the MP2 level of theory using the same basis set. In agreement with experimental results, calculations predict a two steps mechanism resulting in a hydrated cation in which the OH…
Synthesis, characterization and X-ray crystal structures of cyclam derivatives. 7. Hydrogen-bond induced allosteric effects and protonation cooperati…
2005
The unprecedented cooperative protonation properties displayed by a barrel-shaped macrotricyclic tetraamine incorporating two 14-membered bisamide rings maintained in a face-to-face arrangement is rationalized in terms of allosteric effects upon binding of the first and third protons.
Coordination behavior of sulfathiazole. Crystal structure of [Cu (sulfathiazole) (py)3Cl] superoxide dismutase activity
1995
Abstract The preparation, spectroscopic, magnetic properties, and crystal structure of [Cu(stzxpy) 3 Cl] (stz − stands for the deprotonated form of sulfathiazole, 4-amino-N-2-thiazolylbencenosulfonamide) are reported. Crystals are orthorhombic, space group Pbca, with cell constants a = 15.834(2), b = 17.512(4), and c = 18.79(2) A, and Z = 8. The structure was solved and refined to R = 0.041 (R W = 0.040). The structure consists of mononuclear units linked via hydrogen bonds to form the tridimensional pyramid. The geometry of CuN3N*NCl chromophore is distorted square-pyramid. The superoxide-dismutase mimetic activity of the compound is measured and compared with those of the SOD enzyme, the …
Oxidomolybdenum(IV), ‐(V), ‐(VI) Complexes with Relevance to Molybdenum Enzymes: Oxygen Atom Transfer, Redox Chemistry and EPR Spectroscopy
2010
The cis-dioxidomolybdenum(VI) complex Mo(NN′)2O2 (1) [(NN′) = N-(4-hydroxyphenyl)-2-pyrrolatocarbaldimine] transfers one oxygen atom to phosphanes PMenPh3–n (n = 0–3) to give quantitatively the respective phosphane oxides OPMenPh3–n (OAT, oxygen atom transfer). The kinetics of these OAT reactions has been investigated spectrophotometrically. When offering excess PMenPh3–n (n = 1–3), oxido(phoshane)molybdenum(IV) complexes Mo(NN′)2O(PMenPh3–n) 5a–5c are isolated and characterized by multinuclear NMR spectroscopy (1H, 13C, 31P, 15N), IR spectroscopy, UV/Vis spectroscopy and mass spectrometry. The redox chemistry of the molybdenum(IV) complexes 5a–5c and of molybdenum(VI) complex 1 has been pr…
Synthesis, Characterization, and Properties of Some Copper( II ) Complexes of 2‐Pyridineformamide Thiosemicarbazone (HAm4DH)
2006
Reactions between different copper(II) salts and 2-pyridineformamide thiosemicarbazone (HAm4DH) in neutral ethanolic media led to the formation of complexes with the formulae [Cu(HAm4DH)X2] (X = Cl or Br) (1, 2) and [Cu(HAm4DH)2]X2 (X = NO3 or ClO4) (3, 4). The same reactions carried out in the presence of triethylamine gave rise to new complexes with the general formulae [Cu(Am4DH)X] (X = Cl, Br, AcO, or NO3) (5–8), [Cu(H2O)(Am4DH)](ClO4) (9), and [Cu(Am4DH)2] (10), many of which were isolated with different molecules of crystallization and contain a deprotonated thiosemicarbazone (Am4DH). These complexes were characterized by elemental analysis, and different spectroscopic and magnetic te…
Electrochemistry of copper complexes with polyaza[n]paracyclophanes. Influence of ATP as an exogen ligand on the relative stability of the Cu(II) and…
2000
Abstract Interaction of Cu 2+ with the macrocycle 2,6,9,13-tetraaza[14]paracyclophane (L) and ATP has been followed by pH-metric titration, cyclic voltammetry and differential pulse voltammetry (DPV). Mixed adduct species with various degrees of protonation were found to be stable for pH>4. In neutral and alkaline media reduction of mixed complexes occurs in a two-electron quasi-reversible step in contrast with binary Cu 2+ L complexes which display two successive one-electron couples. The potentiometric and voltammetric data suggest that in ternary adducts ATP binds to Cu 2+ ions through the phosphate chain and one N-site of the adenine ring system.
An Iron-Based Molecular Redox Switch as a Model for Iron Release from Enterobactin via the Salicylate Binding Mode
2001
The iron release mechanism from protonated ferric enterobactin [Fe(III)(enterobactinH(3))] via the salicylate binding mode was probed. For this purpose, a tripodal dodecadentate ligand incorporating three salicylamide (OO) and three bipyridine (NN) binding sites was synthesized as well as iron complexes thereof. It was shown that a ferric ion coordinates selectively to the hard salicylamides and a ferrous ion binds to the softer bipyridines. Upon reduction or oxidation, the iron translocates reversibly and intramolecularly from one site to the other, thus displaying switchlike properties. Both states were characterized by cyclic voltammetry and visible and Mössbauer spectroscopy. The Mössba…
Synthesis, X-ray crystal structure, NMR characterization and theoretical calculations on [Cp2Ta(η2-H2)(CO)]+, the first thermally stable group 5 dihy…
2001
Protonation of Cp2TaH(CO) (Cp = C5H5, 1a; C5H4But, 1b) by HBF4·Et2O at −78 °C in CH2Cl2 affords [Cp2TaH2(CO)]BF4 (2, 3) as mixtures of 2 isomers. The minor ones (2a, 2b) contain the known trans-dihydride [Cp2TaH2(CO)]+ cations whereas the major ones (3a, 3b) are [Cp2Ta(η2-H2)(CO)]BF4, the first group 5 dihydrogen complexes. The crystal structure of the analogous complex 3a·BArf4 recorded at 120 K confirms the presence of the coordinated dihydrogen ligand, which displays an H–H separation of 1.09(2) A in agreement with distances calculated from NMR data. Protonation of Cp2TaH2(SiMe2Ph) by (Et2O)2 ·HBArf4 does not lead to an analogous silane derivative but to the new dinuclear complex [(Cp2…
A Bis(mu-phenoxo)-Bridged Dizinc Complex with Hydrolytic Activity
2013
The dinuclear complex [Zn2(papy)2]·2CH3OH [H2papy = N- (2-hydroxybenzyl)-N-(2-picolyl)glycine] was synthesized and characterized. The crystal structure of the complex reveals that both ZnII ions are pentacoordinate with distorted pentagonal bipyramidal coordination arrangements. The phenoxyl groups of each ligand bridge the two metal atoms, whereas each carboxylate of the ligand is terminally bound to one ZnII ion. Potentiometric studies of the ZnII:H2papy system in a methanol/water mixture show the existence of a mononuclear species at lower pH; but at a pH above 5, a dimeric species starts to dominate and transforms further into a bis(μ-phenoxo) bridged dizinc complex by deprotonation of …