Search results for "Protonation"
showing 10 items of 583 documents
Synthesis, structural and magnetic characterizations of new complexes of di-2,6-(2-pyridylcarbonyl)pyridine (pyCOpyCOpy) ligand
2013
International audience; Using the di-2,6-(2-pyridylcarbonyl)pyridine ligand (L1) as starting framework, five new mononuclear complexes were obtained: [Cu(L1)(MeCN)(ClO4)2] (1) [Co(L1)(MeCN)(Br)2]*MeCN (2), [Fe(L1)2](BF4)2*MeOH*H2O (3), [Cr(L2a)Cl2]*2MeOH (where HL2a is (6-(hydroxyl(methoxy)(pyridin-2-yl)methyl)pyridin-2-yl)(pyridin-2-yl)methanone) (4) and one trinuclear [NiII3] complex, [Ni3(L2b)2(Bz)2(EtOH)2](ClO4)2*2EtOH (where HL2b is (6-(hydroxyl(ethoxy)(pyridin-2-yl)methyl)pyridin-2-yl)(pyridin-2-yl)methanone; Bz = benzoato) (5). Their structural and magnetic characterizations are herein reported. All the metal ions show octahedral coordination geometry, which is slightly unusual for t…
Electrochemical and DFT studies of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile
2006
International audience; A detailed electrochemical study of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile is presented. For the Mo complex, the decomposition occurs by four different pathways involving classical and non-classical tautomers, whereas only the classical form is accessible for the W derivative. Each of the decomposition pathways has been quantitatively assessed by analyses of the linear sweep voltammograms. In addition to the previously established (B. Pleune, D. Morales, R. Meunier-Prest, P. Richard, E. Collange, J. C. Fettinger and R. Poli, J. Am. Chem. Soc., 1999, 121, 2209–2225) deprotonation, disproportionation, and H2 red…
Protonation constants and association of polycarboxylic ligands with the major components of seawater
2000
Apparent protonation constants, log βjH*, of 11 carboxylic acids were determined potentiometrically ([H+]-glass electrode) in artificial seawater containing six of the major components (Na+, K+, Mg2+, Ca2+, Cl-, and SO42-) at different salinities: S (‰) = 5, 15, 25, 35, 45. Values of log βjH* were fitted by the simple polynomial equation log βjH* = log TβjH + a1S1/2 + a2S + a3S3/2 (log TβjH = protonation constants at infinite dilution; a1, a2, a3 = empirical parameters), for mono-, di-, and tricarboxylates. For carboxylic anions with charge < −3, a better fit was obtained using the equation log βjH* = log TβjH + b1I + b0z* log(1 + b2I) (b0, b1, b2 = empirical parameters, z* = square sum of…
Molecular recognition of naphthalene diimide ligands by telomeric quadruplex-DNA: the importance of the protonation state and mediated hydrogen bonds.
2016
In depth Monte Carlo conformational scans in combination with molecular dynamics (MD) simulations and electronic structure calculations were applied in order to study the molecular recognition process between tetrasubstituted naphthalene diimide (ND) guests and G-quadruplex (G4) DNA receptors. ND guests are a promising class of telomere stabilizers due to which they are used in novel anticancer therapeutics. Though several ND guests have been studied experimentally in the past, the protonation state under physiological conditions is still unclear. Based on chemical intuition, in the case of N-methyl-piperazine substitution, different protonation states are possible and might play a crucial …
Determination of the electron-detachment energies of 2'-deoxyguanosine 5'-monophosphate anion: influence of the conformation.
2009
The vertical electron-detachment energies (VDEs) of the singly charged 2'-deoxyguanosine 5'-monophosphate anion (dGMP - ) are determined by using the multiconfigurational second-order perturbation CASPT2 method at the MP2 ground-state equilibrium geometry of relevant conformers. The origin of the unique low-energy band in the gas phase photoelectron spectrum of dGMP - , with maximum at around 5.05 eV, is unambiguously assigned to electron detachment from the highest occupied molecular orbital of π-character belonging to guanine fragment of a syn conformation. The presence of a short H-bond linking the 2-amino and phosphate groups, the guanine moiety acting as proton donor, is precisely resp…
Conformations and coordination schemes of carboxylate and carbamoyl derivatives of the tetraazamacrocycles cyclen and cyclam, and the relation to the…
1998
Abstract This paper discusses and rationalizes the metal coordination pattern of 12- and 14-membered tetraazamacrocyclic carboxylate and carbamoyl ligands based on the cyclen and cyclam framework in light of their acido–basic properties. Structural and protonation data are reviewed in order to illustrate the influence of the free ligand's protonation state and of the pH conditions during the complexation reaction on the final coordination mode of the metallic cations.
Unusual binding ability of α,β-dehydrodipeptides towards metal ions
1994
Abstract Ni II , Zn II and Co II complexes of α,β-dehydro-dipeptides (containing Gly, Leu, Ala, Val or Phe residues) were studied by potentiometric and spectroscopic methods. Deprotonation and coordination of amide nitrogens occurred in all cases around the physiological pH range. The dipeptides with composition of Xaa-Δ-Ala formed octahedral species, while Gly-Δ-Xaa (Xaa = Leu or Phe) formed square planar bis complexes with Ni II .
Molecular structure of the compound [Rh2(O2CCH3)3{(C6H4)P(BrC6H4-1,2)(C6H5)} · (HO2CCH3)2].Kinetic study of the exchange reaction of acetate groups w…
1993
Abstract The compound [Rh 2 (O 2 CCH 3 ) 3 {(C 6 H 4 )P(BrC 6 H 4 -1,2) (C 6 H 5 )} · (HO 2 CCH 3 ) 2 ] has been isolated in high yield from the thermal reaction of dirhodium tetraacetate and the phosphine P(BrC 6 H 4 -1,2) (C 6 H 5 ) 2 in acetic acid. The structure of this compound has been determined by X-ray diffraction; it crystallizes in the P 1 (triclinic) space group and contains three acetate groups bridging a Rh 2 4+ unit the RhRh distance being 2.432(1)A; the fourth bridging ligand is an ortho -bromophenyldiphenylphosphine metallated at one of the ortho positions of the unsubstituted phenyl rings. Two molecules of acetic acid occupy the axial coordination positions. Stepwise exch…
Isomerization and rearrangement of (E)- and (Z)-phenylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole: evidence for a “new” type of acid-catalysis …
2008
A kinetic investigation in methanol of the title reaction has evidenced the occurrence of two processes: the 1-E1-Z isomerization and the rearrangement of the (Z)-isomer into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole (1-Z T). The latter reaction is in line with the ability of the (Z)-phenylhydrazones of 3-benzoyl-1,2,4-oxadiazoles to undergo the so called mononuclear rearrangement of heterocycles (MRH). The occurrence of both the examined reactions is dependent on a Lewis-acid-catalysis. The obtained results have shown the possibility of a ‘new’ type of acid-catalysis (bifunctional catalysis by Lewis salts) in the MRH. This catalysis operates through a completely different me…
Syntheses and reactivity of oxo niobocene complexes Cp*2Nb(O)X (X=H, OCH3) and crystal structures of [Cp*2Nb(OH)F]BF4 and Cp*2Nb(O)OC(O)H (Cp*=η5-C…
1998
Abstract Reaction of Cp*2NbCl2 (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF forms the complexes Cp*2Nb(O)X (X=Cl: 2, H: 3). The ratio of 2 and 3 depends on the stoichiometry. If NaOMe is added or MeOH in solution Cp*2Nb(O)OMe 4 is formed in good yields. Reactivity studies with 3 and 4 show that the NbO as well as the Nb–X unit behave as chemically active sites. Protonation of 3 or 4 with HBF4 is followed by an attack of fluoride (from BF4− anion) to give [Cp*2Nb(OH)F]BF4 6 and [Cp*2NbF2]BF4 7. In contrast the reaction of 3 or 4 with HCO2H results in an exchange of X− by formate to give Cp*2Nb(O)OC(O)H 8. The crystal structures of 6 and 8 are reported. Electrochemical investigations of…