- Electronic Structure of a Transient Histidine Radical in Liquid Aqueous Solution: EPR Continuous-Flow Studies and Density Functional Calculations
-
Transient histidine radicals formed in aqueous solutions by oxidation of histidine with a Ti3+/H2O2 Fenton system at pH 2.0 have been studied by EPR using a fast continuous-flow setup and a dielectric ring resonator equipped with a mixing chamber. A histidine peroxy radical with a single EPR line at g = 2.0151 and a histidine cation radical with a complex hyperfine structure and g = 2.0023 have been detected. The hyperfine structure of the latter radical was analyzed by investigating two selectively deuterated histidines and using an EPR simulation and fit program for analysis of the spectra. Isotropic hyperfine coupling constants of two β-protons, three ring protons, and two nitrogen nuclei have been determined in this way and assigned to a histidine-OH adduct cation radical. Density functional theory (DFT) calculations at the B3LYP and PWP86 levels have been performed on protonated cation radicals of 4-ethylimida zole (as histidine models), yielding isotropic hyperfine coupling constants for three different positions of OH addition. The C5 position for OH addition (a 5-oxohistidine cation radical) is clearly supported by the calculated hyperfine coupling constants. The agreement between DFT and EPR is further improved when hydrogen-bonding interactions to the N1 and C2 protons are introduced in the calculations.
- Lassmann, Guenter,Eriksson, Leif A.,Himo, Fahmi,Lendzian, Friedhelm,Lubitz, Wolfgang
-
-
Read Online
- Reductions by titanium(ii) as catalyzed by titanium(iv)
-
The cobalt(iii) complexes, [(NH3)5CoBr]2+ and [(NH3)5CoI]2+ are reduced by Ti(ii) solutions containing Ti(iv), generating nearly linear (zero-order) profiles that become curved only during
- Mukherjee, Ritam,Yang, Zhiyong,Gould, Edwin S.
-
-
Read Online
- Charge transfer of Ti 4+ with Ar and N 2 at electron-volt energy
-
The charge-transfer reactions of ground state Ti4+ (3p6, 1S) with Ar and N2 were studied in a quadrupole r.f. ion trap at the mean collision energy of 4.55 eV. The rate coefficients were measured to be 1.06(0.14)×10-9 cm3/s for Ti4+ with Ar at an equilibrium temperature of 1.6×104 K and 7.45(0.38)×10-10 cm3/s for Ti4+ with N2 at an equilibrium temperature of 1.3×104 K. Both results are comparable with the Langevin rate coefficients.
- Yan, Min,Feng, Mang,Gao, Kelin,Zhu, Xiwen
-
-
Read Online
- Reactions of molybdenum(vi) with metal ion reductants
-
The reactions of aqueous H2MoO4 at low pH with titanium(ii), titanium(iii), europium(ii), vanadium(ii), and germanium(ii), as monitored at 430 nm, give biphasic profiles featuring a sharp rise in absorbance followed by a marked decrease (Fig. 1). The final product is the dimeric Mo(v) cation, [Mo2O4]2+, and the strongly absorbing intermediate is taken as a monomeric Mo(v) species. The molar absorbances of the transients from different reductants are not the same, nor are the rate laws governing the fadings. None of the decay curves exhibits evidence of a second order dependence on the transient. The kinetic behaviors of these systems are consistent with the intervention of successor complexes of the type, (formed by inner sphere reductions of Mo(vi)), which decompose, via first-order processes, to a monomeric Mo(v) species. The latter then experiences rapid dimerization, which is kinetically silent. The possibility that Ge(ii) bypasses the unstable tripositive state by reducing Mo(vi) to Mo(iv) (which then undergoes rapid Mo(vi)-Mo(iv) comproportionation) is considered. The Royal Society of Chemistry 2006.
- Yang, Zhiyong,Gould, Edwin S.
-
-
Read Online
- Electron transfer. Part 165: Oxidations of Ti(II)(aq) with ligated iron(III) and ruthenium(III)
-
Titanium(II) solutions, prepared by dissolving titanium wire in triflic acid + HF, contain equimolar quantities of Ti(IV). Treatment of such solutions with excess Fe(III) or Ru(III) complexes yield Ti(IV), but reactions with Ti(II) in excess give Ti(III). Oxidations by (NH3)5Ru(III) complexes, but not by Fe(III) species, are catalyzed by titanium(IV) and by fluoride. Stoichiometry is unchanged. The observed rate law for the Ru(III)-Ti(II)-Ti(IV) reactions in fluoride media points to competing reaction paths differing by a single F-, with both routes involving a Ti(II)-Ti(IV) complex which is activated by deprotonation. It is suggested that coordination of Ti(IV) to TiII(aq) minimizes the mismatch of Jahn-Teller distortions which would be expected to lower the Ti(II,III) self-exchange rate.
- Mukherjee, Ritam,Manivannan,Gould, Edwin S.
-
p. 3633 - 3636
(2008/10/09)
-
- Molybdenum and copper catalysis of reductions by titanium(II) and titanium(III)
-
Reductions of vanadium(iv), benzoquinone, and tri-iodide, both by titanium(iii) and by titanium(ii), are catalyzed by molybdenum(vi). The VO 2+-Ti(ii) reaction is catalyzed by copper(ii) as well. Reactions of Ti(ii) with the oxidant in excess y
- Yang, Zhiyong,Gould, Edwin S.
-
p. 396 - 398
(2007/10/03)
-
- Titanium (III) reduction of dimethylglyoxime: Electrochemical and kinetic studies
-
Titanium (III) mediated electroreduction of dimethyl glyoxime has been carried out in aqueous sulphuric acid medium and the reduction product has been isolated and characterised. The kinetic investigations have been carried out under stoichiometric and non-stoichiometric conditions at 306K. It has been found that the reaction follows overall second order kinetics, first order each in [Ti(III)] and [DMG] and fractional order in sulphuric acid. The effect of varying concentrations of Ti(III), DMG, H2SO4, ionic strength, and solvent composition has been studied. Effect of temperature has also been studied and activation parameters have been computed from Arrhenius and Eyring plots.
- Yashoda,Padmalatha,Sherigara,Nayak
-
p. 176 - 179
(2007/10/03)
-
- Study of immobilized catalysts. XXV. Mechanism of decomposition of complexes of CH3TiCl3 with polyacrylonitrile grafted to different polymer supports
-
Rupture of the Ti-C bond in complexes with ligands containing nitrile groups (CH3CN, PAN, P-gr.PAN, P = polyethylene, polypropylene, polytetrafluoroethylene, PAN = polyacrylonitrile) takes place according to two mechanisms: coordinate and homolytic. CH3TiCl3·2CH3CN complexes in solution decompose according to the homolytic pathway, and complexes with polymer ligands decompose according to the coordinate pathway (with the participation of the CN or CH bonds in the polymer). The formation of kinetically homogeneous complexes in solution with homo-PAN and complexes of two types in the case of PE-gr.PAN and PPr-gr.PAN was detected. The rate constants of decomposition of these complexes were found. Binding of Ti-CH3 primarily by C≡N bonds in the case of PPr-gr.PAN and with CH bonds in PE-gr.PAN could be obtained by selection of the polymer supports.
- Serebryanaya,Khrushch,Leonov,Pomogailo,D'yachkovskii
-
p. 470 - 475
(2008/10/08)
-