Anna Katafias

Kinetics and mechanism of electron transfer processes in a hydrogen peroxide—trispicolinatoruthenate(II) system

Oxidation of trispicolinatoruthenate(II) complex by hydrogen peroxide leads to the formation of mer-trispicolinatoruthenium(III) in acidic or neutral solutions. Kinetics of the reaction were studied under a large excess of H2O2 at constant pH. The initial rate method gives a rate expression of the form:

Systematic tuning of the reactivity of [RuII(terpy)(N^N)Cl]Cl complexes

- \hbox{d}[{\text{Ru}}({\text{II}})]/{\text{d}}t = k^{II} [{\text{H}}_{2} {\text{O}}_{2} ][{\text{Ru}}({\text{II}})]

Kinetics and mechanism of bromide ions oxidation by cerium(IV) in sulphuric acid solutions revisited

but the overall process examined till completion is far more complex. The rate of the reaction decreases with increasing pH to be practically completely retarded in alkaline media. The key step in the proposed reaction mechanism is the picolinato chelate ring opening followed by the substitution of the coordinated water by H2O2 and two-electron intramolecular ruthenium(II) oxidation. Formation of the final ruthenium(III) complex is assigned rather to the ruthenium(IV) reduction by H2O2 than ruthenium(II)–ruthenium(IV) comproportionation. The obtained results show the much slower rate of the trispicolinatoruthenate(II) oxidation by hydrogen peroxide or dioxygen than the mer-trispicolinatoruthenium(III) reduction by such bioreductants as cytochrome cII or some cobalt(II) reductants.

Hydrogen peroxide as a reductant of hexacyanoferrate(III) in alkaline solutions: kinetic studies

Abstract Three water-soluble ruthenium(III) compounds, Y[cis-RuCl2(pic)2]⋅nH2O (where pic = picolinate anion, Y = H(Hpic)2+ (1), H2pic+ (2) or K+ (3), n = 2, 1.5, and 2.5, respectively), were synthesized and their X-ray structures determined. Compound 1 was fully characterized both as solid and in aqueous solution by elemental analysis, magnetic susceptibility measurements, EPR, IR and UV-visible spectroscopy, cyclic voltammetry, microwave plasma atomic emission, and mass spectrometry, capillary electrophoresis and chromatographic methods. It was shown that the coordination geometry around the low spin (S = ½) RuIII center is distorted octahedral with the chlorido ligands in a cis configuration. Furthermore, all the measurements showed that the structures in the solid state and solution are absolutely identical with the cis-[RuCl2(pic)2]− anion being inert in aqueous solution. Microbial studies showed that 1 exerts a strong inhibition on the growth and increased mortality level of the bacterial strains – Escherichia coli, Pseudomonas sp., Sarcina sp., Micrococcus sp., Serratia sp., Bacillus cereus, Bacillus subtilis and yeast – Saccharomyces cerevisiae.

Kinetics of the Methylene Blue Oxidation by Cerium (IV) in Sulphuric Acid Solutions

Abstract The substitution behavior of the [RuII(terpy)(ampy)Cl]Cl (terpy = 2,2′:6′,2′′-terpyridine, ampy = 2-(aminomethyl)pyridine) complex in water with several bio-relevant ligands such as chloride, thiourea and N,N′-dimethylthiourea, was investigated and compared with the reactivity of the [RuII(terpy)(bipy)Cl]Cl and [RuII(terpy)(en)Cl]Cl (bipy =2,2′-bipyridine and en = ethylenediamine) complexes. Earlier results have shown that the reactivity and pKa values of Ru(II) complexes can be tuned by a systematic variation of electronic effects provided by bidentate spectator chelates. The reactivity of both the chlorido and aqua derivatives of the studied Ru(II) complexes increases in the order [RuII(terpy)(bipy)X]+/2+ < [RuII(terpy)(ampy)X]+/2+ < [RuII(terpy)(en)X]+/2+. This finding can be accounted for in terms of π back-bonding effects provided by the pyridine ligands. The activation parameters for all the studied reactions support an associative interchange substitution mechanism. Graphical Abstract