Kinetics and mechanism of the reaction of hydroxopentaaquarhodium(III) ion with l-Arginine in aqueous solution

Kinetic and Mechanistic Studies on the Interaction of Azide Ion with cis-diaqua-bis(bipyridyl) ruthenium(II) Complex and Hydroxopentaaqua Rhodium(III) complex in Aqueous Medium

The interaction of the aqua ligand substitution from cis-diaqua-bis(bipyridyl) ruthenium(II)complex([Ru(bpy)2(H2O)2]2+) and hydroxopentaaqua rhodium(III) complex ([Rh(H2O)5(OH)]+2) by azide has been studied spectrophotometrically as a function of [substrate complex], [ligand] and temperature at pH 4.5 for the first complex and pH 4.3 for the second complex, at constant ionic strength. The substitution reaction for both complexes shows two consecutive steps. Both steps are [ligand]-dependent. The activation parameters for both steps were evaluated. Thermodynamic parameters calculated from the temperature dependence of the outer-sphere association equilibrium constants are also consistent with an associative mode of activation. The products of the reactions have been characterised by IR, and ESI-mass spectroscopic analysis.

Interaction of Glycyl – Glycine with Hydroxopentaaquarhodium(Iii) Ion in Aqueous Medium: Kinetic and Mechanistic Studies

The kinetics of interaction between glycyl-glycine (L-L'H) and[Formula: see text] [Rh(H2O)5OH] 2+ have been studied spectrophotometrically in aqueous medium as a function of [Rh(H2O)5OH] 2+], [glycyl - glycine], pH and temperature at constant ionic strength. At pH 4.3, the interaction with glycyl-glycine shows two parallel paths: both processes are ligand-dependent. The rate constant for the processes are: k1 ∼ 10 −3 s −1 and k2∼10−5 s−3. The activation parameters calculated from Eyring plots are: ΔH1≠ - 26.7 ± 0.3 kj mol−1, ΔS1≠ =-207+1 JK−1 mol−1, ΔH2≠ = 92.4 ± 1.3 kJ mol−1 and ΔS2≠ = −42±4 JK−1 mol−1. The ligand glycyl-glycine, with different donor atoms (N and O), attacks two rhodium(III) ions (Rh(III) being a borderline acid), with different reactivity. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for both interaction processes. From the temperature dependence of the outer-sphere association equilibrium constant, the thermodynamic parameters calculated are: ΔH1∘ = 21.8 ± 1.9 kJ mol−1, ΔS1∘ = 124± 6 JK−1 mol−1, ΔH2∘ = 12.7 ±0.5 kj mol−1 and ΔS2∘ 89±2 JK−1 mol″−1 which give a negative A G° value for both the steps at all temperatures studied, supporting the spontaneous formation of an outer- sphere association complex for both the parallel paths. The product of the reaction has been characterized from IR and ESI-mass spectroscopic analysis.