Salt and Solvent Effects on the Kinetics and Thermodynamics of the Inclusion of the Ruthenium Complex [Ru(NH₃)₅(4,4‘-bpy)]²⁺ in β-Cyclodextrin

Abstract

The influences of solvents (in water-cosolvent mixtures) and salts on the kinetics and thermodynamics of the inclusion of [Ru(NH3)5(4,4'-bpy)]2+ in beta-cyclodextrin (beta-CD) have been studied. Solvent effects on the kinetics can be described as a consequence of the competition of the cosolvent for the beta-CD cavity. The salt effects on the kinetics depend on the ion pairing of the anions with the [Ru(NH3)5(4,4'-bpy)]2+ complex. On the other hand, the solvent effects on the equilibrium constant depend on the stabilization of the 4,4'-bipyridine ligand in the water-cosolvent mixture relative to water. Finally, salt effects on the equilibrium constant are interpreted as a consequence of ion pairing between the anion of the salt and the inclusion complex.

On the Application of the Pseudophase Model to Excited State Processes: Quenching of Pyrene by the Iodide Ion in β‐Cyclodextrin and Micellar (SDS) Solutions

“…Thus, for an excited species with a lifetime of 100 ns, the decay rate constant k d is of the order of 10 7 s −1 , which is much higher than the rate constant for the exchange processes in Scheme 1. These exchange rate constants, for similar receptors and reactants to those studied here, are of the order of 4 × 10 4 mol −1 dm 3 and 10 2 s −1 for the entry and escape processes, respectively . Consequently, the slow exchange limit holds.…”

Kinetics of Photochemical Reactions under Restricted Geometry Conditions

“…When the receptor is b-cyclodextrin (b-CD) the rate constants corresponding to the forward and reverse processes in Eqn (3), for R ¼ ½RuðNH 3 Þ 5 4; 4 0 bpy 2þ are, respectively, 36610 3 mol À1 dm 3 s À1 and 122 s À 1 [26]. These rate constants are smaller than the rate constant corresponding to the decay of a typical excited species [Ru(bpy) 3 ] 2 þ , k*1:6610 6 s À1 , or to the rate constant of the quenching of this excited probe by S 2 O 8 2 À , k q ¼ 6610 9 mol À1 dm 3 s À1 [27] (both of these values in water).…”

Microheterogeneous Catalysis

“…Thus, β-CD decreases the rate of oxidation of [Fe(CN) 5 4phepy] 3- by [Co(NH 3 ) 4 (H 2 O) 2 ] 3+ whereas the rate of this reaction increases in the presence of 2-hydroxypropyl - β-CD. On the other hand, for a given cyclodextrin, changes in reactivity can also be tuned through the addition to the reaction medium of substances, such as co-solvents or salts, which change the binding constants of the reactants [ 93 , 94 , 95 , 96 , 97 , 98 ].…”