Luminescence Quenching in Supramolecular Systems:  A Comparison of DNA- and SDS Micelle-Mediated Photoinduced Electron Transfer between Metal Complexes

Abstract

Photoinduced electron transfer reactions between photoexcited Ru(phen)2dppz2+ (phen = 1,10-phenanthroline, dppz = dipyridophenazine) and acceptors Rh(phi)2bpy3+ and Rh(phen)2phi3+ (phi = 9,10-phenanthrenequinone diimine, bpy = 2,2‘-bipyridine) are compared in micelles and DNA. Both microheterogeneous environments contain a negatively charged surface and hydrophobic interior and the cationic complexes associate strongly with each. However, reactions between molecules bound to DNA or to micelles show striking differences which can be correlated with the unique character of the highly ordered, π-stacked basepairs in DNA compared to the disordered, aliphatic chains in the micelles. In DNA, Rh(phi)2bpy3+ quenches *Ru(phen)2dppz2+ on a fast time scale (unimolecular rate constant ≥ 108 s-1), whereas no detectable quenching of *Ru(II) emission by Rh(phen)2phi3+ is observed. In contrast, both complexes quench equally well in SDS micelles. Although static quenching on the nanosecond time scale is observed for Rh(phi)2bpy3+ in DNA, reactions in SDS occur dynamically by intramicellar diffusion, with a bimolecular rate constant of 1.1 × 108 M-1 s-1 for Rh(phi)2bpy3+ and 1.2 × 108 M-1 s-1 for Rh(phen)2phi3+. Reactions on DNA are also shown to be DNA-mediated in that no solvent-isotope effects are observed in the quenching. In addition, there is enantioselectivity seen in reactions on the right-handed DNA helix but not in the achiral micelle, indicating that quenching is sensitive to the geometry of intercalation. Efficient electron transfer quenching in DNA compared to SDS micelles therefore provides evidence against the cooperative association of molecules on DNA and for the importance of intercalative stacking of the donor and acceptor for fast electron transfer through the DNA π-stack.

Voltammetric, UV–Vis Spectrometric and Fluorescence Study of the Interaction of Ractopamine and DNA with the Aid of Multivariate Curve Resolution‐Alternating Least Squares

“…A binding ratio is defined as the concentration ratio of the binding ligand to total ligand [6], and the binding number is regarded as the number of participating DNA sites [7]. The interaction of DNA with drugs has been studied by various techniques including fluorescence [8], UV-vis [9], FT-IR [10], luminescence [11], capillary electrophoresis [12], NMR [13], microgravimetry [14], electroanalytical methods [15] and surface plasmon resonance [16]. Voltammetry has also been used to study such interactions [17 -20], and the observed electrochemical signals can provide useful information about the interaction mechanism, binding constant and binding forces.…”

Aggregation of Non Ionic Surfactant Igepal in Aqueous Solution: Fluorescence and Light Scattering Studies

“…the CMC, their aggregation number (n), their size. The most frequently applied methods to determine aggregation number are various scattering methods and fluorescence quenching (FQ) method [11][12][13][14][15][16][17][18][19][20].…”

Photoinduced Intermolecular Electron Transfer in Micelles: Dielectric and Structural Properties of Micelle Headgroup Regions

“…8,15,20,[40][41][42][43][44][45] The difference between the donor and acceptor standard potentials (∆E°), standard free energy of transfer (∆G), and reorganization energy (λ), shown in Figure 2, determine the energetics of the reaction. These quantities are determined by solute energy levels, local dielectric properties, and molecular sizes and charges.…”