Donor-acceptor complexes redox reactions

Electron donor-acceptor complexes, electron transfer in the thermal and photochemical activation of, in organic and organometallic reactions, 29, 185 Electron spin resonance, identification of organic free radicals, 1, 284 Electron spin resonance, studies of short-lived organic radicals, 5, 23 Electron storage and transfer in organic redox systems with multiple electrophores, 28, 1... 

The fundamental theories behind electron transfer were discussed above in Section 2.1. Indeed, some of the most important empirical proofs for these theories have originated from photoinduced electron transfer in supramolecular donor-acceptor complexes. The difference between thermally and photochemi-cally induced electron transfer lies in both the orbitals participating in the reaction and in the additional thermodynamic driving force provided by the excited state. It is therefore important to consider the redox properties of excited-state species. 

Very little is known about the nature of the weak interactions of CAs in solutions where a vast majority of their chemical reactions has been studied. Particularly, the study of donor-acceptor complexes of CAs by modern physical-chemical methods is still of great interest. Besides, complexation of CAs with donors or acceptors of electron density is a useful tool for modifying the stability, reactivity and spectral properties of CAs. Systematic investigations of the redox properties of CAs are needed in order to elucidate the role of electron transfer in the transformations of CAs. 

This paper summarizes chemical grafting techniques explored in this laboratory that have potential biomedical application. These reactions, initiated by ceric ions, persulfate-bisulfite redox systems, or the presence of comonomers forming donor-acceptor complexes, were carried out in an aqueous environment under conditions which, with suitable modifications, might be tolerated in vivo. Grafting onto tissue surfaces by means of ionizing radiation will not be discussed since techniques for avoiding undesirable side reactions have not yet been developed. 

The donor-acceptor approach to solvent effects on the rates of redox reactions between different metal complexes, R. Schmid, Rev. Inorg. Chem., 1979,1,117-131 (48). 

Poly(pyridyl)ruthenium complexes, typically, [Ru(bpy)3]2+ have frequently been used as photocatalysts in the redox reactions between electron donors (Dred) and acceptors (Aox) to yield the oxidized (Dox) and reduced (Ared) forms (Eq. 20) [34-37] ... 

The redox reactions were observed also in the case of TP, MoVI, or Rcv" complexes with the 02 ligand, which is a reductant as well as an oxidant and can serve both as CT donor and CT acceptor. The LC excitation was followed by interligand charge transfer (LLCT) within the ()j moiety, leading in consequence to photo-dismutation to 202 and 02 [48]. 

The thionine function, possessing a relatively high redox potential, acts as an electron acceptor upon irradiation with visible light, which is considered to first form the electron-donor-acceptor (EDA) complex (exciplex) with the electron donor (D reductant). The electron in the exciplex further added to the thionine function to produce the colorless leucothionine and the electron acceptor (A). The A may be an oxidized form of D. The dark reaction may take place either by back electron transfer to the thionine function via the EDA complex or by air oxidation of the leucothionine when atmospheric oxygen is present. 

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