Photoexcited metal ions

V. 1. A. Thermal Reactions with Naked Ions and Atoms V.l.B. Thermal Reactions with Ligated Metal Ions V.l.C. Reactions with Photoexcited Metal Ions V.2. Reactions with Metal Atoms in a Matrix References... 

It turned out that the dodecylsulfate surfactants Co(DS)i Ni(DS)2, Cu(DS)2 and Zn(DS)2 containing catalytically active counterions are extremely potent catalysts for the Diels-Alder reaction between 5.1 and 5.2 (see Scheme 5.1). The physical properties of these micelles have been described in the literature and a small number of catalytic studies have been reported. The influence of Cu(DS)2 micelles on the kinetics of quenching of a photoexcited species has been investigated. Interestingly, Kobayashi recently employed surfactants in scandium triflate catalysed aldol reactions". Robinson et al. have demonshuted that the interaction between metal ions and ligand at the surface of dodecylsulfate micelles can be extremely efficient. ... 

Vames AW, Dodson RB, Wehry EL (1972) Interactions of transition-metal ions with photoexcited states of flavins. Fluorescence quenching studies. J Am Chem Soc 94 946-950... 

Sousa LR, Larson JM (1977) Crown ether model systems for the study of photoexcited state response to geometrically oriented perturbers. The effect of alkali metal ions on emission from naphthalene derivatives. J Am Chem Soc 99 307-310... 

Significant effects of metal ions on photoinduced FT in a zinc porphyrin-naphthalenediimide (ZnP NIm) dyad were reported to attain the long-lived CS state (50). A transient absorption spectrum observed at 0.1 Xs after the laser pulse excitation of a PhCN solution of ZnP NIm is shown in Fig. 10(a) (50). The transient absorption bands at479,531,583,620,685 (sh), and 763 nm are assigned to NIm" by comparison with those of NIm" produced independently by the one-electron reduction of ZnP NIm with tetramethylsemiquinone radical anion [Fig. 10(Z))] (50). The absorption band due to ZnP" + is also observed at 410 nm. Thus, the photoexcitation of ZnP NIm results in FT from ZnP to NIm to give the CS state (ZnP —NIm" ). Fach absorption band decays at the same rate, obeying first-order kinetics [inset of Fig. 10(a)]. The rate constant (Atcr) of the CR process of the CS state is obtained from the first-order plot ZnP —NIm as 7.7 x 10 s (the lifetime x= 1.3 xs) (50). 

In the presence of Y(OTf>3 (1.0 x lO M), photoexcitation of the Fc AQ system using a femtosecond laser also results in efficient ET from Fc to AQ within 500 fs (53). However, the transient absorption band is observed at 700 nm in the presence of Y(OTf>3 and is significantly red-shifted as compared with that observed at 600 nm in the absence of Y(OTf>3, as shown in Fig. 15(a) (53). Such a red-shift was reported for the complex formation of semiquinone radical anions with metal ions (54). The decay of absorbance at 420 and 700 nm due to the Fc + —AQ" Y(OTf)3 complex obeys first-order kinetics to afford... 

Apart from the thermal oxidation-reduction reactions involving metal ions in different valency states, discussed in detail in relation to the initiation of autoxida-tion, one of the most important modes of formation of free radicals is by photoexcitation. The modes of formation can be generally classified as (A) bond-breaking reactions, (B) electron transfer reactions, and (C) reactions which in general form an electronically excited state of the absorbing molecule which produces atoms or free radicals in subsequent bimolecular collisions with other species present. 

Apart from electron-deficient metal fragments, free metal atoms as well as metal ions can insert into C-H and C-C bonds. In 1980, Billups et al. demonstrated that photoexcited Fe atoms in a methane matrix reacted to provide HFeCHg. Ozin and McCaffrey subsequently studied this reaction in greater detail and found that the reaction is reversible at different wavelengths [Eq. 

Hydrogen exchange has been used to map protein binding sites for ligands as small as metal ions. An early HX-MS study examined effects of Ca + binding on recoverin, a sensor that enhances the lifetime of photoexcited rhodopsin by inhibit-... 

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