Ruthenation

Mazin I I, Papaconstantopoulos D A and Singh D J 2000 Tight-binding Flamiltonians for Sr-filled ruthenates Application to the gap anisotropy and Flail coefficient in Sr2RuO Phys. Rev. B 61 5223... 

Ruthenium (IV) oxide [12036-10-1] M 133.1, d 6.97. Freed from nitrates by boiling in distilled water and filtering. A more complete purification is based on fusion in a KOH-KNO3 mix to form the soluble ruthenate and perruthenate salts. The melt is dissolved in water, and filtered, then acetone is added to reduce the ruthenates to the insoluble hydrate oxide which, after making a slurry with paper pulp, is filtered and ignited in air to form the anhydrous oxide [Campbell, Ortner and Anderson Anal Chem 33 58 1961]. 

Ruthenium-ozyd, n. (any) ruthenium oxide, esp. the sesquioxide, ruthenium(III) oxide, -oxydul, n. ruthenium monoxide, ruthenium-(II) oxide, -saure, /. ruthenic acid, -ver-bindung, /. ruthenium compound. 

Anson and co-workers have shown that two Co ions were not necessary for four-electron 02 reduction.266 The mew-substituted complex porphyrin Co(TPyP) (42) complex bears four active pyridyl donors which readily react with four equivalents of [Ru(NH3)5(OH2)]2+ to produce the tetra-ruthenated derivative. The four Ru centers are sufficiently remote that their RuIII/n potentials coincide. Under steady state conditions [Co(TPyP)] Ru(NH3)5 4]8+ (43) adsorbed onto a pyrolytic graphite working electrode catalyzes the reduction of dioxygen (Figure 6). 

A. Cagnini, I. Palchetti, I. Lioni, M. Mascini and A.P.F. Turner, Disposable ruthenized screen-printed biosensors for pesticides monitoring. Sens. Actual B 24, 85-89 (1995). 

Fig. 20. Molecular models of two conformers of 14-mer duplex d(ATACATGGTACATA) ruthenated at N7 of one of the guanine residues with [Ru(ri6-bip)Cl(en)]+ (10). Conformer (a) shows the intercalation of the arene (b) shows the nonintercalated phenyl ring of the arene stacked on a thymine residue.

Recent advances in measuring the kinetics of the various electron-transfer steps in this system have been achieved by use of flash photolysis of ruthenated derivatives of cytochrome c (Ru-Cc) (17-19). In these studies [Ru(bpy)3]2+ is covalently bound to a surface residue at a site that does not interfere with the docking of cytochrome c to cytochrome c oxidase. Solutions are then prepared containing both Ru-Cc and cytochrome c oxidase, and the two proteins associate to form a 1 1 complex. Flash photolysis of the solution leads directly to the excitation of the RuII(bpy)3 site, which then reduces heme c very rapidly. This method thus provides a convenient means to observe the subsequent intracomplex electron transfer from heme c to cytochrome c oxidase and further stages in the process. 

A more recent study was based on horse heart cytochrome c and Rhodobacter sphaeroides cytochrome c oxidase (18). Here, the Lys55 residue was ruthenated and the cytochrome c oxidase was mutated at several surface sites. A model of the complex between cytochrome c and subunit II of cytochrome c oxidase, the heme c and Cua cofactors, and the mutated residues is shown in Fig. 8. 

DR. EARLEY We had expected to find ruthenium(III) dimers as products of the reaction of Ru(Il) with perchlorate ion but we found none. We had expected ruthenium(II) to go to ruthen-ium(IV) and the Ru(IV) to react with a second Ru(II) to form a dimer, but this did not occur. 

A variety of physical methods has been used to ascertain whether or not surface ruthenation alters the structure of a protein. UV-vis, CD, EPR, and resonance Raman spectroscopies have demonstrated that myoglobin [14, 18], cytochrome c [5, 16, 19, 21], and azurin [13] are not perturbed structurally by the attachment of a ruthenium complex to a surface histidine. The reduction potential of the metal redox center of a protein and its temperature dependence are indicators of protein structure as well. Cyclic voltammetry [5, 13], differential pulse polarography [14,21], and spectroelectrochemistry [12,14,22] are commonly used for the determination of the ruthenium and protein redox center potentials in modified proteins. 

Fig. 1. Relative positions of the surface histidines (12, 48, 81, and 116) and the heme with its axial histidine in ruthenated sperm whale myoglobin. The edge-edge ET distances are 12.7 (His48), 19.1 (His81), 20.1 (Hisll6), and 22.1 A (Hisl2) [12]...

Fig. 3. View of the heme and a5Ru(His47) centers in ruthenated Pseudomonas stutzeri cytochrome C551. The edge-edge distance is 7.9 A [15]...

Fig. 4. View of the blue copper and a5Rupis59) centers in ruthenated Anabaena variabilis plastocyanin. The edge-edge distance is 11.9 A [39]...

Intramolecular Ru(II) to Cu(II) ET rates have been measured in two other blue copper proteins, stellacyanin [42, 43] and azurin [9, 13, 28]. Pseudomonas aeruginosa azurin has been ruthenated at His83 [13] (Fig. 5). The intramolecular Ru(II) to Cu(II) ET rate of 1.9 s was found to be independent of temperature [28]. The Cu reorganization enthalpy was estimated to be < 7 kcal/mol [13, 28], a value confirming that blue copper is structured for efficient ET. Again, a blue copper ET rate is low in comparison with heme protein rates over similar distances (at similar driving forces) (Table 1). 

The oxidation of alcohols to carbonyl compounds has been studied by several authors and a variety of methods have been used. Papers concerned vith such oxidations are illustrated (Scheme 3.26). Good results have been obtained using pyridinium chlor-ochromate (PCC) adsorbed onto silica gel for the selective oxidation of unsaturated substrates e.g. terpene [135] and furanyl derivatives [136]. Steroidal homoallylic alcohols can be converted to the corresponding 4-ene-3,6-diones using tetrapropylammo-nium per-ruthenate (TPAP) in catalytic amounts [137]. In this case, the oxidising agent is N-methyl morpholine N-oxide (NMO). 

The Ru(NH3)j+ moiety can be attached to histidine-83 on the azurin surface. It can then be oxidized to Ru(III) without altering the conformation of the protein. This ruthenated protein is mixed with Ru(bpy)3+ and laser irradiated. The sequence of events which occurs is shown in the scheme... 

The reduction of the ruthenated plastocyanin protein PCu"Ru by CO 5 results in 72% PCu Ru and 28% PCu Ru . This very fast stage is followed by a slower one in which PCu Ru" is converted by a first order process into PCu Ru For this conversion... 

Increasing attention is being given to the reactivity of ruthenium species which show unusual behavior compared with their Co analogs. Aspects of current interest are mixed valence states, ruthenated proteins to probe electron transfer in them (Chap. 5) and the photochemistry and photophysics of Ru(II) polypyridine eomplexes. 

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