Ruthenium flash photolysis

Ru(edta)(H20)] reacts very rapidly with nitric oxide (171). Reaction is much more rapid at pH 5 than at low and high pHs. The pH/rate profile for this reaction is very similar to those established earlier for reaction of this ruthenium(III) complex with azide and with dimethylthiourea. Such behavior may be interpreted in terms of the protonation equilibria between [Ru(edtaH)(H20)], [Ru(edta)(H20)], and [Ru(edta)(OH)]2- the [Ru(edta)(H20)] species is always the most reactive. The apparent relative slowness of the reaction of [Ru(edta)(H20)] with nitric oxide in acetate buffer is attributable to rapid formation of less reactive [Ru(edta)(OAc)] [Ru(edta)(H20)] also reacts relatively slowly with nitrite. Laser flash photolysis studies of [Ru(edta)(NO)]-show a complicated kinetic pattern, from which it is possible to extract activation parameters both for dissociation of this complex and for its formation from [Ru(edta)(H20)] . Values of AS = —76 J K-1 mol-1 and A V = —12.8 cm3 mol-1 for the latter are compatible with AS values between —76 and —107 J K-1mol-1 and AV values between —7 and —12 cm3 mol-1 for other complex-formation reactions of [Ru(edta) (H20)]- (168) and with an associative mechanism. In contrast, activation parameters for dissociation of [Ru(edta)(NO)] (AS = —4JK-1mol-1 A V = +10 cm3 mol-1) suggest a dissociative interchange mechanism (172). 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

Intramolecular electron transfer from Ru(II) to Fe(III) in (NH3)3Ru(II) (His-33)cyt(Fe(III)) induced by pulse-radiolysis reduction of Ru(III) in the (NH3)5Ru(III) (His-33)cyt(Fe(III)) complex were investigated [84]. The results obtained differ from those of refs. 77-80 where flash photolysis was used to study the similar electron transfer reaction. It was found [84] that, over the temperature range 276-317 K the rate of electron transfer from Ru(II) to Fe(III) is weakly temperature dependent with EA 3.3 kcal mol 1. At 298 K the value of kt = 53 2 s"1. The small differences in the temperature dependence of the electron tunneling rate in ruthenium-modified cytochrome c reported in refs. 77-80 and 84 was explained [84] by the different experimental conditions used in these two studies. 

Lorkovic IM, Miranda K, Lee B, Bernard S, Schoonover J, Ford PC. Flash photolysis studies of the ruthenium(II) porphyrins Ru(P)(NO)(ONO). Multiple pathways involving reactions of intermediates with nitric oxide. J Am Chem Soc 1998 120 11674. 

Charge transfer between amphipathic ruthenium(II) complexes and N-butylphenothiazine in micelles, synthetic bilayers and liposomes has been studied by flash photolysis (Takayanagi et al., 1980). It was shown that the energy wasting back electron-transfer reaction is less efficient in the vicinity of the charged surface and that it is disfavoured by an increase in temperature. 

Smface modification with ruthenium complexes has proven valuable in studies of both interprotein and intraprotein electron transfer in systems that are difflcult to stndy by traditional kinetic tools. The choice of ruthenium complexes in these investigations stems from an extensive photochemistry as well as exceptional thermal stability. The photochemistry provides a means of examining reactions over a time range of nanoseconds to seconds by laser-flash photolysis and the thermal stability allows researchers to covalently bind a wide variety of complexes to proteins with... 

The interprotein electron-transfer reactions of Ru-65-cyt bs can be studied using a sacrificial electron donor such as aniline to reduce Ru(III) and prevent the back reaction k2, as described in Scheme 2. Appropriate sacrificial electron donors can also reduce Ru(IB) to Ru(I), which then reduces Fe(III) as shown in the top pathway of Scheme 2. Cyt b is rapidly reduced by either pathway, and is then poised to transfer an electron to another protein. The reaction of cyt bs with Cc using this methodology will be described in the next section. Covalent labelling of Cc with ruthenium complexes and subsequent flash photolysis has provided a... 

Finally, recent work has examined in detail the kinetics of the fundamental B-H oxidative addition step which leads to the formation of rhodium(III) [and ruthenium(II)] boryl hydrides. Conversion of fac-(triphos)Rh(H)3 into fac-(triphos)Rh(H)2(Bpin) via sequential H2 reductive elimination/HBpin oxidative addition was induced by laser flash photolysis and kinetic data determined from UV measurements. Thus, an extremely high second-order rate constant was determined for the reaction of the 16-electron intermediate... 

In the first application of ultrafast TRIE spectroscopy (that is, with time-scales of 10 to 10 s), reductive elimination and oxidative addition of H2 have been traced following flash photolysis of the related ruthenium carbonyl dihydride complex Ru(PPh3)3(CO)H2 in benzene solution (90). This precursor is of particular note because it is known to catalyze insertion of alkenes into C-H bonds at the unsaturated carbon center of alkenes or arenes in a position /3 to a carbonyl group. The course of events has been monitored from excitation with an ultrafast UV laser (giving pulses at A = 304 nm with an energy of... 

Flash Photolysis of Ruthenium-Modified Helical Maquettes... 

The triplet states of free-base, zinc-, and ruthenium-porphyrins can be conveniently monitored in nanosecond laser flash photolysis (Fig. 25). The triplet transient spectra exhibit significant differences between the free-base and the metalloporphyrins that can be used for diagnostic pmposes in multi-chromophore supramolecular systems. 

The photoreaction of 2-substituted-1,4-naphthoquinones is accelerated by ionic surfactants but suppressed by cationic ones. Conversely, the flash photolysis of an amphipathic dodecylcarboxamide derivative of a pyridine—ruthenium(ii) complex gives the highest yield for photoreduction in cationic micelles.Anionic micelles increase electron transfer from iron(n) to iron(iii) by ca. 10 —and also the oxidation of ferrocenes by iron(in), but inhibit the oxidation by ferrocyanide. 

DiBenedetto JA, Ryba DW, Eord PC (1989) Reaction dynamics of photosubstitution intermediates of the tri-ruthenium cluster Ru3(CO)i2 as studied by flash photolysis with infrared detection. Inorg Chem 28 3503-3507... 

Stoichiometric and kinetic experiments have indicated the likely reaction sequence and mechanisms for the reaction of trans-[Ru NO)-(N02)4(0H)] " with barbituric acid, which gives a violurato complex as product/ Cyclic voltammetry has demonstrated the conversion of [Ru(terpy)(bipy)(NH3)] into [Ru(terpy)(bipy)(N02)] this is oxidation of the ammonia ligand, but is formally classifiable as substitution with respect to the ruthenium(II)/ Stopped-flow cerium(IV) oxidation, flash photolysis, and electrochemical techniques have been used to probe the analogous ligand modification in equation (4). Here, however, the metal... 

Photolysis of [M(PP3)H2] (M = Ru, Os PP3 = P(GH2GH2PPh2)3) in the presence of GO affords [M(PP3)(GO)], the ruthenium complex also being accessible by reduction of the dichloride complex with sodium naphthalenide under an atmosphere of GO. Nanosecond laser flash photolysis studies on [Ru(etp)(GO)H2] 41 (etp = PhP(GH2GH2PPh2)2) generate the expected 16-eleetron Ru(0) species [Ru(etp)(GO)], which back reacts... 

Polynuclear Carbonyl Derivatives.-Variable temperature MAS n.m.r. methods have been used to probe the exchange processes occurring in solid homonuclear carbonyls containing 3 and 4 metal atoms.A quantitative investigation of the chemistry resulting from both continuous- and flash-photolysis of Ru3(C0)i2 has been carried out, and a new polymeric ruthenium carbonyl, Ru(C0)it n prepared from this precursor. The steric and electronic effects in associative substitution reactions of Iri (C0)i2 have also been examined. The combination of two OS3 units to yield an improved route to Ose raft-like clusters has been achieved, and a comprehensive analysis published on the different Mg cores of stacked Mg triangles in the [Mg C0)i8] "... 

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