Proteins ruthenium complexes

A similar study was performed on ruthenium-modified myoglobins, in which AG variations were obtained by changing the nature of the ruthenium complex covalently bound to the protein, and by substituting a porphyrin to the heme [137]. It is gratifying to observe that, in spite of the rather heterogeneous character of this series, the study leads to an estimation of 1.9 to 2.4 eV for A which is consistent with the value 2.3 eV derived in section 3.2.1 from temperature dependent experiments. Satisfactory agreement between the results given by the two methods is also observed in the case of ruthenium-modified cytochrome c [138]. 

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. 

Ruthenium complexes have been applied successfully to the luminescent detection of proteins on blotting membranes like nitrocellulose [160]. The bipyridyl and phenanthroline complexes modified with aminoreactive NHS-ester or isothiocyanate groups are commercially available [161]. An even higher sensitivity and lower detection limit can be obtained by encapsulating... 

A chromophore such as the quinone, ruthenium complex, C(,o. or viologen is covalently introduced at the terminal of the heme-propionate side chain(s) (94-97). For example, Hamachi et al. (98) appended Ru2+(bpy)3 (bpy = 2,2 -bipyridine) at one of the terminals of the heme-propionate (Fig. 26) and monitored the photoinduced electron transfer from the photoexcited ruthenium complex to the heme-iron in the protein. The reduction of the heme-iron was monitored by the formation of oxyferrous species under aerobic conditions, while the Ru(III) complex was reductively quenched by EDTA as a sacrificial reagent. In addition, when [Co(NH3)5Cl]2+ was added to the system instead of EDTA, the photoexcited ruthenium complex was oxidatively quenched by the cobalt complex, and then one electron is abstracted from the heme-iron(III) to reduce the ruthenium complex (99). As a result, the oxoferryl species was detected due to the deprotonation of the hydroxyiron(III)-porphyrin cation radical species. An extension of this work was the assembly of the Ru2+(bpy)3 complex with a catenane moiety including the cyclic bis(viologen)(100). In the supramolecular system, vectorial electron transfer was achieved with a long-lived charge separation species (f > 2 ms). 

A natural product s bioactivity is often due to a defined shape that complements the binding site of a protein. Meggers and co-workers have demonstrated that simple organometallic scaffolds can be substituted for structurally more complicated natural products in binding at a target protein s active site <2006AGE1580>. A ruthenium complex 41 was synthesized to mimic the shape of the alkaloid staurosporine 42, a potent inhibitor of protein kinase Pim-1. 

Good agreement between the CNDO/S semiempirical HAB calculation and the experimental k j for the Ru/Ru-DNA duplex is found. Of course, this comparison requires use of Eq. (4) and a specified value of (0.9 eV) in addition to the measured driving force of 0.7 eV. Combining these data yields a calculated kB1 = 7.1 x 106 s 1 compared to the experimental k j = 1.6 x 106 s 1. Extensive use of the same ruthenium complexes as D/A groups in protein studies means that there is not much uncertainty in X (ca. 0.2 eV). 

Photochemical methods offer a convenient tool to study intra- and interprotein ET because of their time resolution and selectivity. Various mechanistic and design approaches based on photochemistry of metal complexes have been undertaken. Most of the studies on protein electron transfer processes have been done for hae-moproteins using among others ruthenium complex as a photosensitizer, modified haemoproteins in which haem iron is substituted by another metal (mainly Zn), and CO-bonded haem proteins [6,7],... 

Figure 13.1 Scheme for (a) the reduction or (b) the oxidation of the iron centre of haemo-proteins with photoexcited ruthenium complex, using flash quench procedure. (Adapted from Szacilowski et al. [124])... 

Issues related to the preferred pathways and the distance dependence of electron transfer in biological systems have been addressed by covalently linking electron-transfer donors or acceptors (e.g. a ruthenium complex) to specific sites (e.g. a histidine) of a protein or an enzyme.The distance dependence of the electron-transfer rate constants is generally fitted to equation (44), with most values of for proteins falling in the range of 1.0 to 1.3 A The protein in... 

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... 

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