Pentaammine Ruthenium Research Articles

Synthesis and Electrochemical Characterization of a Transition-Metal-Modified Ligand−Receptor Pair

The energetics of weak interactions (van der Waals forces, hydrogen bonding) are difficult to quantify in biological ligand-receptor pairs. Insight into the biochemical role these forces play is critical to an understanding of signal transduction events and the drug discovery process. Ruthenium pentaammine and iron tetracyano complexes modified with either biotin or desthiobiotin have been synthesized and characterized. These modified biological ligands bind to the protein avidin in a manner similar to that of native biotin. Experiments using redox mediators show that the avidin-bound complexes are electrochemically accessible.

DNA effects upon the reaction between acetonitrile pentacyanoferrate (II) and ruthenium pentammine pyrazine: Kinetic and thermodynamic evidence of the interaction of DNA with anionic species

The kinetics of the reaction between ruthenium pentaammine pyrazine and acetonitrile pentacyanoferrate (II) to obtain the binuclear anionic complex [Fe(CN) 5pzRu(NH 3) 5] −, and the reverse (dissociation) process, have been studied in solutions containing DNA. The results corresponding to this reaction and those corresponding to the reverse (dissociation) process show a clear influence of DNA on their kinetics. The results can be interpreted using a modified Pseudophase Model. From the results obtained for the dissociation reaction one can conclude that the binuclear anionic complex [Fe(CN) 5pzRu(NH 3) 5] − interacts with DNA.

Electron and Energy Transfer through Bridged Systems. 9. Toward a Priori Evaluation of the Intermetallic Coupling in Bis-metal Complexes

It is now commonplace to perform a priori calculations using either density functional or ab initio theory for intramolecular electron-transfer coupling strengths within organic molecules, but generally applicable a priori schemes for intermetallic couplings are yet to be determined. We examine the reasons for this, predominantly the need to treat solvent effects within the calculation, shortcomings of, or the unavailability of, Koopmans' theorem (i.e., the need for configuration interaction), and the difficulty of correctly determining ligand orbital band gaps and positioning metal orbitals within them. In particular, we model the observed intermetallic coupling in the α,ω-dipyridylpolyene-bridged ruthenium pentaammine series designed by Woitellier, Launay, and Spangler. After appropriately positioning the metal and ligand orbitals, couplings calculated using Fock matrices are found to be within 25% of experimental values. However, they attenuate too rapidly with increasing bridge length. Use of B3LYP Kohn−Sham matrices as replacements of Fock matrices yields much poorer results, however; the predicted coupling is too strong and even increases for very long bridge lengths.

Simultaneous detection of three drugs labeled by cationic metal complexes at a nafion-loaded carbon paste electrode

The synthesis of the pentaammine ruthenium(II) complex of N-isonicotinoyl–nortriptyline (NORPy-Ru 2+) was performed and its electrochemical properties at a nafion-loaded carbon paste electrode were examined. The anodic oxidation of the positively charged labeled antidepressant proceeded at −0.06 V (versus Ag/AgCl, 0.05 M Cl −). A detection limit of 0.075 μM (S/N=3) was achieved at physiological pH by square-wave voltammetry after a 5-min preconcentration step, with a linear response over the range 0.075–5.0 μM. With a view to a future triple-analyte immunoassay, the detection of NORPy-Ru 2+ was also examined in the presence of two labeled antiepileptics previously synthesised, i.e. phenytoin labeled by a ferroceneammonium salt (oxidation potential at 0.26 V) and phenobarbital labeled by a cobaltocenium salt (reduction potential at −1.05 V). The simultaneous detection of the three labeled drugs proceeded with analytical performances similar to those corresponding to the separate accumulation of each tracer. However it was observed that the pentaammine ruthenium(II) complexes of pyridine and its derivatives were not stable in the presence of serum, which does not allow for their use as redox cationic labels in a multi-analyte immunoassay to be envisaged.

Molecular design of asymmetric bichromophoric compounds

The goal of the present study is a better understanding of photoinduced electron or energy transfer in a single molecule. The growing interest of this field is caused by its implication in life phenomena such as photosynthesis and in the development of molecular devices. We present molecular design of new compounds consisting of a well-known luminescent organic moiety (porphyrin, carbazole, phthalocyanine) bound to an inorganic one by a bridging ligand. This latter is in the simplest case a triple bond that can be extended easily. In the present work, the inorganic part is a pentaammine—ruthenium which has been extensively studied previously. Our interest is focused on the possible ability of the ruthenium moiety to quench the light emission of the luminescent organic chromophore.

Inhibition of Cellobiohydrolase I from Trichoderma reesei by Palladium

Cellulase from Trichoderma reesei is a multienzyme mixture that hydrolyzes cellulose to glucose. Two enzymes in this mixture, cellobiohydrolase (CBH) and endoglucanase (EG), possess a common structure comprising a distinct cellulose-binding domain (CBD) and catalytic domain. Inhibition of the catalytic domain of cellulases without affecting their CBD function might be useful for structure/function studies of these enzymes. Complexes of the platinum group metals were tested for their ability to inhibit the major cellulase enzyme from T. reesei, cellobiohydrolase I (CBH I). Only palladium complexes inhibited CBH I, inhibition being dependent upon the molar ratio of palladium to CEH I with 1 μM CBH I retaining only 10% of its activity in the presence of 100 μM ammonium hexachloropalladate(IV) and after the incorporation of 28 mol Pd/mol CBH I. Inhibition was irreversible and could be completely prevented by including histidine, cysteine, and cystine in the assay mixture. Although the primary mechanism of inhibition of CBH I by palladium remains to be elucidated, it could involve the binding of palladium to sulfur or cystine residues resulting in their degradation. This is based on the findings that (i) palladium-inhibited CBH I was less thermally stable than native CBH I; (ii) CBH I, chemically modified by the attachment of pentaammine ruthenium(III) to the imidazole-N of either H206 or H228, showed greater sensitivity to inhibition by palladium compared to native CBH I; and (iii) ammonium hexachloropalladate cleaved 5,5′-dithiobis(2-nitrobenzoic acid)-Ellman′s reagent. Binding of CBH I to crystalline cotton linters was not affected by palladium.

Photoinduced intramolecular electron transfer in bimetallic donor-acceptor assemblies

A series of bimetallic complexes containing an (α-diimine)(CO) 3Re 1 chromophore and a covalently attached ruthenium pentaammine moiety has been prepared and characterized. Ground state properties, including absorption spectra and redox potentials, are consistent with very weak metal-metal interaction in these systems. However, picosecond luminescence decay profiles indicate that emission from the Re → α-diimine 3MLCT excited state is strongly quenched by attachment of the Ru center for complexes in both Re I/Ru II and Re I/Ru III oxidation states. Such behaviour is consistent with extremely rapid photoinduced intramolecular electron transfer processes, and the data are interpreted in light of the ‘superexchange’ mechanism. No short-lived transients are observed for the Re I/Ru III bimetallic complexes, suggesting that electron transfer may occur from the 1MLCT state in these systems.

Veratryl Alcohol Oxidase Activity of a Chemically Modified Cellulase Protein

A cellulase, cellobiohydrolase I (CBH I) from Trichoderma reesei was chemically modified by covalent attachment of pentaammine ruthenium (III) without loss in hydrolytic activity. Data suggest that such a modification endowed CBH I with oxidoreductase activity. The modified enzyme was able to carry out hydrogen peroxide-dependent oxidation of veratryl alcohol, a substrate for lignin peroxidase, at a rate of 0.148 μmol substrate oxidized min −1 μmol −1 enzyme. The effects of pH, temperature, and substrate concentration on the oxidation reaction were examined. The optimal temperature was determined to be 45°C, and the optimal pH was 4.3. The K m and V max for veratryl alcohol were determined to be 3.519 mM and 52.27 μM min −1, respectively. Tartrate at concentrations as low as 0.10 mM was found to inhibit the reaction.

Reactivity and Coordination Chemistry of Aromatic Carboxamide RC(O)NH2 and Carboxylate Ligands: Properties of Pentaammine Ruthenium(II) and -(III) Complexes

The pH dependences of the spectral and electrochemical properties of mononuclear carboxamido (NH 3 ) 5 RuNHC(O)R (R=Ph, 4-py-N-Me + , 4-py-N-H + ) and carboxylato (NH 3 ) 5 RuOC(O)R (R=4-py-N-Me + ) complexes of Ru(II) and Ru(III) in aqueous solution have been examined. In contrast to the carboxylate complex (E 1/2 =-0.053 V vs NHE), the deprotonated (-NHC(O)R - ) Ru III / II couples have rather negative reduction potentials, -0.25 (R=ph), -0.23 (R=4-py), and -0.13 (R=N-Me-4-py) V vs NHE, which are pH independent above the pH a of the Ru(II) complex

Binuclear complexes of ruthenium ammines with 4,4′-dithiodipyridine bridging ligand

The binuclear complex of ruthenium pentaammine with 4,4′-dithiodipyridine as the bridging ligand provides the first clear example of the great efficiency of the ‘S–S’ bridge in conducting electrons.

Fluorescence and kinetic properties of Ru(III) (NH 3) 5 modified transferrin

Diferric transferrin was modified using aquopentaammine ruthenium(II), a reagent for surface-accessible uncoordinated histidines. Introduction of the cationic Ru(III) (NH 3) 5 3+ group on the imidazole of only 5.5 of the 17 uncoordinated histidines enhances the rates of pyrophosphate-assisted iron removal from the N-terminal and C-terminal binding sites by 16- and 2-fold, respectively. This differential effect on the kinetics of the two sites may partially explain why in the native protein the N-terminal site is more labile than the C-terminal site in acidic solutions where histidine residues become positively charged through protonation. The distance between the metal site and nearby uncoordinated histidines was estimated from fluorescence energy transfer measurements using Tb (III) as the donor and pentaammine ruthenium(III)-labeled imidazole of histidine as the acceptor chromophore, A Tsou Chen-Lu statistical analysis of the fluorescence quenching data suggest that two residues in each lobe of the protein are involved in quenching the fluorescence. By using estimates for the index of refraction and the quantum yield and assuming the energy transfer follows parallel first-order kinetics, an upper limit for the donor-acceptor distance of about 1.4 nm was obtained, assuming two uncoordinated histidine residues equidistant from the metal. His-207 and His-242 in the N-terminal lobe of transferrin and His-535 and His-577 in the C-terminal lobe are within this distance, based on information from the lactoferrin crystal structure. It is postulated that His-207 in the N-terminal lobe and His-535 in the C-terminal lobe are the uncoordinated residues that, when protonated or modified with Ru(III) (NH 3) 5 3+, lead to accelerated loss of iron from the two binding sites of the protein.

Preparation and characterization of a pentaammine ruthenium (III)-cytochrome c peroxidase derivative

Preparation and characterization of a pentaammine ruthenium (III)-cytochrome c peroxidase derivative

Electron-transfer kinetics of zinc-substituted cytochrome c and its Ru(NH3)5(histidine-33) derivative

The kinetics of the bimolecular electron transfers from triplet-excited zinc-substituted horse heart cytochrome c (Zn-cyt c*) to Ru(NH/sub 3/)/sub 5/L/sup 3 +/ have been measured (L = NH/sub 3/, k(298 K) = 1.4 x 10/sup 7/ M/sup -1/ s/sup -1/; L = histidine, k(298 K) = 2.4 x 10/sup 7/ M/sup -1/ s/sup -1/), along with those of the corresponding thermal back-reactions (L = NH/sub 3/, k(298 K) = 1.5 x 10/sup 8/ M/sup -1/ s/sup -1/; L = histidine, k(298 K) = 3.6 x 10/sup 8/ M/sup -1/ s/sup -1/). The derivatized metalloprotein ruthenium pentaammine histidine-33-zinc-substituted cytochrome c (Ru-Zn-cyt c) has been prepared and characterized by atomic absorption spectroscopy and HPLC analysis of its tryptic digestion fragments. The rate of intraprotein electron transfer from the triplet-excited Zn-porphyrin moiety to the 11.8-A distant Ru(NH/sub 3/)/sub 5/(His-33)/sup 3 +/ residue (k(298 K) = 7.7 x 10/sup 5/ s/sup -1/), as well as that of the thermal back-reaction (k(298 K) = 1.6 x 10/sup 6/ s/sup -1/), has been measured by transient spectroscopy. Intraprotein electron transfer from Ru(II) quenches Zn-cyt c* with a rate constant of 2.4 x 10/sup 2/ s/sup -1/. These kinetics are discussed in terms of the semiclassical theorymore » of electron-transfer reactions.« less