TAP Ligands Research Articles

Nitrile Substituents at the Conjugated Dipyridophenazine Moiety as Infrared Redox Markers in Electrochemically Reduced Heteroleptic Ru(II) Polypyridyl Complexes.

Ruthenium(II) complexes [Ru(tap)2(NN)]2+ (tap = 1,4,5,8-tetraazaphenanthrene, NN = 11-cyano-dipyrido[3,2-a:2',3'-c]phenazine (11-CN-dppz) and 11,12-dicyano-dipyrido[3,2-a:2',3'-c]phenazine (11,12-CN-dppz)) feature the C≡N groups as infrared (IR)-active redox markers. They were studied by cyclic voltammetry, UV-vis, and IR spectroelectrochemistry (SEC), and density functional theory calculations to assign the four 1e- reduction waves R1-R4 observed in dichloromethane. Generally, the NN ligands are reduced first (R1). For [Ru(tap)2(11,12-CN-dppz)]2+, R1 is sufficiently separated from R2 and delocalized over both tap ligands. Accordingly, IR SEC conducted at R1 shows a large red shift of the νs,as(C≡N) modes by -18/-28 cm-1, accompanied by a 4-fold enhancement of the νs(C≡N) intensity, comparably with reference data for free 11,12-CN-dppz. The first tap-based reduction of spin-doublet [Ru(tap)2(11,12-CN-dppz)]+ to spin-triplet [Ru(tap)2(11,12-CN-dppz)] at R2 decreased ν(C≡N) by merely -2 cm-1, while the intensity enhancement reached an overall factor of 8. Comparably, a red shift of ν(C≡N) by -27 cm-1 resulted from the 1e- reduction of [Ru(tap)2(11-CN-dppz)]2+ at R1 (poorly resolved from R2), and the intensity enhancement was roughly 3-fold. Concomitant 1e- reductions of the tap ligands (R2 and R3) caused only minor ν(C≡N) shifts of -3 cm-1 and increased the absorbance by overall factors of 6.5 and 8, respectively.

Structure-Property Relationships in a New Family of Photoactive Diimine-Diphosphine Copper(I) Complexes.

A new family of heteroleptic diimine-diphosphine copper(I) complexes is reported, with six new complexes compared to benchmark [Cu(bcp)(DPEPhos)]PF6 . These new complexes are based on 1,4,5,8-tetraazaphenanthrene (TAP) ligands with representative electronic properties as well as substitution patterns and DPEPhos and XantPhos as diphosphine ligands. Their photophysical and electrochemical properties were investigated and correlated with the number and position of substituents on the TAP ligands. Stern-Volmer studies using Hünig's base as reductive quencher demonstrated the influence of the complex photoreduction potential and of the excited state lifetime on the photoreactivity. This study refines the structure-property relationship profile for heteroleptic copper(I) complexes and confirms that such profiles are of high interest to design new copper complexes as optimized photoredox catalysts.

Ruthenium(II) Polypyridyl Complexes and Their Use as Probes and Photoreactive Agents for G-quadruplexes Labelling.

Due to their optical and electrochemical properties, ruthenium(II) polypyridyl complexes have been used in a wide array of applications. Since the discovery of the light-switch ON effect of [Ru(bpy)2dppz]2+ when interacting with DNA, the design of new Ru(II) complexes as light-up probes for specific regions of DNA has been intensively explored. Amongst them, G-quadruplexes (G4s) are of particular interest. These structures formed by guanine-rich parts of DNA and RNA may be associated with a wide range of biological events. However, locating them and understanding their implications in biological pathways has proven challenging. Elegant approaches to tackle this challenge relies on the use of photoprobes capable of marking, reversibly or irreversibly, these G4s. Indeed, Ru(II) complexes containing ancillary π-deficient TAP ligands can create a covalently linked adduct with G4s after a photoinduced electron transfer from a guanine residue to the excited complex. Through careful design of the ligands, high selectivity of interaction with G4 structures can be achieved. This allows the creation of specific Ru(II) light-up probes and photoreactive agents for G4 labelling, which is at the core of this review composed of an introduction dedicated to a brief description of G-quadruplex structures and two main sections. The first one will provide a general picture of ligands and metal complexes interacting with G4s. The second one will focus on an exhaustive and comprehensive overview of the interactions and (photo)reactions of Ru(II) complexes with G4s.

Photochemistry of Heteroleptic 1,4,5,8-Tetraazaphenanthrene- and Bi-1,2,3-triazolyl-Containing Ruthenium(II) Complexes.

Diimine metal complexes have significant relevance in the development of photodynamic therapy (PDT) and photoactivated chemotherapy (PACT) applications. In particular, complexes of the TAP ligand (1,4,5,8-tetraazaphenanthrene) are known to lead to photoinduced oxidation of DNA, while TAP- and triazole-based complexes are also known to undergo photochemical ligand release processes relevant to PACT. The photophysical and photochemical properties of heteroleptic complexes [Ru(TAP)n(btz)3-n]2+ (btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl, n = 1 (1), 2 (2)) have been explored. Upon irradiation in acetonitrile, 1 displays analogous photochemistry to that previously observed for [Ru(bpy)(btz)2]2+ (bpy = 2,2'-bipyridyl) and generates trans-[Ru(TAP)(btz)(NCMe)2]2+ (5), which has been crystallographically characterized, with the observation of the ligand-loss intermediate trans-[Ru(TAP)(κ2-btz)(κ1-btz)(NCMe)]2+ (4). Complex 2 displays more complicated photochemical behavior with not only preferential photorelease of btz to form cis-[Ru(TAP)2(NCMe)2]2+ (6) but also competitive photorelease of TAP to form 5. Free TAP is then taken up by 6 to form [Ru(TAP)3]2+ (3) with the proportion of 5 and 3 observed to progressively increase during prolonged photolysis. Data suggest a complex set of reversible photochemical ligand scrambling processes in which 2 and 3 are interconverted. Computational DFT calculations have enabled optimization of geometries of the pro-trans 3MCcis states with repelled btz or TAP ligands crucial for the formation of 5 from 1 and 2, respectively, lending weight to recent evidence that such 3MCcis states play an important mechanistic role in the rich photoreactivity of Ru(II) diimine complexes.

Spectro-electrochemical Studies on [Ru(TAP)2(dppz)]2+-Insights into the Mechanism of its Photosensitized Oxidation of Oligonucleotides.

[Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene; dppz = dipyrido[3,2- a:2',3'- c]phenazine) is known to photo-oxidize guanine in DNA. Whether this oxidation proceeds by direct photoelectron transfer or by proton-coupled electron transfer is still unknown. To help distinguish between these mechanisms, spectro-electrochemical experiments have been carried out with [Ru(TAP)2(dppz)]2+ in acetonitrile. The UV-vis and mid-IR spectra obtained for the one-electron reduced product were compared to those obtained by picosecond transient absorption and time-resolved infrared experiments of [Ru(TAP)2(dppz)]2+ bound to guanine-containing DNA. An interesting feature of the singly reduced species is an electronic transition in the near-IR region (with λmax at 1970 and 2820 nm). Density functional and time-dependent density functional theory simulations of the vibrational and electronic spectra of [Ru(TAP)2(dppz)]2+, the reduced complex [Ru(TAP)2(dppz)]+, and four isomers of [Ru(TAP)(TAPH)(dppz)]2+ (a possible product of proton-coupled electron transfer) were performed. Significantly, these predict absorption bands at λ > 1900 nm (attributed to a ligand-to-metal charge-transfer transition) for [Ru(TAP)2(dppz)]+ but not for [Ru(TAP)(TAPH)(dppz)]2+. Both the UV-vis and mid-IR difference absorption spectra of the electrochemically generated singly reduced species [Ru(TAP)2(dppz)]+ agree well with the transient absorption and time-resolved infrared spectra previously determined for the transient species formed by photoexcitation of [Ru(TAP)2(dppz)]2+ intercalated in guanine-containing DNA. This suggests that the photochemical process in DNA proceeds by photoelectron transfer and not by a proton-coupled electron transfer process involving formation of [Ru(TAP)(TAPH)(dppz)]2+, as is proposed for the reaction with 5'-guanosine monophosphate. Additional infrared spectro-electrochemical measurements and density functional calculations have also been carried out on the free TAP ligand. These show that the TAP radical anion in acetonitrile also exhibits strong broad near-IR electronic absorption (λmax at 1750 and 2360 nm).

Preferred orientation in an angled intercalation site of a chloro-substituted Λ -[Ru(TAP) 2 (dppz)] 2+ complex bound to d(TCGGCGCCGA) 2

The crystal structure of the ruthenium DNA 'light-switch' complex Λ-[Ru(TAP)2(11-Cl-dppz)](2+) (TAP=tetraazaphenanthrene, dppz=dipyrido[3,2-a':2',3'-c]phenazine) bound to the oligonucleotide duplex d(TCGGCGCCGA)2 is reported. The synthesis of the racemic ruthenium complex is described for the first time, and the racemate was used in this study. The crystal structure, at atomic resolution (1.0 Å), shows one ligand as a wedge in the minor groove, resulting in the 51(°) kinking of the double helix, as with the parent Λ-[Ru(TAP)2(dppz)](2+). Each complex binds to one duplex by intercalation of the dppz ligand and also by semi-intercalation of one of the orthogonal TAP ligands into a second symmetrically equivalent duplex. The 11-chloro substituent binds with the major component (66%) oriented with the 11-chloro substituent on the purine side of the terminal step of the duplex.

Ru-TAP complexes with btz and pytz ligands: novel candidates as photooxidizing agents

Two ligands containing 1,2,3-triazole moieties 1 and 3 were easily prepared by a Cu(I)-catalysed "click reaction" between commercially available (trimethylsilyl)alkynes and benzyl azide. These ligands were used in the synthesis of Ru(II) complexes with TAP ligands, i.e. [Ru(TAP)(2)btz](2+)2 and [Ru(TAP)(2)pytz](2+)4. The electrochemical and photophysical properties of these complexes were investigated. The data show that both complexes should behave as highly oxidizing agents under illumination. However, complex 4 displays more attractive photophysical properties than complex 2 and constitutes thus a Ru-TAP compound that can be easily derivatized for photodamaging biomolecules.

Photo-reactive RuII-oligonucleotide conjugates: influence of an intercalating ligand on the inter- and intra-strand photo-ligation processes

The damaging efficacy towards OligoDeoxyriboNucleotides (ODNs) of two photoreactive polyazaaromatic ruthenium(II) complexes, Ru(T) and Ru(D), has been evaluated. Both compounds correspond to the known [Ru(TAP)(2)(dppz)](2+) complex, but they are anchored differently to a guanine-containing single strand ODN (probe strand). This has allowed us to investigate the influence of the interactions existing between the tethered complexes and the single or double strand, on the photo-ligation processes. From melting temperature measurements of the duplex formed between these Ru-ODNs and their complementary sequence (target strand), it has been found that Ru(T) anchored via the TAP ligand interacts with the duplex by means of the intercalating dppz ligand (head on geometry), while Ru(D) anchored via the dppz ligand likely adopts a side on geometry without intercalation. Both single stranded Ru conjugates self-inhibit in the absence of their target ODN by forming exclusively a cyclic "seppuku" photo-adduct (intra-molecular photoreaction). In contrast, this intra-molecular photo-product is precluded in presence of the target strand, and the Ru-ODN sequence photo-crosslinks with the latter (inter-molecular photoreaction). Both intra- and inter-molecular processes with both complexes are efficient (80% yields) and lead to stable photo-adducts. Interestingly, detailed studies have revealed that the similar photo-damaging efficacy of crosslinking by Ru(T) and Ru(D) is a consequence of a cascade of events with compensatory effects, originating from the different geometry of interaction of the tethered complexes. Notably, antagonistic effects are present when the complex is intercalated, the guanine oxidation step being highly favoured and the recombination of the quenching products being hindered.

Oxidizing Ru(II) Complexes as Irreversible and Specific Photo-Cross-Linking Agents of Oligonucleotide Duplexes

Oxidizing polyazaaromatic Ru(II) complexes containing two TAP ligands (TAP = 1,4,5,8-tetraazaphenanthrene) are able under illumination to cross-link irreversibly the two strands of an oligonucleotide (ODN) duplex by covalent bond formation. The cross-linking proceeds by two successive absorptions of a photon. An adduct of the metallic complex on a guanine (G) base of one ODN strand is first photoproduced, followed by a second photoaddition of the same Ru species to a G base of the complementary strand, provided that the two G moieties are separated by 0 or 1 base pair. These two processes lead to the cross-linking of the two strands. Such a photo-cross-linking is easily detected with [Ru(TAP)(2)(phen)](2+) (1; phen = 1,10-phenanthroline) and [Ru(HAT)(2)(phen)](2+) (2; HAT = 1,4,5,8,9,12-hexaazatriphenylene), whereas it is not observed with [Ru(TAP)(2)TPAC](2+) (3; TPAC = tetrapyridoacridine) at the same level of loading of the duplex by 3. With a concentration of 3 similar to that of 1 and 2, when the loading of the duplex by 3 is much more important than with 1 and 2, the photo-cross-linking with 3 can thus also be observed. As 3 intercalates its TPAC ligand into the base pairs stack, its mobility is restricted in the duplex. In contrast, 1 and 2 can adopt different geometries of interaction, which probably facilitate the photo-cross-linking.

Exploring Photoreactions between Polyazaaromatic Ru(II) Complexes and Biomolecules by Chemically Induced Dynamic Nuclear Polarization Measurements

Steady-state (1)H photo-chemically induced dynamic nuclear polarization (CIDNP) experiments were conducted at 14.1 T on deoxygenated (buffered pH 7) aqueous solutions of [Ru(phen)(3)](2+), [Ru(tap)(2)(phen)](2+), and [Ru(tap)(3)](2+) (tap = 1,4,5,8-tetraazaphenanthrene; phen = 1,10-phenanthroline) in the presence of guanosine-5'-monophosphate or N-acetyltyrosine. For the first time, CIDNP arising from photo-oxidation by polyazaaromatic Ru(II) complexes is reported. In agreement with the occurrence of a photo-electron-transfer process, photo-CIDNP effects are observed with [Ru(tap)(3)](2+) and [Ru(tap)(2)(phen)](2+) but not with [Ru(phen)(3)](2+). With [Ru(tap)(2)(phen)](2+), no significant photo-CIDNP is observed for the (1)H nuclei of the phen ligand, consistent with the fact that the metal-to-ligand charge-transfer triplet excited states responsible for the photo-oxidation involve a tap ligand. Successive experiments with [Ru(tap)(3)](2+) highlight the accumulation of long-lived radical species in solution that cause (1)H NMR signal broadening and photo-CIDNP extinction. The (1)H photo-CIDNP observed for the biomolecules is rather weak, less than about 30% of the equilibrium magnetization. However, up to 60% polarization enhancement is observed for H-2 and H-7 of the tap ligands, which indicates high unpaired electron density in the vicinity of these atoms in the transient radical pair. This is consistent with the structure of known photoadducts formed, for instance, between the metallic compounds and the guanine base of mono- and polynucleotides. Indeed, in these adducts the covalent bond involves carbon C-2 or C-7 of a tap ligand. The occurrence of photo-CIDNP with polyazaaromatic Ru(II) complexes opens new perspectives for the study of this type of compound.

Effects of Protonation on the Spectroscopic Properties of Tetrapyridoacridine (TPAC) Mono- and Dinuclear Ru(II) Complexes in Their Ground and 3MLCT Excited States

The spectroscopic behavior of mono- and dinuclear Ru(II) complexes (P, T, PP and TT, Figure 1) that contain the extended planar ligand tetrapyrido[3,2-a:2',3'-c:3' ',2' '-h:2' '',3' ''-j]acridine (TPAC) and either 1,10-phenanthroline (phen) or 1,4,5,8-tetraazaphenanthrene (tap) as ancillary ligands is examined in water and as a function of the pH. These four complexes luminesce in aqueous solution. The analyses of the data in absorption lead to the pKa values in the ground state, and the data in emission show that the excited 3MLCT states are much more basic than the ground state. When the complex contains tap ligands (T and TT), a decrease in pH transforms the luminescent excited basic form into another luminescent excited protonated species, which emits more bathochromically. In contrast, with phen ancillary ligands (P and PP), the protonated excited state does not luminesce. The rate constant of first protonation of the 3MLCT state is diffusion controlled, except for the dinuclear PP complex, whose protonation takes place on the nitrogen of the acridine motif. For P, in which the protonation process is the fastest, it would take place on the nitrogen atoms of the nonchelated phen moiety of the TPAC ligand. These results allow also us to gain information on the localization of the excited electron in the 1MLCT state populated upon absorption as well as in the relaxed 3MLCT emissive state. Moreover as these complexes are interesting for their study with DNA, it can be concluded from these data that a portion of the excited species in interaction with DNA will be protonated.

The role of the proteasome in generating cytotoxic T-cell epitopes: insights obtained from improved predictions of proteasomal cleavage

Cytotoxic T cells (CTLs) perceive the world through small peptides that are eight to ten amino acids long. These peptides (epitopes) are initially generated by the proteasome, a multi-subunit protease that is responsible for the majority of intra-cellular protein degradation. The proteasome generates the exact C-terminal of CTL epitopes, and the N-terminal with a possible extension. CTL responses may diminish if the epitopes are destroyed by the proteasomes. Therefore, the prediction of the proteasome cleavage sites is important to identify potential immunogenic regions in the proteomes of pathogenic microorganisms (or humans). We have recently shown that NetChop, a neural network-based prediction method, is the best method available at the moment to do such predictions; however, its performance is still lower than desired. Here, we use novel sequence encoding methods and show that the new version of NetChop predicts approximately 10% more of the cleavage sites correctly while lowering the number of false positives with close to 15%. With this more reliable prediction tool, we study two important questions concerning the function of the proteasome. First, we estimate the N-terminal extension of epitopes after proteasomal cleavage and find that the average extension is relatively short. However, more than 30% of the peptides have N-terminal extensions of three amino acids or more, and thus, N-terminal trimming might play an important role in the presentation of a substantial fraction of the epitopes. Second, we show that good TAP ligands have an increased chance of being cleaved by the proteasome, i.e., the specificity of TAP has evolved to fit the specificity of the proteasome. This evolutionary relationship allows for a more efficient antigen presentation.

Photoadducts of Metallic Compounds with Nucleic Acids − Role Played by the Photoelectron Transfer Process and by the TAP and HAT Ligands in the RuII Complexes

AbstractThe properties that are characteristic of TAP (1,4,5,8‐tetraazaphenanthrene) and HAT (1,4,5,8,9,12‐hexaazatriphenylene) RuII complexes under illumination are highlighted and compared with those of other metallic complexes. In particular, the photo‐oxidizing power of their 3MLCT states leads to a quenching of luminescence accompanied by a photoreaction when they are in presence of nucleic acids. The proton‐coupled photoinduced electron transfer with the guanine nucleobases produces metallic adducts on DNA guanine units. The mechanism of formation, structure, and possible applications of these photoadducts are discussed and compared with other DNA metallic adducts currently in the literature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Ru(TAP)2(dppz)]2+: a DNA intercalating complex, which luminesces strongly in water and undergoes photo-induced proton-coupled electron transfer with guanosine-5'-monophosphate.

The lowest excited state of [Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene, dppz = dipyrido[3,2-a:2',3'-c]phenazine) 1 is strongly luminescent, even in water, and very oxidizing. Therefore it is able to oxidise not only guanosine-5'-monophosphate (GMP), as demonstrated by laser flash photolysis, but also guanine-containing polynucleotides such as calf thymus DNA and [poly(dG-dC)]2. The luminescence quenching was found to be faster in H2O than in D2O, as is the back reaction, indicating that both processes probably proceed by proton-coupled electron transfer. These properties, that are controlled by the triplet MLCT state in which the charge has been transferred from the Ru to a TAP ligand, contrast with those of the well known [Ru(phen)2(dppz)]2+ 2.

Retroviral Constitutive Transport Element Evolved from Cellular TAP(NXF1)-Binding Sequences

The constitutive transport element (CTE) of type D retroviruses serves as a signal of nuclear export of unspliced viral RNAs. The human TAP(NXF1) protein, a cellular mRNA export factor, directly binds to CTE and mediates nuclear export of CTE-containing RNAs. Here, we use genomic SELEX (systematic evolution of ligands by exponential enrichment) to show that the human genome encodes a family of high-affinity TAP ligands. These TAP-binding elements (TBE) are 15-bp minisatellite repeats that are homologous to the core TAP-binding sites in CTE. The repeats are positioned similarly in the RNA secondary structures of CTE and TBE. Like CTE, TBE is an active nuclear export signal. CTE elements of different species share sequence similarities to TBE in the regions that are neutral for CTE function. This conservation points to a possible common ancestry of the two elements, and in fact, TBE has properties expected from a primordial CTE. Additionally, a molecular fossil of a TBE-like minisatellite is found in the genome of a modern retroelement. These findings constitute direct evidence of an evolutionary link between TBE-related minisatellites and CTE.

Photoinduced electron transfer between ruthenium complexes and nucleotides or DNA

Abstract

Photoadduct between tris(1,4,5,8-tetraazaphenanthrene)ruthenium(II) and guanosine monophosphate–a model for a new mode of covalent binding of metal complexes to DNA

Visible light irradiation of [Ru(TAP)3]2+(TAP = 1,4,5,8 -tetraazaphenanthrene) in aqueous solutions containing 5′-guanosine-monophosphate (GMP) and subsequent treatment with 1 mol dm–3 HCl yields Ru(TAP)2(2-TAP-G)2+, in which the guanine moiety is bound via N-2 to C-2 of one of the TAP ligands.

Photochemistry of Ruthenium(II)‐TRIS‐1,4,5,8‐Tetraazaphenanthrene with Mononucleotides: Role of Ligand Photosubstitution

AbstractThe photochemistry of Ru‐tris‐(1,4,5,8‐tetraazaphenanthrene) (Ru(tap)32+) in the absence and in the presence of adenosine‐5′‐monophosphate (AMP) and guanosine‐5′‐monophosphate (GMP) has been studied by flash photolysis and by steady state illumination. Laser pulsed irradiation of Ru(tap)32+ in the presence of AMP produces, with a rather low yield, the transient reduced complex, Ru(tap)31+, by electron transfer from AMP to the excited complex. The flash photolysis of the same solution, after pre‐illumination, shows that a new photoactive compound absorbs at = 500 nm and its efficiency of production decreases at lower temperature and pH. Comparison with the photodechelation of Ru(tap)32+ in the absence of mononucleotide, and with the photoadduct formation between Ru(tap)32+ and GMP/AMP, leads to the conclusion that this photoactive species could correspond to [Ru(tap)2AMP, X]n+ formed by photosubstitution of a tap ligand in the presence of AMP.

Electrochemistry and absorption and emission spectroscopy of new orthometalated complexes of rhodium(III) and iridium(III) with the ligands 1,4,5,8-tetraazaphenanthrene and 1,4,5,8,9,12-hexaazatriphenylene

The electrochcnucal and UV-visible absorption and emission properties of new heterolepticortho-metalated complexes of Rh(III) and Ir(III) are reported and compared to those of similar complexes studied previously in the literature. These novel compounds contain two ortho-metalating ligands (ortho-C-deprotonated forms of 2-phenylpyridine, PPY) and a polyazaaromatic ligand such as 1,4,5,8-tetraazaphenanthrene (TAP) or 1,4,5,8,9,12-hexaazatriphenylene (HAT). The electrochemical behavior, studied by cyclic voltammetry, shows the presence of two reversible reductions, both on a TAP or HAT ligand, and of an irreversible oxidation

8-Quinolinolate complexes of ruthenium(ii). Synthesis, characterization and electron transfer properties

Two stable 8-quinolinolate complexes of ruthenium(II), [Ru(bpy)(Q)]ClO 4 and [Ru(tap) 2(Q)]ClO 4 [bpy = 2,2′-bipyridine, Q=8-quinolinolate anion, tap = 2-( m-tolylazo) pyridine] have been synthesized. The complexes are diamagnetic and show strong absorption near 1100 cm −1 in the IR spectra due to the presence of ClO − 4. In acetonitrile solution they behave as 1:1 electrolytes. The complexes display intense absorption bands in the visible region (400–700 nm) which are assigned to MLCT transitions. The formal potential ( E 0 298), determined cyclic voltammetrically for the ruthenium(II)-ruthenium(III) oxidation, is 0.48 V vs SCE for [Ru(bpy) 2(Q)] +. The same oxidation takes place irreversibly at 1.00 V vs SCE ( E pa value) in the case of [Ru(tap) 2(Q)] +. Reductions of the bound bpy and tap ligands are also observed.