Measurement of apparent diffusion coefficients within ultrathin nafion Langmuir-Schaefer films: comparison of a novel scanning electrochemical microscopy approach with cyclic voltammetry

The use of scanning electrochemical microscopy (SECM) to evaluate the apparent diffusion coefficient, Dapp, of redox-active species in ultrathin Nafion films is described. In this technique, an ultramicroelectrode (UME) tip, positioned close to a film on a macroscopic electrode, is used to oxidize (or reduce) a species in bulk solution, causing the tip-generated oxidant (reductant) to diffuse to the film/solution interface. The oxidation (reduction) of film-confined species regenerates the reductant (oxidant) in solution, leading to feedback to the UME. A numerical model is developed that allows Dapp to be determined. For these studies, ultrathin films of Nafion were prepared using the Langmuir-Schaefer (LS) technique and loaded with an electroactive species, either the ferrocene derivative ferrocenyltrimethylammonium cation, FA+, or tris(2,2'-bipyridyl)ruthenium(II), Ru(bpy)32+. The morphology and the thickness of the Nafion LS films (1.5 +/- 0.2 nm per layer deposited) were evaluated using atomic force microscopy (AFM). For comparison with the SECM measurements, cyclic voltammetry (CV) was employed to evaluate the concentration of electroactive species within the Nafion LS films and to determine Dapp. The latter was found to be essentially invariant with film thickness, but the value for Ru(bpy)32+ was 1 order of magnitude larger than for FA+. CV and SECM measurements yield different values of Dapp, and the underlying reasons are discussed. In general, the Dapp values for these films are considerably smaller than for recast Nafion films, which can be attributed to the compactness of Nafion LS films. Nonetheless, the ultrathin nature of the films leads to fast response times, and we thus expect that these modified electrodes could find applications in sensing, electroanalysis, and electrocatalysis.     

Surface confinement and its effects on the luminescence quenching of a ruthenium-containing metallopolymer

Luminescence quenching of the metallopolymers [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(PVP)(10)Os(bpy)(2)](4+), both in solution and as thin films, is reported, where bpy is 2,2'-bipyridyl and PVP is poly(4-vinylpyridine). When the metallopolymer is dissolved in ethanol, quenching of the ruthenium excited state, Ru(2+*), within [Ru(bpy)(2)(PVP)(10)](2+) by [Os(bpy)(3)](2+) proceeds by a dynamic quenching mechanism and the rate constant is (1.1 +/- 0.1) x 10(11) M(-1) s(-1). This quenching rate is nearly two orders of magnitude larger than that found for quenching of monomeric [Ru(bpy)(3)](2+) under the same conditions. This observation is interpreted in terms of an energy transfer quenching mechanism in which the high local concentration of ruthenium luminophores leads to a single [Os(bpy)(3)](2+) centre quenching the emission of several ruthenium luminophores. Amplifications of this kind will lead to the development of more sensitive sensors based on emission quenching. Quenching by both [Os(bpy)(3)](2+) and molecular oxygen is significantly reduced within a thin film of the metallopolymer. Significantly, in both optically driven emission and electrogenerated chemiluminescence, emission is observed from both ruthenium and osmium centres within [Ru(bpy)(2)(PVP)(10)Os(bpy)(2)](4+) films, i.e. the ruthenium emission is not quenched by the coordinated [Os(bpy)(2)](2+) units. This observation opens up new possibilities in multi-analyte sensing since each luminophore can be used to detect separate analytes, e.g. guanine and oxoguanine.     

Conduction band mediated electron transfer across nanocrystalline TiO2 surfaces

Mesoporous thin films comprised of interconnected nanocrystalline (anatase, 20 nm) TiO2 particles were functionalized with [Ru(bpy)2(deebq)](PF6)2, where bpy is 2,2'-bipyridine and deebq is 4,4'-diethylester-2,2'-biquinoline, or iron(III) protoporphyrin IX chloride (hemin). These compounds bind to TiO2 with saturation surface coverages of 8 (+/-2)x10(-8) mol/cm2. Electrochemical measurements show that the compounds first reduction occurs prior to or commensurate with the reduction of the TiO2 electrode. Apparent diffusion constants, Dapp, abstracted from chronoabsorption data measured in acetonitrile were found to be dependent on the applied potential and the electrolyte used. The Dapp values for reduction of Ru(dcbq)(bpy)2/TiO2, where dcbq is 4,4'-(COO-)2-2,2'-biquinoline, increased with decreasing surface coverage. At near saturation surface coverage, the apparent diffusion constant was 9.0 x 10(-12) m2/s after a potential step from -0.61 to -1.31 vs Fc+/0. The Dapp varied by over a factor of six with applied potential for the oxidation of [Ru(dcbq-)(bpy)2]-/TiO2 to Ru(dcbq)(bpy)2/TiO2. Complete reduction of hemin/TiO2 to heme/TiO2 was observed under conditions where the heme surface coverage was about 1/100 of that expected for monolayer surface coverage. The hemin reduction rates were strongly dependent on the final applied potential. The rates for heme to hemin oxidation were less than or equal to the hemin to heme rates in the presence and absence of pyridine. This behavior was opposite to that observed with Ru(dcbq)(bpy)2/TiO2 where reduction was slower than oxidation. A Gerischer-type model was proposed to rationalize the rectifying properties of the interface.     

Photocurrent amplification by an energy/electron transfer cascade in polymer Langmuir-Blodgett films

Effective photocurrent generation by visible light irradiation on hetero-deposited polymer Langmuir-Blodgett (LB) films containing tris(bipyridine) ruthenium(II) (Ru(bpy)3(2+)) and anthracene derivatives was observed. The photocurrent amplification was found to be assisted by the photoinduced energy/electron transfer cascade, which consists of the interlayer triplet-triplet energy transfer process from photoexcited Ru(bpy)3(2+) to anthracene, and then electron transfer processes from the triplet anthracene to a viologen acceptor, from Ru(bpy)3(2+) to the oxidized anthracene and from the electrode to Ru(bpy)3(3+).     

Preparation and multicolor electrochromic performance of a WO3/tris(2,2'-bipyridine)ruthenium(II)/polymer hybrid film

A tungsten trioxide (WO(3))/tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3)](2+); bpy=2,2'-bipyridine)/poly(sodium 4-styrenesulfonate) (PSS) hybrid film was prepared by electrodeposition from a colloidal triad solution containing peroxotungstic acid (PTA), [Ru(bpy)(3)](2+), and PSS. A binary solution of [Ru(bpy)(3)](2+) and PTA (30 vol % ethanol in water) gradually gave an orange precipitate, possibly caused by the electrostatic interaction between the cationic [Ru(bpy)(3)](2+) and the anionic PTA. The addition of PSS to the binary PTA/[Ru(bpy)(3)](2+) solution remarkably suppressed this precipitation and caused a stable, colloidal triad solution to form. The spectrophotometric measurements and lifetime analyses of the photoluminescence from the excited [Ru(bpy)(3)](2+) ion in the colloidal triad solution suggested that the [Ru(bpy)(3)](2+) ion is partially shielded from electrostatic interaction with anionic PTA by the anionic PSS polymer chain. The formation of the colloidal triad made the ternary [Ru(bpy)(3)](2+)/PTA/PSS solution much more redox active. Consequently, the rate of electrodeposition of WO(3) from PTA increased appreciably by the formation of the colloidal triad, and fast electrodeposition is required for the unique preparation of this hybrid film. The absorption spectrum of the [Ru(bpy)(3)](2+) ion in the film was close to its spectrum in water, but the photoexcited state of the [Ru(bpy)(3)](2+) ion was found to be quenched completely by the presence of WO(3) in the hybrid film. The cyclic voltammogram (CV) of the hybrid film suggested that the [Ru(bpy)(3)](2+) ion performs as it is adsorbed onto WO(3) during the electrochemical oxidation. An ohmic contact between the [Ru(bpy)(3)](2+) ion and the WO(3) surface could allow the electrochemical reaction of adsorbed [Ru(bpy)(3)](2+). The composition of the hybrid film, analyzed by electron probe microanalysis (EPMA), suggested that the positive charge of the [Ru(bpy)(3)](2+) ion could be neutralized by partially reduced WO(3)(-) ions, in addition to Cl(-) and PSS units, based on the charge balance in the film. The electrostatic interaction between the WO(3)(-) ion and the [Ru(bpy)(3)](2+) ion might be responsible for forming the electron transfer channel that causes the complete quenching of the photoexcited [Ru(bpy)(3)](2+) ion, as well as the formation of the ohmic contact between the [Ru(bpy)(3)](2+) ion and WO(3). A multicolor electrochromic performance of the WO(3)/[Ru(bpy)(3)](2+)/PSS hybrid film was observed, in which transmittances at 459 and 800 nm could be changed, either individually or at once, by the selection of a potential switch. Fast responses, of within a few seconds, to these potential switches were exhibited by the electrochromic hybrid film.     

Electrogenerated chemiluminescence reaction of tris(2,2'-bipyridine)ruthenium(II) with 2,5-dimethylthiophene as co-reactant in aqueous solution

A novel effective co-reactant for electrogenerated chemiluminescence (ECL) of Ru(bpy)(3)(2+) has been found. Alpha-position-dialkylated thiophene derivatives such as 2,5-dimethylthiophene (DMT) could be used as a co-reactant for Ru(bpy)(3)(2+) ECL. The reaction mechanism of the Ru(bpy)(3)(2+)/DMT system was proposed on the basis of the identification of the reaction product, the relationship between the molecular structure and the chemiluminescent intensity, and the electrochemical study. The obtained reaction mechanism was similar to that of the Ru(bpy)(3)(2+)/aliphatic tertiary amine system. Based on these results, the preliminary studies of the Ru(bpy)(3)(2+) ECL detection system using DMT as a co-reactant were performed. Under the optimal ECL conditions, the plot of ECL intensity versus the concentration of Ru(bpy)(3)(2+) was linear over the concentration range 1.0x10(-8) to 1.5x10(-7) M (determination coefficient=0.9996).     

Exploring the interaction of ruthenium(II) polypyridyl complexes with DNA using single-molecule techniques

Here we explore DNA binding by a family of ruthenium(II) polypyridyl complexes using an atomic force microscope (AFM) and optical tweezers. We demonstrate using AFM that Ru(bpy)2dppz2+ intercalates into DNA (K(b) = 1.5 x 10(5) M(-1)), as does its close relative Ru(bpy)2dppx2+ (K(b) = 1.5 x 10(5) M(-1)). However, intercalation by Ru(phen)3(2+) and other Ru(II) complexes with K(b) values lower than that of Ru(bpy)2dppz2+ is difficult to determine using AFM because of competing aggregation and surface-binding phenomena. At the high Ru(II) concentrations required to evaluate intercalation, most of the DNA strands acquire a twisted, curled conformation that is impossible to measure accurately. The condensation of DNA on mica in the presence of polycations is well known, but it clearly precludes the accurate assessment by AFM of DNA intercalation by most Ru(II) complexes, though not by ethidium bromide and other monovalent intercalators. When stretching individual DNA molecules using optical tweezers, the same limitation on high metal concentration does not exist. Using optical tweezers, we show that Ru(phen)2dppz2+ intercalates avidly (K(b) = 3.2 x 10(6) M(-1)) whereas Ru(bpy)3(2+) does not intercalate, even at micromolar ruthenium concentrations. Ru(phen)3(2+) is shown to intercalate weakly (i.e., at micromolar concentrations (K(b) = 8.8 x 10(3) M(-1))). The distinct differences in DNA stretching behavior between Ru(phen)3(2+) and Ru(bpy)3(2+) clearly illustrate that intercalation can be distinguished from groove binding by pulling the DNA with optical tweezers. Our results demonstrate both the benefits and challenges of two single-molecule methods of exploring DNA binding and help to elucidate the mode of binding of Ru(phen)3(2+).     

Electrochromic hysteresis performance of a prussian blue film arising from electron-transfer control by a tris(2,2'-bipyridine)ruthenium(II)-doped WO(3) film as studied by a spectrocyclic voltammetry technique

A [Ru(bpy)(3)](2+) (bpy=2,2'-bipyridine)-doped WO(3) film was prepared as a base layer on a substrate by cathodic electrodeposition from a colloidal triad solution containing peroxotungstic acid (PTA), [Ru(bpy)(3)](2+), and poly(sodium 4-styrenesulfonate) (PSS). A Prussian blue (PB; Fe(II)-Fe(III)) film was cathodically electrodeposited on the [Ru(bpy)(3)](2+)-doped WO(3) film or neat WO(3) film from an aqueous Berlin brown (BB; Fe(III)-Fe(III)) colloid solution to yield a [Ru(bpy)(3)](2+)-doped WO(3)/PB bilayer film or WO(3)/PB bilayer film. For the spectrocyclic voltammogram (SCV) of the WO(3)/PB film, a redox response of Prussian white (PW; Fe(II)-Fe(II))/PB was observed at 0.11 V, however, further oxidation of PB to BB was not allowed by the interfacial n-type Schottky barrier between the WO(3) and PB layers. For the [Ru(bpy)(3)](2+)-doped WO(3)/PB film, any electrochemical response assigned to the redox of PB was not observed in the cyclic voltammogram, however, the in situ absorption spectral change recorded simultaneously showed the significant redox reactions based on PB. The SCV revealed that PW on the [Ru(bpy)(3)](2+)-doped WO(3) film is completely oxidized to PB by a geared reaction of Ru(II)/Ru(III) at 1.05 V, and that 32 % of PB formed is further oxidized to BB by the same geared reaction in the potential scan to 1.5 V. PB was completely re-reduced to PW by a geared reaction of H(x)WO(3)/WO(3) at -0.5 V in the reductive potential scan. These geared electrochemical reactions produced an electrochromic hysteresis performance of the PB film layered on the [Ru(bpy)(3)](2+)-doped WO(3) film.     

Dynamic in situ spectroscopic ellipsometry of the reaction of aqueous iron(II) with 2,2'-bipyridine in a thin Nafion film

Dynamic in situ spectroscopic ellipsometry studies of the chemical reaction between ferrous ion and 2,2'-bipyridine (bpy) in a thin Nafion film are presented. A simple prototype system composed of a thin Nafion film on a glass substrate was used throughout the work. The reaction was detected by optically monitoring the formation of the strongly absorbing complex ion, Fe(bpy)3(2+) (epsilon 520 = 7.70 x 10(3) M(-1) cm(-1) in 0.1 M NaCl). The changes in film optical constants, n and k, and the thickness upon exposure of it to various solutions were monitored in a flow cell with the film on the backside of the substrate relative to the interrogation by light. A "step-by-step" approach was used to isolate the component parts of the system in which the film was consecutively exposed to solutions in the following order: supporting electrolyte, bpy, and, last, ferrous iron solution. The optical properties of the materials were quantitatively described before and during mass transport within the film by modeling using the appropriate multilayer optical models, i.e., the Cauchy equation for nonabsorbing media and the Urbach and Tauc-Lorentz (oscillator) functions for a film that absorbed. The experiments done allowed study of the diffusion in the film and the chemical reactions that are important in the sensing scheme for ferrous iron. Ligand (bpy) diffusion followed a two-stage diffusion mechanism described by a Berens-Hopfenberg model for incremental sorption (D25 = 7.04 x 10(-13) cm2 s(-1)). The stabilities of the appropriate systems, i.e., Nafion film with bpy, iron, and iron complex, were studied by exposing equilibrated films to circulating supporting electrolyte solutions. The measurements gave important insights into a set of film chemical reactions and, in turn, selective film dynamics. This work exemplifies the usefulness of spectroscopic ellipsometry in monitoring the kinetics of a chemical reaction in situ, as well as the changes in the film physical properties under dynamic conditions.     

Electroactive planar waveguide studies of Ru(bpy)3(2+) intercalated in a thin clay film: I. Transport and electrochemical phenomena

Electroactive planar waveguide (EAPW) instrumentation was used to perform potential modulated absorbance (PMA) experiments at indium tin oxide (ITO) electrodes coated with 0-, 300-, 800-, and 1200-nm-thick SWy-1 montmorillonite clay. PMA experiments performed at low potential modulation monitor mass transport events within 100 nm of the ITO surface and, thus, when used in conjunction with cyclic voltammetry (CV), can elucidate charge transport mechanisms. The data show that at very thin films electron transfer is controlled by electron hopping (sensitive to the anion species in the electrolyte) in an adsorbed Ru(bpy)(3)(2+) layer. As the thickness of the clay film grows, electron transfer may become controlled by mass transfer of Ru(bpy)(3)(2+) within the clay film to and from the electrode surface, a mechanism that is affected by the swelling of the film. Film swelling is controlled by the cation of the electrolyte. Films loaded with Ru(bpy)(3)(2+) while being subjected to evanescent wave stimulation demonstrate a large hydrophobic layer. The growth of the hydrophobic layer is attributed to the formation of Ru(bpy)(3)(2+*), which has negative charge located at the periphery of the molecule enhancing clay/complex repulsion. The results suggest that the structure of the film and the mechanism of charge transport can be rationally controlled. Simultaneous measurements of the ingress of Ru(bpy)(3)(2+) into the clay film by CV and PMA provide a means to determine the diffusion coefficient of the complex.     

Chemiluminescent investigation of tris(2,2'-bipyridyl)ruthenium(II) immobilized on a cationic ion-exchange resin and its application to analysis

Tris-(2, 2'-bipyridyl)ruthenium(II) complex, Ru(bpy)(3)(2+), was immobilized on the Dowex-50 W cationic ion-exchange resin. The chemiluminescent characteristics of Ru(bpy)(3)(2+) in solution and in resin form were compared by using batch and flow injection methods. A strong chemiluminescence was observed during the reaction of Ru(bpy)(3)(2+) both in solution and in resin with KMnO(4) or Ce(SO(4))(2) under acidic or basic conditions. The Ru(bpy)(3)(2+) immobilized resin is stable, which can be used at least for 6 months when it reacts with the dilute KMnO(4) solution. Based on this property, Ru(bpy)(3)(2+) immobilized in the resin phase was developed as a flow-through chemiluminescent sensor that could be used to determine oxalate, sulfite and ethanol chemically or electronically with Ru(bpy)(3)(3+) generation on the surface of resin. The limits of detection were 1 x 10(-6) M for oxalate, 0.5% (v/v) for ethanol and 1 x 10(-7) M for sulfite. The method has been successfully applied to determine sulfite in sugar.     

Mechanism of hydride donor generation using a Ru(II) complex containing an NAD+ model ligand: pulse and steady-state radiolysis studies

The mechanistic pathways of formation of the NADH-like [Ru(bpy) 2(pbnHH)] (2+) species from [Ru(bpy)2(pbn)](2+) were studied in an aqueous medium. Formation of the one-electron-reduced species as a result of reduction by a solvated electron (k=3.0 x 10(10) M(-1) s(-1)) or CO2(*-) (k=4.6 x 10(9) M(-1) s(-1)) or reductive quenching of an MLCT excited state by 1,4-diazabicyclo[2.2.2]octane (k=1.1 x 10(9) M(-1) s(-1)) is followed by protonation of the reduced species (p K a = 11). Dimerization (k7a=2.2 x 10(8) M(-1) s(-1)) of the singly reduced protonated species, [Ru(bpy) 2(pbnH(*))](2+), followed by disproportionation of the dimer as well as the cross reaction between the singly reduced protonated and nonprotonated species (k8= 1.2 x 10(8) M(-1) s(-1)) results in the formation of the final [Ru(bpy)2(pbnHH)](2+) product together with an equal amount of the starting complex, [Ru(bpy)2(pbn)](2+). At 0.2 degrees C, a dimeric intermediate, most likely a pi-stacking dimer, was observed that decomposes thermally to form an equimolar mixture of [Ru(bpy)2(pbnHH)](2+) and [Ru(bpy)2(pbn)](2+) (pH<9). The absence of a significant kinetic isotope effect in the disproportionation reaction of [Ru(bpy)2(pbnH(*))](2+) and its conjugate base (pH>9) indicates that disproportionation occurs by a stepwise pathway of electron transfer followed by proton transfer.     

Synthesis of PtNPs/AQ/Ru(bpy)3(2+) colloid and its application as a sensitive solid-state electrochemiluminescence sensor material

The facile synthesis of the novel platinum nanoparticles/Eastman AQ55D/ruthenium(II) tris(bipyridine) (PtNPs/AQ/Ru(bpy)3(2+)) colloidal material for ultrasensitive ECL solid-state sensors was reported for the first time. The cation ion-exchanger AQ was used not only to immobilize ECL active species Ru(bpy)3(2+) but also as the dispersant of PtNPs. Colloidal characterization was accomplished by transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS), and UV-vis spectroscopy. Directly coating the as-prepared colloid on the surface of a glassy carbon electrode produces an electrochemiluminescence (ECL) sensor. The electronic conductivity and electroactivity of PtNPs in composite film made the sensor exhibit faster electron transfer, higher ECL intensity of Ru(bpy)3(2+), and a shorter equilibration time than Ru(bpy)3(2+) immobilized in pure AQ film. Furthermore, it was demonstrated that the combination of PtNPs and permselective cation exchanger made the sensor exhibite excellent ECL behavior and stability and a very low limit of detection (1 x 10(-15) M) of tripropylamine with application prospects in bioanalysis. This method was very simple, effective, and low cost.     

Toxicity screening by electrochemical detection of DNA damage by metabolites generated in situ in ultrathin DNA-enzyme films

Rapid detection of DNA damage could serve as a basis for in vitro genotoxicity screening for new organic compounds. Ultrathin films (20-40 nm) containing myoglobin or cytochrome P450(cam) and DNA grown layer-by-layer on electrodes were activated by hydrogen peroxide, and the enzyme in the film generated metabolite styrene oxide from styrene. This styrene oxide reacted with double stranded (ds)-DNA in the same film, mimicking metabolism and DNA damage in human liver. DNA damage was detected by square wave voltammetry (SWV) by using catalytic oxidation with Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) and by monitoring the binding of Co(bpy)(3)(3+). Damaged DNA reacts more rapidly than intact ds-DNA with Ru(bpy)(3)(3+), giving SWV peaks at approximately 1 V versus SCE that grow larger with reaction time. Co(bpy)(3)(3+) binds more strongly to intact ds-DNA, and its SWV peaks at 0.04 V decreased as DNA was damaged. Little change in SWV signals was found for incubations of DNA/enzyme films with unreactive organic controls or hydrogen peroxide. Capillary electrophoresis and HPLC-MS suggested the formation of styrene oxide adducts of DNA bases under similar reaction conditions in thin films and in solution. The catalytic SWV method was more sensitive than the Co(bpy)(3)(3+) binding assay, providing multiple measurements over a 5 min reaction time.     

Electron tunneling in single crystals of Pseudomonas aeruginosa azurins.

Rates of reduction of Os(III), Ru(III), and Re(I) by Cu(I) in His83-modified Pseudomonas aeruginosa azurins (M-Cu distance approximately 17 A) have been measured in single crystals, where protein conformation and surface solvation are precisely defined by high-resolution X-ray structure determinations: 1.7(8) x 10(6) s(-1) (298 K), 1.8(8) x 10(6) s(-1) (140 K), [Ru(bpy)2(im)(3+)-]; 3.0(15) x 10(6) s(-1) (298 K), [Ru(tpy)(bpy)(3+)-]; 3.0(15) x 10(6) s(-1) (298 K), [Ru(tpy)(phen)(3+)-]; 9.0(50) x 10(2) s(-1) (298 K), [Os(bpy)2(im)(3+)-]; 4.4(20) x 10(6) s(-1) (298 K), [Re(CO)3(phen)(+)] (bpy = 2,2'-bipyridine; im = imidazole; tpy = 2,2':6',2' '-terpyridine; phen = 1,10-phenanthroline). The time constants for electron tunneling in crystals are roughly the same as those measured in solution, indicating very similar protein structures in the two states. High-resolution structures of the oxidized (1.5 A) and reduced (1.4 A) states of Ru(II)(tpy)(phen)(His83)Az establish that very small changes in copper coordination accompany reduction but reveal a shorter axial interaction between copper and the Gly45 peptide carbonyl oxygen [2.6 A for Cu(II)] than had been recognized previously. Although Ru(bpy)2(im)(His83)Az is less solvated in the crystal, the reorganization energy for Cu(I) --> Ru(III) electron transfer falls in the range (0.6-0.8 eV) determined experimentally for the reaction in solution. Our work suggests that outer-sphere protein reorganization is the dominant activation component required for electron tunneling.     

Electron-transfer chemistry of Ru-linker-(heme)-modified myoglobin: rapid intraprotein reduction of a photogenerated porphyrin cation radical

We report the synthesis and characterization of RuC7, a complex in which a heme is covalently attached to a [Ru(bpy)(3)](2+) complex through a -(CH(2))(7)- linker. Insertion of RuC7 into horse heart apomyoglobin gives RuC7Mb, a Ru(heme)-protein conjugate in which [Ru(bpy)(3)](2+) emission is highly quenched. The rate of photoinduced electron transfer (ET) from the resting (Ru(2+)/Fe(3+)) to the transient (Ru(3+)/Fe(2+)) state of RuC7Mb is >10(8) s(-1); the back ET rate (to regenerate Ru(2+)/Fe(3+)) is 1.4 x 10(7) s(-1). Irreversible oxidative quenching by [Co(NH(3))(5)Cl](2+) generates Ru(3+)/Fe(3+): the Ru(3+) complex then oxidizes the porphyrin to a cation radical (P*+); in a subsequent step, P*+ oxidizes both Fe(3+) (to give Fe(IV)=O) and an amino acid residue. The rate of intramolecular reduction of P*+ is 9.8 x 10(3) s(-1); the rate of ferryl formation is 2.9 x 10(3) s(-1). Strong EPR signals attributable to tyrosine and tryptophan radicals were recorded after RuC7MbM(3+) (M = Fe, Mn) was flash-quenched/frozen.     

含长链不饱和酯基的三官能度溶胶-凝胶薄膜制备及发光氧气传感的研究

采用溶胶-凝胶法制备了含发光三吡啶钌[Ru(bpy)₃²⁺]分子的三官能度硅氧烷预聚液,并通过旋转涂敷及凝胶处理制备了高性能的薄膜,探讨了载体的微结构和发光分子的微环境效应。与传统的四官能度正硅酸乙酯(TEOS)/Ru(bpy)₃²⁺膜体系相比,含长链不饱和酯基的甲基丙烯酸丙酯基三甲氧基硅烷(PMA-TMS)/Ru(bpy)₃²⁺体系具有成膜性能好,气体的猝灭响应值高,响应时间短等特点。     

Solid-state electrochemiluminescence sensor based on the Nafion/poly(sodium 4-styrene sulfonate) composite film

An effective electrochemiluminescence (ECL) sensor based on Nafion/poly(sodium 4-styrene sulfonate) (PSS) composite film-modified ITO electrode was developed. The Nafion/PSS/Ru composite film was characterized by atomic force microscopy, UV-vis absorbance spectroscopy and electrochemical experiments. The Nafion/PSS composite film could effectively immobilize tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) via ion-exchange and electrostatic interaction. The ECL behavior of Ru(bpy)₃²⁺ immobilized in Nafion/PSS composite film was investigated using tripropylamine (TPA) as an analyte. The detection limit (S/N = 3) for TPA at the Nafion/PSS/Ru composite-modified electrode was estimated to be 3.0 nM, which is 3 orders of magnitude lower than that obtained at the Nafion/Ru modified electrode. The Nafion/PSS/Ru composite film-modified indium tin oxide (ITO) electrode also exhibited good ECL stability. In addition, this kind of immobilization approach was simple, effective, and timesaving.     

Investigations of the optical properties of thin, highly absorbing films under attenuated total reflection conditions: Leaky waveguide mode distortions

Spectra of thin highly absorbing Nafion films doped with Ru(bpy)₃²⁺ on SF11 glass substrates were studied by internal reflection spectroscopy using a single reflection configuration. For the system under study, two modes of light interaction with the film are available: attenuation due to evanescent wave penetration and light propagation within the absorbing film. Unlike evanescent wave spectroscopy, light propagation within the film causes distortions in the measured spectra due to leaky waveguide propagation modes. Upon light propagation in a film doped with Ru(bpy)₃²⁺ spectral shifts up to 50 nm to longer wavelengths can occur and additional absorbance peaks can appear in the spectra. These film-based distortions depend on the complex refractive index, the thickness of the film and the angle of incidence. These effects become significant for an extinction coefficient above 0.01 and a film thickness above 200 nm. It is shown that spectral distortions can lead to quite complex dynamics in the internal reflection spectra upon analyte preconcentration in the film. Ru(bpy)₃²⁺ partitioning into the Nafion film causes significant refractive index changes that in turn alter leaky waveguide mode conditions in the film and, can even lead to a reduction of measured absorbance despite the increase in the extinction coefficient of the film.     

Long-range electron transfer across molecule-nanocrystalline semiconductor interfaces using tripodal sensitizers

Four tripodal sensitizers, Ru(bpy)(2)(Ad-tripod-phen)(2+) (1), Ru(bpy)(2)(Ad-tripod-bpy)(2+) (2), Ru(bpy)(2)(C-tripod-phen)(2+) (3), and Ru(bpy)(2)(C-tripod-bpy)(2+) (4) (where bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, and Ad-tripod-bpy (phen) and C-tripod-bpy (phen) are tripod-shaped bpy (phen) ligands based on 1,3,5,7-tetraphenyladamantane and tetraphenylmethane, respectively), have been synthesized and characterized. The tripodal sensitizers consist of a rigid-rod arm linked to a Ru(II)-polypyridine complex at one end and three COOR groups on the other end that bind to metal oxide nanoparticle surfaces. The excited-state and redox properties of solvated and surface-bound 1-4 have been studied at room temperature. The absorption spectra, emission spectra, and electrochemical properties of 1-4 in acetonitrile solution are preserved when 1-4 are bound to nanocrystalline (anatase) TiO(2) or colloidal ZrO(2) mesoporous films. This behavior is indicative of weak electronic coupling between TiO(2) and the sensitizer. The kinetics for excited-state decay are exponential for 1-4 in solution and are nonexponential when 1-4 are bound to ZrO(2) or TiO(2). Efficient and rapid (k(cs) > 10(8) s(-)(1)) excited-state electron injection is observed for 1-4/TiO(2). The recombination of the injected electron with the oxidized Ru(III) center is well described by a second-order kinetic model with rate constants that are independent of the sensitizer. The sensitizers bound to TiO(2) were reversibly oxidized electrochemically with an apparent diffusion coefficient approximately 1 x 10(-11) cm(2) s(-)(1).