Viologen Complex Research Articles

Effects of sequence context on the binding of tryptophan-containing peptides by the cucurbit[8]uril–methyl viologen complex

This paper describes a novel assay for measuring the relative extent of peptide binding in a large parallel format and the use of this assay to explore the effects of sequence context on the binding of tryptophan (Trp)-containing peptides by the synthetic receptor comprising the noncovalent complex between cucurbit[8]uril and methyl viologen (i.e. Q8√MV). The extent of quenching of Trp fluorescence upon binding to Q8√MV was used to measure the relative extent of binding and thus the relative affinities of 104 Trp-containing peptides, in parallel, using a fluorescence plate reader. This study resulted in the remarkable observation that the identity of the amino acid residues at positions adjacent to the Trp-binding site has little if any influence on the binding affinity. This finding suggests that Q8√MV should be effective for the recognition of Trp residues within a broad range of peptide sequences.

Simultaneous Determination of the Adsorption Constant and the Photoinduced Electron Transfer Rate for a Cds Quantum Dot–Viologen Complex

Transient absorption (TA) spectroscopy of solution-phase mixtures of colloidal CdS quantum dots (QDs) with acid-derivatized viologen molecules, N-[1-heptyl],N'-[3-carboxypropyl]-4,4'-bipyridinium dihexafluorophosphate (V(2+)), indicates electron transfer occurs from the conduction band of the QD to the LUMO of V(2+) after photoexcitation of a band-edge exciton in the QD. Analysis of the magnitude of the ground state bleach of the QD as a function of the molar ratio QD:V(2+) yields the QD-ligand adsorption constant, K(a) (4.4 × 10(4) M(-1)) for V(2+) ligands adsorbed in geometries conducive to electron transfer. The value of K(a), together with the measured rates of (i) formation of the V(+•) electron transfer product and (ii) recovery of the ground state bleach of the QD, enables determination of the intrinsic rate constant for charge separation, k(CS,int) ~ 1.7 × 10(10) s(-1), the rate for a single QD-V(2+) donor-acceptor pair. This analysis confirms previous reports that the number of ligands adsorbed to each QD is well-described by a Poisson distribution. This is the first report where the QD-ligand charge transfer and binding equilibria are quantitatively investigated simultaneously with a single technique.

Ultrasensitive Determination of Cysteine Based on the Photocurrent of Nafion‐Functionalized CdS–MV Quantum Dots on an ITO Electrode

An ultrasensitive cysteine sensor is prepared by using a Nafion assembly of a CdS quantum dot–methyl viologen complex on a conductive ITO surface. It is effective in the readout of the photoelectrochemical response to cysteine with high sensitivity, good selectivity, and fast response. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Light driven formation of a supramolecular system with three CB[8]s locked between redox-active Ru(bpy)3 complexes

Three CB[8]s have been reversibly locked between two Ru(bpy)(3)-viologen complexes by light driven electron transfer reactions.

Kinetics of non-thermal electron transfer controlled by the dynamical solvent effect

Recombination of ion pairs created by photoexcitation of viologen complexes is studied by a theory accounting for diffusion along the reaction coordinate to the crossing points of the electronic terms. The kinetics of recombination convoluted with the instrument response function are shown to differ qualitatively from the simplest exponential decay in both the normal and inverted Marcus regions. The deviations of the exponentiality are minimal only in the case of activationless recombination and are reduced even more by taking into consideration a single quantum mode assisting the electron transfer.

Time-Resolved Optical Spectroscopy of Heterosupramolecular Assemblies Based on Nanostructured TiO2 Films Modified by Chemisorption of Covalently Linked Ruthenium and Viologen Complex Components

Described is the preparation of transparent nanostructured TiO2 (anatase) and Sb-doped SnO2 films supported on F-doped conducting glass. Also described is the modification of these films by chemiso...

Photophysical and Photochemical Properties of Pyranine/Methyl Viologen Complexes in Solution and in Supramolecular Aggregates: A Switchable Complex

The properties of a novel complex between pyranine (a photoacid and an electron donor species) and methyl viologen (an efficient electron acceptor, MV+2) in aqueous and in micellar solutions were d...

Catalytic epoxidation of cyclohexene by covalently linked manganese porphyrin–viologen complex

When a viologen-linked Mn(III)porphyrin complex with a short methylene-chain, in which a viologen is covalently linked by the methylene-chain into one phenyl group of 5,10,15,20-tetraphenylporphyrinatomanganese(III)chloride (Mn(III)(tpp)Cl), was used as a catalyst for a monooxygenation of cyclohexene in an air-equilibrated acetonitrile solution containing insoluble zinc powder as a reductant, more cyclohexene oxide was obtained as a single product than when Mn(tpp)Cl was used as a catalyst. Benzoic acid as a cleaving reagent of the dioxygen double-bond and 1-methylimidazole as a ligand to Mn porphyrin were further contained in the reaction mixture. This result implies that the viologen moiety in the viologen-linked Mn(III)porphyrin acted effectively as a mediator for electron transfer from zinc powder to the Mn(III)porphyrin moiety in the epoxidation cycle activating molecular dioxygen reductively. Though Mn(tpp)Cl was remarkably demetallated by H + ion from benzoic acid during the epoxidation reaction in the mixed system of Mn(III)(tpp)Cl and viologen, the demetallation of the viologen-linked Mn porphyrin with the short methylene-chain was partly prevented because the reduction of a Mn(II)porphyrin-dioxygen adduct was easily caused by fast intramolecular electron-transfer between the two moieties of the viologen and the Mn porphyrin, proceeding the epoxidation cycle smoothly.

A covalently linked ruthenium tris(bipyridine)–viologen complex–polypyrrole film as a molecular photoelectrode

A modified electrode containing a chromophore linked to an electron acceptor has been prepared by anodic electropolymerization of a new ruthenium tris(bipyridine)–viologen–pyrrole complex; thin films of these polymers act as photoelectrodes when irradiated by visible light in the presence of triethanolamine.

Synthesis of photosensitizer pairs containing Ru(bpy)3 2+ and an electron acceptor (viologen) linked by a hydrocarbon chain

Two Ru(bpy)32+-viologen complexes, in which the components are linked by a hydrocarbon chain, were synthesized and characterized by PMR, visible, and UV spectrophotometry.

Fluorescence of covalently bound zinc porphyrin—viologen complexes

A series of porphyrins covalently bound to a single methyl viologen moiety has been synthesised. Fluorescence from the porphyrin is quenched relative to the parent porphyrin; the actual yield depends markedly upon the site of attachment and the length of the chain separating the two reactants. Increasing the number of viologens attached to the porphyrin ring and using non-methylated viologen can increase the fluorescence quenching efficiency. In no case was it possible to detect long-lived redox ion products originating from the fluorescence quencing process.

Electrochemical studies of the viologen system for display applications

The electrochemical and electro-optical behavior of aqueous solutions of diheptyl viologen dibromide on tin oxide conductive glass electrodes was investigated. The viologen dication was found to undergo reduction in two distinct cathodic processes. The first cathodic step leading to the formation of the insoluble purple viologen complex was found to be reversible. The second reduction process was found to be irreversible and resulted in poisoning of the electrode surface. The failure mode of display devices based on the viologen system is attributed to the formation of this second reduction product.