Development of a universal conductive platform for anchoring photo- and electroactive proteins using organometallic terpyridine molecular wires.

The construction of an efficient conductive interface between electrodes and electroactive proteins is a major challenge in the biosensor and bioelectrochemistry fields to achieve the desired nanodevice performance. Concomitantly, metallo-organic terpyridine wires have been extensively studied for their great ability to mediate electron transfer over a long-range distance. In this study, we report a novel stepwise bottom-up approach for assembling bioelectrodes based on a genetically modified model electroactive protein, cytochrome c553 (cyt c553) and an organometallic terpyridine (TPY) molecular wire self-assembled monolayer (SAM). Efficient anchoring of the TPY derivative (TPY-PO(OH)2) onto the ITO surface was achieved by optimising solvent composition. Uniform surface coverage with the electroactive protein was achieved by binding the cyt c553 molecules via the C-terminal His6-tag to the modified TPY macromolecules containing Earth abundant metallic redox centres. Photoelectrochemical characterisation demonstrates the crucial importance of the metal redox centre for the determination of the desired electron transfer properties between cyt and the ITO electrode. Even without the cyt protein, the ITO-TPY nanosystem reported here generates photocurrents whose densities are 2-fold higher that those reported earlier for ITO electrodes functionalised with the photoactive proteins such as photosystem I in the presence of an external mediator, and 30-fold higher than that of the pristine ITO. The universal chemical platform for anchoring and nanostructuring of (photo)electroactive proteins reported in this study provides a major advancement for the construction of efficient (bio)molecular systems requiring a high degree of precise supramolecular organisation as well as efficient charge transfer between (photo)redox-active molecular components and various types of electrode materials.

Preparative Electrosynthesis of Strong Oxidizers at Boron-Doped Diamond Electrode in Anhydrous HF.

The use of the boron-doped diamond electrode as a sufficiently stable electrode for electrochemical measurements/synthesis in liquid anhydrous hydrogen fluoride medium is reported. Electrooxidation of silver(I) has been studied in this solvent by using classical transient electrochemical methods and impedance spectroscopy. It has been found that faradaic currents related to silver(I) oxidation and the fluorine evolution reaction are reasonably separated at the potential scale, which allows efficient electrosynthesis of AgII F2 , a powerful oxidizer. Impedance spectroscopy measurements provide insight into complex mechanism of AgF2 formation. The procedure for electrosynthesis is provided for the first time in both galvanostatic and potentiostatic condition.

[Ag(OH2 )2 ][Ag(SO4 )2 ]: A Hydrate of a Silver(II) Salt.

When exposed to air at ambient conditions, AgSO4 slowly reacts with moisture, yielding AgSO4 ⋅H2 O. The crystal structure determination (powder data) shows that it may be described as [Ag(OH2 )2 ][Ag(SO4 )2 ], with some sulfate groups being shared between different Ag2+ cations, resembling in that way its Cu2+ analogue. [Ag(OH2 )2 ][Ag(SO4 )2 ], the first hydrate of a compound of Ag2+ , was extensively characterized using many physicochemical methods.

Ultrasensitive 4-methylumbelliferone fluorimetric determination of water contents in aprotic solvents.

A novel approach to the quantification of relatively small amounts of water present in low polarity, aprotic solvents is proposed. This method takes advantage of protolitic reaction of 4-methylumbelliferone dissolved in the solvent with water, acting as a base. The low emission intensity neutral 4-methylumbelliferone is transformed in reaction with water to a highly fluorescent anionic form. Thus the increase in emission intensity is observed for increasing water contents in aprotic solvents. For low water contents and highly lipophilic solvents, this method yields (in practical conditions) higher sensitivity compared to biamperometric Karl Fischer titration method in volumetric mode. It is also shown that organic compounds of protolitic character (amines, acids) not only interfere with water contents determination but increase the sensitivity of emission vs. water contents dependence. Introduction of aqueous solution of strong acid or base (HCl or NaOH) has similar effect on the system as introduction of pure water.

CO2 electroreduction at bare and Cu-decorated Pd pseudomorphic layers: catalyst tuning by controlled and indirect supporting onto Au(111).

We report here the results of electrochemical studies on CO2 electroreduction at multilayered catalyst composed of the monatomic layer of copper covering palladium overlayers (0.8-10 monolayers) deposited on the well-defined Au(111) surface. These multilayered systems were obtained by successive underpotential deposition steps: Pd on Au(111) as well as Cu on Pd/Au(111). Low index orientation of Au substrate was chosen to compare Pd overlayers with bulk Pd(111), which is known to reduce CO2 to CO adsorbates in acidic solutions. The process of CO2 electroreduction was studied by using classical transient electrochemical methods. Catalytic activity of bare Pd layers was investigated in acidic and neutral solutions. In the latter case, much higher activity of Pd overlayers was observed. The results showed that the palladium layer thickness significantly changed the catalytic activities of both bare Pd overlayers and the one Cu monolayer covered electrodes toward CO2 electroreduction. Results show that catalytic activity can be finely tuned by using the multilayered near-surface-alloy approach.

Outstanding catalytic activity of ultra-pure platinum nanoparticles.

Small (4 nm) nanoparticles with a narrow size distribution, exceptional surface purity, and increased surface order, which exhibits itself as an increased presence of basal crystallographic planes, can be obtained without the use of any surfactant. These nanoparticles can be used in many applications in an as-received state and are threefold more active towards a model catalytic reaction (oxidation of ethylene glycol). Furthermore, the superior properties of this material are interesting not only due to the increase in their intrinsic catalytic activity, but also due to the exceptional surface purity itself. The nanoparticles can be used directly (i.e., as-received, without any cleaning steps) in biomedical applications (i.e., as more efficient drug carriers due to an increased number of adsorption sites) and in energy-harvesting/data-storage devices.

Media effects on the mechanism of antioxidant action of silybin and 2,3-dehydrosilybin: role of the enol group.

Silybin (SIL) and 2,3-dehydrosilybin (DHS) are constituents of milk thistle extract (silymarin) applied in the treatment of cirrhosis, hepatitis, and alcohol-induced liver disease. The molecular mechanism of their action is usually connected with antioxidant action. However, despite experimental and theoretical evidence for the antioxidant activity of SIL and DHS, the mechanism of their antiradical action still remains unclear. We studied the kinetics of SIL/DHS reactions with 2,2-diphenyl-1-picrylhydrazyl radical in organic solutions of different polarity and with peroxyl radicals in a micellar system mimicking the amphiphilic environment of lipid membranes. Kinetic studies together with determination of acidity and electrochemical measurements allowed us to discuss the structure-activity relationship in detail. In nonpolar solvents the reaction with free radicals proceeds via a one-step hydrogen atom transfer (HAT) mechanism, while significant acceleration of the reaction rates in methanol and water/methanol solutions suggests the dominating contribution of a sequential proton-loss electron-transfer (SPLET) mechanism with participation of the most acidic hydroxyl groups: 7-OH in SIL and 7-OH and 3-OH in DHS. In a heterogeneous water/lipid system, both mechanisms operate; however, the reaction kinetics and the antioxidant efficacy depend on the partition between lipid and water phases.

Stabilization and strong oxidizing properties of Ag(II) in a fluorine-free solvent.

Divalent silver is stabilized in concentrated sulphuric acid and oleums. The formal redox potential of the Ag(II)/Ag(I) redox pair is markedly dependent on the Hammett acidity function and it reaches +2.90 V vs. NHE in 33% oleum thus rivalling E° for the F2/2F(-) redox pair (+2.87 V).

Insights from impedance spectroscopy into the mechanism of thermal decomposition of M(NH2BH3), M = H, Li, Na, Li(0.5)Na(0.5), hydrogen stores.

We report the first solid-state impedance study of hydrogen-rich ammonia borane, AB, and its three alkali metal amidoborane derivatives. Temperature-dependent impedance spectra of solid M(NH(2)BH(3)) salts are predominated by ionic conductivity, which at room temperature ranges from 5.5 µS cm(-1) (M = Li) to 2.2-3.0 mS cm(-1) (Na, Na(0.5)Li(0.5)), while the activation energy for conductivity is rather high (140-158 kJ mol(-1)). Variation of conductivity with time can be used to extract information about the evolution of the system during thermal decomposition. By using a combination of impedance spectroscopy, thermogravimetric analysis, scanning calorimetry, evolved gas analysis, infrared absorption spectroscopy as well as (11)B and (1)H MAS NMR, we were able to reconfirm the complex pathway of thermal decomposition of amidoboranes postulated by two of us earlier (J. Mater. Chem. 2009, 19, 2043).

A highly stable, efficient visible-light driven water photoelectrolysis system using a nanocrystalline WO3 photoanode and a methane sulfonic acid electrolyte.

Nanostructuring of semiconductor films offers the potential means for producing photoelectrodes with improved minority charge carrier collection. Crucial to the effective operation of the photoelectrode is also the choice of a suitable electrolyte. The behaviour of the nanostructured WO(3) photoanodes in methane sulfonic acid solutions, which allow one to obtain large, perfectly stable visible-light driven water splitting photocurrents, is discussed. The important effect of the electrolyte concentration upon the current distribution and the related photocurrent losses within the nanoporous photoelectrodes is pointed out.

Construction of DNA biosensor at glassy carbon surface modified with 4-aminoethylbenzenediazonium salt.

A simple, label-free electrochemical impedance-spectroscopy method for sequence-specific detection of DNA using a 4-aminoethylbenzenediazonium (AEBD) salt as a binder for amino-modified probe DNA is reported. This novel method simplifies the anchoring of DNA at the GC surface and opens new ways for the detection of hybridization. The hybridization of target DNA, without and with mismatches, with the probe DNA anchored at the GC surface modified with AEBD, greatly increases the interfacial electron transfer resistance at the double-stranded DNA modified electrodes for the redox couple Fe(CN)(6)(3-/4-). The resistance was measured using electrochemical impedance spectroscopy. The sensor response increased linearly with logarithm of concentration of target DNA in the range 2×10(-12)÷2×10(-6) M. The obtained quantification limit was circa 6.5×10(-17) mole in a 7 µL droplet and corresponded to a concentration of 9.2×10(-12) M of target DNA in the sample. This limit is equivalent to the detection of circa 4×10(7) copies of DNA in a 7 µL droplet or circa 5.7×10(12) DNA copies in one litre of sample.

Monitoring of spatiotemporal patterns in the oscillatory chemical reactions with the infrared camera: experiments and model interpretation.

An infrared camera was used for the first time to monitor the progress of traveling fronts in oscillatory chemical reactions, taking the Belousov-Zhabotinsky (BZ) reaction as the test system. The experiments involved comparative visual imaging and infrared thermography measurements for the thin-layer of the BZ solution in the Petri dish, including both aqueous and gel media, the latter one hindering the convection. Infrared thermography experiments that supply information on the temperature distribution at the solution surface were compared with the bulk temperature variations of the stirred solution with BZ reaction, measured simultaneously with the oscillatory variations of the Pt electrode potential. The experimentally observed correlation between the ferroin catalyst concentration and the temperature distribution was compared with the results of numerical modeling of these distributions in 2-D reactor space, based on the classical Oregonator. Analogous experiments were performed for the oscillatory oxidation of thiocyanates with hydrogen peroxide, catalyzed with Cu(2+) ions, in search of factors causing the development of traveling fronts, previously reported. The inhomogeneous distribution of the free surface temperature that could contribute to surface instabilities was found. Also, periodical increase and decrease in temperature of solution surface was reported. This was interpreted as periodically predominating cooling of the surface in contact with the surroundings because for the bulk, thermally isolated stirred solution, the temperature monotonically increases. In terms of our nine-variable kinetic model of this system, it was possible to identify the reaction steps responsible for the experimentally observed temperature dynamics and ascribe the appropriate heat effects to them. Our results constitute the first contribution to the thermochemical characteristics of the H(2)O(2)-SCN(-)-OH(-)-Cu(2+) oscillator.

Luminescent chemical waves in the Cu(II)-catalyzed oscillatory oxidation of SCN- ions with hydrogen peroxide.

The oscillatory oxidation of thiocyanate ions with hydrogen peroxide, catalyzed by Cu2+ ions in alkaline media, was so far observed as occurring simultaneously in the entire space of the batch or flow reactor. We performed this reaction for the first time in the thin-layer reactor and observed the spatiotemporal course of the above process, in the presence of luminol as the chemiluminescent indicator. A series of luminescent patterns periodically starting from the random reaction center and spreading throughout the entire solution layer was reported. For a batch-stirred system, the bursts of luminescence were found to correlate with the steep decreases of the oscillating Pt electrode potential. These novel results open possibilities for further experimental and theoretical investigations of those spatiotemporal patterns, including studies of the mechanism of this chemically complex process.

Limitations of the potential step technique to impedance measurements using discrete time Fourier transform.

Recently, a new method of measuring impedance of electrochemical systems was proposed in the literature by Yoo and Park (Yoo, J.-S.; Park, S.-M. Anal. Chem. 2000, 72, 2035). It is based on the analysis of system response to a potential step. Differentiation of the applied potential step and the current response in the time domain followed by applying Fourier transform to both signals allows for determination of the system's impedance. It has been proposed that the measurements carried out in a short time period permit the determination of the system's impedance in the whole frequency range. The aim of the present work was to verify the validity of the impedance spectra obtained using this method, as well as to establish the conditions for which the method may be used. This method was tested using simulated data for a simple ideally polarized electrode and a simple one-electron redox system in the solution. The results show that the reliable impedance spectra may be obtained only for frequencies between 1/(NDeltat) and 1/(2Deltat), where Deltat denotes the sampling time and N is the number of points acquired during the experiment. However, the artifacts are generated when the experimental data are extrapolated to lower frequencies.