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The aberrant autoxidation of norepinephrine (NE) in the presence of oxygen, which is accelerated by Fe(III), has been linked to the pathogenesis of the Parkinson's disease (PD). Adenosine triphosphate (ATP), as a neurotransmitter whose release can be stimulated by tissue damage and oxidative stress, is co-stored and often co-released with NE in presynaptic terminals. We have shown previously that ATP inhibits the iron-catalyzed dopamine oxidation, thereby decreasing the production of certain neurotoxins such as 6-hydroxydopamine. Whether ATP plays a similar role in Fe(III)-catalyzed NE oxidation and how it maintains the NE stability have not been investigated. Here, we studied the coordination in a ternary complex among NE, Fe(III), and ATP, and found that Fe(III) is coordinated as a octahedral center by NE and ATP. Voltammetry and mass spectrometry were employed to examine this ternary complex's modulation of the NE autoxidation. NE-Fe(III)-ATP plays a protective role to modulate the autoxidation and Fe(III)-catalyzed oxidation of NE. The ternary complex can be detected in the substantia nigra (SN), locus coeruleus (LC), and striatum regions of C57BL/6 wild-type mice. In contrast, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse brains displayed a significant decrease of the ternary complex in the SN region and an increase in the LC and striatum areas. We posit that the ternary complex is produced by noradrenergic neurons as a protective regulator against neuronal damage and oxidative stress, contributing to the lower vulnerability of LC neurons with respect to that of SN neurons.

A polythiophene-based solar cell (PTSC) is constructed by photoelectrochemically polymerizing thiophene onto an ultrathin compact TiO2 layer (150 nm thick) covered with a sub-monolayer of tethered 3-{5-[ N, N-bis(4-diphenylamino)phenyl]thieno[3,2- b]thiophen-2-yl}-2-cyano-acrylic acid dye (ca. 10% coverage). The influence of morphology and thickness of the PT film on the photocurrent generated by the PTSC was investigated. With a 270 nm thick PT film and 2,2',7,7'-tetrakis( N, N-di(4-methoxyphenyl)amino)-9,9'-spirobifluorene serving as the hole-transport material, the PTSC exhibited a short-circuit current density JSC of 12.90 ± 0.63 mA/cm2, an open-circuit voltage VOC of 0.81 ± 0.01 V, and a fill factor of 0.72 ± 0.01. The high conversion efficiency (7.52 ± 0.58%) of the PTSC is attributed to the controlled PT growth along the ordered and spatially accessible dye molecules at the compact TiO2 layer, which facilitates charge transfer, prevents the hole/electron recombination, and simplifies the polymer solar cell construction with a stable and easily processable material.

Copper is an essential metal in all organisms. Reliably quantifying and identifying the copper content and oxidation state is crucial, since the information is essential to understanding protein structure and function. Chromophoric ligands, such as Bathocuproine (BC) and its water-soluble analog, Bathocuproinedisulfonic acid (BCS), preferentially bind Cu(I) over Cu(II), and therefore have been widely used as optical probes to determine the oxidation state of copper bound by biomolecules. However, the BCS assay is commonly misused, leading to erroneous conclusions regarding the role of copper in biological processes. By measuring the redox potential of Cu(II)-BCS2 and conducting UV-vis absorption measurements in the presence of oxidizable amino acids, the thermodynamic origin of the potential artifacts becomes evident. The BCS assay was improved by introducing a strong Cu(II) chelator EDTA prior to the addition of BCS to prevent interference that might arise from Cu(II) present in the sample. The strong Cu(II) chelator rids of all the potential errors inherent in the conventional BCS assay. Applications of the improved assay to peptides and protein containing oxidizable amino acid residues confirm that free Cu(II) no longer leads to artifacts, thereby resolving issues related to this persistently misused colorimetric assay of Cu(I) in biological systems.

t-Darpp is a protein encoded by the PPP1R1B gene and is expressed in breast, colon, esophageal, gastric, and prostate cancers, as well as in normal adult brain striatal cells. Overexpression of t-Darpp in cultured cells leads to increased protein kinase A activity and increased phosphorylation of AKT (protein kinase B). In HER2+ breast cancer cells t-Darpp confers resistance to the chemotherapeutic agent trastuzumab. To shed light on t-Darpp function, we studied its secondary structure, oligomerization status, metal-binding properties, and phosphorylation by cyclin dependent kinases 1 and 5. t-Darpp exhibits 12% alpha helix, 29% beta strand, 24% beta turn and 35% random coil structures. t-Darpp binds to calcium, but not to other metals commonly found in biological systems. The T39 site, critical for t-Darpp activation of the AKT signaling pathway, is a substrate for phosphorylation by cyclin-dependent kinase 1 (CDK1) and cyclin-dependent kinase 5 (CDK5). Gel filtration chromatography, sedimentation equilibrium analysis, blue native gel electrophoresis, and glutaraldehyde-mediated crosslinking experiments demonstrate that the majority of t-Darpp exists as a monomer, but forms low levels (< 3%) of hetero-oligomers with its longer isoform Darpp-32. t-Darpp has a large Stokes radius of 4.4 nm relative to its mass of 19 kDa, indicating that it has an elongated structure.

Solar cells constructed with well-ordered polythiophene (PT) or other π-conjugated polymer films are known to yield better photovoltaic characteristics. We recently constructed a PT-based solar cell (PTSC) wherein the photoactive PT film was grown photoelectrochemically along a dye anchor, 3-{5-[N,N-bis(4-diphenylamino)phenyl]thieno[3,2-b]thiophen-2-yl}-2-cyano-acrylic acid (C207) pre-adsorbed onto a compact TiO2 layer. In an effort to understand the effects of other important factors contributing to the PTSC performance, we compared ex-situ and in-situ doping of ordered PT films with three different alkylammonium cations, tetrabutylammonium (TBA+), tetraethylammonium (TEA+), and tetramethylammonium (TMA+). The PT films that have undergone such ex- and in-situ doping both show higher open-circuit voltage (Voc) and short-circuit current density (Jsc) than their pristine counterparts. The optimal conversion efficiency (η) of 7.53 ± 0.58% was achieved via in-situ PT doping with TMA+. The incident photon-to-electron conversion efficiency (IPCE), electrochemical impedance, and electron lifetime measurements all indicate that in-situ doping is less affected by the cation size and can lead to a higher doping level than the ex-situ doping method. The IPCE also benefits from the use of a thin TiO2 layer, as more light reaches the PT film to generate photohole/electron pairs. With the combined use of a thin layer of TiO2 and an ordered PT film containing a large number of dopant ions, the photohole/electron recombination is significantly suppressed.

Parkinson's disease (PD) is characterized by the progressive degeneration of dopaminergic cells, which implicates a role of dopamine (DA) in the etiology of PD. A possible DA degradation pathway is the Fe(III)-catalyzed oxidation of DA by oxygen, which produces neuronal toxins as side products. We investigated how ATP, an abundant and ubiquitous molecule in cellular milieu, affects the catalytic oxidation reaction of dopamine. For the first time, a unique, highly stable DA-Fe(III)-ATP ternary complex was formed and characterized in vitro. ATP as a ligand shifts the catecholate-Fe(III) ligand metal charge transfer (LMCT) band to a longer wavelength and the redox potentials of both DA and the Fe(III) center in the ternary complex. Remarkably, the additional ligation by ATP was found to significantly reverse the catalytic effect of the Fe(III) center on the DA oxidation. The reversal is attributed to the full occupation of the Fe(III) coordination sites by ATP and DA, which blocks O2 from accessing the Fe(III) center and its further reaction with DA. The biological relevance of this complex is strongly implicated by the identification of the ternary complex in the substantia nigra of rat brain and its attenuation of cytotoxicity of the Fe(III)-DA complex. Since ATP deficiency accompanies PD and neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) induced PD, deficiency of ATP and the resultant impairment toward the inhibition of the Fe(III)-catalyzed DA oxidation may contribute to the pathogenesis of PD. Our finding provides new insight into the pathways of DA oxidation and its relationship with synaptic activity.

Copper coexists with amyloid-β (Aβ) peptides at a high concentration in the senile plaques of Alzheimer’s disease (AD) patients and has been linked to oxidative damage associated with AD pathology. However, the origin of copper and the driving force behind its accumulation are unknown. We designed a sensitive fluorescent probe, Aβ(1–16)(Y10W), by substituting the tyrosine residue at position 10 in the hydrophilic domain of Aβ(1–42) with tryptophan. Upon mixing Cu(II), Aβ(1–16)(Y10W), and aliquots of Aβ(1–42) taken from samples incubated for different lengths of time, we found that the Cu(II) binding strength of aggregated Aβ(1–42) has been elevated by more than two orders of magnitude with respect to that of monomeric Aβ(1–42). Electron paramagnetic spectroscopic measurements revealed that the Aβ(1–42) aggregates, unlike their monomeric form, can seize copper from human serum albumin (HSA), an abundant copper-containing protein in brain and cerebrospinal fluid. The significantly elevated binding strength of the Aβ(1–42) aggregates can be rationalized by a Cu(II) coordination sphere constituted by three histidines from two adjacent Aβ(1–42) molecules. Our work demonstrates that the copper binding affinity by Aβ(1–42) is dependent on its aggregation state and provides new insight into how and why senile plaques accumulate copper in vivo.

Super-irons contain the +6 valence state of iron. One advantage of this is that it provides a multiple electron opportunity to store additional battery charge. A decrease of particle size from the micrometer to the nanometer domain provides a higher surface area to volume ratio, and opportunity to facilitate charge transfer, and improve the power, voltage and depth of discharge of cathodes made from such salts. However, super-iron salts are fragile, readily reduced to the ferric state, with both heat and contact with water, and little is known of the resultant passivating and non-passivating ferric oxide products. A pathway to decrease the super-iron particle size to the nano-domain is introduced, which overcomes this fragility, and retains the battery capacity advantage of their Fe(VI) valence state. Time and power controlled mechanosynthesis, through less aggressive, dry ball milling, leads to facile charge transfer of super-iron nanoparticles. Ex-situ X-ray Absorption Spectroscopy is used to explore the oxidation state and structure of these iron oxides during discharge and shows the significant change in stability of the ferrate structure to lower oxidation state when the particle size is in the nano-domain. Keywords: Super-iron, Cathode, Battery, Nanomaterials, Multiple charge transfer, XANES

The first experimental evidence of a new solar process, combining electronic and chemical pathways, to isolate CO2 (carbon capture) is presented. This solar thermal electrochemical photo (STEP) process is a synergy of solid-state and solar thermal processes, and is fundamentally capable of converting more solar energy than photovoltaic or solar thermal processes alone. Here, CO2 is captured using a 750−950 °C electrolysis cell powered by a full spectrum solar simulator in a single step. The process uses the full spectrum; solar thermal energy decreases the energy required for carbon capture, while visible sunlight generates electronic charge to drive the electrolysis. CO2 can be captured from 34% to over 50% solar energy efficiency (depending on the level of solar heat inclusion), as solid carbon and stored, or used as carbon monoxide to be available for a feedstock to synthesize (with STEP generated hydrogen) solar diesel fuel, synthetic jet fuel, or chemical production.

This paper describes the construction of a mixed monolayer of ferrocenylalkanethiol and encapsulated horseradish peroxidase (HRP) at a gold electrode for amperometric detection of H(2)O(2) at trace levels. By tuning the alkanethiol chain lengths that tether the HRP enzyme and the ferrocenylalkanethiol (FcC(11)SH) mediator, facile electron transfer between FcC(11)SH and HRP can be achieved. Unlike most HRP-based electrochemical sensors, which rely on HRP-facilitated H(2)O(2) reduction (to H(2)O), the electrocatalytic current is resulted from an HRP-catalyzed oxidation reaction of H(2)O(2) (to O(2)). Upon optimizing other experimental conditions (surface coverage ratio, pH, and flow rate), the electrocatalytic reaction proceeding at the electrode was used to attain a low amperometric detection level (0.64 nM) and a dynamic range spanning over 3 orders of magnitude. Not only does the thin hydrophilic porous HRP capsule allow facile electron transfer, it also enables H(2)O(2) to permeate. More significantly, the enzymatic activity of the encapsulated HRP is retained for a considerably longer period (3 weeks) than naked HRP molecules attached to an electrode or those wired to a redox polymer thin film. By comparing to electrodes modified with denatured HRP that are subsequently encapsulated or embedded in a poly-L-lysine matrix, it is concluded that the encapsulation has significantly preserved the native structure of HRP and therefore its enzymatic activity. The electrode covered with FcC(11)SH and encapsulated HRP is shown to be capable of rapidly and reproducibly detecting H(2)O(2) present in complex sample media.

The interaction of amyloid-beta (Abeta) and redox-active metals, two important biomarkers present in the senile plaques of Alzheimer's disease (AD) brain, has been suggested to enhance the Abeta aggregation or facilitate the generation of reactive oxygen species (ROS). This study investigates the nature of the interaction between the metal-binding domain of Abeta, viz., Abeta(1-16), and the Fe(III) or Fe(II) complex with nitrilotriacetic acid (NTA). Using electrospray ionization mass spectrometry (ESI-MS), the formation of a ternary complex of Abeta(1-16), Fe(III), and NTA with a stoichiometry of 1:1:1 was identified. MS also revealed that the NTA moiety can be detached via collision-induced dissociation. The cumulative dissociation constants of both Abeta-Fe(III)-NTA and Abeta-Fe(II)-NTA complexes were deduced to be 6.3 x 10(-21) and 5.0 x 10(-12) M(2), respectively, via measurement of the fluorescence quenching of the sole tyrosine residue on Abeta upon formation of the complex. The redox properties of these two complexes were investigated by cyclic voltammetry. The redox potential of the Abeta-Fe(III)-NTA complex was found to be 0.03 V versus Ag/AgCl, which is negatively shifted by 0.54 V when compared to the redox potential of free Fe(III)/Fe(II). Despite such a large potential modulation, the redox potential of the Abeta-Fe(III)-NTA complex is still sufficiently high for a range of redox reactions with cellular species to occur. The Abeta-Fe(II)-NTA complex electrogenerated from the Abeta-Fe(III)-NTA complex was also found to catalyze the reduction of oxygen to produce H(2)O(2). These findings provide significant insight into the role of iron and Abeta in the development of AD. The binding of iron by Abeta modulates the redox potential to a level at which its redox cycling occurs. In the presence of a biological reductant (antioxidant), redox cycling of iron could disrupt the redox balance within the cellular milieu. As a consequence, not only is ROS continuously produced, but oxygen and biological reductants can also be depleted. A cascade of biological processes can therefore be affected. In addition, the strong binding affinity of Abeta toward Fe(III) and Fe(II) indicates Abeta could compete for iron against other iron-containing proteins. In particular, its strong affinity for Fe(II), which is 8 orders of magnitude stronger than that of transferrin, would greatly interfere with iron homeostasis.

A novel fluorescent CdS-encapsulated DNA nanocomposite was synthesized via alternate adsorption of Cd(2+) and S(2-) onto the DNA template affixed inside an agarose gel. Confining DNA molecules in the gel matrix reduces the flexibility of the DNA strand, which facilitates the formation of a uniform coating of CdS onto the DNA template. The resultant rod-shaped nanocomposite (40-90 nm in width and 200-300 nm in length) is well dispersed in solution and fluoresces at 330 nm upon excitation at either 228 or 280 nm. The fluorescence is attributed to tiny particles present in the CdS coating. It was found that the fluorescence can be significantly quenched by trace amount of Hg(2+). The high selectivity toward Hg(2+) and the apparent change in the CdS coating upon exposure to Hg(2+) indicate that Hg(2+) has reacted with the CdS coating through formation of the much more insoluble HgS and the bridging S-Hg-S bonds at the surface. The extent of quenching is dependent on the concentration of Hg(2+) in the range of 0.04-13 microM, and a remarkable detection limit (8.6 nM at 30 degrees C and 4.3 nM at 50 degrees C) can be achieved. The feasibility of the method for the analysis of Hg(2+) in a wastewater sample was demonstrated with an excellent relative standard deviation (RSD, 3.4%). The method described herein is simple, selective, and sensitive and obviates the need of extensive sample pretreatment or special instrumentation.

At the air/buffer solution interface the kinetics of adsorption of amyloid beta peptide, Abeta(1-42), whose bulk concentration (submicromolar) is more than 2 orders of magnitude lower than that typically used in other in vitro aggregation studies, has been studied using a Langmuir-Blodgett trough. The pressure-time curves exhibit a lag phase, wherein the surface pressure essentially remains at zero, and a rising phase, corresponding to the Abeta adsorption at the interface. The duration of the lag phase was found to be highly dependent on both the Abeta bulk concentration and the solution temperature. A large activation energy (62.2 +/- 4.1 KJ/mol) was determined and the apparent adsorption rate constant was found to be linearly dependent on the Abeta bulk concentration. Attenuated total reflection-IR spectra of the adsorbed Abeta transferred to a solid substrate and circular dichroism measurements of Abeta in the solution layer near the interface reveal that the natively unstructured Abeta in the bulk undergo a conformation change (folding) to mainly the alpha-helical structure. The results suggest that, prior to the adsorption step, an equilibrium between Abeta conformations is established within the subsurface. The kinetic equation derived from this model confirms that the overall Abeta adsorption is kinetically controlled and the apparent rate constant is proportional to the Abeta bulk concentration. This model also indicates that interfaces such as cell membranes and lipid bilayers may facilitate Abeta aggregation/ fibrillation by providing a thin hydrophobic layer adjacent to the interface for the initial A/beta conformation change (misfolding) and accumulation. Such a preconcentration effect offers a plausible explanation of the fact that Abeta fibrillation occurs in vivo at nanomolar concentrations. Another important biological implication from our work is that Abeta misfolding may occur before its adsorption onto a cell membrane. This general kinetic model should also find applications in adsorption studies of other types of biomolecules whose overall kinetics exhibits a lag phase that is dependent on the bulk concentration of the adsorbate.

A simple, rapid, and effective photoelectrochemical method is proposed to quantitatively characterise photocatalytic degradation behaviour of organic compounds at nanoporous TiO 2 film electrodes in a thin-layer photoelectrochemical cell. This method uses the charge obtained by integrating the photocurrent originating from the photocatalytic oxidation of organic compounds to quantify the extent of degradation. Complete mineralisation was observed for all organic compounds investigated. A double-exponential kinetic rate expression was acquired using a computer simulation method, indicating two simultaneous kinetic processes. Photocurrent profiles of different organic compounds complied well with the proposed theoretical model. Both pre-exponential and exponential constants were obtained. The rate of the fast kinetic component is 10–25 times faster than that of the slow kinetic component. It was found that the identities of organic compounds have no significant effect on the photocatalytic oxidation kinetics, whereas the availability of the organic compounds to capture photoholes plays a decisive role.

The binding stoichiometry between Cu(II) and the full-length β-amyloid Aβ(1−42) and the oxidation state of copper in the resultant complex were determined by electrospray ionization−Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) and cyclic voltammetry. The same approach was extended to the copper complexes of Aβ(1−16) and Aβ(1−28). A stoichiometric ratio of 1:1 was directly observed, and the oxidation state of copper was deduced to be 2+ for all of the complexes, and residues tyrosine-10 and methionine-35 are not oxidized in the Aβ(1−42)−Cu(II) complex. The stoichiometric ratio remains the same in the presence of more than a 10-fold excess of Cu(II). Redox potentials of the sole tyrosine residue and the Cu(II) center were determined to be ca. 0.75 and 0.08 V vs Ag/AgCl [or 0.95 and 0.28 V vs normal hydrogen electrode (NHE)], respectively. More importantly, for the first time, the Aβ−Cu(I) complex has been generated electrochemically and was found to catalyze the reduction of ox...

In dye-sensitized solar cells (DSSCs), a significant dye-regeneration force (ΔG(reg)(0)≥0.5 eV) is usually required for effective dye regeneration, which results in a major energy loss and limits the energy-conversion efficiency of state-of-art DSSCs. We demonstrate that when dye molecules and redox couples that possess similar conjugated ligands are used, efficient dye regeneration occurs with zero or close-to-zero driving force. By using Ru(dcbpy)(bpy)2(2+) as the dye and Ru(bpy)2(MeIm)2(3+//2+) as the redox couple, a short-circuit current (J(sc)) of 4 mA cm(-2) and an open-circuit voltage (V(oc)) of 0.9 V were obtained with a ΔG(reg)(0) of 0.07 eV. The same was observed for the N3 dye and Ru(bpy)2(SCN)2(1+/0) (ΔG(reg)(0)=0.0 eV), which produced an J(sc) of 2.5 mA cm(-2) and V(oc) of 0.6 V. Charge recombination occurs at pinholes, limiting the performance of the cells. This proof-of-concept study demonstrates that high V(oc) values can be attained by significantly curtailing the dye-regeneration force.

Titanium dioxide (TiO2) thin films fabricated with different TiO2 colloids were characterised using photoelectrochemical techniques. TiO2 colloids were firstly prepared via hydrolysis of titanium butoxide and peptisation process with no hydrothermal process (labelled as NP). The resulting colloids were then subjected to different hydrothermal processes, i.e., 15-h convection hydrothermal (labelled as CH) treatment; 5-, 10- and 15-min microwave hydrothermal treatment (labelled as M5, M10 and M15, respectively). The colloids were used to prepare TiO2 thin films on conducting indium-doped tin oxide (ITO) substrates (i.e., CH, M15, M10, M5 and NP electrodes, respectively) using a controlled dip-coating technique. The experimental results demonstrate that the oxidation capacities of the electrodes for water and glucose are in the order of CH > M15 > M10 > M5 > NP. In contrast, the oxidation capacities of the electrodes for potassium hydrogen phthalate (KHP) are in the order of M15 > M10 > CH. It was also found that the CH electrode could be easily poisoned by high concentration of KHP, while microwave-processed electrodes (M15, M10 and M5) are immune from the KHP poisoning. The results presented demonstrate that microwave hydrothermal processing is a promising alternative method to the traditional convection hydrothermal treatment of colloids that provides electrodes with increased photocatalytic properties for the oxidation processes of adsorption-based organic compounds, such as KHP.

Photoelectrochemical method was adopted to investigate the photocatalytic oxidation of different organic compounds. It was found that at the anatase TiO 2 nanoporous electrode, the potential bias changes the rate-determining step from electron migration in the film at low potentials to photohole capture at relatively high potentials. When the applied potential bias is sufficient, the steady state photocurrent obtained reflects exclusively the rate of photohole capture at TiO 2 surface. Under such conditions, the photocatalytic degradation of various organic compounds with different chemical structures was studied. At very low concentrations, the linear increase of steady state photocurrent with the concentration was observed for all compounds investigated, due to the mass transfer limitation, although the number of electron needed for complete mineralization of these compounds differs markedly. It was demonstrated that the substrate molecules that reaches the electrode surface have been exhaustively mineralized under mass transfer-controlled conditions regardless of their chemical nature. At high concentration, substrate molecules (or intermediates) are accumulated on the surface (or in the reaction zone). As a result, the steady state photocurrent deviated from the linear relationship. Under such conditions, the interaction of substrate molecules and/or partially degraded intermediates with TiO 2 determines the overall photohole capture rate. The differences in photohole capture rate among different organic compounds were observed. The kinetic characteristics of different organic compounds at high concentrations were also explained based on the structural differences.

This work focuses on the experimental optimisation of a newly developed photoelectrochemical system for the determination of chemical oxygen demand (PECOD). This method is developed based on a photoelectrochemical degradation principle. Chemical oxygen demand (COD) is directly quantified by measuring the amount of electron transferred at a TiO2 nanoporous thin-film electrode during an exhaustive photoelectrocatalytic degradation process in a thin-layer photoelectrochemical cell. In this fashion, the COD value of a sample can be determined in a simple, rapid and accurate manner. The PECOD is a direct and absolute method that requires no calibration. The effects of important experimental conditions, such as light intensity, applied potential bias, supporting electrolyte concentration and oxygen concentration, on analytical performance have been investigated and optimum experimental conditions were obtained. Analytical linear range of 0−360 ppm COD with a practical detection limit of 0.2 ppm COD were achieved. Real sample analyses were also carried out. The results demonstrated that the measured COD values using the PECOD and the standard methods were in an excellent agreement.

A unique transient photoelectrolysis technique was developed to study the photocatalytic oxidation kinetics of adsorbed organic compounds at particulate TiO 2 film electrodes. The technique was employed to study the photocatalytic oxidation of a number of adsorbed dicarboxylic acids at TiO 2 porous film electrodes. The adsorption of these compounds was found to be heterogeneous, with three major types of surface complexes identified—each having distinctive binding affinities to the TiO 2 surface. The three thermodynamically distinctive types of surface complexes exhibit two measurable photocatalytic reaction kinetic characteristics, i.e., a fast process and a slow process. The fast kinetic process can be attributed to the photocatalytic degradation of the strongest adsorbed species at more active sites such as edge and corner titanium ions. The slow kinetic process can be attributed to the photocatalytic degradation of the medium-strength bound complexes and the weakest bound surface complexes. The rate constants for these processes were calculated by curve fitting the photocurrent transient response to a double exponential decay expression. For adsorbed oxalic acid both the fast and the slow processes were shown to be the first-order processes in which both rate constants were independent of surface coverage. For the larger dicarboxylic acids adsorbed, the rate constant for the fast photocatalytic process ( k f ) was found to decrease with an increase in the surface coverage. The rate constant for the slow photocatalytic process, however, was shown to be a true first-order process for all adsorbed dicarboxylic acids. The value of the rate constant ( k s ) was similar for all the adsorbates studied and was independent of the surface coverage.

A novel rapid methodology for the determination of chemical oxygen demand (COD) based on photoelectrochemical oxidative degradation principle (PECOD) was proposed and experimentally validated. With this new method, the extent of degradation of dissolved organic matter in a water sample is measured simply by directly quantifying the extent of electron transfer at a TiO2 nanoporous film electrode during an exhaustive photoelectrocatalytic degradation of organic matter in a thin layer photoelectrochemical cell. The PECOD method demonstrated in this work is a direct and absolute method. It does not require the use of standard for calibration. The method, in principle, measures the theoretical COD value due to the extraordinary high oxidation efficiency and accuracy of charge measurement. This new approach overcomes many of the current problems associated with existing oxygen demand techniques (e.g., the matrix effect, one of the serious practical problems that most rapid COD methods suffered because of the in...

The effect of potential bias, light intensity, and the concentration of the photohole scavenger (glucose) on the photocurrent responses of the nanoporous TiO2 film electrodes were investigated with the focus on the overall photoelectrocatalytic oxidation process. The electron transport in TiO2 film was the rate-limiting step at low potential bias, while the interfacial reactions became rate-limiting step at high potential bias. A linear photocurrent/potential characteristic can be obtained within a wide range of applied potential bias. Within this linear range, the electrodes behave as a constant resistance rather than a variable resistance, which is unlike a photoelectrochemical process at a bulk semiconductor electrode. The resistance consists of two components: a variant component and an invariant component. The former is inversely proportional to maximum photocurrent, due to the free electron concentration change as a result of the consumption of photoholes through interfacial reaction. The hypothesi...

A new adsorption measurement method based on photoelectrochemical oxidation principles has been developed. The method can be used to directly quantify the amount of adsorbates at a TiO2 electrode surface in a sensitive and accurate manner. The adsorption of phthalic acid was studied as a test case. The relationship between the amount of adsorbate at the TiO2 surface and the concentration of phthalic acid in the solution was obtained. The adsorption of phthalic acid on TiO2 surface was shown to follow a Langmuir type adsorption model. For the first time, the adsorption equilibrium constant of an adsorbate at TiO2 surface has been photoelectrochemically measured. The adsorption equilibrium constant of phthalate on TiO2 porous film at pH 4.0, K=4.0×104 M−1, was obtained using our method, which was close to that obtained by conventional methods. The effect of solution pH on the amount of adsorbate at TiO2 surface was also investigated. The results indicate the adsorption of phthalic acid is mainly of chemical bonding nature.

t-Darpp, one of two protein isoforms encoded by the PPP1R1B gene, is overexpressed in gastric, esophageal, colon, prostate, and breast cancers; and confers resistance to trastuzumab in Her2+ breast cancer cells. To gain insight into the trastuzumab-resistance mechanism of t-Darpp, we studied its structure, oligomerization status, metal-binding properties, and sites of phosphorylation. Circular dichroism spectroscopy analysis showed that recombinant t-Darpp exhibits 12% alpha helix, 29% beta strand, 24% beta turn and 35% random coil character at 25°C. Upon mild heat treatment (50°C for five min) the secondary structure does not appreciably change. Metal ion-binding analyses through inductively coupled plasma-mass spectrometry and graphite furnace-atomic absorption indicated that t-Darpp co-purifies with calcium, but not other metals commonly found in biological systems. The T75 site, critical for t-Darpp activation of the Akt signaling pathway, is a substrate for phosphorylation by cyclin-dependent kinase 1 (CDK1) and cyclin-dependent kinase 5 (CDK5). Gel filtration chromatography, sedimentation equilibrium analysis, native blue gel electrophoresis, and glutaraldehyde-mediated crosslinking experiments showed that the majority of t-Darpp (calculated mass = 19 kDa) exists as a monomer, but forms low levels (< 3%) of hetero-oligomers with its longer isoform Darpp-32. t-Darpp has a relatively large Stokes radius of 4.4 nm, suggesting an elongated structure. In summary, this study indicates that t-Darpp is an elongated, mild-heat-stable, and monomeric calcium-binding protein that is capable of being phosphorylated at T75 by CDK1 and CDK5. Blockage of t-Darpp calcium binding capacity or T75 phosphorylation may therefore help sustain Her2+ breast cancer sensitivity to trastuzumab therapy. Citation Format: Patrycja Magdziarz, You Feng, Dianlu Jiang, Elizabeth Parga, Arianna Celis, Erin Denny, Xiaoying Wang, Martin Phillips, Feimeng Zhou, Susan E. Kane, Jamil Momand. t-Darpp chemoresistence protein: insights into its structure, oligomerization status, calcium-binding properties and phosphorylation sites [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5866. doi:10.1158/1538-7445.AM2017-5866

The storage of multiple electrons per molecule provides opportunities to greatly enhance electrochemical energy capacity. VB2 releases, via electrochemical oxidation, 11 electrons per molecule at a favorable, electrochemical potential. Coupled with an air cathode, this 4060 mAh/g intrinsic capacity anode, has energy capacity greater than that of gasoline. Nanochemical improvements of VB2 are probed to facilitate charge transfer and discharge voltage. Nanoparticle formation is accomplished with a planetary ball mill media (tungsten carbide) with hardness comparable to that of VB2 (8–9 Mohs2). Mechanochemical synthesized, VB2 nanorods, exhibit higher voltage, sustain higher rate, and depth of discharge than macroscopic VB2.

A study of photoelectrochemical oxidation of methanol at nanoporous TiO2 film electrodes was carried out. The effect of variables such as applied potential, light intensity, methanol concentration and pH on the photoelectrochemical behaviour was investigated. It was found that the photoresponse was greatly influenced by these factors and a unique photocurrent/potential characteristic of the electrode in solution was observed which was similar to that of the single crystal semiconductor electrode. It was also found that the rate-limiting step for the overall photooxidation process varied depending on potential, light intensity and methanol surface coverage. In low potential region at a given light intensity and methanol concentration the migration of electron across the TiO2 film is the rate-limiting step. While in the relatively high potential region the interfacial charge transfer was found to be the rate-limiting step. A deviation of onset potential dependence on pH from the Nernstian relationship was also observed, and based on the energy band theory and the existence of deep electron traps an explanation was given. An unusual abrupt increase of photocurrent in strong basic methanol solution was observed, which was attributed to the existence of acidic hydroxyl group on TiO2 and its stronger adsorption to methanol molecule after its reaction with OH−, and the higher reactivity of the methanol thus adsorbed.

The formation process of sodium lauryl sulfate monolayers on the surface of octadecanethiol self-assembled monolayers was investigated by the method of cyclic voltammetry and ac impedance spectroscopy. The pinhole in an octadecanethiol-coated gold electrode can be patched when adding sodium lauryl sulfate to solution. The charge transfer resistance increased but the membrane capacitance decreased with the addition of sodium lauryl sulfate or other amphiphilic substance, indicating that the adsorption of sodium lauryl sulfate on the electrode surface from solution.

Au supported octadecanethiol/phosphatidylcholine (Au/ODT/PC) bilayers modified with 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) were studied by a.c. impedance. Three kinds of Au/ODT/PC bilayer were prepared: (i) unmodified bilayer (UMB), (ii) bilayer with only the PC monolayer containing TCNQ (ODT/PC-TCNQ) and (iii) bilayer with both the ODT and PC monolayers containing TCNQ (ODT-TCNQ/PC-TCNQ). The Faraday resistances of UMB, ODT/PC-TCNQ and ODT-TCNQ/PC-TCNQ in 1 mmol/l Fe(CN) 6 3−/4− +0.1 mol/l KCl solution were 3.9×10 7 , 5.1×10 6 and 2.2×10 5 Ωcm 2 , respectively. The embedded TCNQ molecules were believed acting as electron mediators and electron transfer by hopping between TCNQ molecules was proposed as the mechanism of electron transfer across ODT-TCNQ/PC-TCNQ.

Electron transfer across the biomembrane is central to photosynthesis, to mitochondrial respiration and to the design of molecular systems for solar energy conversion. We report here that gold supported octadecanethiol/phosphatidylcholine hybrid bilayer membrane mediated by C60 (abbreviated C60 HBM) can act as both a photosensitizer for electron transfer from a donor molecule and a mediator for electron transport across a hybrid bilayer membrane. The steady-state photocurrent behaviors in different concentration of ascorbate, Co(bpy)32+/3+ or Fe(CN)64−/3− solution have been studied. The rate-limiting step of the whole photoinduced electron transfer depends on the applied potential and the redox concentration in solution. The C60 HBM electrode was fabricated for the first time and there is no investigation on C60 incorporated octadecanethiol/phosphatidylcholine hybrid bilayer membrane in literature. The sigmoidal-shaped steady-state photocurrent versus the applied potential curve is first observed and it is different from the linear-shaped iph/E curve of C60 modified bilayer lipid membrane reported by Bensasson et al. [R.V. Bensasson, J.-L. Garaud, S. Leach, G. Miquel, P. Seta, Chem. Phys. Lett. 210 (1993) 141].

Au electrodes are alkylated by self-assembled organic monolayers of octadecanethiol from alcohol solution. The electron tunnelling resistance of a monolayer-coated gold electrode has been investigated by ac impedance. The relation between the fractional coverage of different defects and the corresponding film thickness at these ‘collapsed’ sites has been deduced from electron tunnelling theory. By using the concepts of average film thickness at defect (da) and average fractional coverage of defect (θa), we have obtained the θa∼da plot. The influence of the apparent standard rate constant on the shape of the θa∼da plot has been discussed. In our experiments, Fe(CN)63−/4− is used as a redox probe to study the θa∼da plot of an octadecanethiol monolayer. The θa versus da plot indicates that the defects with da

Octadecanethiol self-assembled monolayers derivatized gold electrode in different concentrations of Fe(CN)6 3−/4− was studied by cyclic voltammetry. The cyclic voltammetric responses display a series of inverse sigmoidal curves for the SAMs in the solution of various concentration of Fe(CN)6 3−/4−. A new concept of apparent effective thickness of self-assembled monolayers is established on the base of the measurements of cyclic voltammetry. It is determined that the apparent effective thickness of the SAMs is lower than the length of chain of octadecanethiol. Defect sites may be present in the alkanethiol monolayers. The apparent effective thickness can be used to describe the quality of SAMs quantitatively.

Supported hybrid bilayers consisting of octadecanethiol and phospholipid incorporated with ferrocene were fabricated through self-assembling methods. Its electrochemical behaviors in solutions containing different concentrations of Fe(CN)6 3-/4− were investigated by ac impedance and cyclic voltammetry. The transmembrane electron transfer across octadecanethiol self-assembled film and an adsorbed phospholipid layer mediated by ferrocene has been observed. It is determined that the apparent heterogeneous rate constant is 2.3 × 10−8 cm·s−1.

Electrochemical impedance spectroscopy was used to investigate the structural disorder of Au supported octadecanethiol-phosphatidylcholine (Au/ODT-PC) bilayers. Results of experiments indicate that collapsed-sites and pinholes exist in octadecanethiol monolayer (ODTM) and phosphatidylcholine monolayer (PCM), respectively.

The electrochemical behavior of the gold electrode modified by hybrid bilayer membranes in different concentrations of Fe(CN)63−/Fe(CN)64− was investigated by electrochemical impedance spectroscopy and cyclic voltammetry technology. The electron transfer between gold and the redox species separated by the hybrid bilayers assembly was completed by an electron tunneling process. A detailed equivalent circuit for electron transport across the HBMs is proposed. It was found that the apparent effective thickness of the hybrid bilayer membranes was lower than that of the sum of the chain length of octadecanethiol and phospholipid so some possible collapsed sites might exist at the hybrid bilayer membranes.

The concept of an apparent effective thickness of a self-assembled monolayer is established and assessed with the measurements of ac impedance spectroscopy in different concentrations of Fe(CN) 6 3− /Fe(CN) 6 4− by alkanethiol self-assembled monolayers on a gold electrode. The complex-plane impedance plots for SAMs in solution of various concentrations of Fe(CN) 6 3− /Fe(CN) 6 4− exhibit arc shapes. The apparent resistance ( R 2 ), obtained from the simulation, decreased with increasing concentration of the redox couples. It is determined that the apparent effective thickness of the SAMs is lower than the length of chain of the alkanethiol. Defect sites may exist at the alkanethiol monolayers.

Supported thiol/lipid bilayer assembly, one of the most spectacular bilayer systems in recent years, has provided a good model to study biomembranes because of its high mechanical stability. In this work, the structural and conducting property of unmodified Au supported octadecanethiol/phosphatidylcholine bilayers were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The forming process of bilayer was monitored by capacitance plane plot. The normalized membrane capacitance of supported bilayer is 0.52 μF cm −2 . Kinetically controlled voltammograms determined by Butler–Volmer equation were obtained for both thiol monolayer and thiol/lipid bilayer in linear sweep voltammetry. Results of EIS experiment indicate that collapsed sites and pinhole defects exist in thiol monolayer and lipid monolayer, respectively. The difference between the values of experimental and theoretical standard electron transfer rate constant indicates that the conducting mechanism of Au supported thiol monolayer is electron tunneling at collapsed sites. The conducting mechanism of Au supported thiol/lipid bilayer is attributed as the following: the electroactive species could diffuse through pinholes in the lipid monolayer and reach collapsed sites in thiol monolayer, where electron transfer occurs via a tunneling process. The fractional coverage of the lipid monolayer measure by EIS experiments is about 0.98 or higher.

Self-assembly of octadecyl mercaptan on gold has been investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments show that well-assembled thiol monolayers on gold are essentially free of pinhole defects. Support for the existence of ‘collapsed’ sites in thiol monolayers is obtained by comparing the apparent electron transfer rate constant, which is obtained from CV experiments at a film covered Au electrode, with the theoretical one, which is calculated by assuming electrons tunnel across the collapsed-site-free monolayer. The empirical relationship Z Rs 1:[s(jv) a ] is used to describe the film coated Au in inert electrolyte and the degree of disorder of the monolayer structure is estimated from the a value. It is demonstrated that the admittance plane plot of an ideally polarizable electrode with constant phase element behavior is a circular arc which can be used to determine a. Results of EIS experiments show that a increases sharply after the initial adsorption time and approaches its final value slowly. This is attributed to the rapid adsorption step followed by a slow crystallization process in the kinetics of alkanethiol adsorption onto the Au electrode. For a well-assembled thiol monolayer on gold, a can approach 0.99, which means that the number of collapsed sites is not large and the surface of the monolayer Au electrode is rather smooth. © 1999 Elsevier Science S.A. All rights reserved.

Self-assembled phosphatidylcholine/cholesterol bilayer lipid membrane (BLM) was fabricated on Pt electrode, which had been cleaned by high power ultrasonic horn. The influence of Ca2+ ions on the electron transfer of Fe(CN)63−/4− couple on Pt supported BLM (Pt-BLM) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments showed directly that Ca2+ ions could induce electron transfer on Pt-BLM. Three possibilities of the cause of redox reaction induced by Ca2+ ions were discussed: (1) electronic tunneling across bilayer, (2) electronic tunneling across monolayer, (3) direct electron transfer between Fe(CN)63−/4− ions and Pt electrode through Ca2+ induced ion-channels. Results of calculations based on Marcus's theory indicate that electronic tunneling across bilayer and monolayer contributes little to the redox current. The theory of partially blocked electrode was employed to analyze the sigmoidal CV curves, and it was concluded that ion-channels generated by Ca2+ ions were the main cause of electron transfer reaction on Pt-BLM. EIS measurement showed that Pt-BLM became porous after Ca2+ ions were added to the electrolyte. This was consistent with the conclusion drawn from CV experiments. Since ion-channels play the role similar to micro defects, it is concluded from CV and EIS experiments that sigmoidal CV curves and depressed circular arcs are evidence for the existence of micro defects on unmodified solid-supported-BLM.

The effect of Ca2+ on the electron transfer of Fe(CN)63−/4− couple at Pt supported lecithin (PC)/cholesterol (CH) bilayer lipid membrane (BLM) electrode has been studied by voltammetry and ac impedance spectroscopy. Experimental results suggest that the interaction of Ca2+ with the BLM can open some kind of channel for Fe(CN)63−/4− ions, allowing increased access of the redox couple to the electrode surface. This phenomenon may be related to the Ca2+ regulation or activation effect of ion channel in some biomembranes.

Effective blockage of recombination electron transfer of a fast electron transfer redox couple (ferrocenium/ferrocene or Fc(+)/Fc) at TiO2 nanowire array electrodes is achieved by silanization of the dye loaded TiO2 nanowire array. FT-IR clearly shows the formation of polysiloxane network at fluorine doped tin electrodes covered with TiO2 nanowire arrays and the dye molecules. Compared to the commonly used TiO2 nanoparticle film electrodes, the TiO2 nanowire array has a more spatially accessible structure, facilitating the formation of uniform polysiloxane films. Energy-dispersive X-ray spectroscopy (EDS) also reveals the presence of Si over multiple spots at the cross sections of the silanized TiO2 nanowire array electrodes. As a result, a rather high open-cell voltage Voc (0.69 V) and an enhanced efficiency (0.749 %) for DSSC with the Fc(+)/Fc couple were obtained. Contrary to the passivated TiO2 nanoparticle film electrodes at which a complex, biphasic dependence of electron lifetime on Voc was observed, we recorded a logarithm linear dependence of the lifetime on Voc after the silanization treatment. The nanowire arrays with optimal salinization treatments afford a useful surface for the study of electron recombination and photovoltaic generation in DSSCs.

Reversed-phase ion-pairing chromatography (RP-IPC) is coupled on-line with electrospray ionization-mass spectrometry (ESI-MS) through an interface comprising a four-way switch valve and an anion exchange column. Regeneration of the anion exchange column can be accomplished on-line by switching the four-way switch valve to interconnect the column to a regeneration solution. Positioning the anion exchange column between the RP-IPC and ESI-MS instruments allows the ion-pairing reagent (IPR) sodium octane sulfonate to be removed. The IPC–ESI-MS method enabled us to separate and detect four intermediates of the Fe(III)-catalyzed dopamine oxidation. In particular, 6-hydroxydopamine, which is short-lived and highly neurotoxic, was detected and quantified. Together with the separation of other intermediates, gaining insight into the mechanism and kinetics of the Fe(III)-catalyzed dopamine oxidation becomes possible.