Changes In Reduction Potential Research Articles

Electrolyte Effects on the Reduction Potential and Carbon Dioxide Binding Affinity of Quinones

CO2 capture and concentration (CCC) is critical to carbon negative technologies and can reduce or eliminate carbon emission of current industrial processes. A popular method for electrochemically-driven CCC uses redox carriers that bind and release CO2 depending on their oxidation state. Two critical properties of redox carriers are the reduction potential required to “activate” the redox carrier for CO2 capture and the CO2 binding constant. The former impacts the stability of the redox carrier towards oxidants such as O2, while the later determines the concentration levels of CO2 that can be captured. Quinones have been heavily studied as redox carriers. However, the impact of electrolyte on these properties has not been systematically explored. The reduction potential and the CO2 binding constant for 6 quinones and 3 alkylammonium hexafluorophophate electrolytes are quantified in acetonitrile. While alkylammonium cations are often considered inert and interchangeable, our studies show up to 100 mV changes in reduction potential with minimal changes to the CO2 binding constant.

Substrate Electronics Dominate the Rate of Reductive Dehalogenation Promoted by the Flavin-Dependent Iodotyrosine Deiodinase.

Iodotyrosine deiodinase (IYD) is unusual in its reliance on flavin to promote reductive dehalogenation of halotyrosines under aerobic conditions. Applications of this activity can be envisioned for bioremediation, but expansion of its specificity requires an understanding of the mechanistic steps that limit the rate of turnover. Key processes capable of controlling steady-state turnover have now been evaluated and described in this study. While proton transfer is necessary for converting the electron-rich substrate into an electrophilic intermediate suitable for reduction, kinetic solvent deuterium isotope effects suggest that this process does not contribute to the overall efficiency of catalysis under neutral conditions. Similarly, reconstituting IYD with flavin analogues demonstrates that a change in reduction potential by as much as 132 mV affects kcat by less than 3-fold. Furthermore, kcat/Km does not correlate with reduction potential and indicates that electron transfer is also not rate determining. Catalytic efficiency is most sensitive to the electronic nature of its substrates. Electron-donating substituents on the ortho position of iodotyrosine stimulate catalysis and conversely electron-withdrawing substituents suppress catalysis. Effects on kcat and kcat/Km range from 22- to 100-fold and fit a linear free-energy correlation with a ρ ranging from -2.1 to -2.8 for human and bacterial IYD. These values are consistent with a rate-determining process of stabilizing the electrophilic and nonaromatic intermediate poised for reduction. Future engineering can now focus on efforts to stabilize this electrophilic intermediate over a broad series of phenolic substrates that are targeted for removal from our environment.

Altered structure and dynamics of pathogenic cytochrome c variants correlate with increased apoptotic activity.

Mutation of cytochrome c in humans causes mild autosomal dominant thrombocytopenia. The role of cytochrome c in platelet formation, and the molecular mechanism underlying the association of cytochrome c mutations with thrombocytopenia remains unknown, although a gain-of-function is most likely. Cytochrome c contributes to several cellular processes, with an exchange between conformational states proposed to regulate changes in function. Here, we use experimental and computational approaches to determine whether pathogenic variants share changes in structure and function, and to understand how these changes might occur. Three pathogenic variants (G41S, Y48H, A51V) cause an increase in apoptosome activation and peroxidase activity. Molecular dynamics simulations of these variants, and two non-naturally occurring variants (G41A, G41T), indicate that increased apoptosome activation correlates with the increased overall flexibility of cytochrome c, particularly movement of the Ω loops. Crystal structures of Y48H and G41T complement these studies which overall suggest that the binding of cytochrome c to apoptotic protease activating factor-1 (Apaf-1) may involve an 'induced fit' mechanism which is enhanced in the more conformationally mobile variants. In contrast, peroxidase activity did not significantly correlate with protein dynamics. Thus, the mechanism by which the variants increase peroxidase activity is not related to the conformational dynamics of the native hexacoordinate state of cytochrome c. Recent molecular dynamics data proposing conformational mobility of specific cytochrome c regions underpins changes in reduction potential and alkaline transition pK was not fully supported. These data highlight that conformational dynamics of cytochrome c drive some but not all of its properties and activities.

Thiosemicarbazone-based bifunctional chemosensors for simultaneous detection of inorganic cations and fluoride anion

Two thiosemicarbazone-based bifunctional chemosensors (L1 and L2) have been synthesized and characterized by various spectroscopic techniques. Sensing behavior of the chemosensors were initially tested by colorimetric signalling, followed by absorption, emission, NMR and CV techniques, and found to behave as bifunctional molecules. These bifunctional chemosensors recognize selected cations (Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) and F¯ anion among the studied cations (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Hg2+ and Pb2+) and anions (F¯, Cl¯, Br¯, I¯ and HSO4¯). Both the sensor molecules displayed remarkable colorimetric and fluorimetric responses in the presence of cations and fluoride anion with a rapid response through color change of the solution. Nitrogen and thione donors of the receptor molecules are liable for cation binding, whereas –NH protons of thiosemicarbazone moiety was found to be responsible for selective fluoride ion sensing. Binding ability of the chemosensors toward cations and F¯ anion were determined with spectrophotometric data by calibration plot, and the binding stoichiometry of the complexes was studied by Job’s plot. Electrochemical measurements showed that the addition of anion to the chemosensors pretreated with cations resulted in greater changes in reduction potentials compared to the addition of anion to the receptors in the absence of cations. Computational studies using density functional theory were also carried out, whereupon comparison of the interactions of copper cation and fluoride anion with the chemosensors explains the selective detection towards respective ions.

Microwave-Assisted Synthesis of ZnO-rGO Core-Shell Nanorod Hybrids with Photo- and Electro-Catalytic Activity.

The unique two-dimensional structure and surface chemistry of reduced graphene oxide (rGO) along with its high electrical conductivity can be exploited to modify the electrochemical properties of ZnO nanoparticles (NPs). ZnO-rGO nanohybrids can be engineered in a simple new two-step synthesis, which is both fast and energy-efficient. The resulting hybrid materials show excellent electrocatalytic and photocatalytic activity. The structure and composition of the as-prepared bare ZnO nanorods (NRs) and the ZnO-rGO hybrids have been extensively characterised and the optical properties subsequently studied by UV/Vis spectroscopy and photoluminescence (PL) spectroscopy (including decay lifetime measurements). The photocatalytic degradation of Rhodamine B (RhB) dye is enhanced using the ZnO-rGO hybrids as compared to bare ZnO NRs. Furthermore, potentiometry comparing ZnO and ZnO-rGO electrodes reveals a featureless capacitive background for an Ar-saturated solution whereas for an O2 -saturated solution a well-defined redox peak was observed using both electrodes. The change in reduction potential and significant increase in current density demonstrates that the hybrid core-shell NRs possess remarkable electrocatalytic activity for the oxygen reduction reaction (ORR) as compared to NRs of ZnO alone.

Modulation of Reduction Potentials of Bis(pyridinium)alkane Dications through Encapsulation within Cucurbit[7]uril

Supramolecular modulation of reduction potentials of two series of bis(pyridinium)alkane salts is described. Study of the encapsulation of bis(pyridinium)alkane guests within the CB[7] cavity revealed the critical influence of the linker length and the position of the heteroatom on the reduction potentials of encapsulated guests. CB[7] complexation of pyridinium salts induced reduction potential changes ranging between +50 and -430 mV. Noncovalent modulation of the electron-accepting ability of organic cations can be utilized in electron-transfer-initiated reactions.

Genistein Binding to Copper(II)-Solvent Dependence and Effects on Radical Scavenging.

Genistein, but not daidzein, binds to copper(II) with a 1:2 stoichiometry in ethanol and with a 1:1 stoichiometry in methanol, indicating chelation by the 5-phenol and the 4-keto group of the isoflavonoid as demonstrated by the Jobs method and UV-visible absorption spectroscopy. In ethanol, the stability constants had the value 1.12 × 1011 L2∙mol−2 for the 1:2 complex and in methanol 6.0 × 105 L∙mol−1 for the 1:1 complex at 25 °C. Binding was not detected in water, as confirmed by an upper limit for the 1:1 stability constant of K = 5 mol−1 L as calculated from the difference in solvation free energy of copper(II) between methanol and the more polar water. Solvent molecules compete with genistein as demonstrated in methanol where binding stoichiometry changes from 1:2 to 1:1 compared to ethanol and methanol/chloroform (7/3, v/v). Genistein binding to copper(II) increases the scavenging rate of the stable, neutral 2,2-diphenyl-1-picrylhydrazyl radical by more than a factor of four, while only small effects were seen for the short-lived but more oxidizing β-carotene radical cation using laser flash photolysis. The increased efficiency of coordinated genistein is concluded to depend on kinetic rather than on thermodynamic factors, as confirmed by the small change in reduction potential of −0.016 V detected by cyclic voltammetry upon binding of genistein to copper(II) in methanol/chloroform solutions.

Prediction of Reduction Potentials of Copper Proteins with Continuum Electrostatics and Density Functional Theory.

Blue copper proteins, such as azurin, show dramatic changes in Cu2+/Cu+ reduction potential upon mutation over the full physiological range. Hence, they have important functions in electron transfer and oxidation chemistry and have applications in industrial biotechnology. The details of what determines these reduction potential changes upon mutation are still unclear. Moreover, it has been difficult to model and predict the reduction potential of azurin mutants and currently no unique procedure or workflow pattern exists. Furthermore, high‐level computational methods can be accurate but are too time consuming for practical use. In this work, a novel approach for calculating reduction potentials of azurin mutants is shown, based on a combination of continuum electrostatics, density functional theory and empirical hydrophobicity factors. Our method accurately reproduces experimental reduction potential changes of 30 mutants with respect to wildtype within experimental error and highlights the factors contributing to the reduction potential change. Finally, reduction potentials are predicted for a series of 124 new mutants that have not yet been investigated experimentally. Several mutants are identified that are located well over 10 Å from the copper center that change the reduction potential by more than 85 mV. The work shows that secondary coordination sphere mutations mostly lead to long‐range electrostatic changes and hence can be modeled accurately with continuum electrostatics.

Redox characterization of the Fe(II)-catalyzed transformation of ferrihydrite to goethite

The reduction potential of Fe(II)-Fe(III) (oxyhydr)oxide systems provides an important control on the biogeochemical cycling of redox-sensitive elements such as carbon and nitrogen as well as trace metals and organic contaminants in natural systems. As such, an in-depth understanding of the factors controlling the reduction potential of such systems is critical to predicting the likely transformation, transport and fate of these species in natural and perturbed environments. In this study the mineralogy and reduction potential of ferrihydrite suspensions at pH 6.50 and pH 7.00 were determined over the course of their Fe(II)-catalyzed transformation to lepidocrocite and goethite using X-ray absorption spectroscopy and mediated electrochemical approaches. The measured reduction potentials were compared to those of analogous Fe(II)-Fe(III) (oxyhydr)oxide suspensions reacted for 5min containing pure ferrihydrite (Fh), lepidocrocite (L) and goethite (Gt). The reduction potentials of the pure Fe(II)-Fe(III) (oxyhydr)oxide suspensions were, respectively, +47.5, −13.5 and −122.3mV vs. SHE at pH 6.5, and −22.9, −84.1 and −189.7mV vs. SHE at pH 7. These values are in good agreement with reduction potentials calculated using the Nernst equation and reported thermodynamic solubility products indicating that these suspensions had reached equilibrium within 5min. The reduction potential of the pH 6.50 Fe(II)-ferrihydrite suspension decreased from +47.4mV to –126.4mV over a week, and from −20.1mV to −188.4mV (all vs. SHE) after 24h at pH 7. The changes in reduction potential over time matched well to those calculated from the relative proportion of each pure Fe(III) (oxyhydr)oxide present suggesting that Fe3+ activity was influenced by the mix of iron oxides present rather than the most insoluble solid species. Finally, evidence is provided that adsorbed Fe(II) has the capacity to reduce a significantly larger fraction of a reducible species than the aqueous Fe(II) species with which it is in equilibrium. As an Fe(III) (oxyhydr)oxide suspension in equilibrium with aqueous and adsorbed Fe(II) species possesses a single, unique reduction potential, this suggests that adsorbed Fe(II) is a more facile reductant than aqueous Fe(II).

Regional energy intensity reduction potential in China: A non-parametric analysis approach

Recently, with increasingly concern on energy and environmental problems, China’s new programs of energy intensity reduction were released in 11th&12th Five-Year-Plan, which results in an urgent need for regional energy intensity reduction potential evaluation. Based upon this recognition, this study mainly focuses on China’s regional energy intensity reduction potential, by employing global data envelopment analysis approach. Moreover, investigating the sources of energy intensity reduction potential change with index decomposition analysis is also one of our targets. The results show that: (1) in the sample period, the energy intensity reduction potential of the western regions is significantly higher than that of central and eastern regions, and the eastern regions have the lowest energy intensity reduction potential. (2) The energy intensity of the eastern regions can be reduced approximately 10–20%, whereas that of the western region can be reduced 30–45%, and that of the whole country can be reduce 25–30% on current basis. (3) According to the sources of energy intensity reduction potential change, it can be found that the energy intensity reduction potential of eastern areas decreased over the sample period. Both the increasing technical efficiency and technical progress contribute to the decline of energy intensity reduction potential. But the western region’s energy intensity reduction potential presents an upward trend during 2000–2011, and the technical regression is the main reason. Therefore, the western regions should pay more attention on optimizing the production technology.

Effects of ruthenium complexes on prion amyloid peptide PrP115-135 aggregation and their interaction mechanism

Protein conformational change and amyloid fibrils deposition are associated with severe diseases. Those proteins include amyloid- β protein (A β , Alzheimer’s disease), human islet amyloid polypeptide (hIAPP, type 2 diabetes mellitus, T2DM), and prion protein (PrP, transmissible spongiform encephalopathies). Scientists have focused on studying these amyloid proteins to develop potential drugs against the diseases. Prion disease is a type of chronic progressive fatal neurodegenerative disease, whose pathogenic mechanism is the conformational conversion of normal prion protein PrPC to a pathogenic type PrPSc. The transition produces amyloid deposition and consequent neurotoxicity. PrP115-135 (115-AAAAGAVVGGLGGYMLGSAMS-135) is an N-terminal fragment of PrP with self-aggregation and cytotoxicity. Metal complexes act as traditional antitumor agents, and non-platinum-based metallodrugs are developed to improve clinical effectiveness in terms of their general toxicity and spectral activity. Besides, they interact with various proteins, enzymes and bioactive peptides. Ruthenium complexes can effectively bind to proteins, such as apotransferrin, apolactoferrin, and serum albumin, resulting in the altered protein structure and binding ability toward other molecules. They are also considered as potential inhibitors of amyloid proteins because of their low cytotoxicity and disaggregation ability to amyloid fibrils. This work studied the interactions of PrP115-135 with two ruthenium complexes NAMI-A and KP418 in order to compare the action mechanisms between different prion neuropeptides and ruthenium complexes. The intrinsic fluorescence method and cyclic voltammetry (CV) were used to study the binding mode and binding affinity of the two complexes to PrP15-135. In addition, we used Thioflavin T fluorescence assay to display the effects of ruthenium complexes on amyloid peptide aggregation. Furthermore, 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to reveal the effects of ruthenium complexes on amyloid peptide-induced cytotoxicity. The change in peptide fluorescence upon metal complex addition could be assumed to reflect the amounts of peptide–ruthenium complex produced and the conformational change of the peptide. The dissociation constant K d values were (6.2±1.4) and (6.4±1.1) μ mol/L for KP418 and NAMI-A respectively, indicating a strong binding affinity between the peptide and ruthenium complexes. CV method showed that, the reduction potential of the complexes changed with the addition of the peptide, reducing the peak current as well. The change of reduction potential indicated that the interaction between them was attributed to electrostatic interaction, and the decrease of the reduction peak current implied that there were other binding forces, such as hydrophobic interaction existed. ThT assay showed that, after incubating ruthenium complexes with aggregated PrP115-135, the fluorescence intensity decreased dramatically. It suggested that the two complexes effectively inhibited the aggregation of peptide. The aggregation kinetics indicated that the complex could significantly prolong the nucleation period and aggregation time of amyloid peptide. Ruthenium complexes could bind to PrP115-135 and inhibit their aggregation, forming oligomers or monomers, thereby reducing the cytotoxicity of PrP115-135 and improving the survival rate of cells. The inhibitory effect of the two complexes on the aggregation of PrP115-135, and their rescue of peptide induced cytotoxicity make it possible for them to be inhibitors of peptide aggregation and potential drugs against amyloidosis. Exploring metal complexes with low toxicity, better disaggregation ability and good water solubility that can penetrate the blood-brain barrier is a principal research direction in this field. So our next step will keep on configuration design of the complexes so as to find potential metallodrugs against prion disease.

Dual Sensing By Simple Heteroditopic Salt Receptors Containing an Anthraquinone Unit

We synthesized simple ion pair receptors consisting of a crown ether cation binding site and an anthraquinone supported thiourea anion binding domain and studied their anion, cation and salt binding properties using spectroscopic, spectrophotometric and electrochemical measurements in acetonitrille solution. Apart from carboxylate anions, which cause deprotonation all the anions tested were found to associate with receptors more strongly in the presence of sodium cations, whereas in the presence of potassium or ammonium cation the anion binding strength was greatly diminished. A homotopic anion receptor lacking a crown ether unit, was unable to bind sodium salt more strongly than tetrabutylammonium salts. Solution and solid state X-ray measurements revealed that strong sodium coordination with the cation binding domain is responsible for the salt binding enhancement. Electrochemical measurements showed that the addition of anions to the ditopic ion pair receptors pretreated with sodium cations resulted in greater changes in reduction potentials compared to the addition of anions to receptors in the absence of Na+. Karbarz, M.; Romanski, J. Inorg. Chem. 2016, 55, 3616-3623. Figure 1

Dual Sensing by Simple Heteroditopic Salt Receptors Containing an Anthraquinone Unit.

We synthesized simple ion pair receptors consisting of a crown ether cation binding site and an anthraquinone-supported thiourea anion binding domain and studied their anion-, cation-, and salt-binding properties using spectroscopic, spectrophotometric, and electrochemical measurements in acetonitrile solution. Apart from carboxylate anions, which cause deprotonation, all the anions tested were found to associate with receptor 1 more strongly in the presence of sodium cations, whereas in the presence of potassium or ammonium cation the anion binding strength was greatly diminished. A homotopic anion receptor 3, lacking a crown ether unit, was unable to bind sodium salt more strongly than tetrabutylammonium salts. Solution and solid-state X-ray measurements revealed that strong sodium coordination with the cation-binding domain is responsible for the salt-binding enhancement. Electrochemical measurements showed that the addition of anions to the receptor 1 pretreated with sodium cations resulted in greater changes in reduction potentials compared to the addition of anions to receptor 1 in the absence of Na(+).

Cyclic voltammetry studies of copper, tin and zinc electrodeposition in a citrate complex system for CZTS solar cell application

Cu2ZnSnS4 (CZTS) has attracted considerable attention as the next generation thin film solar cell to replace CIGS because of its price and availability. The electrodeposition method is one of the fabrication methods. The reduction behaviors of each Cu, Sn and Zn from the unitary system were examined. Cyclic voltammtry (CV) was performed to analyze the behaviors. Trisodium citrate was used as the complexing agent to reduce the difference in the reduction potentials of each material. The effects of pH on the stability of the complexes were also investigated and pH 4.7 was selected to minimize the concentration of H3Cit and Cit3−. The reduction potential of Cu was lowered from −0.2 V (vs. Ag/AgCl) to −0.5 V. The reduction potential of Sn was lowered from −0.5 V (vs. Ag/AgCl) to −0.7 V. The reduction potential of Zn was changed from −1.2 V (vs. Ag/AgCl) to −0.7 V. The change in reduction potential in a complex system can allow the fabrication of CZTS thin films from a Cu, Sn and Zn mixed single bath using an electrodeposition method.

Modified synthesis of nanoscale zero-valent iron and its ultrasound-assisted reactivity study on a reactive dye and textile industry effluents

Synthesized nanoscale zero-valent iron (NZVI) particles were applied for the degradation of a reactive dye Remazol Black B 133 and textile effluent. XRD and HR-TEM analysis of the synthesized particles showed body centered cubic crystal packing. The aggregates were spherical in shape and the size of the particles ranged from 5 to 15 nm. The reactive dye solution was substantially degraded by NZVI particles using ultrasonic irradiation under various experimental conditions created by varying NZVI dosages (0.15–0.30 g/L), initial dye concentration (25–200 mg/L), and pH (2–13). Experimental results suggest that NZVI particles work best within the pH range of 4–10. A unit gram of NZVI was found to degrade a maximum of 749.2 mg of RB B 133 dye and more than 80% of the dye was removed within 15 min of reaction time. During the degradation process, an oxidation–reduction potential change from 196 to −577 mV was detected, indicating reductive condition is necessary for effective dye removal. FT-IR analysis of the end products of the degradation process indicated the presence of an amino (–NH2) group resulting from the breakdown of the azo (–N=N–) group. Results suggest that the degradation followed pseudo-first-order kinetics with respect to dye concentration. The effluents of two textile industries were collected, characterized, and treated with NZVI particles, which led to the significant fall below the standard scale of American Dye Manufacturing Institute (ADMI). This lowering of ADMI value indicates that the overall color removal efficiency is irrespective of any specific dye present in the effluent.

Effects of protein structure on iron-polypeptide vibrational dynamic coupling in cytochrome c.

Cytochrome c (Cyt c) has a heme covalently bound to the polypeptide via a Cys-X-X-Cys-His (CXXCH) linker that is located in the interface region for protein–protein interactions. To determine whether the polypeptide matrix influences iron vibrational dynamics, nuclear resonance vibrational spectroscopy (NRVS) measurements were performed on 57Fe-labeled ferric Hydrogenobacter thermophilus cytochrome c-552, and variants M13V, M13V/K22M, and A7F, which have structural modifications that alter the composition or environment of the CXXCH pentapeptide loop. Simulations of the NRVS data indicate that the 150–325 cm–1 region is dominated by NHis–Fe–SMet axial ligand and polypeptide motions, while the 325–400 cm–1 region shows dominant contributions from ν(Fe–NPyr) (Pyr = pyrrole) and other heme-based modes. Diagnostic spectral signatures that directly relate to structural features of the heme active site are identified using a quantum chemistry-centered normal coordinate analysis (QCC-NCA). In particular, spectral features that directly correlate with CXXCH loop stiffness, the strength of the Fe–His interaction, and the degree of heme distortion are identified. Cumulative results from our investigation suggest that compared to the wild type (wt), variants M13V and M13V/K22M have a more rigid CXXCH pentapeptide segment, a stronger Fe–NHis interaction, and a more ruffled heme. Conversely, the A7F variant has a more planar heme and a weaker Fe–NHis bond. These results are correlated to the observed changes in reduction potential between wt protein and the variants studied here. Implications of these results for Cyt c biogenesis and electron transfer are also discussed.

Evaluation of Heme Peripheral Groups Interactions in Low-Dielectric Constant Media

In this study, we measured the contributions of the ionization of the heme propionates to the reduction potentials of heme b and heme a (bis)N-methylimidazole complexes in various low-dielectric constant conditions. Additionally, we measured the effects of H-bond to the heme a formyl group on the reduction potential of the heme. The performed electrochemical measurements show that ionization of the heme propionates lead to the largest redox change in dichloromethane with no electrolyte. The measured reduction potential changes for heme b and heme a were - 55 and −47 mV (±10 mV) per ionized propionate, respectively. For heme a, the study demonstrates how the dielectric constant of the medium is important in the magnification of the αpKa upon redox-linked ionization of the heme propionates and their roles in the proton pump of cytochrome c oxidase. Additionally, we carried out a detailed study on the H-bonding properties of heme a model compounds (copper mono- and di-acetyl porphyrins) and the effects of the dielectric constant of the solvent on the measured dissociation constant (Kd) between various H-bond donors and the copper porphyrins. Our measurements show that H-bonds between the copper porphyrins and TFA or phenol are significant in benzene and dichloromethane, but extremely weak in the presence of acetonitrile. This study shows how the dielectric constant of the medium also plays a role in modulating the properties of heme a through H-bonding of its formyl group.

Hydrophobic Interactions in Donor-Disulphide-Acceptor (DSSA) Probes Looking Beyond Fluorescence Resonance Energy Transfer Theory

Donor-linker-acceptor (DSSA) is a concept in fluorescence chemistry with acceptor being a fluorescent compound (FRET) or quencher. The DSSA probes used to measure thiol levels in vitro and in vivo. The reduction potential of these dyes are in the range of -0.60 V, much lower than the best thiol reductant reported in literature, the DTT (-0.33 V). DSSA disulphide having an unusually low reduction potential compared to the typical thiol reductants is a puzzle. Secondly, DSSA probes have a cyclized rhodamine ring as acceptor which does not have any spectral overlap with fluorescein, but quenches its absorbance and fluorescence. To understand the structural features of DSSA probes, we have synthesized DSSANa and DSSAOr. The calculated reduction potential of these dyes suggest that DSSA probes have an alternate mechanism from the FRET based quenching, namely hydrophobic interaction or dye to dye quenching. The standard reduction potential change with increasing complexity and steric hindrance of the molecule is small, suggesting that ultra- low Eo' has no contribution from the disulphide linker and is based on structural interactions between fluorescein and cyclized rhodamine. Our results help to understand the DSSA probe quenching mechanism and provide ways to design fluorescent probes.

Evaluation of Heme Peripheral Group Interactions in Extremely Low-Dielectric Constant Media and Their Contributions to the Heme Reduction Potential.

In this study, we measured the contributions of the ionization of the heme propionates to the reduction potentials of heme b and heme a (bis)N-methylimidazole complexes in various low-dielectric constant conditions. Additionally, we measured the effects of H-bond to the heme a formyl group on the reduction potential of the heme. The performed electrochemical measurements show that ionization of the heme propionates lead to the largest redox change in dichloromethane with no electrolyte. The measured reduction potential changes for heme b and heme a were -55 and -47 mV (±10 mV) per ionized propionate, respectively. For heme a, the study demonstrates how the dielectric constant of the medium is important in the magnification of the ΔpKa upon redox-linked ionization of the heme propionates and their roles in the proton pump of cytochrome c oxidase.

Abstract 5466: Butyrate effect on expression of quinone oxidoreductase (NQO1) and cytochrome P450 CYP1A1 enzymes

Abstract Butyrate is a small chain fatic acid formed by bacterial fermentation of plant foods in guts. It has been shown to induce Quinone Oxidoreductase (NQO1) enzyme in tumor cell lines, which may contribute to the detoxification of dietary carcinogens with out any effect to the expression of carcinogen activation enzymes, such as cytochrome P450 CPY1A1 and epoxide hydrolase. The risk from chemical carcinogens and environmental toxins is dependent on the metabolic balance between bioactivation and detoxification enzymes. Cancer chemoprevention therefore may be achieved through alterations in the expression of these enzymes. There is substantial evidence that chemoprevention comprises multiple intervention methods to impede, arrest, or reverse carcinogenesis at various stages. Transcriptional regulation of activation and detoxification enzymes competing for the carcinogen substrate is strongly affected by intracellular oxidation reduction potential change. Treatment of cells with butyrate causes a change in intracellular redox potential which results in transcriptional regulation of activation and detoxification enzymes. Indicators of redox potential may include the concentration ratio of glutathione (GSH): glutathione disulfide (GSSG), cysteine (CYH): cystine (CYSS) and other redox couples. Treatment of human liver HepG2 cells with sodium butyrate (5mM, 48-72Hr) results in an oxidation of both GSH: GSSG and CYH: CYSS to approximately the same extent up on calculation based on Nernst equation of concentrations determined by HPLC analysis. The present study shows that both the steady-state redox potential of the cysteine/cystine couple (Eh = -155 mV) and GSH/GSSG couple (Eh = -255 mV) in cells are sufficiently oxidized (>40 mV) up on treatment of cells with butyrate. The GSH oxidation, in response to 5mM butyrate at 48 -72 Hr for HepG2 cells were associated with an approximately 3-4-fold increase in mRNA for NQO1 as measured by quantitative PCR and 40-85 fold increase as a luciferase measure for relative change in a of transcriptional activation of NQO1 as comparing to the control respectively. However, CYP1A1 expression was not significantly different from controls. Changes in redox potential may directly release transcriptional proteins from within the cytoplasm for traslocation to the nucleus or alter their affinity for transcription response elements. These possibilities are under investigation using nuclear extracts of HepG2 and HT29 cells treated to alter intracellular redox potential. Surface-enhanced laser desorption/ionization (SELDI) allows rapid identification and quantitation of changes in transcription proteins in response to intracellular redox potential change. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5466. doi:1538-7445.AM2012-5466