Redox Potential For Oxidation Research Articles

Removal of Polyvinyl Alcohol in Aqueous Solutions Using an Innovative Paired Photoelectrochemical Oxidative System in a Divided Electrochemical Cell

This study evaluates the performance of an innovative paired photoelectrochemical oxidative system fabricated in our laboratory to determine the removal efficiency of polyvinyl alcohol (PVA) in aqueous solutions. An innovative paired photoelectrochemical oxidative system employed metal redox mediators with high redox potential for anodic oxidation (MEO process) and UV assisted photoelectrochemical oxidation (PEO process) for cathodic oxidation in a divided electrochemical cell. Several parameters were investigated to characterize the removal efficiency of PVA, such as the current density, initial Ce(III) concentration, nitric acid concentration, oxygen flow rate, and UV irradiation intensity. The effects of these parameters on the specific energy consumption were also investigated. Additionally, the conversion yield of Ce(IV) concentration and the electrogeneration of H2O2were calculated in this study. The optimum current density, initial Ce(III) concentration, nitric acid concentration, oxygen flow rate, and UV irradiation intensity were found to be 3 mA cm−2, 0.01 M, 0.3 M, 500 cm3 min−1, and 1.2 mW cm−2, respectively. The synergistic effect of combination process of MEO and PEO would be as a promising alternative for the removal efficiency of PVA.

Deep-sea water containing selenium provides intestinal protection against duodenal ulcers through the upregulation of Bcl-2 and thioredoxin reductase 1.

Deep-sea water (DSW), which is rich in micronutrients and minerals and with antioxidant and anti-inflammatory qualities, may be developed as marine drugs to provide intestinal protection against duodenal ulcers. We determined several characteristics in the modified DSW. We explored duodenal pressure, oxygenation, microvascular blood flow, and changes in pH and oxidative redox potential (ORP) values within the stomach and duodenum in response to tap water (TW, hardness: 2.48 ppm), DSW600 (hardness: 600 ppm), and DSW1200 (hardness: 1200 ppm) in Wistar rats and analyzed oxidative stress and apoptosis gene expressions by cDNA and RNA microarrays in the duodenal epithelium. We compared the effects of drinking DSW, MgCl2, and selenium water on duodenal ulcers using pathologic scoring, immunohistochemical analysis, and Western blotting. Our results showed DSW has a higher pH value, lower ORP value, higher scavenging H2O2 and HOCl activity, higher Mg2+ concentrations, and micronutrients selenium compared with TW samples. Water infusion significantly increased intestinal pressure, O2 levels, and microvascular blood flow in DSW and TW groups. Microarray showed DSW600, DSW1200, selenium water upregulated antioxidant and anti-apoptotic genes and downregulated pro-apoptotic gene expression compared with the TW group. Drinking DSW600, DSW1200, and selenium water but not Mg2+ water significantly enhanced Bcl-2 and thioredoxin reductase 1 expression. Bax/Bcl-2/caspase 3/poly-(ADP-ribose)-polymerase signaling was activated during the pathogenesis of duodenal ulceration. DSW drinking reduced ulcer area as well as apoptotic signaling in acetic acid-induced duodenal ulcers. DSW, which contains selenium, provides intestinal protection against duodenal ulcers through the upregulation of Bcl-2 and thioredoxin reductase 1.

Structure of the Acinetobacter baumannii Dithiol Oxidase DsbA Bound to Elongation Factor EF-Tu Reveals a Novel Protein Interaction Site

The multidrug resistant bacterium Acinetobacter baumannii is a significant cause of nosocomial infection. Biofilm formation, that requires both disulfide bond forming and chaperone-usher pathways, is a major virulence trait in this bacterium. Our biochemical characterizations show that the periplasmic A. baumannii DsbA (AbDsbA) enzyme has an oxidizing redox potential and dithiol oxidase activity. We found an unexpected non-covalent interaction between AbDsbA and the highly conserved prokaryotic elongation factor, EF-Tu. EF-Tu is a cytoplasmic protein but has been localized extracellularly in many bacterial pathogens. The crystal structure of this complex revealed that the EF-Tu switch I region binds to the non-catalytic surface of AbDsbA. Although the physiological and pathological significance of a DsbA/EF-Tu association is unknown, peptides derived from the EF-Tu switch I region bound to AbDsbA with submicromolar affinity. We also identified a seven-residue DsbB-derived peptide that bound to AbDsbA with low micromolar affinity. Further characterization confirmed that the EF-Tu- and DsbB-derived peptides bind at two distinct sites. These data point to the possibility that the non-catalytic surface of DsbA is a potential substrate or regulatory protein interaction site. The two peptides identified in this work together with the newly characterized interaction site provide a novel starting point for inhibitor design targeting AbDsbA.

89: Early Postnatal Exposure to Oxidants Induces Prolonged Oxidative Stress and Increases the Incidence of Oxidative Stress Related Diseases in Preterm Infants les Less than 29 Weeks Gestational Age

In preterm infants, the antioxidant defenses are still poorly developed. The two major sources of oxidants during intensive care stay are oxygen and parenteral nutrition (PN) which is contaminated with peroxides. We hypothesize that early O2 supplementation and longer PN duration increase the risk for oxidative stress associated diseases such as bronchopulmonary dysplasia (BPD), retinopathy of prematurity (ROP) and necrotizing enterocolitis (NEC). To assess the effect of early oxygen (on day 7 and 28) and the PN duration on oxidative stress markers at 36 weeks corrected age and on oxidative stress related diseases. A prospective observational study including all infants <29 weeks GA without major congenital anomalies admitted to our NICU during one year period (116 infants). During the first week of life, in fifty-one out of 116 infants, consent for blood sample at 36 corrected age (CA) was obtained. GSH and GSSG (nmol/mg protein) were measured by capillary electrophoresis and were used for redox potential (mV) calculation using Nernst equation -expressed as mean (sem). BPD was defined as the need of O2 supplement at 36 weeks CA. Significant ROP was defined as any ROP stage 3 or higher or that required laser or anti-VEGF treatment. Cases of NEC grade 2 or higher according to Bell's criteria were included. Student's t test or χ2 were used, as appropriate, *=P<0.05, **=P<0.01. Basline chracteristics was similar in the consent group and the whole cohort. FiO2 ≥25 on day 7 and 28 of life and PN duration >14 days resulted in higher GSSG concentration and more oxidized redox potential at 36 weeks CA indicating prolonged oxidative stress. FiO2 ≥25 early on life and PN duration >14 days increased the incidence of BPD, significant ROP and NEC (Table 1). Early life exposure to oxidants is associated with prolonged oxidative stress and higher incidence of oxidative stress-related diseases. These results suggest that strategies targeting judicious O2 use and either decreasing the duration or using safer formulation PN will help decreasing the incidence of BPD, ROP and NEC.

Effects of Anions, Cations and Supporting Electrolyte on the Electrochemistry and Spectroelectrochemistry of Neutral, Protonated and Deprotonated Free-Base Porphyrins in Nonaqueous Media

A series of free-base porphyrins were examined by electrochemistry and spectroelectrochemistry in nonaqueous media containing a variety of added anions or cations and different supporting electrolytes which were able to bind with the neutral and/or electrogenerated forms of the macrocycle. The investigated neutral porphyrins are represented as H2(P) while the protonated and deprotonated porphyrins are represented as [H4(P)]2+ , [H3(P)]+ , [ H(P)]- and [(P)]2- . The protonated porphyrins were generated by addition of an organic acid to solution, while the deprotonated porphyrins were formed by addition of base to give the compounds shown in Chart 1.UV-vis spectra of the prophyrins were measured before, during and after the addition of different anions, cations and supporting electrolytes to solution. Cyclic voltammetry was used to measure the redox potentials for oxidation or reduction under the different solution conditions, while spectroelectrochemistry was used to monitor UV-vis spectra during each electron addition or electron abstraction. Formation constants for anion or cation binding were measured using both spectroscopic and electrochemical techniques. The measured shifts of absorption bands and shifts of reduction potentials were shown to vary with changes in the binding constants and this was markedly dependent upon both the nature of the porphyrin substituents and the porphyrin geometry, i.e., the planarity of the macrocycle. A proposed mechanism for anion and cation interaction with the free-base porphyrins will be presented.

Estimation of In-Situ Groundwater Conditions Based on Geochemical Equilibrium Simulations

This paper presents a means of estimating in-situ groundwater pH and oxidation-redox potential (ORP), two very important parameters for species migration analysis in safety assessments for radioactive waste disposal or carbon dioxide sequestration. The method was applied to a pumping test in a deep borehole drilled in a tertiary formation in Japan for validation. The following application examples are presented: when applied to several other pumping tests at the same site, it could estimate distributions of the in-situ groundwater pH and ORP; applied to multiple points selected in the groundwater database of Japan, it could help estimate the in-situ redox reaction governing the groundwater conditions in some areas.

A critical review of the reactivity of manganese oxides with organic contaminants.

Naturally occurring manganese (Mn(iii/iv)) oxides are ubiquitous in a wide range of environmental settings and play a key role in numerous biogeochemical cycles. In addition, Mn(iii/iv) oxides are powerful oxidants that are capable of oxidizing a wide range of compounds. This review critically assesses the reactivity of Mn oxides with organic contaminants. Initial work with organic reductants employed high concentrations of model compounds (e.g., substituted phenols and anilines) and emphasized the reductive dissolution of the Mn oxides. Studies with lower concentrations of organic contaminants demonstrate that Mn oxides are capable of oxidizing a wide range of compounds (e.g., antibacterial agents, endocrine disruptors, and pesticides). Both model compounds and organic contaminants undergo similar reaction mechanisms on the oxide surface. The oxidation rates of organic compounds by manganese oxides are dependent upon solution conditions, such as pH and the presence of cations, anions, or dissolved organic matter. Similarly, physicochemical properties of the minerals used affect the rates of organic compound oxidation, which increase with the average oxidation state, redox potential, and specific surface area of the Mn oxides. Due to their reactivity with contaminants under environmentally relevant conditions, Mn oxides may oxidize contaminants in soils and/or be applied in water treatment applications.

Spatial and Seasonal Variation of Dissolved Nitrous Oxide in Wetland Groundwater

Understanding the spatial and temporal pattern of dissolved nitrous oxide (N 2 O) in groundwater is essential to estimate the N 2 O emissions from groundwater to the unsaturated zone and to the atmosphere. In order to study the spatial distribution and seasonal change of dissolved N 2 O in wetland, a headwater wetland in Ichikawa, Chiba Prefecture, Japan, was chosen. Variations of nitrate (NO 3 - ), dissolved N 2 O and ? 15 N-NO 3 - indicated that the dissolved N 2 O in the groundwater of study wetland consists of two parts, one from denitrification within the wetland, and another from nitrification at upland. Principal component analysis (PCA) was used to assess the shallow groundwater parameters in the wetland. And t-test was conducted to find statistically significant differences of the variables between the ASW and NS, warm season and cool season. The concentrations of dissolved N 2 O increased from the upland to the zone of adjacent area between slope and wetland (ASW) and then decreased at the zone near the stream (NS). In sight of dissolved N 2 O associated nitrogen migration, groundwater in the study area can be divided into three stages: upland as the stage 1, ASW as the stage 2, and NS as the stage 3. Higher temperature results in higher denitrification rate, lower dissolved oxygen (DO) and oxidation-redox potential (ORP), yielding higher concentration of N 2 O in the warm season. Therefore, the seasonal change of dissolved N 2 O in study wetland can be mainly interpreted by the variation of temperatures of groundwater.

Inhibition of sulfate reducing bacteria in aquifer sediment by iron nanoparticles

Batch microcosms were setup to determine the impact of different sized zero valent iron (Fe0) particles on microbial sulfate reduction during the in situ bio-precipitation of metals. The microcosms were constructed with aquifer sediment and groundwater from a low pH (3.1), heavy-metal contaminated aquifer. Nano (nFe0), micro (mFe0) and granular (gFe0) sized Fe0 particles were added to separate microcosms. Additionally, selected microcosms were also amended with glycerol as a C-source for sulfate-reducing bacteria. In addition to metal removal, Fe0 in microcosms also raised the pH from 3.1 to 6.5, and decreased the oxidation redox potential from initial values of 249 to −226 mV, providing more favorable conditions for microbial sulfate reduction. mFe0 and gFe0 in combination with glycerol were found to enhance microbial sulfate reduction. However, no sulfate reduction occurred in the controls without Fe0 or in the microcosm amended with nFe0. A separate dose test confirmed the inhibition for sulfate reduction in presence of nFe0. Hydrogen produced by Fe0 was not capable of supporting microbial sulfate reduction as a lone electron donor in this study. Microbial analysis revealed that the addition of Fe0 and glycerol shifted the microbial community towards Desulfosporosinus sp. from a population initially dominated by low pH and metal-resisting Acidithiobacillus ferrooxidans.

Factors Controlling the Redox Potential of ZnCe6 in an Engineered Bacterioferritin Photochemical ‘Reaction Centre’

Photosystem II (PSII) of photosynthesis has the unique ability to photochemically oxidize water. Recently an engineered bacterioferritin photochemical ‘reaction centre’ (BFR-RC) using a zinc chlorin pigment (ZnCe6) in place of its native heme has been shown to photo-oxidize bound manganese ions through a tyrosine residue, thus mimicking two of the key reactions on the electron donor side of PSII. To understand the mechanism of tyrosine oxidation in BFR-RCs, and explore the possibility of water oxidation in such a system we have built an atomic-level model of the BFR-RC using ONIOM methodology. We studied the influence of axial ligands and carboxyl groups on the oxidation potential of ZnCe6 using DFT theory, and finally calculated the shift of the redox potential of ZnCe6 in the BFR-RC protein using the multi-conformational molecular mechanics–Poisson-Boltzmann approach. According to our calculations, the redox potential for the first oxidation of ZnCe6 in the BRF-RC protein is only 0.57 V, too low to oxidize tyrosine. We suggest that the observed tyrosine oxidation in BRF-RC could be driven by the ZnCe6 di-cation. In order to increase the efficiency of tyrosine oxidation, and ultimately oxidize water, the first potential of ZnCe6 would have to attain a value in excess of 0.8 V. We discuss the possibilities for modifying the BFR-RC to achieve this goal.

Impact of Peripheral Ketolytic Deficiency on Hepatic Ketogenesis and Gluconeogenesis during the Transition to Birth

Preservation of bioenergetic homeostasis during the transition from the carbohydrate-laden fetal diet to the high fat, low carbohydrate neonatal diet requires inductions of hepatic fatty acid oxidation, gluconeogenesis, and ketogenesis. Mice with loss-of-function mutation in the extrahepatic mitochondrial enzyme CoA transferase (succinyl-CoA:3-oxoacid CoA transferase, SCOT, encoded by nuclear Oxct1) cannot terminally oxidize ketone bodies and develop lethal hyperketonemic hypoglycemia within 48 h of birth. Here we use this model to demonstrate that loss of ketone body oxidation, an exclusively extrahepatic process, disrupts hepatic intermediary metabolic homeostasis after high fat mother's milk is ingested. Livers of SCOT-knock-out (SCOT-KO) neonates induce the expression of the genes encoding peroxisome proliferator-activated receptor γ co-activator-1a (PGC-1α), phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase, and glucose-6-phosphatase, and the neonate's pools of gluconeogenic alanine and lactate are each diminished by 50%. NMR-based quantitative fate mapping of (13)C-labeled substrates revealed that livers of SCOT-KO newborn mice synthesize glucose from exogenously administered pyruvate. However, the contribution of exogenous pyruvate to the tricarboxylic acid cycle as acetyl-CoA is increased in SCOT-KO livers and is associated with diminished terminal oxidation of fatty acids. After mother's milk provokes hyperketonemia, livers of SCOT-KO mice diminish de novo hepatic β-hydroxybutyrate synthesis by 90%. Disruption of β-hydroxybutyrate production increases hepatic NAD(+)/NADH ratios 3-fold, oxidizing redox potential in liver but not skeletal muscle. Together, these results indicate that peripheral ketone body oxidation prevents hypoglycemia and supports hepatic metabolic homeostasis, which is critical for the maintenance of glycemia during the adaptation to birth.

On Arising Nanohydrides in Reduced Alkaline Solution

Studying electron properties of liquid water in the frame of band theory shows that obtaining its non-stoichiometric state is a simple way to vary physical and chemical properties, and changing a Reduction–Oxidation (RedOx) potential of any aqueous solution. In this connection, Fermi level in the band gap, as a measurable characteristic of non-stoichiometric liquid water, is the most convenient energy for monitoring and managing its RedOx potential. The hypo-stoichiometric state, H2O1–z, of liquid water is realized when the position of Fermi level is shifted to the bottom of conduction band. This state can be fixed by micro emulsifying gaseous hydrogen in liquid water or by electro-reducing the alkaline solution (catholyte) with possible forming alkaline (A) nanohydrides (AH?H2O) n. As strong reducers, they can be quasi-stable in the aqueous solution and be an effective means for holding the negative RedOx potential of liquid water.

Host Nrf2 –glutathione Redox Dysregulation Precedes TNF-α Elevation and Predicts Severity of Graft Versus Host Disease in Experimental Transplantation

AbstractAbstract 4107Graft-versus-host disease (GVHD) is characterized by cytokine and chemokine dysregulation that predicts and also contributes to disease severity. Intermediates in sulfur amino acid (SAA) metabolism are known to modulate cytokines implicated in GVHD, such as TNF-α and IL-2. In this report, a new redox metabolomics assay was used to simultaneously profile 40 SAAs and other amino acid metabolites in plasma and liver 0, 4, and 10 days following experimental allogeneic (Balb/C→ B6, Allo) and syngeneic ((B6Thy1.1→ B6, Syn) bone marrow transplantation (BMT). At day 4 post transplantation (Day +4), prior to increase in plasma TNF-α and subsequent GVHD histopathology, there was a significant decline in both plasma and hepatic glutathione (GSH), resulting in a more oxidized redox potential in Allo relative to Syn mice. Specifically, at Day +4, plasma free GSH concentrations in Allo mice were ∼65% lower than Syn controls (p<0.005), and were accompanied by a ∼3-fold increase in plasma GSSG (p=0.012). The elevated GSSG/GSH ratio indicates a significant shift toward a more oxidized state. Loss of GSH was not due substrate limitation because plasma concentrations of total cysteine, the rate-limiting substrate for GSH synthesis, were significantly higher in Allo vs Syn mice at Day +10, indicating an allo-specific block in GSH synthesis. The plasma GSH redox potential on both Day +4 and Day +10 was significantly lower in Allo (−116.7 ± 5.8 mV, −129.0 ± 11.3 mV, respectively) compared to Syn (−157.9 ± 6.7 mV, −158 ± 2 mV) mice, in which the steady-state GSH redox potential remained similar to values in wild-type controls. Early GSH depletion appears to be a metabolic event associated solely with GVHD pathology, and not a consequence of effects of the conditioning regimen, as shown by the striking difference in hepatic GSH redox potential in an unconditioned paternal to F1 hybrid transplantation model (B6 → B6D2F1) in which some mice develop GVHD (Allo/GVHD+) and some do not (Allo/GVHD-). Specifically, the GSH/GSSG ratio was significantly higher in the Allo/GVHD-compared to Allo/GVHD+ group (17.0 ± 4.91 vs 0.315 ± 0.0601, p=0.015). At day+10, Allo/GVHD+ and Allo/GVHD-mice could be segregated based on hepatic total GSH, free GSH and total cystinylglycine concentrations (Figure 1). Increase in plasma TNF-α lagged behind the redox changes, with no significant differences detected between Syn and Allo mice at Day +4. Also observed at Day +4 in Allo mice was a significant decline in the hepatic nuclear concentration of NF E2-related factor 2 (Nrf2), the transcription factor regulating multiple antioxidant genes that contain the antioxidant response element (ARE) DNA sequence. This decline was accompanied by a decrease in protein and mRNA abundance of phase 2 antioxidant enzymes. For example, hepatic γ-glutamyl cysteine ligase catalytic unit (GCLC) mRNA abundance was decreased by ∼50% (P<0.0001) at Day +4 and further declined to ∼80% by Day +10 (P<0.0004) in Allo compared to Syn mice. Consistent with expectations, hepatic nuclear Nrf2 and TNF-α concentrations at Day +10 were inversely correlated (r2=0.8, p=0.01) in Allo mice (Figure 2 and 3). Together, these observations suggest that down-regulation of the Nrf2-GSH axis precedes stable elevation of TNF-α, and is an early predictor of the severity of GVHD in experimental transplantation. Future experiments will explore potential therapeutic implications of modulating the Nrf2 system in GVHD. [Display omitted] [Display omitted] [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Inhibition of hepatic methionine adenosyltransferase by peroxides contaminating parenteral nutrition leads to a lower level of glutathione in newborn Guinea pigs

Premature newborn infants on total parenteral nutrition (TPN) are at risk of oxidative stress because of peroxides contaminating TPN and low glutathione level. Low cysteine availability limits glutathione synthesis. In this population, the main source of cysteine derives from the hepatic conversion of methionine. The first enzyme of this conversion, methionine adenosyltransferase (MAT), contains redox-sensitive cysteinyl residues. We hypothesize that inhibition of MAT by peroxides contaminating TPN leads to a lower availability of cysteine for glutathione synthesis. At 3 days of life, animals were fitted with a jugular catheter for intravenous infusion. Four groups were compared by ANOVA (P<0.05): (1) Control, without surgery, fed regular chow; (2) Sham, fitted with an obstructed catheter, fed orally regular chow; (3) TPN, fed exclusively TPN (dextrose, amino acids, fat, vitamins) containing 350 μM peroxides; (4) H2O2, fed regular chow orally and infused with 350 μM H2O2. Four days later, MAT activity and glutathione in liver and blood were lower in TPN and H2O2 groups. The redox potential was more oxidized in blood and liver of the TPN group. In conclusion, peroxides generated in TPN inhibit methionine adenosyltransferase activity with, among consequences, a low level of glutathione and a more oxidized redox potential.

Reduction in the Intestinal Epithelial Glutathione Redox Potential May Regulate Proliferation in the Neonatal Murine Gut

The intracellular redox potential of the glutathione (GSH)/glutathione disulfide (GSSG) couple regulates many cellular processes. In vitro studies indicate that a reduced GSH/GSSG redox potential favors proliferation while an oxidized redox potential favors differentiation. Developmental regulation of intestinal growth and adaptation depends upon an appropriate balance between the two. However, how the ontogeny of intestinal epithelial cellular (IEC) GSH/GSSG redox regulates these processes in the developing intestine has not been characterized in vivo. IEC GSH/GSSG redox potential becomes increasingly reduced (primarily driven by a more than 4‐fold increase in IEC GSH concentration) over the first 3 weeks of life in all regions of the murine intestine with the biggest change occurring between 1 and 2 weeks. These changes are accompanied by an increase in intestinal growth and IEC proliferation as assessed by intestinal length, villus height/crypt depth, and Ki67 staining. Understanding how IEC GSH/GSSG redox potential is developmentally regulated may provide insight into how premature human intestinal redox states can be manipulated to optimize intestinal growth and adaptation.

NaCu(Ta1−yNby)4O11 solid solution: A tunable band gap spanning the visible-light wavelengths

The new solid-solution NaCu(Ta1−yNby)4O11 (0≤y≤0.7) was synthesized by solid-state methods in the form of bulk powders that ranged from light-yellow to brown colored and were characterized by powder X-ray diffraction techniques (Space group R-3c (#167); Z=6; a=6.214(1)–6.218(1)Å and c=36.86(1)–36.94(1)Å). Full-profile Rietveld refinements confirmed a site-differentiated ordering of the Cu(I) and Na cations, i.e., occupying the 12c (linear environment) and 18d (seven-coordinate environment) crystallographic sites respectively. Conversely, a statistical mixture of Ta(V) and Nb(V) cations occurred over the 6b (octahedral environment) or the 18e (pentagonal-bipyramidal environment) crystallographic sites, without any preferential segregation. The UV-Vis diffuse reflectance spectra showed a significant red-shift of the optical bandgap size (indirect) from ∼2.70eV to ∼1.80eV across the solid solution with increasing Nb(V) content. Electronic-structure calculations using the tight-binding linear-muffin-tin-orbital approach showed that the reduction in bandgap size arises from the introduction of the lower-energy Nb 4d0 orbitals into the conduction band and consequently a lower energy of the conduction band edge. The lowest-energy bandgap transitions were found to be derived from electronic transitions between the filled Cu(I) and the empty Nb(V) d-orbitals, with a small amount of mixing with the O 2p orbitals. The resulting conduction and valence band energies are found to approximately bracket the redox potentials for water reduction and oxidation, and meeting the thermodynamic requirements for photocatalytic water-splitting reactions.

Cationic State Distribution over the P700 Chlorophyll Pair in Photosystem I

The primary electron donor P700 in photosystem I is composed of two chlorophylls, PA and PB. P700 forms the cationic [PA/PB]•+ state as a result of light-induced electron transfer. We obtained a PA•+/PB•+ ratio of 28:72 and a spin distribution of 22:78 for the entire PSI protein-pigment complex. By considering the influence of the protein components on the redox potential for one-electron oxidation of PA/PB monomers, we found that the following three factors significantly contributed to a large PB•+ population relative to PA•+: 1), Thr-A743 forming a H-bond with PA; 2), PA as a chlorophyll a epimer; and 3), a conserved PsaA/PsaB pair, the Arg-A750/Ser-B734 residue. In addition, 4), the methyl-ester groups of the accessory chlorophylls A−1A/A−1B significantly stabilized the cationic [PA/PB]•+ state and 5), the methyl-ester group orientations were completely different in A−1A and A−1B as seen in the crystal structure. When the methyl-ester group was rotated, the spin-density distribution over PA/PB ranged from 22:78 to 15:85.

Mitochondrial quality control during inheritance is associated with lifespan and mother–daughter age asymmetry in budding yeast

Fluorescence loss in photobleaching experiments and analysis of mitochondrial function using superoxide and redox potential biosensors revealed that mitochondria within individual yeast cells are physically and functionally distinct. Mitochondria that are retained in mother cells during yeast cell division have a significantly more oxidizing redox potential and higher superoxide levels compared to mitochondria in buds. Retention of mitochondria with more oxidizing redox potential in mother cells occurs to the same extent in young and older cells and can account for the age-associated decline in total cellular mitochondrial redox potential in yeast as they age from 0 to 5 generations. Deletion of Mmr1p, a member of the DSL1 family of tethering proteins that localizes to mitochondria at the bud tip and is required for normal mitochondrial inheritance, produces defects in mitochondrial quality control and heterogeneity in replicative lifespan (RLS). Long-lived mmr1Δ cells exhibit prolonged RLS, reduced mean generation times, more reducing mitochondrial redox potential and lower mitochondrial superoxide levels compared to wild-type cells. Short-lived mmr1Δ cells exhibit the opposite phenotypes. Moreover, short-lived cells give rise exclusively to short-lived cells, while the majority of daughters of long-lived cells are long lived. These findings support the model that the mitochondrial inheritance machinery promotes retention of lower-functioning mitochondria in mother cells and that this process contributes to both mother-daughter age asymmetry and age-associated declines in cellular fitness.

Redox Properties of Tanaka’s Water Oxidation Catalyst: Redox Noninnocent Ligands Dominate the Electronic Structure and Reactivity

[Ru(2)(OH)(2)(3,6-(t)Bu(2)Q)(2)(btpyan)](2+) ((t)Bu(2)Q, 3,6-di-tert-butyl-1,2-benzoquinone; btpyan, 1,8-bis(2,2':6',2''-terpyridyl)anthracene) is one of a handful of structurally well-defined homogeneous catalysts that can electrocatalytically oxidize water at room temperature. Unfortunately, the exact composition and the chemical properties of the redox intermediates leading to the catalytically competent species remains poorly resolved. On the basis of the UV-vis spectra the catalyst was previously speculated to lose two protons spontaneously to form an intermediate containing the key O-O bond in water. We evaluated this mechanistic scenario computationally and found that the associated pK(a) values are in the range of 21, much too high to justify spontaneous deprotonation under experimental conditions of pH = 4. In later work, the O-O bond formation was speculated to occur after removal of two protons and two electrons. Extensive exploration of the various oxidation and protonation states that the diruthenium complex may access during catalyst activation reveals surprisingly complex electronic structure patterns in several redox intermediates: the quinone and tpy ligands become redox noninnocent, i.e., they participate actively in the electron transfer processes by temporarily storing redox equivalents. On the basis of this new insight into the electronic structure we propose a novel alternative explanation of the spectroscopic observations reported previously and characterize the electronic structure of the key intermediates in detail. Finally, the redox potential for the first two-electron oxidation is evaluated based on our proposed intermediates and predicted to be 0.411 V, which compares well with the experimentally observed broad two-electron wave at ∼0.32 V.

Development of a high-dynamic range, GFP-based FRET probe sensitive to oxidative microenvironments

We report the optimization of a novel redox-sensitive probe with enhanced dynamic range and an exceptionally well-positioned oxidative midpoint redox potential. The present work characterizes factors that contribute to the improved Förster resonance energy transfer (FRET) performance of this green fluorescent protein (GFP)-based redox sensor. The α-helical linker, which separates the FRET donor and acceptor, has been extended in the new probe and leads to a decreased FRET efficiency in the linker's reduced, 'FRET-off' state. Unexpectedly, the FRET efficiency is increased in the new linker's oxidized, 'FRET-on' state compared with the parent probe, in spite of the longer linker sequence. The combination of a lowered baseline 'FRET-off' and an increased 'FRET-on' signal significantly improves the dynamic range of the probe for a more robust discrimination of its reduced and oxidized linker states. Mutagenesis of the cysteine residues within the α-helix linker reveals the importance of the fourth, C-terminal cysteine and the relative insignificance of the second cysteine in forming the disulfide bridge to clamp the linker into the high-FRET, oxidized state. To further optimize the performance of the redox probe, various cyan fluorescent protein (CFP)/yellow fluorescent protein (YFP) FRET pairs, placed at opposite ends of the improved redox linker (RL7), were quantitatively compared and exchanged. We found that the CyPet/YPet and ECFP/YPet FRET pairs when attached to RL7 do not function well as sensitive redox probes due to a strong tendency to form heterodimers, which disrupt the α-helix. However, monomeric versions of CyPet and YPet (mCyPet and mYPet) eliminate dimerization and restore redox sensitivity of the probe. The best performing probe, ECFP-RL7-EYFP, exhibits an approximately six-fold increase in FRET efficiency in vitro when passing from the oxidized to the reduced state. We determined the midpoint redox potential of the probe to be -143 ± 6 mV, which is ideal for measuring glutathione (GSH/GSSG) redox potentials in oxidative compartments of mammalian cells (e.g. the endoplasmic reticulum).