Oxidative Dissociation Research Articles

Moderate elimination of mycotoxins in vegetable oil triggered by superoxide anion and singlet oxygen

Establishing a moderate elimination strategy for mycotoxins with the maintained food nutrition is significant to food safety. Herein, the Au-NPs decorated defective Bi2WO6 (Au-BWO-OV) with modulated ROS generation was successfully synthesized, integrating the merits of defect-engineering and Au-NPs induced LSPR-effect. The Au-BWO-OV exhibited modified photoelectrochemical property and O2-adsorption capacity, supporting the selective generation of •O2− and 1O2 with moderate oxidizing ability. As a result, >90% of AFB1 and ZEN were eliminated within 100 and 50 min, along with the maintained nutrition in vegetable oil. Moreover, the reasonable degradation mechanism triggered by •O2− and 1O2 was proposed based on the trapping experiments, DFT calculations and LC-MS analysis for intermediate products, including the steps of hydrolysis, oxidative dissociation, cis-trans isomerization, and dehydroxylation. This work not only paved the way for balancing the contradiction between detoxification and nutrient retention, but also casted new insights into the ROS-mediated degradation mechanism.

A New Process for Efficient Recovery of Rhodium from Spent Carbonyl Rhodium Catalyst by Microreactor.

Triphenylphosphine acetylacetone carbonyl rhodium (ROPAC) is an important catalyst in the petrochemical industry, and its deactivated waste catalyst holds significant value for recovery. This study focuses on the existing forms of rhodium (Rh) in waste catalysts and the current status of traditional processes. A green, efficient, and continuous recovery technique was developed using a sealed stainless steel microchannel reactor. The influence of reaction temperature, reaction time, and phase ratio on the Rh recovery rate was investigated, and the process parameters were optimized using response surface methodology (RSM). The results indicate that the magnitude of the impact on the Rh recovery rate follows the order: reaction temperature > reaction time > phase ratio. The optimized process parameters were determined as follows: a reaction time of 29 min, a reaction temperature of 110 °C, and a phase ratio of 1:1, with a corresponding maximum recovery rate of Rh of 66.06%. Furthermore, secondary treatment was performed on the organic phase after primary recovery using the same process conditions, resulting in an overall Rh recovery rate of 95.6%, indicating satisfactory recovery efficiency. Moreover, the application of FTIR and ICP-OES analysis provided definitive evidence that the oxidative dissociation of the rhodium-phosphine chemical bond by H2O2 within ROPAC leads to the conversion of Rh+ into Rh3+. Subsequently, Rh forms chloroaquorhodium (III) complexes that enter the aqueous phase, enabling effective recovery of Rh.

Tunable Ti3C2Tx MXene-Derived TiO2 Nanocrystals at Controlled pH and Temperature.

While two-dimensional (2D) Ti3C2Tx MXene in aqueous dispersions spontaneously oxidizes into titanium dioxide (TiO2) nanocrystals, the crystallization mechanism has not been comprehensively understood and the resultant crystal structures are not controlled among three representative polymorphs: anatase, rutile, and brookite. In this study, such control on the lattice structures and domain sizes of the MXene-derived TiO2 crystallites is demonstrated by means of the oxidation conditions, pH, and temperature (3.0-11.0 and 20-100 °C, respectively). It is observed that the formation of anatase phase is preferred against rutile phase in more basic and hotter oxidizing solutions, and even 100% anatase can be obtained at pH 11.0 and 100 °C. At lower pH and temperature, the portion of rutile phase increases such that it reaches ∼70% at pH 3 and 20 °C. Under certain circumstances, small portion of brookite phase is also observed. Smaller domain sizes of both anatase and rutile phases are observed in more basic oxidizing solutions and at lower temperatures. Based on these experimental results, we propose the crystallization mechanism in which the oxidative dissociation of Ti3C2Tx first produces Ti ions as the intermediate state, and they bind to abundant oxygen in the aqueous dispersions, and nucleate and crystallize into TiO2.

Maternal diabetes-mediated RORA suppression in mice contributes to autism-like offspring through inhibition of aromatase

Retinoic acid-related orphan receptor alpha (RORA) suppression is associated with autism spectrum disorder (ASD) development, although the mechanism remains unclear. In this study, we aim to investigate the potential effect and mechanisms of RORA suppression on autism-like behavior (ALB) through maternal diabetes-mediated mouse model. Our in vitro study in human neural progenitor cells shows that transient hyperglycemia induces persistent RORA suppression through oxidative stress-mediated epigenetic modifications and subsequent dissociation of octamer-binding transcription factor 3/4 from the RORA promoter, subsequently suppressing the expression of aromatase and superoxide dismutase 2. The in vivo mouse study shows that prenatal RORA deficiency in neuron-specific RORA null mice mimics maternal diabetes-mediated ALB; postnatal RORA expression in the amygdala ameliorates, while postnatal RORA knockdown mimics, maternal diabetes-mediated ALB in offspring. In addition, RORA mRNA levels in peripheral blood mononuclear cells decrease to 34.2% in ASD patients (n = 121) compared to the typically developing group (n = 118), and the related Receiver Operating Characteristic curve shows good sensitivity and specificity with a calculated 84.1% of Area Under the Curve for ASD diagnosis. We conclude that maternal diabetes contributes to ALB in offspring through suppression of RORA and aromatase, RORA expression in PBMC could be a potential marker for ASD screening.

Anticancer Potency of Copper(I) Complexes Against a Range Cancer Cell Lines: A Review

The copper(I) complexes of N,N-diimine, N,O- and/or N, S-bidentate systems perform significant dose-dependent anticancer activity toward various cell lines viz. MCF-7, LNCap, PSN-1, A431, BxPC3, H157, A2780, HeLa, MDA-MB231, MGC-803 etc. The copper(I) complexes can cross the cellular plasmalemma that results in the accumulation of copper ion in the cancer cells, exhibit significant anticancer effect and overcome the multidrug resistance because these can slightly induce the DNA cleavage as a result of limited generation of reactive oxygen species (ROS). Copper(I) complexes exhibit significantly higher broad-spectrum antiproliferation and cell apoptosis via mitochondrial pathway than that of their corresponding Cu(II), Co(II), Pd(II), and Ni(II) complexes. The copper(I) complexes inhibit the cancer cells not only via ROS generation but also via DNA interactions possibly by attacking the sugar-phosphate backbone of DNA due to their oxidative and partial dissociation behavior. Copper(II/I) complexes are also able to cleave DNA by hydrolytic pathway and induce caspase-dependent-mitochondrial-mediated cell apoptosis by ROS production or blocking the progression of cell cycles. In many cases, the modification in organic moiety and the placement of electronegative substituent near the metallic center of complexes have been found to enhance their anticancer potency in a significant manner. Thus copper(I) complexes may be used as the better anticancer drugs with multiple modes of action compared to the copper(II) complexes due to having oxidative behavior and generation of empty site on copper(I) ion during partial dissociation.

Electrochemically controlled hydrogen bonding for supramolecular assembly: Challenges and opportunities

The electrostatic nature of the hydrogen bond makes it straightforward, in principle, to electrochemically perturb the strength of hydrogen bonds by using oxidation to create stronger H-donors or reduction to create stronger H-acceptors. However, oxidation or reduction can also lead to proton transfer and subsequent electron transfer, which can nullify the effect of the initial electron transfer. Illustrative examples of these complications based on a series of investigations of electroactive, urea-containing 2 H-bond dimers are described. It is also shown that proton transfer accompanying electron transfer can be used to advantage with two examples of oxidative dissociation of 4 H-bond dimers that are of interest for the construction of supramolecular polymers and gels. In both cases proton transfer is key to achieving the desired outcome. Moving forward, it is argued that proton transfer should always be considered as a possible useful component in the design of electrochemically controllable H-bonding systems.

Heterogenized Water Oxidation Catalysts Prepared by Immobilizing Kläui-Type Organometallic Precursors.

An efficient heterogenized water oxidation catalyst (2_TiO2 ) has been synthesized by immobilizing the Kläui-type organometallic precursor [Cp*Ir{P(O)(OH)2 }3 ]Na (2, Cp*=1,2,3,4,5-pentamethylcyclopentadienyl ligand) onto rutile TiO2 . Iridium is homogeneously distributed at the molecular and atomic/small cluster level in 2_TiO2 and 2'_TiO2 (solid catalyst recovered after the first catalytic run), respectively, as indicated by STEM-HAADF (scanning transmission electron microscopy - high angle annular dark field) studies. 2'_TiO2 exhibits TOF values up to 23.7 min(-1) in the oxidation of water to O2 driven by NaIO4 at nearly neutral pH, and a TON only limited by the amount of NaIO4 used, as indicated by multiple run experiments. Furthermore, while roughly 40 % leaching is observed during the first catalytic run, 2'_TiO2 does not undergo any further leaching even when in contact with strongly basic solutions and completely maintains its activity for thousands of cycles. NMR studies, in combination with ICP-OES (inductively coupled plasma optical emission spectrometry), indicate that the activation of 2_TiO2 occurs through the initial oxidative dissociation of PO4 (3-) , ultimately leading to active centers in which a 1:1 P/Ir ratio is present (derived from the removal of two PO4 (3-) units) likely missing the Cp* ligand.

Polymorphism and thermodynamic properties of chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium(II) complex

A new crystalline polymorph of known chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium(II) complex [RuCl(PPh3)2(η5-C5H5)] was obtained and characterized by various analytical methods including single-crystal and powder X-ray diffraction (XRPD) and differential scanning calorimetry (DSC) in combination with thermo-gravimetric analysis (TG-DSC). The obtained crystals of new polymorph are monoclinic, space group P21/n, with a = 11.125(4), b = 19.184(6), c = 15.946(5) Å, α = 90, β = 100.174(5), γ = 90, and Z = 4. It has been found that real melting point of the complex (M.p. = 252–253 °C) can be determined only in inert atmosphere while an apparent melting is observed in the range 142–150 °C due oxygen promoted oxidative dissociation of triphenylphosphine ligand.

Abstract 3872: Genotoxicity of zinc oxid nanoparticles and the activation of ATM-Chk2 DNA-damage-response pathway are caused by zinc-ions

Abstract Zinc oxide nanoparticles (ZnO-NP) are used in a variety of applications including cosmetics and pharmaceuticals. The common utilization of ZnO-NPs results in an increasing environmental release with unknown health effects. Recent studies have shown that ZnO-NP exposure cause cellular toxicity including DNA-damages. Discussed mechanisms are interactions of the ZnO-NP with intracellular structures and molecules after internalization, extracellular or intracellular dissociation of the particles, and the generation of ROS. In the present study we evaluated the genotoxic properties of ZnO-NP as well as the cellular DNA damage response in dependence of oxidative distress and ZnO-NP dissociation into Zn2+. For this purpose, we exposed the human epithelial cell line A549 to defined ZnO-NP (100μg/ml). Genotoxic effects of the particles were evaluated by Comet assay and γH2AX-foci, measuring DNA double-strand breaks (DNA-DSBs). Dissociation of ZnO-NP and the intracellular increase of Zn2+ were performed with spectrofluorimetric and cLSM measurements by the use of FluoZin3. Oxidative distress was determined by the compound dihydrodichlorofluorescein diacetate (H2DCF-DA). The Activation of the DNA damage response pathway was proven by analyses of H2AX-, ATM-, Chk1- and Chk2 phosphorylation, and p21, p53 up-regulation after ZnO-NP exposure by western blot or ELISA. To figure out, if the genotoxic potential of ZnO-NP is dependent of released Zn2+ or the generation of ROS we inhibited oxidative distress by the antioxidant N-acetyl-L-cysteine (NAC) and Zn2+ were extracellular chelated by diethylene triamine pentaacetic acid (DTPA). We found a fast extracellular dissociation of ZnO-NP and a quick intracellular increase of Zn2+. Furthermore, we ascertained an activation of H2AX induced by ZnO-NP; this phosphorylation is totally inhibited by DTPA. ZnO-NP activated the DSB-damage response indicated by ATM-, Chk2-phosphorylation as well as an up-regulation of p53 and p21. Pretreatment with NAC scavenging ROS leads to a reduced and Zn2+ complexation to no activation of ATM-Chk2-DNA damage pathway. The ATR/Chk1 pathway was not activated by ZnO-NP. We demonstrated ZnO-NP induced DNA-damages and the activation of the ATM/Chk2 DNA damage response pathway but not the ATR/Chk1 pathway, indicating that ZnO-NP exposure induces DNA-DSBs. Scavanging of ROS leads to a slight reduction of DNA-DSBs but extracellular Zn2+ compelxation to a complete impairment suggesting that the mechanism of ZnO-NP genotoxicity is not mediated via ROS-generation but rather a direct interaction of dissociated Zn-ions with the DNA. Citation Format: Julia Heim, Nawaz Muhammad Tahir, Anke Kaltbeitzel, Volker Mailänder, Hartmut Lüddens, Wolfgang Tremel, Jürgen Brieger. Genotoxicity of zinc oxid nanoparticles and the activation of ATM-Chk2 DNA-damage-response pathway are caused by zinc-ions. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3872. doi:10.1158/1538-7445.AM2015-3872

Tip enhanced Raman spectroscopy, DFT and PED calculations of 4″-trimethylsilylethylsulfanyl-4,4′-di(phenyleneethynylene)benzene thiol adsorbed on silver

Monolayers of α,ω-dithiol oligo(phenyleneethynlene) molecules are critical to the field of molecular electronics because of their abilities to form bonds with many metallic surfaces and rectify current. In this study Fourier Transformation-Raman, surface-enhanced Raman scattering (SERS) spectroscopy and Tip-enhanced Raman Spectroscopy (TERS) were used to characterize a selectively oriented self-assembled monolayer of 4″-trimethylsilylethylsulfanyl-4,4′-bis-(phenyleneethynylene)benzenethiol (OPE′) on silver coated nanospheres. Selective orientation was achieved by synthesizing 4″-trimethylsilylethylsulfanyl-4,4′-bis-(phenyleneethynylene)benzene disulfide, which undergoes oxidative dissociation and covalently bonds to the metal surface. The Ag coated nanosphere surfaces were characterized by scanning electron microscopy (SEM), which showed a large area of surface charging. The SERS and TERS spectra show similar results; however, a greater enhancement was achieved with the TERS relative to the SERS spectra. Assignments of vibrational bands were based on DFT calculations performed at the B3LYP level with good agreement between theoretical and experimental values. An average percent difference of 2.5 cm−1 was obtained for the non-CH stretching frequencies and a scaling factor was not applied to theoretically generated frequencies. A red shift of the ν(C–S) peak at 1087 cm−1 was observed when OPE′ was adsorbed on a Ag surface. Vibrations specific to the trimethylsilylethyl (TMSE) group were visible in the TERS spectra, and disappear upon deprotection.

Oxidation of p53 through DNA charge transport involves a network of disulfides within the DNA-binding domain.

Transcription factor p53 plays a critical role in the cellular response to stress stimuli. We have seen that p53 dissociates selectively from various promoter sites as a result of oxidation at long-range through DNA-mediated charge transport (CT). Here, we examine this chemical oxidation and determine the residues in p53 that are essential for oxidative dissociation, focusing on the network of cysteine residues adjacent to the DNA-binding site. Of the eight mutants studied, only the C275S mutation shows decreased affinity for the Gadd45 promoter site. However, both mutations C275S and C277S result in substantial attenuation of oxidative dissociation, with C275S causing the most severe attenuation. Differential thiol labeling was used to determine the oxidation states of cysteine residues within p53 after DNA-mediated oxidation. Reduced cysteines were iodoacetamide-labeled, whereas oxidized cysteines participating in disulfide bonds were 13C2D2-iodoacetamide-labeled. Intensities of respective iodoacetamide-modified peptide fragments were analyzed by mass spectrometry. A distinct shift in peptide labeling toward 13C2D2-iodoacetamide-labeled cysteines is observed in oxidized samples, confirming that chemical oxidation of p53 occurs at long range. All observable cysteine residues trend toward the heavy label under conditions of DNA CT, indicating the formation of multiple disulfide bonds among the cysteine network. On the basis of these data, it is proposed that disulfide formation involving C275 is critical for inducing oxidative dissociation of p53 from DNA.

Nickel/carbon core/shell nanotubes: Lanthanum nickel alloy catalyzed synthesis, characterization and studies on their ferromagnetic and lithium-ion storage properties

A method was developed to synthesize ferromagnetic nickel core/carbon shell nanotubes (Ni/CNTs) by chemical vapor deposition using Pauli paramagnetic lanthanum nickel (LaNi5) alloy both as a catalyst and as a source for the Ni-core. The Ni-core was obtained through oxidative dissociation followed by hydrogen reduction during the catalytic growth of the CNTs. Transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD) analyses reveal that the Ni-core exists as a face centered cubic single crystal. The magnetic hysteresis loop of Ni/CNTs particle shows increased coercivity (446.42Oe) than bulk Ni at room temperature. Furthermore, the Ni/CNTs core/shell particles were investigated as anode materials in lithium-ion batteries. The Ni/CNTs electrode delivered a high discharge capacity of 309mAhg−1 at 0.2C, and a stable cycle-life, which is attributed to high structural stability of Ni/CNTs electrode during electrochemical lithium-ion insertion and de-insertion redox reactions.

DNA-mediated oxidation of p53.

Transcription factor p53 is the most commonly altered gene in human cancer. As a redox-active protein in direct contact with DNA, p53 can directly sense oxidative stress through DNA-mediated charge transport. Electron hole transport occurs over long distances through the π-stacked bases and leads to the oxidative dissociation of p53. The extent of protein dissociation depends upon the redox potential of the DNA in direct contact with each p53 monomer. The DNA sequence dependence of p53 oxidative dissociation was examined by electrophoretic mobility shift assays using oligonucleotides containing both synthetic and human p53 consensus sequences with an appended photooxidant, anthraquinone. Greater p53 dissociation is observed from sequences containing low-redox potential purine regions, particularly guanine triplets. Using denaturing polyacrylamide gel electrophoresis of irradiated anthraquinone-modified DNA, the DNA damage sites corresponding to sites of preferred electron hole localization were determined. The resulting DNA damage preferentially localizes to guanine doublets and triplets. Oxidative DNA damage is inhibited in the presence of p53, but only at sites in direct contact with p53. From these data, predictions about the sensitivity of human p53-binding sites to oxidative stress as well as possible biological implications have been made. On the basis of our data, the guanine pattern within the purine region of each p53-binding site determines the response of p53 to DNA oxidation, yielding for some sequences the oxidative dissociation of p53 from a distance and thereby providing another potential role for DNA charge transport chemistry within the cell.

General and efficient copper-catalyzed aerobic oxidative synthesis of N-fused heterocycles using amino acids as the nitrogen source

A general and efficient copper-catalyzed aerobic oxidative method for the synthesis of N-fused heterocycles has been developed by using readily available α-amino acids as the nitrogen source. The reactions underwent N-arylation, aerobic oxidative dehydrogenation, intramolecular cyclization and dissociation of formic acid. This method should provide a general and practical strategy for the construction of N-fused heterocycles.

The effect of TEMPO in the hydroxylation of benzene to phenol on the [(CH 3) 4N] 4PMo 11VO 40/ascorbic acid/TEMPO/O 2 catalytic system: Formation of ascorbic acid radicals through hydrogen exchange of ascorbic acid and TEMPO

Hydroxylation of benzene to phenol in the [(CH 3) 4N] 4PMo 11VO 40/ascorbic acid/TEMPO/O 2 catalytic system was carefully investigated. UV–vis, ESR and 1H NMR studies showed ascorbic acid radicals were formed through the hydrogen exchange of ascorbic acid with TEMPO (2,2,6,6-tetramethyl-1-piperidine-N-oxyl radicals) during the reaction. In acetonitrile, the ascorbic acid would be partly oxidized to 2-hydroxy-2-buten-4-olide (α-tetronic acid, isotetronic acid, compound 1) without TEMPO. The interaction of TEMPO and ascorbic acid restrained the oxidative dissociation of ascorbic acid and promoted the rate of the hydroxylation. Aqueous acetic acid solvent can also restrain the oxidative dissociation of ascorbic acid. In aqueous acetic acid, the yield of phenol could reach 18.9% in the [(CH 3) 4N] 4PMo 11VO 40/ascorbic acid/TEMPO/O 2 catalytic system with sufficient ascorbic acid after 400 min.

Synthesis of helical carbon nanofibres and its application in hydrogen desorption

In this communication, we report the synthesis of helical carbon nanofibres (HCNFs) by employing hydrogen storage intermetallic LaNi 5 as the catalyst precursor. It was observed that oxidative dissociation of LaNi 5 alloy (2LaNi 5 + 3/2O 2 → La 2O 3 + 10Ni) occurred during synthesis. The Ni particles obtained through this process instantly interacted with C 2H 2 and H 2 gases, and fragmented to nanoparticles of Ni (∼150 nm) with polygonal shape. These polygonal shapes of Ni nanoparticles were decisive for the growth of helical carbon nanofibres (HCNFs) at 650 °C. TEM, SAED and EDAX studies have shown that HCNFs have grown on Ni nanoparticles. Typical diameter and length of the HCNFs are ∼150 nm and 6–8 μm respectively. BET surface area of these typical HCNFs has been found to be 127 m 2/g. It was found that at temperature 750 °C, spherical shapes of Ni nanoparticles were produced and decisive for the growth of planar carbon nanofibres (PCNFs). The diameter and length of the PCNFs are ∼200 nm and 6–8 μm respectively. In order to explore the application potential of the present as-synthesized CNFs, they were used as a catalyst for enhancing the hydrogen desorption kinetics of sodium aluminum hydride (NaAlH 4). We have found that the present as-synthesized HCNFs, with metallic impurities, indeed work as an effective catalyst. The pristine NaAlH 4 and 8 mol% as-synthesized HCNFs admixed NaAlH 4, at 160 °C–180 °C and for the duration of 5 h, liberate 0.8 wt% and 4.36 wt% of hydrogen, respectively. Thus there is an enhancement of ∼5 times in kinetics when as-synthesized HCNFs are used as the catalyst. To the best of our knowledge, the use of hydrogen storage alloy LaNi 5 as the catalyst precursor for the growth of HCNFs has not yet been done and thus represents a new feature relating to the growth of HCNFs. Furthermore, we have shown that the as-synthesized HCNFs work as an effective new catalyst for improving the dehydrogenation kinetics of the complex hydride, NaAlH 4.

Surface-enhanced Raman scattering of a Ag/oligo(phenyleneethynylene)/Ag sandwich

α,ω-Dithiols are a useful class of compounds in molecular electronics because of their ability to easily adsorb to two metal surfaces, producing a molecular junction. We have prepared Ag nanosphere/oligo(phenyleneethynylene)/Ag sol (AgNS/OPE/Ag sol) and Ag nanowire/oligo(phenyleneethynylene)/Ag sol (AgNW/OPE/Ag sol) sandwiches to simulate the architecture of a molecular electronic device. This was achieved by self-assembly of OPE on the silver nanosurface, deprotection of the terminal sulfur, and deposition of Ag sol atop the monolayer. These sandwiches were then characterized by surface-enhanced Raman scattering (SERS) spectroscopy. The resulting spectra were compared to the bulk spectrum of the dimer and to the Ag nanosurface/OPE SERS spectra. The intensities of the SERS spectra in both systems exhibit a strong dependence on Ag deposition time and the results are also suggestive of intense interparticle coupling of the electromagnetic fields in both the AgNW/OPE/Ag and the AgNS/OPE/Ag systems. Three previously unobserved bands (1219, 1234, 2037 cm −1) arose in the SER spectra of the sandwiches and their presence is attributed to the strong enhancement of the electromagnetic field which is predicted from the COSMOL computational package. The 544 cm −1 disulfide bond which is observed in the spectrum of solid OPE but is absent in the AgNS/OPE/Ag and AgNW/OPE/Ag spectra is indicative of chemisorption of OPE to the nanoparticles through oxidative dissociation of the disulfide bond.

Effect of admixing different carbon structural variants on the decomposition and hydrogen sorption kinetics of magnesium hydride

The effect of admixing catalysts comprised of carbon nanostructures, specifically planar, helical and twisted carbon nanofibers, spherical carbon particles and multi-walled carbon nanotubes, on the hydrogen storage properties of magnesium hydride has been investigated. Optimum results were achieved with the mixture containing twisted carbon nanofibers (TCNF) synthesized by Ni catalyst derived by oxidative dissociation of catalyst precursor LaNi 5. The desorption temperature of 2 wt.% TCNF admixed MgH 2 is ∼65 K lower than that of pristine MgH 2 milled for the same duration. The enhancement in hydrogen absorption capacity of MgH 2 admixed with 2 wt.% TCNF has been found to be two-fold in the first 10 minutes at 573 K and under a hydrogen pressure of 2 MPa, i.e. 4.8wt% as compared to 2.5 wt% for MgH 2 alone. The increase in capacity by a factor of about two within the first 10 minutes as a result of the catalytic activity of TCNF is one of the exciting results obtained for hydrogen absorption in catalyzed MgH 2.

Electrochemical Reactions and Ionization Processes

Electrochemical or photo-electrochemical reactions in both electrospray ionization and laser desorption ionization are discussed stressing the role of the electrode reaction in influencing the ionization process. In particular, upon application of a high voltage during electrospray ionization, the emitter includes a working electrode, where redox reactions are observed, such as electro-generation of benzoquinone and metal ions. In contrast, the target plate in laser-induced desorption ionization also acts as a photo-electrode, especially when modified with a mesoporous semiconductor. We illustrate here how these electrochemical reactions can be used for tagging purposes, and for oxidative or reductive dissociation reactions.

A role for DNA-mediated charge transport in regulating p53: Oxidation of the DNA-bound protein from a distance

Charge transport (CT) through the DNA base pairs provides a means to promote redox reactions at a remote site and potentially to effect signaling between molecules bound to DNA. Here we describe the oxidation of a cell-cycle regulatory protein, p53, from a distance through DNA-mediated CT. A consensus p53 binding site as well as three DNA promoters regulated by p53 were synthesized containing a tethered DNA photooxidant, anthraquinone. Photoinduced oxidation of the protein occurs from a distance; introduction of an intervening CA mismatch, which inhibits DNA-mediated CT, prevents oxidation of p53. DNA-mediated oxidation is shown to promote dissociation of p53 from only some promoters, and this sequence-selectivity in oxidative dissociation correlates with the biological regulation of p53. Under severe oxidative stress, effected here through oxidation at long range, p53 dissociates from a promoter that activates DNA repair as well as the promoter for the negative regulator of p53, Mdm2, but not from a promoter activating cell-cycle arrest. Mass spectrometry results are consistent with disulfide bond formation in p53 upon DNA-mediated oxidation. Furthermore, DNA-bound p53 oxidation is shown in vivo by up-regulation of p53 and subsequent irradiation in the presence of a rhodium photooxidant to give a new p53 adduct that can be reversed with thiol treatment. This DNA-mediated oxidation of p53 parallels that seen by treating cells with hydrogen peroxide. These results indicate a unique mechanism using DNA-mediated CT chemistry by which p53 activity on different promoters may be controlled globally under conditions of oxidative stress.