Electrochemistry of hydroquinone derivatives at metal and iodine-modified metal electrodes

The difference in the electrochemical behavior of hydroquinone and pyrocatechol. at platinum and gold surfaces was analyzed using voltammetry and attenuated total reflection Fourier transform infrared spectroscopy. The results show that the hydroquinone derivatives are adsorbed on a gold surface with vertical orientation, which makes the electron transfer between the bulk species and the electrode surface easier than that in the case of flat adsorption of hydroquinone derivatives that occurs at a platinum electrode. The formation of the vertical conformation and the rapid process of electron transfer were also confirmed by quantum chemistry calculations. In addition, the pre-adsorbed iodine on the electrodes played a key role on the adsorbed configuration and. electron transfer of redox species.

Amperometric quantification of polar organic solvents based on a tyrosinase biosensor

A novel amperometric biosensor for quantification of the electrochemically inert polar organic solvents based on tyrosinase electrode was preliminarily reported. The biosensor was fabricated by simply syringing an aqueous solution of tyrosinase/PVAVP (PVAVP: copolymer of poly(vinyl alcohol) grafting with 4-vinylpyridine) onto glassy carbon electrode surface followed by drying the modified electrode at +4 degrees C in a refrigerator. The current generated from electrochemical reduction of quinone is a probe signal. The biosensor can be used for quantification of polar organic solvents, and its mechanism was characterized with in situ steady-state amperometry-quartz crystal microbalance experiments. The detection limit, sensitivity, and dynamic range for certain organic solvents are dependent on the kind and concentration of the substrate probe and the hydrophobicity of the immobilization matrix. The response time for all the tested organic solvents is less than 2 min.

Role of electron transfer of quinones in hydroxylation of phenol

It was found that at neutral pH the hydroxylation reaction rate of phenol was accelerated with an increase of the amounts of 1,4-quinone (1,4-BQ), This acceleration was ascribed to the formation of semiquinone from 1,4-BQ. The semiquinone and 1,4-BQ were suggested to play a role of actual oxidant (electron transfer) in the catalytic cycle. With further reaction, most 1,4-BQ was converted into 1,4-hydroquinone (HQ) and the corresponding mechanism was proposed.

Thermal decomposition processes of polyaniline and poly-o-toluidine investigated by direct pyrolysis mass spectrometry

The thermal decomposition of polyaniline(PAn) and poly-o-toluidine(POT) was studied by means of direct pyrolysis mass spectrometry(DM) and MS/MS, The results showed that both benzene-diamine and quinone-diimine units were produced, and the intensities of fragments corresponding to quinone-diimine units increased as the oxidation degrees increased, The mechanism of thermal decomposition of PAn and POT was given for the first time.

ON THE IODINE-DOPING OF POLYANILINE AND POLY-ORTHO-METHYLANILINE

The reactions of polyaniline and poly-omicron-methylaniline of different oxidation degrees with I2 were followed by FTIR and electrical conductivity measurements. The results showed that the reaction of common polyanilines with I2 was oxidation in nature whereas that of the fully reduced ones was doping. The latter took place in two steps: oxidation of benzene-diamine units into quinone-diimine units (redox between I2 and the polymer chain) and formation of a conjugated system consisting of four aromatic rings (intramolecular chain redox).

MOLECULAR CHAIN STRUCTURE OF DOPED POLYANILINE

The chain structure of polyaniline doped with HCl or CF_3COOH has been investigated by FTIR, solid state ~(13)CNMR, resonance laser Raman and UV-VIS spectroscopies. The results show that during the protonic acid doping, a partial redox reaction takes place between the quinone-diimine and benzene-diamine units and it leads to a long conjugate system with a certain charge distribution.

Wangia profunda gen. nov., sp nov., a novel marine bacterium of the family Flavobacteriaceae isolated from southern Okinawa Trough deep-sea sediment

An orange-pigmented, Gram-negative, nonmotile, strictly aerobic and oxidase- and catalase-positive bacterium (SM-A87(T)) was isolated from the deep-sea sediment of the southern Okinawa Trough area. The main fatty acids were i15 : 0, i17 : 0 3OH, i15 : 1 G, i17 : 1 omega 9c, 15 : 0, i15 : 0 3OH and summed feature 3 (comprising i-15 : 0 2OH and/or 16 : 1 omega 7c). MK-6 was the predominant respiratory quinone. DNA G+C content was 35.8 mol%. Flexirubin-type pigments were absent. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain SM-A87(T) formed a distinct lineage within the family Flavobacteriaceae, with < 93% sequence similarity to the nearest strain of genus Salegentibacter. Moreover, strain SM-A87(T) could be distinguished from the nearest phylogenetic neighbors by a number of chemotaxonomic and phenotypic properties. On the basis of polyphasic analyses, it is proposed that strain SM-A87(T) be classified in a novel genus and a new species in the family Flavobacteriaceae, designated Wangia profunda gen. nov., sp. nov. The type strain is SM-A87(T) (CCTCC AB 206139(T)=DSM 18752).

Myroides profundi sp nov., isolated from deep-sea sediment of the southern Okinawa Trough

A Gram-negative, nonmotile, aerobic and oxidase- and catalase-positive bacterium,, designated D25(T), was isolated from the deep-sea sediments of the southern Okinawa Trough area. Phylogenetic analyses of 16S rRNA gene sequences showed that strain D25(T), fell within the genus Myroides, with 99.2%, 96.0% and 93.4% sequence similarities to the only three recognized species of Myroides. However, the DNA-DNA similarity Value between strain D25(T) and its nearest neighbour Myroides odoratimimus JCM 7460(T) was only 49.9% ( < 70%). Several phenotypic properties could be used to distinguish strain D25(T) from other Myroides species. The main cellular fatty acids of strain D25(T) were iso-C-15:0, iso-C-17:1 omega 9C, iso-C(17:0)3-OH and Summed Feature 3 (comprising C-16:1 omega 7c and/or iso-C(15:0)2-OH). The major respiratory quinone was MK-6. The DNA G+C content was 33.0 mol%. The results of the polyphasic taxonomy analysis suggested that strain D251(T) represents a novel species of the genus Myroides, for which the name Myroides profundi sp. nov. is proposed. The type strain is D25(T) (=CCTCC M 208030(T) = DSM 19823(T)).

XoxF encoding an alternative methanol dehydrogenase is widespread in coastal marine environments

The xoxF gene, encoding a pyrroloquinoline quinone-dependent methanol dehydrogenase, is found in all known proteobacterial methylotrophs. In several newly discovered methylotrophs, XoxF is the active methanol dehydrogenase, catalysing the oxidation of methanol to formaldehyde. Apart from that, its potential role in methylotrophy and carbon cycling is unknown. So far, the diversity of xoxF in the environment has received little attention. We designed PCR primer sets targeting clades of the xoxF gene, and used 454 pyrosequencing of PCR amplicons obtained from DNA of four coastal marine environments for a unique assessment of the diversity of xoxF in these habitats. Phylogenetic analysis of the data obtained revealed a high diversity of xoxF genes from two of the investigated clades, and substantial differences in sequence composition between environments. Sequences were classified as being related to a wide range of both methylotrophs and non-methylotrophs from Alpha-, Beta- and Gammaproteobacteria. The most prominent sequences detected were related to the family Rhodobacteraceae, the genus Methylotenera and the OM43 clade of Methylophilales, and are thus related to organisms that employ XoxF for methanol oxidation. Furthermore, our analyses revealed a high degree of so far undescribed sequences, suggesting a high number of unknown species in these habitats.

The use of Raman microscopy to determine and localize vitamin E in biological samples

Alpha-tocopherol (aT), the predominant form of vitamin E in mammals, is thought to prevent oxidation of polyunsaturated fatty acids. In the lung, aT is perceived to be accumulated in alveolar type II cells and secreted together with surfactant into the epithelial lining fluid. Conventionally, determination of aT and related compounds requires extraction with organic solvents. This study describes a new method to determine and image the distribution of aT and related compounds within cells and tissue sections using the light-scattering technique of Raman microscopy to enable high spatial as well as spectral resolution. This study compared the nondestructive analysis by Raman microscopy of vitamin E, in particular aT, in biological samples with data obtained using conventional HPLC analysis. Raman spectra were acquired at spatial resolutions of 2-0.8 microm. Multivariate analysis techniques were used for analyses and construction of corresponding maps showing the distribution of aT, alpha-tocopherol quinone (aTQ), and other constituents (hemes, proteins, DNA, and surfactant lipids). A combination of images enabled identification of colocalized constituents (heme/aTQ and aT/surfactant lipids). Our data demonstrate the ability of Raman microscopy to discriminate between different tocopherols and oxidation products in biological specimens without sample destruction. By enabling the visualization of lipid-protein interactions, Raman microscopy offers a novel method of investigating biological characterization of lipid-soluble compounds, including those that may be embedded in biological membranes such as aT.

H+/2e- stoichiometry of the NADH : ubiquinone reductase reaction catalyzed by submitochondrial particles

Nitochondrial NADH:ubiquinone-reductase (Complex I) catalyzes proton translocation into inside-out submitochondrial particles. Here we describe a method for determining the stoichiometric ratio (H) over right arrow (+)/2e(-) (n) for the coupled reaction of NADH oxidation by the quinone accepters. Comparison of the initial rates of NADH oxidation and alkalinization of the surrounding medium after addition of small amounts of NADH to coupled particles in the presence of Q(1) gives the value of n = 4. Thermally induced deactivation of Complex I [1, 2] results in complete inhibition of the NADH oxidase reaction but only partial inhibition of the NADH:Q(1)-reductase reaction. N-Ethylmaleimide (NEM) prevents reactivation and thus completely blocks the thermally deactivated enzyme. The residual NADH:Q(1)-reductase activity of the deactivated, NEM-treated enzyme is shown to be coupled with the transmembraneous proton translocation (n = 4). Thus, thermally induced deactivation of Complex 1 as well as specific inhibitors of the endogenous ubiquinone reduction (rotenone, piericidin A) do not inhibit the proton translocating activity of the enzyme.

The electrochemical oxidation of catechol and dopamine on platinum in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) and 1-Butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF4]): Adsorption effects in ionic liquid voltammetry

The electrochemical oxidation of catechol and dopamine has been studied at a platinum micro-electrode (10 pm diameter) in two room temperature ionic liquids (RTILs): 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) and 1-Butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BE4]). For catechol in [C(2)mim][NTf2], an electrochemically quasi-reversible oxidation peak was observed at 1.1 V vs. Pt with a back peak at 0.4 V vs. Pt. This is assigned to the two-electron oxidation of catechol to doubly protonated o-benzoquinone. Double-step chronoamperometry gave a diffusion coefficient for the catechol and the oxidised species which is 3.8 x 10(-11) m(2) s(-1) for both. For catechol in [C(4)mim][BF4], a two-electron oxidation wave was observed at 1.0 V vs. Pt with no back peak. Another peak at less positive potential was also observed at 0.6 V vs. Pt in [C(4)mim][BF4] but not in [C(2)mim][NTf2] which is assigned to the adsorption of electrochemically formed neutral o-benzoquinone on the platinum electrode. The oxidised protonated o-benzoquinone is suggested to be deprotonated by the [BF4](-) anion, but not by the [NTf2](-) anion: hence adsorption of the neutral species at the platinum electrode, not the charged species. For dopamine in both RTILs, two chemically irreversible oxidation peaks were observed at 0.75 V and 1.1 V vs. Pt, and assigned to the oxidation of dopamine to the corresponding semi-quinone and the quinone. Potential-step chronoamperometry was carried out on the oxidation waves of dopamine in [C(2)mim][NTf2] and the diffusion coefficient of species in solution was calculated to be 6.85 x 10(-12) m(2) s(-1) and confirmed that the waves corresponded to one and two electron processes. A third wave was observed at 1.8 V vs. Pt which is attributed to the oxidation of the amine group to a radical cation with likely subsequent follow up chemistry. In [C(4)mim][BF4] a peak at less positive potential was observed for dopamine, similar to catechol which is assigned to the adsorption of the neutral quinone species on the platinum electrode formed by the reaction of the removal of protons from the oxidised dopamine with the [BF4](-) anion. (C) 2009 Elsevier B.V. All rights reserved.

β-Lapachone alleviates alcoholic fatty liver disease in rats

Alcohol-induced liver injury is the most common liver disease in which fatty acid metabolism is altered. It is thought that altered NAD+/NADH redox potential by alcohol in the liver causes fatty liver by inhibiting fatty acid oxidation and the activity of tricarboxylic acid cycle reactions. β-Lapachone (βL), a naturally occurring quinone, has been shown to stimulate fatty acid oxidation in an obese mouse model by activating adenosine monophosphate-activated protein kinase (AMPK). In this report, we clearly show that βL reduced alcohol-induced hepatic steatosis and induced fatty acid oxidizing capacity in ethanol-fed rats. βL treatment markedly decreased hepatic lipids while serum levels of lipids and lipoproteins were increased in rats fed ethanol-containing liquid diets with βL administration. Furthermore, inhibition of lipolysis, enhancement of lipid mobilization to mitochondria and upregulation of mitochondrial β-oxidation activity in the soleus muscle were observed in ethanol/βL-treated animals compared to the ethanol-fed rats. In addition, the activity of alcohol dehydrogenase, but not aldehyde dehydrogenase, was significantly increased in rats fed βL diets. βL-mediated modulation of NAD+/NADH ratio led to the activation of AMPK signaling in these animals. Conclusion: Our results suggest that improvement of fatty liver by βL administration is mediated by the upregulation of apoB100 synthesis and lipid mobilization from the liver as well as the direct involvement of βL on NAD+/NADH ratio changes, resulting in the activation of AMPK signaling and PPARα-mediated β-oxidation. Therefore, βL-mediated alteration of NAD+/NADH redox potential may be of potential therapeutic benefit in the clinical setting.

ND3, ND1 and 39 kDa subunits are more exposed in the de-active form of bovine mitochondrial complex I

An intriguing feature of mitochondrial complex I from several species is the so-called A/D transition, whereby the idle enzyme spontaneously converts from the active (A) form to the de-active (D) form. The A/D transition plays an important role in tissue response to the lack of oxygen and hypoxic deactivation of the enzyme is one of the key regulatory events that occur in mitochondria during ischaemia. We demonstrate for the first time that the A/D conformational change of complex I does not affect the macromolecular organisation of supercomplexes in vitro as revealed by two types of native electrophoresis. Cysteine 39 of the mitochondrially-encoded ND3 subunit is known to become exposed upon de-activation. Here we show that even if complex I is a constituent of the I + III + IV (S) supercomplex, cysteine 39 is accessible for chemical modification in only the D-form. Using lysine-specific fluorescent labelling and a DIGE-like approach we further identified two new subunits involved in structural rearrangements during the A/D transition: ND1 (MT-ND1) and 39 kDa (NDUFA9). These results clearly show that structural rearrangements during de-activation of complex I include several subunits located at the junction between hydrophilic and hydrophobic domains, in the region of the quinone binding site. De-activation of mitochondrial complex I results in concerted structural rearrangement of membrane subunits which leads to the disruption of the sealed quinone chamber required for catalytic turnover.

Characterisation of the active/de-active transition of mitochondrial complex I

Oxidation of NADH in the mitochondrial matrix of aerobic cells is catalysed by mitochondrial complex I. The regulation of this mitochondrial enzyme is not completely understood. An interesting characteristic of complex I from some organisms is the ability to adopt two distinct states: the so-called catalytically active (A) and the de-active, dormant state (D). The A-form in situ can undergo de-activation when the activity of the respiratory chain is limited (i.e. in the absence of oxygen). The mechanisms and driving force behind the A/D transition of the enzyme are currently unknown, but several subunits are most likely involved in the conformational rearrangements: the accessory subunit 39 kDa (NDUFA9) and the mitochondrially encoded subunits, ND3 and ND1. These three subunits are located in the region of the quinone binding site. The A/D transition could represent an intrinsic mechanism which provides a fast response of the mitochondrial respiratory chain to oxygen deprivation. The physiological role of the accumulation of the D-form in anoxia is most probably to protect mitochondria from ROS generation due to the rapid burst of respiration following reoxygenation. The de-activation rate varies in different tissues and can be modulated by the temperature, the presence of free fatty acids and divalent cations, the NAD/NADH ratio in the matrix, the presence of nitric oxide and oxygen availability. Cysteine-39 of the ND3 subunit, exposed in the D-form, is susceptible to covalent modification by nitrosothiols, ROS and RNS. The D-form in situ could react with natural effectors in mitochondria or with pharmacological agents. Therefore the modulation of the re-activation rate of complex I could be a way to ameliorate the ischaemia/reperfusion damage. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference. Guest Editors: Manuela Pereira and Miguel Teixeira.