Severe inhibition of maize wall degradation by synthetic lignins formed with coniferaldehyde

Although the enzymatic or ruminal degradability of plants deficient in cinnamyl alcohol dehydrogenase (CAD) is often greater than their normal counterparts, factors responsible for these degradability differences have not been identified. Since lignins in CAD deficient plants often contain elevated concentrations of aldehydes, we used a cell-wall model system to evaluate what effect aldehyde-containing lignins have on the hydrolysis of cell walls by fungal enzymes. Varying ratios of coniferaldehyde and coniferyl alcohol were polymerised into non-lignified primary walls of maize (Zea mays L) by wall-bound peroxidase and exogenously supplied H₂O₂. Coniferaldehyde lignins formed fewer cross-linked structures with other wall components, but they were much more inhibitory to cell wall degradation than lignins formed with coniferyl alcohol. This suggests that the improved degradability of CAD deficient plants is not related to the incorporation of p-hydroxycinnamaldehyde units into lignin. Degradability differences were diminished if enzyme loadings were increased and if hydrophobic aldehyde groups in lignins were reduced to their corresponding alcohols by ethanolic sodium borohydride. © 1998 Society of Chemical Industry.     

Study and quantification of monomeric flavan‐3‐ol and dimeric procyanidin quinonic forms by HPLC/ESI‐MS. Application to red wine oxidation

Monomeric flavan‐3‐ols and dimeric procyanidins of red wine were oxidised by two processes, chemical and enzymatic. Unstable quinonic forms were stabilised by sulphonation, and the resulting sulphones were quantified by coupled HPLC/ESI‐MS. The effects of temperature and UV light on the oxidation of phenolic compounds were also investigated. The concentration of quinones increased with increasing temperature, but the kinetics of the reaction was independent of temperature. Likewise, more quinones were formed in the presence of UV light than in its absence, but UV light also did not affect the kinetics of the reaction. Thus temperature and UV light affect the quantity of quinones formed but not the rate at which they appear. © 2001 Society of Chemical Industry     

Macrokinetics and mathematical modelling of quinone reduction by cyanobacteria

The kinetics of the reduction of externally added 2-hydroxy-1,4-naphthoquinone by blue-green algae of the strains Anabaena PCC 7120 and Anacystis nidulans PCC 6301 were studied in aqueous cell suspensions by electrochemical monitoring of the concentration of the formed hydroquinone. This reaction is of potential interest for bioelectrochemical fuel cells. The experimental curves obtained could be interpreted by a model that takes into account that both substrate and product have to be transported through the microbial cell walls and that the conversion reaction takes place with firstorder kinetics within the microbial cells. No clear evidence was found for the involvement of photosynthesis. It is suggested that the reduction of the quinone probably occurs via the enzyme-catalyzed oxidation of endogenous storage product(s), presumably glycogen.     

A Versatile Photoinduced Electron Transfer‐Based Upconversion Fluorescent Biosensing Platform for the Detection of Disease Biomarkers and Nerve Agent

Upconversion nanoparticles (UCNPs) have emerged to be a new family of fluorescent probes for bioanalytical applications. In a typical design, the UCNPs act as the energy donors in a fluorescence resonance energy transfer (FRET) system, in which the target molecules mediate the energy transfer from the UCNPs to the acceptors, and their quantity information is consequently converted into the “on‐off” upconverting signals for readout. However, each UCNP contains thousands of emitting center ions and most of them are beyond the FRET critical distance, which hinders the fluorescence energy transfer efficiency, resulting in a low signal‐to‐background ratio (SBR). Herein, a new design is presented in which the energy of UCNPs is transferred to the o‐quinones on their surface via the photoinduced electron transfer (PET) mechanism. In this system, the quenching efficiency of UCNPs' fluorescence can be up to 94.73%, providing a high SBR. The performance of the PET‐based design is systematically testified, and the high‐sensitivity detection of disease biomarkers (tyrosinase and alkaline phosphatase) is demonstrated. Moreover, this UCNP‐PET platform is also capable of sensing the simulant of nerve agent sarin. This work will pave new ways to the design of UCNP‐based platforms toward bioanalytical applications.     

Effects of protein and juglone on gypsy moths: Growth performance and detoxification enzyme activity

The individual and interactive effects of dietary protein and juglone on larval performance and midgut detoxification enxymes were investigated for the gypsy moth,Lymantria dispar. The experimental design was a 2 × 3 factorial, with two levels of protein and three levels of juglone. We monitored survival/development rates from egg hatch to pupation and conducted fourth-instar feeding trials for determination of nutritional indices. Enzyme solutions were prepared from midguts of fifth instars and assayed for polysubstrate monooxygenase, esterase, quinone reductase, and glutathione transferase activities. Results showed that low protein levels prolonged development times, increased consumption rates, and reduced pupal weights. Juglone markedly reduced survival, growth, and consumption rates, increased development times, and reduced pupal weights. The interaction between protein and juglone influenced larval digestion efficiencies and female pupal weights. Polysubstrate monooxygenase activities were unaffected by diet, whereas esterase activities increased in response to both low dietary protein and presence of juglone. Low protein levels increased soluble quinone reductase activities but decreased glutathione transferase activities. Glutathione transferase activities were lowest in larvae fed low-protein, high-juglone diets and may have contributed to the especially poor performance of larvae on those diets. Quinone reductase and glutathione transferase are the systems of importance in detoxification of juglone, and moderate to low activities of these enzymes may explain why gypsy moths perform poorly on members of the Juglandaceae.     

High‐Performance Mesostructured Organic Hybrid Pseudocapacitor Electrodes

The electrodes of a hybrid electrochemical capacitor which utilize the quinone (Q)‐hydroquinone (QH₂) couple, a prototypical organic redox system known to provide fast and reversible proton‐coupled electron‐transfer reactions, are deterministically mesostructured via a colloidal templating strategy to provide good ion and electron transport pathways, enabling a high rate performance. Specifically, a conducting polymer, polypyrrole (PPy), is functionalized with a pseudocapacitive material, a Q/QH₂‐containing catechol derivative, by noncovalent interactions. The mesostructure of this hybrid material is formed into an ordered 3D porous structure by a polystyrene colloidal crystal template‐assisted electrosynthesis. The catechol derivative is sufficiently bound to the PPy through noncovalent interactions to provide a volumetric capacitance as high as ≈130 F cm^?3 and a capacitance retention of ≈75% over 10 000 charging/discharging cycles. When compared with a randomly structured electrode, the deterministically structured electrode exhibits an improved rate performance due to the mesostructure facilitated electron and ion transport.     

Application of polyethyleneimine-quinone modified electrodes for voltammetric measurements of pH

A modified polymer, ie benzylated polyethyleneimine (PEI), coated on a glassy carbon electrode in which negatively charged quinones have been incorporated, has been used for voltammetric measurement of pH. A linear dependence of the average of the peak potentials as a function of pH was observed. The system has been successfully applied also to ultramicroelectrodes.     

Chemistry on the decay of the phenoxy radical from butylated hydroxytoluene

Decay of unstable 2,6-di-tert-butyl-4-methylphenoxy radical (2) was investigated in various solvents. Radical 2 was conveniently generated by dissociation of bis(methylcyclohexadienone) (1a), unstable dimer of 2, in solution. The products were butylated hydroxytoluene (3), 1,2-bis(4-hydroxyphenyl)ethane (7), 4,4′-stilbenequinone (8), and 4-(4-hydroxybenzyl)cyclohexadienone (5). Unidentified products also were formed. The formation of 5 was favored in polar solvents, but was not subject to catalysis with Et₃N or HCl. In contrast, the rates of formation of 7 and 8 appeared to be independent of solvent polarity. The mechanism of formation of the dimeric productsvia reactive intermediate quinone methide 4, generated from 2 by disproportionation, is discussed. Gradual disintegration of 5 in solution into 3 and 4 was investigated.     

Central Carbon Metabolism,Sodium-Motive Electron Transfer,and Ammonium Formation by the Vaginal Pathogen Prevotella bivia

Replacement of the Lactobacillus dominated vaginal microbiome by a mixed bacterial population including Prevotella bivia is associated with bacterial vaginosis (BV). To understand the impact of P. bivia on this microbiome, its growth requirements and mode of energy production were studied. Anoxic growth with glucose depended on CO₂ and resulted in succinate formation, indicating phosphoenolpyruvate carboxylation and fumarate reduction as critical steps. The reductive branch of fermentation relied on two highly active, membrane-bound enzymes, namely the quinol:fumarate reductase (QFR) and Na⁺-translocating NADH:quinone oxidoreductase (NQR). Both enzymes were characterized by activity measurements, in-gel fluorography, and VIS difference spectroscopy, and the Na⁺-dependent build-up of a transmembrane voltage was demonstrated. NQR is a potential drug target for BV treatment since it is neither found in humans nor in Lactobacillus. In P. bivia, the highly active enzymes L-asparaginase and aspartate ammonia lyase catalyze the conversion of asparagine to the electron acceptor fumarate. However, the by-product ammonium is highly toxic. It has been proposed that P. bivia depends on ammonium-utilizing Gardnerella vaginalis, another typical pathogen associated with BV, and provides key nutrients to it. The product pattern of P. bivia growing on glucose in the presence of mixed amino acids substantiates this notion.     

变形假单胞菌吡咯喹啉醌合成基因簇的克隆与分析

从变形假单胞菌JUIM01中克隆到吡咯喹啉醌(PQQ)合成基因簇,阐明了其基因组成和生物学信息。根据已报道的假单胞菌的基因组进行简并引物设计,采用LA-PCR技术克隆变形假单胞菌的PQQ合成基因簇,对克隆的基因片段进行测序并使用生物信息学方法进行综合分析。结果表明:克隆到的基因片段全长为11 659 bp,其中包括pqqF、pqqA、pqqB、pqqC、pqqD、pqqE、pqqM、pqqH和pqqI共9个基因,编码PQQ生物合成的前体短肽PqqA和合成途径的相关酶;这些基因与荧光假单胞菌Pf0-1的PQQ合成基因簇的基因组成类似,相应基因的序列一致性达41%～94%。本研究中首次从变形假单胞菌中克隆到PQQ合成基因簇,并对其进行生物信息学分析,为变形假单胞菌的PQQ生物合成途径和胞内再生机制的研究奠定了基础,进而为提高2KGA的生产强度提供了理论支撑。