Electro catalytic generation of reactive species at diamond electrodes and applications in microbial inactivation

Use of robust and safe water disinfection technologies which are inexpensive and energy-efficient are need of the hour to combat the problem of inadequate access of safe and clean drinking water. Energy and chemically intensive water treatment technologies warrant the need for a safe and environmentally sound treatment technology. Electrochemical disinfection or electrodisinfection (ED) is experiencing a great resurgence among the scientific communities owing to its novel use of electrode materials and electric current in an inexpensive and energy-efficient way for achieving the inactivation of microorganisms. Among the various electrodes used in the ED, boron-doped diamonds emerge as a sustainable alternate for their ability to electro generate strong potent oxidants which result in effective pathogen control in drinking water. ED for disinfecting waters occurs via generation of the reactive species which act in the bacterial inactivation mechanisms. In this mini-review, a critical discussion on the fundamentals and applications of promising electrochemical methods using boron-doped diamond anodes (namely electrochemical oxidation), evidencing their advantages for the remediation of drinking water infected with waterborne agents, is given.     

PbO2阳极在硫酸溶液中的析氧失活行为

采用热分解鄄电镀法制备了以Sb 掺杂SnO₂(Sb-SnO₂)为底层的Ti 基PbO₂阳极(Ti/PbO₂). 采用加速电解寿命测试、电化学阻抗谱、XRD、SEM-EDX 等技术, 研究了Ti/PbO₂阳极在硫酸溶液中的电解失效行为和机制.结果表明,在新制备的PbO₂镀层中, 由于氧空位的存在, PbO₂镀层的内应力表现为拉应力, 随着电解的进行, 阳极表面生成的活性氧原子在向基底扩散的过程中, 将Pb³⁺态氧化为Pb⁴⁺态, 逐渐占据镀层内作为自由电子施主的氧空位, 这不仅导致镀层的导电性能下降, 同时使镀层的应力逐渐由拉应力转变为压应力, 镀层性质逐渐劣化. 这一过程基本结束时,活性氧原子才大量扩散至Ti基底导致基底的钝化, 在Ti 基底和镀层界面出现显著的界面应力, 在界面应力和镀层内压应力的共同作用下, 阳极出现鼓泡、脱落, 迅速进入失活阶段.     

Inactivation of Escherichia coli and properties of medical poly(vinyl chloride) in remote-oxygen plasma

This paper reports the germicidal effect (GE) of Escherichia coli on the surface of medical poly(vinyl chloride) (PVC) in remote-oxygen plasma. The concentration of active species in plasma is determined by means of double Langmuir electron probe and electron-spin resonance (ESR) diagnosis. Moreover, surface properties of sterilized PVC are characterized by the water contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The distribution of electrons, ions, and radicals in plasma reactor is different. High-purity radicals are obtained at 40 cm from the induction coil which is called remote-plasma zone. By remote-oxygen-plasma sterilization, GE value reach 4.12 under the conditions of treatment time of 60 s, plasma RF power of 100 W and oxygen flux of 60 cm³/min. Compared with direct-oxygen-plasma sterilization, remote plasma can enhance the hydrophilic property and limit the degradation of the PVC surface. After remote-plasma sterilization, PVC surface energy is increased more than twice, which mainly resulted from the increase of surface polar force , and hydrogen bonding force . Moreover, remote-plasma sterilization can increase oxygenated functional groups on PVC surface. Experimental results show that remote plasma can inactivate E. coli on the medical PVC substrate effectively. Furthermore, it can optimize the surface properties.     

改性血红蛋白诱导手性聚苯胺的合成

The synthesis of chiral polyaniline (PANI) induced by modified hemoglobin (Hb) was profoundly explored for the first time. Results revealed that after being separated, inactivated or immobilized, Hb can still induce the formation of chiral PANI successfully, suggesting that Hb can be used as the chiral inducers regardless of harsh reaction conditions. By examining the properties of PANI induced by modified Hb, it was found that Hb(inactivated)-PANI possessed excellent chirality, stability, and crystalline structure. The globin separated from Hb was demonstrated to have the ability of inducing the production of chiral PANI whereas the hematin from Hb had no capacity to direct enantio specificity for the PANI chains. Results indicated that Hb(immobilized)-PANI exhibited poor yield, doping state, and crystalline structure, indicating that the immobilization of Hb by entrapment was not bene cial to the polymerization reaction. Results also showed that the structure of Hb may have significant effects on the morphologies of chiral PANI.     

Ultrasound-enhanced interfacial adsorption and inactivation of soy trypsin inhibitors

In this study, liquid–liquid interfacial protein adsorption was proposed as a means of inactivating soy trypsin inhibitors (TIs, including Kunitz (KTI) and Bowman-Birk inhibitor (BBI)). Hexane-water was first selected as a model system to compare three emulsification methods (hand shaking, rotor–stator and ultrasound mixing). Ultrasound could generate the smallest and least polydisperse emulsion droplets, resulting in highest interfacial adsorption amount of KTI and BBI as well as the highest inactivation percentage of TIs (p < 0.05). Therefore, ultrasound was selected to further explore the effect of the non-aqueous phase on interfacial adsorption and inactivation kinetics of TIs in a food emulsion system containing vegetable oil (VTO). The adsorption amounts of KTI and BBI in the VTO-aqueous emulsion increased by ∼ 25 % compared to the hexane-aqueous emulsion. In addition, the adsorption amounts of KTI and BBI were rapidly increased as a function of sonication time, especially for the hexane-aqueous emulsion system. This result suggests that such inactivation of TIs could be implemented in continuous systems for large-scale processing. Finally, the pathways of interface-induced inactivation of BBI and KTI were investigated based on separate experiments on individual BBI and KTI systems. The results showed that the interface adsorption caused the changes in the secondary and tertiary structure of KTI that led to its activitation. However, BBI was quite stable at the liquid–liquid interface without significant conformational change. Overall, ultrasound-assisted interfacial adsorption can be considered a rapid and highly efficient method to inactivate KTI.     

Indirect plasma inactivation by a low temperature atmospheric pressure plasma (LTAPP) system

The aim of this paper is to evaluate the inactivation effect of indirect low temperature plasma exposure at atmospheric pressure produced by the original Low Temperature Atmospheric Pressure Plasma (LTAPP) system. In this system, the low temperature plasma is generated using a high voltage power supply in oxygen at atmospheric pressure. The obtained survivor curves for Escherichia coli (G⁻), Bacillus subtilis (G⁺), Staphylococcus aureus (G⁺), Candida albicans (Yeast), and Saccharomyces cerevisiae (Yeast) showed that the LTAPP system could inactivate them. The optical microscope images of B. subtilis and S. cerevisiae treated have confirmed the inactivation effect of the LTAPP system.     

Pressure inactivation of microorganisms

Abstract

The kinetics of inactivation by hydrostatic pressure is measured for Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, bacteriophage T4, and the spores of Bacillus subtilis. Temperature and pressure effects are discussed as well as the interrelation between germination and inactivation in the case of bacterial spores.     

Effects of flat sweep frequency and pulsed ultrasound on the activity,conformation and microstructure of mushroom polyphenol oxidase

The effects of thermal processing (TP) and flat sweep frequency and pulsed ultrasound (FSFPU) treatment with different frequency modes on the activity, conformation and physicochemical properties of mushroom polyphenol oxidase (PPO) were investigated. The results showed that the relative enzymatic activity of PPO gradually decreased with increasing temperature and duration, and thermosonication decreased the PPO activity to a greater extent compared with thermal processing. FSFPU treatment with dual-frequency of 22/40 kHz mode showed the most significant effect. Circular dichroism (CD) showed that the content of α-helix and β-turn dropped, while that of β-sheet and random coil raised after FSFPU treatment. The intensity of endogenous fluorescence decreased, indicating that PPO protein unfolded and the tertiary structure was destroyed. The amount of free sulfhydryl, protein aggregation index, and turbidity all rose. Moreover, FSFPU treatment led to the aggregation of protein from the analysis of atomic force microscope (AFM). Conclusively, FSFPU can be used as an effective method to inhibit the activity of endogenous enzymes in food.     

Small-angle X-ray scattering studies on the X-ray induced aggregation of malate synthase II. Inactivation and aggregation experiments

The X-ray induced inactivation and aggregation of the enzyme malate synthase in aqueous solution were investigated by small-angle X-ray scattering and enzymic tests.Enzymic activity decreases about exponentially with increasing dose. The rate of inactivation depends linearly on the dose rate; the extrapolation to zero dose rate yielded a finite limiting value of the rate constant of inactivation. The inactivation doseD ₃₇ is a linear function of enzyme concentration.Enzymic tests and small-angle X-ray scattering on samples, which had been X-irradiated before the measurements, showed no direct relation between aggregation and inactivation. The substrates glyoxylate and acetyl-CoA and the substrate analogue pyruvate are able to protect the enzyme against radiation damage, however to a different extent against aggregation (pyruvate > glyoxylate > acetyl-CoA) or inactivation (glyoxylate > pyruvate acetyl-CoA; the latter showed no effect). These findings and the protective effect of dithiothreitol against aggregation and inactivation of the enzyme are discussed in context with the formation of hydrogen peroxide. A possible shielding of radiosensitive groups of the enzyme by the substrates and scavenging are also taken into consideration as explanations for the protective effects.While the novel application of small-angle X-ray scattering in the field of radiation biology delivers information on X-ray induced structural changes of biopolymers and on their kinetics, the occurrence of radiation damages in conventional small-angle X-ray scattering measurements on biopolymers can be reduced by a variety of precautions.

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Röntgenkleinwinkeluntersuchungen der durch Röntgenstrahlen induzierten Aggregation der Malatsynthase. II. Inaktivierungs- und Aggregationsexperimente

Zusammenfassung Die durch Röntgenbestrahlung in wäßriger Lösung induzierte Inaktivierung und Aggregation des Enzyms Malatsynthase wurden mit der Methode der Röntgenkleinwinkelstreuung und mit Enzymtests untersucht.Die Enzymaktivität nimmt mit zunehmender Dosis annähernd exponentiell ab. Die Inaktivierungsgeschwindigkeit hängt linear von der Dosisleistung ab; die Extrapolation auf Dosisleistung null ergab einen endlichen Grenzwert der Inaktivierungsgeschwindigkeitskonstante. Die InaktivierungsdosisD ₃₇ ist eine lineare Funktion der Enzymkonzentration.Enzymtests und Röntgenkleinwinkelstreuexperimente an Proben, welche vorher bereits bestrahlt worden waren, zeigten keinen direkten Zusammenhang zwischen Aggregation und Inaktivierung. Die Substrate Glyoxylat und Acetyl-CoA sowie das Substratanaloge Pyruvat vermögen das Enzym gegen Strahlenschäden zu schützen, jedoch in unterschiedlichem Ausmß gegen Aggregation (Pyruvat > Glyoxylat > Acetyl-CoA) oder Inaktivierung (Glyoxylat > Pyruvat Acetyl-CoA; letzteres zeigte keinen Effekt). Diese Befunde und die Schutzwirkung von Dithiothreitol gegen die Aggregation und Inaktivierung des Enzyms werden in Zusammenhang mit der Bildung von Wasserstoffperoxid diskutiert. Als weitere Erklärungen für die Schutzwirkungen werden die mögliche Abschirmung strahlenempfindlicher Gruppen des Enzyms durch die Substrate und der Einfang von Radikalen in Erwägung gezogen.Während die neuartige Anwendung der Röntgenkleinwinkelstreuung auf dem Gebiet der Radiobiologie Aufschluß über strahleninduzierte Strukturänderungen von Biopolymeren und deren Kinetik gibt, läßt sich das Auftreten von Strahlenschäden bei konventionellen Röntgenkleinwinkelmessungen an Biopolymeren durch verschiedene Vorkehrungen reduzieren.