Direct and Indirect Bactericidal Effects of Cold Atmospheric-Pressure Microplasma and Plasma Jet

The direct and indirect bactericidal effects of dielectric barrier discharge (DBD) cold atmospheric-pressure microplasma in an air and plasma jet generated in an argon-oxygen gas mixture was investigated on Staphylococcus aureus and Cutibacterium acnes. An AC power supply was used to generate plasma at relatively low discharge voltages (0.9–2.4 kV) and frequency (27–30 kHz). Cultured bacteria were cultivated at a serial dilution of 10⁻⁵, then exposed to direct microplasma treatment and indirect treatment through plasma-activated water (PAW). The obtained results revealed that these methods of bacterial inactivation showed a 2 and 1 log reduction in the number of survived CFU/mL with direct treatment being the most effective means of treatment at just 3 min using air. UV–Vis spectroscopy confirmed that an increase in treatment time at 1.2% O₂, 98.8% Ar caused a decrease in O₂ concentration in the water as well as a decrease in absorbance of the peaks at 210 nm, which are attributed NO₂⁻ and NO₃⁻ concentration in the water, termed denitratification and denitritification in the treated water, respectively.     

Molecular Species Generated by Surface Dielectric Barrier Discharge Micro-plasma in Small Chambers Enclosing Atmospheric Air and Water Samples

In many applications of the atmospheric pressure plasmas, the plasma is generated in chambers that enclose samples to be treated. In the case of plasma treatments of water or water-containing materials, the humidity in gaseous medium rises during the treatment, and this affects considerably the plasma generation of reactive oxygen and nitrogen species (RONS). In this study, Fourier transform infrared absorption spectroscopy is used to investigate the kinetics of reactive species generated by surface dielectric barrier (SDBD) micro-plasma in a small volume of atmospheric air (0.5 L) enclosed in a discharge chamber. The investigations were made for dry air (in absence of liquid water) and for humid air in presence of liquid water. The SDBD plasma contributes to desorption of water from the inner wall of the discharge chamber and enhances evaporation of liquid water, which increases air humidity and decreases the generation rates of reactive species. Kinetics of RONS generated in small samples of liquid water in contact with discharge medium is investigated by ex situ UV absorption spectroscopy measurements of plasma treated water.

     

Stable Subporphyrin meso-Aminyl Radicals without Resonance Stabilization by a Neighboring Heteroatom

Most aminyl radicals studied so far are resonance-stabilized by neighboring heteroatoms, and those without such stabilization are usually short-lived. We report herein that subporphyrin meso-2,4,6-trichlorophenylaminyl radicals and a bis(5-subporphyrinyl)aminyl radical are fairly stable under ambient conditions without such stabilization. The subporphyrin meso-2,4,6-trichlorophenylaminyl radical crystal structure displays a characteristically short C_meso−N bond and a perpendicular arrangement of the meso-arylamino group. The stabilities of these radicals have been ascribed to extensive spin delocalization over the subporphyrin π-electronic network as well as steric protection around the aminyl radical center.     

Studies on the conformation of a polyelectrolyte in solution: local conformation of cucumber green mottle mosaic virus RNA compared with tobacco mosaic virus RNA

The thermal stability of the local structures of cucumber green mottle mosaic virus RNA, CGMMV-RNA, and tobacco mosaic virus RNA, TMV-RNA, was studied by circular dichroism (CD) and small-angle X-ray scattering (SAXS) and compared with each other in the temperature domain from 20 to 50 degrees C. The temperature dependence of the molar ellipticity and mean-square radius of the cross section of a chain shows that the structure of CGMMV-RNA is more vulnerable than that of TMV-RNA. Such a different thermal stability of their structures was also reflected in the temperature dependence of the length and number of the constituent rods when the structures of the two RNA chains were represented by a model which consisted of rods joined with freely hinged joints. From these results, a possibility was suggested that the structural stability of CGMMV-RNA and TMV-RNA might be correlated with the infectivity of the corresponding virus, CGMMV and TMV, respectively.     

<Emphasis Type="Italic">S,S,S</Emphasis>-Tris(2-ethylhexyl) phosphorotrithioate as an effective solvent mediator for a mexiletine-sensitive membrane electrode

S,S,S-Tris(2-ethylhexyl) phosphorotrithioate proved to be an effective solvent mediator for constructing a mexiletine-sensitive membrane electrode in combination with an ion-exchanger, sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate. Among a series of phosphorus compounds containing phosphoryl (P=O) groups, this solvent mediator showed the highest sensitivity to mexiletine in phosphate-buffered physiological saline containing 0.15 mol L⁻¹ NaCl and 0.01 mol L⁻¹ NaH₂PO₄/Na₂HPO₄ (pH 7.4), giving a detection limit of 2 × 10⁻⁶ mol L⁻¹ with a slope of 58.8 mV decade⁻¹. This is the best reported detection limit of any mexiletine-sensitive electrode developed to date. Owing to its high selectivity toward inorganic cations, the electrode was used to determine the level of mexiletine in saliva, the monitoring of which is quite effective for controlling the dose of this drug noninvasively. The mexiletine concentrations determined with the mexiletine-sensitive electrode compared favorably with those determined by high-performance liquid chromatography.     

Inactivation of Escherichia coli by sonoelectrocatalytic disinfection using TiO2 as electrode

This is the first study to demonstrate sonoelectrocatalytic disinfection using titanium dioxide (TiO₂) as an anode for effective inactivation of Escherichia coli. In brief, a non-woven TiO₂ fabric used as an anode and a platinum cathode were immersed in an E. coli suspension in which a positive potential was applied to TiO₂ concomitant with ultrasound (US) irradiation. Two control experiments were performed using E. coli suspensions to exhibit the effects of the sonoelectrocatalytic disinfection. One was disinfection by applying a positive potential to a TiO₂ electrode, but without US irradiation (electrochemical disinfection). The other was disinfection without applying a potential, but with US irradiation in the presence of TiO₂ (sonocatalytic disinfection). The cell inactivation rate in sonoelectrocatalytic disinfection was synergistically much more enhanced than the combined inactivation rates in electrochemical disinfection and sonocatalytic disinfection. This synergistically enhanced inactivation rate of E. coli cells was attributable to effective reaction of the sonocatalytically generated OH radicals with E. coli cells at the surface of the TiO₂ anode, which resulted from the electroadsorption of E. coli cells toward the TiO₂ anode.     

Combined two-dimensional velocity and temperature measurements of natural convection using a high-speed camera and temperature-sensitive particles

This paper proposes a combined method for two-dimensional temperature and velocity measurements in liquid and gas flows using temperature-sensitive particles (TSPs), a pulsed ultraviolet laser, and a high-speed camera. TSPs respond to temperature changes in the flow and can also serve as tracers for the velocity field. The luminescence from the TSPs was recorded at 15,000 frames per second as sequential images for a lifetime-based temperature analysis. These images were also used for the particle image velocimetry calculations. The temperature field was estimated using several images, based on the lifetime method. The decay curves for various temperature conditions fit well to exponential functions, and from these the decay constants at each temperature were obtained. The proposed technique was applied to measure the temperature and velocity fields in natural convection driven by a Marangoni force and buoyancy in a rectangular tank. The accuracy of the temperature measurement of the proposed technique was ±0.35–0.40°C.