Production of Photons in the Bactericidal Effect of Transient Electric Arcs in Aqueous Systems

The radiation in the visible and ultraviolet regions from submerged, transient electrical arcs was measured with a K(3)Fe(C(2)O(4))(3) chemical actinometer and was compared to the bactericidal effect obtained with the same electrical arrangements. Photon production and bactericidal effect were obtained at lower voltages with a smaller electrode separation than with a wider one. At higher voltages, both increased with wider electrode separations. The voltages at maximal photon production efficiency coincided with those of maximal bactericidal efficiency. However, the same photon radiation produced by different electrical arrangements did not always yield the same bactericidal effect in the small discharge vessel usually employed. In a larger discharge vessel, the bactericidal effect was closely correlated with the photon production. The efficiency of photon production by transient arcs was smaller than that of germicidal mercury lamps, particularly with respect to wavelengths of great bactericidal activity. The mechanisms of inactivation and their use for practical disinfection purposes are discussed.     

Influence of the Conductivity of the Discharge Liquid on the Microbicidal Effect of Transient Electric Arcs in Aqueous Systems

The microbicidal effect of electrical discharges on microorganisms suspended in the discharge liquid was reduced when the liquid contained high concentrations of inorganic salts (conductivity k >/= 5 mmho/cm). A higher discharge voltage and a smaller distance between the submerged electrodes counteracted this reduction. The decrease in the microbicidal effect was accompanied by a change in the electrical current and by a decreased yield of microbicidal photons from the electric discharge.     

Computer Simulation of Aqueous Biomolecular Systems

Abstract

Computer simulation techniques are increasingly being used to predict structural and thermodynamic properties of large heterogeneous macromolecule and solvent assemblies. We discuss, with examples from our own studies, some problems we and others have experienced in using these techniques, which were originally devised for simple liquids. In particular, we consider the problems which arise from the large size and heterogeneity of macromolecule water systems, comparisons with experimental data and equilibration and sampling procedures.     

Biodegradation of N-Nitrosodimethylamine in Aqueous and Soil Systems

N-Nitrosodimethylamine (NDMA) was mineralized by microorganisms in aqueous and soil systems. Initial rates of mineralization (micrograms per milliliter per day) were calculated for a wide range of initial concentrations of NDMA (micrograms per milliliter to picograms per milliliter). Log-log plots of the data were fitted with both linear and nonlinear least-squares analyses; however, linear models provided better fits for the kinetic data in all cases. The slopes of the linear fits were not significantly different than 1.0 (P < 0.05); thus, first-order reaction kinetics were in effect over the range of concentrations tested, and saturation kinetics were not achieved. Rate constants (day⁻¹) and total percent mineralized increased with decreasing initial concentrations of NDMA. Rates of mineralization were reduced in aqueous systems when supplemental carbon was available, whereas in soils, percentages of organic matter and supplemental carbon had little effect on rates of mineralization. Implications of these results for predictions of rates and threshold limits of mineralization activity in natural systems are discussed. A laboratory scale simulated trickling filter containing an activated charcoal bed provided a suitable environment for mineralization of NDMA at concentrations of 50 and 100 μg/ml on a continuous basis. NDMA was not toxic to natural populations of microorganisms at concentrations up to 10 mg/ml. Using high-pressure liquid chromatography coupled with radioactivity detection, we identified formaldehyde and methylamine as intermediates produced during the biodegradation of NDMA.     

Transient Potentials in Dendritic Systems of Arbitrary Geometry

A simple graphical calculus is developed that generates analytic solutions for membrane potential transforms at any point on the dendritic tree of neurons with arbitrary dendritic geometries, in response to synaptic “current” inputs. Such solutions permit the computation of transients in neurons with arbitrary geometry and may facilitate analysis of the role of dendrites in such cells.     

Some Surface-Active Agents and Their Virucidal Effect on Foot-and-Mouth Disease Virus

Selected cationic and anionic surface-active compounds were tested to determine their virucidal effect on the foot-and-mouth disease virus, type O, strain M11, propagated in primary calf kidney cells. The chemical inactivation of the virus was tested with 0.5, 1.0, 2.0, and 5.0% concentrations of the selected compounds. Virus controls with pH adjusted to cover the expected range of the mixtures of the chemicals and virus were also tested. The absence of virus from the mixtures of chemical and virus after reaction at 28 C for 2 hr was assayed by inoculating suckling mice with the mixtures. One cationic compound, alkyl methyl isoquinilinium chloride, showed considerable antiviral activity due largely to pH effect. The use of the surface-active agents investigated in this study, in the presence of organic material, would not be recommended as virucides.     

Transient Responses to Spatial Perturbations in Advective Systems

We study the transient dynamics, following a spatially-extended perturbation of models describing populations residing in advective media such as streams and rivers. Our analyses emphasize metrics that are independent of initial perturbations—resilience, reactivity, and the amplification envelope—and relate them to component spatial wavelengths of the perturbation using spatial Fourier transforms of the state variables. This approach offers a powerful way of understanding the influence of spatial scale on the initial dynamics of a population following a spatially variable environmental perturbation, an important property in determining the ecological implications of transient dynamics in advective systems. We find that asymptotically stable systems may exhibit transient amplification of perturbations (i.e., have positive reactivity) for some spatial wavelengths and not others. Furthermore, the degree and duration of amplification varies strongly with spatial wavelength. For two single-population models, there is a relationship between transient dynamics and the response length that characterizes the steady state response to spatial perturbations: a long response length implies that peak amplification of perturbations is small and occurs fast. This relationship holds less generally in a specialist consumer-resource model, likely due to the model’s tendency for flow-induced instabilities at an alternative characteristic spatial scale.     

Separation of Fungal Propagules by Partition in Aqueous Polymer Two-Phase Systems

Conidia of Penicillium chrysogenum and Penicillium frequentans and sporangiospores of Rhizopus rhizopodiformis, Rhizomucor pusillus, and Mucor racemosus were subjected to partition in aqueous polymer two-phase systems. The partition behavior differed drastically between the conidia of the two Penicillium species and the sporangiospores of the three species of phycomycetes. This difference in partition behavior can be used for purification of fungi belonging to different taxonomical groups. P. frequentans was completely separated from M. racemosus by two extractions, whereas four extractions were needed to purify M. racemosus. This method was used on an air sample from a locality where wood fuel chips are handled. The conidia of the fungi Trichoderma viride and Rhizopus rhizopodiformis were removed completely by only two extractions.     

Assessment of Virucidal Ability of Chemical Disinfectants

Increasing interest has been shown in studying and testing the virucidal properties of disinfectants. At the moment there are no well-established standard methods available; quite different procedures have been employed. Therefore, there is no satisfactory way of comparing the results obtained in this field. We present some of these problems and propose standard test methods to overcome these difficulties.     

Partitioning of Isolated Pea Leaf Protoplasts in Two-Polymer Aqueous Phase Systems: Feasibility and Effect of Growth Temperature on Partitioning

Protoplasts were enzymatically isolated from leaves of Pisumsativum cv. Meteor grown in environments differing only in temperature:5 °C, 15 °C or 25 °C. Methods are described forpartitioning these protoplasts between the upper phase, interfaceand lower phase of two-polymer aqueous phase systems. The polymerswere dextran T500 and poly (ethylene glycol) 6000. Sorbitolwas used to stabilize the protoplasts osmotically. Partitioningwas independent of the number of protoplasts added to the two-polymeraqueous phases, over the range 0.5 to 1.5 x 10⁶ protoplastsper 40 ml of system. Many protoplasts (above about 70% of thoseadded) accumulated at the interface and often occurred thereas small aggregates. Sufficient individual protoplasts weredispersed in the phases for accurate estimates of partitioningto be determined using numbers of replicates. Polymer contentand ionic composition (e. g. addition of KN0₃) of the systemsaffected partitioning. Protoplasts from plants grown at the different temperatureswere partitioned in systems composed of 6.5% dextran–4.5%PEG, buffered at pH 4.8, 5.8 or 6.8 and containing 0, 10, 50or 100 mM KNO₃. Partitioning was unaffected by pH when protoplastswere taken from plants grown at 15 °C or 25 °C. Growthtemperature affected partitioning in the absence and presenceof KNO₃. The results imply that growth temperature altered thecomposition or structure of the outer surface of the protoplasts,i.e. probably of the plasmalemmza.     

Transient Features in Nanosecond Pulsed Electric Fields Differentially Modulate Mitochondria and Viability

It is hypothesized that high frequency components of nanosecond pulsed electric fields (nsPEFs), determined by transient pulse features, are important for maximizing electric field interactions with intracellular structures. For monopolar square wave pulses, these transient features are determined by the rapid rise and fall of the pulsed electric fields. To determine effects on mitochondria membranes and plasma membranes, N1-S1 hepatocellular carcinoma cells were exposed to single 600 ns pulses with varying electric fields (0–80 kV/cm) and short (15 ns) or long (150 ns) rise and fall times. Plasma membrane effects were evaluated using Fluo-4 to determine calcium influx, the only measurable source of increases in intracellular calcium. Mitochondria membrane effects were evaluated using tetramethylrhodamine ethyl ester (TMRE) to determine mitochondria membrane potentials (ΔΨm). Single pulses with short rise and fall times caused electric field-dependent increases in calcium influx, dissipation of ΔΨm and cell death. Pulses with long rise and fall times exhibited electric field-dependent increases in calcium influx, but diminished effects on dissipation of ΔΨm and viability. Results indicate that high frequency components have significant differential impact on mitochondria membranes, which determines cell death, but lesser variances on plasma membranes, which allows calcium influxes, a primary determinant for dissipation of ΔΨm and cell death.