Two separate mechanisms are involved in membrane permeabilization during lipid oxidation

Lipid oxidation is a universal degradative process of cell membrane lipids that is induced by oxidative stress and reactive oxygen and nitrogen species (RONS) in multiple pathophysiological situations. It has been shown that certain oxidized lipids alter membrane properties, leading to a loss of membrane function. Alteration of membrane properties is thought to depend on the initial membrane lipid composition, such as the number of acyl chain unsaturations. However, it is unclear how oxidative damage is related to biophysical properties of membranes. We therefore set out to quantify lipid oxidation through various analytical methods and determine key biophysical membrane parameters using model membranes containing lipids with different degrees of lipid unsaturation. As source for RONS, we used cold plasma, which is currently developed as treatment for infections and cancer. Our data revealed complex lipid oxidation that can lead to two main permeabilization mechanisms. The first one appears upon direct contact of membranes with RONS and depends on the formation of truncated oxidized phospholipids. These lipids seem to be partly released from the bilayer, implying that they are likely to interact with other membranes and potentially act as signaling molecules. This mechanism is independent of lipid unsaturation, does not rely on large variations in lipid packing, and is most probably mediated via short-living RONS. The second mechanism takes over after longer incubation periods and probably depends on the continued formation of lipid oxygen adducts such as lipid hydroperoxides or ketones. This mechanism depends on lipid unsaturation and involves large variations in lipid packing. This study indicates that polyunsaturated lipids, which are present in mammalian membranes rather than in bacteria, do not sensitize membranes to instant permeabilization by RONS but could promote long-term damage.</p

Synergistic effects of oxidative and acid stress on bacterial membranes of Escherichia coli and Staphylococcus simulans

Oxidative stress in combination with acid stress has been shown to inactivate a wide spectrum of microorganisms, including multi-resistant bacteria. This occurs e.g. in phagolysosomes or during treatment by cold atmospheric pressure plasmas (CAP) and possibly depends on the cell membrane. We therefore explored the effects of CAP-generated reactive oxygen and nitrogen species (RONS) on bacterial growth inhibition and membranes in neutral and acidic suspensions. We observed that growth inhibition was most efficient when bacteria were treated by a mix of short and long-lived RONS in an acidic environment. Membrane packing was affected mainly upon contact with short-lived RONS, while also acidity strongly modulated packing. Under these conditions, Gram-negative bacteria displayed large potassium release while SYTOX Green influx remained marginal. Growth inhibition of Gram-negative bacteria correlated well with outer membrane (OM) permeabilization that occurred upon contact with short and/or long-lived RONS in synergy with acidity. In Gram-positive bacteria, CAP impaired membrane potential possibly through pore formation upon contact with short-lived RONS while formation of membrane protein hydroperoxides was probably involved in these effects. In summary, our study provides a wide perspective on understanding inactivation mechanisms of bacteria by RONS in combination with acidity. (Figure presented.)</p

Two separate mechanisms are involved in membrane permeabilization during lipid oxidation

Lipid oxidation is a universal degradative process of cell membrane lipids that is induced by oxidative stress and reactive oxygen and nitrogen species (RONS) in multiple pathophysiological situations. It has been shown that certain oxidized lipids alter membrane properties, leading to a loss of membrane function. Alteration of membrane properties is thought to depend on the initial membrane lipid composition, such as the number of acyl chain unsaturations. However, it is unclear how oxidative damage is related to biophysical properties of membranes. We therefore set out to quantify lipid oxidation through various analytical methods and determine key biophysical membrane parameters using model membranes containing lipids with different degrees of lipid unsaturation. As source for RONS, we used cold plasma, which is currently developed as treatment for infections and cancer. Our data revealed complex lipid oxidation that can lead to two main permeabilization mechanisms. The first one appears upon direct contact of membranes with RONS and depends on the formation of truncated oxidized phospholipids. These lipids seem to be partly released from the bilayer, implying that they are likely to interact with other membranes and potentially act as signaling molecules. This mechanism is independent of lipid unsaturation, does not rely on large variations in lipid packing, and is most probably mediated via short-living RONS. The second mechanism takes over after longer incubation periods and probably depends on the continued formation of lipid oxygen adducts such as lipid hydroperoxides or ketones. This mechanism depends on lipid unsaturation and involves large variations in lipid packing. This study indicates that polyunsaturated lipids, which are present in mammalian membranes rather than in bacteria, do not sensitize membranes to instant permeabilization by RONS but could promote long-term damage

Meta-analysis of CO2 conversion, energy efficiency, and other performance data of plasma-catalysis reactors with the open access PIONEER database

This paper brings the comparison of performances of CO2 conversion by plasma and plasma-assisted catalysis based on the data collected from literature in this field, organised in an open access online database. This tool is open to all users to carry out their own analyses, but also to contributors who wish to add their data to the database in order to improve the relevance of the comparisons made, and ultimately to improve the efficiency of CO2 conversion by plasma-catalysis. The creation of this database and database user interface is motivated by the fact that plasma-catalysis is a fast-growing field for all CO2 conversion processes, be it methanation, dry reforming of methane, methanolisation, or others. As a result of this rapid increase, there is a need for a set of standard procedures to rigorously compare performances of different systems. However, this is currently not possible because the fundamental mechanisms of plasma-catalysis are still too poorly understood to define these standard procedures. Fortunately however, the accumulated data within the CO2 plasma-catalysis community has become large enough to warrant so-called “big data” studies more familiar in the fields of medicine and the social sciences. To enable comparisons between multiple data sets and make future research more effective, this work proposes the first database on CO2 conversion performances by plasma-catalysis open to the whole community. This database has been initiated in the framework of a H2020 European project and is called the “PIONEER DataBase”. The database gathers a large amount of CO2 conversion performance data such as conversion rate, energy efficiency, and selectivity for numerous plasma sources coupled with or without a catalyst. Each data set is associated with metadata describing the gas mixture, the plasma source, the nature of the catalyst, and the form of coupling with the plasma. Beyond the database itself, a data extraction tool with direct visualisation features or advanced filtering functionalities has been developed and is available online to the public. The simple and fast visualisation of the state of the art puts new results into context, identifies literal gaps in data, and consequently points towards promising research routes. More advanced data extraction illustrates the impact that the database can have in the understanding of plasma-catalyst coupling. Lessons learned from the review of a large amount of literature during the setup of the database lead to best practice advice to increase comparability between future CO2 plasma-catalytic studies. Finally, the community is strongly encouraged to contribute to the database not only to increase the visibility of their data but also the relevance of the comparisons allowed by this tool

Influence of a target on the electric field profile in a kHz atmospheric pressure plasma jet with the full calculation of the Stark shifts

\u3cp\u3eThe electric field in the head of the plasma bullet (ionization wave) in a cold atmospheric pressure plasma jet is measured using the Stark polarization spectroscopy technique, a noninvasive method. The jet is driven by 1 μ s long voltage pulses at 6 kV amplitude and 5 kHz frequency, and a helium gas flow of 1.5 slm. Two helium lines (447.1 nm and 492.2 nm) are studied, from which the peak-to-peak wavelength difference between the allowed and forbidden band of the spectral lines is determined. The full derivation to obtain the electric field from this peak-to-peak difference is included in this paper. The electric field is determined both inside and outside the capillary of the jet, up to about 2 cm in the effluent of the jet. Measurements are performed on the freely expanding jet, but especially the influence is studied when a target is placed in front of the plasma jet. Targets with different properties are used: insulating (polyvinyl chloride, PVC), conducting (copper), liquid (distilled water and saline), and organic (chicken breast). It is found that a target changes the electric field of the plasma jet and thus changes the plasma itself. This change depends on the dielectric constant or conductivity of the target: a higher dielectric constant or higher conductivity yields a higher electric field. For a low dielectric constant ( ϵ r ≈ 3), the change in the electric field is negligible. Decreasing the distance between the target and the capillary to below 2 cm yields an increase in the electric field.\u3c/p\u3

Atmospheric pressure plasma jet in controlled atmosphere:electric fields and propagation dynamics

\u3cp\u3eWe investigate the influence of the surrounding gas on the behaviour of guided ionization waves by measuring the electric field, propagation dynamics and emission spectra of a kHz operated helium plasma jet in surrounding gases such as nitrogen, oxygen and dry air. The electric field measurements performed using an electro-optic BSO crystal and the amount of deposited charge on the dielectric surface were calculated. These measurements showed a unique growth profile of the surface discharge in each of these surrounding gases after the guided ionization waves reaches the dielectric surface. The branching of surface discharges is observed when the nitrogen was used as the surrounding gas. The surface discharge profile in dry air and oxygen was diffused without any branching and it is wider in oxygen. The speed of growth of the discharge on the surface also decreases in nitrogen compared to dry air and oxygen. The measurements of propagation dynamics showed that the velocity of guided ionization waves is higher in oxygen containing gases. The result of this study showed that the presence of oxygen in the surrounding gas has a significant effect on guided ionization waves. These effects are mainly due to the photoionization of oxygen in the surrounding gas and also the electron detachment from the anions formed from oxygen.\u3c/p\u3

Cold atmospheric pressure plasma jets - charge carried by plasma bullets

Cold atmospheric pressure plasma jets are re-searched for applications in surface modification, synthesis, sterilization, medicine. Partially due to the relative ease of constructing a plasma jet, a great amount of work has been published on jets in a va-riety of gases, using excitation in a wide frequency range and in several typical geometries. Most com-monly reported on are descriptions of discharge dy-namics, densities of various reactive species, fol-lowed by gas temperature measurements, imaging of flow fields, and rarely electron densities and associ-ated electric fields. The first reported measurement of the electric field associated with plasma bullets has been performed by using a spectroscopic technique and published in 2011 by Sretenovic ́ et al [1], fol

Atmospheric pressure plasma jets in Helium – the electric field and the charge delivered to a dielectric surface

The family of non-thermal atmospheric pressure discharges has been the focus of intense research of a large number of research groups in the last fifteen years, as they are easy and cheap to assemble and run, and exhibit properties that can be used in surface treatment or biological applications. In this discharge family the non-thermal atmospheric pressure plasma jet commands a good deal of attention.\u3cbr/\u3eThe mentioned applications all involve the presence of a surface (target for treatment) in the vicinity of the discharge, and it has been shown that in many cases the presence of the surface alters the properties of the discharge. There are many types of surfaces to consider, from metals, dielectrics, to liquid surfaces, and they all leave a different mark on the discharge properties. Still, most of the research has been done on plasma jets expanding freely into the open air. \u3cbr/\u3eThis paper reports on the electric field and charge measurements delivered to a dielectric surface by an atmospheric-pressure plasma jet working in the bullet mode in helium. Imaging will be presented alongside the measurements of charge, as it will be evident that the charge distribution on the dielectric surface will mirror the observations obtained by imaging. The central results contain the charge packed in one ionization wave leaving the capillary towards the target, around 20 pC. The associated electric fields vary between 3×105 and 6×105 V/m

Dielectric barrier discharge in air with a controllable spatial distribution : a tomographic investigation

A novel dielectric barrier discharge source with a controllable discharge distribution has been designed for operation in atmospheric air. A predictable distribution has been achieved through the design of the powered electrode and the dielectric barrier. Optical emission tomography is used to study the discharge distribution. The method and its applicability in studies of non-symmetric plasmas are discussed in the paper. The results show that a desired discharge distribution may be achieved through the manipulation of the electric field amplification by the powered electrode and it is found that the discharge shape resembles the field imposed at the powered electrode only. Together with the flexibility of the plasma source design, this can prove highly advantageous for the treatment of irregularly shaped surfaces in plasma medicine and plasma surface processing at atmospheric pressure