Study on chemical modifications of glutathione by cold atmospheric pressure plasma (Cap) operated in air in the presence of Fe(II) and Fe(III) complexes

Cold atmospheric pressure plasma is an attractive new research area in clinical trials to treat skin diseases. However, the principles of plasma modification of biomolecules in aqueous solutions remain elusive. It is intriguing how reactive oxygen and nitrogen species (RONS) produced by plasma interact on a molecular level in a biological environment. Previously, we identified the chemical effects of dielectric barrier discharges (DBD) on the glutathione (GSH) and glutathione disulphide (GSSG) molecules as the most important redox pair in organisms responsible for detoxification of intracellular reactive species. However, in the human body there are also present redox-active metals such as iron, which is the most abundant transition metal in healthy humans. In the present study, the time-dependent chemical modifications on GSH and GSSG in the presence of iron(II) and iron(III) complexes caused by a dielectric barrier discharge (DBD) under ambient conditions were investigated by IR spectroscopy, mass spectrometry and High Performance Liquid Chromatography (HPLC). HPLC chromatograms revealed one clean peak after treatment of both GSH and GSSH with the dielectric barrier discharge (DBD) plasma, which corresponded to glutathione sulfonic acid GSO$_3$H. The ESI-MS measurements confirmed the presence of glutathione sulfonic acid. In our experiments, involving either iron(II) or iron(III) complexes, glutathione sulfonic acid GSO$_3$H appeared as the main oxidation product. This is in sharp contrast to GSH/GSSG treatment with DBD plasma in the absence of metal ions, which gave a wild mixture of products. Also interesting, no nitrosylation of GSH/GSSG was oberved in the presence of iron complexes, which seems to indicate a preferential oxygen activation chemistry by this transition metal ion

Microscale atmospheric pressure plasma jet as a source for plasma-driven biocatalysis

The use of a microscale atmospheric pressure plasma jet ($\mu$APPJ) was investigated for its potential to supply hydrogen peroxide in biocatalysis. Compared to a previously employed dielectric barrier discharge (DBD), the $\mu$APPJ offered significantly higher H$_2$O$_2$ production rates and better handling of larger reaction volumes. The performance of the $\mu$APPJ was evaluated with recombinant unspecific peroxygenase from $\textit {Agrocybe aegerita}$ (r$\it Aae$UPO). Using plasma-treated buffer, no side reactions with other plasma-generated species were detected. For long-term treatment, r$\it Aae$UPO was immobilized, transferred to a rotating bed reactor, and reactions performed using the $\mu$APPJ. The enzyme had a turnover of 36,415 mol mol$^{−}$1 and retained almost full activity even after prolonged plasma treatment. Overall, the $\mu$APPJ presents a promising plasma source for plasma-driven biocatalysis

Catalytic oxidation of small organic molecules by cold plasma in solution in the presence of molecular iron complexes†

The plasma-mediated decomposition of volatile organic compounds has previously been investigated in the gas phase with metal oxides as heterogeneous catalysts. While the reactive species in plasma itself are well investigated, very little is known about the influence of metal catalysts in solution. Here, we present initial investigations on the time-dependent plasma-supported oxidation of benzyl alcohol, benzaldehyde and phenol in the presence of molecular iron complexes $\textit {in solution}$. Products were identified by HPLC, ESI-MS, FT-IR, and $^{1}\textbf {H NMR}$ spectroscopy. Compared to metal-free oxidation of the substrates, which is caused by reactive oxygen species and leads to a mixture of products, the metal-mediated reactions lead to one product cleanly, and faster than in the metal-free reactions. Most noteworthy, even catalytic amounts of metal complexes induce these clean transformations. The findings described here bear important implications for plasma-supported industrial waste transformations, as well as for plasma-mediated applications in biomedicine, given the fact that iron is the most abundant redox-active metal in the human body