<em>(Invited) </em>Synthesis of Dinitrogen Pentoxide Using Air Atmospheric Pressure Plasmas and Application for Biomaterial Processes

Kaneko, Toshiro

Atmospheric-pressure plasma (APP) technology, enabling to convert air molecules into multi-functional reactive species [e.g., reactive oxygen and nitrogen species (RONS)] with electricity, has been of great interest and extensively investigated. In particular, air APP devices, working only with air and electricity, can potentially allow for ubiquitous supply of RONS, which can be applied in a wide range of fields such as medical, agricultural, environmental, and biomaterial fields [1-4]. Recently, we have developed a new composite air APP device consisting low temperature and high temperature plasma reactors, enabling to supply RONS [e.g., dinitrogen pentoxide (N₂O₅), ozone (O₃), nitric oxides (NO_x), ...] with fine control and good reproducibility [5]. Specifically, its ability to generate high density (up to 200 ppm) N₂O₅ with high selectivity is quite unique and could accelerate scientific and industrial N₂O₅ applications. In addition, the APP device can utilize room air and renewable energy sources, such as a solar cell, and thus can realize sustainable and ubiquitous N₂O₅ supply.

N₂O₅ is well known as a powerful oxidizing and nitrating agent and can potentially be bioactive. However, there are no previous studies using N₂O₅ in bio-applications, to our best knowledge. The reason is possibly due to its ordinary synthesis methods requiring multiple hazardous raw materials (requiring handling with much care). The air APP devices is user-friendly and can easily supply N₂O₅ to biomaterials (e.g., amino acid, protein, cells, virus, bacteria, ...). Thus, we are exploring the inactivation effects of N₂O₅ exposure on pathogen and virus, and modification of amino acid by the plasma-synthesized N₂O₅.

Using the air APP device, we have investigated the inactivation effects on C. gloeosporioides (strawberry pathogen) and Qβ phage (RNA virus). 10μL of water droplet containing C. gloeosporioides was exposed to the plasma-synthesized N₂O₅_gas for 60 s, and typically 8h later, the germination rate of C. gloeosporioides conidium was evaluated as an indicator of inactivation effects. As a result, the N₂O₅ exposure significantly decreased the germination rate and the inactivation effect was not only due to pH decrease by HNO_3aq transfer into the droplet from N₂O₅_gas. This indicates that N₂O_5aq, [NO₂⁺][ NO₃^-]_aq, or NO₂⁺_aq may contribute to the inactivation. Also, mist particles containing Qβ phage were exposed to the plasma-synthesized N₂O_5gas, and the N₂O_5gas treatment resulted in over 3-log reduction in titer of Qβ phage. In addition, there were no significant difference of the inactivation effect between water and phosphate buffer mists, suggesting unique inactivation effects of N₂O_5gas other than pH decrease as noted above.

Furthermore, we conducted experiments on the modification of amino acids such as tyrosine by plasma-synthesized N₂O_5gas. Tyrosine solution was treated by N₂O_5gas together with several reactive species such as O_3gas or NO_2gas, and it is found that dopachrome and nitrotyrosine were generated by the modification of tyrosine. Interestingly, dopachrome generation rate in N₂O_5gas with excess O_3gas was most high, and the dopachrome generation was correlated with O_3gas density. Further analysis using LC-PDA (liquid chromatography-photodiode array) and MS (mass spectrometer) quantified the tyrosine and tyrosine derivatives, and tyrosine was consumed at high rate, especially under N₂O_5gas with O_3gas treatment.

Major role of NO₂⁺_aq is considered to be strong oxidizing capacity like OH radical, and N₂O_5gas triggers the generation of tyrosine intermediates. The tyrosine intermediates rapidly react with other reactive species such as O_3gas and NO_2gas, and then, dopachrome was significantly generated in N₂O_5gas with O_3gas treatment and nitrotyrosine was in N₂O_5gas with NO_2gas treatment.

In the presentation, the details of the various biomaterial APP processes and plasma-synthesized N₂O₅ reaction pathway in the gas and liquid phase will be discussed.

[1] Y. Kimura, K. Takashima, S. Sasaki, and T. Kaneko: J. Phys. D. Appl. Phys. 52, 064003 (2019).

[2] K. Shimada, K. Takashima, Y. Kimura, K. Nihei, H. Konishi, and T. Kaneko: Plasma Process. Polym. 17, e1900004 (2020).

[3] K. Takashima, Y. Hu, T. Goto, S. Sasaki, and T. Kaneko: J. Phys. D. Appl. Phys. 53, 354004 (2020).

[4] K. Takashima, A.S. bin Ahmad Nor, S. Ando, H. Takahashi, and T. Kaneko: Jpn. J. Appl. Phys. 60, 010504 (2020).

[5] S. Sasaki, K. Takashima, and T. Kaneko: Ind. Eng. Chem. Res. 60, 798 (2021).

(Invited) Synthesis of Dinitrogen Pentoxide Using Air Atmospheric Pressure Plasmas and Application for Biomaterial Processes