Reaction Mechanism for the Atmospheric Pressure Plasma Jet Treatment of Cysteine in Solution

Atmospheric-pressure-plasma-jets (e.g., KINpen, COST-jet) are a source of reactive oxygen and nitrogen species (RONS) for applications in biology and medicine. Recent fundamental investigations utilizing these devices have focused on plasma-liquid interactions of RONS with simple biologically-relevant amino acids (e.g., cysteine, glycine) in solution. Experimental studies have shown RONS are depleted in reactions with simple amino acids in solution, producing oxidation products that are similar to those formed by treatment of organic molecules with gas-phase plasmas [1]. Reaction mechanisms for plasma-liquid interactions are generally available for solutions that do not contain organic molecules and materials. Development of these mechanisms based on analogous reactions of gas-phase plasmas with organic molecules could provide insight for biological applications.

In this work we developed a reaction mechanism for the computational investigation of atmospheric pressure plasma jet treatment of cysteine in water and saline solutions. Analogous reactions for gas-phase RONS with organic molecules are extended to solution. The validity of this approach is discussed. A global plasma chemistry model adapted for plasma-liquid interactions was used to investigate the effects of plasma activated oxidizing (e.g., O, OH) and biocidal (e.g., OCl^-) species on the final oxidation states of cysteine in solution. The interactions of these RONS with the cysteine molecule will be discussed and compared to experiments.

[1] K. Stapelmann et al., J. Phys. D Appl. Phys. 54, 434003 (2021).