Reaction mechanism for atmospheric pressure plasma treatment of cysteine in solution

Abstract

Mechanisms for the cold atmospheric plasma (CAP) treatment of cells in solution are needed for more optimum design of plasma devices for wound healing, cancer treatment, and bacterial inactivation. However, the complexity of organic molecules on cell membranes makes understanding mechanisms that result in modifications (i.e., oxidation) of such compounds difficult. As a surrogate to these systems, a reaction mechanism for the oxidation of cysteine in CAP activated water was developed and implemented in a 0-dimensional (plug-flow) global plasma chemistry model with the capability to address plasma-liquid interactions. Reaction rate coefficients for organic reactions in water were estimated based on available data in the literature or by analog to gas-phase reactions. The mechanism was validated by comparison to experimental mass-spectrometry data for COST-jets sustained in He/O2, He/H2O and He/N2/O2 mixtures treating cysteine in water. Results from the model were used to determine the consequences of changing COST-jet operating parameters, such as distance from the substrate and inlet gas composition, on cysteine oxidation product formation. Results indicate that operating parameters can be adjusted to select for desired cysteine oxidation products, including nitrosylated products.

A hierarchal model for bacterial cell inactivation in solution by direct and indirect treatment using cold atmospheric plasmas

“…More O 3 is also formed in the argon mixture compared to the He mixtures (1.5 × 10 16 cm −3 in argon, 1.8 × 10 15 cm −3 in helium). However, in the hierarchal cell death mechanism, O 3 does not directly impact cell viability and in previous studies was found to hinder modifications of organic molecules in solution [26]. The helium mixture is more efficient at producing atomic O, which both interacts directly with the CFU and contributes to the formation of other RONS in the air gap and in the liquid-phase after solvation.…”

“…Cysteine contains biologically relevant functionalities (-SH, -NH 2 , -COOH, -H) and is often used in biological models to quantify complex reaction pathways [32]. Previous work established a reaction mechanism for plasma-assisted modifications of cysteine in solution that was in good agreement with experimental data [26]. Only rates for hydrogen…”

“…were also included as these species have been shown to be important for wound healing and for bacterial inactivation [33,34]. Rates for cell interaction with RONS were adjusted from those published in [26]. to be consistent with timescales for achieving bacterial cell inactivation reported in the literature.…”

“…If the liquid analogue is supersaturated, the liquid phase species desolvates with rate proportional to S i,l = n i,l −hini,g hini,g . Henry's law constants used in this work are the same as reported in [26]. Heavy charged particles and electrons solvate into the liquid with unity probability.…”

“…To date, models have characterized plasma-production of RONS and delivery of those RONS to the target [22,23] and have predicted post-treatment modifications of key amino acids [24,25], but little work has been done to represent the mechanism by which RONS interact with large organic molecules or cells in wet conditions. Previous work has shown success in approximating reaction rates of organic molecules in solution by starting from analogous gas-phase reaction rates of RONS with long-chain alkanes [26]. Since cells membranes are, at the most basic level, surfaces made of organic molecules, it follows that a first approximation to determine a reaction mechanism for RONS with cells may be to start with previous mechanisms for RONS with organic molecules.…”