Interaction of N-acetyl-l-cysteine with Na⁺, Ca²⁺, Mg²⁺ and Zn²⁺. Thermodynamic aspects, chemical speciation and sequestering ability in natural fluids.

ABSTRACT: The estimation of thermodynamic parameters of N-Acetyl-L-cysteine (NAC) protonation were determined in NaCl_(aq), (CH₃)₄NCl_(aq), (C₂H₅)₄NI_(aq), employing various temperature and ionic strengths conditions, by potentiometric measurements. The interaction of NAC with some essential metal cations (e.g., Ca²⁺, Mg²⁺ and Zn²⁺) was investigated as well at 298.15 K in NaCl_(aq) in the ionic strength range 0.1 ? I/mol dm^-3 ? 1.0. The values of protonation constants at infinite dilution and at T = 298.15 K are: log K ₁ ^H = 9.962 ± 0.005 (S-H) and log K ₂ ^H = 3.347 ± 0.008 (COO-H). In the presence of a background electrolyte, both log K ₁ ^H and log K ₂ ^H values followed the trend (C₂H₅)₄NI ? (CH₃)₄NCl ? NaCl. The differences in the values of protonation constants among the three ionic media were interpreted in terms of variation of activity coefficients and formation of weak complexes. Accordingly, the determination of the stability of 4 species, namely: NaL^-, NaHL⁰ _(aq), (CH₃)₄NL^-, (CH₃)₄NHL⁰ _(aq) was assessed. In addition, as regards the interactions of Mg²⁺, Ca²⁺ and Zn²⁺ with NAC, the main species where the ML⁰ _(aq), ML(OH)^-, and ML₂ ^2-, that were found to be important in the chemical speciation of NAC in real multicomponent solutions. The whole set of the data collected may be crucial for the development of NAC-based materials for natural fluids selective decontamination from heavy metals.

SUBMITTER: Bretti C 

PROVIDER: S-EPMC7455796 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature