N n dimethylformamide (dmf)

First, 2 g of graphite fluoride (61 < at% F, polymer, Sigma-Aldrich) was dispersed in 120 ml of DMF (for peptide synthesis, Merck), followed by continuous stirring for 72 h at room temperature. Then, the dispersion was sonicated in an ultrasonication bath for 4 h (<60 °C) and was kept stirring for another 24 h at room temperature. Last, 10.2 g K₂CO₃ (Penta) and 5 g cysteamine (Sigma-Aldrich) were added to the dispersion and left stirring under heating at 130 °C for 24 h in an oil bath in the hood with a condenser for reflux.
When cooling down, the formed product was centrifuged (20 000 rcf per 10 min) and washed with DMF (2×), hot DMF (1×), acetone (2×), hot acetone (1×), ethanol (3×), distilled water (2×), and hot distilled water (1×).
To decompose the possible unwanted disulfide bonds in the GSH, the whole amount of the synthesized material was mixed with 420 μL of 2-mercaptoethanol (Carl Roth; ∼2× molar ratio of –SH groups considered as 20% F.D.), and left shaking for 30 min. Then, the material was additionally washed with ethanol (1×), acidified distilled water (2×), and distilled water (1×) using centrifugation (20 000 rcf per 10 min) and purified by being placed into the dialysis membrane (cut-off 14 kDa) in a container of distilled water (5L) that was changed every day until the dispersion containing the material reached a conductivity <100 μS cm⁻¹.