Fig. 5: FTIR analysis of LDPE films treated with “Ceres”.

The figure shows parts of the FTIR spectra of “Ceres”-treated films, buffer-treated films, and pristine non-treated films before (panel A) and after cleaning with 1 M NaOH (panel B). Red arrows indicate the expected position (≈1745 cm⁻¹) of a carbonyl peak which was not observed in our experiments but was previously reported as a result of polyethene oxidation by “Ceres”. Each trace shown in the figure represents the average of signals obtained for 3 film discs. The FTIR peaks resulting from the incubation of polyethene with “Ceres” that are visible in panel A are signals from the protein, and not from reaction products (see the main text for discussion). In-house made additive-free LDPE films were incubated at 25 °C for 70 h in 20 mM HEPES, pH 7.0, supplied with 150 mM NaCl and 5% (v/v) glycerol in the absence or presence of 1 mg/mL “Ceres”. The absorbance signals were normalized using the CH₂ asymmetric C–H stretch peak of PE (≈2913 cm⁻¹) as the reference (not visible in this zoomed-in view). See Supplementary Fig. 7 for the complete FTIR dataset used to produce this figure. The data were acquired with 8 cm⁻¹ resolution. The same results were obtained when repeating the experiment using a higher (3 mg/mL) concentration of “Ceres” and recording the FTIR data with higher (2 cm⁻¹) resolution (Supplementary Fig. 8). Source data are provided as a Source Data file.