Infrared spectra in the attenuated total reflection mode (FTIR-ATR) were obtained using a Bruker Alpha spectrophotometer (Bruker Optik, Ettlingen, Germany). The samples were prepared in a form of film with 100µm of thickness and the ATR FT-IR spectra were recorded from 400 to 4000 cm -1 at a resolution of 2 cm -1 with 32 scans.