Mass spectra were recorded using AXIMA CFR MALDI-TOF Mass Spectrometer from Kratos Analytical Ltd. (Manchester, UK), equipped with a nitrogen laser (337 nm). The laser energy was selected from 0 to 180 a.u. (arbitrary units). The repetition mode of experiments was performed at a frequency of 5 Hz and a pulse time width of 3 ns. Analyses were carried out in linear/reflectron positive/negative ion modes. Generally, MALDI-TOF MS of amino acids and peptides is usually measured in the positive ion mode, therefore, the study was performed in the positive ion mode. The irradiated spot size was about 150 µm in diameter and the maximum laser power was 6 mW (180 a.u.). The resulting laser energy fluence was ~ 1 J/cm2.
UV–Visible spectra were measured using a UV mini-1240 spectrophotometer from Shimadzu Corporation (Kyoto, Japan). A spectrofluorometer Aminco-Bowman Series 2 (Thermo Fisher Scientific, MA, USA) equipped with a 150 W Xe lamp was used. Excitation wavelength was set at 445 nm and emission wavelength was set at 525 nm. The spectra were acquired with 1 nm resolution and a scanning speed of 1 nm/s. A MiniSpin Plus of Eppendorf (Hamburg, Germany) centrifuge machine was used for centrifugation.
UV–Visible spectra were measured using a UV mini-1240 spectrophotometer from Shimadzu Corporation (Kyoto, Japan). A spectrofluorometer Aminco-Bowman Series 2 (Thermo Fisher Scientific, MA, USA) equipped with a 150 W Xe lamp was used. Excitation wavelength was set at 445 nm and emission wavelength was set at 525 nm. The spectra were acquired with 1 nm resolution and a scanning speed of 1 nm/s. A MiniSpin Plus of Eppendorf (Hamburg, Germany) centrifuge machine was used for centrifugation.