The existence of the second β-turn is assumed by the presence of a free carboxamide group of isoglutamine [43, 44]. Correlation between amide frequency and protein secondary #MK-1775 chemical structure randurls[1|1|,|CHEM1|]# structure found in the literature is listed in Table 2. We can assume from the comparison correlation between amide frequency in FTIR spectra of SPhMDPOBn (Table 2) and protein secondary structure found in the literature (Table 3) that, probably, SPhMDPOBn in the pristine state adopt β-sheet conformation and in the adsorb state, combination of β-sheet and β-turn structures. Table 3 Assignments of amide bands to the secondary structure of peptides and proteins

(literature data) Assignment Amide I, ν (сm−1) Amide II, ν (сm−1) Reference α-helix 1,649; 1,653 to 1,657; 1,655 1,545 [45]   1,648 to 1,660 – [46]   1,650 to 1,652 1,540 to 1,546; 1,516 [47] β-sheet 1,621 to 1,623; 1,630; 1,634 to 1,639; 1,647 to 1,648 1,530 [45]   1,620 to 1,640; 1,670 to 1,695 – [46]   1,633 1,530 [47] β-turn 1,661; QNZ molecular weight 1,667; 1,673; 1,677 1,528; 1,577 [45]   1,620 to 1,640; 1,650 to 1,695 – [46]

  1,663; 1,670; 1,683; 1,688; 1,694   [47] Random coil 1,648; 1,654; 1,642 to 1,657 – [45]   1,640 to 1,657; 1,660 to 1,670 – [46] The spectral region 1,400 to 1,200 сm−1 is characterized by overlapping deformation vibrations of the C-H bond in methyl and methylene groups of peptide fragment, stretching vibrations of the С-О bond in carbonyl group and amide III vibrations (stretching vibrations of С-N bond and N-H bend in plane) and the Si-O-Si, Si-O and O-Si-O

vibration bands of the silica matrix. Conclusions The stages of pyrolysis of aglycone, peptide fragment and carbohydrate residue of thiophenylglycoside of muramyl dipeptide in the pristine state and adsorbed on the silica surface have been determined. Decomposition of thiophenylglycoside of muramyl dipeptide in pristine state occurs enough within the narrow temperature range from 150°C to 250°C. The decomposition of thiophenylglycoside of muramyl dipeptide adsorbed on the silica surface undergoes certain reactions to produce pyrolysis products such as thiophenol, benzyl alcohol and carbohydrate fragment with m/z 125 in the temperature range from 50°C to 450°C. Probably, the hydrogen-bonded complex forms between silanol surface groups and the C = O group of the acetamide moiety NH-(CH3)-C = O…H-O-Si≡. The thermal transformations of such hydrogen-bonded complex result in the pyrolysis of SPhMDPOBn immobilized on the silica surface under TPD-MS conditions. The intensity of the infrared band at 3,745 cm−l assigned to the OH stretching vibrations of isolated silanol groups on silica decreased after the immobilization of SPhMDPOBn. This indicated the hydrogen-bonding of SPhMDPOBn molecule with silanol groups.