Identification of protein remnants in insoluble geopolymers using TMAH thermochemolysis/GC–MS

Thermochemolysis with tetramethylammonium hydroxide (TMAH) was utilized to analyze peptide-like material in insoluble residues of geochemical samples. Product identification was performed by gas chromatography/mass spectrometry using bovine albumin and di-, tri- and oligo-peptides. Most of the identified amino acid derivatives originate from the cleavage of the peptide bonds and subsequent methylation of the carboxylic and the amino groups. Some products are explained by deamination of aromatic amino acids. Only two products were identified that experienced chemical rearrangement after methylation. TMAH/thermochemolysis of algal material resulted in products comparable to those obtained from albumin. Amino acid derivatives were also identified among the TMAH/thermochemolysis products of refractory biopolymer of the alga Scenedesmus communis and the HCl-hydrolysis residue of the humin from an algal sapropel. These results strongly indicate that for those samples, hydrolysis fails to extract all proteinaceous and peptide-like components, possibly because these approaches rely on extraction of peptides and amino acids into solution and some of these are entrapped within a non-extractable hydrophobic network. However, alternative explanations for this behavior are possible. For example, at the higher temperatures and pressures and strongly basic conditions used in TMAH themochemolysis, penetration of this hydrophobic barrier takes place thus allowing breakdown and methylation of protein remnants.