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 spectromet ry using bovine albumin and di-, tri- and oligo-peptides. Most of the ident ified amino acid derivatives originate from the cleavage of the peptide bon ds and subsequent methylation of the carboxylic and the amino groups. Some products are explained by deamination of aromatic amino acids. Only two pro ducts were identified that experienced chemical rearrangement after methyla tion. TMAH/thermochemolysis of algal material resulted in products comparab le to those obtained from albumin. Amino acid derivatives were also identif ied among the TMAH/thermochemolysis products of refractory biopolymer of th e alga Scenedesmus communis and the HCl-hydrolysis residue of the humin fro m 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 amin o acids into solution and some of these are entrapped within a non-extracta ble hydrophobic network. However, alternative explanations for this behavio r are possible. For example, at the higher temperatures and pressures and s trongly basic conditions used in TMAH themochemolysis, penetration of this hydrophobic barrier takes place thus allowing breakdown and methylation of protein remnants. (C) 2001 Elsevier Science Ltd. All rights reserved.