Abstract
Four hydrophobic amino acids (Leu, Tyr, Phe, Trp) were oligomerized by the protease papain in homo-oligomerization, binary co-oligomerization and ternary co-oligomerization. After 24 h, solid polydisperse reaction products of the homo-oligomerization were obtained in yields ranging from 30–80% by weight. A DPavg was calculated based on MALDI-ToF MS results using the ion counts for the chains in the product. Based on the DPavg and the yield of the homo-oligomerization it was determined that the amino acids can be ranked according to reactivity in the order: Tyr > Leu > Phe > Trp. Thermal degradation of the homo-oligomers shows two degradation steps: at 178–239 °C and at 300–330 °C. All the products left a significant amount of char ranging from 18–57% by weight at 800 °C. Binary co-oligomers were obtained as a polydisperse precipitate with a compositional distribution of the chains. Both the compositional and chain length distribution are calculated from MALDI-ToF mass spectra. By comparing the amount of each amino acid present in the chains it was determined that the amino acids are incorporated with a preference: Leu > Tyr > Phe > Trp. Ternary co-oligomers were also obtained as a precipitate and analyzed by MALDI-ToF MS. The compositional distribution and the chain length distribution were calculated from the MALDI-ToF data. The quantity of every amino acid in the chains was determined. Also determined was the influence on the DPavg when the oligomers were compared with corresponding binary co-oligomers. From the combined results it was concluded that in the co-oligomerization of three amino acids the reactivity preference is Leu > Tyr > Phe > Trp. Thermal degradation of all the co-oligomers showed a weight loss of 2 wt% before the main oligomer degradation step at 300–325 °C.
Highlights
In the past decades enzymes have become part of the chemists’ toolbox and they have proven to be effective in different organic reactions
Homo-oligomers of leucine, tyrosine and tryptophan were synthesized with papain from the corresponding methyl ester hydrochlorides in phosphate buffer
Papain catalyzed the oligomerization of the amino acids leucine, tyrosine, phenylalanine and tryptophan
Summary
In the past decades enzymes have become part of the chemists’ toolbox and they have proven to be effective in different organic reactions. In addition to replacing traditional processes, biocatalysis opened new synthetic routes not available before. Enzymes perform their catalytic activity under mild reaction conditions with a high chemo-, regio- and stereospecificity. Oligomers produced by enzymatic oligomerizations include polysaccharides, polyesters and even vinyl oligomers [1,2,3,4]. Polyamides are versatile engineering plastics and excellent fiber materials due to their toughness over wide ranges of temperatures. While there are many reports on enzymatic polyester formation, there are, surprisingly, only few publications on enzyme-catalyzed synthesis of polyamides [5,6,7,8,9] which were recently reviewed in an excellent review [10]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have