Interaction of vegetable tannins with polyamides as proof of the dominant function of the peptide bond of collagen for its binding of tannins

Publisher Website
Google Scholar
Abstract
The irreversible fixation of vegetable tannins (mimosa) by collagen and esterified collagen, as well as by a hydrated polyamide, has been investigated. The polyamide possesses a marked affinity for the vegetable tannins and binds them irreversibly, proving that the peptide linkages function as binding sites for vegetable tannins. This fixation is independent of pH value of the system in the pH range 2–8. The same independence is shown in the fixation of tannins by collagen from solutions containing sodium chloride which prevents the swelling of collagen. The typical fixation curve of vegetable tannins by intact collagen is highly pH‐dependent. In this instance the tannin fixation is directly related to the degree of swelling of collagen as a function of the pH value of the system. This is due to the fact that the degree of swelling of the protein governs the number of coordination‐active peptide bonds present in collagen for the fixation of tannins. Esterified collagen, in which the major part of the potential hydrogen binding sites are free to react, fixes large amounts of tannins independently of the hydrogen‐ion concentration of the system in the pH range 2–7. The rapid drop in fixation of tannins at pH values >8 is due to the ionization of phenolic groups, leaving fewer hydrogen bonds available on the tannin molecule. Evidence is presented in support of the view that the main reaction of polyphenolic tannins of the major type represented by mimosa tannins consists in coordination of a polyphenolic molecule to peptide bonds of adjacent protein chains, probably by means of hydrogen bonds. This multipoint attachment will explain the stabilization of the protein lattice effected by the tanning agent.

This publication has 11 references indexed in Scilit: