Effect of Oxazolidine E on Collagen Fibril Formation and Stabilization of the Collagen Matrix

Abstract

Oxazolidine E, an aldehydic cross-linking agent, is used to impart hydrothermal stability to collagen. The purpose of this study was to investigate the exact nature of oxazolidine E induced cross-links with collagen by using synthetic peptides having sequence homology with collagen type I. Tandem mass spectrometry revealed the formation of methylol and Schiff-base adducts upon reaction of oxazolidine E with the peptides. This was confirmed by allowing the reaction to proceed under reducing conditions using cyanoborohydride. Mass spectrometry (MS)-MS analysis clearly showed interaction of tryptophan and lysine residues with oxazolidine E and demonstrated that arginine could be cross-linked with glycine in the presence of oxazolidine E through the formation of a methylene bridge. Collagen fibrils regenerated from monomers in the presence and absence of oxazolidine E were studied using atomic force microscopy to investigate morphological alterations. Regenerated fibrils showing the typical 65 nm D-banding pattern were obtained from those formed both in the presence and absence of oxazolidine E, and there was no evidence of a change in the D-periodicity of these fibrils. This indicated that oxazolidine E does not hinder collagen molecules from correctly aligning to form the quarter-stagger structure.

Can sodium silicates affect collagen structure during tanning? Insights from small angle X-ray scattering (SAXS) studies

“…The aldehyde groups of Zoldine ZE are known to react with the amine groups of lysine to form imines, that subsequently cross-link by means of covalent bonds with primary amine groups and other amino acid residues. 24 This can cause changes in the overall gap/overlap regions of the collagen molecule, in our case leading to a decrease in the D-period. However, during main tanning (stage 3) for all three treatments, no such changes in D-period were observed.…”

“…Aer pretanning with Zoldine ZE an increase in hydrothermal stability of around 18 C was observed for all samples, which is consistent with previous reports and can be attributed to the Zoldine ZE induced covalent cross-links between lysine and other amino acid groups on collagen. 24 Aer tanning with BCS, an increase in denaturation temperature to 110 C was observed. Chrome tanning is known to inuence the association of bound water with collagen, resulting in an increase in the denaturation temperature.…”

Real-Time Synchrotron Small-Angle X-ray Scattering Studies of Collagen Structure during Leather Processing

“…The decrease in D-period observed following pretanning can be attributed to the reaction between the aldehyde groups of Zoldine ZE with the amino groups of the lysine side chains on collagen, forming a Schiff's base adduct which are then covalently cross-linked with other amino acid residues. 19 This could disrupt the electrostatic environment of the hydrogen bonds between amino acid side chains and water molecules, thus affecting the gap regions of the axial staggering of the collagen molecules, resulting in a decrease in the D-period. 10 During the main tanning step (stage 3) only slight changes in D-period were observed for all three tanning agents.…”

“…Three features were observed: (1) a decrease in the D -period between the pickling and pretanning stages (from 65.5 to 64.5 nm), (2) a steady D -period from the main tanning through to the fatliquoring stages, and (3) a substantial decrease in D -period between wet and dry leather. The decrease in D -period observed following pretanning can be attributed to the reaction between the aldehyde groups of Zoldine ZE with the amino groups of the lysine side chains on collagen, forming a Schiff’s base adduct which are then covalently cross-linked with other amino acid residues . This could disrupt the electrostatic environment of the hydrogen bonds between amino acid side chains and water molecules, thus affecting the gap regions of the axial staggering of the collagen molecules, resulting in a decrease in the D -period .…”

“…Ovine skins were fleshed and acidified during the pickling process (stage 1, pH = 2.5–3.0) to protonate the amino acid side chain groups of collagen molecules in preparation for tanning . The pickled samples were then treated with Zoldine ZE (Oxazolidine E, stage 2, pH = 7.5–8.0), a five-membered heterocyclic compound derived from the reaction between an amino-hydroxy compound and aldehyde to pretan the skins. , Such pretanning agents are commonly used to improve the penetration of main tanning agents through the collagen matrix by decreasing the availability of amino acid side chain groups on the collagen molecule. The main tanning (stage 3) was carried out with either basic chromium sulfate (BCS, pH = 3.8–4.2), zirconium sulfate (ZIR, pH = 3.8–4.2), or aluminosilicate/poly­(carboxylic acid) based tanning system (ALS, pH = 4.2–4.5) followed by retanning (stage 4, pH = 4.0–4.5) and fatliquoring (stage 5, pH = 4.0–4.5) to improve the organoleptic properties of the final leather.…”