Reactions of aldehyde with collagen: a DFT study.

The reaction mechanisms of several amino acids (Asn, Gln, Arg, His, and Lys) in the collagen with aldehyde were studied using density functional theory method. Based on the geometry optimization, results expounded the singlet and doublet reaction mechanisms, respectively, and discussed the structural properties of intermediates, transition states, and products that appeared along the corresponding potential energy surfaces. The reaction along the doublet potential energy surface is more thermodynamically favorable than that along the singlet one. However, the reactions obeying the doublet route only produce the carbinolamine type of compounds, rather than the Schiff bases. It is because that the doublet mechanism involves only the hydrogen abstraction or hydrogen exchange process, without the dehydration process. The Schiff base types of compounds are most likely to be obtained from the singlet reactions of Asn, Gln, Arg, and Lys with aldehyde. In order to assist the experiment in identification of product structures and reaction mechanism correctly, the vibrational modes of each product with distinctive features were analyzed and compared in detail. [ABSTRACT FROM AUTHOR]