Molecular Level Insights on Collagen–Polyphenols Interaction Using Spin–Relaxation and Saturation Transfer Difference NMR

Abstract

Interaction of small molecules with collagen has far reaching consequences in biological and industrial processes. The interaction between collagen and selected polyphenols, viz., gallic acid (GA), pyrogallol (PG), catechin (CA), and epigallocatechin gallate (EGCG), has been investigated by various solution NMR measurements, viz., ¹H and ¹³C chemical shifts (δ_H and δ_C), ¹H nonselective spin–lattice relaxation times (<i>T</i>_1NS) and selective spin–lattice relaxation times (<i>T</i>_1SEL), as well as spin–spin relaxation times (<i>T</i>₂). Furthermore, we have employed saturation transfer difference (STD) NMR method to monitor the site of GA, CA, PG, and EGCG which are in close proximity to collagen. It is found that −COOH group of GA provides an important contribution for the interaction of GA with collagen, as evidenced from ¹³C analysis, while PG, which is devoid of −COOH group in comparison to GA, does not show any significant interaction with collagen. STD NMR data indicates that the resonances of A-ring (H2′, H5′ and H6′) and C-ring (H6 and H8) protons of CA, and A-ring (H2′ and H6′), C-ring (H6 and H8), and D-ring (H2″and H6″) protons of EGCG persist in the spectra, demonstrating that these protons are in spatial proximity to collagen, which is further validated by independent proton spin-relaxation measurement and analysis. The selective ¹H <i>T</i>₁ measurements of polyphenols in the presence of protein at various concentrations have enabled us to determine their binding affinities with collagen. EGCG exhibits high binding affinity with collagen followed by CA, GA, and PG. Further, NMR results propose that presence of gallic acid moiety in a small molecule increases its affinity with collagen. Our experimental findings provide molecular insights on the binding of collagen and plant polyphenols