An acyclic phane receptor with a pair of disulfonaphthalene arms recognizing 2,3-trans-gallate-type catechins in water

Detection of catechins using a fluorescent molecule and its application toward the evaluation of astringent intensity

It is possible to estimate astringent intensities of catechin solutions based on changes in the intensity of fluorescence emission.

Polyphenol-Binding Amyloid Fibrils Self-Assemble into Reversible Hydrogels with Antibacterial Activity

Adaptable hydrogel networks with reversible connectivity have emerged as a promising platform for biomedical applications. Synthetic copolymers and low-molecular-weight gelators (LMWG) have been shown to form reversible hydrogels through self-assembly of the molecules driven by self-complementary hydrophobic interaction and hydrogen bonding. Here, inspired by the adhesive proteins secreted by mussels, we found that simply adding natural polyphenols, such as epigallocatechin gallate (EGCG) to amyloid fibrils present in the nematic phase, successfully drives the formation of hydrogels through self-assembly of the hybrid supramolecules. The hydrogels show birefringence under polarized light, indicating that the nematic orientation is preserved in the gel phase. Gel stiffness enhances with incubation time and with an increase in molecular ratios between polyphenol and fibrils, fibril concentration, and pH. The hydrogels are shear thinning and thermostable from 25 to 90 °C without any phase transition. The integrity of the trihydroxyl groups, the gallate ester moiety in EGCG, and the hydrophobicity of the polyphenols govern the interactions with the amyloid fibrils and thus the properties of the ensuing hydrogels. The EGCG-binding amyloid fibrils, produced from lysozyme and peptidoglycans, retain the main binding functions of the enzyme, inducing bacterial agglomeration and immobilization on both Gram-positive and Gram-negative bacteria. Furthermore, the antibacterial mechanism of the lysozyme amyloid fibril hydrogels is initiated by membrane disintegration. In combination with the lack of cytotoxicity to human colonic epithelial cells demonstrated for these hybrid supramolecules, a potential role in combating multidrug-resistant bacteria in biomedical applications is suggested, such as in targeting diseases related to infection of the small intestine.

Association of Catechin Molecules in Water: Quantitative Binding Study and Complex Structure Analysis

Associations between catechin molecules were investigated by (1)H NMR titration experiments. Eight green tea catechins formed self-assembled dimers in water, and gallate-type catechins had a greater tendency to self-associate than non-gallate-type catechins. All eight catechins also associated as 1:1 heterodimer complexes. Investigation of complex formation of epigallocatechin-3-O-gallate (EGCg) and epigallocatechin (EGC) with the other catechins showed that the affinity between EGCg and 2,3-trans-gallate-type catechins was remarkably high, and the binding affinity of EGCg for ECg was also rather strong. In contrast, the non-gallate-type catechin EGC exhibited generally low binding affinity for other catechins. Structural analyses of the complexes by ROESY experiments and density functional theory calculations demonstrated that the higher binding abilities of gallate-type catechins are due to providing multiple intermolecular interactions that remain effective in an aqueous environment, such as aromatic/aromatic or CH/π interactions.