Terence H. Lilley

Polyphenol complexation—some thoughts and observations

Abstract Current views and opinions on polyphenol (tannin)-protein complexation are outlined. ‘Structure-activity’ relationships are delineated as are experimental approaches which seek to define the modes and sites of binding of ligand (polyphenol) to the receptor (protein). A model for polyphenol-protein complexation is proposed.

Polyphenols, astringency and proline-rich proteins

Recent, NMR and precipitation, studies of molecular recognition of proline-rich proteins and peptides by plant polyphenols are described and rationalized. The action of polysaccharides and caseins in the moderation of the astringent response, which is engendered by polyphenols present in foodstuffs and beverages, is described. The possible influence of plant cell wall glycoproteins on the process of lignification is discussed in the light of the observed affinity of phenolic substrates for prolyl residues in protein structures.

Natural astringency in foodstuffs — A molecular interpretation

The structures of plant polyphenols (vegetable tannins) are briefly reviewed. Their interactions with proteins, polysaccharides, and the alkaloid caffeine are discussed at the molecular level, and these fundamental properties are related to the quality of astringency that polyphenols possess. The various ways in which astringency may be modified and ultimately lost are outlined in relation to the aging of red wines, the formation of nonbiological hazes in beers and lagers, and the ripening of fruit.

Polyphenol interactions. Part 1. Introduction; some observations on the reversible complexation of polyphenols with proteins and polysaccharides

Early studies of the interactions between polyphenols and proteins are reviewed. The complexation of some simple phenols and a group of biosynthetically inter-related esters of gallic acid with bovine serum albumin (BSA) is examined by equilibrium dialysis and microcalorimetry. The phenomenon is pH dependent. The results indicate that molecular size and conformational flexibility of the polyphenol substrate lead to enhanced interactions with the protein. Preliminary studies with polysaccharides indicate that the binding here is pH independent. These studies suggest that whilst the binding of polyphenols to these macromolecules is influenced by similar structural features the ability of the polysaccharide to form structures which encapsulate the polyphenol is, in this instance, a further critical feature of the complexation.

Polyphenol interactions: astringency and the loss of astringency in ripening fruit☆

Abstract The inhibition of the enzyme β-glucosidase by natural polyphenolic substrates is described. The kinetic data suggest that the pattern of inhibition w

Tannin interactions with a full‐length human salivary proline‐rich protein display a stronger affinity than with single proline‐rich repeats

The protein IB5 has been purified from human parotid saliva. This protein contains several repeats of a short proline‐rich sequence. Dissociation constants have been measured at several discrete binding sites using 1H‐NMR for the hydrolysable tannins (polyphenols) ( , and and the condensed proanthocyanidin (−)‐epicatechin. The dissociation constants for trigalloyl glucose and pentagalloyl glucose were 15 × 10−5 and 1.7 × 10−5 M, respectively, which are 115 and 1660 times stronger than those previously measured under the same conditions for a single repeat of a mouse salivary proline‐rich protein. The increase in affinity is ascribed to intramolecular secondary interactions, which are strengthened by the rigidity of the interacting molecules.

Plant polyphenols—secondary metabolism and chemical defence: Some observations

Abstract Secondary metabolism and theories of plant-animal co-evolution are briefly discussed. Current ideas concerning the role of polyphenols as mediators of a general form of chemical defence in plants are outlined. Studies are described of the association of a group of biosynthetically inter-related polyphenols based on gallic acid and D -glucose with the protein bovine serum albumin. The results are interpreted in terms of structure-activity relationships in protein-polyphenol complexation and are used to comment on the co-evolution theory and the position of plant polyphenols in higher plant secondary metabolism and defence.

Aqueous solutions containing amino acids and peptides. Part 27.—Partial molar heat capacities and partial molar volumes of some N-acetyl amino acid amides, some N-acetyl peptide amides and two peptides at 25 °C

Partial molar heat capacities, in water at 25 °C, of the compounds N-acetylglycinamide, N-acetyl-L-alaninamide, N-acetylglycylglycinamide, N-acetylglycyl-L-alaninamide, N-acetyl-L-alanylglycinamide, N-acetyl-L-alanyl-L-alaninamide, glycyl-DL-alanine and DL-alanylglycine have been obtained. The information obtained, for the amides, is discussed in terms of group-additivity approaches, and group contributions are evaluated. The values for these differ in some instances, and particularly that for the heat capacity of the peptide group, from those obtained in an earlier study. Comparison of the parent amino acids and peptides with the amides shows that there is a marked contribution to the heat capacities of the zwitterionic compounds from electrostatic sources.Some results are presented of the partial molar volumes, also at 25 °C, of N-acetylglycyl-L-alaninamide, N-acetyl-L-alanylglycinamide and DL-alanylglycine.A correlation is evident between the heat capacity and volumetric interaction coefficients, for amino acids, peptides and N-acetylamides, obtained from the molality dependences of the apparent molar properties, and this has been rationalised using a simple electrostatic approach.

Carbohydrate — Polyphenol Complexation

Comprehensive studies of the complexation of polyphenols (vegetable tannins) with other substrates are of great practical significance and utility. Fundamental studies of these phenomena form part of the strategy adopted in Sheffield to pursue an understanding of the possible function and metabolic role of this distinctive group of natural products. With regard to polyphenols, molecular size, conformational mobility and shape, and water solubility are the three principal critera that most strongly influence association with polysaccharides. The differing affinities of polyphenols for polysaccharides result from a balance between a variety of effects- adsorption, sequestration, and solvation. The importance of polyphenol sequestration into “pores” in the polysaccharide structure has been demonstrated by model studies with Schardinger dextrans or cyclodextrins.

The association of proteins with polyphenols

The complexation of phenols with proteins has been quantitatively examined using a range of physical methods; a theory is put forward for the precipitation of proteins from solution by complex polyphenols and by simple phenols.