Modeling Procyanidin Self-Association Processes and Understanding Their Micellar Organization: A Study by Diffusion NMR and Molecular Mechanics

Abstract

The colloidal behavior of eight synthetic procyanidins (three monomers, four dimers, and a trimer) has been investigated in water or in a winelike medium using DOSY NMR spectroscopy and molecular dynamics simulations. Different behavior was observed for monomers and oligomers. Monomers self-associate with a high affinity constant (37-53 M(-1)) to form micelles at low cmc (critical micelle concentration) values (1-5 g.L(-1)). These micelles undergo a time-dependent coalescence process to form hazes and precipitates. As for dimers and the trimer, self-association also occurs but with a lower affinity (approximately 6 M(-1)) and at higher cmc values (10-20 g.L(-1)) to form small micelles (<5 nm) that remain stable throughout the experiment. The presence of 10% ethanol does not significantly affect the self-association constant for monomers and oligomers but increases their cmc values by approximately 50% and decreases the micelle size by a factor 2. However, the presence of 20 mM NaCl appears to negate the effect of ethanol. This study helps to clarify the role of procyanidin monomers versus oligomers in wine turbidity and demonstrates that procyanidin oligomers are fully available to interact with saliva proteins.

Stealth Amphiphiles: Self-Assembly of Polyhedral Boron Clusters

“…[48][49][50][51][52] Information on the self-diffusion of boron clusters can be directly obtained from 1 In the case of Na[CoD] -see Figure 2B, there are only single clusters below the CAC (with 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 metallacarboranes fully dissociate in water and counterions are not condensed on the aggregates due to relatively low charge density of bulky metallacarborane cluster, the Na[CoD] aggregates cannot grow beyond a certain limit due to electrostatic restrictions. 20,23 In the case of small boron clusters, we assume that the aggregation number grows with increasing concentration without a limit (see Figure 2A), which resembles the isodesmic association model employed for a self-assembly of dyes, [55][56][57][58] …”

NMR and molecular modeling of wine tannins binding to saliva proteins: revisiting astringency from molecular and colloidal prospects

“…Physicochemical parameters of interest, such as the stoichiometry of the complex, the number of binding sites and their nature, and the affinity of the different tannins toward the peptide, were obtained by following the peptide proton chemical shift or the diffusion coefficient variations induced by adding the different procyanidins to the peptide mixture. This study is based on lengthy experience in synthesis of different procyanidin dimers and trimers (18) and of saliva PRPs (19) to gram scale, on the choice of adapted techniques for studying these interactions (10), and on the determination of the 3‐D structure (8, 9) or colloidal behavior of tannins to identify the active fraction of tannins that can interact with proteins (20). In the present work, we provide evidence that tannin‐PRP interactions can occur according to two different processes depending on the tannin colloidal state.…”

“…A 1 mM protein sample was prepared in a water/D 2 O/EtOD (80:8:12) mixture, with 5 mM deuterated acetic acid, pH 3.5, to mimic wine conditions. Tannins were added progressively to the protein sample to scan a tannin concentration range from 1 to 7 mM; i.e ., all tannins of the study were always in conditions below their CMC value (15–27 mM) (20). To keep the protein concentration constant, tannins were added as a lyophilized powder.…”

“…Diffusion‐ordered spectroscopy (DOSY) NMR was used to measure the translational diffusion coefficient D . It allows differentiating species related to their effective molecular weight, size, and shape, leading very different applications from intermolecular interaction, (24–26) to molecular aggregation processes (20, 27, 28) or ionic liquids (29). Diffusion measurements were performed using 1 H‐NMR pulsed gradients (PGSE) (30).…”

Susceptibility to Dental Caries and the Salivary Proline-Rich Proteins

“…Above a critical concentration, polyphenol/basic PRP complexes precipitate. Below it, the precise mixture of polyphenols determines their structure in solution [56]: compact with π - π electron-bonded phenol groups stacked above each other and pointing away from the fluid; or extended with individual phenol groups pointing into the fluid and away from each other. Compact structures bind poorly to basic PRPs, but remain in solution as colloidal complexes that promotes low astringency; extended structures interact strongly with basic PRPs, precipitate from solution, and exhibit high astringency [57].…”