Ellagitannin–Lipid Interaction by HR-MAS NMR Spectroscopy

Abstract

Ellagitannins have antimicrobial activity, which might be related to their interactions with membrane lipids. We studied the interactions of 12 different ellagitannins and pentagalloylglucose with a lipid extract of Escherichia coli by high-resolution magic angle spinning NMR spectroscopy. The nuclear Overhauser effect was utilized to measure the cross relaxation rates between ellagitannin and lipid protons. The shifting of lipid signals in 1H NMR spectra of ellagitannin–lipid mixture due to ring current effect was also observed. The ellagitannins that showed interaction with lipids had clear structural similarities. All ellagitannins that had interactions with lipids had glucopyranose cores. In addition to the central polyol, the most important structural feature affecting the interaction seemed to be the structural flexibility of the ellagitannin. Even dimeric and trimeric ellagitannins could penetrate to the lipid bilayers if their structures were flexible with free galloyl and hexahydroxydiphenoyl groups.

Interactions between Hydrolysable Tannins and Lipid Vesicles from Escherichia coli with Isothermal Titration Calorimetry

“…The idea was that the higher the heat the addition of each HT produces is an indication of the degree to which the HT is able to interact with the lipid vesicles, or inversely if the HT molecules do not interact with lipid vesicles. Similarly, in our recent high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopic study using the same lipid extract and a subset of the same HTs used in this study, the importance of certain structural features was observed [ 25 ]. The initial premise was that the same features would prove dominant in this thermodynamic study as well.…”

“…This correlated with our previous results. Vescalagin is highly hydrophilic and has not shown any interaction with the lipids studied by HR-MAS NMR measurements [ 25 , 28 ]. The 1 C 4 ellagitannins ( 12 – 15 ) also produced heats that were barely detectable, which was expected based on the results of our previous NMR study, where it was shown that geraniin ( 12 ) did not move spatially close to these phospholipid vesicles [ 25 ].…”

“…Vescalagin is highly hydrophilic and has not shown any interaction with the lipids studied by HR-MAS NMR measurements [ 25 , 28 ]. The 1 C 4 ellagitannins ( 12 – 15 ) also produced heats that were barely detectable, which was expected based on the results of our previous NMR study, where it was shown that geraniin ( 12 ) did not move spatially close to these phospholipid vesicles [ 25 ]. This result was still unexpected because compounds 12 – 14 are moderately hydrophobic, which suggests that high hydrophobicity does not necessarily dictate if a compound will have high affinity to interact with lipid vesicles [ 28 , 29 ].…”

“…The composition of the phospholipids of the E . coli extract has previously been investigated by NMR [ 25 ]. Here, an attempt was made to lower the particle size and dispersity (Đ) of the lipid solution prepared via the freeze–thaw treatment described in Section 3.3 , with sonication and various sonication times, after which the lowered particle size and dispersity of the lipid vesicles were confirmed by DLS.…”

“…The measured HTs were selected to represent the structural diversity of the compound group as extensively as possible, and emphasis was also placed on previous knowledge about the lipid interactions and the hydrophobicity of HTs [ 25 , 28 ]. In total, 24 HTs ( Figure 1 and Figure 2 ) were used, and their purification from plants followed previously outlined methods [ 1 , 10 , 32 , 37 , 38 , 39 , 40 ].…”