Lipids and polysaccharides are essential components of living order and understanding their interactions is of great importance. Among the different experimental approaches used to analyze such molecular complexes, solid-state NMR is a method of choice. However, realistic models at the atomic scale are sometimes necessary to understand the NMR spectral signatures obtained experimentally and to reveal the detailed three dimension structure of such complexes. Theoretical approaches such as classical molecular dynamics (MD) or quantum chemical methods are suitable to bring support to these studies. Before using these computational method in a routine manners, several validation steps are necessary, based on the quantum chemical calculations of 13C NMR spectra on one hand and on molecular dynamics simulations of complexation process on the other. For this purpose, several calculations have been carried out on amylose-palmitic acid complexes. First, molecular dynamic simulations using modified GLYCAM force field have been undergone using increasing degree of polymerization in order to study the complexation process as a function of amylose size. This study has revealed the minimal amylose size necessary to undertake a stable complex with characteristic V-helix structure in presence of lipids. On a second time, based on structures extracted from MD simulations, Density Functional Theory (DFT) B3LYP using GIAO method has been employed in order to simulate 13C NMR spectra of these amylose-lipid complexes. Then, this process has been applied to POPC-amylose complexes. This study revealed the ability of the protocol to explain 13C CP-MAS spectra recorded on samples containing amylose complexes with different lipid concentrations. These spectra present self-complexed amylose and/or POPC-amylose V-helix signals at different intensity ratios. This strategy leading to comparison between simulated and experimental NMR spectra can be employed to study the interactions of different polysaccharides with others lipids or with others components (DNA, proteins …) and help to decipher the structuration of heterogeneous systems.

Polysaccharide-lipid interactions: Theoretical and experimental study using molecular dynamics simulations, quantum chemical 13C NMR spectra computation and solid-state 13C NMR

2019 Fall National Meeting

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