Influence of Amylose Size on the Structure and NMR Spectrum of Amylose-Palmitic Acid Complexes. Insight from Classical Molecular Dynamics Simulations and DFT Quantum Chemical Computations.
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We present, first, structural analysis of small sized amyloses complexed to palmitic acid studied using classical molecular dynamics. We show that even if amylose with a minimum of 11 residues exhibits transitional appearance of a V-type structure, 15 glucoses residues are necessary for the amylose to fold around the palmitic acid in a well-established helix conformation. Second, simulating 13C NMR spectrum using a strategy that combines molecular dynamics and quantum chemical DFT calculations, we demonstrate that part of the NMR spectrum is affected by the amylose size and by the presence of specific intramolecular hydrogen bonds. By mean of deconvolution procedure of NMR spectra of a 19-residues amylose calculated using a series of structures extracted from molecular dynamics, we have been able to precise the attribution of each characteristic resonances. In this context, we postulate that one chemical shift that is usually attributed to a specific carbon can, also, correspond to the presence of two different local conformations of amylose.