title: Direct prediction of residual dipolar couplings of small molecules in a stretched gel by stochastic molecular dynamics simulations.
abstract: Residual dipolar couplings are highly useful NMR parameters for calculating and refining molecular structures, dynamics, and interactions. For some applications, however, it is inevitable that the preferred orientation of a molecule in an alignment medium is calculated a priori. Several methods have been developed to predict molecular orientations and residual dipolar couplings. Being beneficial for macromolecules and selected small-molecule applications, such approaches lack sufficient accuracy for a large number of organic compounds for which the fine structure and eventually the flexibility of all involved molecules have to be considered or are limited to specific, well-studied liquid crystals. We introduce a simplified model for detailed all-atom molecular dynamics calculations with a polymer strand lined up along the principal axis as a new approach to simulate the preferred orientation of small to medium-sized solutes in polymer-based, gel-type alignment media. As is shown by a first example of strychnine in a polystyrene/CDCl3 gel, the simulations potentially enable the accurate prediction of residual dipolar couplings taking into account structural details and dynamic averaging effects of both the polymer and the solute.
authors.affiliation: Institute for Advanced Study at the Department Chemie, Technische Universität München, Lichtenbergstr. 4, 85747, Garching, Germany.
authors.forename: Andreas O
authors.initials: AO
authors.lastname: Frank
authors.forename: J Christoph
authors.initials: JC
authors.lastname: Freudenberger
authors.forename: Alexey K
authors.initials: AK
authors.lastname: Shaytan
authors.forename: Horst
authors.initials: H
authors.lastname: Kessler
authors.forename: Burkhard
authors.initials: B
authors.lastname: Luy
mesh_terms: D005782:Gels; D056004:Molecular Dynamics Simulation; D013269:Stochastic Processes
chemical_list: D005782:Gels
keywords: 13C; 1H; MD simulations; NMR; RDC prediction; molecular alignment; orientational model; residual dipolar couplings; stochastic dynamics