title: Toward a molecular understanding of the detection of amyloid proteins with flexible conjugated oligothiophenes.
abstract: Molecular and electronic structures and optical absorption properties of oligothiophenes used for spectral assignment of amyloid deposits have been investigated for a family of probes known as luminescent conjugated oligothiophenes (LCOs). Theoretical absorption spectra have been determined using conformational averaging, combining classical molecular dynamics (MD) simulations with quantum mechanical/molecular mechanics (QM/MM) time-dependent density functional theory (TD-DFT) spectrum calculations. Theoretical absorption spectra are in excellent agreement with experiments, showing average errors below 5 nm for absorption maxima. To couple observed properties to molecular structures, a measure of planarity is defined, revealing a strong correlation between the transition wavelength of the first and dominating electronically excited state and dihedral rotations. It is shown that from this correlation, predictions can be made of the absorption properties of probes based only on information from MD trajectories. We show experimentally that red shifts observed in the excitation maxima of LCOs when bound to amyloid protein aggregates are also evident in absorption spectra. We predict that these red shifts are due to conformational restriction of the LCO in a protein binding pocket, causing a planarization of the conjugated backbone. On the basis of our studies of planarity, it is shown that such shifts are both possible and realistic.
authors.affiliation: Department of Physics, Chemistry and Biology, Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Jonas
authors.initials: J
authors.lastname: Sjöqvist
authors.forename: Jerôme
authors.initials: J
authors.lastname: Maria
authors.forename: Rozalyn A
authors.initials: RA
authors.lastname: Simon
authors.forename: Mathieu
authors.initials: M
authors.lastname: Linares
authors.forename: Patrick
authors.initials: P
authors.lastname: Norman
authors.forename: K Peter R
authors.initials: KP
authors.lastname: Nilsson
authors.forename: Mikael
authors.initials: M
authors.lastname: Lindgren
mesh_terms: D058227:Amyloidogenic Proteins / Q000737:chemistry*; D006801:Humans; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D013876:Thiophenes / Q000737:chemistry*
chemical_list: D058227:Amyloidogenic Proteins; D013876:Thiophenes