title: Force-field dependence of Boltzmann weighting factors on predicted pi-pi* circular dichroic spectra of cyclo (Gly-Pro-Gly)2.
abstract: Semi-empirical energy calculations were performed for published conformations of cyclo (Gly-Pro-Gly)2 using different force fields (DISCOVER cvff and cff91, AMBER, and CHARMM). The resulting potential energies were then used to create Boltzmann weighting factors for an ensemble of cyclo(Gly-Pro-Gly)2 structures. The dipole interaction model was used to predict pi-pi* circular dichroic spectra (CD) for the individual structures of cyclo(Gly-Pro-Gly)2. The Boltzmann weighting factors were applied to the individual spectra so that a composite spectrum was constructed to represent a CD arising from a collection of different structures in solution. Weighting factors determined from different force fields were compared. Boltzmann-weighted spectra better resembled the experimental CD than any calculated spectrum using only a single conformation of cyclo (Gly-Pro-Gly)2. The structures most heavily weighted contained at least one type I beta-turn.
authors.affiliation: Chemistry Department, University of North Dakota, Grand Forks, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: MacFarlane
authors.forename: M M
authors.initials: MM
authors.lastname: Humbert
authors.forename: K A
authors.initials: KA
authors.lastname: Thomasson
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism; D008962:Models, Theoretical; D010456:Peptides, Cyclic / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D010456:Peptides, Cyclic