The relative signs of coupling constants in fluorinated cyclopropanes and the aggregation of amyloid-beta (25-35) peptide

Cyclopropanes present interesting molecules to study due to their unique bond angles and strain in the three-membered ring. Protonated cyclopropanes have been extensively studied using nuclear magnetic resonance (NMR), but little work has been done with their fluorinated analogues. Double-resonance, or spin-tickling, NMR was used to determine the signs of three-bond vicinal fluorine-fluorine coupling constants and their relationship with temperature. Certain molecules were shown to conflict with the previously published relationship between the sign of the coupling constants in cyclopropanes and their temperature dependence.;Amyloid-beta peptide (Abeta) is the main component of plaques found in the brains of patients with Alzheimer's disease. Abeta is a soluble 39 to 42 residue peptide resulting from the proteolytic cleavage of the amyloid precursor protein. As a result of conformational changes, Abeta transforms from independent soluble monomers to insoluble, plaque-forming oligomers. This transformation is assumed to lead to the deleterious effects of Alzheimer's disease (AD). Some debate remains as to whether the symptoms associated with AD are a direct result of the plaque formation, or if the aggregation of Abeta is a secondary result. However, there is no question that the brains of patients who display signs of AD at time of death contain abnormally high amounts of Abeta plaque.;NMR was shown to be a useful analytical tool for the in vitro analysis of Abeta. Pulsed-field-gradient NMR (pfg-NMR) is particularly useful as it allows for the determination of diffusion coefficients. By subjecting the sample to a gradient magnetic field, the nuclei of an analyte can be spatially marked along an axis. Any movement along that axis results in signal attenuation. The signal attenuation was plotted against an array of the gradient strength and diffusion coefficients were calculated. This work involved altering sample conditions and measuring the diffusion of Abeta with the intent of finding a trigger for the aggregation of the peptide. The diffusion of Abeta(25-35), an 11 residue fragment of the Abeta peptide, was examined over a range of temperatures, pH, and in solutions with common biological metal ions.