Intermolecular Overhauser effects in fluoroalcohol solutions of cyclo-alanylglycine.
Interactions between the diketopiperazine cyclo-alanylglycine and four fluorinated alcohols in water-fluoroalcohol mixtures were examined by (1)H[(19)F] intermolecular nuclear Overhauser effects (NOE) experiments. The alcohols studied were trifluoroethanol, hexafluoroacetone trihydrate, 1,1,1,3,3,3-hexafluoroisopropanol and perfluoro-t-butanol. The experimental methods used permit detection of solvent-solute NOEs of 0.1% or less. Solute and solvent diffusion coefficients were determined and apparent molecular radii of the fluoroalcohols estimated. Using these data, it was shown that observed (1)H[(19)F] intermolecular NOEs are consistent with expectations based on theory. A method for extending conventional theory to take into account the shape of a solute and the exposure of its hydrogens to solvent is described. This approach gives reasonable agreement with experimental results, particularly if it is assumed that solute-solvent interactions take place in such a way that the fluorines of a fluoroalcohol are preferentially oriented toward the solute during solute-solvent encounters. The results support the suggestion that intermolecular (1)H[(19)F] NOEs may become a useful tool for studies of peptide and protein conformations in fluoroalcohol-water solvent mixtures.
Strickler
M A
MA
Department of Chemistry and Biochemistry, University of California, Santa Barbara 93106, USA.
Gerig
J T
JT
D000438:Alcohols; D001704:Biopolymers / Q000737:chemistry; D004151:Dipeptides / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D012996:Solutions
D000438:Alcohols; D001704:Biopolymers; D004151:Dipeptides; D010456:Peptides, Cyclic; D012996:Solutions; C464581:cyclo-alanylglycine