Carbon-13 Relaxation and Proton Nuclear Magnetic Resonance Studies of Prostaglandin F_2α

Abstract

Carbon magnetic resonance T₁ relaxation and chemical shift measurements at 22.63 MHz establish hydrophobic aggregation of prostaglandin F_2α in phosphate buffer solutions between 0.05 and 0.2 M. Analysis of the proton magnetic resonance spectra of prostaglandin F_2α at 270 MHz by double resonance techniques yield all the proton-proton coupling constants for the five-membered ring indicating a favored half-chair conformation for the ring in which the dihedral angle for the C-8 and C-12 protons is close to 180°. Effective correlation times derived from carbon magnetic resonance T₁ values for all the carbon atoms show segmental motion for ring carbon C-10 and in the aliphatic portions of both side chains, while the double bonded portions of the side chains and the ring carbons act as a more rigidly interconnected network. Chemical shift changes in the carbon magnetic resonance and proton magnetic resonance spectra upon aggregation suggest that the 5-6 double bond, C-7, and C-9 participate in the aggregation process.

• chemical shift measurements
• conformation in solutions
• proton-proton coupling constants
• dihedral angles