Solvent dependence of the rotational diffusion of TOAC-spin-labeled alamethicin.
Three derivatives of the hydrophobic, channel-forming peptaibiotic alamethicin (F50/5) have been synthesized, the original Aib residue at position 1, 8, or 16 being replaced with the spin-labeled amino acid TOAC (=2,2,6,6-tetramethylpiperidin-1-oxyl-4-amino-4-carboxylic acid). Electron-paramagnetic-resonance (EPR) spectroscopy was used to characterize the rotational diffusion of these compounds in five isotropic solvents of differing viscosity and polarity, including MeOH, EtOH, PrOH, i-PrOH, and hexanol (HxOH). In MeOH, the labeled alamethicins were found to rotate anisotropically as a monomer (axial ratio a/b=3). In aliphatic alcohols of increasing viscosity (and hydrophobicity), the rotational correlation times progressively increased. Even in HxOH, the (fivefold) increase in correlation time was no greater than the increase in viscosity. We conclude that TOAC-labeled alamethicins remain monomeric in these solvents of relatively high polarity.
Marsh
Derek
D
Max-Planck-Institut für biophysikalische Chemie, Abteilung Spektroskopie, Göttingen, Germany.
Jost
Micha
M
Peggion
Cristina
C
Toniolo
Claudio
C
D000408:Alamethicin / Q000737:chemistry*; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D012997:Solvents / Q000737:chemistry*; D013113:Spin Labels
D003497:Cyclic N-Oxides; D012997:Solvents; D013113:Spin Labels; D000408:Alamethicin; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid