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Solvent Dependence of the Rotational Diffusion of TOAC‐Spin‐Labeled Alamethicin
Author(s) -
Marsh Derek,
Jost Micha,
Peggion Cristina,
Toniolo Claudio
Publication year - 2007
Publication title -
chemistry and biodiversity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 70
eISSN - 1612-1880
pISSN - 1612-1872
DOI - 10.1002/cbdv.200790109
Subject(s) - chemistry , rotational diffusion , alamethicin , electron paramagnetic resonance , monomer , solvent , hexanol , rotational correlation time , viscosity , solvophobic , organic chemistry , nuclear magnetic resonance , molecule , polymer , thermodynamics , membrane , biochemistry , physics , alcohol , lipid bilayer
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.