ESR study of rotational motions of spin-labeled long-chain nitroxides in solution

✍ Scribed by Yoshimi Sueishi; Takashi Takeuchi

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 448 KB
• Volume: 9
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199604)9:4<234::aid-poc776>3.0.co;2-#

✦ Synopsis

Information on the rotational motion of various types of spin-labelled long-chain nitroxides was obtained from the anisotropic ESR signals. By varying the position of the nitroxide moiety along the chain, the intrinsic flexibility of molecular chain was examined. The rotational correlation times (t,) of spin-labelled long-chain nitroxides were about lo-'". The activation parameters for rotational motion were estimated from the temperature and pressure dependences of t,. It was found that the activation entropy observed for methyl 16-doxy1 stearate is obviously large compared with those for methyl 5and methyl 12-doxy1 stearates. The results suggest an increase in the molecular motions at the end of the hydrocarbon chain. The viscosity dependence of t, is discussed in terms of the difference in the strength between solute-solvent and solvent-solvent interactions.