Dynamics of cyclohexaamylose (alpha cyclodextrin)·6 H2O by 1H solid state n.m.r. spectroscopy

✍ Scribed by Serge Lacelle; Bernard C. Gerstein

• Publisher: Elsevier Science
• Year: 1989
• Tongue: English
• Weight: 566 KB
• Volume: 186
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(89)84002-9

✦ Synopsis

In the present 'H-n.m.r.-studies, we investigated the dynamics of the spins associated with the narrow component of the absorption lineshape of solid cyclohexaamylose (alpha cyclodextrin) .6 H,O. The presence of dipolar interactions in both the narrow and the broad components of the lineshape is demonstrated with the detection of double quantum coherences. On the assumption of a dominant relaxation mechanism, the temperature dependence of the lineshape and the spinlattice relaxation time (TJ in local dipolar fields yield, at -35", a distribution of motional correlation time with a mean of 13.0 +0.7~s and an apparent energy of activation of 3.25 -to.33 kcal/mol. The "freezing" of the motions of the distribution occurs around -6O", with a corresponding measured T," of 6.8 +0.3 ps. The calculation of the second moment of the lineshape due to 'H homonuclear dipolar interactions from the crystal structure gives a T, value of 6.5 ks. The assignment of motion causing the T,d minimum and the transition of a composite single absorption lineshape is discussed in light of the present and previous n.m.r. studies, crystallographic data, and molecular dynamics simulations.