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Oscillations, Waves, and Interactions - GWDG

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376 U. Kaatze <strong>and</strong> R. Behrends<br />

Figure 7. Ultrasonic excess attenuation spectra for aqueous solutions of 1 mol/l D-xylose<br />

at 25 ◦ C without CaCl2 (◦) <strong>and</strong> with 1 mol/l CaCl2 added (•). Dotted <strong>and</strong> dashed lines<br />

indicate the subdivision of the former <strong>and</strong> the latter spectrum, respectively, in Debye-type<br />

relaxation terms. Solid lines represent the sum of these terms, respectively [46].<br />

form inclusion complexes with a variety of molecules [51–55] <strong>and</strong> ions [56–60], including<br />

drugs [61,62]. Due to the hydrophilic outer surface of the cyclodextrin cone the<br />

complexes with guest molecules are soluble in water. Cyclodextrins are thus used to<br />

enhance or provide the solubility of molecules or organic ions, they act as stabilizers,<br />

selective agents, molecular recognition systems <strong>and</strong> also as capsules for the controlled<br />

delivery of specific molecules, with wide fields of applications.<br />

Recently α-cyclodextrin (α-CD)-iodide (I − ) complex formation has been found [60]<br />

that follows the simple equilibrium<br />

kf<br />

−<br />

α − CD + I ⇋<br />

r k<br />

α − CD · I−<br />

where α − CD · I − denotes the monoiodide inclusion complex <strong>and</strong> k f <strong>and</strong> k r are<br />

the forward <strong>and</strong> reverse rate constants, respectively, related to one another by the<br />

(17)<br />

Figure 8. Structure of a tridentate calcium<br />

ion-anhydroglucopyranoside complex.

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