ISSN:
1435-1536
Schlagwort(e):
Key words Photosurfactant
;
trans/cis-isomerization
;
cyclodextrin
;
complexation constant
;
enthalpy/entropy compensation
;
surfactant-selective electrode
;
induced circular dichroism
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
,
Maschinenbau
Notizen:
Abstract The stoichiometry, stability, and structure of the inclusion complex between the photosurfactants, 2-[4-(4-alkylphenylazo) phenoxy]ethyltrimethylammonium bromides (alkyl=ethyl, and butyl, where the abbreviations are EZ and BZ, and ZT for both, respectively), and γ-cyclodextrins (γ-CDx) in aqueous solution have been studied by the induced circular dichroism (ICD) and UV/VIS spectra as well as the potentiometric titration method. It is shown that the trans-ZT/γ-CDx systems form not only 1:1 (EZ) or 2:2 (BZ) but also 2:1 (ZT:γ-CDx) inclusion complexes. On the contrary, the steric hindrance of cis-ZT destabilizes the inclusion so that there is only 1:1 complex formation with γ-CDx. The thermodynamic discussion suggests that the stability of ZT complex is governed by the hydrophobic and the van der Waals interaction between the photosurfactants and cyclodextrins. However, the van der Waals interaction is more predominant in the trans-ZT/α-CDx system than in the β- and γ-CDx’s except for (BZ/γ-CDx)2 system. Moreover, the alkylchain-length dependence of the free energy changes of complex formation of ZT and CDx are less than those of micellization of ZT because the cavity depth of CDx is limited to incorporate all hydrophobic parts of ZT. Finally, the iso-equibrium temperature is estimated by the compensation plot of thermo-dynamic parameters.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/s003960050108
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