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Thermal Behavior, Molecular Assembly and Isomers Recognition in Supramolecular System

Author: ZhuLinHong
Tutor: SongLeXin
School: University of Science and Technology of China
Course: Inorganic Chemistry
Keywords: Cyclodextrin Crown Degradation Push-Pull effect Synergistic effect
CLC: O641.3
Type: Master's thesis
Year: 2011
Downloads: 45
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Abstract


Cyclodextrin (CD) is an typical host of supramolecular chemistry, and it is made up of several glucose units throughα-1,4 linkages. The special structure of CD with a hydrophobic lumen and a hydrophilic appearance allows it to form complexes with various kinds of guests. Although there are lots of reports about CD inclusion complex, little attentions is foucused on the interaction between CD and another macrocyclic host crown. We prepared the complexes formed by CD and crown, and then researched the push-pull effect and synergistic effect of the mixed host to amphiphilic guests. On the other hand, in this work, the themal behaviors of CD, its derivative and adduct were investigated comprehensively. Simultaneously, we evaluated the effect of the fragments generated from CD, its derivative and adduct when they were heated. The main contents are as follows:1. The thermal behaviors of homologues, derivatives and adducts ofβ-cyclodextrin (β-CD) are compared based on thermogravimetry (TG) and gas chromatography coupled to time-of-flight mass spectrometry (GC-TOF-MS) analyses in this paper. Our results indicate that the number of glucose units and the introduced groups cause a considerable change in thermal decomposition mechanisms of these carbohydrates. Further, it is observed that the mass loss of the bicomponent aggregate formed by phenylarsonic acid (PAA) andβ-CD is larger than that of each of the components at higher temperatures. Additionally, the decomposition of the adduct produces a series of arsenic compounds with high relative abundances, such as AsO~+, As2O2~+, As3O4~+ and As4O6~+, which is rather different from the decomposition behaviors of free PAA and the adduct ofβ-CD with sodium arsenite.2. The formation of a 1:1 supramolecular complex ofβ-CD and 18-crown-6 (18C6) was confirmed by elemental analysis, 1H nuclear magnetic resonance and electrospray ionization mass spectrometry. The probable interaction sites between them were proposed by two-dimensional rotating frame nuclear Overhauser effect spectroscopy. Also, the degradation process including degradation degree and degradation products of the complex was carefully compared with those ofβ-CD and 18C6 through TG and GC-TOF-MS. These results gave a strong impression that a supramolecular complex can be constructed by the flexible macrocyclic molecule 18C6 as a guest and the rigid macrocyclic moleculeβ-CD as a host via a molecular assembly behavior between them.3. The present work was devoted to the study of the effect of one host (18-crown-6, 18C6) on the binding behavior of the other host (β-cyclodextrin,β-CD) to amphiphilic guests such as sodium dodecyl benzene sulfonate (SDBS) and D-, L-tryptophan (D-, L-Trp). Our results indicated that different combinations of the two hosts exhibited different push-pull effects in their binding process to SDBS, and the extent of the push-pull effect was dramatically dependent on the initial stoichiometric ratios of the two hosts. That is to say, the effect of 18C6 on the binding behavior ofβ-CD to SDBS was not linear with its mole fraction, but first decreased and then increased with the increase of its mole fraction. On the other hand, there was a concentration dependence of synergistic effect of 18C6 andβ-CD on the binding behavior to D- or L-Trp. And there were rather remarkable differences in the molecular recognition abilities (K_L/K_D) ofβ-CD to D- and L-Trp in the presence of 18C6, such as freeβ-CD (0.48), 18C6-β-CD-a (0.27), 18C6-β-CD-b (4.03), 18C6-β-CD-c (4.16), 18C6-β-CD-d (1.72) and 18C6-β-CD-e (2.31). These results clearly revealed the important role of 18C6 in mediating the intermolecular interaction between the amphiphilic guests andβ-CD, providing a new insight into the mutual effect between two hosts in multicomponent systems.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Structural Chemistry > Molecular interactions,supramolecular chemistry
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