Nanotubes Formed By The Self-assembly Of Thiacalixarenes Bearing Hydrogen-bonding Groups

Calixarenes, as the third host molecules after cyclodextrins and crown ethers in supramolecular chemistry, have attracted considerable attentions. As calixarenes contain a hydroxyl array, aπ-based cavity and several reactable positions, they are broadly used as building blocks to construct well preorganized host molecules which have widely been applied in the field of molecular recognition, enzyme mimics, etc. Great achievements of calixarenes chemistry have been made in recent 20 years. Especially the chemical modifications of calix[4]arenes have gotten mature now. Much attention has been given to the self-assembly of calixarenes. The nanotubes formed by the self-assembly of calixarenes containing hydrogen-bonding groups will be discussed in this dissertation.In chapter one, the survey of supramolecular chemistry was briefly introduced. The four approaches used in the construction of supramolecular organic nanotubes and the nanotubes formed by the self-assembly of calixarenes were reviewed. In light of the above introduction, the design strategies of this thesis are outlined.In chapter two, three types of 1,3-alternate calixarene derivatives contaning hydrogen-bonding groups were synthesized:the 1,3-alternate p-tert-butylthiacalix[4]arene derivatives bearing carboxylic acid, urea, thiourea, aminothiourea or amide groups at the lower rim; the 1,3-alternate p-H-thiacalix[4]arene derivatives bearing carboxylic acid or urea groups at the lower rim and the 1,3-alternate p-H-calix[4]arene derivatives bearing carboxylic acid or urea groups at the lower rim. The mainly reactions involved in the synthesis process were the hydrolysis, chloroacylation and aminolysis of 1,3-alt-tetrakis((ethoxycarbonyl)methoxy) calix[4]arene. The molecular structures of the compounds were characterized by 1H NMR, ESI-MS and EA.In chapter three, the influence of the pendant orientation on the self-assembly of four 1,3-alternate p-tert-butylthiacalix[4]arene derivatives bearing urea groups at the lower rim and on the formation of hydrogen-bonded nanotubes were studied. The pendant arms either orientate towards the inner side of the cavities, or orientate towards the outside, depending on the types of hydrogen-bonding groups and the position of these groups. When the same groups are in the same side, the opposite chains in the molecule will locate away from each other which may be due to the steric repulsions. But when the urea group and carboxylic acid group are in the same side, the opposite chains all orientate inwards because of the intramolecular, inter-chain hydrogen bonds between the opposite chains. In the extended structure, neighboring calixarenes connect in a "head-to-head" or "head-to-tail" manner if the pendant arms orientate towards the cavity. They connect "side-by-side" if the pendant arms orientate outwards. Through the study of the self-assembly behavior of the four compounds, we find that there are two requirements in the construction of nanotubes formed by the stacking of the calixarene cavities:the "head-to-head" or "head-to-tail" connection manner and the cavity of calixarenes should not be occupied by the atoms of the inwardly orientated pendant arms.In chapter four, the influence of the crystallization medium (solvent/guest type) and the t-butyl groups on the self-assembly of two 1,3-alternate thiacalix[4]arene derivatives bearing carboxylic acid groups at the lower rim and on the formation of hydrogen-bonded nanotubes were studied. For 1,3-alternate p-tert-butylthiacalix[4]arene tetraacetic acid:in ethanol and in the existence of 4,4'-bipyridine, infinite aquatubes are generated; while in acetone, a sandwich-like structure is formed. For 1,3-alternate p-H-thiacalix[4]arene tetraacetic acid:in ethanol, acetone and in the existence of 4,4'-bipyridine, a 2D stair-like structure, a 2D sheet-like structure and infinite nanotubes are formed, respectively. The different self-assembly behavior of the two compounds in different crystallization medium is mainly induced by the different hydrogen bonding interaction sites that provided by ethanol, acetone and 4,4'-bipyridine. Because of the steric hindrances posed by the t-Bu groups, the self-assembly behavior of the two compounds is affected by the crystallization medium in different degrees. For 1,3-alternate p-tert-butylthiacalix[4]arene tetraacetic acid, the influence of crystallization medium on its self-assembly behavior is based on the [1+2] supramolecular unit. Its tubular shape molecular structure and water inclusion property are not affected. While for 1,3-alternate p-H-thiacalix[4]arene tetraacetic acid, its molecular structure are susceptible to the crystallization medium due to the absence of the t-Bu groups. Through the study of the self-assembly behavior of the two compounds in different crystallization medium, we find that in the construction of nanotubes formed by the stacking of the calixarene cavities, the orientation of the pendant arms can be regulated by the introduction of appropriate guest molecules.In chapter five, the self-assembly of two 1,3-alternate thiacalix[4]arene derivatives bearing amide groups at the lower rim was studied. Because of the steric hindrances posed by the t-Bu groups, neighboring 1,3-alternate p-tert-butylthiacalix[4]arene tetraamide can't connect to each other directly. Instead, they are linked together through the connection of water molecules. For 1,3-alternate p-H-thiacalix[4]arene tetraamide, its molecular structures are mutable because of the absence of the t-Bu groups. The length of the pendant arms should be considered when 1,3-alternate p-tert-butylthiacalix[4]arene derivatives are used as the platform for nanotube construction. If the length of the pendant arms is not long enough to conquer the steric hindrance posed by the t-butyl groups, appropriate guest molecules should be introduced to facilitate neighboring molecules connecting to each other in the "head-to-head" or "head-to-tail" manner.