Self-assembly of tubular supramolecular architectures via a combination of endo- and exo-recognition processes
Molecular design of noncovalent interactions provides a powerful tool for the engineering of complex systems which result from molecular recognition directed self-assembly of supramolecular architectures. This work has used several approaches to generate cylindrically shaped tubular supramolecular structures. Exo-recognition has been provided by the 3,4,5-tris (p-(n-dodecan-1-yloxy)benzyloxy) benzoyl or 3,4,5-tris(n-alkan-1-yloxy)benzoyl groups on the exterior surfaces of the structures. Endo-recognition is provided on the interior of the tubular structure by carboxylic acids, amides, oligooxyethylene, and hydroxy groups as well as the interactions resulting from the oligooxyethylene when LiCF3SO3 (LiOTf) is added in the core of the tubular supramolecular architecture. In some cases the endo-recognition has been supplemented with the covalent attachment to a polymer backbone. This allows for a comparison of a covalent polymeric structure with a supramolecular polymeric structure resulting from nonbonding interactions. These cylindrical shaped structures generate hexagonal columnar liquid crystalline (? h) phases in the bulk. The compounds have been characterized by 1H-NMR, IR, and HLPC. The phases that they generate have been characterized by DSC, thermal optically polarized mi croscopy, with representative samples additionally characterized by X-ray scattering experiments. Molecular models have been constructed to help speculate about the principle endo- and exo-recognition interactions involved in the self-assembly process. Poly(vinylethers) based on the above mentioned exo-receptors show that the formation of the cylindrical shape is strongly dependent on the shape of the polymer repeat unit. The inner cores of these cylinders have been functionalized to allow for the complexation of salts within these structures which resembles the organization of an ionic channel. These experiments also help in comparing the difference between a covalent and a noncovalent polymer backbone and the noncovalent interactions involved. Conductivity experiments show that the low molecular weight compounds have a lower activation energy associated with the transport of ions in the cores of these structures than do the polymeric compounds. Increasing the size of the wide end of the exo-receptor results in the transformation of the ? h into a cubic phase which also allows for the complexation of inorganic salts. Bisamides with taper shaped exo-receptors on opposite sides were found to form tubular supramolecular structures which generate ? h phases. The molecular organization responsible for this appears, by molecular modelling, to be formed from the hydrogen bonding of the bisamides along the column axis.
School:Case Western Reserve University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:self assembly tubular supramolecular architectures endo exo recognition
Date of Publication:01/01/1995