Nano-scale structures of supramolecules: From fractal bio-microgels to micellar aggregates.

摘要

Supramolecular microgels were produced through self-assembling multifunctional biopolymers with different aggregation forces. Both static and dynamic light scattering were employed to determine the internal morphologies of the microgels in terms of fractal dimension. There are three kinds of functional molecules in the system: three way DNA junctions (TWJ), biotin-ylated PNA molecules and avidin. Microgels can be formed selectively due to avidin-biotin or PNA-DNA combination. The interaction between avidin and biotin molecules has strong structure instruction to aggregation, and very selective, regular and compact aggregation motif was observed in initial microgels. The interaction between PNA and DNA strands possesses weak structure instruction; therefore, irregular and loose topology was found in thermal reversible microgels. The DNA-PNA helices contribute the thermoreversibilty to microgels and make the melting point of microgels adjustable; whereas, the structure formed by avidin-biotin combination is solidified upon formation in our experiments. Fractal structures were observed in both initial and reversible microgels. Fractal dimensions have been obtained from the angular dependence of the scattered intensity from microgels when the sizes of aggregates were large enough. The initial microgels were generated by slowly adding avidin to a solution of biotinylated-PNA bound to the TWJ at room temperature, the observed fractal dimension was around 2.60; while the reversible microgels were formed by cooling melting microgel solution below the melting point of PNA-DNA helices, reversible structure with Df ∼ 1.85 were formed. The fractal dimensions are consistent with the point-cluster and the cluster-cluster aggregation mechanisms, respectively. Thus, the structure of microgels was controlled through different aggregation mechanisms. The relationships between aggregated patterns with the concentration or the molecular configuration of subunits were also studied, and no dependent tendency has been observed in either situation. A narrow size distribution of microgels was found in equilibrium condition and explained in terms of the Flory theory. Enzyme modified avidin molecules were employed to introduce functional moieties into microgels and control the physical dimension of microgels.; Micellar systems also belong to the supramolecular chemistry, and are widely used in industry. Despite this, the structures of the micelles and the transition between their aggregation patterns in a solution are not yet fully studied. Cetyltrimethylammonium p-toluenesulfonate (CTAT) was employed to produce micellar supramolecules in water solution without any salt. (Abstract shortened by UMI.)