Synthesis and molecular recognition of conjugated polymer with DNA-mimetic properties

The synthesis of a new DNA-mimetic pi-conjugated poly(p-phenylenebutadiynylene) (polymer 9), which is functionalized with thymine nucleobases, as well as polyethylene glycol chains at every repeat unit is reported. This polymer was characterized by UV-vis, fluorescence, nuclear magnetic resonance, infrared, and Raman spectroscopy as well as gel permeation chromatography. These show its water-induced aggregation and a sharp transition from the aggregated phase to a more molecularly dissolved species when the temperature is increased. Molecular recognition properties of 9 with a number of guest molecules, including (i) 2,6-diacetamidopyrimidine and thymine derivatives in chloroform, (ii) adenosine and thymidine in m ater, and (iii) DNA d[A(20)] and DNA d[T-20] in water, were investigated by UV-vis, fluorescence, thermal denaturation, circular dichroism (CD), nuclear magnetic resonance, and some control experiments. These results demonstrate that polymer 9 selectively binds complementary small molecules, both in organic solvents and in water, with concomitant enhancement in its fluorescence intensity and effectively discriminates between complementary and noncomplementary molecules. Importantly as well, this polymer forms a complex with complementary DNA. which shows enhanced fluorescence, a sharp thermal transition reminiscent of a natural DNA duplex, and a dramatic change in the secondary structure of the DNA guest. This is the first example of the hydrogen-bonding association of a conjugated polymer selectively to complementary DNA, with excellent discrimination between complementary and noncomplementary strands. Thus, the incorporation of nucleobases into conjugated polymers presents a useful toot to control chain-chain interactions and phototophysical proper-ties through selective binding to DNA and its derivatives, to evolve sensor platforms for these biomolecules, and to possibly probe and modify the structure of the guest DNA.