Enzymatic synthesis of polyaniline complexed with DNA and other polyelectrolyte templates

In the field of inherently conducting polymers, polyaniline has elicited tremendous interest due to its promising electrical properties and unique redox tunability. Recently, synthetic routes involving the use of polyelectrolytes have significantly improved the processability of polyaniline. A template guided synthesis catalyzed by an enzyme, Horseradish peroxidase (HRP), developed recently has provided a means of polymerizing aniline in milder pH conditions (pH 4.3) and has widened the choice of templates.; With the objective of creating a unique molecular complex of a conducting polymer and a bio-macromolecule, this thesis presents a generic methodology involving a biological polyelectrolyte (DNA), utilized as a template for the synthesis of polyaniline. A phosphate containing polyelectrolyte, poly (vinyl phosphonic acid) [PVP] has been used as a proof-of-concept template for the enzyme catalyzed synthesis of polyaniline. The molecular complex of PVP-Polyaniline has been found to be redox-active with conductivities of the order of 0.01 S/cm. Appropriate control on the polymerization has also provided a means of tuning the water solubility and conductivity of the PVP-polyaniline complex.; The inherent molecular order and the polyelectrolyte behavior of DNA have been utilized for assembling and synthesizing polyaniline. The electrostatic interaction between the phosphate groups (from DNA) and the protonated aniline has aided in organizing the aniline molecules prior to polymerization and promoting a para-directed coupling of the aniline molecules. The wrapping of polyaniline on DNA has been found to induce changes in the secondary structure of DNA leading to the formation of an over-wound polymorph. The polyaniline synthesized on DNA also exhibited a template-induced macro-asymmetry. Circular dichroism studies on the complex have suggested that the redox state of the polyaniline formed on the DNA can be used to reversibly switch the conformation of DNA between the loosely wound polymorph and a more tightly wound polymorph. AFM and TEM studies have indicated that the overall secondary structure of the DNA has been preserved subsequent to the formation of polyaniline.; These results suggest new possibilities in the use of this complex for the fabrication of biosensors, diagnostic tools and for fundamental studies to "probe" the structure of DNA. The remarkable specificity in the recognition capabilities of DNA can be combined with the doping dependent electrical properties of polyaniline to develop methods for highly selective detection of DNA hybridization.