Precise Sequence Control in Linear and Cyclic Copolymers
of 2,5-Bis(2-thienyl)pyrrole and Aniline by DNA-Programmed Assembly
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Abstract
A series
of linear and cyclic, sequence controlled, DNA-conjoined
copolymers of aniline (ANi) and 2,5-bis(2-thienyl)pyrrole (SNS) were
synthesized. In one approach, linear copolymers were prepared from
complementary DNA oligomers containing covalently attached SNS and
ANi monomers. Hybridization of the oligomers aligns the monomers in
the major groove of the DNA. Treatment of the SNS- and ANi-containing
duplexes with horseradish peroxidase (HRP) and H<sub>2</sub>O<sub>2</sub> causes rapid and efficient polymerization. In this way, linear
copolymers (SNS)<sub>4</sub>(ANi)<sub>6</sub> and (ANi)<sub>2</sub>(SNS)<sub>2</sub>(ANi)<sub>2</sub>(SNS)<sub>2</sub>(ANi)<sub>2</sub> were prepared and analyzed. A second approach to the preparation
of linear and cyclic copolymers of ANi and SNS employed a DNA encoded
module strategy. In this approach, single-stranded DNA oligomers composed
of a central region containing (SNS)<sub>6</sub> or (ANi)<sub>5</sub> covalently attached monomer blocks and flanking 5′- and 3′-single-strand
DNA recognition sequences were combined in buffer solution. Self-assembly
of these oligomers by Watson–Crick base pairing of the recognition
sequences creates linear or cyclic arrays of SNS and ANi monomer blocks.
Treatment of these arrays with HRP/H<sub>2</sub>O<sub>2</sub> causes
rapid and efficient polymerization to form copolymers having patterns
such as cyclic BBA and linear ABA, where B stands for an (SNS)<sub>6</sub> block and A stands for an (ANi)<sub>5</sub> block. These
DNA-conjoined copolymers were characterized by melting temperature
analysis, circular dichroism spectroscopy, native and denaturing polyacrylamide
gel electrophoresis, and UV–visible–near-IR optical
spectroscopy. The optical spectra of these copolymers are typical
of those of conducting polymers and are uniquely dependent on the
specific order of monomers in the copolymer