Conformational transitions of a free amino-acid-functionalized polythiophene induced by different buffer systems

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Abstract
A chiral, 3-substituted polythiophene with an amino-acid function shows pH-dependent visible, emission and circular dichroism spectra in buffered aqueous solution. At pH equal to the pI of the amino-acid, the backbone adopts a nonplanar right-handed helical conformation and the polymer chains are separated from each other. Increasing pH leads to a more planar conformation of the backbone and an aggregation of the polymer chains occurs. A lower pH will also lead to a more planar conformation of the backbone, but aggregation of the polymer chains appears to be absent. The aggregates are disrupted by increasing ionic strength in alkaline buffer systems, indicating hydrogen bonding is important for aggregation. On the other hand, ions containing an amino group and one or more hydroxyl groups induce a more planar conformation of the polymer backbone.