Conformation of Poly(methacrylic acid) Chains in Dilute Aqueous Solution

TLDR: In this article, the authors present a comprehensive investigation of the conformational switch of poly(methacrylic acid) using techniques which report on various length scales: fluorescence energy transfer experiments provide unique information on the nanometer length scale while dynamic light scattering (DLS) offers an insight into longer range interactions involved in the transition.

Abstract: Poly(methacrylic acid) (PMAA) undergoes a conformational transition between pH 4 and 6 from a hypercoiled structure to a water-swollen state. There has been much speculation as to the exact nature and driving force of the transition. In this paper, we present a comprehensive investigation of the conformational switch of PMAA using techniques which report on various length scales:  fluorescence energy transfer experiments provide unique information on the nanometer length scale while dynamic light scattering (DLS) offers an insight into longer range interactions involved in the transition. Fluorescence energy transfer measurements demonstrate that PMAA undergoes subtle molecular rearrangements between pH 2 and 5 as short-range hydrophobic interactions between methyl groups are broken down by increasing concentrations of mutually repulsive carboxylate anions. Although such rearrangements have been proposed to account for the pH behavior of PMAA, we reveal them experimentally using techniques sensitive to na...