(200d) Monitoring Conformational Changes of Amphiphilic Polyesters in Different Solvents by Hyper-Rayleigh Scattering (HRS)

Hyper-Rayleigh Scattering has recently been employed in several chemical applications. Beyond them are the investigation of supra-molecular structure formation, the determination of dissociation constants, of the critical micelle concentration and the binding constant of a molecule with another molecule have been measured by the HRS [1]. HRS is an incoherent nonlinear optical process which depends linearly from the number concentration of the investigated molecules as well as of their hyperpolarizabilities.

We applied HRS to investigate amphiphilic polyesters with both hydrophilic and hydrophobic functionalities which have been synthesized in our group [2]. These polyesters are soluble in organic and aqueous media and reveal the formation of inverse architectures whose behavior can be correlated to their chemical structure. For example the values of hydrodynamic radius in non-polar toluene are systematically higher than those in polar acetone, which can be explained by the solubility parameters, since toluene is a better solvent for hydrocarbon blocks as compared to acetone. The application of HRS measurements to these polymers in different solvents reveal different hyperpolarizabilities, which can be correlated to the conformation of the molecules in their corresponding environment [3]. In contrast no changes in the hyperpolarizabilities can be observed when increasing the polymer concentration, since the HRS signal increases linearly with the polymer concentration.

Being an optical method with instantaneous response HRS also provides the possibility to perform time resolved measurements of the structural changes. In this context the solubilization of malachite green in toluene was investigated by HRS and common UV-Vis experiments. While the UV-Vis measurements show a continuous trend ending in an absorbance saturation, the HRS measurements reveal a dynamic processes of a confirmational change in the polyester solution during solubilization.

[1] P. K. Das: Chemical Applications of Hyper-Rayleigh Scattering in Solution J. Phys. Chem., 2006, 110, 7621-7630

[2] A. Voronov, A. Kohut, W. Peukert, S. Voronov, O. Gevus, V. Tokarev: Invertible Architectures from Amphiphilic Polyesters Langmuir, 2006, 22, 1946-1948

[3] L. Schneider, A. Voronov, A. Kohut, W. Peukert: Monitoring Conformational Changes of Micelles formed of an Amphiphilic Polyester by Hyper-Rayleigh Scattering, submitted for publication