Chiroptical Spectroscopic Studies on Surfactants, Other Aggregating Systems, and Natural Products

Abstract

Recent experimental studies have shown unexpected chiroptical response from some chiral surfactant molecules. In these cases, the magnitude of the specific optical rotation was seen to change as a function of surfactant concentration, which is considered to be due to molecular aggregation and contrary to that known for typical organic molecules. To explain these experimental results on the +10,000 atom surfactant systems, non-traditional methods are necessary. To that end, a large number of molecular dynamics simulations, quantum mechanical calculations, and extensive analysis have been performed on a model system, the lauryl ester of phenylalanine. Monomer-dimer equilibrium, representing the simplest form of aggregation, and its influence on the Horeau effect, have also been investigated using pantolactone and 2-hydroxy-3-pinanone as test cases. Also a novel chiroptical spectral analysis method utilizing the Dissymmetry Factor (DF) spectrum has been developed. Studies ranging from rigid to flexible molecules have demonstrated the advantages of the DF method, especially when several diastereomers are involved. Using the DF spectrum as an additional means of analysis, the previously undetermined absolute configurations of four natural products have been determined.