1H and 13C NMR investigation of conformational and aggregation behavior of sodium N-lauroyl sarcosinate

Abstract

Complementary experiments with NMR 1H and 13C spectroscopy, proton diffusometry, and relaxometry have been used to investigate the sodium N-lauroyl sarcosinate (SLS) micellar systems in aqueous solutions. The effects of concentration and temperature on molecular conformation, micellar structure, and molecular kinetic in the SLS solutions were studied. Each NMR spectral line of the SLS spectrum splits but there are two variants of the effect: (i) for the head-groups this effect exists in the whole concentration range and it is due to the presence of two conformational isomers, (ii) for the hydrophobic part the splitting of resonance lines is observed in certain concentration range and caused by the existence of two different realizations of micellar aggregates. The concentration of the cis-conformers is a bit higher in a “monomer” (diluted) solution as well as the trans-conformers are more favorable in the micellar state. The relation of cis- and trans-conformer fractions is nearly independent of temperature. The transient concentration range, where different types of micellar sub-structures co-exist, is discovered. Moreover, the SLS solutions are characterized by four kinetic processes with different time scale.