Origins of Micellar Diastereoselectivity

Article abstract of DOI:10.1021/ja00336a034

Thiol-functionalized surfactant micelles (n-C12H25N⁺Me2CH2CH2SH,Cl^-) were used to cleave Z-Trp-Pro p-nitrophenyl dipeptide esters.Marked kinetic diastereoselectivity was observed in these reactions.For example at pH 8 and concentrations (ca.6-7)x1E-3 M, the micellar thiol cleaved the LL substrate 5-6 times more rapidly than its DL diastereomer.This kinetic diastereoselectivity was shown to develop at surfactant concentrations ca.5x1E-3 M, considerably above the cmc (ca.1x1E-3 M), i.e., at a second "critical concentration".Dynamic light-scattering measurements showed that micelles which had reacted with the LL (but not the DL) substrate underwent a marked increase in apparent hydrodynamic diameter (from ca. 15 to 26 nm) near this second critical concentration.Similar phenomena could be induced upon addition of 2x1E-5 M LL dipeptide surfactant reaction product to the thiol micelles.Micelles of n-C12H25N⁺Me2CH2CH2OH,Cl^- or n-C12H25N⁺Me3,Cl^- were unresponsive to such additions (light scattering).The results are discussed in terms of molecular and supramolecular interactions between surfactant and solubilizate molecules.