Leaving group effect in the cleavage of picolinate esters catalyzed by hydroxy-functionalized metallomicelles
摘要:
Micellar aggregates of complexes of transition metal ions with the hydroxy-functionalized surfactant 1a are very effective catalysts of the cleavage of activated esters of alpha-amino acids. To ascertain their effectiveness toward unactivated esters, a systematic kinetic study was undertaken employing as substrates the picolinic acid esters 3a-1, the pK(a) of their alcoholic portion spanning more than 12 units from 3.6 to 16. The leaving group effect was investigated in water, pH=6.3, in the absence and presence of CU2+ ions, in the presence of the nonmicellar complex 2-CU2+, and in the presence of micellar aggregates made of 1a-Cu2+ or of its O-methylated analog 1b-Cu2+. In the presence of free metal ions the leaving group effect is negligible in the case of esters with good leaving groups (pK(a)
Leaving group effect in the cleavage of picolinate esters catalyzed by hydroxy-functionalized metallomicelles
摘要:
Micellar aggregates of complexes of transition metal ions with the hydroxy-functionalized surfactant 1a are very effective catalysts of the cleavage of activated esters of alpha-amino acids. To ascertain their effectiveness toward unactivated esters, a systematic kinetic study was undertaken employing as substrates the picolinic acid esters 3a-1, the pK(a) of their alcoholic portion spanning more than 12 units from 3.6 to 16. The leaving group effect was investigated in water, pH=6.3, in the absence and presence of CU2+ ions, in the presence of the nonmicellar complex 2-CU2+, and in the presence of micellar aggregates made of 1a-Cu2+ or of its O-methylated analog 1b-Cu2+. In the presence of free metal ions the leaving group effect is negligible in the case of esters with good leaving groups (pK(a)