INTRA-MOLECULAR HYDROLYSIS OF GLYCINAMIDE AND GLYCINE DIPEPTIDES COORDINATED TO COBALT(III) .2. REACTIONS OF THE CIS-[CO(EN)2(OH2-OH)(GLYNHR)]3+-2+IONS(R=H, CH2CO2C3H7,CH2CO2-) AND THE EFFECT OF BUFFER SPECIES

The intramolecular addition of cobalt(III) bound H2O and OH- to glycinamide. glvcylglycine isopropyl ester, and glvcylglycine also coordinated to Co(III) in the cis-[Co(en)2(OH2/OH)(glyNHR)]3+/2+ ions (R = H. CH2CO2C3H7, CH2CO2-) has been investigated both in the absence and presence of buffers. For the dipeptide complex (R = CH2CO2C3H7) both the aqua and hydroxo species form [Co(en)2(glyO)]2+, but loss of hydroxide also occurs resulting in the chelated amide[Co(en)2 (glyNHR))3+. A combination of rate and product analysis data suggests that the initial cyclization is rate determining under all conditions Buffer species act as general bases in this rate-determining process, but they also enhance the formation of the hydrolysis product. Coordinated water is more reactive than coordinated hydroxide owing largely to a more positive ΔS≠. © 1979, American Chemical Society. All rights reserved.