PNPP Cleavage Catalyzed by Schiff Base Mn(III) Complexes Containing Polyether Side Chains in CTAB Micellar Solutions

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k ₀) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k _obsd) of PNPP catalytic hydrolysis are 1.93×10³ fold for MnL¹ ₂Cl and 1.06×10³ fold for MnL² ₂Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10⁻⁴mol · dm⁻³, respectively. Furthermore, comparing the k _obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL₂(L=L¹, L²) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL¹ ₂Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL² ₂Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.

Keywords:

• Kinetics
• PNPP hydrolysis
• crowned Schiff base manganese(III) complexes
• metallomicellar solution

Acknowledgments

The authors gratefully acknowledge financial support from China National Natural Science Foundation (No.: 20072025, 20173038) and Key Project of Sichuan Province Education Office (No.: 2005D007).