Effects of Various Schiff Base Ligands and Micelles on the Hydrolytic Kinetics of p-Nitrophenyl Picolinate

Abstract

In this article, the effects of different micelles and Schiff base ligands on the hydrolytic kinetics of p-nitrophenyl picolinate (PNPP) were evaluated. The results reveal that the biggest rate enhancement for PNPP hydrolysis was given in Gemini 16-6-16 micellar solution relative to other four reaction media, that is, cetyltrimethylammonium bromide (CTAB), n-lauroylsarcosine sodium (LSS), polyoxyethylene (23) lauryl ether (Brij35) and pure buffer. Moreover, the hydrolytic rates of PNPP in other four media decreased in the order LSS > CTAB > Buffer > Brij35. The structural effects of Mn(III) catalysts clearly testify that a relatively open active site facilitates the formation of reactive substrate-catalyst complex.

Keywords:

• Complex structure
• hydrolysis
• kinetics
• micelles
• p-nitrophenyl picolinate

We gratefully thank the financial support by Scientific Research Foundation for the PhD (Sichuan University of Science & Engineering, No: 07ZR14) and Key Project of China Sichuan Province Education Office (No. 08ZA160).

Notes

^a Conditions: 25°C, I = 0.1MKCl, [catalyst] = 1.0 × 10⁻⁵ mol L⁻¹, [16-6-16] = 1.0 × 10⁻⁴ mol L⁻¹, [LSS] = 5.0 × 10⁻³ mol L⁻¹, [CTAB] = 1.0 × 10⁻³ mol L⁻¹, [Brij35] = 1.0 × 10⁻³ mol L⁻¹.

Note: Superscripts b–e, respectively, denote the hydrolytic rates of PNPP promoted by the two complexes in Brij35, Buffer, CTAB, LSS media at pH 7.00, [PNPP] = 2.0 × 10⁻⁴ mol L⁻¹. Other data without footnote are the hydrolytic rate constants for the hydrolysis of PNPP promoted by MnL₂Cl/16-6-16.

Conditions: 25°C, I = 0.1MKCl, [catalyst] = 1.0 × 10⁻⁵ mol L⁻¹, [16-6-16] = 1.0 × 10⁻⁴ mol L⁻¹, [LSS] = 5.0 × 10⁻³ mol L⁻¹, [CTAB] = 1.0 × 10⁻³ mol L⁻¹, [Brij35] = 1.0 × 10⁻³ mol L⁻¹.

Note: Superscripts a–d, respectively, denote the hydrolytic rates of PNPP promoted by the two complexes in Brij35, Buffer, CTAB, LSS media at pH7.00, [PNPP] = 2.0 × 10⁻⁴ mol L⁻¹. Entries 5–9 list the related data for the Mn(III)-promoted hydrolysis of PNPP in Gemini 16-6-16 micellar solution.