Ester hydrolysis by a cyclodextrin dimer catalyst with a tridentate N,N',N''-zinc linking group

Area of Science:

• Supramolecular Chemistry
• Catalysis
• Coordination Chemistry

Background:

• Beta-cyclodextrin dimers are effective host molecules.
• Metal complexes of cyclodextrins can exhibit catalytic activity.
• Developing efficient catalysts for ester hydrolysis is important.

Purpose of the Study:

• To synthesize and characterize a new beta-cyclodextrin dimer, 2,6-dimethylpyridine-bridged-bis(6-monoammonio-beta-cyclodextrin) (pyridyl BisCD, L).
• To prepare and evaluate the catalytic activity of its zinc complex (ZnL) for diester and phosphate ester hydrolysis.
• To determine the coordination properties and kinetic parameters of the ZnL catalyst.

Main Methods:

• Synthesis and characterization of the pyridyl BisCD ligand and its zinc complex.
• Potentiometric pH titration to determine formation and deprotonation constants.
• Kinetic studies of ester hydrolysis using substrates like bis(4-nitrophenyl)carbonate (BNPC), 4-nitrophenyl acetate (NA), bis(4-nitrophenyl)phosphate (BNPP), and disodium 4-nitrophenyl phosphate (NPP).

Main Results:

• The ZnL complex exhibits tridentate N,N',N''-zinc coordination with determined formation and deprotonation constants.
• ZnL demonstrated a high catalytic rate enhancement (8.98x10(3)-fold) for BNPC hydrolysis compared to uncatalyzed reactions.
• Catalytic hydrolysis of BNPP by ZnL showed a significant acceleration (approx. 1600-fold) with a rate constant of 1.68x10(-3) M(-1) s(-1), outperforming other tridentate N,N',N''-zinc analogues.

Conclusions:

• The synthesized pyridyl BisCD ligand forms a stable tridentate zinc complex (ZnL).
• ZnL is a highly effective catalyst for the hydrolysis of diesters and phosphate esters.
• The catalytic efficiency of ZnL highlights its potential for applications in chemical transformations.