PNPP Hydrolysis Catalyzed by Manganese(III) Complexes with Crowned Salicylaldimine Schiff Base Ligand

Abstract

Four manganese(III) complexes (MnL 1 Cl, MnL 2 Cl, MnL 4 2 Cl, MnL 5 2 Cl) with a crowned salicylaldimine Schiff base ligand have been synthesized and employed as models to mimic hydrolase in the hydrolysis of p-nitrophenyl picolinate (PNPP). The kinetics and mechanism of catalytic PNPP hydrolysis have been investigated. The kinetic mathematical model of PNPP cleavage catalyzed by these complexes has been proposed. The effects of the ligand structure and crown ether ring in complexes, and the reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results show that compared with the crown-free analogous MnL 3 Cl and MnL 6 2 Cl, the crowned Schiff base manganese(III) complexes, MnL 1 Cl, MnL 2 Cl, MnL 4 2 Cl and MnL 5 2 Cl, exhibit more high catalytic activity, which follow the order: MnL 1 Cl >MnL 2 Cl >MnL 4 2 Cl >MnL 5 2 Cl >MnL 3 Cl >MnL 6 2 Cl; the pseudo-first-order-rate (k obs ) for the PNPP hydrolysis catalyzed by the complex MnL 1 Cl containing three crown ether rings is highest among six complexes and is 1.81 times that of MnL 3 Cl, 1.49 · 10 3 times that of spontaneous hydrolysis of PNPP, respectively, at pH = 7.00, [S] = 2.0 · 10 )4 mol dm )3 .

Synthesis and spectroscopic characterization of asymmetric Schiff bases derived from 4′-formylbenzo-15-crown-5 containing recognition sites for alkali and transition metal guest cations

“…The UV-vis spectra of the mono-imines, Ni(II) (1-3) and Zn(II) complexes (4)(5)(6) in EtOH have been measured and data are given in Table 5. The asymmetric ligands (L 1 -L 4 ) and their mononuclear sodium perchlorate complexes were The isomer ratio given in parentheses investigated in various solvents, acidic (CF 3 COOH) and basic (NEt 3 ) media (Table 5).…”

“…The zinc(II) complexes are naturally diamagnetic and exhibit no d-d transition; all their UV bands can be assigned to p-p* transitions of the azomethine chromophore of the ligands. (9) C (14) C (3,4) C (2,5,6,(10)(11)(12)(13) C (13) C (18) C (2,5,6,(10)(11)(12)(13)(14)(15)(16)(17) Table 5 UV-vis spectral data for the ligands and complexes a A 2 /A 1 = x/(100 -x) where A 1 = the absorbance of the phenol-imine form (p-p*); A 2 = the absorbance of the keto-amine form (n-p*); x = the percentage of ketoamine form b Keto-amine form 0% in basic medium. Basic medium is attained by addition of NEt 3 (1 mL) to the given solution (ligand concentration: 1 9 10 -5 mol dm -3 ) c Acidic medium is attained by addition of CF 3 COOH (1 mL) to the given solution (ligand concentration: …”

“…Schiff base ligands derived from the reaction of o-hydroxyaromatic aldehydes and amines have been extensively studied, due to their thermo-, photochromic and complexation properties [1][2][3][4][5][6] and tautomeric equilibria [7,8]. Salicylaldimines show photochromism, where the light absorption causes interconversion between phenol-imine and keto-amine tautomers via intramolecular hydrogen transfer.…”

“…The position of the tautomeric equilibrium in the series of Schiff bases and sodium complexes was investigated by UV-vis spectrophotometry. The absorption spectra of the investigated nickel and zinc complexes(1)(2)(3)(4)(5)(6) in different organic solvents are composed of several bands in the 200-500 nm region.…”

(E)-1-(4-Ethoxy-3-methoxybenzylidene)-2-(4-nitrophenyl)hydrazine

“…Metal complexes based on Schiff bases have attracted much attention because of their biological activity (Kahwa et al, 1986). Consequently, a large number of Schiff base derivatives have been synthesized and employed to develop protein and enzyme mimics, such as models to mimic hydrolase in the hydrolysis of p-nitrophenyl picolinate (Li et al, 2005).…”