Zhi-Fen Zhou

Kinetics and mechanism of carboxyester hydrolysis using Zn(II) complexes with functionalized phenanthroline complexes

Abstract Zinc(II) complexes of six new functionalized phenanthrolines have been examined as catalysts for the hydrolysis of 4-nitrophenyl acetate (NA). The new ligands form a 1:1 zinc complex in the pH range 6.5–9.0. In the kinetic studies using the zinc complexes in 10% (v/v) CH3CN at 298 K, I=0.10 mol dm−3 KNO3 and pH 6.8–9.0, it was shown than an axial OH− serves as a good nucleophile that effectively catalyzes NA hydrolysis. The hydrolysis rate follows the law v=(kplus[complex]+kOH[OH−]+ko)[NA]. The second-order rate constants of ZnLH−1 are 0.934, 0.420, 0.360, 0.307, 0.257 and 0.143 mol−1 dm3 s−1 for L1, L2, L3, L4, L5 and L6, respectively, obviously larger than the corresponding value of 0.047 mol−1 dm3 s−1 for the N-methylcyclen-Zn(II)OH− complex catalyst.

Studies of artificial hydrolytic metalloenzymes: The catalyzed carboxyester hydrolysis by copper(II), zinc(II) and cobalt(II) complexes of the tripod ligand tris(2-benzimidazylmethyl)amine

The hydrolysis kinetics of p-nitrophenyl acetate (NA) catalyzed by CuII, ZnII and CoII complexes of tris(2-benzimidazylmethyl)amine (NBT) have been studied. The hydrolysis rate is first-order in both metal(II) complex and NA. The second-order rate constants, kcat are 0.083, 0.241 and 0.285 mol−1Ls−1 (298 K, I = 0.10 molL−1 KNO3, 0.02 molL−1 tris buffer, 40% MeCN aqueous solution) for Zn–NBT, Co–NBT and Cu–NBT complexes, respectively. The result indicates that the hydrolytic metalloenzyme activity of different metal complexes increases with the electrophilicity of the metal ions and that the complexes, in this paper, constitute that most efficient hydrolytic metalloenzyme models reported to date. An increase in MeCN content in the solution greatly reduces the hydrolytic activity of the nucleophiles.

High-yield calix[4]pyrroles as αβαβ isomers and X-ray structure analysis

Two calix[4]pyrroles as aβaβ isomers were prepared by the reactions of pyrrole with asymmetry ketones in high yields. In addition, two single crystals of calix[4]pyrrole 2 and 2·MeOH were solved by X-ray analysis, which further proved that either in free form or inclusion complex calix[4]pyrrole 2 is aβaβ isomer and adopts 1,3-alternate conformation.

Synthesis of novel 1,10-phenanthroline-2,9-bis-α-amino acid conjugates

Starting from 2,9-dimethyl-1,10-phenanthroline, the syntheses of eight novel 1,10-phenanthroline-2,9-bis-α-aminoacid conjugates (α-amino acids: DL-Ala, L-Val, L-Phe, L-His, L-Ile, L-Met, L-Glu, L-Asp) are described in detail.

Calorimetric determination of the heats of coordination of competitive ternary mixed-ligand complex compounds. Copper(II)-12-(Z′-hydroxy-3′-methoxy-benzyl)-1,4,7,10-tetraazacyclotridecane-11, 13-dione-α-aminoacids and 5-substituted 1,10-phenanthrolines system

Abstract The enthalpies of protonation of 12-(2′-hydroxy-5′-bormo-benzyl)-1,4,7,10-tetraazacyclotridecane-11,13-dione(HBTADO) have been determined in aqueous solution at 25.0±0.1°C and ionic strength 0.1 mol dm−3 KNO3 by means of model RD-1 automatic conduction calorimeter. The enthalpies of coordination of the binary complex compounds of this ligand with copper(II) and the ternary complex compounds of this ligand copper(II)-5-substituted 1,10-phenathrolines have also been determined under identical conditions of the ternary complex compounds of the type Cu(II)-α-aminoacids-HBTADO have been evaluated through “overall calculation”. Linear enthalpiesrelationships, linear enthalphy-entropy relationships have been found to exist between the enthalpies of formation of ternary complex compounds Cu(II)-R′Phen-HRTADO and the enthalpies, entropies of protonation of ligands HRTADO. In addition, linear enthalpy relationships have been found to exist between the enthalpies of formation of ternary complex compounds Cu(II)-α-aminoacids-HRTADO and the enthalpies of formation of binary complex compounds Cu(II)H−1A and linear entropy relationships have been found to exist between the entropies of formation of ternary complex compounds Cu(II)-α-aminoacids-HRTADO and the entropies of formation of binary complex compounds Cu(II)H−1A.

Kinetics of acid-catalysed dissociation of N,N′-dialkyl-1,10-phenanthroline-2,9-dimethanamine copper(II) complexes

The kinetics of the acid-catalysed dissociation of CuII complexes of four N,N′-dialkyl-1,10-phenanthroline-2,9-dimethanamine ligands (alkyl = Me, Et, i-Pr, t-Bu) have been studied using a stopped-flow spectrophotometer in 6.6 × 10−3 ∼ 0.5 mol dm−3 HCl (I = 0.5 mol dm−3 HCl + NaCl) over a range of temperatures. The kinetic data can be fitted to the rate expression kobs = kK′2[H+]/(1 + K′2[H+]). The acid dissociation can be rationalized in terms of a six-step kinetic process involving rapid pre-equilibrium cleavage of the two CuII–N(aliphatic amine) bonds, two rapid pre-equilibrium protonations and rate-determining cleavage of the CuII–N(phenanthroline) bond. The temperature dependence of the rate was determined and the appropriate thermodynamic parameters obtained.