Hydrolysis of linear DNA duplex catalyzed by Co(III) complex of cyclen attached to polystyrene

Catalytic Hydrolysis of Phosphate Monoester by Supramolecular Phosphatases Formed from a Monoalkylated Dizinc(II) Complex, Cyclic Diimide Units, and Copper(II) in Two-Phase Solvent System

Design and synthesis of enzyme mimic with programmed molecular interaction among several building blocks including metal complexes and metal chelators is of intellectual and practical significance. The preparation of artificial enzymes that mimic the natural enzymes such as hydrolases, phosphatases, etc. remains a great challenge in the field of supramolecular chemistry. Herein we report on the design and synthesis of asymmetric (nonsymmetric) supermolecules by the 2:2:2 self-assembly of an amphiphilic zinc(II)-cyclen complex containing a 2,2'-bipyridyl linker and one long alkyl chain (Zn₂L³), barbital analogues, and Cu²⁺ as model compounds of an enzyme alkaline phosphatase that catalyzes the hydrolysis of phosphate monoesters such as mono(4-nitrophenyl)phosphate at neutral pH in two-phase solvent system (H₂O/CHCl₃) in pH 7.4 and 37 °C. Hydrolytic activity of these complexes was found to be catalytic, and their catalytic turnover numbers are 3-4. The mechanistic studies based on the UV/vis and emission spectra of the H₂O and CHCl₃ phases of the reaction mixtures suggest that the hydrophilicity/hydrophobicity balance of the supramolecular catalysts is an important factor for catalytic activity.

Incorporation of Cobalt-Cyclen Complexes into Templated Nanogels Results in Enhanced Activity

Recent advances in nanomaterials have identified nanogels as an excellent matrix for novel biomimetic catalysts using the molecular imprinting approach. Polymerisable Co‐cyclen complexes with phosphonate and carbonate templates have been prepared, fully characterised and used to obtain nanogels that show high activity and turnover with low catalytic load, compared to the free complex, in the hydrolysis of 4‐nitrophenyl phosphate, a nerve agent simulant. This work demonstrates that the chemical structure of the template has an impact on the coordination geometry and oxidation state of the metal centre in the polymerisable complex resulting in very significant changes in the catalytic properties of the polymeric matrix. Both pseudo‐octahedral cobalt(III) and trigonal‐bipyramidal cobalt(II) structures have been used for the synthesis of imprinted nanogels, and the catalytic data demonstrate that: i) the imprinted nanogels can be used in 15 % load and show turnover; ii) the structural differences in the polymeric matrices resulting from the imprinting approach with different templates are responsible for the molecular recognition capabilities and the catalytic activity. Nanogel P1, imprinted with the carbonate template, shows >50 % higher catalytic activity than P2 imprinted with the phosphonate.

An IDB-containing low molecular weight short peptide as an efficient DNA cleavage reagent

We present poly(aspartic acid) grafting bis-amine conjugates as artificial nucleases, which can effectively induce double-strand DNA cleavage.

A kinetic study on nucleophilic displacement reactions of aryl benzenesulfonates with potassium ethoxide: role of K+ ion and reaction mechanism deduced from analyses of LFERs and activation parameters

Pseudofirst-order rate constants (k(obsd)) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates 4a-f and Y-substituted phenyl benzenesulfonates 5a-k with EtOK in anhydrous ethanol. Dissection of k(obsd) into k(EtO(-)) and k(EtOK) (i.e., the second-order rate constants for the reactions with the dissociated EtO(-) and ion-paired EtOK, respectively) shows that the ion-paired EtOK is more reactive than the dissociated EtO(-), indicating that K(+) ion catalyzes the reaction. The catalytic effect exerted by K(+) ion (e.g., the k(EtOK)/k(EtO(-)) ratio) decreases linearly as the substituent X in the benzenesulfonyl moiety changes from an electron-donating group (EDG) to an electron-withdrawing group (EWG), but it is independent of the electronic nature of the substituent Y in the leaving group. The reactions have been concluded to proceed through a concerted mechanism from analyses of the kinetic data through linear free energy relationships (e.g., the Brønsted-type, Hammett, and Yukawa-Tsuno plots). K(+) ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a cyclic transition state (TS) rather than by increasing the nucleofugality of the leaving group. Activation parameters (e.g., ΔH(‡) and ΔS(‡)) determined from the reactions performed at five different temperatures further support the proposed mechanism and TS structures.

Synthesis and Studies of Hydrolysis of p-nitrophenyl picolinate catalysed by Schiff base zinc (II) complexes with aza-crown ether or morpholino-pendants

Four Schiff base zinc (II) complexes with either benzo-10-aza-crown ether pendants or morpholino-pendants have been synthesised and employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalysed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of catalytic PNPP hydrolysis have been also examined. The rate increases with pH of the buffer solution; all four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with their crown-free analogues, the crowned Schiff base complexes exhibit higher catalytic activity. The catalytic activity of a phenyl-bridged Schiff base complex is larger than that of an ethyl-bridged Schiff base complex under the same substitute groups and metal ion.

Cyclen-based side-chain homopolymer self-assembly with plasmid DNA: protection of DNA from enzymatic degradation

In this study, a 1,4,7,10-tetraazacyclododecane (cyclen)-based side-chain homopolymer was developed for the first time; this polymer can self-assembly with plasmid DNA to form polyelectrolyte complexes (polyplex), which can protect DNA from enzymatic degradation. Moreover, the polyplex can disassembly and release free DNA when NaCl solution is added to this system. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used for imaging of the surface structure of the polyplex, and results indicated that the polyplex structures respond to the polymer concentration. Circular dichroism (CD) spectrum suggested that the DNA configuration in the polyplex was retained.

Angiotensin-cleaving catalysts: conversion of N-terminal aspartate to pyruvate through oxidative decarboxylation catalyzed by Co(III)cyclen

To provide a firm basis for the new paradigm of drug discovery based on peptide-cleaving catalysts, oligopeptide-cleaving catalysts were searched for by using human angiotensin I (Ang-I) and angiotensin II (Ang-II) as the substrates. Catalyst candidates containing the Co(III) complex of cyclen as the catalytic center were prepared by multicomponent condensation reactions. From two types of chemical libraries containing about 3,600 catalyst candidates, two compounds [SS-Co(III)X and S-Co(III)Y] were selected as the most active catalysts. On incubation with SS-Co(III)X and S-Co(III)Y, both Ang-I and Ang-II were cleaved by oxidative decarboxylation instead of peptide hydrolysis: the N-terminal Asp residues of Ang-I and Ang-II were converted to pyruvate residues. Catalysts for oxidative decarboxylation of the N-terminal Asp residue contained in an oligopeptide are unprecedented in both biological and chemical systems. Detailed kinetics analysis suggested that Ang-I and Ang-II can be cleaved with half-lives much less than 1 h if the structures of the chelating ligands of the catalysts are further improved. The results indicated that the concept of the peptide-cleaving catalysts can be expanded to include oligopeptides as the targets and nonhydrolytic reactions as the means for cleavage.

Metalated hybrid polymers as catalytic reagents for phosphate ester hydrolysis and plasmid modification

Pendant pyrazolylcyclophosphazene containing hybrid cross-linked polymer (CPPL) has been utilized for binding Zn(II). The metalated polymer (CPPL-Zn) has been found to be very effective catalyst for the hydrolysis of a RNA model phosphodiester substrate [2-(hydroxypropyl)-p-nitrophenyl phosphate, hNPP]. In addition, CPPL-Zn also cleaved supercoiled plasmid DNA pBR322 thus providing a novel structural motif of inorganic-organic hybrid polymers as synthetic nucleases.

Toward protein-cleaving catalytic drugs: artificial protease selective for myoglobin

A protein-cleaving catalyst highly selective for a disease-related protein can be used as a catalytic drug. As the first protein-cleaving catalyst selective for a protein substrate, a catalyst for myoglobin (Mb) was designed by attaching the Cu(II) or Co(III) complex of cyclen to a binding site searched by a combinatorial method using peptide nucleic acid monomers as building units. Various linkers were inserted between the catalytic Co(III) center and the binding site of the Mb-cleaving catalyst. Kinetic data revealed catalytic turnover of the Mb cleavage by the Cu(II) or Co(III) complex. MALDI-TOF MS revealed cleavage of the polypeptide backbone of Mb at selected positions. N-Terminal sequencing of the cleavage products identified the cleavage site and provided evidence for the hydrolytic nature of the Mb cleavage. Various chelating ligands were tested as the ligand for the Co(III) center of the Mb-cleaving catalyst. Among the nine chelating ligands examined, only cyclen and its triaza-monooxo analogue manifested catalytic activity.