DNA-binding and hydrolytic cleavage promoted by tetraazamacycle La(III) and Ce(III) complexes

Nuclease Activity of Diaza-Crown Ether Complexes of Cerium(III) with Different Functional Groups as Side Arms

Cerium(III) complexes of two ligands of a diaza-crown ether with different functional groups as side arms were synthesised and characterised. The catalytic ability of the cerium(III) complexes for pUC19 DNA cleavage was investigated and compared using agarose gel electrophoresis. The results indicate that the catalytic activity of the complex CeL2 [L2 = 2,2′- (1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl) diacetamide] with two carbamoylmethyl groups is significantly higher than the complex CeL1 [L1 = 2,2′- (1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl) diethanol] with two hydroxyethyl groups under the same conditions. The optimum catalytic concentrations of CeL1 and CeL2 were 7.69 × 10−5 and 3.08 × 10−5 mol L−1 respectively and excessively high concentrations of the complexes can reduce their catalytic efficiency due to the formation of inactive μ-hydroxo dimers. The optimum catalytic acidities of CeL1 and CeL2 were pH 7.0 and 7.5 respectively and excessively high pH of the reaction system can reduce the catalytic efficiency of the complexes due to the formation of cerium(III) hydroxide. DNA cleavage promoted by the two complexes takes place via the same hydrolytic pathway and so the activity difference of the two complexes is attributed to the stability of the complexes, rather than the catalytic mechanism.

Catalytic Capacity of Diaza-Crown Ether Lanthanum Complexes with Varied Ligands for Phosphate Ester Hydrolysis in Different Media

Two diaza-crown ether compounds, 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (L0) and its derivative with double acetamide side arms 2,2'-(1,4,10,13-teteaoxa-7,16-diazacyclooctadecane-7,16-diyl)diacetamide (L), and the corresponding two lanthanum complexes were synthesised and characterised. The catalytic capacity of the lanthanum complexes was investigated for the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP) in aqueous solution and in CTAB micelles. Kinetic studies show that the catalytic efficiency of complex LaL is obviously higher than that of complex LaL0, and introducing acetamide into the ring of the diaza-crown ether can improve the catalytic ability of the complexes for BNPP hydrolysis. A rate enhancement of about two times was observed for the complex–micelle in contrast with the complex–water system for BNPP catalytic hydrolysis. The optimal pH for the catalytic reaction in the two kinds of media systems show an approximately 0.4 pH unit difference. The two complexes possess higher thermostability, and are more stable in the micelle than in aqueous solution. Based on the results and their analysis, a catalytic mechanism with cooperation of acetamide is proposed.

Efficient non-enzymatic cleavage of Staphylococcus aureus plasmid DNAs mediated by neodymium ions

Staphylococcus aureus plasmids are the main factor in the spreading of antibacterial resistance among bacterial strains that has emerged on a worldwide scale. Plasmids recovered from 12 clinical and food isolates of S. aureus were treated with 10 mM free lanthanide Nd(3+) ions (non-enzymatic cleavage agent) in Hepes buffer (pH 7.5) at 70 °C. Topological forms of plasmids-closed circular (ccc), open circular (oc), and linear (lin)-produced by cleavage at different times were separated using pulsed-field agarose gel electrophoresis. The method is proposed to detect and differentiate several plasmids in the same bacterial strain according to their size.

DNA binding and cleavage properties of the Ce (III) complex of a diaza-crown ether

The hydrolytic cleavage of pUC19 DNA as promoted by the trivalent cerium complex (CeL) of diaza-crown ether ligand L (1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) was examined in detail. The interaction of CeL with calf thymus DNA was investigated by UV-Vis spectroscopy. Furthermore, studies on the effects of pH, reaction time, and the concentration of CeL on cleavage of pUC19 DNA were carried out by gel electrophoresis. The results indicate that CeL can bind to DNA electrostatically with a binding constant of 2.18x104 M−1; CeL can promote the cleavage of plasmid pUC19 DNA from supercoiled to the nicked form under the appropriate conditions, and the optimal pH value is 7.54. The lack of effect of radical scavengers indicates that the cleavage involves hydrolytic cleavage.

Development of the aza-crown ether metal complexes as artificial hydrolase

Hydrolases play a crucial role in the biochemical process, which can catalyze the hydrolysis of various compounds like carboxylic esters, phosphoesters, amides, nucleic acids, peptides, and so on. The design of artificial hydrolases has attracted extensive attention due to their scientific significance and potential applications in the field of gene medicine and molecular biology. Numerous macrocyclic metal complexes have been used as artificial hydrolase in the catalytic hydrolysis of the organic substrate. Aza-crown ether for this comment is a special class of the macrocyclic ligand containing both the nitrogen atoms and oxygen atoms in the ring. The studies showed that the aza-crown complexes exhibited high activity of hydrolytic enzyme. However, the aza-crown ether metal complex as artificial hydrolase is still very limited because of its difficulty in synthesis. This review summarizes the development of the aza-crown ether metal complexes as the artificial hydrolase, including the synthesis and catalysis of the transition metal complexes and lanthanide metal complexes of aza-crown ethers. The purpose of this review is to highlight: (1) the relationship between the structure and hydrolytic activity of synthetic hydrolase; (2) the synergistic effect of metal sites and ligands in the course of organic compound hydrolysis; and (3) the design strategies of the aza-crown ethers as hydrolase.

Copper and zinc complexes of a diaza-crown ether as artificial nucleases for the efficient hydrolytic cleavage of DNA

Copper and zinc complexes of a diaza-crown ether, serving as artificial nucleases, exhibited high nuclease activities towards the hydrolytic cleavage of DNA.