Mechanistic Insights Into the Factors That Influence the DNA Nuclease Activity of Mononuclear Facial Copper Complexes Containing Hetero-Substituted Cyclens

The factors that influence the DNA nuclease activity of mononuclear facial copper complexes containing heterosubstituted cyclens were systematically investigated in this work using density functional theory (DFT) calculations. The heterosubstitution of cyclens were found to significantly affect the dimerization tendency of the mononuclear Cu­(II) complexes examined and their respective p<i>K</i>_a values of the metal-bonded water molecules. The Cu­(II)–oxacyclen complex was found to be more favorable for the hydrolytic cleavage of the DNA dinucleotide analogue BNPP^–(bis (<i>p</i>-nitrophenyl) phosphate). This was due to this species having a higher dimerization resistance to give rise to a higher concentration of the active catalyst and a lower p<i>K</i>_a value of the Cu­(II)-coordinated water molecule to facilitate an easier generation of the better nucleophile hydroxyl ion, which gave a lower reaction barrier. The dimerization of the Cu­(I) complexes studied and their corresponding redox potentials were determined, and a remarkable reaction barrier was observed for the generation of a superoxide ROS (reactive oxygen species) mediated by the Cu­(I)–oxacyclen complex. This behavior was attributed to the higher electronegativity of the O heteroatom, which facilitates the nucleophilic attack of the oxygen molecule and the Cu–O­(OH₂) bond fission via an enhancement of the Lewis acidity of the metal center and the formation of a significant hydrogen bond between the heterocyclic oxygen and the metal-bonded water molecule. The theoretical results reported here are in good agreement with the literature experimental observations and more importantly help to systematically elucidate the factors that influence the DNA nuclease activity of mononuclear facial copper complexes containing heterosubstituted cyclens in detail

Comparison of Fe/surfactant improved montmorillonite: adsorbing and in situ decomposing methylene blue and recycling use

<p>Montmorillonite (MMt) was intercalated by polymeric Fe, or by N-ethyl dodecyl nicotinate bromide (EDNB), or by both. The improved MMt designated as Fe/MMt, EDNB/MMt, and EDNB/MMt/Fe, respectively. A comparison was performed on the improved MMt in the uptake and in the degradation of methylene blue (MB) as well as in the recycling use. The results showed that EDNB/MMt adsorbed more MB than the other two; however, Fe/MMt and EDNB/MMt/Fe acted faster than the former. The adsorption of MB on the three adsorbents followed Langmuir isotherm and pseudo-second-order kinetics. In addition, MB adsorbing on EDNB/MMt was also well described by intraparticle diffusion model. MB removal by EDNB/MMt experienced an endothermic and entropy driving process, but an exothermic and entropy declining process by the other two. pH of the solution affected MB removal. When pH of the solution is high than 10, MB uptake diminished on Fe/MMt and EDNB/MMt/Fe; however, it slightly increased on EDNB/MMt. MB could be decomposed by Fenton reagent on the improved MMt, and the adsorbents could be reused. By coupling the adsorption and degradation <i>in situ</i> by H₂O₂/Fe²⁺ or Fe³⁺, MB removal by Fe/MMt and EDNB/MMt/Fe was almost maintained in the ten cycles. So, present work deepens the understanding of modified MMt in the application of dye wastewater treatment.</p