The recent chemical exfoliation of layered MAX phase compounds to novel two-dimensional transition metal carbides and nitrides, the so-called MXenes, has brought a new opportunity to materials science and technology. This review highlights the computational attempts that have been made to understand the physics and chemistry of this very promising family of advanced two-dimensional materials, and to exploit their novel and exceptional properties for electronic and energy harvesting applications.

Electronic properties and applications of MXenes: a theoretical review

Surface and Heterointerface Engineering of 2D MXenes and Their Nanocomposites: Insights into Electro- and Photocatalysis

Two-dimensional MXenes: From morphological to optical, electric, and magnetic properties and applications

Recent chemical exfoliation of layered MAX phase compounds to novel two-dimensional transition metal carbides and nitrides, so called MXenes, has brought new opportunity to materials science and technology. This review highlights the computational attempts that have been made to understand the physics and chemistry of this very promising family of advanced two-dimensional materials, and to exploit their novel and exceptional properties for electronic and energy harvesting applications.

Structure and mechanism in organic chemistry

Phosphate bond cleavage is essential to physiological, antibacterial, or antitumor activity, as well as the elimination of chemical warfare agents. In this work, three transition metal binuclear complexes (Cu2LCl4, Co2LCl4, and Zn2LCl4) with a novel hexadentate imidazole derivative (L) were conveniently ‘one-pot’ synthesized to test their ability to cleave phosphate diesters, c-Myc oligonucleotides, and plasmid pBR322 DNA. Single crystal structures indicated that each central metal ion is penta-coordinated for each binuclear complex. Cu2LCl4 with a space group of P21/n is monoclinic, and Zn2LCl4 with a P space group is triclinic. Co2LCl4 with a C2/c space group is monoclinic and cis-configurational. Unfortunately, the tested complexes displayed low activity in the hydrolysis of two diesters and pBR322 plasmid DNA (although stronger ability was exhibited for c-Myc) used in this work, which is probably ascribed to the lack of bimetallic cooperation due to a relatively larger metal–metal distance in excess of 10 A. Density function theory (DFT) calculation provides evidence for the highest activity of Co2LCl4 among these three complexes in the hydrolysis reaction. With respect to the oxidative cleavage, only Cu2LCl4 displayed catalytic activity for these substrates in this work. As compared to the hydrolytic cleavage, the Cu2LCl4-mediated oxidative cleavage or destruction of each substrate was more efficient, and was accompanied by an excess of six orders of magnitude (approximately 7.75 million-fold) rate acceleration in the oxidative cleavage of HPNP, probably originating from the dominant nucleophilic attack of a greater amount of reactive hydroxyl free radicals against hydroxyl anions. The HPNP oxidative cleavage produces one attractive non-lactone phosphate monoester due to the direct attack of metal-activated hydroxyl radicals.

Binuclear metal complexes with a novel hexadentate imidazole derivative for the cleavage of phosphate diesters and biomolecules: distinguishable mechanisms

Two alkoxo/hydroxide-bridged dinuclear copper(II) complexes (Cu2L1 and Cu2L2) were prepared for evaluating their activity towards the hydrolysis of p-nitrophenyl picolinate (PNPP). Importantly, this work investigated the effects of varied micelles of four surfactants, e.g., cationic gemini 16-2-16 and 16-6-16, single-chain CTAB (hexadecyltrimethylammonium bromide), and LSS (n-lauroylsarcosine sodium), on the PNPP hydrolysis by the as-prepared copper(II) complexes. The experimental results indicate that at neutral pH both of complexes exhibited much better activity by excess four-order of magnitude rate enhancement. For instant, rate constants of PNPP hydrolysis by Cu2L1 and bromo-containing Cu2L2 are approximate 49,569.6- and 31,123.5-fold than that of PNPP spontaneous hydrolysis. In addition, the hydrolytic reactivity of the bromo-containing Cu2L2 is subordinate to that one without bromine, Cu2L1. Moreover, it is found that the micellar solution of gemini 16-6-16 is proved to be the best medium, and whereas LSS micellar solution is the worst one. Particularly, the pK
 a values of the Cu(II)-bound H2O are determined by a new methodology which is correlative to second derivatives.

Distinguishable effects of varied micelles on the hydrolysis of PNPP by dinuclear copper(II) complexes containing oxo-bridged unit

One new hydroxyl-functionalized imidazole derivative (L) was synthesized and characterized. Further, the related mononuclear zinc(II) and cobalt(II) complexes were prepared and used as mimic hydrolases to catalyze the hydrolytic cleavage of p-nitrophenyl picolinate (PNPP) in buffered aqueous solution and a micellar solution of cetyltrimethylammonium bromide (CTAB). Observations show that for all of catalytic systems, the hydrolysis of PNPP was pH-dependent in the pH range of 7.00–8.20. Besides, hydrolysis rates of PNPP displayed a constant increase with the increasing concentration of substrate. In the case of CoL-containing system, moreover, much greater acceleration for PNPP hydrolysis was observed in comparison with the ZnL-containing system. However, micellar effect of CTAB micelle aggregates on the PNPP hydrolysis was not obvious only showing 1.0 ∼ 1.3 folds rate difference in contrast to buffered aqueous solution.

Hydrolytic cleavage of p -nitrophenyl picolinate by mononuclear Zn(II) and Co(II) complexes with imidazole derivative in CTAB micellar solution

In this article, the effects of different micelles and Schiff base ligands on the hydrolytic kinetics of p-nitrophenyl picolinate (PNPP) were evaluated. The results reveal that the biggest rate enhancement for PNPP hydrolysis was given in Gemini 16-6-16 micellar solution relative to other four reaction media, that is, cetyltrimethylammonium bromide (CTAB), n-lauroylsarcosine sodium (LSS), polyoxyethylene (23) lauryl ether (Brij35) and pure buffer. Moreover, the hydrolytic rates of PNPP in other four media decreased in the order LSS > CTAB > Buffer > Brij35. The structural effects of Mn(III) catalysts clearly testify that a relatively open active site facilitates the formation of reactive substrate-catalyst complex.

Bin Xu

Papers

Binuclear metal complexes with a novel hexadentate imidazole derivative for the cleavage of phosphate diesters and biomolecules: distinguishable mechanisms

Distinguishable effects of varied micelles on the hydrolysis of PNPP by dinuclear copper(II) complexes containing oxo-bridged unit

Hydrolytic cleavage of p -nitrophenyl picolinate by mononuclear Zn(II) and Co(II) complexes with imidazole derivative in CTAB micellar solution

Effects of Various Schiff Base Ligands and Micelles on the Hydrolytic Kinetics of p-Nitrophenyl Picolinate