Sequential Alkylation of Tröger's Base. An Approach to New Chiral Ligands

Heterocycles derived from Tröger's base were shown to complex with metal salts in 2:1 ligand:salt ratios as monodentate or bidentate ligands depending on structure.     

Metallomicellar Catalysis: Hydrolysis of Phosphodiester with Cu(II) and Zn(II) Complexes in Micellar Solution

Abstract

The effects of two metal complexes of 2,2′‐dipyridylamine (bpya) ligand, [(bpya)Cu]Cl₂ and [(bpya)Zn]Cl₂, in promoting the hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) have been kinetically investigated in Brij35 micellar solution and at 298 K, pH ranging from 6.41 to 8.6. In neutral micellar solution at 298 K, pH 7.02, the rate constants for the catalytic hydrolysis of BNPP by [(bpya)Cu]Cl₂ and [(bpya)Zn]Cl₂ are 1.2 × 10⁶ times and 1.5 × 10⁵ times higher than those for the spontaneous hydrolysis, respectively. Kinetic studies show that the active species in the catalytic hydrolysis of BNPP is the aquo‐hydroxy form, and the relative kinetic and thermodynamic parameters indicate that the mechanism of the reaction involves intramolecular nucleophilic attack on the metal center‐bound diester.     

Synthesis of bifunctional chelating agents based on mono and diphosphonic derivatives of diethylenetriaminepentaacetic acid

Bifunctional chelating agents (BFCAs) are small molecules containing a chelating unit, able to strongly coordinate a metal ion, and a reactive functional group, devised to form a stable covalent bond with another molecule. BFCAs are widely employed since their conjugation to a suitable biomolecule (e.g., a peptide or an antibody) allows the synthesis of diagnostic or therapeutic agents that specifically target diseased tissue with metals or radiometals. For this reason, BFCAs find application in diagnostic imaging, molecular imaging, and radiotherapy of cancer. The synthesis of new BFCAs based on a diethylenetriaminepentaacetic acid (DTPA) structure in which one or two carboxylic groups are replaced with phosphonic units is described. The phosphonic group, aside from being a classical isostere of the carboxylic acid in coordination chemistry, allows to modulate the physico-chemical properties of the ligands and of the corresponding complexes.     

Thermal and spectroscopic studies of some metal complexes with a new enaminone ligand 3-chloro-4-((4-methoxyphenyl)amino)pent-3-en-2-one and their investigation as anti-urease and cytotoxic potential drugs

Complexes of transition metals [Co(II), Cd(II) and Mo(0)] with a new enaminone (PA) 3-chloro-4-((4-methoxyphenyl)amino)pent-3-en-2-one were synthesized and afterwards characterized by ¹H NMR, ¹³C NMR, FAB-MS, UV–Vis, ICP-OES, TGA and FTIR. The spectroscopic and conductance data suggested that the ligand (PA) is attached to the metal ions in bidentate, neutral form through the nitrogen atom of amino group and the oxygen of carbonyl group. Metal complexes displayed octahedral geometries. In vitro urease inhibition and cytotoxic activities of all the compounds were evaluated. Results revealed that Co(II) complex (PA-Co) was even more significant than the reference drug thiourea. Analysis of the cytotoxicity indicated that, the Co(II) complex has more cytotoxic effect than enaminone ligand and other complexes when assessed on the human cancer cell lines MCF-7.Molecular docking simulation was also performed to find out the putative binding mode within the target protein.     

Utilization of photocatalysts in decarboxylative coupling of carboxylic N-hydroxyphthalimide (NHPI) esters

Recently, the visible-light photoredox decarboxylative couplings of N-(acyloxy)phthalimides (NHPI esters) and its derivatives have become an efficient chemical transformation. Under visible light, the NHPI esters undergo a single-electron transfer (SET) process to afford the corresponding carbon or nitrogen radicals that participate in many chemical transformations. The photoredox decarboxylative couplings have been applied to achieve construction of an array of carbon–carbon and carbon–heteroatom bonds as well as the synthesis of carbocycles and heterocycles. This review categorises photocatalysts, discusses the application and catalysis mechanisms of NHPI esters, and details recent progress in this field.     

Hydrogen evolution reaction on Pt and Ru in alkali with volmer-step promotors and electronic structure modulators

Alkaline water electrolysis despite having a variety of choices for anodic oxygen evolution reaction (OER) catalysts out of non-precious metals suffers significantly due to the poor kinetics of cathodic hydrogen evolution reaction (HER) even with the state-of-the-art Pt and equally active Ru. The Volmer-step (water dissociation (WD) coupled proton adsorption) of alkaline HER is mostly the rate-determining step (RDS) and costs most of the work required. In this review, recent developments in improving the HER kinetics of Pt and Ru with Volmer-step promotors and electronic structure modulators have been comprehensively analyzed and critically presented with the challenges and prospects.     

Study the electrical conductivity of crosslinked polyester doped with different metal salts

Three crosslinked polymers were prepared via condensation polymerization between triethanolamine and glycerol [(25:75%), (50:50%) and (0:100%) (G:TEA)] with maleic anhydride which produced polymers I, II and III consequently. All the prepared polymers were doped with metal salts (CuCl₂, NiCl₂ and FeCl₂). D.C. conductivity was measured in the temperature range of (298–373 K), the result showed that the electrical conductivity increased several orders of magnitude with increasing temperature, the activation energy decreased with increasing conductivity. A.C. measurement is used to calculate the dielectric constant for the polymers in both pure and doped state.     

Unstable Ni leaching in MOF-derived PtNi-C catalyst with improved performance for alcohols fuel electro-oxidation

Significance of unstable species leaching was for the first time demonstrated on MOF-derived catalysts by taking PtNi-C as an example, that was instructive for the relevant catalyst fabrication and performance study. PtNi-C catalyst was synthesized by combining Pt nanoparticles with Ni-BTC after annealing in the tube furnace and the unstable Ni species can be easily leached out in nitric acid, and the stable PtNi nanoparticles trapped in the graphite carbon layer were obtained. The greatly improved catalytic ability for alcohol fuels oxidation was verified by comparing the fresh and acid leached catalysts in terms of the high peak current density, specific and mass activity and rapid charge transfer kinetics and high catalytic stability. The current work guides the importance of unstable assistant promoter removal for the MOF derived catalysts.     

Capillary zone electrophoresis with UV-scanning detection for the analysis of metal species and their organic binding partners in biological systems

A capillary zone electrophoretic method with UV-scanning detection for the separation and identification of both free ligands and metal species is presented. The electrophoretic behavior of naturally occurring binding partners such as organic acids and amino acids was studied and compared with their metal-complexes. Copper(II) complexes of citrate and amino acids showed decreased electrophoretic mobilities and altered UV spectra. The optimized method was validated on ultrafiltered cow's milk and human milk samples. In cow's milk six low molecular weight substances, including citrate, orotate, and hippurate, could be separated. Metal supplementation with Cu(II), Ni(II), or Zn(II) decreased not only the citrate peak but also the orotate signal and in the case of copper(II) supplementation a new signal for the copper(II)-citrate complex appeared. In human milk samples various amino acids such as glutamate, phenylalanine, tyrosine, and tryptophan could be identified besides citrate. The electrophoretic mobilites and peak areas of the amino acids were also influenced by the metal supplementation.     

One-step ultrasonic synthesis of Co/Ni-catecholates for improved performance in oxygen reduction reaction

The inherent periodically arranged M−N_X, M−S_X and M−O_X units (M are usually Fe, Co, Ni, etc.) in metal–organic frameworks (MOFs) can be promising active centers in electrocatalysis. In previous studies, MOFs were usually constructed by energy-consuming hydro- or solvo-thermal reactions. Ultrasonic synthesis is a rapid and environment-friendly technique when envisaging MOFs’ industrial applications. In addition, different synthetic pathways for MOFs may lead to difference in their microstructure, resulting in different electrocatalytic performance. Nevertheless, only a handful of MOFs were successfully prepared by ultrasonic synthesis and few were applied in electrochemical catalysis. Herein, we constructed Ni/Co-catecholates (Ni/Co-CATs) synthesized by one-step ultrasonic method (250 W, 40 KHz, 25 W/L, Ultrasonic clearing machine) and compared their performance in oxygen reduction reaction (ORR) with that of Ni/Co-CATs synthesized by hydrothermal method. Ni-CAT and Co-CAT prepared by ultrasonic showed the half-wave potential of −0.196 V and −0.116 V (vs. Ag/AgCl), respectively. The potentials were more positive than those prepared by hydro-thermal method. And they showed excellent electrochemical stability in neutral solution. The latter was only 32 mV lower than that of commercial Pt/C. The improved performance in ORR was attributed to higher specific surface area and mesopore volume as well as more structural defects generated in the ultrasonic synthesis process, which could facilitate their exposure of electrocatalytic active sites and their mass transport. This work gives some perspective into cost-effective synthetic strategies of efficient MOFs-based electrocatalysts.