Inter- and intramolecular non-covalent interactions in 1-methylimidazole-2-carbaldehyde complexes of copper,silver, and gold

Three new imidazole compounds, [CuBr₂(mimc)₂] (1), [Ag(mimc)₂][CF₃SO₃] (2), and [AuCl₃(mimc)] (3) (mimc = 1-methylimidazole-2-carbaldehyde), have been synthesized, structurally characterized, and further analyzed using the QTAIM analysis. The compounds exhibit self-assembled 3D networks arising from intermolecular non-covalent interactions such as metallophilic interactions, metal-π contacts, halogens–halogen interactions, and hydrogen bonds. These weak interactions have a strong impact on the coordination sphere of the metal atoms and on the packing of compounds 1, 2, and 3.     

Impact of divalent metal cations on the catalysis of peptide bonds: a DFT study

Within the ATP-grasp family of enzymes, divalent alkaline earth metals are proposed to chelate terminal ATP phosphates and facilitate the formation of peptide bonds. Density functional theory methods are used to explore the impact of metal ions on peptide bond formation, providing an insight into experimental metal substitution studies. Calculations show that alkaline earth and transition metal cations coordinate with an acylphosphate reactant and aid in the separation of the phosphate leaving group. The critical biochemical reaction is proposed to proceed through the formation of a six-membered transition state in the relatively nonpolar active site of human glutathione synthetase, an ATP-grasp enzyme. While the identity of the metal ion has a moderate impact on the thermodynamics of peptide bond formation, kinetic differences are much sharper. Simulations indicate that several transition metal ions, most notably Cu²⁺, may be particularly advantageous for catalysis. The detailed mechanistic study serves to elucidate the vital role of coordination chemistry in the formation of peptide bonds.     

Synthesis,anti‐migration and burning rate catalytic mechanism of ferrocene‐based compounds

One of the most important components of solid rocket propellant is the burning rate catalysts (BRC) which enhance burning rate of solid composite propellant. Low‐pressure exponents and stable burning rate are the key features of an excellent solid propellant. Addition of BRC to the propellant results in the increase of burning rate of the propellant and decrease in pressure exponents. Among all BRC, ferrocene‐based BRC have attracted much attention because of their better microscopic homogeneities in distribution, ignitability of the propellants and good compatibility with organic binder. However, the main barrier for the development and practical applications of ferrocene‐based BRC is their migration property. This article reviews the field and highlights recent progress. Copyright © 2014 John Wiley & Sons, Ltd.     

A cation trap for anodic stripping voltammetry: NH3–plasma treated carbon nanotubes for adsorption and detection of metal ions

NH₃–plasma treated multi-walled carbon nanotubes (pn-MWCNTs) with cation traps for the detection of ultratrace quantities of Zn(II), Cd(II), Cu(II), and Hg(II) using square wave anodic stripping voltammetry (SWASV) is described. The pn-MWCNTs use their adsorption performance to enhance the sensitivity. It is found that under optimized conditions Zn(II), Cd(II), Cu(II) and Hg(II) were individually detected at potentials of −1.16, −0.78, −0.268 and 0.108 V, respectively. The detection limit (3σ method) of 0.314, 0.0272, 0.2263, and 0.1439 nM toward Zn(II), Cd(II), Cu(II), and Hg(II) is achievable, respectively. No interference could be seen during the simultaneous detection of Zn(II), Cd(II), Cu(II), and Hg(II). The pn-MWCNTs exhibit excellent selectivity owing to the different ability of adsorption. A study of the ability of pn-MWCNTs in practical application is carried out using a sample of water collected from Dongpu Reservoir in Hefei City, Anhui, China. It is found that the results were favorable when compared against inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis.     

Early transition metal dopants in cuprous oxide: To spin or not to spin

We present a trend study of a large variety of dopants at the cation site in Cu₂O (i.e. substituting Cu), focussing largely on the early 3d-, 4d-, and 5d-transition metals (TMs) in which many of them are known to be non-magnetic. We also include s-, sp- and d¹⁰-metals for comparison. We find that doping with sp-elements results in zero spin moment while dopants with a partially filled d-band show a stronger tendency to magnetize and 3d-TM dopants exhibit a larger magnetic moment than most of the 4d- and 5d-TM dopants. From this trend study, we also find a correlation between their substitution enthalpy and associated interatomic relaxations. In particular, Ti-doped Cu₂O appears to be an interesting system, given its “peculiar” ability to exhibit a spin moment when doped with a non-magnetic substituent like Ti. We also find that the interaction between two doped Ti atoms in Ti₂:Cu₂O is predominantly antiferromagnetic, and interestingly (and unexpectedly), this interaction rapidly declines as a function of inter-dopant distance, as in the case for the magnetic late-TM dopants like Co₂:Cu₂O.     

Nanoindentation as a Probe for Mechanically‐Induced Molecular Migration in Layered Organic Donor–Acceptor Complexes

Nanoindentation and scratch experiments on 1:1 donor–acceptor complexes, 1 and 2 , of 1,2,4,5‐tetracyanobenzene with pyrene and phenanthrene, respectively, reveal long‐range molecular layer gliding and large interaction anisotropy. Due to the layered arrangements in these crystals, these experiments that apply stress in particular directions result in the breaking of interlayer interactions, thus allowing molecular sheets to glide over one another with ease. Complex 1 has a layered crystal packing wherein the layers are 68° skew under the (002) face and the interlayer space is stabilized by van der Waals interactions. Upon indenting this surface with a Berkovich tip, pile‐up of material was observed on just one side of the indenter due to the close angular alignment of the layers with the half angle of the indenter tip (65.35°). The interfacial differences in the elastic modulus (21 %) and hardness (16 %) demonstrate the anisotropic nature of crystal packing. In 2 , the molecular stacks are arranged in a staggered manner; there is no layer arrangement, and the interlayer stabilization involves C? H???N hydrogen bonds and π???π interactions. This results in a higher modulus (20 %) for (020) as compared to (001), although the anisotropy in hardness is minimal (4 %). The anisotropy within a face was analyzed using AFM image scans and the coefficient of friction of four orthogonal nanoscratches on the cleavage planes of 1 and 2 . A higher friction coefficient was obtained for 2 as compared to 1 even in the cleavage direction due to the presence of hydrogen bonds in the interlayer region making the tip movement more hindered.     

Two coordination polymers based on 2,2′-biimidazoles and d10 metal ions: syntheses,structures, and luminescence

Two d¹⁰ metal coordination polymers, [Zn(µ-Me₂biim)Cl₂] _n (1) and [Cd₃(MeHbiim)₂(1,4-BDC)₃] _n (2) (Me₂biim?=?N,N′-dimethyl-2,2′-biimidazole, MeHbiim?=?N-methyl-2,2′-biimidazole, 1,4-BDC?=?1,4-benzenedicarboxylate), were synthesized under hydrothermal conditions and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single-crystal X-ray crystallography. Complex 1 features an infinite neutral zigzag 1-D chain. Interchain hydrogen-bonding interactions further extend the 1-D arrangement to generate a 2-D supramolecular architecture. Complex 2 features a 3-D coordination polymer with α-Po net topology, based on linear trinuclear {Cd₃O₁₄N₄} clusters. Both complexes have high thermal stability and exhibit strong luminescence at room temperature.     

Acyl migration from N to C in aziridine-2-carboxylic esters

Acyl group migration from N to C in aziridine-2-carboxylates takes place in deprotonation reactions and, as a result, aziridine-2,2-dicarboxylates are formed. Mechanistic studies proved that the observed migration is an intramolecular reaction.     

The fabrication of ReS2 flowers at controlled locations by chemical vapor deposition

Here we report a metal induced nucleation to realize the growth of ReS₂ flowers at controlled locations. The ordered arrays of ReS₂ flowers have been successfully prepared on SiO₂/Si substrate using Pt metal dots as nucleation sites and S, NH₄ReO₄ powders as precursors by a chemical vapor depostion method. The NH₄ReO₄ powders are used as the rhenium sources. The ReS₂ flowers are grown above the pre-patterned Pt dots, Raman and transmission electron microscopy measurements indicated that the prepared ReS₂ flowers have excellent crystalline quality.     

Surface oxidability of pure liquid metals and alloys

The analysis of the oxygen-liquid metal interaction is a topic of particular technological interest. A deep knowledge of the kinetics and transport mechanisms involved in the oxidation phenomena is necessary: the effect of oxidation reactions taking place in the gas phase and the evaporation of oxides must be considered.This paper aims to review our works in order to provide a systematic analysis of the oxidation of pure metals and determine the most likely to keeping oxygen-free the surface in a binary alloy.In addition, the upgrading of this theoretical approach, here briefly described, is addressed to give a contribution to a better understanding of the evolution of oxidation phenomena close to the solid-liquid-gas interfaces.