Electroneutral Ligands Research Articles

Metal–N4 model single‐atom catalyst with electroneutral quadri‐pyridine macrocyclic ligand for CO2 electroreduction

AbstractMetal–N–C single‐atom catalysts, mostly prepared from pyrolysis of metal‐organic precursors, are widely used in heterogeneous electrocatalysis. Since metal sites with diverse local structures coexist in this type of material and it is challenging to characterize the local structure, a reliable structure–property relationship is difficult to establish. Conjugated macrocyclic complexes adsorbed on carbon support are well‐defined models to mimic the single‐atom catalysts. Metal–N4 site with four electroneutral pyridine‐type ligands embedded in a graphene layer is the most commonly proposed structure of the active site of single‐atom catalysts, but its molecular counterpart has not been reported. In this work, we synthesized the conjugated macrocyclic complexes with a metal center (Co, Fe, or Ni) coordinated with four electroneutral pyridinic ligands as model catalysts for CO2 electroreduction. For comparison, the complexes with anionic quadri‐pyridine macrocyclic ligand were also prepared. The Co complex with the electroneutral ligand expressed a turnover frequency of CO formation more than an order of magnitude higher than that of the Co complex with the anionic ligand. Constrained ab initio molecular dynamics simulations based on the well‐defined structures of the model catalysts indicate that the Co complex with the electroneutral ligand possesses a stronger ability to mediate electron transfer from carbon to CO2.

Np(V) dicyanamide complexes with electroneutral N-donor ligands

Abstract Three new complexes of Np(V) dicyanamide with electroneutral N-donor ligands have been synthesized and structurally characterized: two with terpyridine derivatives: [(NpO2)(Cl-Terpy)(DMA)(N(CN)2)]·0.5DMA (1), [(NpO2)(TPTZ)(N(CN)2)(H2O)]·2H2O·CH3OH (2) and a dimeric complex with bipyridine [(NpO2)(Bipy)(N(CN)2)(H2O)]2·2(CH3OH) (3). In compounds 1–3, the coordination polyhedra of Np atoms are pentagonal bipyramids with “yl” oxygen atoms in apical positions. The equatorial plane of the bipyramids is formed by nitrogen atoms of the anions [N(CN)2]− and N-donor electroneutral ligands (Cl-Terpy, TPTZ, Bipy) and the oxygen atom of water molecule (1, 3) or DMA (2). In compounds 1 and 2, the [N(CN)2]− anions manifest themselves as monodentate ligands, and in compound 3 dicyanamide is a bidentate-bridging ligand.

The Sodium Ion Binding Region at the Focus of P1 Helices Attracts both Charged and Electroneutral Ligands of Sodium Channels

The inner pore of eukaryotic voltage-gated sodium channels is targeted by ligands of dramatically different chemical structures. These include organic cations such as a local anesthetic lidocaine and electroneutral drugs such as an anticonvulsant carbamazepine. Mutations of the critical phenylalanine residue in helix IVS6 and some other inner pore-facing residues are known to affect action of both charged and neutral ligands. The structural cause of this ligand-binding promiscuity of sodium channels is unclear. Here we used the X-ray structure of a prokaryotic sodium channel NavMs to model the pore domain of the Nav1.x channels. We further employed the Monte Carlo energy-minimization method to perform intensive docking of lidocaine and carbamazepine from thousands starting points in the inner-pore region. The sodium ion NaIII, which is located between the four backbone carbonyls at the C-ends of P1 helices and does not make direct contacts with the channel protein, attracted carbamazepine, but repelled lidocaine. Therefore we further docked electroneutral ligands (lamotrigine, carbamazepine, phenytoin, lacosamide and bisphenol A) and cationic ligands (lidocaine, QX-314, cocaine, quinidine, and sipatrigine) in the channel models, respectively, with and without NaIII. In our models all the ligands interacted with the phenylalanine residue in IVS6 and most of the ligands also interacted with the tyrosine residue in IVS6. Some ligands extended their moieties in the III/IV sidewalk (fenestration). The electroneutral ligands bound the sodium ion with their electronegative groups and lacosamide chelated this ion. The ligand-bound ion remained close to the NaIII position due to attraction to the pore-facing backbone carbonyls. The same region attracted the charged group of the cationic ligands. In the predicted binding modes even small-size ligands would block the ion permeation by the electrostatic and steric mechanisms. Our study proposes a common pharmacophore for the diverse ligands. It includes a cation (the ligand's ammonium group or the ligand-bound sodium ion) and an aromatic moiety, which are usually linked by four bonds. Supported by NSERC and RFBR.

Homology modeling of Kv1.5 channel block by cationic and electroneutral ligands

The inner pore of potassium channels is targeted by many ligands of intriguingly different chemical structures. Previous studies revealed common and diverse characteristics of action of ligands including cooperativity of ligand binding, voltage- and use-dependencies, and patterns of ligand-sensing residues. Not all these data are rationalized in published models of ligand-channel complexes. Here we have used energy calculations with experimentally defined constraints to dock flecainide, ICAGEN-4, benzocaine, vernakalant, and AVE0118 into the inner pore of Kv1.5 channel. We arrived at ligand-binding models that suggest possible explanations for different values of the Hill coefficient, different voltage dependencies of ligands action, and effects of mutations of residues in subunit interfaces. Two concepts were crucial to build the models. First, the inner-pore block of a potassium channel requires a cationic “blocking particle”. A ligand, which lacks a positively charged group, blocks the channel in a complex with a permeant ion. Second, hydrophobic moieties of a flexible ligand have a tendency to bind in hydrophobic subunit interfaces.

Effect of anion type on monolayers and Langmuir–Blodgett films of gadolinium stearate

This work is focused on the preparation and characterization of gadolinium-containing stearic acid (SA) Langmuir–Blodgett (LB) films. SA monolayer behavior on the gadolinium-containing aqueous subphase has been analyzed by thermodynamic measurements. The compression isotherm shape changed substantially under varying anion type at the constant rare-earth cation content and pH in aqueous subphase. Those changes were ascribed to different monolayer surface charging under gadolinium binding. Small angle X-ray diffraction was used to study the structure of formed multilayer rare-earth-containing LB films. Considerable structural defects in multilayer LB films were found when gadolinium chloride solution was exploited as aqueous subphase for LB film formation, caused presumably by electrostatic interactions under charged monolayer deposition. The use of monodentate complexions like acetic acid residue was proposed to form bulk phase low-charged complexes with trivalent cations. The electroneutral ligand exchange reactions of such complexes with fatty acid Langmuir monolayer results in the formation of quasi-neutral trivalent cation complexes bound to the monolayer surface. This approach allowed effective neutralization of the monolayer surface under gadolinium binding and formation of condensed monolayer below the triple-point temperature. The compression and subsequent deposition of such monolayers resulted in the formation of highly ordered LB films with high content of adsorbed gadolinium cations arranged in two-dimensional (2-D) monatomic layers.

Formation of langmuir‐blodgett films containing two‐dimensional monoatomic arrays of rare‐earth cations

AbstractThe work is focused on the preparation and characterisation of rare‐earth containing stearic acid Langmuir‐Blodgett (LB) films. Stearic acid monolayer behavior on the rare‐earth containing aqueous subphase have been analyzed by thermodynamic measurements. The compression isotherm shape changed substantially under varying the anion type at the constant rare‐earth cation content in aqueous subphase. The structure of formed multilayer rare‐earth containing LB films was studied using small angle X‐rays diffraction. The considerable structural defects in multilayer films were found when rare‐earth chloride solution was exploited as aqueous subphase, caused presumably by electrostatic interactions at the monolayer surface under high binding of rare‐earth cations. The use of monodentate complexones like acetic acid was proposed to form bulk phase quasi‐neutral rare‐earth complexes. The electroneutral ligand exchange reactions of such complexes with stearic acid monolayer allowed to neutralise monolayer surface under rare‐earth cations binding and to form condenced monolayer below the triple‐point temperature. The compression of such monolayer to the state of minimal compressibility and subsequent monolayer deposition resulted in the formation of high ordered LB films with high content of adsorbed multivalent rare‐earth cations arranged in two‐dimensional monoatomic arrays.

A novel electrolyte: CdS nanoparticle capped with 2,2′-bipyridine

The use of an electroneutral ligand modified the Cd 2+-rich surface of CdS leads to the surrounding of CdS/2,2′-bpy by the counter ion (anion) to balance the charge of the Cd 2+ ions, resulting in the CdS cluster with strong electrolyte behavior.

Stability constants of tris(2,2′-bipyridine) complexes of Fe 2+, Co 2+, Ni 2+, Cu 2+ and Zn 2+ in 1,2-dichloroethane saturated with water

From the extraction measurements, the equilibrium distribution constant K D(L) for the electroneutral ligand 2,2′-bipyridine between the 1,2-dichloroethane and the aqueous phases has been determined in the form log K D(L) = 2.03 ± 0.01, where L represents the ligand. Using known thermodynamic parameters and general relations, the stability constants of the metal chelate complexes [M(bipy) 3] 2+ (M 2+ = Fe 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+; bipy = 2,2′-bipyridine) in 1,2-dichloroethane saturated with water have been evaluated. It has been found that the stability constants determined in this medium are essentially higher than the corresponding stability constants of these complexes in water.

Short Information. Proton transfer across the water/nitrobenzene interface facilitated by some electroneutral ligands

Short Information. Proton transfer across the water/nitrobenzene interface facilitated by some electroneutral ligands