Neutral Planar Research Articles

Old Acquaintances and Novel Complex Structures for the Ni(II) and Cu(II) Complexes of bis-Chelate Oxime-Amide Ligands.

In the process of systematically studying the methylhydroxyiminoethaneamide bis-chelate ligands with polymethylene spacers of different lengths, L1-L3, and their transition metal complexes, a number of new Ni(II) and Cu(II) species have been isolated, and their molecular and crystal structures were determined using single-crystal X-ray diffraction. In all of these compounds, the divalent metal is coordinated by the ligand donor atoms in a square-planar arrangement. In addition, a serendipitously discovered new type of neutral Ni(II) complex, where the propane spacer of ligand L2 underwent oxidation to the propene spacer, and one of the amide groups was oxidised to the ketoimine, is also reported. The resulting ligand L2' affords the formation of neutral planar Ni(II) complexes, which are assembled in the solid state on top of each other, and yield two polymorphic structures. In both structures, the resulting infinite, exclusively parallel metal ion columns in ligand insulation may serve as precursor materials for sub-nano-conducting connectors. Overall, this paper reports the synthesis and characterisation of seven new anionic, cationic, and neutral Ni(II) and Cu(II) complexes, their crystal structures, as well as experimental and computed UV-Vis absorption spectra for two structurally similar Ni(II) complexes, yellow and red.

Neutral and Anionic Square Planar Palladium(0) Complexes Stabilized by a Silicon Z-Type Ligand.

Anionic [Pd(0)-X]- ate complex were proposed as key intermediates in Pd-catalyzed cross-coupling for decades, but their isolation remained elusive. Herein, a chelating Lewis acidic bis(amidophenolato)silane is introduced as a strong Z-type ligand which enables the characterization of the first anionic [Pd(0)-X]- ate complex. Intriguingly, these compounds and the neutral L-Pd(0) analogs exhibit a square planar coordination that is highly unusual for a d10 metal. Theoretical methods scrutinize the interaction between the Lewis acidic Si(IV) center and the late transition metal, while reactivity studies shed light on the potential role of anionic additives in oxidative addition reactions.

Neutral and Anionic Square Planar Palladium(0) Complexes Stabilized by a Silicon Z‐Type Ligand

AbstractAnionic [Pd(0)−X]− ate complex were proposed as key intermediates in Pd‐catalyzed cross‐coupling for decades, but their isolation remained elusive. Herein, a chelating Lewis acidic bis(amidophenolato)silane is introduced as a strong Z‐type ligand which enables the characterization of the first anionic [Pd(0)−X]− ate complex. Intriguingly, these compounds and the neutral L−Pd(0) analogs exhibit a square planar coordination that is highly unusual for a d10 metal. Theoretical methods scrutinize the interaction between the Lewis acidic Si(IV) center and the late transition metal, while reactivity studies shed light on the potential role of anionic additives in oxidative addition reactions.

A Neutral Planar Four-Membered Si2B2 2π-Aromatic Ring.

The synthesis of the first inorganic four-membered neutral 2π-aromatic compound 2 is reported. This unique ring has been synthesized from a simple and straightforward reaction of amidinato-silylene with dichlorophenylborane, followed by the reduction with KC8 in THF. Compound 2 has been fully characterized by single-crystal X-ray diffraction (SC-XRD), NMR spectroscopy, and mass spectrometry. The computational calculations reveal that the Si2B2 ring is a π-delocalized system resulting from the interaction of pπ orbital of B and Si-N σ* orbitals having pseudo π symmetry. Compound 2 is the first known example of a neutral planar inorganic analogue of cyclobutenyl dication.

Evolution of complexity for critical neutral Gauss-Bonnet-anti-de Sitter black holes

General Gauss-Bonnet gravity with a cosmological constant allows two anti-de Sitter (AdS) spacetimes to be taken as its vacuum solutions. It is found that there is a critical point in the parameter space where the two AdS vacuums coalesce into one, which is very different from the general Gauss-Bonnet gravity. Susskind’s team proposed a Complexity/Action duality based on AdS/CFT duality, which provides a new method of studying the complexity of black holes. Fan and Liang (Fan Z Y, Liang H Z 2019 <i>Phys. Rev. D</i> <b>100</b> 086016) gave the formula of the evolution of complexity for general higher derivative gravity, and discussed the complexity evolution of the neutral planar Gauss-Bonnet-AdS black holes in detail by the numerical method. With the method of studying the complexity of general higher derivative gravity proposed by Fan and Liang (2019), we investigate the complexity evolution of critical neutral Gauss-Bonnet-AdS black holes, and compare these results with the results of the general neutral Gauss-Bonnet-AdS black holes, showing that the overall regularities of the evolution of the complexity of these two objects are consistent, and their main difference lies in the dimensionless critical time. As for the five-dimensional critical neutral Gauss-Bonnet-AdS black holes, when the event horizon of the black holes is flat or spherical, the dimensionless critical times of black holes with different sizes are identical, all reaching their minimum values. While in the higher dimensional cases, the differences in dimensionless critical time among spherically symmetric critical neutral Gauss-Bonnet-AdS black holes with different sizes are obviously less than those of general ones. These differences are probably related to the criticality of the neutral Gauss-Bonnet-AdS black holes.

Mechanochemical Synthesis of an Ionic Cocrystal with Large Birefringence Resulting from Neutral Planar π-Conjugated Groups

Birefringent materials with strong optical anisotropy are indispensable for optoelectronic devices as polarizers, isolators, and beam splitters, etc. Here, a new ionic cocrystal KBr·H3C3N3O3 (I) wa...

Advances in Theoretical Studies on the Design of Single Boron Atom Compounds.

Single Boron Atom Compounds (SBACs) have been used for drug discovery in diseaseassociated proteins due to the empty p-orbital in the atomic structure of boron, which allows it to experience diverse binding modes during molecular recognition with a range of proteins. During the molecular recognition process with a protein target, SBACs can assume an anionic tetragonal arrangement or a neutral trigonal planar structure to produce four possible reversible covalent or non-covalent binding modes with a protein. However, the development of new SBACs has been hampered by the fact that most of the force fields present in many of the software packages used in drug design lack the various types of boron atom parameters. We review in silico studies in which a series of theory-based computational strategies have been used to overcome the lack of boron parameters in most of the force fields used in drug design. The modeling studies discussed in this review have provided substantial insight into the molecular recognition of SBACs targeting different receptors, including the elucidation of some of the key interactions, which serve as a guide for the development of selective SBACs. Although the strategies employed in many of the studies presented here should serve in the development of selective SBACs, it is clear that the development of the precise force field parameters, which include not only the individual atom types but also the entire molecule, is still lacking, yet it is a necessary requirement for the design of new SBACS as well as for gaining insight into their molecular recognition.

Wetting Transition of Nonpolar Neutral Molecule System on a Neutral and Atomic Length Scale Roughness Substrate

One recently proposed new method for accurately determining wetting temperature is applied to the wetting transition occurring in a single component nonpolar neutral molecule system near a neutral planar substrate with roughness produced by cosinusoidal modulation(s). New observations are summarized into five points: (i) for a planar substrate superimposed with one cosinusoidal modulation, with increasing of the periodicity length or the surface attraction force field, or decreasing of the amplitude, wetting temperature \(T_W\) drops accordingly and the three parameters show multiplication effect; moreover, both the periodicity length and amplitude effect curves display pole phenomena and saturation phenomena, and the \(T_W\) saturation occurs at small (for case of large amplitude) or large (for case of small amplitude) periodicity length side, respectively. (ii) In the case of the planar substrate superimposed with two cosinusoidal modulations with equal periodicity length, the initial phase difference is critical issue that influences the \(T_W\), which decreases with the initial phase difference. (iii) In the case of the planar substrate superimposed with two cosinusoidal modulations with zero phase difference, change of the \(T_W\) with one periodicity length under the condition of another periodicity length unchanged is non-monotonous. (iv) When the parameters are chosen such that the \(T_W\) draws ever closer to the bulk critical temperature, wetting transition on the roughness substrate eventually does not occur. (v) The present microscopic calculation challenges traditional macroscopic theory by confirming that the atomic length scale roughness always renders the surface less hydrophilic and whereas the mesoscopical roughness renders the surface more hydrophilic. All of these observations summarized can be reasonably explained by the relative strength of the attraction actually enjoyed by the surface gas molecules to the attraction the gas molecules can get when in bulk.

Interfacial Effects Dominate Ion Permeation through Membrane Channels in Low Ionic Strength Solutions

A number of protein channels and solid-state nanopores share the importance of electrostatic interactions between the permeating ions and the nanochannel. Ion transport at the nanoscale occurs under confinement conditions so that interfacial effects such as access resistance (AR) become relevant. Here we show that interpreting correctly electrophysiological measurements in terms of channel ion selective properties requires the consideration of interfacial effects, up to the point that they dominate protein channel conductance in diluted solutions. We measure AR in a large ion channel, the bacterial porin OmpF, by means of single-channel conductance measurements in salt solutions with varying concentrations of high molecular weight PEG, sterically excluded from the pore. Comparison of experiments done in charged and neutral planar bilayers shows that lipid surface charges modify the ion distribution and determine the value of AR, indicating that lipid molecules are more than passive scaffolds even in the case of large transmembrane proteins. We also found that AR might reach up to 80% of the total channel conductance in diluted solutions, where current recordings reflect essentially the AR of the system and depend marginally on the pore ion concentrations and selective properties. These findings are of key importance for several low aspect ratio biological channels that perform their physiological function in a low ionic strength and macromolecule crowded environment, just the two conditions enhancing the AR contribution.

Coulomb Planar Periodic Motion of n Equal Charges in the Field of n Equal Positive Charges Fixed at a Line and Constant Magnetic Field

We consider a neutral Coulomb planar system of n equal negative charges in a constant magnetic field and a field of n equal fixed positive charges and construct a periodic solution of the equation of motion such that each negative charge is close to its own positive fixed charge.

A pH-induced conformational switch in a tyrosine kinase inhibitor identified by electronic spectroscopy and quantum chemical calculations

Tyrosine kinase inhibitors (TKIs) are a major class of drug utilised in the clinic. During transit to their cognate kinases, TKIs will encounter different pH environments that could have a major influence on TKI structure. To address this, we report UV-Vis spectroscopic and computational studies of the TKI, AG1478, as a function of pH. The electronic absorption spectrum of AG1478 shifted by 10 nm (from 342 nm to 332 nm) from acid to neutral pH and split into two peaks (at 334 nm and 345 nm) in highly alkaline conditions. From these transitions, the pKa value was calculated as 5.58 ± 0.01. To compute structures and spectra, time-dependent density functional theory (TD-DFT) calculations were performed along with conductor-like polarizable continuum model (CPCM) to account for implicit solvent effect. On the basis of the theoretical spectra, we could assign the AG1478 experimental spectrum at acidic pH to a mixture of two twisted conformers (71% AG1478 protonated at quinazolyl nitrogen N(1) and 29% AG1478 protonated at quinazolyl nitrogen N(3)) and at neutral pH to the neutral planar conformer. The AG1478 absorption spectrum (pH 13.3) was fitted to a mixture of neutral (70%) and NH-deprotonated species (30%). These studies reveal a pH-induced conformational transition in a TKI.

Ion Transport in Confined Geometries below the Nanoscale: Access Resistance Dominates Protein Channel Conductance in Diluted Solutions.

Synthetic nanopores and mesoscopic protein channels have common traits like the importance of electrostatic interactions between the permeating ions and the nanochannel. Ion transport at the nanoscale occurs under confinement conditions so that the usual assumptions made in microfluidics are challenged, among others, by interfacial effects such as access resistance (AR). Here, we show that a sound interpretation of electrophysiological measurements in terms of channel ion selective properties requires the consideration of interfacial effects, up to the point that they dominate protein channel conductance in diluted solutions. We measure AR in a large ion channel, the bacterial porin OmpF, by means of single-channel conductance measurements in electrolyte solutions containing varying concentrations of high molecular weight PEG, sterically excluded from the pore. Comparison of experiments performed in charged and neutral planar membranes shows that lipid surface charges modify the ion distribution and determine the value of AR, indicating that lipid molecules are more than passive scaffolds even in the case of large transmembrane proteins. We also found that AR may reach up to 80% of the total channel conductance in diluted solutions, where electrophysiological recordings register essentially the AR of the system and depend marginally on the pore characteristics. These findings may have implications for several low aspect ratio biological channels that perform their physiological function in a low ionic strength and macromolecule crowded environment, just the two conditions enhancing the AR contribution.

Benchmarking Quantum Chemical Methods for Optical Absorption in Boron Wheels.

We benchmark various quantum chemical methods for calculating the optical absorption in planar boron wheel clusters. The geometries of neutral planar boron wheels B7, B8, and B9 clusters are optimized at the coupled-cluster singles doubles level of theory. The optical absorption spectra of these clusters are calculated using three wave-function-based methods, namely, configuration interaction singles, random phase approximation, and equation-of-motion coupled-cluster singles doubles (EOM-CCSD) as well as using a time-dependent density-functional-theory-based method using various hybrid and long-range-corrected exchange and correlation functionals. There is an ample variation in the optical absorption spectra computed using different density functionals. When compared to the EOM-CCSD spectrum, an excellent agreement is provided by CAM-B3LYP functional, followed by ωB97xD functional. PBE0, B3LYP, and B3PW91 functionals agree among each other. However, their spectra are red-shifted with respect to the EOM-CCSD counterpart. On the basis of the natural transition orbital analysis, the nature of optical excitation is also discussed.

Small Cu Clusters Adsorbed on ZnO(101̅0) Show Even–Odd Alternations in Stability and Charge Transfer

Using hybrid density functional theory, we investigate structural and electronic properties of small Cun clusters (with n ≤ 9) adsorbed on the nonpolar ZnO(101̅0) surface. The Cu clusters grow in a planar fashion up to a size of six atoms, after which the clusters take on a polyhedral shape. We find even–odd alternations with respect to both cluster stability (for n = 1–6) and cluster charge, as a function of the number of atoms. Even-numbered clusters are always charge-neutral, while odd-numbered clusters can become positively charged by donation of an electron to the ZnO conduction band, which can be traced back to the fact that the ionization energies of odd-numbered gas-phase Cu clusters are lower than for even-numbered ones. The most stable adsorbed odd-numbered clusters are neutral and planar for n ≤ 3 and positively charged and polyhedral for n ≥ 7. For n = 5, both neutral planar and positively charged polyhedral configurations are similarly stable.

ChemInform Abstract: Ion‐Based Materials Comprising Planar Charged Species

AbstractReview: 126 refs.

Ion-based materials comprising planar charged species

Materials comprising planar units have the propensity to form stacking assemblies with nanoscale architectures and intriguing properties. In this feature article, some recent examples of ion-based materials comprising positively and negatively charged planar species are described. Various ion-based solid and soft materials can be formed by planar charged species alone or with the aid of other components. It is more challenging to prepare planar anions than planar cations; however, the noncovalent association of electronically neutral planar anion receptors and anions is an efficient strategy for the preparation of planar anions. Suitable candidates include dipyrrolyldiketone boron complexes, which exhibit the formation of various receptor-anion complexes and can be used to fabricate advanced materials in combination with countercations. Ion-based materials consisting of planar charged components have potential as electrically conductive materials, resulting from the ordered arrangement of the planar charged species.

Simulating Electrode-Solution Interfaces Using 3D Cellular Automation

A three-dimensional cellular automation model is applied to study the spatial distribution of water molecules contacting a structureless planar electrode. Water molecules occupying each cell are modeled as electric dipoles comprising separated positive and negative charges. Electrostatic interactions between cells are computed to determine local torques on water dipoles. Meanwhile, the dipole rotational response is modeled as a thermally activated event. Interfacial phenomena, such as the parallel alignment of water molecules to a neutral planar electrode emerge spontaneously from the simulation. When solvated ions are available in the water, attraction and repulsion due to charges cause a non-uniform distribution of anions and cations. The simulation results presented here, including the computed distribution profiles for anions and cations influenced by the electrode charge density, the resulting electric fields, and the variation of the dielectric constant of water, are consistent with theoretical calculations and existing simulations based on molecular dynamics.

Unexpected isomerism in “[Pd(2,9-dimethylphenanthroline)X2]” (X = Cl, Br, I) complexes: a neutral and an ionic form exist

Complexes of composition "[Pd(2,9-dimethylphenanthroline)X(2)]" (X = Cl, Br, I) have long been known and they are used as precursors for the synthesis of other derivatives or as catalysts. In the previous literature, they have invariably been described as neutral square planar complexes, but we have found that a second ionic isomer also exists, having composition [Pd(Neoc)(2)X](2)[Pd(2)X(6)], and that the formation of this isomer occurs under a wider range of conditions than that of the neutral one. Retrospectively, the ionic isomer had surely been obtained in most previous reports even if formation of the neutral one was claimed.

Cholesterol Regulates Assembly of Human Islet Amyloid Polypeptide on Model Membranes

Amylin, a 37-aa pancreatic hormone, is the major constituent of islet amyloid, a hallmark of type II diabetes mellitus. Recent studies have revealed a pivotal role of anionic phospholipids in membrane-catalyzed amylin fibrillogenesis and aggregation. However, cholesterol, an integral component of eukaryotic cell membranes, also could have a role. In this study, we have examined the effect of cholesterol on amylin polymerization both on planar membranes and in solution. Using time-lapse atomic force microscopy, we have studied the dynamics and macromolecular organization of amylin on anionic and neutral planar membranes that lack or include cholesterol. On cholesterol-depleted planar membranes, amylin formed highly symmetrical tetrameric and pentameric pore-like supramolecular structures composed of 25- to 35-nm intermediate-sized globular structures or oligomers. Conversely, on membranes incorporating cholesterol, amylin formed highly compact ∼ 200- to 500-nm protein clusters that constituted seeds or nuclei for continuing amylin binding and aggregation. However, cholesterol inhibited amylin nucleation with a 7-fold decrease in the number of amylin particles. Consequently, cholesterol-containing membranes accumulated significantly less amyloid with some membrane areas completely free of amyloid particles. The inhibitory effect of cholesterol on amylin aggregation in solution was also demonstrated as a 16-fold decrease in the aggregation rate. Consistent with this, circular dichroism spectroscopy revealed a stable, soluble random-coil conformation for amylin in the presence of cholesterol that could explain the inhibitory effect of cholesterol on amylin polymerization in solution and on membranes. The modulatory effect of cholesterol was largely independent of membrane charge or phospholipids, suggesting a novel cholesterol-regulated amylin polymerization process.

Spontaneous Polarization of the Neutral Interface for Valence Asymmetric Coulombic Systems

In this paper, we discuss the phenomenon of a spontaneous polarization of a neutral hard planar interface for valence asymmetric Coulombic systems. Within a field theoretical description, we account for the existence of nontrivial charge density and electric potential profiles. The analysis of the phenomenon shows that the effect is related to combinatorics in relation with the existence of the two independent species cations and anions. This simple and basic feature is related to the quantum mechanical properties of the system. The theoretical results are compared with numerical simulations data and are shown to be in very good agreement, which a fortiori justifies our physical interpretation.