Theoretical Study on Cooperativity Effects between Anion–π and Halogen‐Bonding Interactions

This article analyzes the interplay between lone pair–π (lp–π) or anion–π interactions and halogen‐bonding interactions. Interesting cooperativity effects are observed when lp/anion–π and halogen‐bonding interactions coexist in the same complex, and they are found even in systems in which the distance between the anion and halogen‐bond donor molecule is longer than 9 Å. These effects are studied theoretically in terms of energetic and geometric features of the complexes, which are computed by ab initio methods. Bader′s theory of “atoms in molecules” is used to characterize the interactions and to analyze their strengthening or weakening depending upon the variation of charge density at critical points. The physical nature of the interactions and cooperativity effects are studied by means of molecular interaction potential with polarization partition scheme. By taking advantage of all aforementioned computational methods, the present study examines how these interactions mutually influence each other. Additionally, experimental evidence for such interactions is obtained from the Cambridge Structural Database (CSD).     

A density functional theory study of uranium(VI) nitrate monoamide complexes

Density functional theory calculations were performed on uranyl complexed with nitrate and monoamide ligands (L) [UO(2)(NO(3))(2)·2L]. The obtained results show that the complex stability is mainly governed by two factors: (i) the maximization of the polarizability of the coordinating ligand and (ii) the minimization of the steric hindrance effects. Furthermore, the electrostatic interaction between ligands and uranium(vi) was found to be a crucial parameter for the complex stability. These results pave the way to the definition of (quantitative) property/structure relationships for the in silico screening of monoamide ligands with improved extraction efficiency of uranium(vi) in nitrate acidic solution.     

The effect of selective contact electrodes on the interfacial charge recombination kinetics and device efficiency of organic polymer solar cells

Organic polymer solar cells (OPSCs) have been prepared using TiO(x) metal oxides as selective electrodes for electron collection. The interfacial charge transfer reactions, under working conditions, that limit the energy conversion efficiency of these devices have been measured and compared to the standard OPSC geometry which collects the electrons through a low work function metal contact.     

Divalent cations reduce the pH sensitivity of OmpF channel inducing the pK(a) shift of key acidic residues

In contrast to the highly-selective channels of neurophysiology employing mostly the exclusion mechanism, different factors account for the selectivity of large channels. Elucidation of these factors is essential for understanding the permeation mechanisms in ion channels and their regulation in vivo. The interaction between divalent cations and a protein channel, the bacterial porin OmpF, has been investigated paying attention to the channel selectivity and its dependence on the solution pH. Unlike the experiments performed in salts of monovalent cations, the channel is now practically insensitive to pH, being anion selective all over the pH range considered. Electrostatic calculations based on the available structural data suggest that the binding of divalent cations has two main effects: (i) the pK(a) values of key ionizable groups differ significantly from those of the isolated groups in solution and (ii) the cation binding has a decisive impact on the effective electric charge regulating the channel selectivity. A simple molecular model based on statistical thermodynamics provides additional qualitative explanations to the experimental findings that could also be useful for other related systems like synthetic nanopores, ion exchange membranes, and polyelectrolyte multilayers.     

Role of axially coordinated surface sites for electrochemically controlled carbon monoxide adsorption on single crystal copper electrodes

The adsorption of CO on low index copper single crystals in electrochemical environments has been investigated. The results, analysed through a combination of in situ infrared spectroscopy, DFT and cyclic voltammetry, reveal a unique adsorption behaviour when compared to previous studies on copper and the more widely studied noble metal surfaces. By employing small, weakly specifically adsorbed electrolytes, it is shown that carbon monoxide is adsorbed over a much wider electrode potential range than previously reported. The electrochemical Stark shift (δν/δE) observed is similar for the three Cu(hkl) surfaces examined despite different surface coverages. Most notably, however, is an electrochemical feature observed at ca. -1.0 V (vs. Ag/AgCl) on the (110) surface. It is proposed that this voltammetric feature arises from the reduction/oxidation of Cu(δ+) surface sites involved in the binding of carbon monoxide with the participation of the electrolyte anion. This provides additional specific sites for CO adsorption. DFT calculations support the proposed presence of low-coordination copper sites stabilised by electrolyte anions. An experimental electron transfer rate constant of 4.2 s(-1) to the Cu(δ+) surface sites formed was found. These new observations concerning the surface electrochemistry of CO on Cu indicate that the electrocatalytic behaviour of Cu electrodes in processes such as CO(2) reduction need to be re-evaluated to take account of the rich adsorption behaviour of CO, including the co-adsorption of the electrolyte anion to these sites.     

Efficient crystallization induced emissive materials based on a simple push-pull molecular structure

Solid state luminescent materials are the subject of ever growing interest both from a scientific and a technological point of view. Aggregation caused quenching (ACQ) processes however represent an obstacle to the development of most luminogens in the condensed phase. This is why particularly fascinating are those materials showing higher emission intensity in the solid state than in solution. Here we report on three 4-dialkylamino-2-benzylidene malonic acid dialkyl esters, very simple push-pull molecules, which are hardly emissive in solution and in the amorphous phase but become good emitters in the crystalline phase according to what has been indicated as crystallization induced emission (CIE). Thanks to combined emission and NMR spectroscopies at different temperatures on the prototype compound 4-dimethylamino-2-benzylidene malonic acid dimethyl ester in solution, we give full evidence that a restricted intramolecular rotation (RIR) phenomenon, in particular the hindered rotation around the aryl main axis of the compound, is at the origin of this behaviour. In addition, solid state photophysical and X-ray diffraction structural characterization allow us to identify J-dimeric interactions as responsible for the particularly intense emission of two of the three compounds. Moreover, by exploiting the compounds' acidochromic properties, applications in sensors and optoelectronics are envisaged.     

On the spatial behavior of solutions for non-linear type II heat conduction

In this paper we study the spatial behavior of the solutions for a problem determined by the non-linear version of the Green and Naghdi type II heat conduction theory. We obtain a spatial decay estimates for the usual boundary-initial-value problem and also an upper bound for the amplitude term of the spatial estimate. Finally, we analyze a non-standard initial value problem defined on a particular family of heat conductors.     

A Model of Joined Beams as Limit of a 2<Emphasis Type="Italic">D</Emphasis> Plate

In this paper, we consider an elastic multi-structure composed of two joined beams forming an angle \(\alpha\in \, ]0,\frac{\pi}{2}]\) at the junction, clamped at the three extremities and submitted to forces transverse to the plane containing the skeleton of the multi-structure. We derive the equilibrium configuration of the transverse displacement and the torsional rotation of the multi-structure, via an asymptotic analysis based on a dimensional reduction of a Kirchhoff-Love plate. More generally, we obtain the equilibrium configuration of the transverse displacement and the torsional rotation of a multi-structure whose skeleton is composed of a line and a planar curve joined together.     

Structure of saddle-node and cusp bifurcations of periodic orbits near a non-transversal T-point

Non-transversal T-points have been recently found in problems from many different fields: electronic circuits, pendula, and laser problems. In this work, we study a model based on the construction of a Poincaré map that describes the behaviour of curves of saddle-node and cusp bifurcations in the vicinity of such a non-transversal T-point. This model is also able to predict, reproduce, and explain the numerical results previously obtained in Chua’s equation.