Unexpected Nonadditivity Effects in Anion−π Complexes

A theoretical investigation on the synergetic effect of hydrogen-bonding interactions and thermodynamic property in the 1: 2 (azacyclopentane-2-one: N-methylolacetamide) ternary complex

CONTEXT

Using chemical penetration enhancers to improve the penetration effect is one kind of important strategies in transdermal drug delivery system. Azone is a widely used transdermal absorption enhancer for transdermal drug delivery. To shed light on the permeation-promoting mechanism of azone, we selected ternary systems formed by azacyclopentane-2-one and N-methylolacetamide (1: 2) and explored the synergetic effect of hydrogen-bonding interactions among them and their thermodynamic properties. The findings indicate that the synergetic effects can enhance the ability of azone to change the original conformation of ceramides and even break the original hydrogen bonds, which is more beneficial for azone to destroy the 3D network structure of ceramides. When azone interacts with ceramide, the order of action tends to interact with one molecule of ceramide first and then with another molecule of ceramide.

METHODS

The synergetic effects of hydrogen-bonding interactions in ternary systems were computed at the B3LYP/6-311 +  + G** and MP2(full)/6-311 +  + G** levels. Thermodynamic parameters for two ternary-complex routes were worked out at the B3LYP/aug-cc-pVDZ level. The shift of the electron density occurring simultaneously with trimer formation was analyzed at the MP2(full)/6-311 +  + G** level. The above calculations were carried out using the Gaussian 03 program packages. Atoms in molecules (AIM) method and the AIMPAC program showed the topological charge density at the MP2(full)/6-311 +  + G** level. The synergetic effects of hydrogen-bonding interactions and thermodynamic property in the 1: 2 (azacyclopentane-2-one: N-methylolacetamide) ternary systems were investigated using the B3LYP and MP2(full) methods.

Unfurling Anion-π Interactions Involving Graphynes

Ever since the inception of anion-π interactions, their nature and functional relevance have intrigued researchers. We address the twin challenge of elucidation of the role of extended conjugation and design of all-carbon neutral anion receptors by computations on the anion-π complexes of the halide ions with graphynes. Leveraging on the extended π-conjugation effects, we unfurl the functional relevance of graphynes as anion receptors using descriptors such as electrostatic potential, quadrupole moments, molecular polarizabilities and binding energies. Further, employing natural energy decomposition analysis, we assert that anion-π interactions are not merely dominated by electrostatic interactions. The polarization components do indeed play a crucial role in governing the binding of the anions to the graphynes.

The modulation effect of electron-rich solvents on the supramolecular networks and photochromic properties of naphthalene diimide molecules

The electron-rich solvents can effectively regulate the interfacial contacts of electron donors/acceptors and the photochromic properties of naphthalene diimide molecules.

Tracking the absence of anion–π interactions in modified [23](1,3,5)cyclophanes: insights from computation

[2₃](1,3,5)Cyclophanes containing 1,3,5-triazine and 1,3,5-triphosphinine planar rings present different degrees of aromaticity as well as σ-donor and π-acceptor abilities.

Molecular Borromean Rings Based on Half-Sandwich Organometallic Rectangles

Over the last two decades, interlocked molecular species have received considerable attention, not only because of their intriguing structures and topological importance, but also because of their potential applications as smart materials, nanoscale devices, and molecular machines. Through judicious choice of metal centers and their adjoining ligands, a range of interesting interlocked structures have been realized by coordination-driven self-assembly. In addition, researchers have extensively developed synthetic methodologies for the construction of organized self-assemblies. One fascinating and challenging synthetic target in this field is the family of molecular Borromean rings, which consist of three chemically independent rings that are locked in such a way that no two of the three rings are linked with each other. Toward this goal, we have developed a template-free self-assembly method for synthesizing molecular Borromean rings by rationally designing metal-containing precursors and organic ligands. In this Account, we present our recent work, focusing on interlocked structures comprising half-sandwich iridium- and rhodium-based organometallic assemblies obtained by rational design. We first describe a series of template-free self-assembled organometallic molecular Borromean rings, which we constructed from preorganized binuclear half-sandwich molecular clips and suitable pyridyl ligands. These molecular Borromean rings can be sorted into four types according to their different bridging ligands, including those based on metallaligands, dihalogenated ligands, naphthazarin and π-acceptor ligands. By single-crystal X-ray crystallographic analysis, NMR experiment, and DFT calculation, we discuss their driving forces and the inter-ring interactions. Furthermore, we took advantage of the dissimilarity in their interactions to realize selective, reversible conversions between molecular Borromean rings and monomeric rectangles by the use of suitable solvents or guest molecules. Subsequently, a stepwise chemoseparation method based on molecular Borromean rings was established, with the molecular Borromean rings used in the separation being recoverable and recyclable. Due to their structural complexity and difficult synthesis, useful guidelines or rules to help design complicated interlocked molecules are highly desirable. We also highlight our efforts to develop empirical guidelines to uncover the relationship between the aspect ratio of metallarectangles and the formation or stability of molecular Borromean rings. An empirical formula has further been established to show the approximate ratio of lengths of the short arm and the long arm in molecular Borromean rings based on π-π (or p-π) stacking. We then demonstrate how to use these guidelines to design new molecular Borromean rings and further lead to other interlocked structures, for example, [2]- and [3]catenane structures. Taken together, our results may lead to a promising future for the design of fascinating and useful interlocked structures by coordination-driven self-assembly.

The mutual interactions based on amphipathic tetraoxacalix[2]arene[2]triazine: recognition cases of anion and cation investigated by a computational study

This work provides insights into the interaction nature of amphiphilic tetraoxacalix[2]arene[2]triazine with the system (J. Am. Chem. Soc., 2013, 135, 892) as well as the recognition cases of anion and cation.

Anion induced formation of supramolecular associations involving lone pair-π and anion-π interactions in Co(II) malonate complexes: experimental observations, Hirshfeld surface analyses and DFT studies

Three Co(II)-malonate complexes, namely, (C(5)H(7)N(2))(4)[Co(C(3)H(2)O(4))(2)(H(2)O)(2)](NO(3))(2) (1), (C(5)H(7)N(2))(4)[Co(C(3)H(2)O(4))(2)(H(2)O)(2)](ClO(4))(2) (2), and (C(5)H(7)N(2))(4)[Co(C(3)H(2)O(4))(2)(H(2)O)(2)](PF(6))(2) (3) [C(5)H(7)N(2) = protonated 2-aminopyridine, C(3)H(4)O(4) = malonic acid, NO(3)(-) = nitrate, ClO(4)(-) = perchlorate, PF(6)(-) = hexafluorophosphate], have been synthesized from purely aqueous media, and their crystal structures have been determined by single crystal X-ray diffraction. A thorough analysis of Hirshfeld surfaces and fingerprint plots facilitates a comparison of intermolecular interactions in 1-3, which are crucial in building supramolecular architectures. When these complexes are structurally compared with their previously reported analogous Ni(II) or Mg(II) compounds, a very interesting feature regarding the role of counteranions has emerged. This phenomenon can be best described as anion-induced formation of extended supramolecular networks of the type lone pair-π/π-π/π-anion-π/π-lone pair and lone pair-π/π-π/π-anion involving various weak forces like lone pair-π, π-π, and anion-π interactions. The strength of these π contacts has been estimated using DFT calculations (M06/6-31+G*), and the formation energy of the supramolecular networks has been also evaluated. The influence of the anion (NO(3)(-), ClO(4)(-), and PF(6)(-)) on the total interaction energy of the assembly is also studied.

Substituent effects on non-covalent interactions with aromatic rings: insights from computational chemistry

Non-covalent interactions with aromatic rings pervade modern chemical research. The strength and orientation of these interactions can be tuned and controlled through substituent effects. Computational studies of model complexes have provided a detailed understanding of the origin and nature of these substituent effects, and pinpointed flaws in entrenched models of these interactions in the literature. Here, we provide a brief review of efforts over the last decade to unravel the origin of substituent effects in π-stacking, XH/π, and ion/π interactions through detailed computational studies. We highlight recent progress that has been made, while also uncovering areas where future studies are warranted.