Molecular Clusters of pi-Systems: Theoretical Studies of Structures, Spectra, and Origin of Interaction Energies

Internal Energy Dependence of the Pyrrole Dimer Cation Structures Formed in a Supersonic Plasma Expansion: Charge-Resonance and Hydrogen-Bonded Isomers

The structures of the pyrrole dimer cation (Py2+) formed in an electron-ionization-driven supersonic plasma expansion of Py seeded in Ar or N2 are probed as a function of its internal energy by infrared photodissociation (IRPD) spectroscopy in a tandem mass spectrometer. The IRPD spectra recorded in the CH and NH stretch ranges are analyzed by dispersion-corrected density functional theory (DFT) calculations at the B3LYP-D3/aug-cc-pVTZ level. The spectra of the cold Ar/N2-tagged Py2+ clusters, Py2+Ln (n = 1-5 for Ar, n = 1 for N2), indicate the exclusive formation of the most stable antiparallel π-stacked Py2+ structure under cold conditions, which is stabilized by charge-resonance interaction. The bare Py2+ dimers produced in the ion source have higher internal energy, and the observation of additional transitions in their IRPD spectra suggests a minor population of less stable hydrogen-bonded isomers composed of heterocyclic Py/Py+ structures formed after intramolecular H atom transfer and ring opening. These intermolecular isomers differ from the chemically bonded structures proposed earlier in the analysis of IRPD spectra of Py2+ generated by VUV ionization of neutral Pyn clusters.

Analyzing the aromatic-aromatic interactions in proteins: A2ID 2.0

The Aromatic-Aromatic Interactions Database (A2ID) is a comprehensive repository dedicated to documenting aromatic-aromatic (π-π) networks observed in experimentally determined protein structures. The first version of A2ID was reported in 2011 [Int J Biol Macromol, 2011, 48, 540]. It has undergone a series of significant updates, leading to its current version, which focuses on the identification and analysis of 3,444,619 π-π networks from proteins. The geometrical parameters such as centroid-centroid distances (r) and interplanar angles (ϕ) were used to identify and characterize π-π networks. It was observed that among the 84,500 proteins with at least one aromatic π-π network, about 92.50 % of the instances are found to be either 2π (77.34 %) or 3π (15.23 %) networks. The analysis of interacting amino acid pairs in 2π networks indicated a dominance of PHE residues followed by TYR. The updated version of A2ID incorporates analysis of π-π networks based on SCOP2 and ECOD classifiers, in addition to the existing SCOP, CATH, and EC classifications. This expanded scope allows researchers to explore the characteristics and functional implications of π-π networks in protein structures from multiple perspectives. The current version of A2ID along with its extensive dataset and detailed geometric information is publicly accessible using https://acds.neist.res.in/a2idv2.

Structure-directing role of CH⋯X (X = C, N, S, Cl) interactions in three ionic cobalt complexes: X-ray investigation and DFT study using QTAIM Vr predictor to eliminate the effect of pure Coulombic forces

Three cobalt complexes, namely [CoIII(HL1)2(N3)2]ClO4 (1), [CoIII(L2)(HL2)(N3)]ClO4·1.5H2O (2), and [CoIII(L3)(HL3)(NCS)]2 [CoIICl2(NCS)2] (3), where HL1 = 2-(3-(dimethylamino)propyliminomethyl)-6-methoxyphenol, HL2 = 2-(2-(dimethylamino)ethyliminomethyl)-4,6-dichlorophenol, and HL3 = 2-(2-(dimethylamino)ethyliminomethyl)-6-methoxyphenol, as potential tridentate N2O-donor Schiff base ligands, were synthesized and characterized using elemental analysis, IR and UV-vis spectroscopy, and single-crystal X-ray diffraction studies. All three were found to be monomeric ionic complexes. Complex 1 crystallizes in the orthorhombic space group Pbcn, whereas both complexes 2 and 3 crystallize in triclinic space groups, P1̄. Further, 1 and 2 are cationic complexes of octahedral cobalt(iii) with perchlorate anions, whereas complex 3 contains a cationic part of octahedral cobalt(iii) and an anionic part of tetrahedral cobalt(ii). Hydrogen-bonding interactions involving aromatic and aliphatic CH bonds as H-bond donors and the pseudo-halide co-ligands as H-bond acceptors were established, which are important aspects governing the X-ray packing. These interactions were analyzed theoretically using the quantum theory of atoms in molecules (QTAIM) and non-covalent interaction plot (NCI plot) analyses. Moreover, energy decomposition analysis (EDA) was performed to analyze the stabilization of the complexes in terms of the electrostatic, dispersion, and correlation forces.

Anion-π Interaction in a Diketopyrrolopyrrole Derivative

In this work, an N-substituted diketopyrrolopyrrole (DPP) derivative Ph-DPP was synthesized, showing interaction toward Lewis alkaline anions such as F-. The typical electron-transfer-dominated anion-π interaction product Ph-DPP•- and unexpected isomer product i-Ph-DPP were both observed, and their formation mechanism was studied by density functional theory calculations, suggesting that a deprotonation initiation route is favored, which gives interesting insight for understanding the debatable role of F- in such non-covalent intermolecular interactions.

Interheteromolecular Hyperconjugation Boosts (De)hydrogenation for Reversible H2 Storage

Interheteromolecular hyperconjugation is ubiquitous in organic systems, affecting bond length, dipole moments, conformations and so on, while its effect on (de)hydrogenation reactivity in a heterogeneous thermo-catalytic system has rarely been explored. Herein, the N-heterocycles containing a benzene ring and aliphatic chain [N-ethylcarbazole (NEC) and N-propylcarbazole (NPC)] were utilized to study the correlation between interheteromolecular hyperconjugation and catalytic (de)hydrogenation. Density functional theory calculations, variable-temperature ¹ H nuclear magnetic resonance spectroscopy, and catalytic experiments showed that the presented hyperconjugation between NEC and NPC weakened the electron cloud density of aromatic rings and thus facilitated the reactivity with hydrogen featuring unpaired electrons. Therefore, an extremely low temperature of 80 °C was enough for the hydrogenation. Moreover, this interheteromolecular hyperconjugation was general in other N-heterocycles (e. g., N-methyindole and NPC) and was also effective to (de)deuterate as revealed by isotope experiments. This work expands the application of interheteromolecular hyperconjugation to heterogeneous thermocatalysis for reversible H₂ storage.

Perfluoroarenes: A Versatile Platform for Hybrid Perovskite Photovoltaics

The instability of hybrid organic-inorganic halide perovskites presents one of the pressing challenges for their application. This is associated with the sensitivity to moisture as well as mixed ionic-electronic conductivity that leads to enhanced ion migration under conditions of voltage and light bias. Some of the most effective strategies to stabilize hybrid perovskite materials during operation involve the use of interfacial molecular assemblies and low-dimensional perovskite architectures based on hydrophobic organic moieties that could suppress the effects of moisture or ion migration. For this purpose, perfluoroarenes have provided a versatile platform due to their enhanced hydrophobicity as well as the capacity to engage in various noncovalent interactions that affect the characteristics of the resulting assemblies as well as ion migration. This Perspective discusses the emerging role of perfluoroarenes in stabilizing hybrid perovskite materials and their photovoltaic devices through different modes of action, offering insights for the design of advanced materials.

Triple ionization and fragmentation of benzene trimers following ultrafast intermolecular Coulombic decay

Intermolecular interactions involving aromatic rings are ubiquitous in biochemistry and they govern the properties of many organic materials. Nevertheless, our understanding of the structures and dynamics of aromatic clusters remains incomplete, in particular for systems beyond the dimers, despite their high presence in many macromolecular systems such as DNA and proteins. Here, we study the fragmentation dynamics of benzene trimer that represents a prototype of higher-order aromatic clusters. The trimers are initially ionized by electron-collision with the creation of a deep-lying carbon 2s⁻¹ state or one outer-valence and one inner-valence vacancies at two separate molecules. The system can thus relax via ultrafast intermolecular decay mechanisms, leading to the formation of C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}_{6}{{{{{{{{{\rm{H}}}}}}}}}_{6}}^{+}\cdot$$\end{document}6H6+⋅C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}_{6}{{{{{{{{{\rm{H}}}}}}}}}_{6}}^{+}\cdot$$\end{document}6H6+⋅C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}_{6}{{{{{{{{{\rm{H}}}}}}}}}_{6}}^{+}$$\end{document}6H6+ trications and followed by a concerted three-body Coulomb explosion. Triple-coincidence ion momentum spectroscopy, accompanied by ab-initio calculations and further supported by strong-field laser experiments, allows us to elucidate the details on the fragmentation dynamics of benzene trimers.

Higher-order aromatic clusters are prevalent in biochemical systems, but a full understanding of their structural and dynamical properties is lacking. Here, the authors demonstrate that inner-valence ionization can induce ultrafast relaxation and further fragmentation mechanisms in benzene trimers.

Bonding and 13 C-NMR properties of coinage metal tris(ethylene) and tris(norbornene) complexes: Evaluation of the role of relativistic effects from DFT calculations

The π-complexes of cationic coinage metal ions (Cu(I), Ag(I), Au(I)) provide useful experimental support for understanding fundamental characteristics of bonding and ¹³ C-NMR patterns of the group 11 triad. Here, we account for the role of relativistic effects on olefin-coinage metal ion interaction for cationic, homoleptic tris-ethylene, and tris-norbornene complexes, [M(η² -C₂ H₄ )₃ ]⁺ and [M(η² -C₇ H₁₀ )₃ ]⁺ (M = Cu, Ag, Au), as representative case of studies. The M-(CC) bond strength in the cationic, tris-ethylene complexes is affected sizably for Au and to a lesser extent for Ag and Cu (48.6%, 16.7%, and 4.3%, respectively), owing to the influence on the different stabilizing terms accounting for the interaction energy in the formation of coinage metal cation-π complexes. The bonding elements provided by olefin → M σ-donation and olefin ← M π-backbonding are consequently affected, leading to a lesser covalent interaction going down in the triad if the relativistic effects are ignored. Analysis of the ¹³ C-NMR tensors provides further understanding of the observed experimental values, where the degree of backbonding charge donation to π₂ *-olefin orbital is the main influence on the observed high-field shifts in comparison to the free olefin. This donation is larger for ethylene complexes and lower for norbornene counterparts. However, the bonding energy in the later complexes is slightly stabilized given by the enhancement in the electrostatic character of the interaction. Thus, the theoretical evaluation of metal-alkene bonds, and other metal-bonding situations, benefits from the incorporation of relativistic effects even in lighter counterparts, which have an increasing role going down in the group.

A computational study on acetaminophen drug complexed with Mn+, Fe2+, Co+, Ni2+, and Cu+ ions: structural analysis, electronic properties, and solvent effects

In the present research, the cation-π interactions in acetaminophen-M complexes (M = Mn⁺, Fe²⁺, Co⁺, Ni²⁺, and Cu⁺) are investigated using density functional theory (DFT/ωB97XD) in the gas phase and solution. The results show that the absolute values of energy are reduced in going from the gas phase to the solution. Based on the obtained data, the complexes in water are the most stable. The natural bond orbital (NBO) and the atoms in molecules (AIM) analyses are also applied to achieve more details about the nature of interactions. These results are useful for understanding the role of the drug-receptor interactions in the complexes. According to AIM outcomes, the cation-π interactions are the closed-shell and may indicate the partially covalent nature in the complexes. A comprehensive analysis is also performed on the conceptual DFT parameters of the complexes to evaluate their electronic properties. Our findings show increasing the stability and decreasing the reactivity of the complexes in the solution phase with respect to the gas phase. These interactions are ubiquitous in biological systems, and their importance in theoretical models led us to study such important interactions. The results of this study may be useful for the design and synthesis of a variety of supramolecular complexes with the desired properties.

Probing and Manipulating Noncovalent Interactions in Functional Polymeric Systems

Noncovalent interactions, which usually feature tunable strength, reversibility, and environmental adaptability, have been recognized as driving forces in a variety of biological and chemical processes, contributing to the recognition between molecules, the formation of molecule clusters, and the establishment of complex structures of macromolecules. The marriage of noncovalent interactions and conventional covalent polymers offers the systems novel mechanical, physicochemical, and biological properties, which are highly dependent on the binding mechanisms of the noncovalent interactions that can be illuminated via quantification. This review systematically discusses the nanomechanical characterization of typical noncovalent interactions in polymeric systems, mainly through direct force measurements at microscopic, nanoscopic, and molecular levels, which provide quantitative information (e.g., ranges, strengths, and dynamics) on the binding behaviors. The fundamental understandings of intermolecular and interfacial interactions are then correlated to the macroscopic performances of a series of noncovalently bonded polymers, whose functions (e.g., stimuli-responsiveness, self-healing capacity, universal adhesiveness) can be customized through the manipulation of the noncovalent interactions, providing insights into the rational design of advanced materials with applications in biomedical, energy, environmental, and other engineering fields.

Influence of cation-π interactions to the structural stability of phycocyanin proteins: A computational study

The influences of cation-π interactions in phycocyanin proteins and their environmental preferences were analyzed. The number of interactions formed by arginine showed to be higher than those formed by the lysine in the cationic group, while histidine is comparatively higher than phenylalanine and N-terminal residue in the π group. Arg-Tyr and Arg-Phe interacting pairs are predominant among the various pairs analyzed. Cation-π interactions are distance-dependent and can be realized above a wider area above the π ring. We analyzed the energy contribution resulting from cation-π interactions using ab initio calculations. The energy contribution resulting from the most frequent cation-π interactions was in the lower range of strong hydrogen bonds. The results showed that, while most of their interaction energies lay ranged from - 2 to - 8 kcal/mol, those energies could be up to -12- 12 kcal/mol. Stabilization centers for these proteins showed that all residues found in cation-π interactions are important in locating one or more of such centers. In the cation-π interacting residues, 54% of the amino acid residues involved in these interactions might be conserved in phycocyanins. From this study, we infer that cation-π forming residues play an important role in the stability of the multiply commercially used phycocyanin proteins and could help structural biologists and medicinal chemists to design better and safer drugs.

Mechanism for selective binding of aromatic compounds on oxygen-rich graphene nanosheets based on molecule size/polarity matching

Selective binding of organic compounds is the cornerstone of many important industrial and pharmaceutical applications. Here, we achieved highly selective binding of aromatic compounds in aqueous solution and gas phase by oxygen-enriched graphene oxide (GO) nanosheets via a previously unknown mechanism based on size matching and polarity matching. Oxygen-containing functional groups (predominately epoxies and hydroxyls) on the nongraphitized aliphatic carbons of the basal plane of GO formed highly polar regions that encompass graphitic regions slightly larger than the benzene ring. This facilitated size match-based interactions between small apolar compounds and the isolated aromatic region of GO, resulting in high binding selectivity relative to larger apolar compounds. The interactions between the functional group(s) of polar aromatics and the epoxy/hydroxyl groups around the isolated aromatic region of GO enhanced binding selectivity relative to similar-sized apolar aromatics. These findings provide opportunities for precision separations and molecular recognition enabled by size/polarity match-based selectivity.

Nanosegregation in arene-perfluoroarene π-systems for hybrid layered Dion-Jacobson perovskites

Layered hybrid perovskites are based on organic spacers separating hybrid perovskite slabs. We employ arene and perfluoroarene moieties based on 1,4-phenylenedimethylammonium (PDMA) and its perfluorinated analogue (F-PDMA) in the assembly of hybrid layered Dion-Jacobson perovskite phases. The resulting materials are investigated by X-ray diffraction, UV-vis absorption, photoluminescence, and solid-state NMR spectroscopy to demonstrate the formation of layered perovskite phases. Moreover, their behaviour was probed in humid environments to reveal nanoscale segregation of layered perovskite species based on PDMA and F-PDMA components, along with enhanced stabilities of perfluoroarene systems, which is relevant to their application.

Uptake of Hydrogen Bonding Molecules by Benzene Nanoparticles

The uptake of molecules on nanometer-size clusters of polyaromatic hydrocarbons (PAHs) is important for the condensation of water on PAH aerosols in the atmosphere and for ice mantle growth on nanoparticles in the interstellar medium. We generate benzene clusters Bz_N of mean size N̅ ≈ 300 (radius R̅ ≈ 2.2 Å) as a model system for the PAH nanoparticles. Using molecular beams and mass spectrometry detection, we investigate the uptake of water, methanol, and ethanol by these clusters. All picked up molecules are highly mobile on Bz_N and generate clusters within <3 ms. The relative uptakes for the different investigated molecules can be directly compared and quantified. Water molecules exhibit the lowest relative pickup probability that is ∼30% lower than those for methanol and ethanol, which are approximately the same.

In silico and in vitro Estimation of Structure and Biological Affinity of 1,3- Oxazoles: Fragment-to-fragment Approach

Background:

The fragment-to-fragment approach for the estimation of the biological af-finity of the pharmacophores with biologically active molecules has been proposed. It is the next step in the elaboration of molecular docking and using the quantum-chemical methods for the complex modeling of pharmacophores with biomolecule fragments.

Methods:

The parameter 0 was used to estimate the contribution of -electron interactions in bio-logical affinity. It is directly related to the position of the frontier levels and reflects the donor-accep-tor properties of the pharmacophores and stabilization energy of the [Pharm꞉BioM] complex.

Results:

By using quantum-chemical calculations, it was found that the stacking interaction of oxa-zoles with phenylalanine is 7-11 kcal/mol, while the energy of hydrogen bonding of oxazoles with the amino group of lysine is 5-9 kcal/mol. The fragment-to-fragment approach can be applied for the investigation of the dependence of biological affinity on the electronic structure of pharmacophores.

Conclusion:

The founded quantum-chemical regularities are confirmed with the structure-activity relationships of substituted oxazoles.

Ultrafast energy transfer between π-stacked aromatic rings upon inner-valence ionization

Non-covalently bound aromatic systems are ubiquitous and govern the physicochemical properties of various organic materials. They are important to many phenomena of biological and technological relevance, such as protein folding, base-pair stacking in nucleic acids, molecular recognition and self-assembly, DNA-drug interactions, crystal engineering and organic electronics. Nevertheless, their molecular dynamics and chemical reactivity, particularly in electronic excited states, are not fully understood. Here, we observe intermolecular Coulombic decay in benzene dimers, (C₆H₆)₂-the simplest prototypes of noncovalent π-π interactions between aromatic systems. Intermolecular Coulombic decay is initiated by a carbon 2s vacancy state produced by electron-impact ionization and proceeds through ultrafast energy transfer between the benzene molecules. As a result, the dimer relaxes with the emission of a further low-energy electron (<10 eV) and a pair of C₆H₆⁺ cations undergoing Coulomb explosion. Coincident fragment-ion and electron momentum spectroscopy, accompanied by ab initio calculations, enables us to elucidate the dynamical details of this ultrafast relaxation process.

Investigations on the role of cation-π interactions in active centers of superoxide dismutase

In this study, we have analysed the influence of cation-? interactions on stability and properties of superoxide dismutase (SOD) active centres. The number of interactions formed by arginine is higher than lysine in the cationic group, while histidine is comparatively higher in the ? group. The energy contribution resulting from most frequent cation-? interactions was in the lower range of strong hydrogen bonds. The cation-? interactions involving transition metal ions as cation have energy more negative than -418.4 kJ mol-1. Stabilization centres for these proteins showed that all residues involved in cation-? interactions were important in locating one or more of such centres. The majority of the residues involved in cation-p interactions were evolutionarily conserved and might have a significant contribution towards the stability of SOD proteins. The results presented in this work can be very useful for understanding the contribution of cation-? interactions to the stability of SOD active canters.

Tailoring long-range superlattice chirality in molecular self-assemblies via weak fluorine-mediated interactions

Controllable fabrication of enantiospecific molecular superlattices is a matter of imminent scientific and technological interest. Herein, we demonstrate that long-range superlattice chirality in molecular self-assemblies can be tailored by tuning the interplay of weak intermolecular non-covalent interactions between hexaphenylbenzene-based enantiomers. By means of high-resolution scanning tunneling microscopy measurements, we demonstrate that the functionalization of a hexaphenylbenzene-based molecule with fluorine (F) atoms leads to the formation of molecular self-assemblies with distinct long-range chiral recognition patterns. We employed density functional theory calculations to quantify F-mediated lone pair F⋯π, C-H⋯F, and F⋯F interactions attributed to the distinct enantiospecific molecular self-organizations. Our findings underpin a viable route to fabricate long-range chiral recognition patterns in supramolecular assemblies by engineering the weak non-covalent intermolecular interactions.

Vibrational Spectroscopy of Benzonitrile-(Water)1-2 Clusters in Helium Droplets

Polycyclic aromatic hydrocarbons are considered as primary carriers of the unidentified interstellar bands. The recent discovery of the first interstellar aromatic molecule, benzonitrile (C₆H₅CN), suggests a repository of aromatic hydrocarbons in the outer earth environment. Herein, we report an infrared (IR) study of benzonitrile-(D₂O)_n clusters using mass-selective detection in helium nanodroplets. In this work, we use isotopically substituted water, D₂O, instead of H₂O because of our restricted IR frequency range (2565-3100 cm^-1). A comparison of the experimental and predicted spectra computed at the MP2/6-311++G(d,p) level of benzonitrile-(water)_1-2 clusters reveals the formation of a unique local minimum structure, which was not detected in previous gas-phase molecular beam experiments. Here, the solvent water forms a nearly linear hydrogen bond (H-bond) with the nitrile nitrogen of benzonitrile, while the previously reported most stable cyclic H-bonded isomer is not observed. This can be rationalized by the stepwise aggregation process of precooled monomers. The addition of a second water molecule results in the formation of two different isomers. In one of the observed isomers, a H-bonded water chain binds linearly to the nitrile nitrogen similar to the monohydrated benzonitrile-water complex. In the other observed isomer, the water dimer forms a ring-type structure, where a H-bonded water dimer simultaneously interacts with the nitrile nitrogen and the adjacent ortho CH group. Finally, we compare the water-binding motif in the neutral benzonitrile-water complex with the corresponding positively and negatively charged benzonitrile-water monohydrates to comprehend the charge-induced alteration of the solvent binding motif.

Crystal structures of three N-acyl-hydrazone isomers

The crystal structures of three isomers of (E)-4-chloro-N-{2-[2-(chloro-benzyl-idene)hydrazin-yl]-2-oxoeth-yl}-benzene-sulfonamide, namely, (E)-4-chloro-N-{2-[2-(2-chloro-benzyl-idene)hydrazin-yl]-2-oxoeth-yl}-benzene-sulfonamide (I), (E)-4-chloro-N-{2-[2-(3-chloro-benzyl-idene)hydrazin-yl]-2-oxoeth-yl}-benzene-sul-fon-amide (II) and (E)-4-chloro-N-{2-[2-(4-chloro-benzyl-idene)hydrazin-yl]-2-oxo-eth-yl}-benzene-sulfonamide (III), with the general formula C15H13Cl2N3O3S are described, with the chloro group in ortho, meta and para positions in the benzyl-idene benzene ring. All the three isomeric compounds crystallize in the centrosymmetric triclinic P space group with one mol-ecule each in the asymmetric unit and two mol-ecules in the unit cell. The dihedral angles between the two phenyl rings are 11.09 (14), 53.79 (18) and 72.37 (11)° in (I), (II) and (III), respectively. The central part of the mol-ecule (-C-N-N=C-) is almost linear with C-N-N-C torsion angles of 179.1 (2), -169.5 (3) and 178.5 (2)° for (I), (II) and (III), respectively. In all the three crystals, the mol-ecules form inversion dimers with R 2 2(8) ring motifs, which are further augmented by C-H⋯O inter-actions.

Fragment-Based Local Coupled Cluster Embedding Approach for the Quantification and Analysis of Noncovalent Interactions: Exploring the Many-Body Expansion of the Local Coupled Cluster Energy

Herein, we introduce a fragment-based local coupled cluster embedding approach for the accurate quantification and analysis of noncovalent interactions in molecular aggregates. Our scheme combines two different expansions of the domain-based local pair natural orbital coupled cluster (DLPNO-CCSD(T)) energy: the many-body expansion (MBE) and the local energy decomposition (LED). The low-order terms in the MBE are initially computed in the presence of an environment that is treated at a low level of theory. Then, LED is used to decompose the energy of each term in the embedded MBE into additive fragment and fragment-pairwise contributions. This information is used to quantify the total energy of the system while providing at the same time in-depth insights into the nature and cooperativity of noncovalent interactions. Two different approaches are introduced and tested, in which the environment is treated at different levels of theory: the local coupled cluster in the Hartree-Fock (LCC-in-HF) method, in which the environment is treated at the HF level; and the electrostatically embedded local coupled cluster method (LCC-in-EE), in which the environment is replaced by point charges. Both schemes are designed to preserve as much as possible the accuracy of the parent local coupled cluster method for total energies, while being embarrassingly parallel and less memory intensive. These schemes appear to be particularly promising for the study of large and complex molecular aggregates at the coupled cluster level, such as condensed phase systems and protein-ligand interactions.

Multiwavelets applied to metal-ligand interactions: Energies free from basis set errors

Transition metal-catalyzed reactions invariably include steps where ligands associate or dissociate. In order to obtain reliable energies for such reactions, sufficiently large basis sets need to be employed. In this paper, we have used high-precision multiwavelet calculations to compute the metal-ligand association energies for 27 transition metal complexes with common ligands, such as H₂, CO, olefins, and solvent molecules. By comparing our multiwavelet results to a variety of frequently used Gaussian-type basis sets, we show that counterpoise corrections, which are widely employed to correct for basis set superposition errors, often lead to underbinding. Additionally, counterpoise corrections are difficult to employ when the association step also involves a chemical transformation. Multiwavelets, which can be conveniently applied to all types of reactions, provide a promising alternative for computing electronic interaction energies free from any basis set errors.

Use of 1-octyl-3-methylimidazole hexafluorophosphate modified magnetic hyperbranched polyamideamine as sorbent for the extraction of pyrethroid insecticides from tea infusion

Magnetic hyperbranched polyamideamine was carboxylated using succinic anhydride and modified further with 1-octyl-3-methylimidazole hexafluorophosphate successively. The morphology and chemical composition of the prepared material was characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller measurement, X-ray photoelectron spectroscopy, etc. 1-Octyl-3-methylimidazole hexafluorophosphate modified magnetic hyperbranched polyamideamine was used as sorbent in the magnetic solid-phase extraction for the separation and enrichment of five pyrethroid insecticides from tea infusion. The magnetic solid-phase extraction method proposed in this article has low method detection limits (0.53-0.71 ng/mL), acceptable coefficient of determination (0.9992-0.9998), wide linear ranges (2.5-500.0 ng/mL), and good repeatability (intraday: 1.2-6.3%; interday: 1.6-5.4%). In the detection of five pyrethroid insecticides in tea infusion, relative recoveries were in the range from 87.7 to 114.7% with satisfactory relative standard deviations (0.2-7.4%). With the aid of quantum chemistry calculations, the interaction energy between the sorbent and five pyrethroid insecticides was calculated, which proved the necessity of the modification of 1-octyl-3-methylimidazole hexafluorophosphate.

The Crystal Structure and Intermolecular Interactions in Fenamic Acids-Acridine Complexes

In order to improve pharmaceutical properties of drugs, complexes are synthesized as combinations with other chemical substances. The complexes of fenamic acid and its derivatives, such as mefenamic-, tolfenamic- and flufenamic acid, with acridine were obtained and the X-ray structures were discussed. Formation of the crystals is determined by the presence of the intermolecular O–H^…N hydrogen bond that occur between fenamic acids and acridine. Intermolecular interactions stabilizing the crystals such as π^…π stacking, C–H^…X (X = O, Cl) intermolecular hydrogen bonds as well as C–H^…π and other dispersive interactions were analyzed by theoretical methods: the quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) approaches.

Open-Framework Zn Compound with Cationic-π Interaction: Photochromism and Benzene Series Detection

Photochromic open-framework compounds are of potential application in detection/sensors. The issue of improving the detection limits has received much attention. We synthesized a new open-framework Zn compound, namely, compound 1 ([Zn(MQ)(IPA)Cl]·5H₂O) (MQ = N-methyl-4,4'-bipyridinium, IPA = m-phthalic acid), which showed a 1D channel structure by a cationic-π interaction. It is noteworthy that this compound is an effective detector for aniline though luminescence emission, which exhibited unprecedented detection limits in photochromic open-framework compounds.

Unravelling the microhydration frameworks of prototype PAH by infrared spectroscopy: naphthalene–(water)1–3

Microhydration structures of the prototypical PAH, naphthalene, are probed by IR spectroscopy in helium droplets. The sequential water addition produces an extended hydrogen-bonded hydration network bound via π hydrogen bond to the aromatic ring.

Anion-dependent structural variations and charge transport property analysis of 4′-(3-pyridyl)-4,2′:6′,4′′-terpyridinium salts

Anion-dependent structural variations and charge transport analysis of three 4′-(3-pyridyl)-4,2′:6′,4′′-terpyridinium salts are reported. They exhibit pronounced photosensing behavior when illuminated using visible light.

The σ-hole⋯σ-hole stacking interaction: An unrecognized type of noncovalent interaction

The σ-hole⋯σ-hole stacking interaction, an unrecognized type of noncovalent interaction, has been found to be present in large quantities in the Cambridge Structural Database. In the σ-hole⋯σ-hole stacking interaction, each of the two interacting σ-holes has the dual electron donor/electron acceptor character; when one σ-hole acts as an electron donor, the other σ-hole acts as an electron acceptor, and vice versa. The σ-hole⋯σ-hole stacking interaction is clearly different from the σ-hole bond in which the charge transfer occurs mainly from the electron donor to the σ-hole. Energy component analysis shows that the σ-hole⋯σ-hole stacking interaction is dominated by the dispersion energy, which is similar to the nature of the aromatic stacking interaction between unsaturated molecules or the σ⋯σ stacking interaction between saturated molecules.

The effect of cation-π interactions on the stability and electronic properties of anticancer drug Altretamine: a theoretical study

The present work utilizes density functional theory (DFT) calculations to study the influence of cation-π interactions on the electronic properties of the complexes formed by Altretamine [2,4,6-tris(dimethylamino)-1,3,5-triazine], an anticancer drug, with mono- and divalent (Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺ and Ca²⁺) metal cations. The structures were optimized with the M06-2X method and the 6-311++G(d,p) basis set in the gas phase and in solution. The theory of `Atoms in Molecules' (AIM) was applied to study the nature of the interactions by calculating the electron density ρ(r) and its Laplacian at the bond critical points. The charge-transfer process during complexation was evaluated using natural bond orbital (NBO) analysis. The results of DFT calculations demonstrate that the strongest/weakest interactions belong to Be²⁺/K⁺ complexes. There are good correlations between the achieved densities and the amounts of charge transfer with the interaction energies. Finally, the stability and reactivity of the cation-π interactions can be determined by quantum chemical computation based on the molecular orbital (MO) theory.

Sodium cationization can disrupt the intramolecular hydrogen bond that mediates the sunscreen activity of oxybenzone

A key decay pathway by which organic sunscreen molecules dissipate harmful UV energy involves excited-state hydrogen atom transfer between proximal enol and keto functional groups. Structural modifications of this molecular architecture have the potential to block ultrafast decay processes, and hence promote direct excited-state molecular dissociation, profoundly affecting the efficiency of an organic sunscreen. Herein, we investigate the binding of alkali metal cations to a prototype organic sunscreen molecule, oxybenzone, using IR characterization. Mass-selective IR action spectroscopy was conducted at the free electron laser for infrared experiments, FELIX (600-1800 cm-1), on complexes of Na+, K+ and Rb+ bound to oxybenzone. The IR spectra reveal that K+ and Rb+ adopt binding positions away from the key OH intermolecular hydrogen bond, while the smaller Na+ cation binds directly between the keto and enol oxygens, thus breaking the intramolecular hydrogen bond. UV laser photodissociation spectroscopy was also performed on the series of complexes, with the Na+ complex displaying a distinctive electronic spectrum compared to those of K+ and Rb+, in line with the IR spectroscopy results. TD-DFT calculations reveal that the origin of the changes in the electronic spectra can be linked to rupture of the intramolecular bond in the sodium cationized complex. The implications of our results for the performance of sunscreens in mixtures and environments with high concentrations of metal cations are discussed.

Cation-π Interactions in Graphene-Containing Systems for Water Treatment and Beyond

Cation-π interactions are common in nature, especially in organisms. Their profound influences in chemistry, physics, and biology have been continuously investigated since they were discovered in 1981. However, the importance of cation-π interactions in materials science, regarding carbonaceous nanomaterials, has just been realized. The interplay between cations and delocalized polarizable π electrons of graphene would bring about significant changes to the intrinsic characteristics of graphene and greatly affect the device performance based on graphene and its derivatives. Here, the cation-π interactions in graphene containing systems for water treatment applications (e.g., separation membranes, adsorbents) are highlighted. The cross-linking effects caused by cation-π interactions contribute to membrane stability and selectivity and enhanced adsorption. Their roles in dominating the performance of graphene-based structures for other specific applications are also discussed. Relevant theoretical modeling and calculations are summarized to offer an in-depth understanding of the underlying mechanisms which can help in designing more functional materials and structures. Perspectives on the potential directions that deserve effort are also presented.

Theoretical investigation of AhR binding property with relevant structural requirements for AhR-mediated toxicity of polybrominated diphenyl ethers

Polybrominated diphenyl ethers (PBDEs) are more frequently suspected with the induction of toxicity via signal transduction pathway of cytosolic aryl hydrocarbon receptor (AhR), the initial binding to which is assumed to be an essential prerequisite during the ligand-dependent activation. However, the AhR binding property and associated toxicity of PBDEs is yet to be clearly known for lacking insights into the structural requirements at molecular level. To understand the AhR binding property of PBDEs, the ligand binding domain (LBD) of AhR was simulatively developed on homologous protein after basic validation of geometrical rationality and the binding interaction profile was visually described using molecular docking approach. For AhR binding, the offset or edge-on π-π stackings with aromatic motifs including Phe289, Phe345 and His285 were shown to be structurally required whereas the electrostatic attraction validated for AhR binding to dioxins might be less effective for 2,2',3,4,4'-pentabromodiphenyl ether (BDE-85). Besides the demands of less steric hindrance from alanines and weak formulation of hydrogen bonds, the dispersion force through large contact and polarization of S-π electrons seemed to be impactful when BDE-85 were closer to Cys327, Met334 or Met342. With theoretical computation of AhR binding energies, the more significant correlativity with bioassays was derived especially for the lowly/moderately brominated congeners, and could be used to predict the AhR binding affinity on certain degree. The informative results would thus not only help well understand the molecular basis of AhR-mediated toxicity but give an approach for accelerative evaluation of AhR binding and toxicity of PBDEs.

Phase Change Materials for Electro-Thermal Conversion and Storage: From Fundamental Understanding to Engineering Design

Advanced functional electro-thermal conversion phase change materials (PCMs) can efficiently manage the energy conversion from electrical energy to thermal energy, thereby playing a significant role in sustainable energy utilization. Considering the inherent insulating properties of pristine PCMs, electrically conductive supporting materials are widely used to encapsulate PCMs to prepare composite PCMs for electro-thermal conversion and storage. Herein, we comprehensively review the recent advances in different electro-thermal conversion PCMs, mainly including carbon-based PCMs (carbon nanotubes [CNTs], graphene, biomass-derived carbon, graphite, highly graphitized carbon, and metal organic frameworks [MOFs]-derived carbon) and MXene-based PCMs. This review aims to provide an in-depth understanding of the electrothermal conversion mechanism and the relationships between structure design (random and array-oriented structure or single and hybrid supporting materials) and electrothermal properties, thereby contributing profound theoretical and experimental bases for the construction of high-performance electro-thermal conversion PCMs. Finally, we highlight the current challenges and future prospects.

Interaction and selectivity of 14-crown-4 derivatives with Li+, Na+, and Mg2+ metal ions

The interactions between crown ether ligands (14-crown-4, 14C4; 4,4,5,5-tetramethylbenzo-14-crown-4, BC₄H₁₂-14C4; 4,4,5,5,9,9,10,10-octamethyl-14-crown-4, C₈H₂₄-14C4; dibenzo-14-crown ether-4, DB14C4) and alkaline and alkaline earth metal ions (Li⁺, Na⁺, Mg²⁺) were investigated using density functional theory modeling at the M062X/def2SVP and def2TZVP level. The condensed softness analysis of crown ethers, a condensed Fukui function, a condensed dual descriptor, and frontier molecular orbital theory were used to analyze the reactivities of the complexes. The complex stability was analyzed in terms of the binding energies, standard Gibbs free energy of formation, and energy decomposition of the interaction in aqueous solution. The results show that the active sites were mainly located at the carbon atoms of the benzene ring and oxygen atoms. The reactivities of DB14C4 and BC₄H₁₂-14C4 are higher than those of 14C4 and C₈H₂₄-14C4. The electrostatic interaction is the principal factor determining the stability of the complexes. The complexes containing Li⁺ has the greatest stability in aqueous solution among the complexes containing Li⁺, Na⁺, and Mg²⁺. BC₄H₁₂-14C4 shows selective adsorption toward Li⁺ in a mixed solution of Li⁺, Na⁺, and Mg²⁺. To evaluate the stability of complexes containing Mg²⁺, the solvent effect must be accurately described. An energy decomposition analysis was used to evaluate the stability of complexes containing Li⁺, Na⁺, and Mg²⁺, and the solvent effects were considered.

A close competition between O–H⋯O and O–H⋯π hydrogen bonding: IR spectroscopy of anisole–methanol complex in helium nanodroplets

Anisole forms O–H⋯O as well O–H⋯π bound complexes with methanol.

The combination of halogen and hydrogen bonding: a versatile tool in coordination chemistry

4-Iodo-N-(4-pyridyl)benzamide (INPBA) and four derived coordination complexes were synthesized in order to explore the combination of halogen and hydrogen bonding interactions in coordination chemistry.