Investigation of H-bonding and halogen-bonding effects in dichloroacetic acid: DFT calculations of NQR parameters and QTAIM analysis

Synthesis of Stable Hypervalent Bromine(III) Complexes by in Situ Oxidation with Lewis Acids Containing sp-Hybridized Nitrogen

Stable hypervalent bromine(III) compounds were synthesized via aryl bromine oxidation with sp-hybridized nitrogen cations generated by oxime N-O bond cleavage in trifluoroacetic acid. The resulting intramolecular N-Br hypervalent bond is effectively stabilized by the planar xanthone structure. The structures and physicochemical properties of these λ3-bromanes were characterized by X-ray crystallography, cyclic voltammetry, UV-vis spectroscopy, and computational analysis.

Stabilization of sp-Hybridized Nitrogen Cation by Lewis Acid-Base Complex Formation with Intramolecular Iodine

Here we show that the sp-hybridized nitrogen cation is strongly stabilized by a peri-iodine substituent in the tetralone system. The cation is captured by anionic species such as CF3 CO2 - , affording hypervalent iodine(III) compounds with a short nitrogen-iodine (N-I) bond, in which the cation serves as a Lewis acid. Notably, the O-I bond of the O-trifluoroacetate or O-acetate is intrinsically weaker than the N-I bond due to its more ionic character and is further weakened by protonation in trifluoroacetic acid. As a result, the oxygen ligand can dissociate in the presence of a Brønsted acid, affording a I+ cation intermediate that retains the N-I bond. We isolated the cation as the tetrafluoroborate, and characterized it experimentally by 1 H NMR spectroscopy and X-ray structure analysis, and theoretically by means of DFT calculation. The results suggest that the N-I bonded cation is intrinsically stable, and is weakly coordinated with water and the BF4 counter anion or trifluoroacetate anion. This cation can be employed as a reagent for α-oxidation of ketones.

Alkali metals doped cycloparaphenylene nanohoops: Promising nonlinear optical materials with enhanced performance

In the ongoing pursuit of novel and efficient NLO materials, the potential of alkali metal-doped {6}cycloparaphenylene ({6}CPP) and methylene bridged {6} cycloparaphenylene (MB{6}CPP) nanohoops as excellent NLO candidates has been explored. The geometric, electronic, linear, and nonlinear optical properties of designed systems have been investigated theoretically. All the nanohoops demonstrated thermodynamic stability, with remarkable interaction energies reaching up to -1.39 eV (-0.0511 au). Notably, the introduction of alkali metals led to a significant reduction in the HOMO-LUMO energy gaps, with values as low as 2.92 eV, compared to 6.80 eV and 6.06 eV for undoped {6}CPP and MB{6}CPP, respectively. Moreover, the alkali metal-doped nanohoops exhibited exceptional NLO response, with the K@r6-{6}CPP complex achieving the highest first hyperpolarizability of 56,221.7 × 10-30 esu. Additionally, the frequency-dependent first hyperpolarizability values are also computed at two commonly used wavelengths of 1550 nm and 1907 nm, respectively. These findings highlight the potential of designed nanohoops as promising candidates for advanced NLO materials with high-tech applications.

Studies on charge transfer of enalapril maleate: from solid-state to molecular dynamics

INTRODUCTION

Enalapril maleate is an antihypertensive ethyl ester pro-drug with two crystalline forms. A network of hydrogen bonds in both polymorphs plays an important role on solid-state stability, charge transfer process and degradation reactions (when exposed to high humidity, temperature and/or pH changes).

COMPUTATIONAL PROCEDURES

Supramolecular arrangement was proposed by Hirshfeld surface using the CrystalExplorer17 software and quantum theory of atoms in molecules. The electronic structure properties were calculated using the functional hybrid M06-2X with 6-311++G** base function employing diffuse and polarization functions to improve the description of hydrogen atoms on intermolecular interactions. Also, the H+ charge transfer between enalapril and maleate molecules was performed using Car-Parrinello molecular dynamics with the Verlet algorithm. In both simulations, the temperature of the ionic system was maintained around 300 K using the Nosé-Hoover thermostat and the electronic system evolved without the use of the thermostat.

RESULTS

This work evaluates the effect of maleate on the structural stability of enalapril maleate solid state. The electronic structural analysis points out a partially covalent character for N1-H∙∙∙O7 interaction; and the molecular dynamic showed a decentralized hydrogen on maleate driving a decomposition by charge transfer process while a centered hydrogen driving the stabilization. The charge transfer process and the mobility of the proton (H+) between enalapril and maleate molecules was demonstrated using supramolecular modeling analyses and molecular dynamics calculations.

Halogen bonds on substituted dibromonitrobenzene derivatives

Halogen bonding is a noncovalent interaction that has attracted great attention because of its importance in several areas, such as photonics, nonlinear optics, pharmaceutical products, supramolecular engineering, biochemistry, protein-ligand complexes, and polymer interactions. In this context, we describe the synthesis, molecular structure, supramolecular arrangement, and theoretical calculations of five dibromonitrobenzene derivatives, which present different halogen atoms substituted. The solid-state characterization was carried out by X-ray diffraction with the contribution of Hirshfeld surfaces for analysis of molecular interactions. The frontier molecular orbital, molecular electrostatic potential, and quantum theory of atoms in molecules were carried out at the M06-2X/6-311+G(d,p) level of theory. Those observed halogen interactions indicate the crystalline solid-state stabilization for the dibromonitrobenzene derivatives.

Nuclear quadrupole resonance supported by periodic quantum calculations: a sensitive tool for precise structural characterization of short hydrogen bonds

Systems with short hydrogen bonds (H-bonds) are notoriously difficult to describe even using cutting edge experimental techniques supported by advanced computational protocols. One of the most challenging issues is the highly dislocated H-bonded proton, which is typically smeared over a large area, featuring complex dynamics governed by pronounced nuclear quantum effects. Thus, in combination with experimental results, these systems offer a rich platform for the benchmarking of various computational approaches and methods. Herein, we present a methodology combining experimental and computational assessment of H-bond observables probed by the nuclear quadrupole resonance technique. Focusing on the case of picolinic acid N-oxide featuring one of the shortest known hydrogen bonds (ROO ∼ 2.425 Å), we compare the predictions of nuclear quadrupole coupling constants (NQCCs) for a series of computational models differing in fine structural details of the H-bond. By comparing the computed 14N and 17O NQCCs with the measured ones and by analyzing the sensitivity of NQCCs to H-bond geometry variations, we demonstrate that NQCCs represent a very sensitive probe for H-bond geometry, particularly the proton location, thereby offering, in conjunction with computations, an accurate and reliable tool for the fine structural characterization of short H-bonds. Importantly, the present methodology is a good compromise between accuracy and computational cost.

Extremely Strong Halogen Bond. The Case of a Double-Charge-Assisted Halogen Bridge

The stable model of a double (±)charge-assisted halogen bridge has been built on the basis of searches of the Crystal Structure Database. The model, investigated by DFT theory, consists of quinuclidine-like cation derivatives and a set of simple anions. These charged fragments form halogen-bonded complexes of which the energy of complexation in some cases reaches 100 kcal/mol. Even for such strong interactions, the QTAIM characteristics are similar to those of the more classic, relatively weak halogen bonds. An important effect of complexation is the charge transfer measured by means of QTAIM and NBO. It can also be supposed, on the basis of detailed structural and QTAIM analysis, that the delocalization of the charge in a quinuclidine moiety occurs through space and not necessarily along formal bonds. The analysis of only partially charged and fully neutral counterparts of a double (±)charge-assisted halogen bridge shows significantly weaker bonding, being less than 10 kcal/mol.

Theoretical investigation of NMR–NQR tensors of hallucinogenic harmine in monomeric and cluster states

In the present study, density functional theory was employed to analyze the structure and nuclear magnetic resonance (NMR) — nuclear quadrupole resonance (NQR) spectra of hallucinogenic harmine in monomeric, dimeric, trimeric, and tetrameric states in the gas phase. Furthermore, the effects of hydrogen and resonance interactions on the values of NMR and NQR parameters of nitrogen nuclei in the four states mentioned above were investigated. The computations at the B3LYP/6-311[Formula: see text]G** level of theory indicated that NQR — NMR parameters of nitrogen nuclei varied for each of the four states and were strongly affected by chemical environment, molecular cluster size and molecular interactions. Accordingly, by increasing the participation of lone pair electrons in resonance interactions and aromaticity development, the values of NMR chemical shielding around them increased, whereas their NQR parameters ([Formula: see text] and [Formula: see text] decreased. In contrast, it could be observed that resonance interaction was not the only effective factor influencing changes in values and trends of NMR — NQR parameters by passing from monomeric state to other ones. Moreover, the negative charge on nitrogen atoms and the possibility of hydrogen bond formation were other important factors influencing NMR — NQR parameters.

A theoretical study on the characteristics of the intermolecular interactions in the active site of human androsterone sulphotransferase: DFT calculations of NQR and NMR parameters and QTAIM analysis

A theoretical study at the level of density functional theory (DFT) was performed to characterize noncovalent intermolecular interactions, especially hydrogen bond interactions, in the active site of enzyme human androsterone sulphotransferase (SULT2A1/ADT). Geometry optimization, interaction energy, (2)H, (14)N, and (17)O electric field gradient (EFG) tensors, (1)H, (13)C, (17)O, and (15)N chemical shielding (CS) tensors, Natural Bonding Orbital (NBO) analysis, and quantum theory of atoms in molecules (QTAIM) analysis of this active site were investigated. It was found that androsterone (ADT) is able to form hydrogen bonds with residues Ser80, Ile82, and His99 of the active site. The interaction energy calculations and NBO analysis revealed that the ADT molecule forms the strongest hydrogen bond with Ser80. Results revealed that ADT interacts with the other residues through electrostatic and Van der Waals interactions. Results showed that these hydrogen bonds influence on the calculated (2)H, (14)N, and (17)O quadrupole coupling constants (QCCs), as well as (1)H, (13)C, (17)O, and (15)N CS tensors. The magnitude of the QCC and CS changes at each nucleus depends directly on its amount of contribution to the hydrogen bond interaction.

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Asymmetric bifurcated halogen bonds

Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as 'σ-hole - lone pair' or 'σ-hole - π' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction.

Topological insights into the 1/1 diacetyl/water complex gained using a new methodological approach

The 1/1 diacetyl/water complex is of atmospheric relevance. Previous experimental and theoretical studies have focused on two isomeric forms, and geometry optimizations were carried out on them. Herein, we propose a six-step methodological approach based on topological properties to search for and characterize all of the isomeric forms of the 1/1 noncovalent diacetyl/water complex: (1) a molecular electrostatic potential (MESP) study to get an overview of the V min and V max regions on the molecular surfaces of the separate molecules (diacetyl and water); (2) a topological (QTAIM and ELF) study allowing thorough characterization of the electron densities (QTAIM) and irreducible ELF basins of the separate molecules; (3) full optimization of the predicted structures based on the interaction between complementary reaction sites; (4) energetic characterization based on a symmetry-adapted perturbation theory (SAPT) analysis; (5) topological characterization of the optimized complexes; (6) analysis of the complexes in terms of orbital overlaps (natural bond orbitals, NBO analysis). Using this approach, in addition to achieving the topological characterization of the two isomeric forms already reported, a third possible isomer was identified and characterized. Graphical Abstract Topological tools to study monohydrated complexes.

Halogen vs hydrogen bonding in thiazoline-2-thione stabilization with σ- and π-electron acceptors adducts: theoretical and experimental study

Molecular charge-transfer complexes (CT) between thiazoline-2-thione (THZ) and different σ- (I2) and π-acceptors (Tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL)) were investigated. UV-Vis absorption spectroscopy and theoretical calculations using both MP2/aug-cc-pVDZ-PP and B3LYP/6-311++G(d,p) level of theory were corroborated to study the nature of the stabilizing forces for THZ-I2, THZ-DDQ, THZ-TCNE, and THZ-CHL. Halogen bonding (XB) was the stabilizing attractive force in THZ-I2 and THZ-CHL whereas; hydrogen bonding (HB) was dominated in both THZ-TCNE, and THZ-DDQ complexes. Formation constant (K), extinction coefficient (ɛ), thermodynamic parameters such as enthalpy change (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) were measured in different solvents.

CNXeCl and CNXeBr species as halogen bond donors: a quantum chemical study on the structure, properties, and nature of halogen···nitrogen interactions

In the present study, strength and characteristic of halogen bond interactions between CNXeY and NCZ molecules are investigated, where Y = Cl, Br and Z = H, CN, F, OH, CH₃, OCH₃, NH₂. MP2/aug-cc-pVTZ calculations indicate that the interaction energies for CNXeY⋯NCZ complexes lie in the range between -1.0 and -3.1 kcal mol⁻¹. Not surprisingly, the calculated interaction energies show a strong correlation with the negative electrostatic potentials on nitrogen atoms. One of the most important results of this study is that, according to energy decomposition analyses, Cl⋯N halogen bonds are largely dependent on dispersion effects, while electrostatic interactions are the major source of the attraction in Br⋯N bonds. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis are used in this study to deepen the nature of the interactions considered. This appears to be the first report on a halogen bond involving halogenated xenon isocyanides.

On the strength and nature of intermolecular X···O interactions in CF2ClBr−O3 complexes (X = F, Cl, Br): an ab initio investigation

Ab initio calculations were realized to analyze the existence of intermolecular X···O interactions in bromochlorodifluoromethane (CF2ClBr) complexes with ozone, where X = F, Cl, and Br. These calculations have been carried out using MP2 and CCSD(T) methods, through analysis of surface electrostatic potentials V(r), intermolecular interaction energies, and electron density analysis. Coupled cluster (CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ) calculations indicate that the stabilization energies for the CF2ClBr−O3 complexes lie in the range between –3.9 and –7.7 kJ/mol. The characteristic of X···O interactions has been identified in terms of the electron density analysis within the quantum theory of atoms in molecules. Energy decomposition analysis shows that the attractive nature of the X···O interactions within the title complexes is chiefly due to dispersion effects, but electrostatic contribution also plays an important role.

Insights into the strength and nature of carbene···halogen bond interactions: a theoretical perspective

Halogen-bonding, a noncovalent interaction between a halogen atom X in one molecule and a negative site in another, plays critical roles in fields as diverse as molecular biology, drug design and material engineering. In this work, we have examined the strength and origin of halogen bonds between carbene CH₂ and XCCY molecules, where X = Cl, Br, I, and Y = H, F, COF, COOH, CF₃, NO₂, CN, NH₂, CH₃, OH. These calculations have been carried out using M06-2X, MP2 and CCSD(T) methods, through analyses of surface electrostatic potentials V S(r) and intermolecular interaction energies. Not surprisingly, the strength of the halogen bonds in the CH₂···XCCY complexes depend on the polarizability of the halogen X and the electron-withdrawing power of the Y group. It is revealed that for a given carbene···X interaction, the electrostatic term is slightly larger (i.e., more negative) than the dispersion term. Comparing the data for the chlorine, bromine and iodine substituted CH₂···XCCY systems, it can be seen that both the polarization and dispersion components of the interaction energy increase with increasing halogen size. One can see that increasing the size and positive nature of a halogen's σ-hole markedly enhances the electrostatic contribution of the halogen-bonding interaction.