Effect of "magic chlorine" in drug discovery: an in silico approach

The chlorine atom plays a vital role in drug design, yet the benefits of chlorine in 250 FDA-approved chlorine-containing drugs have not been studied properly. To see the "magic chloro" effect, computational studies have been carried out for 35 inhibitors, which are numbered as 12 complexes with (parent (-H), one chlorine, or two chlorine) substituents. The physicochemical properties are studied by conceptual density functional theory (CDFT). The pharmacokinetics, toxicity and metabolic properties of the studied inhibitors are estimated using chemoinformatics tools. SwissTargetPrediction is used to predict the multitarget activities of the studied inhibitors. Four FDA-approved drugs, diazepam, chloroquine, chloramphenicol, and bendamustine, are referenced to validate the studies. A higher HOMO-LUMO gap predicted high stability for the studied one and two chlorine-substituted analogues. Most of the studied inhibitors show "drug likeliness", nontoxicity, and high gastrointestinal (GI) absorption. The addition of one or two chloro substituents has increased the physicochemical properties and stability of most of the inhibitors compared to the parent analogues, whereas the toxicity is not affected. No change in metabolic properties is observed on addition of one or two chlorine substituents. The multi-target activities of all the studied inhibitors are validated by the reference drugs and experimental results.

Cobalt Deposition from Ionothermally Dissolved Cobalt Oxides

Owing to the environmental problems of numerous metal production processes, there is a growing need for more energy-efficient approaches. Cobalt is considered a strategic element that is extracted not only from ores but also from spent Li-ion batteries. One promising new approach is ionometallurgy, which is the extraction of metal oxides by ionic liquids (ILs). This study concerns new investigations into ionometallurgical processing of CoO, Co₃ O₄ , and LiCoO₂ in the IL betainium bis(trifluoromethylsulfonyl)imide, [Hbet][NTf₂ ]. Three crystal structures of cobalt-betaine complex compounds and combined spectroscopic and diffraction studies provide insights into the dissolution process. In addition, an optimized dissolution procedure for metal oxides is presented, avoiding the previously reported decomposition of the IL. Subsequent cobalt electrodeposition is only possible from cationic complex species, highlighting the importance of a thorough understanding of the complex equilibria. The presented method is also compared to other recently reported approaches.

Type I-IV Halogen⋯Halogen Interactions: A Comparative Theoretical Study in Halobenzene⋯Halobenzene Homodimers

In the current study, unexplored type IV halogen⋯halogen interaction was thoroughly elucidated, for the first time, and compared to the well-established types I−III interactions by means of the second-order Møller−Plesset (MP2) method. For this aim, the halobenzene⋯halobenzene homodimers (where halogen = Cl, Br, and I) were designed into four different types, parodying the considered interactions. From the energetic perspective, the preference of scouted homodimers was ascribed to type II interactions (i.e., highest binding energy), whereas the lowest binding energies were discerned in type III interactions. Generally, binding energies of the studied interactions were observed to decline with the decrease in the σ-hole size in the order, C6H5I⋯IC6H5 > C6H5Br⋯BrC6H5 > C6H5Cl⋯ClC6H5 homodimers and the reverse was noticed in the case of type IV interactions. Such peculiar observations were relevant to the ample contributions of negative-belt⋯negative-belt interactions within the C6H5Cl⋯ClC6H5 homodimer. Further, type IV torsional trans → cis interconversion of C6H5X⋯XC6H5 homodimers was investigated to quantify the π⋯π contributions into the total binding energies. Evidently, the energetic features illustrated the amelioration of the considered homodimers (i.e., more negative binding energy) along the prolonged scope of torsional trans → cis interconversion. In turn, these findings outlined the efficiency of the cis configuration over the trans analog. Generally, symmetry-adapted perturbation theory-based energy decomposition analysis (SAPT-EDA) demonstrated the predominance of all the scouted homodimers by the dispersion forces. The obtained results would be beneficial for the omnipresent studies relevant to the applications of halogen bonds in the fields of materials science and crystal engineering.

Halogen-Bonded Assemblies of Arylene Imides and Diimides: Insight from Electronic, Structural, and Computational Studies

Halogen-bonding interactions in electron-deficient π scaffolds have largely been underexplored. Herein, the halogen-bonding properties of arylene imide/diimide-based electron-deficient scaffolds were studied. The influence of scaffold size, from small (phthalimide) to moderately sized (pyromellitic diimide or naphthalenediimides) to large (perylenediimide), axial-group modification, and number of halo substituents on the halogen bonding and its self-assembly was probed in a set of nine compounds. The structural modification leads to tunable optical and redox properties. The first reduction potential E 1 / 2 1 ranges between -1.09 and -0.17 V (vs. SCE). Two of the compounds, that is, 6 and 9, have deep-lying LUMOs with values reaching -4.2 eV. Single crystals of all nine systems were obtained, which showed Br⋅⋅⋅O, Br⋅⋅⋅Br, or Br⋅⋅⋅π halogen-bonding interactions, and a few systems are capable of forming all three types. These interactions lead to halogen-bonded rings (up to 12-membered), which propagate to form stacked 1D, 2D, or corrugated sheets. A few outliers were also identified, for example, molecules that prefer C-H⋅⋅⋅O hydrogen bonding over halogen bonding, or noncentrosymmetric rather than centrosymmetric organization. Computational studies based on Atoms in Molecules and Natural Bond Orbital analysis provided further insight into the halogen-bonding interactions. This study can lead to a predictive design tool-box to further explore related systems on surfaces reinforced by these weak directional forces.

Towards a Stronger Halogen Bond Involving Astatine: Unexpected Adduct with Bu3 PO Stabilized by Hydrogen Bonding

The halogen bond is a powerful tool for the molecular design and pushing the limits of its strength is of major interest. Bearing the most potent halogen-bond donor atom, astatine monoiodide (AtI) was recently successfully probed [Nat. Chem. 2018, 10, 428-434]. In this work, we continue the exploration of adducts between AtI and Lewis bases with the tributylphosphine oxide (Bu₃ PO) ligand, revealing the unexpected experimental occurrence of two distinct chemical species with 1:1 and 2:1 stoichiometries. The 1:1 Bu₃ PO⋅⋅⋅AtI complex is found to exhibit the strongest astatine-mediated halogen bond so far (with a formation constant of 10^(4.24±0.35) ). Quantum chemical calculations unveil the intriguing nature of the 2:1 2Bu₃ PO⋅⋅⋅AtI adduct, involving a halogen bond between AtI and one Bu₃ PO molecular unit plus CH⋅⋅⋅O hydrogen bonds chelating the second Bu₃ PO unit.

Two-dimensional halogen-bonded organic frameworks based on the tetrabromobenzene-1,4-dicarboxylic acid building molecule

2D halogen-bonded organic frameworks were readily engineered by strong and directional effects of the primary Br⋯O and the secondary Br⋯π halogen bonding interactions from the tetrabromobenzene-1,4-dicarboxylic acid building molecule involving 100% supramolecular yields.

Straightening out halogen bonds

A new parameter is proposed to quantify the linearity of halogen bonds.

Halogen⋯halogen interactions in decahalo-closo-carboranes: CSD analysis and theoretical study

We theoretically (PBE0-D3/def2TZVP) and experimentally (CSD analysis) demonstrate the importance of “like–like” halogen interactions for the stability of several decahalo-closo-carborane dimers.

Benchmarking of Halogen Bond Strength in Solution with Nickel Fluorides: Bromine versus Iodine and Perfluoroaryl versus Perfluoroalkyl Donors

The energetics of halogen bond formation in solution have been investigated for a series of nickel fluoride halogen bond acceptors; trans-[NiF(2-C5 NF4 )(PEt3 )2 ] (A1), trans-[NiF{2-C5 NF3 (4-H)}(PEt3 )2 ] (A2), trans-[NiF{2-C5 NF3 (4-NMe2 )}(PEt3 )2 ] (A3) and trans-[NiF{2-C5 NF2 H(4-CF3 )}(PCy3 )2 ] (A4) with neutral organic halogen bond donors, iodopentafluorobenzene (D1), 1-iodononafluorobutane (D2) and bromopentafluorobenzene (D3), in order to establish the significance of changes from perfluoroaryl to perfluoroalkyl donors and from iodine to bromine donors. 19 F NMR titration experiments have been employed to obtain the association constants, enthalpy, and entropy for the halogen bond formed between these donor-acceptor partners in protiotoluene. For A2-A4, association constants of the halogen bonds formed with iodoperfluoroalkane (D2) are consistently larger than those obtained for analogous complexes with the iodoperfluoroarene (D1). For complexes formed with A2-A4, the strength of the halogen bond is significantly lowered upon modification of the halogen donor atom from I (in D1) to Br (in D3) (for D1: 5≤K285 ≤12 m-1 , for D3: 1.0≤K193 ≤1.6 m-1 ). The presence of the electron donating NMe2 substituent on the pyridyl ring of acceptor A3 led to an increase in -ΔH, and the association constants of the halogen bond complexes formed with D1-D3, compared to those formed by A1, A2 and A4 with the same donors.

Regioselective C3-H Trifluoromethylation of 2 H-Indazole under Transition-Metal-Free Photoredox Catalysis

Trifluoromethyl-substituted heteroarenes are biologically active compounds and useful building blocks. In this sequence, we have developed a visible-light-promoted regioselective C3-H trifluoromethylation of 2 H-indazole under metal-free conditions, which proceeds via a radical mechanism. The combination of photocatalysis and hypervalent iodine reagent provides a practical approach to a library of trifluoromethylated indazoles in 35-83% yields.

Mechano-responsive luminescent emissions of an organic molecular crystal: effects of aromatic stacking interactions and solid state packing

Three polymorphs of 2-hydroxynaphthaldehyde semicarbazone (2-NOH-S) have been identified, and their mechano-responsive luminescent emissions and interconversions are discussed.

Mechanically Responsive Crystalline Coordination Polymers with Controllable Elasticity

Crystalline coordination polymers tend to be brittle and inelastic, however, we now describe a family of such compounds that are capable of displaying mechanical elasticity in response to external pressure. The design approach successfully targets structural features that are critical for producing the desired mechanical output. The elastic crystals all comprise 1D cadmium(II) halide polymeric chains with adjacent metal centres bridged by two halide ions resulting in the required stacking interactions and short "4 Å" crystallographic axes. These polymeric chains (structural "spines") are further organized via hydrogen bonds and halogen bonds perpendicular to the direction of the chains. By carefully altering the strength and the geometry of these non-covalent interactions, we have demonstrated that it is possible to control the extent of elastic bending in crystalline coordination compounds.

Probing halogen⋯halogen interactions via thermal expansion analysis

The magnitude of the thermal expansion of the 1-D chain coordination polymer Cu(MeCN)₂[AuX₂(CN)₂] (X = Cl, Br, I) is significantly reduced in the presence of interchain halogen⋯halogen interactions.

Cyanine dyes: synergistic action of hydrogen, halogen and chalcogen bonds allows discrete I42− anions in crystals

Discrete tetraiodide dianions (I₄²⁻) are formed in crystals via halogen bond coordination of I₂ by iodide anions which are pinned in their positions by a network of hydrogen bonds involving a benzoselenazole cyanine dye.

Halogen bonding in hypervalent iodine and bromine derivatives: halonium salts

Halogen bonds have been identified in a series of ionic compounds involving bromonium and iodonium cations and several different anions, some also containing hypervalent atoms. The hypervalent bromine and iodine atoms in the examined compounds are found to have positive σ-holes on the extensions of their covalent bonds, while the hypervalent atoms in the anions have negative σ-holes. The positive σ-holes on the halogens of the studied halonium salts determine the linearity of the short contacts between the halogen and neutral or anionic electron donors, as usual in halogen bonds.

Anion-driven tetrel bond-induced engineering of lead(ii) architectures with N′-(1-(2-pyridyl)ethylidene)nicotinohydrazide: experimental and theoretical findings

A new series of Pb^II coordination compounds was assembled with the N′-(1-(2-pyridyl)ethylidene)nicotinohydrazide ligand and various auxiliary inorganic counterions.

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.

C–H⋯Br–C vs. C–Br⋯Br–C vs. C–Br⋯N bonding in molecular self-assembly of pyridine-containing dyes

We have studied N-(5-bromosalicylidene)-x-aminopyridine dyes (x = 2, 1; 3, 2; 4, 3) by means of single crystal X-ray diffraction and Hirshfeld surface analysis. Their optical properties were also examined and correlated with structural findings.

Supramolecular interactions in the solid state

In the last few decades, supramolecular chemistry has been at the forefront of chemical research, with the aim of understanding chemistry beyond the covalent bond. Since the long-range periodicity in crystals is a product of the directionally specific short-range intermolecular interactions that are responsible for molecular assembly, analysis of crystalline solids provides a primary means to investigate intermolecular interactions and recognition phenomena. This article discusses some areas of contemporary research involving supramolecular interactions in the solid state. The topics covered are: (1) an overview and historical review of halogen bonding; (2) exploring non-ambient conditions to investigate intermolecular interactions in crystals; (3) the role of intermolecular interactions in morphotropy, being the link between isostructurality and polymorphism; (4) strategic realisation of kinetic coordination polymers by exploiting multi-interactive linker molecules. The discussion touches upon many of the prerequisites for controlled preparation and characterization of crystalline materials.

The role of weak hydrogen and halogen bonding interactions in the assembly of a series of Hg(ii) coordination polymers

A series of eight new Hg(ii) complexes based on the L^4-X ligands, where L is (E)-4-halo-N-(pyridin-4-ylmethylene)aniline, were synthesized and characterized and their supramolecular crystal structures were studied by different geometrical and theoretical methods.

Halogen bonding directed supramolecular assembly in bromo-substituted trezimides and tennimides

The imide-based trezimide and tennimide macrocycle crystal structures typically aggregate as 1-D chains through C–Br⋯OC/N/π(arene) halogen bonds (withN_c≤ 0.90) that dominate the solid-state aggregation process in the absence of classical strong hydrogen bond donors.