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CONTENTS 1. Introduction to Halogen Bonding 7119 1.1. Nature of the Halogen Bond 7119 1.2. Scope of the Review 7120 2. Computational and Theoretical Investigations of Halogen Bonding 7120 2.1.Quantum Mechanics Methods 7120 2.2. σ-Hole Model of Halogen Bonding 7120 2.3. Other Contributions to the Nature of Halogen Bonding 7122 2.4. Recent Examples of Computationally Investigated Halogen-Bonded Complexes 7123 2.4.1. XB to Neutral Species 7123 2.4.2. XB to Anions 7126 2.4.3. XB in Protein−Ligand Complexes 7127 2.4.4. Electron-Transfer Processes Affected by XB Interactions 7127 2.5. Classical Force Field Calculations 7127 2.6. Conclusions and Outlook 7129 3. Gas-Phase Studies of Halogen-Bonding Interactions 7130 4. Halogen Bonding in the Solid State 7131 4.1. Introduction to Crystal Engineering and Functional Materials 7131 4.2. Fundamentals 7132 4.3. Halogen-Bonding Hierarchy 7134 4.3.1. Ranking Halogen-Bond Donors 7134 4.3.2. HB/XB Complementarity/Competition 7136 4.3.3. Predicting XBs 7138 4.4. Control of Solid-State Supramolecular Architectures 7138 4.4.1. Polymorphism 7138 4.4.2. Stoichiometry 7139 4.4.3. Tautomeric Control 7140 4.4.4. XBs Involving Metals and Metal-Bound XBs 7140 4.4.5. XB with Anions in the Solid State 4.5. Solid-State Architectures 4.6.

Halogen bonding (XB), the attractive interaction between an electron-deficient halogen atom and a Lewis base, has undergone a dramatic development as an intermolecular force analogous to hydrogen bonding (HB). However, its utilization in the solution phase remains underdeveloped. Furthermore, the design of receptors capable of strong and selective recognition of anions in water remains a significant challenge. Here we demonstrate the superiority of halogen bonding over hydrogen bonding for strong anion binding in water, to the extent that halide recognition by a simple acyclic mono-charged receptor is achievable. Quantification of iodide binding by rotaxane hosts reveals the strong binding by the XB-rotaxane is driven exclusively by favourable enthalpic contributions arising from the halogen-bonding interactions, whereas weaker association with the HB-rotaxanes is entropically driven. These observations demonstrate the unique nature of halogen bonding in water as a strong alternative interaction to the ubiquitous hydrogen bonding in molecular recognition and assembly.

The synthesis and anion binding properties of novel halogen-bonding (XB) bis-iodotriazole-pyridinium-containing acyclic and [2]catenane anion host systems are described. The XB acyclic receptor displays selectivity for acetate over halides with enhanced anion recognition properties compared to the analogous hydrogen-bonding (HB) acyclic receptor. A reversal in halide selectivity is observed in the XB [2]catenane, in comparison to the acyclic XB receptor, due to the interlocked host’s unique three-dimensional binding cavity, and no binding is observed for oxoanions. Notable halide anion association constant values determined for the [2]catenane in competitive organic–aqueous solvent mixtures demonstrate considerable enhancement of anion recognition as compared to the HB catenane analogue. X-ray crystallographic analysis of a series of halide catenane complexes reveal strong XB interactions in the solid state. These interactions were studied using Cl and Br K-edge X-ray Absorption Spectroscopy (XAS) indicating intense pre-edge features characteristic of charge transfer from the halide to its bonding partner (σAX←X–* ← X1s), and providing a direct measure of the degree of covalency in the halogen bond(s). The data reveal that the degree of covalency is similar to that which is observed in transition metal coordinate covalent bonds. These results are supported by DFT results, which correlate well with the experimental data.

Rhinoviruses are the pathogens most often responsible for the common cold, and are a frequent cause of exacerbations in asthma, chronic obstructive pulmonary disease and cystic fibrosis. Here we report discovery of IMP-1088, a picomolar dual inhibitor of the human N-myristoyltransferases NMT1 and NMT2, and use it to demonstrate that pharmacological inhibition of host cell N-myristoylation rapidly and completely prevents rhinoviral replication without inducing cytotoxicity. Identification of cooperative binding between weak-binding fragments led to rapid inhibitor optimization through fragment reconstruction, structure-guided fragment linking, and conformational control over linker geometry. We show that inhibition of co-translational myristoylation of a specific virus-encoded protein (VP0) by IMP-1088 potently blocks a key step in viral capsid assembly, delivering low nanomolar antiviral activity against multiple rhinovirus strains, poliovirus and foot-and-mouth disease virus, and protection of cells against virus-induced killing, highlighting the potential of host myristoylation as a drug target in picornaviral infections.