Semin Lee

Intramolecular hydrogen bonds preorganize an aryl-triazole receptor into a crescent for chloride binding.

Aryl-triazole pentads have been preorganized with intramolecular hydrogen bonds to enhance chloride binding. This outcome highlights the dual hydrogen bond donor and acceptor properties of 1,2,3-triazoles.

Multifunctional Tricarbazolo Triazolophane Macrocycles: One‐Pot Preparation, Anion Binding, and Hierarchical Self‐Organization of Multilayers

Programming the synthesis and self-assembly of molecules is a compelling strategy for the bottom-up fabrication of ordered materials. To this end, shape-persistent macrocycles were designed with alternating carbazoles and triazoles to program a one-pot synthesis and to bind large anions. The macrocycles bind anions that were once considered too weak to be coordinated, such as PF6 (-) , with surprisingly high affinities (β2 =10(11)  M(-2) in 80:20 chloroform/methanol) and positive cooperativity, α=(4 K2 /K1 )=1200. We also discovered that the macrocycles assemble into ultrathin films of hierarchically ordered tubes on graphite surfaces. The remarkable surface-templated self-assembly properties, as was observed by using scanning tunneling microscopy, are attributed to the complementary pairing of alternating triazoles and carbazoles inscribed into both the co-facial and edge-sharing seams that exist between shape-persistent macrocycles. The multilayer assembly is also consistent with the high degree of molecular self-association observed in solution, with self-association constants of K=300 000 M(-1) (chloroform/methanol 80:20). Scanning tunneling microscopy data also showed that surface assemblies readily sequester iodide anions from solution, modulating their assembly. This multifunctional macrocycle provides a foundation for materials composed of hierarchically organized and nanotubular self-assemblies.

Macromolecular Crystallography for Synthetic Abiological Molecules: Combining xMDFF and PHENIX for Structure Determination of Cyanostar Macrocycles

Crystal structure determination has long provided insight into structure and bonding of small molecules. When those same small molecules are designed to come together in multimolecular assemblies, such as in coordination cages, supramolecular architectures and organic-based frameworks, their crystallographic characteristics closely resemble biological macromolecules. This resemblance suggests that biomacromolecular refinement approaches be used for structure determination of abiological molecular complexes that arise in an aggregate state. Following this suggestion we investigated the crystal structure of a pentagonal macrocycle, cyanostar, by means of biological structure analysis methods and compared results to traditional small molecule methods. Cyanostar presents difficulties seen in supramolecular crystallography including whole molecule disorder and highly flexible solvent molecules sitting in macrocyclic and intermolecule void spaces. We used the force-field assisted refinement method, molecular dynamics flexible fitting algorithm for X-ray crystallography (xMDFF), along with tools from the macromolecular structure determination suite PHENIX. We found that a standard implementation of PHENIX, namely one without xMDFF, either fails to produce a solution by molecular replacement alone or produces an inaccurate structure when using generic geometry restraints, even at a very high diffraction data resolution of 0.84 Å. The problems disappear when taking advantage of xMDFF, which applies an optimized force field to realign molecular models during phasing by providing accurate restraints. The structure determination for this model system shows excellent agreement with the small-molecule methods. Therefore, the joint xMDFF-PHENIX refinement protocol provides a new strategy that uses macromolecule methods for structure determination of small molecules and their assemblies.

How to print a crystal structure model in 3D

We present a simple procedure for the conversion of Crystallographic Information Files (CIFs) into Virtual Reality Modelling Language (VRML2, .wrl) files, which can be used as input files for three-dimensional (3D) printing. This procedure permits facile production of customized full-colour 3D models of X-ray crystal structures of segments of extended structures, including metal–organic frameworks (MOFs) as well as small molecules. The method uses freely available software that runs under Microsoft Windows, MacOSX and Linux operating systems.

Binding Anions in Rigid and Reconfigurable Triazole Receptors

The use of triazole CH•••anion hydrogen bonds, strong and easy to install, has expanded dramatically since 2008. Various aryl-triazole derivatives have been synthesized and investigated to obtain fundamental understandings of anion stabilization as well as to develop new receptors for applications. Receptors have now been created to make use of triazole, triazolium, or iodotriazolium. The triazole CH•••anion binding motif has also been utilized in sophisticated structures such as interlocked molecules and toward fluorescent sensors and ion-selective electrodes. Furthermore, demonstrations on the transport of anions across membranes and studies of light-induced anion regulation have broadened the scope of application for this new anion binding motif. This chapter will focus on these recent developments.

A high-yield synthesis and acid–base response of phosphate-templated [3]rotaxanes

Anion-templated rotaxanes are a rare class of functional organic molecules capable of novel switching and mechanical behaviors. Yet, investigations of these properties are limited by existing synthetic strategies. We show a high-yielding synthesis (80%) of [3]rotaxanes using shape-persistent macrocycles, cyanostars, and anionic organo-phosphate templates catalyzed by low steric-demand click chemistry. The reaction yields correlate with the templates binding affinities. Use of longer linkers relieves steric congestion to enable a reversible acid-base response, opening the way to molecular switching.

Ion-Pair Oligomerization of Chromogenic Triangulenium Cations with Cyanostar-Modified Anions That Controls Emission in Hierarchical Materials

The hierarchical assembly of colored cationic molecules with receptor-modified counteranions can be used to control optical properties in materials. However, our knowledge of when the optical properties emerge in the hierarchical organization and the variety of cation-anion salts that are available to create these materials is limited. In this work, we extend the salts from small halides to large inorganic anions and determine how the structure coevolves with the emission properties using solution assemblies. We study the chromogenic trioxatriangulenium (TOTA+) cation and its coassembly with cyanostar (CS) macrocycles selected to modify tetrafluoroborate (BF4-) counteranions through formation of 2:1 sandwich complexes. In the solid state, the TOTA+ cation stacks in an alternating manner with the sandwich complexes producing new red-shifted emission and absorption bands. Critical to assigning the structural origin of the new optical features across the four levels of organization (1° → 4°) is the selection of specific solvents to produce and characterize different assemblies present in the hierarchical structure. A key species is the electrostatically stabilized ion pair between the TOTA+ cation and sandwich complex. The red-shifted features only emerge when the ion pairs oligomerize together into larger (TOTA·[CS2BF4])n assemblies. New electronic states emerge as a result of multiple copies of the TOTA+ making π-contact with cyanostar-anion complexes. Our findings and the ease with which the materials can be prepared as crystals and films by mixing the salt with a receptor provide a strong platform for the de novo design of new optical materials.