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1. Meso ‐Carbon Atom Nucleophilic Attack Susceptibility in the Sterically Strained Antiaromatic Bis‐BODIPY Macrocycle and Extended Electron‐Deficient BODIPY Precursor**

   https://doi.org/10.1002/chem.202201261  

   Zatsikha, Yuriy V. ; Schrage, Briana R. ; Blesener, Tanner S. ; Harrison, Laurel A. ; Ziegler, Christopher J. ; Nemykin, Victor N. ( August 2022 , Chemistry – A European Journal)

   A sterically strained 32π‐electron antiaromatic bis‐BODIPY macrocycle in which two BODIPY fragments are linked byp‐divinylbenzene groups was prepared and characterized. Unlike regular BODIPYs, the fluorescence in this macrocycle is quenched. The broad signals in the NMR spectra of the macrocycle were explained by the vibronic freedom of thep‐divinylbenzene fragments. The possible diradicaloid nature of the macrocycle was excluded on the basis of variable‐temperature EPR spectra in solution and in solid state, which is indicative of its closed‐shell quinoidal structure. Themeso‐C−H bond in the macrocycle and its precursor BODIPY dialdehyde3forms a weak hydrogen bond with THF and is susceptible for the nucleophilic attack by organic amines and cyanide anion. The reaction products of such a nucleophilic attack havemeso‐sp³carbon atoms and were characterized by NMR, mass spectrometry and, in one case, X‐ray crystallography. Unlike the initial bis‐BODIPY macrocycle, the adducts have strong fluorescence in the 400 nm region. The electronic structure and spectroscopic properties of new chromophores were probed by density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations and correlate well with the experimental data.

    

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2. Selective host–guest chemistry, self-assembly and conformational preferences of m -xylene macrocycles probed by ion-mobility spectrometry mass spectrometry

   https://doi.org/10.1039/C9CP06938K  

   Link, Benjamin A. ; Sindt, Ammon J. ; Shimizu, Linda S. ; Do, Thanh D. ( May 2020 , Physical Chemistry Chemical Physics)

   We demonstrated ion-mobility spectrometry mass spectrometry (IMS-MS) as a powerful tool for interrogating and preserving selective chemistry including non-covalent and host–guest complexes of m -xylene macrocycles formed in solution. The technique readily revealed the unique favorability of a thiourea-containing macrocycle MXT to Zn 2+ to form a dimer complex with the cation in an off-axis sandwich structure having the Zn–S bonds in a tetrahedral coordination environment. Replacing thiourea with urea generates MXU which formed high-order oligomerization with weak binding interactions to neutral DMSO guests detected at every oligomer size. The self-assembly pathway observed for this macrocycle is consistent with the crystalline assembly. Further transformation of urea into squaramide produces MXS, a rare receptor for probing sulfate in solution. Tight complexes were observed for both monomeric and dimeric of MXS in which HSO 4 − bound stronger than SO 4 2− to the host. The position of HSO 4 − at the binding cavity is a 180° inversion of the reported crystallographic SO 4 2− . The MXS dimer formed a prism-like shape with HSO 4 − exhibiting strong contacts with the 8 amine protons of two MXS macrocycles. By eliminating intermolecular interferences, we detected the low energy structures of MXS with collisional cross section (CCS) matching cis – trans and cis – cis squaramides-amines, both were not observed in crystallization trials. The experiments collectively unravel multiple facets of macrocycle chemistry including conformational flexibility, self-assembly and ligand binding; all in one analysis. Our findings illustrate an inexpensive and widely applicable approach to investigate weak but important interactions that define the shape and binding of macrocycles. 

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3. Folding-controlled assembly of ortho -phenylene-based macrocycles

   https://doi.org/10.1039/d1sc01270c  

   Kirinda, Viraj C. ; Hartley, C. Scott ( May 2021 , Chemical Science)

   null (Ed.)

   The self-assembly of foldamers into macrocycles is a simple approach to non-biological higher-order structure. Previous work on the co-assembly of ortho -phenylene foldamers with rod-shaped linkers has shown that folding and self-assembly affect each other; that is, the combination leads to new emergent behavior, such as access to otherwise unfavorable folding states. To this point this relationship has been passive. Here, we demonstrate control of self-assembly by manipulating the foldamers' conformational energy surfaces. A series of o -phenylene decamers and octamers have been assembled into macrocycles using imine condensation. Product distributions were analyzed by gel-permeation chromatography and molecular geometries extracted from a combination of NMR spectroscopy and computational chemistry. The assembly of o -phenylene decamers functionalized with alkoxy groups or hydrogens gives both [2 + 2] and [3 + 3] macrocycles. The mixture results from a subtle balance of entropic and enthalpic effects in these systems: the smaller [2 + 2] macrocycles are entropically favored but require the oligomer to misfold, whereas a perfectly folded decamer fits well within the larger [3 + 3] macrocycle that is entropically disfavored. Changing the substituents to fluoro groups, however, shifts assembly quantitatively to the [3 + 3] macrocycle products, even though the structural changes are well-removed from the functional groups directly participating in bond formation. The electron-withdrawing groups favor folding in these systems by strengthening arene–arene stacking interactions, increasing the enthalpic penalty to misfolding. The architectural changes are substantial even though the chemical perturbation is small: analogous o -phenylene octamers do not fit within macrocycles when perfectly folded, and quantitatively misfold to give small macrocycles regardless of substitution. Taken together, these results represent both a high level of structural control in structurally complex foldamer systems and the demonstration of large-amplitude structural changes as a consequence of a small structural effects. 

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4. Discovery and Biosynthesis of Ureidopeptide Natural Products Macrocyclized via Indole N ‐acylation in Marine Microbulbifer spp. Bacteria

   https://doi.org/10.1002/cbic.202300190  

   Zhong, Weimao ; Deutsch, Jessica M. ; Yi, Dongqi ; Abrahamse, Nadine H. ; Mohanty, Ipsita ; Moore, Samuel G. ; McShan, Andrew C. ; Garg, Neha ; Agarwal, Vinayak ( May 2023 , ChemBioChem)

   Commensal bacteria associated with marine invertebrates are underappreciated sources of chemically novel natural products. Using mass spectrometry, we had previously detected the presence of peptidic natural products in obligate marine bacteria of the genusMicrobulbifercultured from marine sponges. In this report, the isolation and structural characterization of a panel of ureidohexapeptide natural products, termed the bulbiferamides, fromMicrobulbiferstrains is reported wherein the tryptophan side chain indole participates in a macrocyclizing peptide bond formation. Genome sequencing identifies biosynthetic gene clusters encoding production of the bulbiferamides and implicates the involvement of a thioesterase in the indolic macrocycle formation. The structural diversity and widespread presence of bulbiferamides in commensal microbiomes of marine invertebrates point toward a possible ecological role for these natural products.

    

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5. Assembled triphenylamine bis -urea macrocycles: exploring photodriven electron transfer from host to guests

   https://doi.org/10.1039/D1CP03000K  

   Islam, Md Faizul ; Sindt, Ammon J. ; Hossain, Muhammad Saddam ; Ayare, Pooja J. ; Smith, Mark D. ; Vannucci, Aaron K. ; Garashchuk, Sophya ; Shimizu, Linda S. ( October 2021 , Physical Chemistry Chemical Physics)

   Absorption of electronic acceptors in the accessible channels of an assembled triphenylamine (TPA) bis -urea macrocycle 1 enabled the study of electron transfer from the walls of the TPA framework to the encapsulated guests. The TPA host is isoskeletal in all host–guest structures analyzed with guests 2,1,3-benzothiadiazole, 2,5-dichlorobenzoquinone and I 2 loading in single-crystal-to-single-crystal transformations. Analysis of the crystal structures highlights how the spatial proximity and orientation of the TPA host and the entrapped guests influence their resulting photophysical properties and allow direct comparison of the different donor–acceptor complexes. Diffuse reflectance spectroscopy shows that upon complex formation 1·2,5-dichlorobenzoquinone exhibits a charge transfer (CT) transition. Whereas, the 1·2,1,3-benzothiadiazole complex undergoes a photoinduced electron transfer (PET) upon irradiation with 365 nm LEDs. The CT absorptions were also identified with the aid of time dependent density functional theory (TD-DFT) calculations. Cyclic voltammetry experiments show that 2,1,3-benzothiadiazole undergoes reversible reduction within the host–guest complex. Moreover, the optical band gaps of the host 1·2,5-dichlorobenzoquinone (1.66 eV), and host 1·2,1,3-benzothiadiazole (2.15 eV) complexes are significantly smaller as compared to the free host 1 material (3.19 eV). Overall, understanding this supramolecular electron transfer strategy should pave the way towards designing lower band gap inclusion complexes. 

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