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1. Picking on Carbonate: Kinetic Selectivity in the Encapsulation of Anions

   https://doi.org/10.1002/ange.202116518  

   Xie, Han ; Gunawardana, Vageesha W. Liyana ; Finnegan, Tyler J. ; Xie, William ; Badjić, Jovica D. ( January 2022 , Angewandte Chemie)

   Supramolecular hosts bind to inorganic anions at a fast rate and select them in proportion with thermodynamic stability of the corresponding [anion⊂host] complexes, forming in a reversible manner. In this study, we describe the action of hexapodal capsule1and its remarkable ability to select anions based on a large span of rates by which they enter this host. The thermodynamic affinity of1toward eighteen anions extends over eight orders of magnitude (0<K_a<10⁸ M⁻¹;¹H NMR spectroscopy). The capsule would retain CO₃²⁻(K_a=10⁷ M⁻¹) for hours in the presence of eleven competing anions, including stronger binding SO₄²⁻, HAsO₄²⁻and HPO₄²⁻(K_a=10⁷–10⁸ M⁻¹). The observed selection resulted from1possessing narrow apertures (ca. 3×6 Å) comparable in size to anions (d=3.5–7.1 Å) slowing down the encapsulation to last from seconds to days. The unorthodox mode of action of1sets the stage for creating hosts that pick anions by their ability to access the host.

    

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2. A Molecular Capsule with Revolving Doors Partitioning Its Inner Space

   https://doi.org/10.1002/chem.202003247  

   Lei, Zhiquan ; Finnegan, Tyler J. ; Gunawardana, Vageesha W. Liyana ; Pavlović, Radoslav Z. ; Xie, Han ; Moore, Curtis E. ; Badjić, Jovica D. ( November 2020 , Chemistry – A European Journal)

   Covalent capsule1was designed to include two molecular baskets linked with three mobile pyridines tucked into its inner space. On the basis of both theory (DFT) and experiments (NMR and X‐ray crystallography), we found that the pyridine “doors” split the chamber (380 ų) of1so that two equally sizeable compartments (190 ų) became joined through a conformationally flexible aromatic barrier. The compartments of such unique host could be populated with CCl₄(88 ų; PC=46 %), CBr₄(106 ų; 56 %) or their combination CCl₄/CBr₄(PC=51 %), with thermodynamic stabilities ΔG° tracking the values of packing coefficients (PC). Halogen (C−X⋅⋅⋅π) and hydrogen bonding (C−H⋅⋅⋅X) contacts held the haloalkane guests in the cavities of1. The consecutive complexations were found to occur in a negative allosteric manner, which we propose to result from the induced‐fit mode of complexation. Newly designed1opens a way for probing the effects of inner conformational dynamics on noncovalent interactions, reactivity and intramolecular translation in confined spaces of hollow molecules.

    

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3. Bipyridine‐Containing Host Materials for High Performance Yellow Thermally Activated Delayed Fluorescence‐Based Organic Light Emitting Diodes with Very Low Efficiency Roll‐Off

   https://doi.org/10.1002/adom.201901283  

   Chen, Dongyang ; Rajamalli, Pachaiyappan ; Tenopala‐Carmona, Francisco ; Carpenter‐Warren, Cameron L. ; Cordes, David B. ; Keum, Chang‐Min ; Slawin, Alexandra M. Z. ; Gather, Malte C. ; Zysman‐Colman, Eli ( November 2019 , Advanced Optical Materials)

   Two bipolar host materials3‐CBPyand4‐mCBPyare reported. These hosts are structural analogs of the common host materials CBP and mCBP wherein the phenyl rings have been replaced with pyridines. The two materials possess deep highest occupied molecular orbital (HOMO) and shallow lowest unoccupied molecular orbital (LUMO) levels along with sufficiently high energyS₁andT₁states that make them suitable hosts for yellow emitters in electroluminescent devices. Yellow‐emitting thermally activated delayed fluorescence organic light‐emitting diodes are fabricated using 2,4,6‐tris (4‐(10H‐phenoxazin‐10‐yl)phenyl)‐1,3,5‐triazine (tri‐PXZ‐TRZ) as the dopant emitter with either3‐CBPyor4‐mCBPyemployed as the host. Their device performance is compared to analogous devices using CBP and mCBP as host materials. The pyridine‐containing host devices show markedly improved external quantum efficiencies (EQE) and decreased roll‐off. The 7 wt% tri‐PXZ‐TRZ‐doped device exhibits very low turn‐on voltage (2.5 V for both3‐CBPyand4‐mCBPy) along with maximum external quantum efficiencies (EQE_max) reaching 15.6% (for3‐CBPy) and 19.4% (for4‐mCBPy). The device using4‐mCBPyalso exhibits very low efficiency roll‐off with an EQE of 16.0% at a luminance of 10 000 cd m⁻².

    

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4. From Selection to Instruction and Back: Competing Conformational Selection and Induced Fit Pathways in Abiotic Hosts

   https://doi.org/10.1002/ange.202107091  

   Pavlović, Radoslav Z. ; Lalisse, Remy F. ; Hansen, Alexandar L. ; Waudby, Christopher A. ; Lei, Zhiquan ; Güney, Murat ; Wang, Xiuze ; Hadad, Christopher M. ; Badjić, Jovica D. ( July 2021 , Angewandte Chemie)

   Two limiting cases of molecular recognition, induced fit (IF) and conformational selection (CS), play a central role in allosteric regulation of natural systems. The IF paradigm states that a substrate “instructs” the host to change its shape after complexation, while CS asserts that a guest “selects” the optimal fit from an ensemble of preexisting host conformations. With no studies that quantitatively address the interplay of two limiting pathways in abiotic systems, we herein and for the first time describe the way by which twisted capsuleM‐1, encompassing two conformersM‐1(+) andM‐1(−), trap CX₄(X=Cl, Br) to give CX₄⊂M‐1(+) and CX₄⊂M‐1(−), with all four states being in thermal equilibrium. With the assistance of 2D EXSY, we found that CBr₄would, at its lower concentrations, bindM‐1via aM‐1(+)→M‐1(−)→CBr₄⊂M‐1(−) pathway corresponding to conformational selection. ForM‐1complexing CCl₄though, data from 2D EXSY measurements and 1D NMR line‐shape analysis suggested that lower CCl₄concentrations would favor CS while the IF pathway prevailed at higher proportions of the guest. Since CS and IF are not mutually exclusive, we reason that our work sets the stage for characterizing the dynamics of a wide range of already existing hosts to broaden our fundamental understanding of their action. The objective is to master the way in which encapsulation takes place for designing novel and allosteric sequestering agents, catalysts and chemosensors akin to those found in nature.

    

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5. From Selection to Instruction and Back: Competing Conformational Selection and Induced Fit Pathways in Abiotic Hosts

   https://doi.org/10.1002/anie.202107091  

   Pavlović, Radoslav Z. ; Lalisse, Remy F. ; Hansen, Alexandar L. ; Waudby, Christopher A. ; Lei, Zhiquan ; Güney, Murat ; Wang, Xiuze ; Hadad, Christopher M. ; Badjić, Jovica D. ( July 2021 , Angewandte Chemie International Edition)

   Two limiting cases of molecular recognition, induced fit (IF) and conformational selection (CS), play a central role in allosteric regulation of natural systems. The IF paradigm states that a substrate “instructs” the host to change its shape after complexation, while CS asserts that a guest “selects” the optimal fit from an ensemble of preexisting host conformations. With no studies that quantitatively address the interplay of two limiting pathways in abiotic systems, we herein and for the first time describe the way by which twisted capsuleM‐1, encompassing two conformersM‐1(+) andM‐1(−), trap CX₄(X=Cl, Br) to give CX₄⊂M‐1(+) and CX₄⊂M‐1(−), with all four states being in thermal equilibrium. With the assistance of 2D EXSY, we found that CBr₄would, at its lower concentrations, bindM‐1via aM‐1(+)→M‐1(−)→CBr₄⊂M‐1(−) pathway corresponding to conformational selection. ForM‐1complexing CCl₄though, data from 2D EXSY measurements and 1D NMR line‐shape analysis suggested that lower CCl₄concentrations would favor CS while the IF pathway prevailed at higher proportions of the guest. Since CS and IF are not mutually exclusive, we reason that our work sets the stage for characterizing the dynamics of a wide range of already existing hosts to broaden our fundamental understanding of their action. The objective is to master the way in which encapsulation takes place for designing novel and allosteric sequestering agents, catalysts and chemosensors akin to those found in nature.

    

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