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1. Inverse CO 2 /C 2 H 2 Separation with MFU‐4 and Selectivity Reversal via Postsynthetic Ligand Exchange

   https://doi.org/10.1002/ange.202218854  

   Liu, Qiao ; Cho, Sung Gu ; Hilliard, Jordon ; Wang, Ting‐Yuan ; Chien, Szu‐Chia ; Lin, Li‐Chiang ; Co, Anne C. ; Wade, Casey R. ( March 2023 , Angewandte Chemie)

   Although many porous materials, including metal–organic frameworks (MOFs), have been reported to selectively adsorb C₂H₂in C₂H₂/CO₂separation processes, CO₂‐selective sorbents are much less common. Here, we report the remarkable performance ofMFU‐4(Zn₅Cl₄(bbta)₃, bbta=benzo‐1,2,4,5‐bistriazolate) toward inverse CO₂/C₂H₂separation. The MOF facilitates kinetic separation of CO₂from C₂H₂, enabling the generation of high purity C₂H₂(>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C₂H₂is excluded fromMFU‐4by narrow pore windows formed by Zn−Cl groups. Postsynthetic F⁻/Cl⁻ligand exchange was used to synthesize an analogue (MFU‐4‐F) with expanded pore apertures, resulting in equilibrium C₂H₂/CO₂separation with reversed selectivity compared toMFU‐4.MFU‐4‐Falso exhibits a remarkably high C₂H₂adsorption capacity (6.7 mmol g⁻¹), allowing fuel grade C₂H₂(98 % purity) to be harvested from C₂H₂/CO₂mixtures by room temperature desorption.

    

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2. Inverse CO 2 /C 2 H 2 Separation with MFU‐4 and Selectivity Reversal via Postsynthetic Ligand Exchange

   https://doi.org/10.1002/anie.202218854  

   Liu, Qiao ; Cho, Sung Gu ; Hilliard, Jordon ; Wang, Ting‐Yuan ; Chien, Szu‐Chia ; Lin, Li‐Chiang ; Co, Anne C. ; Wade, Casey R. ( March 2023 , Angewandte Chemie International Edition)

   Although many porous materials, including metal–organic frameworks (MOFs), have been reported to selectively adsorb C₂H₂in C₂H₂/CO₂separation processes, CO₂‐selective sorbents are much less common. Here, we report the remarkable performance ofMFU‐4(Zn₅Cl₄(bbta)₃, bbta=benzo‐1,2,4,5‐bistriazolate) toward inverse CO₂/C₂H₂separation. The MOF facilitates kinetic separation of CO₂from C₂H₂, enabling the generation of high purity C₂H₂(>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C₂H₂is excluded fromMFU‐4by narrow pore windows formed by Zn−Cl groups. Postsynthetic F⁻/Cl⁻ligand exchange was used to synthesize an analogue (MFU‐4‐F) with expanded pore apertures, resulting in equilibrium C₂H₂/CO₂separation with reversed selectivity compared toMFU‐4.MFU‐4‐Falso exhibits a remarkably high C₂H₂adsorption capacity (6.7 mmol g⁻¹), allowing fuel grade C₂H₂(98 % purity) to be harvested from C₂H₂/CO₂mixtures by room temperature desorption.

    

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3. Solid‐State [4+4] Cycloaddition and Cycloreversion with Use of Unpaired Hydrogen‐Bond Donors to Achieve Solvatomorphism and Stabilization

   https://doi.org/10.1002/chem.202302482  

   George, III, Gary C. ; Hutchins, Kristin M. ( October 2023 , Chemistry – A European Journal)

   The crystal structure of a commercially available anthracene derivative, anthracene‐9‐thiocarboxamide, is reported here for the first time. The compound undergoes a [4+4] cycloaddition in the solid state to afford facile synthesis of the cycloadduct (CA). The cycloaddition is also reversible in the solid state using heat or mechanical force. Due to the presence of unpaired, strong hydrogen‐bond donor atoms on the CA, significant solvatomorphism is achieved, and components of the solvatomorphs self‐assemble into four different classes of supramolecular structures. The CA readily crystallizes with a variety of structurally‐diverse solvents including those containing oxygen‐, nitrogen‐, or pi‐acceptors. Some of the solvents the CA crystallized with include thiophene, benzene, and the three xylene isomers; thus, the CA was employed in industrially‐relevant solvent separation. However, in competition studies, the CA did not exhibit selectivity. Lastly, it is demonstrated that the CA crystallizes with vinyl‐containing monomers and is currently the only compound that crystallizes with both widely used monomers 4‐vinylpyridine and styrene. Solid‐state complexation of the CA with the monomers affords over a 50 °C increase in the monomer's thermal stabilities. The strategy of designing molecules with unused donors can be applied to achieve separations or volatile liquid stabilization.

    

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4. 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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5. Metal ions induced secondary structure rearrangements: mechanically interlocked lasso vs. unthreaded branched-cyclic topoisomers

   https://doi.org/10.1039/c8an00138c  

   Jeanne Dit Fouque, Kevin ; Moreno, Javier ; Hegemann, Julian D. ; Zirah, Séverine ; Rebuffat, Sylvie ; Fernandez-Lima, Francisco ( January 2018 , The Analyst)

   Metal ions can play a significant role in a variety of important functions in protein systems including cofactor for catalysis, protein folding, assembly, structural stability and conformational change. In the present work, we examined the influence of alkali (Na, K and Cs), alkaline earth (Mg and Ca) and transition (Co, Ni and Zn) metal ions on the conformational space and analytical separation of mechanically interlocked lasso peptides. Syanodin I, sphingonodin I, caulonodin III and microcin J25, selected as models of lasso peptides, and their respective branched-cyclic topoisomers were submitted to native nESI trapped ion mobility spectrometry-mass spectrometry (TIMS-MS). The high mobility resolving power of TIMS permitted to group conformational families regardless of the metal ion. The lower diversity of conformational families for syanodin I as compared to the other lasso peptides supports that syanodin I probably forms tighter binding interactions with metal ions limiting their conformational space in the gas-phase. Conversely, the higher diversity of conformational families for the branched-cyclic topologies further supports that the metal ions probably interact with a higher number of electronegative groups arising from the fully unconstraint C-terminal part. A correlation between the lengths of the loop and the C-terminal tail with the conformational space of lasso peptides becomes apparent upon addition of metal ions. It was shown that the threaded C-terminal region in lasso peptides allows only for distinct interactions of the metal ion with either residues in the loop or tail region. This limits the size of the interacting region and apparently leads to a bias of metal ion binding in either the loop or tail region, depending whichever section is larger in the respective lasso peptide. For branched-cyclic peptides, the non-restricted C-terminal tail allows metal coordination by residues throughout this region, which can result in gas-phase structures that are sometimes even more compact than the lasso peptides. The high TIMS resolution also resulted in the separation of almost all lasso and branched-cyclic topoisomer metal ions ( r ∼ 2.1 on average). It is also shown that the metal incorporation ( e.g. , doubly cesiated species) can lead to the formation of a simplified IMS pattern (or preferential conformers), which results in baseline analytical separation and discrimination between lasso and branched-cyclic topologies using TIMS-MS. 

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