Atropisomer-based construction of macrocyclic hosts that selectively recognize tryptophan from standard amino acids

A syn-atropisomer precursor was employed to construct trapezoid-shape macrocycles, which can selectively recognize tryptophan from 20 standard amino acids.

用球磨法制备的主客体Fe-TPP⊂ZIF前驱体制备用于ORR和锌空电池的Fe单原子催化剂 (Well-elaborated, mechanochemically synthesized Fe-TPP⊂ZIF precursors (Fe-TPP = tetraphenylporphine iron) to atomically dispersed iron–nitrogen species for oxygen reduction reaction and Zn-air batteries)

在这篇论文中，我们使用主客体型Fe-TPP⊂ZIF复合化合物作为前驱体热解得到了Fe单原子级分散的铁氮掺杂的多孔碳材料，并作为电催化剂用于氧还原反应和锌空电池。论文主要要点有： 1.主客体型Fe-TPP⊂ZIF为首次报道，其中ZIF基质为较难制备的rho型ZIF（该类ZIF内腔直径约为22埃，可以容纳Fe四苯基卟啉客体分子，远大于常见的内径约12埃的sod型ZIF-8），卟啉客体以分子级别分散在ZIF内腔中。 2.前驱体制备过程使用原位机械球磨法，Fe单原子材料使用高温热解，因此整个制备为两步非溶液过程，具有简易绿色高效的优势。 3.Fe单原子状态通过球差电镜和X射线精细吸收谱表征，并模拟其配位环境为Fe-N4，表征较为全面。 4.ORR测试碱性条件下半波电位约0.895 V，优于Pt-C，经10000次循环无明显衰减。 Although atomically dispersed Fe-N species as electrocatalysts often exhibit high activity for oxygen reduction reaction (ORR), the rational design and facile fabrication of single-atom Fe-N species-based catalysts remains a great challenge because of their easy aggregation. Herein, a new precursor of host-guest Fe-TPPrho-ZIF (Fe-TPP = tetraphenylporphyrin iron; rho-ZIF = zeolitic imidazolate framework with the rho topology) for the first time was elaborately designed and readily prepared by one-pot mechanochemical method, and then was pyrolyzed into Fe-N/C catalysts with no need of solution-based steps and post-ammonia/acid treatments, which greatly simplified the preparation procedures. Owing to the host-guest confinement at the molecular level, the encapsulated Fe centers within interior cavities of rho-ZIF host matrice can be effectively isolated during pyrolysis to afford atomically dispersed Fe-N4 moieties anchored on the carbon matrice. Such a well-elaborated precursor not only endows the final product with the single-atom characteristic, but also with high Fe loading (up to 3.8 wt%) and specific surface area. Benefitting from the outstanding compositional and structural advantages, the resultant Fe-N/C exhibits highly efficient ORR activity with E1/2 of 0.895 V in 0.1 M KOH, ~50 mV more positive than that of the commercial Pt/C, which is among the top-level ORR electrocatalysts to date. It has excellent stability and displays a negligible change after a 10000-cycle accelerated durability test. Moreover, rechargeable Zn-air batteries were also assembled to demonstrate the practical application of the as-obtained Fe-N/C as air cathode catalyst. Our work may provide an insight into the facile and large-scale production of high-performance and durable non-precious metal catalysts with atomic-level dispersion.

Versatile and Efficient Mechanochemical Synthesis of Crystalline Guest⊂Zeolitic Imidazolate Framework Complexes by in Situ Host−Guest Nanoconfinement

In this work, the one-pot mechanochemical synthesis has been demonstrated to be a versatile and efficient method to prepare hybrid guestZIF materials with high crystallinity, and up to 18 functional guest molecules with different sizes, shapes and properties have been encapsulated into interior cavities of ZIFs with high guest loading. These guest molecules can be accommodated within the different cavities of sod- or rho-ZIFs, depending on the sizes of guest. Because of the relatively small opening of ZIFs, the guest molecules can be immobilized by physical imprisonment and cannot be released without destroying the host matrix. More importantly, the obtained guestZIF materials have been endowed with various interesting properties originated from the encaged guest molecules, which significantly extends the functionality of MOFs. For instance, PEG-decorated nanoparticles of a sod-ZIF (i.e. ZIF-8) encapsulating gadolinium complex exhibit interesting property of magnetic resonance imaging (MRI) and a rho-ZIF (i.e. MAF-6) with metalloporphyrin embedded can be used as an effective heterogeneous catalyst for epoxidation of styrene.

Postsynthetic Addition of Ligand Struts in MOFs: Effect of Syn/anti Addition on Framework Structures with Distinct Topologies

Dynamic behaviours of a rationally prepared flexible MOF by postsynthetic modification of ligand struts

Through postsynthetic modification of ligand struts, controllable conversion of a Zr MOF between rigidity and flexibility is realized. The rationally prepared flexible MOF exhibits interesting dynamic behaviours, such as reversible structural deformation, vapour sorption hysteresis and unexpected adsorption of bulky guest molecules.

Efficient Mechanochemical Synthesis of Polyoxometalate⊂ZIF Complexes as Reusable Catalysts for Highly Selective Oxidation

One-pot mechanochemical synthesis was demonstrated to be an efficient strategy to synthesize host−guest POM⊂rho-ZIF complexes (POM = polyoxometalate; rho-ZIF = zeolitic imidazolate framework with rho topology) with high crystallinity. In this work, the metastable rho-ZIF with large interior cavities and windows was used as host matrix for encapsulating and immobilizing bulky guest molecules with high loading efficiency and chemical stability. As novel catalysts, POM⊂rho-ZIF complexes were found effective for the selective oxidation of a series of sulfides to sulfoxides. Moreover, the heterogeneity of these composite catalysts was confirmed by leaching tests, and they can be recycled at least four times without significant loss of activity.

High-valent cationic metal–organic macrocycles as novel supports for immobilization and enhancement of activity of polyoxometalate catalysts

Developing new strategy for preparing highly active and recyclable heterogeneous polyoxometalate (POM) catalysts has attracted much attention in the past decades. In this work, we prepared a hexagonal terpyridine-cadmium metal-organic macrocycles (Cd-MOMs) with dodeca-valent positive charge, and subsequently employed it as a new catalyst support for immobilizing mono-transition-metal-substituted Keggin-type HPW11MO394- (PW11M, M = Ni, Co, Cu, Zn). Because of strong electrostatic interaction, the obtained polyoxometalate-metal-organic-macrocycle (PW11M-Cd-MOM or POM-MOM) catalyst exhibits high thermal stability and insolubility in common solvents. The composite catalyst was found effective for the epoxidation of cyclooctene and the sulfides oxidation with hydrogen peroxide. In the epoxidation reaction of cyclooctene, PW11Ni-Cd-MOM shows the highest catalyst performance with 96.4% conversion and 95.7% selectivity of epoxide. Compared with homogeneous POM and non-cyclic hybrid analogue catalysts, the conversion and selectivity of POM-MOM catalyst are both enhanced enormously, showing remarkable synergistic reactivity. Moreover, leaching tests confirmed the heterogeneity of POM-MOM catalyst and it can be recycled at least four times with no significant loss of activity.

Stabilization and Controlled Release of Reactive Molecules by Solid-State van der Waals Capsules

We have shown that the isolated environment provided by a solid-state van der Waals capsule with an interdigitated structure can efficiently stabilize a series of reactive molecules, such as cyclopentadiene and trichlorosilane, in the crystalline state, even under relatively harsh conditions. More importantly, in CH3OH/H2O liquid medium, the capsule compound can be stimulated to conveniently release its guest molecules by adjusting the temperature of the system, and the host molecules are easily separated and reused because of their insolubility in CH3OH/H2O solution. As a representative application, the capsule can stabilize molecules of cyclopentadiene at ambient temperature and then controllably release it upon heating for further reaction to produce a Diels–Alder adduct. This work demonstrates that stabilization and extraordinary control over reactive molecules can be achieved by solid-state vdW assemblies which are facilely prepared and recycled. Furthermore, the approach could be generalized to a wide variety of different reactive molecules through rational tailoring of the supramolecular hosts.

A Designed Three-Dimensional Porous Hydrogen-Bonding Network Based on a Metal−Organic Polyhedron

By employment of sulfonate-decorated metal−organic cuboctahedra (MOCs) as tectons, we report an interesting example of molecular tectonics strategy for the rational construction of three-dimensional (3D) porous network 1 through complementary and metrically matched N−H+···−O−S hydrogen bonds between guanidinium and sulfonate (GS) moieties. Built from the MOCs as 24-connected nodes and the GS H-bonding motifs as 3-connected nodes, 1 was expected to have a (3,24)-connected network topology, which has been verified by the single crystal X-ray analysis. In addition, the porous H-bonding network 1 displays good stability under ambient conditions and modest absorption of cationic dye molecules.

A Versatile Tripodal Host with Cylindrical Conformation: Solvatomorphism, Inclusion Behavior and Separation of Guests

A new tripodal host molecule 2,4,6-tris(1-phenyl-1H-tetrazol -sulfanylmethyl) mesitylene (TPTM) has been synthesized through a facile procedure. As expected, this molecule adopts an all-syn cylindrical configuration, thereby delimiting an inner cavity. To explore the solvatomorphism chemistry and inclusion behavior of TPTM, a series of organic and inorganic species have been employed as guests to afford 17 inclusion compounds (1, 2, 3a-3f, 4a-4i), which can be classified into four distinct forms (Form I-IV) under similar conditions. These compounds have been characterized by single-crystal and powder X-ray diffraction methods, and 1H NMR studies. In compound 1 with Form I, one foot of a TPTM molecule inserts into the cavity of the other TPTM in the opposite to form a dimeric “hand-shake” motif with one acetonitrile molecule occupying the void. Compound 2 with Form II contains three types of capsule-shaped dimers each holding a CH2Cl2 molecule as guest. In compounds 3a-3f with Form III, each pair of TPTM molecules interdigitate to form a capsule-shaped dimeric unit accommodating a guest molecule in endo-cavity. In compounds 4a-4i with Form IV, each TPTM makes contact with three nearby TPTM molecules in a “self-including” manner to generate a graphite-like organic layer, and through further superposition to form open hexagonal channels. From experimental and theoretical results, the intrinsic properties of guest molecules such as size, shape and self-interaction can be regarded as the main factors leading to these solvatomorphism phenomena and the subtle inclusion behavior of TPTM. Thermogravimetric analyses show that the encapsulated guest molecules in these compounds can be evacuated at relatively high temperatures, which demonstrates an outstanding inclusion capability of TPTM. In addition, based on compound 4a with benzenes in channels, reversible exchange of toluene and separation of xylene isomers on single crystals have been observed.