Engineering micromechanics of soft porous crystals for negative gas adsorption

Framework materials at the molecular level, such as metal–organic frameworks (MOF), were recently found to exhibit exotic and counterintuitive micromechanical properties. Stimulated by host–guest interactions, these so-called soft porous crystals can display counterintuitive adsorption phenomena such as negative gas adsorption (NGA). NGA materials are bistable frameworks where the occurrence of a metastable overloaded state leads to pressure amplification upon a sudden framework contraction. How can we control activation barriers and energetics via functionalization of the molecular building blocks that dictate the frameworks'' mechanical response? In this work we tune the elastic and inelastic properties of building blocks at the molecular level and analyze the mechanical response of the resulting frameworks. From a set of 11 frameworks, we demonstrate that widening of the backbone increases stiffness, while elongation of the building blocks results in a decrease in critical yield stress of buckling. We further functionalize the backbone by incorporation of sp³ hybridized carbon atoms to soften the molecular building blocks, or stiffen them with sp² and sp carbons. Computational modeling shows how these modifications of the building blocks tune the activation barriers within the energy landscape of the guest-free bistable frameworks. Only frameworks with free energy barriers in the range of 800 to 1100 kJ mol⁻¹ per unit cell, and moderate yield stress of 0.6 to 1.2 nN for single ligand buckling, exhibit adsorption-induced contraction and negative gas adsorption. Advanced experimental in situ methodologies give detailed insights into the structural transitions and the adsorption behavior. The new framework DUT-160 shows the highest magnitude of NGA ever observed for nitrogen adsorption at 77 K. Our computational and experimental analysis of the energetics and mechanical response functions of porous frameworks is an important step towards tuning activation barriers in dynamic framework materials and provides critical design principles for molecular building blocks leading to pressure amplifying materials.

We characterise the elastic properties of molecular building blocks and how they impact the mechanical properties of soft porous crystals.     

烷基修饰寡聚脱氧核苷酸磷酸残基的化学合成及稳定性研究

分别采用格氏试剂和三氯化磷三步取代法合成了4个新的烷基修饰磷酸残基的亚磷酸酰胺单体, 其结构经1H NMR和31P NMR表征. 利用这些单体合成模型序列5'-dTTTx TT-3', 考察了单体及寡聚核苷酸序列在DNA/RNA合成条件下的稳定性, 提出了固相合成含有烷基修饰磷酸残基的寡聚核苷酸序列裂解及脱保护条件.     

What kinds of three-dimensional nets are possible with tris-chelated metal complexes as building blocks?

Tris-chelated metal complexes with octahedral geometry are sometimes used as building blocks for "self assembly" and "crystal engineering". These versatile building blocks easily form honey-comb type 2D nets. However, in this Perspective we discuss the different types of 3D nets that can be formed with these starting materials using Wells classification, and concentrate on the (10,3) nets. We show that several of these, and not only the (10,3)-a net, are possible by analysing the geometrical requirements of each net. We note that each possible net implies a specific assembly order of Delta or Lambda chirality of the building blocks.     

Achieving a stable COF with the combination of “flat” and “twist” large-size rigid synthons for selective gas adsorption and separation

A new type of covalent organic framework(COF) was achieved using combination of structrally rigid and conformationally othorganal building blocks. The N-2-aryl-substituted triazole derivative(NAT-CHO)was prepared with co-planar conformation among the three aromatic rings as the “flat” building block.The 4,4,4,4-(ethene-1,1,2,2-tetrayl)tetraaniline)(ETTA) was applied as the “twist” building block. A 2 D sheet of network was obtained through imine formation. The resulting NAT-COF gave excellent th...     

Temperature and Composition Dependent Optical Properties of CdSe/CdS Dot/Rod-Based Aerogel Networks

Employing nanocrystals (NCs) as building blocks of porous aerogel network structures allows the conversion of NC materials into macroscopic solid structures while conserving their unique nanoscopic properties. Understanding the interplay of the network formation and its influence on these properties like size-dependent emission is a key to apply techniques for the fabrication of novel nanocrystal aerogels. In this work, CdSe/CdS dot/rod NCs possessing two different CdSe core sizes were synthesized and converted into porous aerogel network structures. Temperature-dependent steady-state and time-resolved photoluminescence measurements were performed to expand the understanding of the optical and electronic properties of these network structures generated from these two different building blocks and correlate their optical with the structural properties. These investigations reveal the influence of network formation and aerogel production on the network-forming nanocrystals. Based on the two investigated NC building blocks and their aerogel networks, mixed network structures with various ratios of the two building blocks were produced and likewise optically characterized. Since the different building blocks show diverse optical response, this technique presents a straightforward way to color-tune the resulting networks simply by choosing the building block ratio in connection with their quantum yield.     

Endohedral zintl ions: intermetalloid clusters

Tetrels can be regarded as most promising candidates for the construction of larger clusters. Recent examples have shown that larger clusters are particularly stable if they contain interstitial atoms (e.g. [Pt@Pb12]2-). Many salts of the polyhedral anions are soluble, but a number of examples-usually those with higher charges-occur only as quasi-discrete units in saltlike crystals (Zintl phases) or as building blocks in intermetallic phases. In this Minireview, the chemistry of intermetalloid clusters is reviewed with reference to the endohedral Zintl ions, Zintl phases, and polyhedral building blocks of intermetallic compounds, including heteroatomic species in the gas phase. We focus on selected examples and discuss the new findings in the context of recent advances in the field of metalloid clusters and (endohedral) fullerenes and fullerides.     

Synthesis of thiol-derivatized europium porphyrinic triple-decker sandwich complexes for multibit molecular information storage

The storage of multiple bits of information at the molecular level requires molecules with a large number of distinct oxidation states. Lanthanide triple-decker sandwich molecules employing porphyrins and phthalocyanines afford four cationic states and are very attractive for molecular information storage applications. Five triple-decker building blocks have been prepared of the type (phthalocyanine)Eu(phthalocyanine)Eu(porphyrin), each bearing one iodo, one ethyne, or one iodo and one ethyne group attached to the porphyrin unit. Two triple-decker building blocks with different oxidation potentials were derivatized with an S-acetylthiophenyl unit for attachment to an electroactive surface. To explore the preparation of arrays comprised of triple deckers, which may lead to the storage of a larger number of bits, two types of dyads of triple deckers were prepared. An ethyne-linked dyad of triple deckers bearing one S-acetylthiophenyl unit was prepared via repetitive Sonogashira couplings, and a butadiyne-linked dyad was prepared via a modified Glaser coupling. The triple deckers were characterized by absorption spectroscopy, laser-desorption mass spectrometry, and (1)H NMR spectroscopy. The thiol-derivatized triple deckers form self-assembled monolayers (SAMs) on gold via in situ cleavage of the thiol protecting group. The SAM of each array is electrochemically robust and exhibits three well-resolved, reversible oxidation waves. These electrochemical characteristics indicate that these types of molecules are well suited for storing multiple bits of information.     

Synthesis of Spirocyclic and Fused Isoxazoline Building Blocks

A highly efficient multigram synthesis of spirocyclic and fused isoxazoline building blocks is described. Isoxazoline-3-carboxylates were synthesized via a regioselective 1,3-dipolar cycloaddition reaction of 2-chloro-2-(hydroxyimino)acetate and carbo- or heterocyclic alkenes bearing endo- or exocyclic C=C double bonds, resulting in fused or spirocyclic isoxazolines, respectively. The preparation of up to 300 g of these compounds was achieved in a single run. The ester group of isoxazolines was then subjected to common synthetic transformations for the synthesis of corresponding building blocks, including alcohols, chlorides, azides, amines, aldehydes, carboxylic acids, amino acids and their derivatives, difluoromethyl-substituted compounds, and bicyclic γ-lactones. Additionally, a direct cycloaddition-based approach to the synthesis of aminoalkyl- and chloromethyl-substituted isoxazolines was proposed to improve their preparation. The described isoxazoline building blocks are expected to be valuable tools for drug discovery.     

A renaissance of color: New structures and building blocks for organic electronics

Natural dyes and pigments like indigo and its derivatives valued for their bright colors and photochemical stability has been used since antiquity. Recently, the need for better performing materials in the organic electronics field has inspired a resurgence of these historical molecules and their subsequent transformation into new families of π‐conjugated building blocks used to construct new (macro)molecular semiconductors. This Highlight will explore the renaissance of notable building blocks including diketopyrrolopyrrole, (iso)indigo, benzodipyrrolidone, and benzodifuranone, as well as nonfullerene acceptor structures 9,9′‐bifluorenylidene and quinacridone. In addition, as the organic electronics field continues to evolve, the design of molecules with precise structure and function embodies a new paradigm for the next generation of materials. Representative examples will be described that embrace this new model and point the direction for advanced technologies. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Convenient Syntheses of Some C4 Chiral Building Blocks Starting From (S)-Malic Acid

In the field of chiral technology, the synthesis of chiral intermediates and chiral building blocks occupies an important position. Chiral building blocks bearing double and / or multiple functionalities is particularly useful for the synthesis of chiral pharmaceuticals and chiral agrochemicals. In the recent years, we have been engaged in the development of synthetic methodology based on (S)-malic acid1-s. In these studies, malimide 2, easily accessible from (S)-malic acid, was shown to be a useful multifunctional building block in the asymmetric synthesis of natural products and chiral drugs (Scheme 1).     

Cluster-assembled materials based on M12N12 (M = Al, Ga) fullerene-like clusters

We report the results of density functional theory calculations on cluster-assembled materials based on M(12)N(12) (M = Al, Ga) fullerene-like clusters. Our results show that the M(12)N(12) fullerene-like structure with six isolated four-membered rings (4NRs) and eight six-membered rings (6NRs) has a T(h) symmetry and a large HOMO-LUMO gap, indicating that the M(12)N(12) cluster would be ideal building blocks for the synthesis of cluster-assembled materials. Via the coalescence of M(12)N(12) building blocks, we find that the M(12)N(12) clusters can bind into stable assemblies by either 6NR or 4NR face coalescence, which enables the construction of rhombohedral or cubic nanoporous framework of varying porosity. The rhombohedral-MN phase is energetically more favorable than the cubic-MN phase. The M(12)N(12) fullerene-like structures in both phases are maintained and the M-N bond lengths between M(12)N(12) monomers are slightly larger than that in isolated M(12)N(12) clusters and the bulk wurtzite phases. The band analysis of both phases reveals that they are all wide-gap semiconductors. Because of the nanoporous character of these phases, they could be used for gas storage, heterogeneous catalysis, filtration and so on.     

Self-assembly of anisotropic tethered nanoparticle shape amphiphiles

The varied and exotic shapes of new nanoscale organic and inorganic building blocks provide new opportunities to engineer materials possessing specific functionality and physical properties dictated by the unique packings of these particles. We briefly review some of the current strategies for inducing the self-assembly of these building blocks focusing on one strategy in particular—the attachment of tethers to the building blocks at precise locations to create tethered nanoparticle “shape amphiphiles”. We use computer simulation to demonstrate that the resulting anisotropy imparted to nanocrystals or nanocolloids by the tethers can be used to encode simple design rules into the building blocks that ultimately result in a unique self-assembled structure. We present a general classification scheme for tethered nanoparticles wherein the anisotropy of a shape amphiphile is described by a vector comprised of one or more axes each describing a measure of anisotropy.     

Identification of polymer building blocks by Py–GC/MS and MALDI-TOF MS

The main goal of this work is to identify polyurethane (PU) building blocks by pyrolysis gas chromatography/mass spectrometry (Py–GC/MS) and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). Toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI) are widely used polymer building blocks. Py–GC/MS and MALDI-TOF MS were proved to be powerful methods to distinguish TDI-PU and MDI-PU according to the characteristic pyrolysis products and the different repeated units, respectively. In Py–GC/MS, the specific pyrolyzates are TDI for TDI-PU and MDI for MDI-PU. In MALDI-TOF MS, the weights of repeated units are 264?g/mol for TDI-PU and 340?g/mol for MDI-PU.     

BINOL-based foldamers--access to oligomers with diverse structural architectures

In this article, we report on the synthesis and conformation of a new family of aromatic oligoamide foldamers based on binaphthol (BINOL) monomers. A series of oligomers with differing chirality of the individual BINOL building blocks and mixed sequences of alternate BINOL and pyridyl building blocks has been synthesized and structurally characterized. NMR and quantum chemical calculations on the basis of ab initio MO theory were performed to obtain insight into the conformational features of these oligomers. It is shown that the combination of these inherently chiral aromatic building blocks provides a novel access to a wide variety of conformationally ordered synthetic oligomers with diverse and dazzling structural architectures distinct from those classically observed.     

Total Synthesis of Sialylated Glycans Related to Avian and Human Influenza Virus Infection

Human and avian influenza type A viruses bind sialylated pentasaccharides. Herein, the total synthesis of four of these glycans is reported. Efficient sialylations relied on two N‐Troc‐protected (Troc=2,2,2‐trichloroethoxycarbonyl) sialic acid building blocks. The first, a thiophenyl glycoside, readily produced the sialyl‐α(2‐6)galactose disaccharide. Combination of the second building block, a novel glycosyl phosphite, and a benzylidene‐protected galactoside produced the best results for the formation of the sialyl‐α(2‐3)galactose. Two common trisaccharides were assembled by the introduction of glucose, galactose, and glucosamine building blocks followed by selective deprotection. Two sets of pentasaccharides were obtained by the union of two sialylgalactose N‐phenyl trifluoroacetimidate building blocks with the two trisaccharides above. Global deprotection furnished the desired pentasaccharides. The products of these total syntheses are currently employed on the surface of carbohydrate microarrays to detect and type different strains of the influenza virus.     

A Carbon Dioxide Bubble-Induced Vortex Triggers Co-Assembly of Nanotubes with Controlled Chirality

It is challenging to prepare co-organized nanotube systems with controlled nanoscale chirality in an aqueous liquid flow field. Such systems are responsive to a bubbled external gas. A liquid vortex induced by bubbling carbon dioxide (CO₂) gas was used to stimulate the formation of nanotubes with controlled chirality; two kinds of achiral cationic building blocks were co-assembled in aqueous solution. CO₂-triggered nanotube formation occurs by formation of metastable intermediate structures (short helical ribbons and short tubules) and by transition from short tubules to long tubules in response to chirality matching self-assembly. Interestingly, the chirality sign of these assemblies can be selected for by the circulation direction of the CO₂ bubble-induced vortex during the co-assembly process.     

Phenols-useful templates for the synthesis of bi-functional orthogonally protected dendron building blocks via solid phase Mitsunobu reaction

Bi-functional dendritic building blocks for convergent dendrimer growth were successfully synthesized from phenolic templates in the solid phase via a Mitsunobu reaction. Each arm of the dendron building block carries an orthogonally protected secondary amine along the arm, and a peripheral primary amine or phenol group (building block type 1) or a tertiary amine junction with orthogonally protected peripheral primary amine or carboxyl groups (building block type 2). The synthetic routes reported in this work are general and applicable for the preparation of diverse building blocks, controlling protection, arm length, and peripheral moieties. These novel dendron units can form unusual dendritic architectures by solid-phase chemistry, which may be incorporated into specific complex structures expanding the scope of dendrimer science.     

Discrete Stimuli‐Responsive Multirotaxanes with Supramolecular Cores Constructed through a Modular Approach

The synthesis of discrete multirotaxanes with well‐defined structures remains a great challenge. Herein, we present the successful construction of diverse discrete multirotaxanes with well‐defined supramolecular metallacycles as cores by a modular approach. Moreover, these novel multirotaxanes featured a stimuli‐responsive property that enabled the introduction and removal of the bromide anion by taking advantage of dynamic nature of the supramolecular metallacycle scaffold. Through the combination of rotaxane‐containing prefunctionalized building blocks with the corresponding different organoplatinum(II) acceptor building blocks (60, 120, or 180°), diverse discrete multirotaxanes with well‐defined metallacycles (rhomboid or hexagon) as cores as well as certain numbers of rotaxane units were successfully obtained quantitatively by means of coordination‐driven self‐assembly. Furthermore, owing to the existence of a dynamic metallacycle as the supramolecular cores, the resultant multirotaxanes showed anion‐induced disassembly and reassembly properties, which allowed for the reversible transformation between multirotaxanes and the corresponding individual rotaxane‐containing building blocks. Therefore, this research not only enriches the family of discrete multirotaxanes, but also provides a novel strategy for the construction of “smart” stimuli‐responsive multirotaxane systems.     

New peptide labels containing covalently bonded platinum(II) centers as diagnostic biomarkers and biosensors

[reaction: see text] Water- and acid-resistant arylplatinum(II) complexes have been covalently bonded to the N-terminus of L-valine, thus providing organometallic biomolecules with excellent stability properties. Owing to the (195)Pt nucleus (I = (1)/(2)), these building blocks are potentially versatile biomarkers (e.g., MRI). Moreover, they display efficient in vitro biosensor characteristics since they detect SO(2) gas selectively and fully reversibly by an instantaneous change of the spectroscopic properties including a diagnostic (195)Pt NMR signal.