从超分子聚合物到超分子有机框架:组装溶液相超分子结构的周期性

单体分子在溶液相自发形成周期性的网络结构,是超分子化学和分子自组装研究领域的重大挑战.多头基分子在溶液相通过分子间非共价键作用可以形成超分子聚合物.提高多头基(三头基和四头基)分子骨架的刚性,可以提高结合位点的结构预组织,进而增强分子间相互作用的协同性和多价性特征,提高自组装结构的有序性或周期性.本文综述了多头基分子自组装形成超分子聚合物的一些重要进展,介绍了二维超分子有机框架(一类新的溶液相周期性自组装网络结构研究的最新进展.     

Design of new macromolecular architectures by using quasi-equivalent monodendrons as building blocks

Quasi-equivalent building blocks are chemically identical subunits which self-control their shape by switching between different conformational states. Classic biological examples are the flat-tapered and conical protein coats which jacket nucleic acids during the self-assembly of rod-like and icosahedral viruses, respectively. This paper advances the hypothesis that monodendrons can act as synthetic quasi-equivalent building blocks. The rational design of flat-tapered and cone shaped quasi-equivalent monodendrons and their use in the construction of three dimensional supramolecular and macromolecular rod-like and spherical systems demonstrates the above hypothesis. Mechanisms which interconvert the spherical systems into rod-like ones by using the same monodendron building blocks, thus demonstrating their quasi-equivalence, will be exemplified.     

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.     

Synthesis of Differentially Protected Glucosamine Building Blocks and Their Evaluation as Glycosylating Agents

The modular assembly of heparin oligosaccharides requires glucosamine building blocks with amine protecting groups for α-selective glycosylations that can be readily removed. The synthesis of N-4-nitrobenzensulphonamide (nosyl)- and N-2,4-dinitrophenyl (DNP)-protected glucosamine building blocks and their evaluation as glycosylating agents is described. The N-nosyl-protected glucosamine building blocks were challenging to prepare and their glycosylations resulted in inseparable mixtures of products. The N-DNP-protected glucosamines, however, were readily synthesized and resulted in α-selective couplings to protected l-iduronic acid derivatives.     

Compound clusters

The cluster beam technique offers promise of becoming a useful tool for chemists in their search for new compounds. Using this technique elemental vapors can be made to react under controlled conditions to form units of condensed matter (clusters) small enough to be analyzed in a mass spectrometer but still large enough to contain several structural building blocks. Periodic patterns in cluster mass spectra often allow these building blocks to be uniquely identified. Of particular interest is the identification of building blocks unknown in the crystalline state.     

Divergent synthesis and optoelectronic properties of oligodiacetylene building blocks

A new and divergent synthetic route to oligodiacetylene (ODA) building blocks has been developed via Sonogashira reactions under a reductive atmosphere. These central building blocks provide a new way for rapid preparation of long ODAs. In addition, we report on their optoelectronic properties which are dependent on their end cap. Finally, the formation of their radical cations, and their optical properties and reactivity towards nucleophiles are investigated.     

Pristine DNA Hydrogels from Biotechnologically Derived Plasmid DNA

DNA hydrogels are of great interest for a variety of biomedical applications owing to their biocompatibility and biodegradability but the advantages of DNA hydrogels have not been exploited yet because of their limited availability. Thus far, DNA hydrogels have been prepared from synthetically derived building blocks, and their production on large scale would be far too expensive. As an alternative, here the generation of DNA hydrogels from plasmid DNA is reported. Plasmid DNA can be prepared on large scale at reasonable costs by a fermentation process. The desired linear DNA building blocks are then obtained from the plasmid DNA by enzymatic digestion. Gel formation is carried out by covalent bond formation between individual building blocks via enzymatic ligation. The generation of pristine DNA hydrogels from plasmid DNA is thus presented for the first time. The viscoelastic properties of the hydrogels were studied by rheology, which confirmed that the gels have storage moduli G′ of >100 Pa.     

Total synthesis of the CP-molecules (CP-263,114 and CP-225,917, phomoidrides B and A). 1. Racemic and asymmetric synthesis of bicyclo[4.3.1] key building blocks

A brief introduction into the chemistry of the CP-molecules is followed by first-generation synthetic sequences toward key building blocks for their total synthesis. Processes for both racemic and enantiomerically enriched bicyclo[4.3.1] ketone 6 or its equivalent are described, and the absolute stereochemistries of the optically enriched intermediates are determined. The efficient route developed to racemic 6 and the ready access to both enantiomers of key building blocks provided the opportunity for the total synthesis of the CP-molecules and determination of their absolute stereochemistry.     

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.     

Synthesis and one‐dimensional assembly of cylindrical polymer nanoparticles prepared from tricomponent bottlebrush copolymers

Biological systems feature controlled assembly of well‐defined building blocks at different length scales. While major progress has been achieved in directing the assembly of synthetic molecular building blocks, controlled organization of nanostructured units into micro‐ and macroscale aggregates remains a challenge. Herein, we report the synthesis of well‐defined nanostructured building blocks, cylindrical polymeric nanoparticles with controlled dimensions and inner surface chemistry, and their dynamic anisotropic organization into one‐dimensional assemblies. Nanoparticle building blocks were produced by molecular templating of cylindrical bottlebrush copolymers featuring tricomponent side chains. The produced nanostructures were composed of a nonionic and bioinert polyethylene glycol (PEG) shell and stimuli‐responsive poly(methacrylic acid) (PMA) chains grafted on the interior. We show that pH‐dependent interactions between PMA chains exposed only at the nanoparticle ends lead to anisotropic end‐to‐end association of parent cylindrical nanostructures into elongated superstructures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3868–3874     

Computational Design of Hybrid Frameworks: Structure and Energetics of Two Me3OF3{‐O2C‐C6H4‐CO2‐}3 Metal‐Dicarboxylate Polymorphs,MIL‐hypo‐1 and MIL‐hypo‐2

The present paper aims at exploring the candidate hybrid structures of the Cr/trimesic acid system by assembling pre‐defined hybrid building‐blocks in direct space. Two possible hybrid building‐blocks were identified where the connection of the 1, 4 BDC molecules to an inorganic metal‐containing trimer forms a large supertetrahedron (ST) or alternatively a large supercube (SC). From existing topologies derived from the space filling packing of corner‐sharing cubes and tetrahedra, two candidates hybrid crystal structures were constructed. Lattice energy minimizations were performed on each candidate structure, as a preliminary step towards the estimation of their relative stabilities. This work further illustrates the computational design of very open hybrid frameworks using the concept of pre‐defined building blocks and their assembly in 3D space.     

Synthesis of covalently linked unsymmetrical porphyrin pentads containing three different porphyrin subunits

The tetrafunctionalized AB3-type porphyrin building blocks containing two different types of functional groups with N4, N3O, N3S, and N2S2 porphyrin cores were synthesized by following various synthetic routes. The AB3-type tetrafunctionalized N4 porphyrin building block was synthesized by a mixed condensation approach, the N3S and N3O porphyrin building blocks by a mono-ol method, and N2S2 porphyrin building block by an unsymmetrical diol method. The tetrafunctionalized porphyrin building blocks were used to synthesize monofunctionalized porphyrin tetrads containing two different types of porphyrin subunits by coupling of 1 equiv of tetrafunctionalized N4, N3O, N3S, and N2S2 porphyrin building block with 3 equiv of monofunctionalized ZnN4 porphyrin building block under mild copper-free Pd(0) coupling conditions. The monofunctionalized porphyrin tetrads were used further to synthesize unsymmetrical porphyrin pentads containing three different types of porphyrin subunits by coupling 1 equiv of monofunctionalized porphyrin tetrad with 1 equiv of monofunctionalized N2S2 porphyrin building blocks under the same mild Pd(0) coupling conditions. The NMR, absorption, and electrochemical studies on porphyrin tetrads and porphyrin pentads indicated that the monomeric porphyrin subunits in tetrads and pentads retain their individual characteristic features and exhibit weak interaction among the porphyrin subunits. The steady state and time-resolved fluorescence studies support an efficient energy transfer from donor porphyrin subunit to acceptor porphyrin subunit in unsymmetrical porphyrin tetrads and porphyrin pentads.     

A Modular Synthesis of Modified Phosphoanhydrides

Phosphoanhydrides (P‐anhydrides) are ubiquitously occurring modifications in nature. Nucleotides and their conjugates, for example, are among the most important building blocks and signaling molecules in cell biology. To study and manipulate their biological functions, a diverse range of analogues have been developed. Phosphate‐modified analogues have been successfully applied to study proteins that depend on these abundant cellular building blocks, but very often both the preparation and purification of these molecules are challenging. This study discloses a general access to P‐anhydrides, including different nucleotide probes, that greatly facilitates their preparation and isolation. The convenient and scalable synthesis of, for example, ¹⁸O labeled nucleoside triphosphates holds promise for future applications in phosphoproteomics.     

Self-assembling porphyrins and phthalocyanines for photoinduced charge separation and charge transport

Large π-conjugated compounds are promising building blocks for organic thin-film electronics such as organic light-emitting diodes, organic field-effect transistors, and organic photovoltaics. Utilization of porphyrins and phthalocyanines for this purpose is highly fascinating because of their excellent electric, photophysical, and electrochemical properties as well as intense self-assembling abilities arising from π-π stacking interactions. This paper focuses on fundamental aspects of self-assembled structures that have been obtained from porphyrin and phthalocyanine building blocks and more complex composites for photoinduced charge separation and charge transport toward the potential applications to organic thin-film electronics.     

Recent advances in biocompatible supramolecular assemblies for biomolecular detection and delivery

Inspired by sophisticated biological structures and their physiological processes,supramolecular chemistry has been developed for understanding and mimicking the behaviors of natural species. Through spontaneous self-assembly of functional building blocks,we are able to control the structures and regulate the functions of resulting supramolecular assemblies.Up to now,numerous functional supramolecular assemblies have been constructed and successfully employed as molecular devices, machines and biological diagnostic platforms.This review will focus on molecular structures of functional molecular building blocks and their assembled superstructures for biological detection and delivery.     

Coarse-graining the self-assembly of beta-helical protein building blocks

Nanotubular structures constructed using self-assembled beta-helical protein building blocks one atop the other have been coarsened to develop a mesoscopic potential that reproduces the intermolecular interaction energies provided by atomistic force-fields. The resulting potential consists of an analytical expression that depends exclusively on the distance and the relative orientation between the two interacting entities. In spite of its complexity, this coarse-grained potential reproduces satisfactorily the energetic properties of two interacting building blocks. The coarse-grained potential has been used to predict that the interaction between building blocks formed by residues 131-165 of E. coli galactoside acteyltransferase becomes repulsive when the size of the nanotube is larger than a threshold, that is, about 45 self-assembled building blocks.     

Ag, Ag2S, and Ag2Se nanocrystals: synthesis, assembly, and construction of mesoporous structures

Synthesis of mesoporous materials has become more and more important due to their wide application. Nowadays, there are two main ideas in their preparation. One is focused on the templating method. The other is based on metal-organic frameworks (MOFs) constructed from molecular building blocks. Herein, we exploit a new idea for their facile and general synthesis, namely, using "artificial atoms" (monodisperse nanoparticles) as uniform building blocks to construct ordered mesoporous materials. Mesoporous Ag, Ag2S, and Ag2Se have been obtained to demonstrate this concept. On the other hand, we also describe a facile method to prepare the "building blocks". Ag nanoparticles were obtained by direct thermal decomposition of AgNO3 in octadecylamine, and Ag2S/Ag2Se nanoparticles were synthesized by reaction between sulfur or selenium powder and Ag nanoparticles formed in situ. This approach for Ag, Ag2S, and Ag2Se nanoparticles is efficient, economical, and easy to scale up in industrial production.     

8-Oxabicyclo[3.2.1]oct-6-en-3-ones: application to the asymmetric synthesis of polyoxygenated building blocks

The development and design of reliable and efficient methods for the construction of chiral building blocks are crucial in modern natural product synthesis. 8-Oxabicyclo[3.2.1]oct-6-en-3-ones are readily accessible scaffolds with defined stereochemical features which have been exploited for non-aldol approaches to the preparation of chiral building blocks. Strategies for their enantioselective synthesis, including asymmetric cycloaddition methods, desymmetrization protocols, and "racemic switch operations", are presented and evaluated.     

Non‐Covalent Functionalization of Carbon Nanotubes with Surfactants and Polymers

Carbon nanotubes (CNTs) possessing unique structure and properties are attractive building blocks for novel materials and devices of important practical interest. However, the insolubility or poor dispersibility of pristine CNTs in common solvents poses a serious obstacle to their further development. To effectively utilize CNTs as building blocks for nanotechnology, CNTs have been covalently and noncovalently functionalized in a number of ways to render them soluble in aqueous or organic solutions. Here, we review recent progress and advances that have been made on dispersion of carbon nanotubes in aqueous and organic media by non‐covalent functionalization with surfactants and polymers.     

Function‐Led Design of Aerogels: Self‐Assembly of Alloyed PdNi Hollow Nanospheres for Efficient Electrocatalysis

One plausible approach to endow aerogels with specific properties while preserving their other attributes is to fine‐tune the building blocks. However, the preparation of metallic aerogels with designated properties, for example catalytically beneficial morphologies and transition‐metal doping, still remains a challenge. Here, we report on the first aerogel electrocatalyst composed entirely of alloyed PdNi hollow nanospheres (HNSs) with controllable chemical composition and shell thickness. The combination of transition‐metal doping, hollow building blocks, and the three‐dimensional network structure make the PdNi HNS aerogels promising electrocatalysts for ethanol oxidation. The mass activity of the Pd₈₃Ni₁₇ HNS aerogel is 5.6‐fold higher than that of the commercial Pd/C catalyst. This work expands the exploitation of the electrocatalysis properties of aerogels through the morphology and composition control of its building blocks.