Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

In this Review, we aim to provide an updated summary of the research related to hollow micro- and nanostructures, covering both their synthesis and their applications. After a brief introduction to the definition and classification of the hollow micro-/nanostructures, we discuss various synthetic strategies that can be grouped into three major categories, including hard templating, soft templating, and self-templating synthesis. For both hard and soft templating strategies, we focus on how different types of templates are generated and then used for creating hollow structures. At the end of each section, the structural and morphological control over the product is discussed. For the self-templating strategy, we survey a number of unconventional synthetic methods, such as surface-protected etching, Ostwald ripening, the Kirkendall effect, and galvanic replacement. We then discuss the unique properties and niche applications of the hollow structures in diverse fields, including micro-/nanocontainers and rea...

Synthesis, Properties, and Applications of Hollow Micro-/Nanostructures

Hollow-structured mesoporous materials (HMMs), as a kind of mesoporous material with unique morphology, have been of great interest in the past decade because of the subtle combination of the hollow architecture with the mesoporous nanostructure. Benefitting from the merits of low density, large void space, large specific surface area, and, especially, the good biocompatibility, HMMs present promising application prospects in various fields, such as adsorption and storage, confined catalysis when catalytically active species are incorporated in the core and/or shell, controlled drug release, targeted drug delivery, and simultaneous diagnosis and therapy of cancers when the surface and/or core of the HMMs are functionalized with functional ligands and/or nanoparticles, and so on. In this review, recent progress in the design, synthesis, functionalization, and applications of hollow mesoporous materials are discussed. Two main synthetic strategies, soft-templating and hard-templating routes, are broadly sorted and described in detail. Progress in the main application aspects of HMMs, such as adsorption and storage, catalysis, and biomedicine, are also discussed in detail in this article, in terms of the unique features of the combined large void space in the core and the mesoporous network in the shell. Functionalization of the core and pore/outer surfaces with functional organic groups and/or nanoparticles, and their performance, are summarized in this article. Finally, an outlook of their prospects and challenges in terms of their controlled synthesis and scaled application is presented.

Hollow‐Structured Mesoporous Materials: Chemical Synthesis, Functionalization and Applications

Surface chemistry of porphyrins and phthalocyanines

The effect of solvent on a two-dimensional (2D) self-assembly of 1,3,5-tris(10-ethoxycarbonyldecyloxy)benzene (TECDB) has been systematically investigated by scanning tunneling microscopy. Through careful investigation of the solvent effect on molecular self-assembly, the solution concentration is also found to be a factor in assembly formation and transition. The same self-assembled structure is obtained using 1-phenyloctane, 1-octanol, n-tridecane, and n-tetradecane as a solvent under high solution concentrations. When the solution concentration decreases, a structural transition of the TECDB adlayer in 1-phenyloctane can be seen and n-tetradecane molecules coadsorb with TECDB molecules, forming two kinds of patterns. Furthermore, the affect of mixed solvents on the TECDB adlayer is also investigated. No self-assembled monolayer of TECDB is observed in 1,2,4-trichlorobenzene. After all samples are placed in ambient conditions over 24 h, a denser-packed structure appears, which corresponds to the result ...

Solvent-Induced Structural Transitions of a 1,3,5-Tris(10-ethoxycarbonyldecyloxy)benzene Assembly Revealed by Scanning Tunneling Microscopy

We report a single-step, emulsion-templating method using triblock copolymer poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) (PEG–PPG–PEG) as template, sodium silicate or tetraethylorthosilicate (TEOS) as precursor and n -octane and benzyl alcohol as cosolvents. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results revealed that ordered mesoporous silica hollow microspheres with thickness of shell about 50 nm and mean diameter 1 μm were prepared by changing the concentration of the reactant, pH and reaction time. Brunauer–Emmett–Teller (BET) analysis confirmed that silica hollow microspheres were porous. Generally, the hierarchical structures of mesoporous silica can be regulated from hollow spheres to solid particles by changing the concentration of benzyl alcohol. This methodology provides a versatile and effective route for preparation of mesoporous hollow materials.

Fabrication of mesoporous silica hollow spheres using triblock copolymer PEG–PPG–PEG as template

Investigating and regulating the self-assembly structure is of great importance in 2D crystal engineering and it is also gaining significant interest in surface studies. In this work, we systematically explored the variation of self-assembled patterns induced by the changeable side chain position. Moreover, molecules with different alkyl chain lengths (n = 15, 16) were also synthesized and probed for the purpose of understanding how an odd/even number of carbon atoms in the peripheral chains can affect the molecular adlayers. Structural isomers of bis-substituted anthraquinone derivatives 1,8-A-2OCn, 2,6-A-2OCn, 1,4-A-2OCn and 1,5-A-2OCn (n = 15, 16) were used and investigated by STM. 1,8-A-2OC16 and 1,8-A-2OC15 molecules adopted Z-like I and Linear I structures, respectively. 2,6-A-2OC16 and 2,6-A-2OC15 molecules were severally arranged in Linear II and Linear III configurations. 1,4-A-2OCn (n = 15, 16) molecules were staggered in a Z-like II fashion and 1,5-A-2OCn (n = 15, 16) molecules displayed a Linear IV nanostructure. Therefore, we arrive at a conclusion that self-assembly structures of anthraquinone isomers are chain-position-dependent, and designing isomeric compounds can be taken into consideration in regulating assembled structures. Besides, 2D nanopatterns of 1,8-A-2OCn and 2,6-A-2OCn can be regulated by the odd/even property of the side chains, but this is not the case for 1,4-A-2OCn and 1,5-A-2OCn, ascribed to the difference in driving forces for them. It is believed that the results are of significance to the alkyl chain position induced assembly configurations and surface research studies of structural isomers.

Wenli Deng

Papers

Solvent-Induced Structural Transitions of a 1,3,5-Tris(10-ethoxycarbonyldecyloxy)benzene Assembly Revealed by Scanning Tunneling Microscopy

Fabrication of mesoporous silica hollow spheres using triblock copolymer PEG–PPG–PEG as template

STM investigation of structural isomers: alkyl chain position induced self-assembly at the liquid/solid interface

Tuning the packing density of host molecular self-assemblies at the solid-liquid interface using guest molecule.

Highly efficient separation of surfactant stabilized water-in-oil emulsion based on surface energy gradient and flame retardancy.