Hydrogen bonding-mediated self-assembly of square and triangular metallocyclophanes

Intramolecular three-centered hydrogen bonding has been used to induce dipyridyl anthranilamide 5 and diphenylacetylene anthranilamide 11 to adopt rigid straight conformation. Compound 5 reacted with Pd(dppp)(OTf)₂ (12a) or Pt(dppp)(OTf)₂ (12b) in dichloromethane to afford square metallocyclophanes 13a and 13b in 70% and 40% yield, respectively. In contrast, the reaction of 11 with 12b in dichloromethane gave triangular metallocyclophane 14 in 15% yield.     

Hydrogen bonding-mediated self-assembly of rigid and planar metallocyclophanes and their recognition for mono- and disaccharides

A hydrogen bonding approach has been developed to facilitate the self-assembly of a new series of rigid and planar metallocyclophanes. Two new anthranilamide derivatives 1 and 2, which are incorporated with two acetylene units, respectively, have been synthesized and characterized. X-ray analysis (for 1), 1D and 2D ¹H NMR and IR experiments reveal that, due to the formation of intramolecular three-centered hydrogen bonding, both compounds adopt rigid and planar conformations with the two acetylene units located at the same side of the anthranilamide skeleton. Two new metallocyclophanes 17 and 18 have been constructed in moderate yields from the reaction of 1 and 2 with trans-Pt(PEt₃)₂Cl₂, respectively, in dichloromethane in the presence of diethylamine and cupric chloride. Fluorescent and ¹H NMR investigations reveal that both 17 and 18 can efficiently complex mono- and disaccharide derivatives in chloroform, with a binding selectivity for disaccharides, which is driven by intermolecular hydrogen bonding.     

Tailoring the Self-assembly of Melamine on Au (111) via Doping with Cu Atoms

The doping effect of Cu on the self-assembly film of melamine on an Au(111) surface has been investigated with scanning tunneling microscopy (STM). The evaporated Cu adatoms occupy the positions underneath the amino groups and change the hydrogen bonding pattern between the melamine molecules. Accordingly, the self-assembly structure has changed stepwise from a well-defined honeycomb into a track-like and then a triangular structure depending on the amount of Cu adatoms. The interaction between Cu adatom and melamine is moderate thus the Cu adatoms can be released upon mild heating to around 100℃. These findings are different from previous observations of either the coordination assembly or the physically trapped metal adatoms.     

Anarchy in the solid state: structural dependence on glass-forming ability in triazine-based molecular glasses

We have recently shown that molecular glasses, small molecules capable of readily forming glassy solids as opposed to crystals, can be designed by exploiting molecular association through strong and directional intermolecular interactions, as exemplified by several members of the bis(mexylamino)triazine family. Herein, 43 new bis(mexylamino)triazine derivatives were synthesized, 31 of which have been found to spontaneously form glassy phases and did not crystallize upon heating.     

Properties of large organic molecules on metal surfaces

The adsorption of large organic molecules on surfaces has recently been the subject of intensive investigation, both because of the molecules’ intrinsic physical and chemical properties, and for prospective applications in the emerging field of nanotechnology. Certain complex molecules are considered good candidates as basic building blocks for molecular electronics and nanomechanical devices. In general, molecular ordering on a surface is controlled by a delicate balance between intermolecular forces and molecule–substrate interactions. Under certain conditions, these interactions can be controlled to some extent, and sometimes even tuned by the appropriate choice of substrate material and symmetry. Several studies have indicated that, upon molecular adsorption, surfaces do not always behave as static templates, but may rearrange dramatically to accommodate different molecular species. In this context, it has been demonstrated that the scanning tunnelling microscope (STM) is a very powerful tool for exploring the atomic-scale realm of surfaces, and for investigating adsorbate–surface interactions. By means of high-resolution, fast-scanning STM unprecedented new insight was recently achieved into a number of fundamental processes related to the interaction of largish molecules with surfaces such as molecular diffusion, bonding of adsorbates on surfaces, and molecular self-assembly. In addition to the normal imaging mode, the STM tip can also be employed to manipulate single atoms and molecules in a bottom–up fashion, collectively or one at a time. In this way, molecule-induced surface restructuring processes can be revealed directly and nanostructures can be engineered with atomic precision to study surface quantum phenomena of fundamental interest. Here we will present a short review of some recent results, several of which were obtained by our group, in which several features of the complex interaction between large organic molecules and metal surfaces were revealed. The focus is on experiments performed using STM and other complementary surface-sensitive techniques.     

Hydrogen bonding-mediated self-assembly of anthranilamide-based homodimers through preorganization of the amido and ureido binding sites

The self-assembly of a novel series of hydrogen bonding-mediated homodimers in chloroform-d has been described. Six anthranilamide-based monomers have been prepared, in which two self-binding formamido, trifluoroacetamido, acetamido, butyl or methyl ureido units are introduced at the two ends of the backbones. Quantitative ¹H NMR investigations in chloroform-d revealed that the formamido and ureido units are more efficient than acetamido to induce the formation of stable homodimers. The association constants of all the new homodimers have been determined by ¹H NMR dilution method. Multiply hydrogen bonding-driven binding patterns have been proposed for the homodimers. It is also found that ureido-derived homodimers do not adopt common linear binding pattern observed for simple urea derivatives.     

Micelle-like particles based on self-assembly of rod-like FPEEK and coil-like PVA

The self-assembly of a rod-like polymer [hydroxyl-terminated trifluoromethylphenyl-substituted fluorinated poly(ether ether ketone) (FPEEK)] and a coil-like polymer (polyvinyl alcohol, PVA) in water has been studied. It was found that this polymer pair could form micelle-like particles. Hydrogen bonding between the hydroxy groups of rod-like FPEEK and coil-like PVA, and parallel packing of the rod-like FPEEK are the main factors affecting the formation of micelle-like particles. Over a broad range, when the FPEEK/PVA mass ratio or the tetrahydrofolate/H₂O volume ratio is decreased, the diameter of micelle-like particles is decreased. The diameters (around 250 nm) of micelle-like particles measured by scanning electron microscopy and dynamic light scattering are similar, but are different from that measured by transmission electron microscopy (around 150 nm). Thus, it can be concluded that micelle-like particles have a core–shell structure and the cores of micelles are composed of FPEEK, and that the shells of micelles are composed of PVA. When polyethylene glycol was used instead of PVA, micelle-like particles were also formed, but the average diameter was bigger than that of the particles formed by PVA and FPEEK. This work was supported by the National Nature Science Foundation of China (50203004).     

Hydrogen bonded aromatic hydrazide foldamers for the self-assembly of vesicles and gels

This paper describes an investigation of the structural and side-chain factors for the formation of vesicles and gels by hydrogen bonding-mediated aromatic hydrazide foldamers. Six foldamers and one straight analog that bear discrete side chains have been synthesized. SEM and AFM studies reveal that the molecules with the appended 2-(2-(dialkyl-amino)-2-oxoethylamino)-2-oxoethoxyl chains form vesicles, hydrogels or organogels, depending on the solvents. Both the inner amide units and the terminal N,N-dialkylamide units in the chains are revealed to play essential roles in controlling the self-assembly. The former facilitates it by forming the intermolecular hydrogen bonding, while the latter modulates it by providing solubility and balancing the hydrophobicity of the whole molecules in solvents of varying polarity.     

Advances in self-assembly and regulation of aromatic carboxylic acid derivatives at HOPG interface

Aromatic carboxylic acid self-assembly has been a hot research field for many scientists due to its strong coordination ability and flexible coordination mode.The hydrogen bond formed between aromatic carboxylic acids is a strong intermolecular force and has directionality and saturation,which plays a very important role in the self-assembly and regulation of aromatic carboxylic acids.In this review,we introduce surface organization formed by aromatic carboxylic acids with the aid of scanning tunneling microscopy(STM).These two-dimensional structures include molecular templates,host-guest systems,and photo-isomerization structures.We also emphasize the thermodynamics and dynamics,which are important research topics of current and future study.     

Molecular capsules of tetrakis(N-hydantoinylimino)cavitand: Selective encapsulation of 1,4-diiodobenzene

Resorcin[4]arene-based iminocavitand 2 with four hydantoinyl moieties was designed and synthesized. This cavitand 2 self-assembled into thermally stable molecular capsules G@2₂ in the presence of suitable guests through 8 intermolecular hydrogen bonds of imide NH?OC, two for each four paired hydantoinyl units. Molecular capsule 2₂ showed selective complexation for p-disubstituted benzenes, especially for 1,4-diiodobenzene.     

Strapped porphyrin rosettes based on the melamine-cyanuric acid motif. Self-assembly and supramolecular recognition

This paper describes studies on the synthesis, self-assembly behavior, and complexing properties of several strapped porphyrin-incorporated melamine-cyanuric or melamine-barbiturate-based rosette supramolecules in chloroform-d. Strapped porpyrin cyanuric acid H₂1 and its Zn (II) complex Zn1 were designed and synthesized. Both H₂1 and Zn1 could combine melamine derivatives 11 or 12 to afford porphyrin rosettes, which are more stable than the model rosette initially reported by Whitesides due to the larger size of the porphyrin unit. The new porphyrin rosettes could efficiently complex tripyridyl derivative 13 through intermolecular, cooperative coordination between Zn (II) and pyridine. Two new pyridine-bearing barbiturates 18a and 18b were also synthesized. Mixing the identical amount of 18a or 18b with 11 or 12 in chloroform-d led to the formation of new isomeric rosettes as a result of different orientation of the pyridine unit of 18a or 18b in the rosettes. ¹H NMR study also revealed that porpyrin-bearing rosette Zn1₃·11₃ could complex pyridine-bearing rosette 11₃·18a₃, leading to the formation of new two-layer-typed supramolecular architectures.     

Coordination-driven self-assembly in a single pot

New multinuclear discrete heteroleptic complexes have been synthesized by mixing Pd(II), 2,2′-bipyridine and N,N′-(1,2-phenylene)diisonicotinamide in a single pot as a new approach. A dimeric molecular rhombus and a trimer in equilibrium are obtained where the dimer is the major product. Similar equilibrium is also observed when classical method is employed for the synthesis. The equilibrium is shifted exclusively in favour of the dimer upon addition of benzene. The complexes are characterized by NMR and ESI-MS methods. Crystal structure of the benzene encapsulated rhombus is presented.     

Influence of functional groups on the self-assembly of liquid crystals

Functional groups in the molecule play an important role in the molecular o rganization process.To reveal the influence of functional groups on the self-assembly at interface,herein,the self-assembly structures of three liquid crystal molecules,which only differ in the functional groups,are explicitly characterized by using scanning tunneling microscopy(STM).The high-resolution STM images demonstrate the difference between the supramolecular assembly structures of three liquid crystal molecules,which attribute to the hydrogen bonding interaction and π-π stacking interaction between different functional groups.The density functional theory(DFT) results also confirm the influence of these functional groups on the self-assemblies.The effort on the self-assembly of liquid crystal molecules at interface could enhance the understanding of the supramolecular assembly mechanism and benefit the further application of liquid crystals.     

分子尺度电致发光器件

近年来,有机单分子电致发光研究在材料和器件方面取得了突破,是分子电子学新兴的研究方向之一。本文综述了扫描隧道显微镜法、纳米间隙电极法等测量单分子尺度电致发光的研究进展。根据电致发光谱图,可以确定分子器件的发光类型,并得到单个分子的指纹信息。     

Adsorption behavior and photoelectric response characteristics of bacteriorhodopsin thin films fabricated by self-assembly technique

The characteristics of bacteriorhodopsin (bR)-based thin films fabricated by self-assembly (SA) technique were investigated. Self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (11-MUA) were spontaneously formed onto a pretreated gold substrate by soaking it into the ethanolic solution of 11-MUA, and used as a template for the adsorption of bR. Using poly- -lysine as a bridging molecule for bR adsorption onto SAMs of 11-MUA, bR-embedded purple membrane fragments were adsorbed by electrostatic attractive force. By ellipsometry and atomic force microscopy, the properties of the prepared bR-based thin films were investigated with the various fabrication conditions, such as bR suspension concentration and pH. An artificial photoreceptor was then fabricated with a sandwich-type structure of ITO/electrolyte gel/bR-based thin films/gold substrate. According to the monochromatic light illumination (560 nm) using Xenon lamp system, photoelectric responses of the fabricated photoreceptor were detected and analyzed. The stability of photoreceptors composed of the bR films fabricated by different technique was also examined over the period of 60 days. It is concluded that the SA technique could be usefully applied to the protein-based thin films preparation for the development of bioelectronic devices.     

Construction of two-dimensional (2D) H-bonded supramolecular nanostructures studied by STM

In this review,a group of two-dimensional（2D） hydrogen-bonded supramolecular networks developed in our laboratory are discussed.Our attention is mainly focused on:（1） recognition of Fe³⁺ through twocomponent molecular networks;（2） site-selective fabrication of 2D fullerene arrays;and（3） fabrication of the nanoporous structure regulated by photoisomerization reaction process.It is envisioned that special supramolecular nanostructures,through H-bonding interactions,can be constructed or reconstructed to be further investigated toward the research of multi-component systems,molecule recognition,single molecular switches,and host-guest supramolecular chemistry.     

Square-planar nickel(II) complexes with a tridentate Schiff base and monodentate heterocycles: self-assembly to dimeric and one-dimensional array via hydrogen bonding

Square-planar nickel(II) complex with tridentate ONO-donor 4-[(2-hydroxyphenyl)imino]-2-pentanone (H₂hpac) and imidazole (Himdz) are reported. The complex was synthesized in moderate yield by reacting Ni(O₂CCH₃)₂ · 4H₂O, H₂hpac and imidazole in 1 : 1 : 1 mole ratio and characterized by elemental analysis, IR, ¹H NMR spectroscopy. An X-ray structure determination of the complex has been completed. In the solid state, a one-dimensional assembly of the [Ni(hpac)(Himdz)] molecules is formed via intermolecular hydrogen bonds between the imidazole N–H groups and the coordinated hydroxyphenyl-O atoms.     

Benzyl and tert-butyl carbamate derivatives of 1,ω-amino acids as simple yet efficient gelators

We report the synthesis and a study of the gelation properties of a series of N-protected long-chain amino acids. Especially, benzyl and tert-butyl carbamate derivatives of 11-aminoundecanoic acid in their deprotonated form can gelate polar organic solvents and water at very low concentration (less than 5 mM). This is explained by the contribution of multiple forces—H-bond, van der Waals and ionic interactions—in the gel aggregate formation and stabilization, which is confirmed by the experimental data. Among the series of compounds investigated, only a dimer of 11-aminoundecanoic acid is capable of gelating toluene, which stems from the increased number of hydrogen bonding sites in the main aliphatic chain.     

Structure and hydrogen bonding in polyhydrated complexes of guanine

Abstract Molecular structure of complexes of guanine with 12, 13, 16, and 17 water molecules were calculated using B3LYP/6-311G(d,p) level of theory. Interaction with water results in some deformation of geometrical parameters of guanine, which can be described as contribution of zwitter-ionic resonant form into the structure of DNA base. Saturation of water binding sites within guanine creates possibilities for the formation of the N···H–O hydrogen bond where the nitrogen atom of amino group acts as proton acceptor. The NBO analysis of guanine–water interactions reveals that hydrogen bonds involving the N(3) and N(7) atoms of guanine represent a case of mixed N···H–O/π···H–O hydrogen bonds where contribution of π-system into total energy of interaction varies from 3% to 41%. This contribution significantly depends on orientation of the hydrogen atom of water molecule with respect to plane of purine bicycle and influence of neighboring water molecules. Graphical Abstract      

BIC和HA体系的氢键驱动的HOPG表面手性自组装分子动力学模拟

5-（苄氧基）-间苯二甲酸衍生物（BIC）与庚醇（HA）分子在高定向热解石墨（HOPG）表面吸附,通过氢键等弱相互作用会形成具有手性特征的二维网络结构。对该过程进行分子动力学模拟,通过几何结构、能量、氢键数目、氢键键长、氢键键角等特征性参数的定量分析,并与实验结果比照,进行氢键与手性自组装结构的形成趋势和稳定性的相关性研究。