Creation of polynucleotide-assisted molecular assemblies in organic solvents: general strategy toward the creation of artificial DNA-like nanoarchitectures

The influence of added polynucleotide on the gelation ability of nucleobase-appended organogelators was investigated. Uracil-appended cholesterol gelator formed a stable organogel in polar organic solvents such as n-butanol. It was found that the addition of the complementary polyadenylic acid (poly(A)) not only stabilizes the gel but also creates the helical structure in the original gel phase. Thymidine and thymine-appended gelators can form stable gel in apolar solvents, such as benzene, where poly(A)-lipid complex can act as a complementary template for the gelator molecules to create the fibrous composites. Based on these findings, we can conclude that self-assembling modes and gelation properties of nucleobase-appended organogelators are controllable by the addition of their complementary polynucleotide in organic solvents. We believe, therefore, that the present system can open the new paths to accelerate development of well-controlled one-dimensional molecular assembly systems, which would be indispensable for the creation of novel nanomaterials based on organic compounds.     

Super organogelator based on tetrathiafulvalene with four amide derivatives and its F4TCNQ charge-transfer complex

A new series of tetrathiafulvalene-based organogelators endowed with four hydrophobic chains incorporating amide groups was synthesised and characterised. The resulting transparent organogels were obtained with organic solvents such as cyclohexane, carbon tetrachloride and chlorobenzene. Additionally, the length of the alkyl chain influenced the gelation ability of organogels. Considering the results, we concluded that compounds were ‘super gelators’. Interestingly, the gelators reacted with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane to form charge-transfer (CT) complexes and binary organogels. ¹HNMR and FT-IR revealed that cooperation of hydrogen bonding, π–π and CT interactions was the main driving force for formation of the native and CT gels. The scanning electron microscopy images of native xerogels revealed characteristic gelation morphologies of three-dimensional cross-linking networks, whereas the morphologies of CT complex xerogels showed amorphous rod-like aggregates. X-ray powder diffraction studies suggested that both gelator and CT complex maintained lamellar molecular packing mode in organogel phase.     

Use of a self-assembling organogel as a reverse template in the preparation of imprinted porous polymer films

The concept of reverse templating of an organogel to form imprinted porous divinylbenzene polymer films with submicrometer channels is demonstrated. The organogel comprising a 1:1 molar ratio of two organogelators, that is, bis(2-ethylhexyl) sodium sulfosuccinate and 4-chlorophenol, was formed in divinylbenzene. The gel was cast as a thin film before UV polymerization of the solvent, and the organogelators were later removed by simple washing with water and isooctane. The integrity of the fiber bundles of the organogel was preserved during polymerization, and an exact hollow replica was obtained after the organogelators were leached away. It is easily possible to imprint gel fiber bundle structures into polymeric films through this technique. The gel can also be formed on macroporous substrates to yield supported thin porous polymeric films. With the incorporation of functional nanoparticles in AOT inverse micelles and hence the organogel, nanoparticle-containing porous polymer films exhibiting luminescence or magnetic properties are envisioned.     

Self-aggregates of natural chlorophylls and their synthetic analogues in aqueous media for making light-harvesting systems

Chlorophyll molecules are well organized for efficient energy or electron transfer in a light-harvesting antenna or a reaction center of photosynthetic organisms. In order to make effective photosynthetic mimics, self-aggregates of natural chlorophylls and their synthetic analogues have been prepared with the specific intermolecular interactions. Many studies have been carried out to prepare aqueous chlorophyll aggregates by use of surfactants or chemical modifications of the natural pigments, because chlorophylls basically are poorly soluble in water. This review article focuses on the preparation and function of aqueous chlorophyll aggregates used in making artificial photosynthetic systems.     

Photoreactions in hydrophobic pockets

Organic chemists have long recognized the important role that reaction media play in controlling rates, product distributions and stereochemistry. Recently, much effort has been directed towards the use of organized media to modify reactivity as compared to that in isotropic liquids. Judicious selection of a given organized system for a given application requires sufficient understanding of the properties of the organized media themselves and those of the substrate interactions therein. The multimolecular aggregation of hydrophobic solutes in water could prove to be of immense value to the organic chemist. The aggregation of simple olefinic systems in water, would enable photocycloaddition to compete efficiently with the various other modes of dacay of the short-lived excited state. Investigations of a few systems (dimerization of coumarins, stilbenes and alkylcinnamates), in our laboratory have been successful and they bring to light the significance of the hydrophobic effect. One of the most accepted manifestations of the hydrophobic interactions is probably the formation of micellar aggregates in aqueous solutions. Micelles provide a unique interface between aqueous and non-aqueous phases at which the non-polar solute can orient itself. While intermolecular orientation at micellar interfaces can provide selectivity in dimerization reactions, intramolecular orientation can be utilized to bring about selectivity in unimolecular photo-transformations. Such examples are presented.     

Theoretical investigation of the interactions between the π‐systems of molecular organic semiconductors and an analysis of the contributions of repulsion and electrostatics

A concept for the interactions between π‐systems is necessary to understand a number of phenomena in modern material sciences such as supramolecular properties and self‐assembly. In the present article, we investigate the intermolecular interaction energies between organic semiconductors with extended π‐systems using SAPT (symmetry‐adapted perturbation theory), LMO‐EDA (localized molecular orbital energy decomposition analysis), DFT‐D (density functional theory including dispersion corrections), and force‐field approaches. Both apolar organic molecules such as acenes and highly polarized π‐systems of merocyanines and squaraines were used to probe the influence of electrostatics on the shape of the potential energy surfaces (PES) governing the geometric structures of aggregates. Our results reveal that the shapes of the PESs result from variations in the short‐range, highly specific repulsion forces even for highly polar molecules. Using distributed quadrupoles, we show that it is nevertheless possible to mimic the intermolecular potentials with electrostatics. This is also possible with van‐der‐Waals potentials and a simple overlap‐based force‐field ansatz based on the overlap between p‐orbitals. © 2016 Wiley Periodicals, Inc.     

Supramolecular Chemistry of Bile Acid Derivatives: Formation of Gels

This article describes some of the exciting results obtained during the study of the gelation behavior of bile acid derivatives in the authors laboratory. The serendipitous discovery of charge-transfer interaction promoted gelation of organic solvents by (steroid)pyrene derivatives/TNF is presented. In this class of molecules, the effect of the location of the chiral center in chiral gelators on the overall chirality of the aggregates in the gel was studied. Also described are the aggregation behavior of bile acid based aqueous gelators which led us to postulate design principals to obtain bile acid based aqueous/organogelators.     

Supramolecular gels formed by amphiphilic low-molecular-weight gelators of N alpha,N epsilon-diacyl-L-lysine derivatives

Simple L-lysine derivatives, N(alpha)-hexanoyl-N(epsilon)-lauroyl-L-lysine (1), its alkali metal salts (2-4), and two-component compounds that consist of 1 with 2 to 4, were synthesized and their hydrogelation and organogelation properties were studied. Addition of hydrochloric acid to an aqueous solution of the alkali metal salt at room temperature produced a translucent hydrogel. This hydrogelation occurred as a result of a change in nanostructure from micelle-like aggregates to nanofibers, which was induced by partial protonation of the carboxylate to form a carboxylic acid. On the other hand, two-component low-molecular-weight gelators exhibited amphiphilic gelation behavior and functioned as not only hydrogelators, but also as organogelators. FTIR studies revealed that lateral ionic interactions between the carboxylate, alkali metal cation, carboxylic acid, and protons, in addition to hydrogen-bonding and van der Waals interactions play a very important role in hydrogelation. Furthermore, it was found that the water-insoluble carboxylic acid compound underwent a precipitation-dissolution transition with a thermally reversible sol-gel transition in the two-component gelator systems.     

Aggregation of hydrophobically modified polysaccharides in solution and at the air-water interface

The present article focuses on the comparative study of physicochemical properties of two ionic pullulan derivatives modified by 10 or 35 C8 chains per 100 anhydroglucose units, named CMP10C8 and CMP35C8, respectively. In aqueous solutions, these derivatives exhibited an associative behavior as evidenced by pyrene fluorescence spectroscopy. This phenomenon, which stems from intra- and/or intermolecular interactions between the hydrophobic groups grafted on the polymer backbone, results in the formation of more or less condensed aggregates depending on the C8 ratio and the ionic strength of the media. The hydrophobically modified pullulans also displayed surface properties. Their adsorption at the air-solution interface was assessed from surface tension measurements. The results showed that both hydrophobized polymers adsorb in a coil conformation occupying a large interfacial molecular area. The comparison of these molecular areas indicated that CMP35C8 adopts a more shrunken conformation at the interface than CMP10C8, due to stronger intramolecular interactions. The stability of the adsorbed monolayer under bulk dilution was investigated by ellipsometric measurements. Whereas bulk dilution had no effect on the stability of the adsorbed CMP35C8 film, it provoked significant changes in the adsorbed CMP10C8 monolayer. The stability of the CMP35C8 monolayers was attributed to the existence of intermolecular associations between the adsorbed coils.     

Organogels formed in various organic solvents by different alkyl L-phenylalanine dihydrazide derivatives

A new group of organogelators, L-phenylalanine dihydrazide derivatives were synthesized, which can self-assemble in various organic solvents and turned them into thermally reversible physical supramolecular organogels at extremely low concentrations (<2 wt %). Scanning electron microscopy measurements revealed that the gelator self-assembled into different supramolecular network structures in different solvents. FT-IR spectroscopy studies revealed that intermolecular hydrogen bonding between N-H and C=O of amide group and hydrophobic interaction of the alkyl groups were the driving forces for the formation of the gels. Based on the data of XRD and molecular modeling, one possible packing mode for the formation of organogelator aggregates was proposed.     

New polymer organogelators with L‐isoleucine and L‐valine as a gelation‐causing segment: Organogelation by a combination of supramolecular polymer and conventional polymer

New polymer organogelators, which are composed of poly(ethylene glycol), poly(propylene glycol), and poly(dimethylsiloxane)s as a polymer segment and L ‐isoleucine and L ‐valine derivatives as a gelation‐causing segment, were synthesized, and their organogelation properties were examined in organic solvents and oils. These polymer organogelators formed organogels in many organic solvents and oils, and their gels were thermally stable and had a high mechanical strength. Furthermore, the effects of the polymer backbone on the organogelation is discussed using FTIR spectroscopy, field emission scanning electron microscope observation, and analysis of thermal stability and strength of the organogel. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 353–361, 2008     

The magnetochemistry of verdazyl radical-based materials

Stable organic radicals have received much attention as building blocks for the construction of molecular magnetic materials because they are readily functionalized using modern synthetic techniques. In this context, the nitroxide radical family has been the dominant class of radicals in molecular magnetochemistry. However, other stable radical systems have also been explored. One such example is the verdazyl family of radicals. Their high chemical stability and synthetic versatility make verdazyls one of the more attractive alternatives to nitroxides in molecular magnet design. This article reviews the magnetism of verdazyl-based systems, including through-bond coupling in polyradicals, coordination complexes and intermolecular interactions in the solid state.     

Light‐Controlled Formation of Vesicles and Supramolecular Organogels by a Cholesterol‐Bearing Amphiphilic Molecular Switch

A new responsive material composed of an amphiphilic light‐switchable dithienylethene unit functionalized with a hydrophobic cholesterol unit and a hydrophilic poly(ethylene glycol)‐modified pyridinium group has been designed. This unique single‐molecule system shows responsive light‐switchable self‐assembly in both water and organic solvents. Light‐triggered reversible vesicle formation in aqueous solutions is reported. The molecule shows a different behavior in apolar aromatic solvents, in which light‐controlled formation of organogel fibers is observed. The light‐triggered aggregation behavior of this molecule demonstrates that control of a supramolecular structure with light can be achieved in both aqueous and organic media and that this ability can be present in a single molecule. This opens the way toward the effective development of new strategies in soft nanotechnology for applications in controlled chemical release systems.     

Elucidation of the Structure of Organic Solutions in Solvent Extraction by Combining Molecular Dynamics and X‐ray Scattering

Knowledge of the supramolecular structure of the organic phase containing amphiphilic ligand molecules is mandatory for full comprehension of ionic separation during solvent extraction. Existing structural models are based on simple geometric aggregates, but no consensus exists on the interaction potentials. Herein, we show that molecular dynamics crossed with scattering techniques offers key insight into the complex fluid involving weak interactions without any long‐range ordering. Two systems containing mono‐ or diamide extractants in heptane and contacted with an aqueous phase were selected as examples to demonstrate the advantages of coupling the two approaches for furthering fundamental studies on solvent extraction.     

Intermolecular interactions and spectral and luminescent properties of optical molecular sensors

The effect of intermolecular interactions of different types (universal interactions, H-bonding, electronic donor-acceptor interactions, and interactions with proton transfer) on the absorption and luminescence spectra of organic molecules of different classes, which are or can be used as optical molecular sensors, was considered. The classification of the types of intermolecular interactions and corresponding spectroscopic effects is given, which can be used, particular, in the development of optical sensors for detection of organic molecules in liquid and gaseous media.     

Organogelators based on TTF supramolecular assemblies: synthesis, characterization, and conductive property

A closely related family of organogelators 1-2 appended one or two electroactive tetrathiafulvalene (TTF) residues, has been designed and readily synthesized by Sonogashira reactions. These compounds can gelate a variety of organic solvents in view of multiple intermolecular interactions, and compounds 2 with two TTF subunits exhibit higher gelation ability than their corresponding 1. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigation of the xerogels from toluene gave a visual image showing that fibrillar aggregates are entangled in three-dimensional network structures. The columnar TTF cores stacking in the fiber, evidenced by the mixed-valence states absorption at around 2000 nm in ultraviolet-visible-near-infrared (UV-vis-NIR) spectra, provide an efficient pathway for the electron conduction. Upon oxidized by iodine, these xerogels exhibit semiconductive behaviors with moderate levels of conductivity. Additionally, the electrical conductivity of doped-xerogels 2 is 1 order of magnitude higher than that of 1 under identical conditions.     

赖氨酸环二肽有机凝胶因子的合成及其选择性凝胶化与染料吸附

在利用半胱氨酸修饰赖氨酸环二肽制备对称性四肽的过程中, 通过两种脱除Trt(三苯甲基)的方法分别得到含有Fmoc(芴甲氧羰基)的非环与大环四肽产物, 其结构得到了核磁、质谱、红外、元素分析等证实。 它们能使多种有机溶剂凝胶化, 且具有热可逆性, 由扫描电子显微镜(SEM)可观察到凝胶内部均为三维网络结构。 在体积分数低至0.1%的含氯有机溶剂/水两相体系中, 它们依然可以进行选择性凝胶化。 此外, 该有机凝胶干胶由于内部微纳米网络结构以及Fmoc基团的存在, 可以直接从水溶液中吸收多种染料分子, 且吸附能力随温度的升高而提高。     

An Overview of Molecular Packing Mode in Two‐Dimensional Organic Nanomaterials via Supramolecular Assembly

Two‐dimensional (2D) organic nanomaterials are attracting increasing research interest and expected to be the ideal candidate for future‐ proofed flexible electronics and biotechnologies. Owing to the complex molecular structures and multiple intermolecular interactions in organic systems, deeper understanding of rational molecular design and assembly principles is urgently required. In this review, a collection of molecular packing mode in the 2D organic nanomaterials via supramolecular assembly is presented, so as to help explicit the relationship among molecular structures, supramolecular interactions and molecular packing motifs in 2D assembly systems. We also provide a rational and accessible schematic model to demonstrate several typical kinds of molecular packing motifs for the prediction of the 2D morphology.     

Cyclohexane bis-urea compounds for the gelation of water and aqueous solutions

A new class of efficient hydrogelators has been developed by a simple modification of the peripheral substituents of cyclohexane bis-urea organogelators with hydrophilic hydroxy or amino functionalities. These bis-urea hydrogelators were synthesised in two or three steps using an alternative procedure to the common isocyanate method. Gelation was obtained with organic solvents, water and strongly basic aqueous solutions like 25% ammonia. Hydrogelation was found to depend on a delicate balance between the hydrophobicity of the alkyl chains, hydrophilicity of the terminal substituents and the enantiomeric purity of the compound. The hydrogels consisted of a network of fibers, in which all urea groups are involved in intermolecular hydrogen bonding. Most likely, gelation is driven by hydrophobic interactions of the methylene units, whereas hydrogen bond formation between the urea groups provides the necessary anisotropy of the aggregation and the high thermal stability of the gels.     

Molecular assemblies of perylene bisimide dyes in water

Perylene bisimides are among the most valuable functional dyes and have numerous potential applications. As a result of their chemical robustness, photostability, and outstanding optical and electronic properties, these dyes have been applied as pigments, fluorescence sensors, and n‐semiconductors in organic electronics and photovoltaics. Moreover, the extended quadrupolar π system of this class of dyes has facilitated the construction of numerous supramolecular architectures with fascinating photophysical properties. However, the supramolecular approach to the formation of perylene bisimide aggregates has been restricted mostly to organic media. Pleasingly, considerable progress has been made in the last few years in developing water‐soluble perylene bisimides and their application in aqueous media. This Review provides an up‐to‐date overview on the self‐assembly of perylene bisimides through π–π interactions in aqueous media. Synthetic strategies for the preparation of water‐soluble perylene bisimides and the influence of water on the π–π stacking of perylene bisimides as well as the resulting applications are discussed.