由凝胶因子形成的十四酸异丙酯超分子凝胶制备与表征

采用双十八烷基-L-苯丙氨酸(Bis18-L-Phe)为凝胶因子,制备了具有热可逆性的十四酸异丙酯(IPM)超分子凝胶。IPM凝胶相转变温度(Tgel)随Bis18-L-Phe浓度增大而增加。偏光显微镜(POM)显示在整个IPM凝胶中形成了相互缠绕的针状聚集体。FT-IR光谱分析表明Bis18-L-Phe分子间酰胺的氢键作用是IPM凝胶形成的一个重要驱动力。IPM凝胶动力学研究表明凝胶时间随Bis18-L-Phe浓度的增大而缩短,随着温度升高而延长,因此IPM凝胶时间可以通过温度和Bis18-L-Phe浓度调控。     

Influence of gelator structures on formation and stability of supramolecular hydrogels

A supramolecular hydrogel(defined as G1) formed from 1,2,4,5-benzene tetracarboxylic acid (BTCA) and 2-amino-3- hydroxypyridine possessed higher T_(gel) than that of another hydrogel(defined as G2) formed from BTCA and 3-hydroxypyridine. Based on the analysis of their xerogels by ~1H NMR,IR and XRD,the higher stability of G1 was attributed to the formation of stronger hydrogen binding enhanced by the ortho amino group of 2-amino-3-hydroxypyridine.     

Selective adsorption of D- and L-phenylalanine on molecularly-imprinted polymerized organogels formed using polymerizable gelator N-octadecyl maleamic acid

The polymerizable gelator N-octadecyl maleamic acid (ODMA) can self-assemble in selected polymerizable organic solvents, such as 2-hydroxyethyl methacrylate (HEMA) and methylacrylic acid (MAA) to form thermally stable polymerizable organogels. A mixture consisting of HEMA and MAA as the monomer and functional monomer, PEG dimethacrylates (PEG200DMA) as the crosslinker, BOC-L-phenylalanine (BPA) or L-phenylalanine ethyl ester (PEE) as the chiral templates, was gelatinized by ODMA firstly and subsequently polymerized by in situ UV irradiation or thermal initiation. The molecularly imprinted polymerized organogels were obtained after the removal of the templates through ethanol extraction. Selective adsorption of D- and L-phenylalanine was performed on the polymerized organogels. The results indicate rather high adsorption efficiency obtained for L-phenylalanine compared with that for D-phenylalanine, which was found to be dependent on the concentrations of ODMA, content of template, and the method of polymerization. Herein, the concentration of ODMA in the organogels played an important role for the adsorption efficiency of D- and L-phenylalanine.     

Effect of the peptide secondary structure on the peptide amphiphile supramolecular structure and interactions

Bottom-up fabrication of self-assembled nanomaterials requires control over forces and interactions between building blocks. We report here on the formation and architecture of supramolecular structures constructed from two different peptide amphiphiles. Inclusion of four alanines between a 16-mer peptide and a 16 carbon long aliphatic tail resulted in a secondary structure shift of the peptide headgroups from α helices to β sheets. A concomitant shift in self-assembled morphology from nanoribbons to core-shell worm-like micelles was observed by cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). In the presence of divalent magnesium ions, these a priori formed supramolecular structures interacted in distinct manners, highlighting the importance of peptide amphiphile design in self-assembly.     

Elucidating excited state electronic structure and intercomponent interactions in multicomponent and supramolecular systems

Rational design of supramolecular systems for application in photonic devices requires a clear understanding of both the mechanism of energy and electron transfer processes and how these processes can be manipulated. Central to achieving these goals is a detailed picture of their electronic structure and of the interaction between the constituent components. We review several approaches that have been taken towards gaining such understanding, with particular focus on the physical techniques employed. In the discussion, case studies are introduced to illustrate the key issues under consideration.     

Silica structures templated on fibers of tetraalkylphosphonium salt gelators in organogels

Phosphonium cations (18(n)RP(+)) consisting of three or four n-octadecyl chains and R = PhCH(2) or C(m)H(2)(m+1) (m = 1-5 or 12) when n = 3 and with iodide, bromide, chloride, fluoride, or perchlorate anions are used to gelate and polymerize solutions of 2-10 wt % tetraethyl orthosilicate in ethanol, benzene, tetrahydrofuran, and dimethyl sulfoxide using acid or base catalysis and under hydrolytic or nonhydrolytic conditions. These are the simplest low-molecular-mass organic gelator structures of which we are aware that have been able to template silica. The silica objects that are obtained after the hydrolytic sol-gel process include porous, spherulitic, and tubular objects in the size range of several micrometers to tens of nanometers. Their specific shapes and sizes depend on the specific conditions of the hydrolytic sol-gel process, including the nature of the catalyst. The electrostatic interaction between silicate intermediates and gelator strands is the driving force for templating. The template effect is strongly influenced by several factors, including (1) the competition between silicate/solvent and silicate/template interactions, (2) the period of the sol-gel process, (3) the hardness of the anion of the gelator salt, (4) the surface tension of the solvent, (5) and the sequence of drying and template removal processes. The nature of the R group influences the stability of the molecular gels but appears to have little effect on the silica morph obtained. In addition, it is shown in one case, where a direct comparison is possible, that the fibers of one of our phosphonium salts are a much more efficient template for silica than those of the corresponding ammonium salt (with its "harder" cationic center). The specific nature of the objects and the conditions under which they can be formed are discussed.     

Changes in the supramolecular structure of heat-resistant polyimide fibers in the course of thermal treatment

Changes in the supramolecular structure of heat-resistant fibers based on polyimide PM were studied by X-ray diffraction analysis and NMR spectroscopy.     

Molecular interactions and structure of a supramolecular arrangement of glucose oxidase and palladium nanoparticles

This paper presents studies about the molecular interactions and redox processes involved in the formation of palladium nanoparticles associated to glucose oxidase (GOx-PdNPs) in a supramolecular arrangement. The synthesis occurs in two steps, the Pd reduction and the formation of the 80 nm sized supramolecular aggregates containing multiples units of GOx associated to 3.5 nm sized PdNPs. During synthesis, GOx molecules interact with Pd salt leading to metal ion and FAD reduction probably via the thiol group of the cysteine 521 residue. For the growing of PdNPs, formic acid was necessary as a co-adjuvant reducing agent. Besides the contribution for the redox processes, GOx is also necessary for the NP stability preventing the formation of precipitates resulted from uncontrolled growing of NPs Cyclic voltammetry of the GOx-PdNPs demonstrated electroactivity of the bionanocomposite immobilized on ITO (indium-tin oxide) electrode surface and also the NP is partially blocked due to strong interaction GOx and the surface of PdNPs. Vibrational spectroscopy (FTIR) showed that significant structural changes occurred in GOx after the association to PdNP. These mechanistics and structural studies can contribute for modulation of bionanocomposites properties.     

A fluorescent supramolecular crosslinked polymer gel formed by crown ether based host-guest interactions and aggregation induced emission

Based on the combination of B21C7/dialkylammonium salt host-guest interactions and tetraphenylethylene(TPE)-based aggregation-induced emission(AIE) effect, a fluorescent supramolecular crosslinked polymer gel was successfully prepared. Compared with the solution of TPE-containing small molecules, this gel exhibited remarkable fluorescence enhancement due to the AIE effect of TPE units. The "gelation induced fluorescence emission" phenomenon can be explained by the hindered intramolecular rotation of phenyl rings of TPE. Because of the reversibility and stimuli-responsiveness of the B21C7/dialkylammonium salt host-guest interactions, the transition between the fluorescent supramolecular crosslinked polymer gel and the disassembled sol with very weak fluorescence can be realized by adding p H and thermal stimuli. This novel material contributes to the development of supramolecular chemistry, polymer science and fluorescent materials and offers a new method to construct functional supramolecular materials.     

Testing electronic structure methods for describing intermolecular H...H interactions in supramolecular chemistry

In this article a wide variety of computational approaches (molecular mechanics force fields, semiempirical formalisms, and hybrid methods, namely ONIOM calculations) have been used to calculate the energy and geometry of the supramolecular system 2-(2'-hydroxyphenyl)-4-methyloxazole (HPMO) encapsulated in beta-cyclodextrin (beta-CD). The main objective of the present study has been to examine the performance of these computational methods when describing the short range H. H intermolecular interactions between guest (HPMO) and host (beta-CD) molecules. The analyzed molecular mechanics methods do not provide unphysical short H...H contacts, but it is obvious that their applicability to the study of supramolecular systems is rather limited. For the semiempirical methods, MNDO is found to generate more reliable geometries than AM1, PM3 and the two recently developed schemes PDDG/MNDO and PDDG/PM3. MNDO results only give one slightly short H...H distance, whereas the NDDO formalisms with modifications of the Core Repulsion Function (CRF) via Gaussians exhibit a large number of short to very short and unphysical H...H intermolecular distances. In contrast, the PM5 method, which is the successor to PM3, gives very promising results. Our ONIOM calculations indicate that the unphysical optimized geometries from PM3 are retained when this semiempirical method is used as the low level layer in a QM:QM formulation. On the other hand, ab initio methods involving good enough basis sets, at least for the high level layer in a hybrid ONIOM calculation, behave well, but they may be too expensive in practice for most supramolecular chemistry applications. Finally, the performance of the evaluated computational methods has also been tested by evaluating the energetic difference between the two most stable conformations of the host(beta-CD)-guest(HPMO) system.     

Two novel quadruple hydrogen-bonding motifs: the formation of supramolecular polymers, vesicles, and organogels

Two new hydrazide-based quadruple hydrogen-bonding motifs are described. Dipodals based on these two motifs are revealed to form supramolecular polymers, which can further aggregate to form vesicles and/or organogels in hydrocarbons. The quadruple hydrogen-bonding motifs are characterized by the X-ray diffraction and (2D) ¹H NMR experiments, while the vesicles and organogels are evidenced by SEM, AFM, TEM, and fluorescent microscopy.     

Inclusion of DNA into organic gelator fibers made of amphipathic molecules and its controlled release

When methyl 4,6-O-(p-nitrobenzylidene)-alpha-D-glucopyranoside (p-NO(2)Glu) was dissolved in water, p-NO(2)Glu molecules self-assembled to form a fiber (elemental fiber), and as a result, the solution became a partially transparent gel. When an equal (or more) amount of DNA was added to the gel, a white and crystalline gel was obtained. Energy-dispersive X-ray spectroscopy coupled with TEM and confocal microscopy suggested that DNA was included in the gel fibers made of p-NO(2)Glu molecules. The results imply that p-NO(2)Glu molecules are self-assembled to form an elemental fiber and these elemental fibers and DNA are twisted together to form higher hierarchic fibers. When the complexed gel made of plasmid DNA (pDNA) and p-NO(2)Glu was added to E. coli T7 S30 extract solution, the pDNA had less expression ability compared with naked one. When we added methyl-beta-cyclodextrin (MbetaCyD), the expression rate was recovered with increasing added amount of MbetaCyD. The present paper shows inclusion and controlled release of DNA from a novel supporting material of DNA and that technology could play an important role in the development of localized approaches to gene therapy.     

Novel silver-containing supramolecular frameworks constructed by combination of coordination bonds and supramolecular interactions

The hydrothermal reactions of AgNO(3), 4,4'-bipy, and carboxylate ligands gave rise to three supramolecular architectures, namely [Ag(bipy)].H(2)SIPA.1/2bipy.H(2)O (1), [Ag(bipy)].1/2H(2)btec.H(2)O (2), and [Ag(bipy)](2).H(2)dpstc.2H(2)O (3) (H(3)SIPA = 5-sulfoisophthalic acid, bipy = 4,4'-bipyridine, H(4)btec = 1,2,4,5-benzenetetracarboxylic acid, H(4)dpstc = 3,3',4,4'-tetracarboxydiphenyl sulfone). All complexes are extended from Ag-bipy linear chains by the combination of coordination bonds and supramolecular interactions in two different approaches. Complexes 1 and 3 comprise two-dimensional frameworks. In the two complexes, a one-dimensional ladderlike structure is first formed by the connection of a Ag-bipy chain through hydrogen bonding between a free carboxylate/bipy ligand and weak coordinative interactions between a free carboxylate ligand and silver ion. The ladderlike structure is then extended to a two-dimensional layer architecture by pi...pi interactions between bipy ligands of the Ag-bipy chains. Complex 2 possesses a three-dimensional framework. The free H(2)btec(2)(-) ligands form a two-dimensional layer network by hydrogen-bonding interactions between protonated and deprotonated carboxylate groups; meanwhile, pi.pi interactions between bipy ligands of Ag-bipy chains also result in a two-dimensional layer. The two layers are further connected by weak Ag-O interactions to generate a three-dimensional supramolecular structure.     

Combination of orthogonal supramolecular interactions in polymeric architectures

Supramolecular polymers represent a highly interesting approach towards new "smart materials". A recent strategy includes the combination of different "orthogonal" non-covalent binding sites within one polymer system. Different functionalities can be introduced in a highly defined way by controlled self-assembly processes. This feature article presents highlights in the supramolecular polymer chemistry of multiple hydrogen-bonding, metal complexation (especially of bi- and terpyridines) and host-guest interactions as well as recent advances in combining these interactions in novel polymers.     

Solvent interactions in the allylation of piperidine

The reaction between allylbromide and piperidine has been studied in different protic and aprotic solvents. The reaction is first order with respect to [allylbromide] and [piperidine]. A correlation analysis of the rate data with solvent properties shows that polarity (Y), polarizability (P), and electrophilicity (E) of the solvent simultaneously influence the rate of reaction. From the regression analysis, information regarding the relative solvation of the reactants and the activated complex is obtained and a solvation model is proposed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 421–425, 2009     

Structural characterization and chemical response of a Ag-coordinated supramolecular gel

Supramolecular gels exhibit potential applications in the areas of sensors, nanodevices, drug and catalyst carriers, and so on. To develop a novel organogel with a multiresponse, we designed a component molecule bearing a pyridyl group for metal coordination and an amide group for the formation of intermolecular hydrogen bonding. A complex building block with a symmetrical structure was selectively constructed by the coordination of a silver cation to the organic component. The coordination existing in the complex and the hydrogen bonding existing between complexes were examined by IR, Raman, and 1H NMR spectroscopy. The gel formation and phase transition were examined by viscosity and differential scanning calorimetry measurements. The selection of metal ions for the formation of a gel has proved to be crucial as only the complex of a binary coordinated metal ion, Ag+, was found to form a gel structure. From the band shift of the L1 solution with different amounts of silver ion, the binding ratio of silver ion to L1 was estimated to be 1:2 and the calculated stability constant was 3.6 x 10(8) M(-2). On the basis of the analysis of X-ray diffraction and transmission electron microscopy results, we proposed a possible stacking structure of the complex in the fibrous aggregates. Of interest is that the organogel exhibits a 3-D network structure of a beltlike fiber composed of ordered lamellar arrangements of the coordinated complex and shows a rapid response to wide chemical stimulations such as anions I-, Br-, and Cl-, gases such as H(2)S and NH(3), and a change of pH.     

Solid-state NMR studies of weak interactions in supramolecular systems

The field of application of solid-state NMR to the study of supramolecular systems is growing rapidly, with many research groups involved in the development of techniques for the study of crystalline and amorphous phases. This Feature Article aims to provide an overview of the recent contributions of our research group to this field, paying particular attention to the study of the weak interactions such as hydrogen bonds in supramolecular systems through solid-state NMR investigations. The structure and dynamic behaviour of selected host-guest systems will be also discussed.     

Solution and solid-state interactions in a supramolecular ruthenium photosensitizer-polyoxometalate aggregate

The intermolecular interactions between a ruthenium-based photosensitizer ([Ru(tbbpy)(2)(biH(2))](2+)) and a molecular metal oxide ([β-Mo(8)O(26)](4-)) are investigated in solution and in the solid state. The supramolecular interactions were studied using (1)H-NMR, UV-Vis and emission spectroscopy, ESI mass spectrometry and single-crystal X-ray diffraction. The formation of supramolecular aggregates was observed both in the crystal lattice and in solution. In addition, it is shown that aggregation in solution can be controlled by the competitive formation of ion pairs.     

Two-phase structure of polyelectrolyte gel/surfactant complexes

The behavior of lightly cross-linked polyelectrolyte hydrogel swelling in the solution of oppositely charged surfactants is studied theoretically. It is shown that if there is a lack of surfactant in the solution intragel separation into two phases differing in swelling ratios and surfactant content can take place. The surfactant ions concentrate and form micelles in a part of the gel and this part collapses while the rest of the gel remains swollen. The two-phase region widens with an increase of ionization degree of the gel subchains.