Supramolecular polymers having chiral interactions

Poly(L-glutamate) having amphiphilic side chains was designed as membrane materials for optical resolution of α-amino acids. Solvent-cast films of the poly(glutamate) (PLG) had a self-ordered structure containing α-helix of the poly(L-glutamate). Optical resolutions of various amino acids were carried out through the thin membranes of the amphiphilic poly(L-glutamate). Racemic mixtures of Tryptophan were completely separated through the membrane. Mechanism of the optical resolutions was investigated in terms of molecular recognitions of racemic Tryptophan by the ordered structure of the membrane. Polymers having pendant PLG and α-amino acids were synthesized and their permeation behaviors were investigated.     

Supramolecular polymers based on cyclodextrins

Two types of supramolecular polymers based on cyclodextrins were prepared. One was a host–guest type, and the other was a polyrotaxane type. When a guest part was covalently attached to cyclodextrin, they formed supramolecular dimers, a cyclic daisy chain, supramolecular oligomers, and polymers. t-Boc-cinnamamide-α-cyclodextrin was found to form chiral supramolecular polymers in aqueous solutions. Supramolecular poly[2]rotaxane polymers and supramolecular α,β-cyclodextrin copolymers were obtained. Polyrotaxanes containing β-cyclodextrin or γ-cyclodextrin were prepared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5113–5119, 2006     

Supramolecular polymers based on dative boron-nitrogen bonds

Heteroditopic monomers containing an arylboronate ester and a dialkyl-4-aminopyridine group aggregate via dative boron-nitrogen bonds to give main chain supramolecular polymers. The degree of polymerization can be tuned by changing the electronic and steric properties of the boronate ester.     

Host-guest interactions with hydrophobic cyclophanes in aqueous media

Hydrophobic cyclophanes containing amide nitrogens in a rigid macrocyclic skeleton and flexible hydrocarbon chains, branched out at such nitrogen atoms, were prepared and their substrate-binding behavior was studied in aqueous media. the fluorescence spectroscopy was primarily adopted for the investigation of host-guest interactions by the aid of various hydrophobic probes. These host molecules provide cavities that are deep and hydrophobic enough to incorporate hydrophobic substrates of various bulkiness through an induced-fit mechanism originated from the flexible character of the alkyl branches. In addition to the hydrophobic interaction, the roles of electrostatic and charge-transfer interactions in molecular recognitions were clarified. Much hydrophobic, less polar, and highly viscous binding sites for hydrophobic guest molecules were provided by the octopus azaparacyclophane bearing eight hydrocarbon chains and the tetraazacyclotetradecane-capped azaparacyclophane having four flexible hydrocarbon chains connecting both macrocycles.     

Supramolecular polymers fabricated by orthogonal self-assembly based on multiple hydrogen bonding and macrocyclic host–guest interactions

Supramolecular polymers constructed by orthogonal self-assembly based on multiple hydrogen bonding and macrocyclic host-guest interactions have received increasing attention due to their elegant structures,outstanding properties,and potential applications.Hydrogen bonding endows these supramolecular polymers with good adaptability and reversibility,while macrocyclic host-guest interactions give them good selectivity and versatile stimuli-responsiveness.Therefore,functional supramolecular polymers fabricated by these two highly specific,noninterfering interactions in an orthogonal way have shown wide applications in the fields of molecular machines,electronics,soft materials,etc.In this review,we discuss the recent advances of functional supramolecular polymers fabricated by orthogonal self-assembly based on multiple hydroge n bonding and host-guest interactions.In particular,we focus on crown ether-and pillar[n]arene-based supramolecular polymers due to their compatibility with multiple hydrogen bonds in organic solution.The fabrication strategies,interesting properties,and potential applications of these advanced supramolecular materials are mainly concerned.     

Supramolecular chemosensor for selective detection of iron in aqueous medium

We have successfully developed a ‘turn-on’ colorimetric chemosensor for Fe³⁺ based on 1,10-phenanthroline. An amide derivative of 1,10-phenanthroline 4 was developed for the selective recognition of Fe³⁺ over Co²⁺, Cr³⁺, Cu²⁺, Mn²⁺, Ni²⁺, Ag⁺ and Zn²⁺ and could measure Fe³⁺ concentration in the range of 15–210 μM by UV–vis spectroscopy. Moreover, the addition of Fe³⁺ to a colourless solution of 4 turned its colour to light pink, indicating that 4 is capable of detecting Fe³⁺ by the naked eye. Compound 4 exhibits a major absorption band centred at 268 which shifted to 278 nm after addition of Fe³⁺, and a shoulder band around 514 nm was also observed. The complexation of Fe³⁺ with 4 was analysed at a different pH and favourable binding was observed at pH 6.2.     

Supramolecular coordination chemistry: the synergistic effect of serendipity and rational design

Supramolecular coordination compounds bear exceptional advantages over their organic counterparts. They are available in one-pot reactions and in high yields and display physical properties that are generally inaccessible with organic species. Moreover, their weak, reversible, noncovalent bonding interactions facilitate error checking and self-correction. This Review emphasizes the achievements in supramolecular coordination chemistry initiated by serendipity and their materialization based on rational design. The recognition of similarities in the synthesis of different supramolecular assemblies allows prediction of potential results in related cases. Supramolecular synthesis obeys guidelines comparable to the "lead sheet" used by small jazz ensembles for improvisation and therefore more often leads to unpredicted results. The combination of detailed symmetry considerations with the basic rules of coordination chemistry has only recently allowed for the design of rational strategies for the construction of a variety of nanosized systems with specified size and shape.     

Amphiphilic copolymers in aqueous medium: Characterization of the structure of the hydrophobic microdomains

The behaviour of new cationic amphiphilic copolymers derived from 3-vinylpyridine was studied in aqueous medium. The formation of hydrophobic microdomains was evidenced by fluorescence spectroscopy using a molecular rotor as a fluorescent probe and their structure was visualized by cryo-transmission electron microcospy (Cryo-TEM). The parameters (shape and size) obtained from Cryo-TEM were discussed in relation to the copolymers composition and to the local viscosity defined by the rotor fluorescence quantum yield.     

Supramolecular binding of protonated amines to a receptor microgel in aqueous medium

Polyanionic microgels containing negatively charged tetrazole binding sites show supramolecular binding of various protonated amines (e.g. dibucaine and spermine) in a competitive aqueous medium at millimolar concentration.     

Approaches to the rational design of molecularly imprinted polymers

In our experience the efficient design of molecularly imprinted polymer (MIPs) for novel templates has proved difficult. Following commonly used imprinting protocols, MIPs designed against one template show both a lack of capacity and poor specificity for rebinding either the template or structurally similar analytes. Optimisation methods that involve changing one factor at a time can be laborious.A novel approach for the optimisation of MIPs using chemometrics is described. Sulfonamides, common drug residues in foodstuffs, were used as the model analytes with a methacrylic acid/ethylene glycol dimethacrylate MIP. To avoid the inaccuracies in measurement caused by template bleed a multi-analyte competition rebind assay was developed to select suitable sulfonamides to be used as the template for the MIP, and for the rebind analyte in the chemometric optimisation study. The rebinding efficiencies were monitored by HPLC. The template sulfonamide was selected as sulfamethazine (SMZ), and the rebind analyte as sulfadimethoxine (SDIM). The template:monomer:cross-linker (T:M:X) ratio of the SMZ block MIP was then optimised using a three-level full factorial design to predict a MIP with the highest rebind capacity. On synthesis this was 38.8% for SDIM in a solid phase extraction (SPE) application agreeing with the predication. The factorial design was further utilised to predict an optimum T:M:X ratio for the production of a class specific MIP, capable of binding a range of sulfonamides simultaneously. The predicted optimum T:M:X ratios of (1:10:55) and (1:10:10) were found to be different to commonly used ratios from the MIP literature.     

Preparation of stable aqueous suspension of a hydrophobic drug with polymers

Pharmaceutical preparation of a hydrophobic aldose reductase inhibitor 5-(3-ethoxy-4-pentyloxyphenyl)-2,4-thiazolidinedione (CT112) was investigated. CT112 dissolved in a basic solution with different kinds of polymers was neutralized by acid to obtain a suspension preparation. In particular, the addition of a polymer, hydroxypropyl methyl cellulose (HPMC) provided a stable CT112 suspension with a homogeneous particle size, and there seemed to be an optimal concentration of HPMC for the stable suspension. The addition of polysorbate 80 brought higher CT112 solubility in water, but did not provide a stable suspension. X-ray diffraction, IR spectrum, and thermal analysis revealed that the particles in the suspension with HPMC had lower degree of crystallinity, less hydrophobic particle surface, and lower melting point and decreased fusion enthalpy than the suspension without HPMC. These results suggested that the highly stable CT112 suspension could be attained by the adsorption of the polymer.     

A supramolecular model of hydrophobic interactions in aqueous solutions of acenes

The optical spectra of aqueous suspensions of tetracene (obtained by heating crystals in water) and 9,10-bromoanthracene (obtained by mixing alcoholic solutions of the compound with water) were studied. Both optical pictures were turbidity spectra related to the formation of comparatively large colloidal light scatterers superimposed upon the absorption bands of light hydrophobic ensembles; the absorption bands of free acene molecules were absent. An analysis of the optical spectra and the construction of models with the use of molecular mechanics programs led us to conclude that light hydrophobic ensembles were molecular dimers comparatively stable in the aqueous phase because of the formation of hydration capsules around them. A model of spontaneous dispersion of crystalline tetracene in water under heating was suggested. The model included the stages of the emergence of tetracene molecules from the surface of crystals and their hydration in water layers adjacent to crystals, formation of molecular dimers on the surface of crystals, and diffusion of dimers into the bulk phase, where they experienced clusterization with the formation and sedimentation of fairly large light scattering colloidal particles.     

Supramolecular ensembles based on the donor-acceptor interactions of porphyrins

Dimeric and trimeric supramolecular structures were synthesized on the basis of donor-acceptor interactions of manganese(III) and tin(IV) complexes of 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrin with 5-(4′-oxyphenyl)-15-phenyl-3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrin. The structure of the compounds was studied by NMR spectroscopy and TLC.     

基于柱芳烃主客体作用构筑的超分子纳米载体

近年来,基于主客体相互作用的超分子纳米载体因其独特的自组装特性在癌症治疗领域引起了广泛的关注。柱芳烃作为一种新型的大环分子,因其独特的化学结构和优越的主客体包合能力而成为近年来研究的热点。本文根据不同的治疗机制综述了柱状链纳米载体及其在化疗、光动力治疗、联合治疗等领域的应用。在此基础上,展望了柱芳烃基纳米载体的研究方向和发展趋势。     

Deuterium isotope effects on hydrophobic interactions: the importance of dispersion interactions in the hydrophobic phase

Hydrogen/deuterium isotope effects on hydrophobic binding were examined by means of reversed-phase chromatographic separation of protiated and deuterated isotopologue pairs for a set of 10 nonpolar and low-polarity compounds with 10 stationary phases having alkyl and aryl groups bonded to the silica surface. It was found that protiated compounds bind to nonpolar moieties attached to silica more strongly than deuterated ones, demonstrating that the CH/CD bonds of the solutes are weakened or have less restricted motions when bound in the stationary phase compared with the aqueous solvent (mobile phase). The interactions responsible for binding have been further characterized by studies of the effects of changes in mobile phase composition, temperature dependence of binding, and QSRR (quantitative structure-chromatographic retention relationship) analysis, demonstrating the importance of enthalpic effects in binding and differentiation between the isotopologues. To explain our results showing the active role of the hydrophobic (stationary) phase we propose a plausible model that includes specific contributions from aromatic edge-to-face attractive interactions and attractive interactions of aliphatic groups with the pi clouds of aromatic groups present as the solute or in the stationary phase.     

Toward the rational design of lanthanide coordination polymers: a new topological approach

The implementation of four bidentate building blocks into a high-denticity linker with a flexible spacer leads to a predisposed ligand that allows one to direct the self-assembly of 1D functional coordination polymers. This is illustrated by the assembly under mild conditions of the luminescent metal-organic framework [Tb(Htpabn)] . 14H2O infinity (1; H4tpabn = N,N,N',N'-tetrakis[(6-carboxypyridin-2-yl)methyl]butylenediamine). The X-ray crystal structure shows that the monoprotonated Htpabn binds two equivalent lanthanide ions to form a one-directional staircase chain. The high ligand denticity prevents solvent coordination and leads to a high luminescence quantum yield (Q = 39%), which is maintained after solvent removal.     

Particle-macromolecule interactions in aqueous solutions Part 1: Solution and flow behaviour of polyvinylalcohol in an aqueous medium

Summary Shear and concentration dependent flow studies on solutions of a narrow molecular weight fraction of 90.3 % hydrolysed polyvinylalcohol are reported, together with precise density measurements on these same solutions. From the derived flowing volume and partial molar volume values it is concluded that two association processes occur; the first appears similar to micellization of surfactants, the second is association of micellar spheres.

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Zusammenfassung Es wurde die Scher- und Konzentrationsabhängigkeit des Fließverhaltens von Polyvinylalkohollösungen (90,3 % hydrolysiert) mit niedriger Polydispersität untersucht. An den gleichen Lösungen wurden auch Präzisionsdichtemessungen ausgeführt. Aus dem berechneten Fließvolumen und dem partiellen Molvolumen kann gefolgert werden, daß zwei Assoziationsprozesse vorliegen. Der erste davon gleicht der Mizellbildung von Tensiden, der zweite entspricht der Assoziation kugelförmiger Mizellen.

     

The effect of aqueous solutions of trimethylamine-N-oxide on pressure induced modifications of hydrophobic interactions

To understand the mechanism of protein protection by the osmolyte trimethylamine-N-oxide (TMAO) at high pressure, using molecular dynamics (MD) simulations, solvation of hydrophobic group is probed in aqueous solutions of TMAO over a wide range of pressures relevant to protein denaturation. The hydrophobic solute considered in this study is neopentane which is a considerably large molecule. The concentrations of TMAO range from 0 to 4 M and for each TMAO concentration, simulations are performed at five different pressures ranging from 1 atm to 8000 atm. Potentials of mean force are calculated and the relative stability of solvent-separated state over the associated state of hydrophobic solute are estimated. Results suggest that high pressure reduces association of hydrophobic solutes. From computations of site-site radial distribution function followed by analysis of coordination number, it is found that water molecules are tightly packed around the nonpolar particle at high pressure and the hydration number increases with increasing pressure. On the other hand, neopentane interacts preferentially with TMAO over water and although hydration of neopentane reduces in presence of this osmolyte, TMAO does not show any tendency to prevent the pressure-induced dispersion of neopentane moieties. It is also observed that TMAO molecules prefer a side-on orientation near the neopentane surface, allowing its oxygen atom to form favorable hydrogen bonds with water while maintaining some hydrophobic contacts with neopentane. Analysis of hydrogen-bond properties and solvation characteristics of TMAO reveals that TMAO can form hydrogen bonds with water and it reduces the identical nearest neighbor water molecules caused by high hydrostatic pressures. Moreover, TMAO enhances life-time of water-water hydrogen bonds and makes these hydrogen bonds more attractive. Implication of these results for counteracting effect of TMAO against protein denaturation at high pressures are discussed.