Hydrogen bonded supramolecular polymers in moderately polar solvents

Hydrogen bonded assemblies are usually decomposed by polar organic solvents. However, we have succeeded in preparing a strongly associated supramolecular polymer which forms viscous solutions in competitive solvents such as tetrahydrofuran.     

Anions as templates in coordination and supramolecular chemistry

This review aims to highlight the most important recent advances in the area of anion-templated syntheses in supramolecular and coordination chemistry. We published a comprehensive review on this area in 2003 and hence examples prior to this date will only be discussed when essential for clarity of presentation. The current review has been divided into three main sections: (a) anion-templated synthesis of systems with well-defined molecular weights; this includes macrocycles and cages, interlocked species (such as catenanes and rotaxanes), helical assemblies and other selected examples. (b) Anions as templates in polymeric systems; this includes metal-organic frameworks, molecularly imprinted polymers and other selected examples, such as liquid crystalline materials. (c) Anion templates in dynamic combinatorial libraries.     

Enzyme mimics based upon supramolecular coordination chemistry

Recent advances in supramolecular coordination chemistry have allowed chemists to synthesize macromolecular complexes that exhibit various properties intrinsic to enzymes. This Review focuses on structures inspired by properties and functions observed in enzymes rather than precise models of enzyme active sites. These structures are synthesized using convergent, modular, and high-yielding coordination-chemistry-based methods, which allow one to tailor the size, shape, and properties of the resulting complexes. Many of the structures discussed exhibit reactivity and specificity reminiscent of natural systems, and some of them have functions that exceed the natural systems which provided the inspiration for initially making them.     

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.     

Ion spray-tandem mass spectrometry of supramolecular coordination complexes

Double-helical [M₂L₂] ⁿ⁺, triple-helical [M₂L₃] ⁿ⁺, and toroidal [M₃L₃] ⁿ⁺ (M = Cu, Co, Fe, Ni, La, Eu, Gd, Tb, or Lu) supramolecular complexes have been fully characterized by ion spray mass spectrometry (IS-MS). The IS-MS spectra from pure acetonitrile solutions reflect the nature of the cations present in solution with conservation of the charge state and allow an efficient qualitative speciation of the compounds. The mass spectrometry results can be correlated with other powerful techniques (nuclear magnetic resonance and electronic spectroscopy) for the characterization of supramolecular complexes in solution, Structural information is obtained by collision-induced dissociation, which strongly depends on the metal ions used in the supramolecular complexes and on the various connectivities and topologies of the ligands. When the ligand contains 3,5dimethoxybenzyl groups bound to the benzimidazole rings, the partial fragmentation of the complexes is associated with a decrease of the total charge of the complexes and the appearance of the characteristic fragment at m/z 151 that corresponds to the 3,5-dimethoxybenzyl cation. A detailed analysis of the fragmentation pathways of these supramolecular complexes suggests that the metal-nitrogen coordination bonds are very strong in the gas phase.     

Template-directed supramolecular self-assembly of coordination dumbbells at surfaces

Scanning tunneling microscopy reveals, at single-molecular resolution, how external parameters--substrate morphology and guest addition--re-direct the assembly of dumbbell-shaped coordination supramolecules towards different surface-confined supramolecular organizations.     

From micelle supramolecular assemblies in selective solvents to isoporous membranes

The supramolecular assembly of PS-b-P4VP copolymer micelles induced by selective solvent mixtures was used to manufacture isoporous membranes. Micelle order in solution was confirmed by cryo-scanning electron microscopy in casting solutions, leading to ordered pore morphology. When dioxane, a solvent that interacts poorly with the micelle corona, was added to the solution, polymer-polymer segment contact was preferential, increasing the intermicelle contact. Immersion in water gave rise to asymmetric porous membranes with exceptional pore uniformity and high porosity. The introduction of a small number of carbon nanotubes to the casting solution improved the membrane stability and the reversibility of the gate response in the presence of different pH values.     

金属胶束超分子体系研究新进展

综述了近年来金属胶束超分子体系的研究新进展,着重介绍了本科研组应用金属胶束超分子体系模拟羧肽酶A、磷酸酯水解酶、细胞色素P-450等方面的研究成果。并对建立金属胶束超分子体系的动力学处理模型及催化水解反应的机理进行了讨论。     

Potential of supramolecular solvents for the extraction of contaminants in liquid foods

Amphiphile-based supramolecular solvents (ASSs), which are water immiscible liquids consisting of supramolecular aggregates in the nano- and micro-scale regimes dispersed in a continuous phase, were assessed for the extraction of trace contaminants in liquid foods. The ASS selected was made up of reversed micelles of decanoic dispersed in tetrahydrofuran (THF)-water and the contaminants used as a model were bisphenol A (BPA), ochratoxin A (OTA) and benzo(a)pyrene (BaPy). The influence of matrix components on the extractant solvent production, extraction recoveries and actual concentration factors was investigated by using commercial foods such as wine and wine-based products, beer, soft drinks and tea and coffee brews, and/or aqueous synthetic solutions containing specific food matrix components. The method involved the addition of decanoic acid (80mg) and THF (0.8-1.7mL) to the food sample (15mL), stirring of the mixture for 5min, centrifugation for 10min and analysis of 10-20microL of the extract by liquid chromatography coupled to fluorimetry for OTA and BaPy or to mass spectrometry for BPA. No clean-up of the crude extracts was required for any of the samples analysed. The quantification limits for the contaminants (14-31ngL(-1), 0.37-0.39ngL(-1) and 562-602ngL(-1) for OTA, BaPy and BPA, respectively) were far below their respective European legislative threshold limits. Recoveries for food samples were in the ranges 79-93%, 90-96% and 78-82% for OTA, BaPy and BPA, respectively, with relative standard deviations ranging from 1 to 7%, and actual concentrations factors between 65 and 141. The methods developed were applied to the determination of the target compounds in a variety of commercial foods. OTA was found in vinegar, must and beer samples, the concentrations ranging from 92 to 177ngL(-1), BaPy was quantified in samples of tea and coffee at concentrations between 1.5 and 16.6ngL(-1) whereas BPA was detected in two canned soft drinks and quantified in one of them (tea beverage) at a level of 2.3microgL(-1).     

Consequences of cooperativity in racemizing supramolecular systems

Saluting the sergeant: Phg-BTA (see scheme) cooperatively self-assembles into helical aggregates and shows unprecedented racemization behavior in the presence of base. In thermodynamically controlled conditions, the addition of a small amount of chiral auxiliary to this mixture results in a deracemization reaction and a final enantiomeric excess of 32?%. A theoretical model is presented to understand in detail the results obtained.     

Hydrogen bond mediated supramolecular micellization of diblock copolymer mixture in common solvents

We report a new approach toward preparing self-assembled hydrogen-bonded complexes having vesicle and patched spherical structures from two species of block copolymers in nonselective solvents. Two diblock copolymers, poly(styrene-b-vinyl phenol) (PS-b-PVPh) and poly(methyl methacrylate-b-4-vinylpyridine) (PMMA-b-P4VP), were synthesized through anionic polymerization. The assembly of vesicles from the intermolecular complex formed after mixing PS-b-PVPH with PMMA-b-P4VP in THF was driven by strong hydrogen bonding between the complementary binding sites on the PVPH and P4VP blocks. In contrast, well-defined patched spherical micelles formed after blending PS-b-PVPh with PMMA-b-P4VP in DMF: the weaker hydrogen bonds formed between the PVPh and P4VP blocks in DMF, relative to those in THF, resulted in the formation of spherical micelles having compartmentalized coronas consisting of PS and PMMA blocks.     

Control of electron transfer in supramolecular systems

The fluorescence quantum yield of zinc porphyrin (ZnP) covalently linked to 9,10-bis(phenylethynyl)anthracene (AB) is strongly dependent upon the solvent properties. The bichromophoric system ZnP-AB exhibits 'normal' zinc porphyrin fluorescence in solvents that cannot coordinate to the central zinc atom. In contrast, if a Lewis base, such as pyridine, is added to a sufficiently polar solvent, the fluorescence is significantly quenched. Picosecond transient absorption measurements, in conjunction with fluorescence quenching and cyclic voltammetric measurements, suggest that the quenching mechanism is intramolecular electron transfer from ZnP to AB. The charge separated state. ZnP*+-AB*-, has a lifetime of not more than 220 ps before recombining. If a secondary electron acceptor, iron(III) porphyrin (FeP), is covalently connected to the AB unit, a second electron transfer from AB*- to FeP occurs and the charge separated state, ZnP*+-AB-FeP*-, has a lifetime of at least 5 ns. This demonstrates that electron transfer might be sensitively tuned (switched on) by specific solvent effects.     

High pressure and supramolecular systems

The present review summarizes the results of studies of supramolecular systems under high hydrostatic pressure. The possibilities of using high pressure for the preparation of new supramolecular structures, investigation of intermolecular interactions in these structures, and control over the physical and chemical properties of supramolecular assemblies are considered.     

Role of solvents in stability of collagen

The influence of hydroxymethyl chain length of the solvents on collagen was established with conformational stability and thermal stability. Thermal stability of monomeric collagen and RTT fibres (rat tail tendon) treated with methanol, ethylene glycol (EG) and glycerol were reported using the melting temperature for helix-coil transition and the peak temperature for collagen-gelatin transition. Both melting temperature and peak temperature increases as the hydroxymethyl chain length increases. Conformational stability of collagen solution treated with lower and higher concentrations of methanol, ethylene glycol and glycerol indicates that aggregation of collagen molecule is more at higher concentrations of these solvents. The concentration dependence is greater for the increased number of OH groups. Since protein aggregation is associated with neuro degenerative diseases, aggregation of collagen molecule in the presence of solvents is of great importance for biomedical application.     

Structural, thermal and spectroscopic properties of supramolecular coordination solids

Molecules in metal isonicotinate tetrahydrates, M(NC₅H₄-p-CO₂)₂.4H₂O with M = Mn, Fe, Co, Ni, Cu, Zn, consisting of the hexacoordinate complexestrans-[M(NC₅H₄-p-CO₂)(OH₂)₄], participate in exhaustive hydrogen-bond formation among themselves to lead to a robust 3D supramolecular network in the solid state. Solid-state diffuse reflectance UV-Vis-NIR spectra of the complexes have been assigned to ligand field and charge transfer transitions. Sharp weight loss due to dehydration, as shown by TGA of Cu(NC₅H₄-p-CO₂)₂.4H₂O, suggests the suitability of this complex for the gravimetric estimation of copper.     

Utilizing dual responsive supramolecular gel to stabilize graphene oxide in apolar solvents

Here, we report a dual stimuli-responsive organogel which can stabilize graphene oxide (GO) in apolar solvents. The gelator 1-octadecyl-ureido-naphthalene (OUN) was synthesized, and it could form organogel in toluene and xylene. The resultant gels can respond to thermal and anion stimuli, bringing about fluorescent changes. Thin nanoribbons are entangled together to form three dimensional networks that can immobilize solvents in gel, providing large superficial area to interact with GO sheets. The addition of GO influences the gel properties, which are studied through rheological, fluorescent, and DSC measurements.     

Standardless structural-group analysis of supramolecular systems

The basics of the standardless structural-group analysis of supramolecular systems are proposed. The steps of analysis approbated on the example of studying the structure of a sulfo and a carboxyl cation exchanger are described.     

Sulfate ion encapsulation in caged supramolecular structures assembled by second-sphere coordination

A tripodal tris(3-pyridylurea) receptor (L) assembles with metal sulfate salts MSO(4) (M=Mn, Zn) to afford supramolecular cages [SO(4) subset L(2)] that encapsulate the SO(4)(2-) ion via multiple hydrogen bonds in a three-dimensional structure held by second-sphere coordination; (1)H NMR and negative-ion mode ESI-MS spectra reveal significantly strong sulfate binding in solution.