An amphiphilic molecular basket sensitive to both solvent changes and UV irradiation

A molecular basket was obtained by linking four cholate units to a cone-shaped calix[4]arene scaffold through azobenzene spacers. The molecule turns its polar faces inward in nonpolar solvents to bind polar molecules such as sugar derivatives. In polar solvents, the nonpolar faces turn inward, allowing the binding of hydrophobic guests such as pyrene. The molecule can also respond to UV irradiation by trans-cis isomerization of the azobenzene spacers. Response toward both solvents and UV light is fully reversible.     

Solvent-induced amphiphilic molecular baskets: unimolecular reversed micelles with different size, shape, and flexibility

Amphiphilic molecular baskets were obtained by attaching facially amphiphilic cholate groups to a covalent scaffold (calix[4]arene or 1,3,5-2,4,6-hexasubstituted benzene). In a solvent mixture consisting of mostly a nonpolar solvent (i.e., CCl4) and a polar solvent (i.e., DMSO), the hydrophilic faces of cholates turned inward to form a reversed-micelle-like conformer whose stability was strongly influenced by the number of the cholates and the topology of the scaffold. Preferential solvation of the hydrophilic faces of cholates within the molecule by the polar solvent was cooperative and gave the fundamental driving force to the conformational change. The reversed-micelle-like conformer was most stable in structures that allowed multiple cholates to form a microenvironment that could efficiently enrich the polar solvent molecules from the bulk solvent mixture.     

Environmentally responsive molecular baskets: unimolecular mimics of both micelles and reversed micelles

[structure: see text] When four facially amphiphilic cholate derivatives are attached to a tetraaminocalixarene scaffold, the resulting molecule responds to environmental changes by rotation of the cholate units. In polar solvents, the molecule adopts a micellelike conformation with the hydrophilic alpha-faces of the cholates pointing outward. In nonpolar solvents, it turns inside out, assuming a reversed micellelike conformation with the hydrophobic beta-faces pointing outward. Switching between the two conformations is driven by solvophobic interactions and is fully reversible.     

Deep cavitand vesicles - multicompartmental hosts

The synthesis and characterization of vesicles assembled from deep cavitands in water is reported. These vesicles act as hosts for three different types of guests: the cavitands bind small guest molecules, the bilayer attracts larger hydrophobic guests and the inner aqueous compartment contains hydrophilic molecules.     

Probing Helical Hydrophobic Binding Sites in Branched Starch Polysaccharides Using NMR Spectroscopy

Branched starch polysaccharides are capable of binding multiple hydrophobic guests, but their exploitation as multivalent hosts and in functional materials is limited by their structural complexity and diversity. Linear α(1–4)‐linked glucose oligosaccharides are known to bind hydrophobic guests inside left‐handed single helices in solution and the solid state. Here, we describe the development of an amphiphilic probe that binds to linear α(1–4)‐linked glucose oligosaccharides and undergoes a conformational switch upon complexation, which gives rise to dramatic changes in the ¹H NMR spectrum of the probe. We use this probe to explore hydrophobic binding sites in the branched starch polysaccharides amylopectin and β‐limit dextrin. Diffusion‐ordered (DOSY), nuclear Overhauser effect (NOESY) and chemical shift perturbation (HSQC) NMR experiments are utilised to provide evidence that, in aqueous solution, branched polysaccharides bind hydrophobic guests in well‐defined helical binding sites, similar to those reported for complexation by linear oligosaccharides. By examining the binding affinity of the probe to systematically enzymatically degraded polysaccharides, we deduce that the binding sites for hydrophobic guests can be located on internal as well as external branches and that proximal α(1–6)‐linked branch points weaken but do not prevent complexation.     

Gd(III)[15-metallacrown-5] recognition of chiral α-amino acid analogues

Chiral Ln(III)[15-metallacrown-5] complexes with phenyl side chains have been shown to encapsulate aromatic carboxylates reversibly in their hydrophobic cavities. Given the importance of selective guest binding for applications of supramolecular containers in synthesis, separations, and materials design, the affinity of Gd(III)[15-metallacrown(Cu(II), L-pheHA)-5] hosts for a series of chiral carboxylate guests with varying substitutions on the α-carbon (phenylalanine, N-acetyl-phenylalanine, phenyllactate, mandelate, methoxyphenylacetate) has been investigated. Differential binding of S- and R-phenylalanine was revealed by X-ray crystallography, as the S-enantiomer exclusively forms associative hydrogen bonds with oxygen atoms in the metallacrown ring. Selective guest binding in solution was assessed with isothermal titration calorimetry, which measures the sequential guest binding in the hydrophobic cavity first and the hydrophilic face of the host, and a cyclic voltammetry assay, which quantifies guest binding strength in the hydrophobic cavity of the host exclusively. In solution, the Gd(III)[15-metallacrown(Cu(II), L-pheHA)-5] hydrophobic cavity exhibits modest chiral selectivity for enantiomers of phenylalanine (K(S)/K(R) = 2.4) and mandelate (K(S)/K(R) = 1.22). Weak binding constants of ～100 M(-1) were measured for neutral and -1 charged carboxylates with hydrophilic functional groups (ammonium, N-acetyl, methyl ether). Weaker binding relative to the unsubstituted guests is attributed to unfavorable interactions between the hydrophilic functionalities of the guest and the hydrophobic cavity of the host. In contrast, binding constants greater than 2000 M(-1) were measured for α-hydroxy analogues phenyllactate and mandelate. The significantly increased affinity likely arises from the guests being bound as a -2 anion upon metal-assisted deprotonation in the Gd(III)[15-metallacrown(Cu(II), l-pheHA)-5] cavity. It is established that guest binding affinity in the hydrophobic cavity of the host follows the general trend of neutral zwitterion < monoanion < dianion, with hydrophilic functional groups decreasing the binding affinity. These results have broad implications for the development of metallacrowns as supramolecular catalysts or in chiral separations.     

pH敏感性两亲聚合物网络PAA—l—PTHF的研究

以具有良好柔性和生物相容性的聚四氢呋喃（ＰＴＨＦ）为疏水链段,具有ｐＨ敏感性的聚丙烯酸（ＰＡＡ）为亲水链段,通过ＰＴＨＦ双端基大分子单体与丙烯酸自由基共聚,首次合成了聚丙烯酸－ｌ－聚四氢呋喃（ＰＡＡ－ｌ－ＰＴＨＦ）两亲聚合物网络,并对网络的结构、组成以及交联点密度进行了表征。两亲聚合物网络溶胀行为研究表明,ＰＡＡ－ｌ－ＰＴＨＦ既能在水中溶胀又能在有机溶剂中溶胀,在水中的溶胀度随网络亲水链段ＰＡＡ含     

Preferential solvation within hydrophilic nanocavities and its effect on the folding of cholate foldamers

The conformations of three cholate foldamers and one molecular basket were studied by fluorescence and NMR spectroscopy. In nonpolar solvents (e.g., hexane/ethyl acetate or ethyl acetate) mixed with a small amount of a polar solvent (e.g., alcohol or DMSO), the cholate oligomer folded into a helix with the hydrophilic faces of the cholates turned inward. Folding created a hydrophilic nanocavity preferentially solvated by the entrapped polar solvent concentrated from the bulk. This microphase separation of the polar solvent was critical to the folding process. Folding was favored by larger-sized polar solvent molecules, as fewer such molecules could occupy and solvate the nanocavity, thus requiring a smaller extent of phase separation during folding. Folding was also favored by smaller/acyclic nonpolar solvent molecules, probably because they could avoid contact with the OH/NH groups within the nanocavity better than larger/cyclic nonpolar solvent molecules.     

Artificial receptors that provides a preorganized hydrophobic environment: a biomimetic approach to dopamine recognition in water

[structure: see text] The recognition of dopamine in water has been achieved with tripodal oxazoline-based artificial receptors, capable of providing a preorganized hydrophobic environment by rational design, which mimics a hydrophobic pocket predicted for a human D2 receptor. The receptors show an amphiphilic nature owing to the presence of hydrophilic sulfonate groups at the periphery of the tripodal oxazoline ligands, which seems to contribute in forming the preorganized hydrophobic environment. The artificial receptors recognized dopamine hydrochloride in water with reasonable selectivity among various organoammonium guests examined. The observed binding behavior of the receptors was explained by evoking guest inclusion in the preorganized hydrophobic pocket-like environment and not by simple ion-pairing interactions. The rationally predicted 1:1 inclusion binding mode was supported by binding studies such as with a reference receptor that cannot provide a similar binding pocket, Job and VT-NMR experiments, electrospray ionization mass analysis, and guest selectivity data. This study implies that an effective hydrophobic environment can be generated even from an acyclic, small molecular artificial receptor. Such a preorganized hydrophobic environment, as being utilized in biological systems, can be effectively used as a complementary binding force for the recognition of organoammonium guests such as dopamine hydrochloride in water.     

Controllable Self‐Assembly of Amphiphilic Zwitterionic PBI Towards Tunable Surface Wettability of the Nanostructures

Amphiphilic molecules have received wide attention as they possess both hydrophobic and hydrophilic properties, and can form diverse nanostructures in selective solvents. Herein, we report an asymmetric amphiphilic zwitterionic perylene bisimide ( AZP ) with an octyl chain and a zwitterionic group on the opposite imide positions of perylene tetracarboxylic dianhydride. The controllable nanostructures of AZP with tunable hydrophilic/hydrophobic surface have been investigated through solvent‐dependent amphiphilic self‐assembly as confirmed by SEM, TEM, and contact angle measurements. The planar perylene core of AZP contributes to strong π–π stacking, while the amphiphilic balance of asymmetric AZP adjusts the self‐assembly property. Additionally, due to intermolecular π–π stacking and solvent–solute interactions, AZP could self‐assemble into hydrophilic microtubes in a polar solvent (acetone) and hydrophobic nanofibers in an apolar solvent (hexane). This facile method provides a new pathway for controlling the surface properties based on an asymmetric amphiphilic zwitterionic perylene bisimide.     

双亲性稠环双卟啉的合成和自组装研究

在稠环双卟啉分子两侧的卟啉环上分别连接亲水和疏水性取代基,合成双亲性稠环双卟啉分子。利用紫外-可见光谱和核磁氢谱考察了它们在不同溶剂中的溶解行为。结果表明,当双卟啉环两侧取代基的亲疏水性差异足够大时,在亲水性溶剂中,两侧取代基溶解性的差异所提供的附加亲疏水作用,可以引导稠环双卟啉分子通过π-π堆积作用形成H-聚集体。这种自组装形成的一维柱状超分子聚集体,在分子光电器件等领域具有潜在的应用前景。     

Energetics of small molecule and water complexation in hydrophobic calixarene cavities

Calixarenes grafted on silica are energetically uniform hosts that bind aromatic guests with 1:1 stoichiometry, as shown by binding energies that depend upon the calixarene upper rim composition but not on their grafted surface density (0.02-0.23 nm(-2)). These materials are unique in maintaining a hydrophilic silica surface, as probed by H2O physisorption measurements, while possessing a high density of hydrophobic binding sites that are orthogonal to the silica surface below them. The covalently enforced cone-shaped cavities and complete accessibility of these rigidly grafted calixarenes allow the first unambiguous measurements of the thermodynamics of guest interaction with the same calixarene cavities in aqueous solution and vapor phase. Similar to adsorption into nonpolar protein cavities, adsorption into these hydrophobic cavities from aqueous solution is enthalpy-driven, which is in contrast to entropy-driven adsorption into water-soluble hydrophobic hosts such as beta cyclodextrin. The adsorption thermodynamics of several substituted aromatics from vapor and liquid are compared by (i) describing guest chemical potentials relative to pure guest, which removes differences among guests because of aqueous solvation and van der Waals contacts in the pure condensed phase, and (ii) passivating residual guest binding sites on exposed silica, titrated by water during adsorption from aqueous solution, using inorganic salts before vapor adsorption. Adsorption isotherms depend only upon the saturation vapor pressure of each guest, indicating that guest binding from aqueous or vapor media is controlled by van der Waals contacts with hydrophobic calixarene cavities acting as covalently assembled condensation nuclei, without apparent contributions from CH-pi or other directional interactions. These data also provide the first direct quantification of free energies for interactions of water with the calixarene cavity interior. The calixarene-water interface is stabilized by approximately 20 kJ/mol relative to the water-vapor interface, indicating that water significantly competes with the aromatic guests for adsorption at these ostensibly hydrophobic cavities. This result is useful for understanding models of water interactions with other concave hydrophobic surfaces, including those commonly observed within proteins.     

Equilibrium isotope effects on noncovalent interactions in a supramolecular host-guest system

The self-assembled supramolecular complex [Ga(4)L(6)](12-) (1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) can act as a molecular host in aqueous solution and bind cationic guest molecules to its highly charged exterior surface or within its hydrophobic interior cavity. The distinct internal cavity of host 1 modifies the physical properties and reactivity of bound guest molecules and can be used to catalyze a variety of chemical transformations. Noncovalent host-guest interactions in large part control guest binding, molecular recognition and the chemical reactivity of bound guests. Herein we examine equilibrium isotope effects (EIEs) on both exterior and interior guest binding to host 1 and use these effects to probe the details of noncovalent host-guest interactions. For both interior and exterior binding of a benzylphosphonium guest in aqueous solution, protiated guests are found to bind more strongly to host 1 (K(H)/K(D) > 1) and the preferred association of protiated guests is driven by enthalpy and opposed by entropy. Deuteration of guest methyl and benzyl C-H bonds results in a larger EIE than deuteration of guest aromatic C-H bonds. The observed EIEs can be well explained by considering changes in guest vibrational force constants and zero-point energies. DFT calculations further confirm the origins of these EIEs and suggest that changes in low-frequency guest C-H/D vibrational motions (bends, wags, etc.) are primarily responsible for the observed EIEs.     

Facial amphiphiles in molecular recognition: From unusual aggregates to solvophobically driven foldamers

The term “facial amphiphiles” was originally used for molecules with the hydrophilic and hydrophobic groups located on two opposite faces, rather than at two ends as in the more conventional head/tail amphiphiles. Recent research has expanded this concept and created facially amphiphilic molecules with diverse topologies and intriguing properties. The geometry and the distribution of hydrophilic/hydrophobic groups on facial amphiphiles were key parameters influencing their properties. Intermolecular aggregation of facial amphiphiles generated a range of structures including dimers, vesicles, nanoclusters, and nanotubes. Intramolecular aggregation of facially amphiphilic repeat units in a molecule, on the other hand, allowed the molecule to respond to environmental stimuli through controlled conformational changes.     

Amphiphilic α-helix mimetics based on a benzoylurea scaffold

The design and synthesis of amphiphilic benzoylurea α-helix mimetics is described. These conformationally constrained molecules allow for the correct angular and spatial projection of hydrophobic and hydrophilic groups and thus the reproduction of side-chains on both faces of an α-helix.     

High guest inclusion in 3β-amino-7α,12α-dihydroxycholan-24-oic acid enabled by charge-assisted hydrogen bonds

3β-Amino-7α,12α-dihydroxycholan-24-oic acid (2) forms inclusion compounds with high ratio (host/guest=1/4) of guest methanol. Both hydrogen bonds and hydrophobic interactions are important to the solid structure. The cholates assemble in a head-to-tail fashion to form infinite hydrogen-bonded chains. The chains are interconnected between cholates and also through the guests. Large channels are formed along the crystallographic a axis where most of the methanol molecules are located. Presence of a dominant hydrogen-bonding motif (i.e., ammonium-carboxylate ion pairing) is probably responsible for high guest incorporation.     

Self-assembly of organic-inorganic hybrid amphiphilic surfactants with large polyoxometalates as polar head groups

Mn-Anderson-C6 and Mn-Anderson-C16, A type of inorganic-organic hybrid molecules containing a large anionic polyoxometalate (POM) cluster and two C6 and C16 alkyl chains, respectively, demonstrate amphiphilic surfactant behavior in the mixed solvents of acetonitrile and water. The amphiphilic hybrid molecules can slowly assemble into membrane-like vesicles by using the POM clusters as polar head groups, as studied by laser light scattering and TEM techniques. The hollow vesicles have a typical bilayer structure with the hydrophilic Mn-Anderson cluster facing outside and long hydrophobic alkyl chains staying inside to form the solvent-phobic layer. Due to the rigidity of the POM polar heads, the two alkyl tails have to bend significantly for the vesicle formation, which makes the vesicle formation more difficult compared to some conventional surfactants. This is the first example of using hydrophilic POM macroions as polar head groups for a surfactant system.     

无规共聚物自组装球形胶束表面亲水性的耗散粒子动力学模拟

建立了含不同亲疏水粒子比的双亲性无规共聚物粗粒化模型. 采用耗散粒子动力学方法模拟了两亲性无规共聚物选择性溶剂自组装球形胶束表面的亲水性能. 模拟结果表明, 无规共聚物在选择性溶剂中自组装得到实心球形胶束, 球形胶束表面的亲水性与聚合物链亲水粒子含量、溶剂的选择性有关. 随着聚合物链所含亲水粒子增加, 球形胶束表面的亲水性增强. 球形胶束表面的亲水性随着疏水粒子与溶剂粒子间的排斥参数增大而增强, 模拟结果与实验结论一致. 该模拟方法给出的胶束微结构信息可以为双亲无规共聚物分子设计及自组装双亲胶束制备提供一定的理论指导.     

聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质的研究

采用核磁共振 (NMR)、动态激光光散射 (DLS)、透射电子显微镜 (TEM )等方法研究了规整性聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质 ,研究表明两亲接枝共聚物在选择性溶剂中可形成球状胶束 ,溶液的浓度、温度和聚合物结构等因素影响其胶束的大小、形态     

Supramolecular reactor from self-assembly of rod-coil molecule in aqueous environment

We synthesized an amphiphilic coil-rod-coil triblock molecule consisting of hexa-p-phenylene as a rod block and poly(ethylene oxide) with the number of repeating units of 17 as coil blocks and investigated aggregation behavior in aqueous environment. The rod-coil molecule was observed to aggregate into discrete micelles consisting of hydrophobic disklike rod bundles encapsulated by hydrophilic poly(ethylene oxide) coils. The aromatic bundles of the micelles were demonstrated to be used as an efficient supramolecular reactor for the room temperature Suzuki cross-coupling reaction of a wide range of aryl halides, including even aryl chlorides with phenylboronic acids in aqueous environment. These results demonstrate that self-assembly of amphiphilic rod-coil molecules can provide a useful strategy to construct an efficient supramolecular reactor for aromatic coupling reaction.