Bis(crown ether) bolaamphiphiles derived from 18-crown-6 dicarboxylic acid were prepared, and their ability to release vesicle encapsulated 5[6]-carboxyfluorescein was determined. Bolaamphiphiles with a linear central spacer are poor membrane disrupting agents except in the presence of alkaline earth metal cations or ethylenediammonium cation. Divalent ion enhancement of membrane disruption is cation selective and can be used to determine the apparent association constant of the bolaamphiphile crown ether with the added cation. The cis-isomer of a thioindigo bis(crown ether) bolaamphiphile is an active membrane disrupting agent, but the trans-isomer is significantly less active. In homogeneous solution, cis-to-trans thermal and photochemical isomerization is retarded by added alkaline earth metal salts, indicating that cooperative ditopic binding of the cations occurs despite the inherent flexibility of the bolaamphiphile. The membrane disruption mechanism occurs via U-shaped conformations of the bolaamphiphile. All available data indicate that divalent cations accelerate membrane disruption by stabilization of the U-shaped conformation via cooperative interaction of the crown ethers with the dication. Thus the membrane disruption process is switched "on" by molecular recognition.Semiochemistry is the chemistry of the generation, propagation, conversion, and detection of molecular signals. 1 Much of the current effort to develop chemical model systems which illustrate semiochemical principles is focused on switching phenomena, typically involving photochemical or redox processes. 2 Less attention has been paid to direct molecular or ionic switching, whereby a molecular recognition event controls another supramolecular process. 3 The potential of ionic switching is amply illustrated by the stunning array of biological signaling phenomena, from "simple" receptor-mediated cellular processes to the complex neurophysiological processes of thought and memory. 4 These processes are intimately associated with membranes: ionic signals are propagated along membranes, are transduced through membranes, and are amplified by release of vesicle encapsulated (ionic) signal molecules. Model systems which explore these phenomena must therefore be membrane-based and must be switched by the recognition of molecular signals near the membrane surface.Interfacial molecular recognition has been demonstrated for a variety of systems (guanidinium-phosphate, 5a melamine-barbiturate, 5b,c other hydrogen bonding recognition 5d ) at a variety of interfaces (air-water, 5e supported monolayer-water, 5f vesicle bilayer 5g ). The selectivities and energetics of the molecular recognition are generally those expected from related recognition processes in homogeneous solutions. 5 However, the organization and structure of the interface imposed by the intermolecular organization of the amphiphiles can also play a role. In some cases this effect is reciprocal (binding influences organization 5d ) implying that the interfacial environment can be used t...

Release of liposome-entrapped carboxyfluorescein is switched 'on' via molecular recognition of barium ion by a bis(crown ether carboxylate) bola-amphiphiie.

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Waterborne polyurethane (WPU) has attracted significant interest as a promising alternative to solvent-based polyurethane (SPU) due to its positive impact on safety and sustainability. However, significant limitations of WPU, such as its weaker mechanical strength, limit its ability to replace SPU. Triblock amphiphilic diols are promising materials to enhance the performance of WPU due to their well-defined hydrophobic–hydrophilic structures. Yet, our understanding of the relationship between the hydrophobic–hydrophilic arrangements of triblock amphiphilic diols and the physical properties of WPU remains limited. In this study, we show that by controlling the micellar structure of WPU in aqueous solution via the introduction of triblock amphiphilic diols, the postcuring efficiency and the resulting mechanical strength of WPU can be significantly enhanced. Small-angle neutron scattering confirmed the microstructure and spatial distribution of hydrophilic and hydrophobic segments in the engineered WPU micelles. In addition, we show that the control of the WPU micellar structure through triblock amphiphilic diols renders WPU attractive in the applications of controlled release, such as drug delivery. Here, curcumin was used as a model hydrophobic drug, and the drug release behavior from WPU-micellar-based drug delivery systems was characterized. It was found that curcumin-loaded WPU drug delivery systems were highly biocompatible and exhibited antibacterial properties in vitro. Furthermore, the sustained release profile of the drug was found to be dependent on the structure of the triblock amphiphilic diols, suggesting the possibility of controlling the drug release profile via the selection of triblock amphiphilic diols. This work shows that by shedding light on the structure–property relationship of triblock amphiphilic diol-containing WPU micelles, we may enhance the applicability of WPU systems and move closer to realizing their promising potential in real-life applications.

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