Controlled Self-Assembly Mediated by the Complexation of Calixpyridinium: Diverse Assembled Morphology, Solid-State Fluorescence, and Iodine Capture Capacity.

It is a great challenge to precisely control the molecules that self-assemble into diverse shapes with diverse properties. Herein, the self-assembled behaviors between calixpyridinium and two pyrenesulfonate guests, 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PyTS) and sodium 1-pyrenesulfonate (PS), were studied. The morphology and property of the two assemblies were quite different. PS guests self-assembled into spherical aggregates upon complexation with calixpyridinium, while the self-assembled rodlike aggregates were formed via the binding between calixpyridinium and PyTS guests. The calixpyridinium-PS supramolecular aggregates could not emit fluorescence in the solid state, while a strong green fluorescence was emitted by the calixpyridinium-PyTS supramolecular aggregates in the solid state. More interestingly and importantly, the solid calixpyridinium-PyTS supramolecular aggregates exhibited an adsorbent ability to iodine in both the aqueous solution and the vapor phase, while the solid calixpyridinium-PS supramolecular aggregates could not capture iodine. The diverse iodine capture capability of the two supramolecular aggregates was determined by the self-assembled structure at the molecular level.

Synthesis of Two Anionic Gemini Surfactants and Their Self-Assembly Induced by the Complexation of Calixpyridinium.

The information in the literature concerned with lowering the critical aggregation concentration of anionic surfactants by macrocyclic compounds is scarce. This research develops an effective route for lowering the critical aggregation concentration of anionic gemini surfactants by the complexation of calixpyridinium. Furthermore, the size of complex self-assembled nanostructures can be well controlled by the different mixing ratio of the host and the guest.

A calixpyridinium-based supramolecular tandem assay for alkaline phosphatase and its application to ATP hydrolysis reaction.

We have successfully implemented the supramolecular tandem assay principle for the real-time, continuous, direct, and label-free monitoring of alkaline phosphatase activity through a fluorescence "switch-off" assay based on a novel calixpyridinium/dye reporter pair. Because several diseases can be preliminarily diagnosed in light of an abnormal level of alkaline phosphatase in serum, the application of tandem assays to selectively monitor alkaline phosphatase activity has feasible implications in disease diagnosis.

Molecular binding behavior of water-soluble calix[4]arenes with asymmetric 4,4'-bipyridinium guests in aqueous solution: regioselective recognition or not?

The molecular binding behavior of water-soluble calix[4]arenes (p-sulfonatocalix[4]arene (SC4A) and p-sulfonatothiacalix[4]arene (STC4A)) with two asymmetric 4,4'-bipyridinium guests (N-methyl-N'-adamantane carbomethyl-4,4'-bipyridinium dibromide (MVAd2+) and N-methyl-N'-(naphthalen-2-ylmethyl)-4,4'-bipyridinium bromide iodide (MVNp2+)) was systematically studied using NMR spectroscopy and microcalorimetry in a neutral aqueous solution. Either the methyl group or the adamantane moiety in MVAd2+ could enter into the SC4A and STC4A cavities, without regioselectivity. The STC4A cavity can also accommodate MVNp2+, either through incorporation of the methyl group or the naphthalene moiety, without regioselectivity. However, we were surprised to find that MVNp2+ could only be included within the SC4A cavity through incorporation of the methyl group, with regioselectivity, which is rare for a flexible host. Furthermore, both SC4A and STC4A can form stable inclusion complexes with the two investigated asymmetric 4,4'-bipyridinium guests, driven by very favorable enthalpy changes, and the thermodynamic origins of the host selectivities for MVAd2+ and MVNp2+ can be well explained through their binding modes. The finding of this novel regioselective recognition is promising for potential applications in the development of more sophisticated biomimetic materials.

The effect of terminal groups of viologens on their binding behaviors and thermodynamics upon complexation with sulfonated calixarenes.

The binding modes, inclusion abilities, and thermodynamic parameters for the intermolecular complexation of p-sulfonatocalix[4]arene (SC4A), p-sulfonatocalix[5]arene (SC5A), and p-sulfonatothiacalix[4]arene (STC4A), with methyl viologen (MV(2+)), ethyl viologen (EV(2+)), propyl viologen (PV(2+)), butyl viologen (BV(2+)), and benzyl viologen (BnV(2+)), were systematically investigated by NMR spectroscopy, molecular mechanics calculation, and microcalorimetry in neutral aqueous solutions. The obtained results show that all the sulfonated calixarene hosts can form stable inclusion complexes with viologen guests driven by much favorable enthalpy changes. All the viologen guests are encapsulated into the smaller SC4A cavity in their axial orientation. The larger SC5A cavity can accommodate all the viologen guests at its upper-rim midsection in the latitudinal orientation. The binding modes of more flexible STC4A with the smaller MV(2+) and EV(2+) guests are similar to those of SC5A with the two guests, while the binding modes of STC4A with the larger PV(2+) and BV(2+) guests are similar to those of SC4A with the two guests. The host selectivity for all the investigated viologen guests is the same: SC5A > SC4A > STC4A. The magnitude of the host selectivity is associated with the size of the guest. Moreover, the thermodynamic origin of the host selectivity for these viologen guests can be explained well by host-guest binding modes.

Photolysis of a calixpyridinium-based supramolecular amphiphilic assembly and its selective turn-on fluorescence recognition of lysine in water.

A new calixpyridinium-based light-responsive host-guest recognition motif was found in this work. This host-guest recognition motif was further discovered to be applied as a selective turn-on fluorescent sensor for lysine over other natural amino acids.

Comparative Study on the Supramolecular Assemblies Formed by Calixpyridinium and Two Alginates with Different Viscosities.

In this work, a comparative study on the supramolecular assemblies formed by calixpyridinium and two alginates with different viscosities was performed. We found that sodium alginate (SA) with medium viscosity (SA-M) had a better capability to induce aggregation of calixpyridinium in comparison with SA with low viscosity (SA-L) because of the stronger electrostatic interactions between calixpyridinium and SA-M. Therefore, the morphology of calixpyridinium-SA-M supramolecular aggregates was a compact spherical structure, while that of calixpyridinium-SA-L supramolecular aggregates was an incompact lamellar structure. As a result, adding much more amount of 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt to calixpyridinium-SA-M solution was required to achieve the balance of the competitive binding, and in comparison with calixpyridinium-SA-L supramolecular aggregates, calixpyridinium-SA-M supramolecular aggregates were more sensitive to alkali. However, for the same reason, in comparison with calixpyridinium-SA-M supramolecular aggregates, calixpyridinium-SA-L supramolecular aggregates were much more stable in water not only at room temperature but also at a higher temperature, and even in salt solution. Therefore, in comparison with calixpyridinium-SA-L supramolecular aggregates, calixpyridinium-SA-M supramolecular aggregates exhibited a completely opposite response to acid because of the generation of salt. Because SA is an important biomaterial with excellent biocompatibility, it is anticipated that this comparative study is extremely important in constructing functional supramolecular biomaterials.