The ability to finely tune the solution viscosity of an aqueous system is critical in many applications ranging from large-scale fluid-based industrial processes to free-standing hydrogels important in regenerative medicine, controlled drug delivery, and 'green' self-healing materials. Herein we demonstrate the use of the macrocyclic host molecule cucurbit[8]uril (CB[8]) to facilitate reversible cross-linking of multivalent copolymers with high binding constants (K(a) > 10(11)-10(12) M(-2)) leading to a supramolecular hydrogel. Multivalent copolymers were prepared by free radical polymerization techniques and contained either pendant methyl viologen (a good first guest for CB[8]) or naphthoxy derivatives (good second guests for CB[8]). A colorless solution of the two multivalent copolymers bearing first and second guests, respectively, can be transformed into a highly viscous, colored supramolecular hydrogel with the cross-link density being easily controlled through CB[8] addition. Moreover, the cross-links (1:1:1 supramolecular ternary complexes of CB[8]/viologen/naphthoxy) are dynamic and stimuli-responsive, and the material properties can be modulated by temperature or other external stimuli. Rheological characterization of the bulk material properties of these dynamically cross-linked networks provided insight into the kinetics of CB[8] ternary complexation responsible for elastically active cross-linking with a second guest dissociation rate constant (k(d)) of 1200 s(-1) for the ternary complex. These materials exhibited intermediate mechanical properties at 5 wt % in water (plateau modulus = 350-600 Pa and zero-shear viscosity = 5-55 Pa·s), which is complementary to existing supramolecular hydrogels. Additionally, these supramolecular hydrogels exhibited thermal reversibility and subsequent facile modulation of microstructure upon further addition of CB[8] and thermal treatment. The fundamental knowledge gained from the study of these dynamic materials will facilitate progress in the field of smart, self-healing materials, self-assembled hydrogels, and controlled solution viscosity.

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Aqueous supramolecular chemistry, the non-covalent assembly of simple building blocks into higher ordered architectures in water has received much focus recently. Biological systems are able to form complex, and well-defined microstructures essential to cellular function, and supramolecular chemistry has demonstrated its utility in assembling molecules to form increasingly complex assemblies. This tutorial review will summarise non-covalent building blocks based on both synthetic and biological systems in an aqueous environment, emphasising the complexity of the assemblies formed. Examples of higher ordered assemblies will be highlighted, from supramolecular plastics to spider silks, towards more compartmentalised protocell precursors.

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Fluorine makes the difference: FIBX (see structure), the tetrafluoro derivative of the hypervalent iodine reagent, is more soluble and has higher reactivity than its nonfluorinated counterpart. An efficient synthesis of FIBX and initial reactions are presented. Some of these reactions can be conducted in standard organic solvents. Owing to the increased reactivity, new transformations and catalytic reactions may be possible.