A light-gated regulation of the reaction site by a cucurbit[7]uril macrocycle.

Competitive inhibition can be overcome by increasing the amount of catalyst in the reaction mixture. Here we present a pseudorotaxane system that circumvents this rule. A merocyanine inhibitor linked with the substrate obstructs the binding of the macrocyclic catalyst at the electrophilic reaction site preventing catalysis. Under UV light merocyanine is converted to the spiropyran form, losing its inhibition properties, thereby allowing the catalyst to bind the reaction center and promote the reaction. Moreover, when more than one nucleophile is present in the reaction mixture, the pseudorotaxane can scavenge a selected nucleophile and change the final product ratio. This work is a step forward in the development of new types of regulation in catalytic systems with remote control.

Effect of Na+ and K+ on the cucurbituril-mediated hydrolysis of a phenyl acetate.

The environment around the active site affects the catalytic activity of enzymes. Studying the cucurbit[7]uril-promoted acid hydrolysis of a cationic phenyl acetate derivative, we found that the hydrophobic cavity of the macrocycle screens the reaction centre from the positively charged neighbouring group. Moreover, the chelation of alkali metal cations with the cucurbit[7]uril portal and acetyl group of the substrate reduces the hydrolysis rate of the encapsulated ester in an aqueous solution. This type of inhibition corresponds to a rare uncompetitive model in contrast to the more common competitive model that relies on substrate displacement.

Visual discrimination of aromatic acid substitution patterns by supramolecular nanocooperativity.

Physicochemical and, in particular, visual recognition of positional isomers, due to their similar appearance and properties, is an extremely challenging task. Here we present an easy-to-prepare assay for the naked-eye differentiation of all possible isomers of phthalic acids. The desired optical response is attained through specific non-covalent interactions between the acids and a cationic macrocyclic host. These interactions are then translated to and amplified by gold nanoparticles which subsequently aggregate to various extents producing a color palette.

Reversing Chemoselectivity: Simultaneous Positive and Negative Catalysis by Chemically Equivalent Rims of a Cucurbit[7]uril Host.

Enzyme catalysis has always been an inspiration and an unattainable goal for chemists due to features such as high specificity, selectivity, and efficiency. Here, we disclose a feature neither common in enzymes nor ever described for enzyme mimics, but one that could prove crucial for the catalytic performance of the latter, namely the ability to catalyze and inhibit two different reactions at the same time. Remarkably, this can be realized by two identical, spatially resolved catalytic sites. In the future, such a synchronized catalyst action could be used not only for controlling chemoselectivity, as in the present case, but also for regulating other types of chemical reactivity.

2-[(2Z,3E)-2-Hy-droxy-imino-5-phenyl-2,3-dihydro-3-thienyl-idene]-2-phenyl-acetonitrile.

In the crystal structure of the title compound, C(18)H(12)N(2)OS, centrosymmetric dimers are stabilized both by van der Waals inter-actions and by two types of inter-molecular O-H⋯N hydrogen bonds. In addition, an intra-molecular C-H⋯S hydrogen bond is observed. The dihedral angles between the central ring and the two pendant phenyl rings are 7.4 (1) and 45.06 (9)°.