An allosteric crown ether-induced activity control for the cleavage of a phosphodiester bond

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.

Reversible modulation of the activity of thiourea catalysts with anions: a simple approach to switchable asymmetric catalysis

A simple and straightforward approach to switchable asymmetric catalysis is presented, based on the interactions of thiourea catalysts with anions.

Artificial switchable catalysts

Catalysis is key to the effective and efficient transformation of readily available building blocks into high value functional molecules and materials. For many years research in this field has largely focussed on the invention of new catalysts and the optimization of their performance to achieve high conversions and/or selectivities. However, inspired by Nature, chemists are beginning to turn their attention to the development of catalysts whose activity in different chemical processes can be switched by an external stimulus. Potential applications include using the states of multiple switchable catalysts to control sequences of transformations, producing different products from a pool of building blocks according to the order and type of stimuli applied. Here we outline the state-of-art in artificial switchable catalysis, classifying systems according to the trigger used to achieve control over the catalytic activity and stereochemical or other structural outcomes of the reaction.

Nucleic Acid and Phosphoester Hydrolytic Cleavage Catalysed by Aza-Crown Ether Metal Complexes as Synthetic Nucleases

Aza-crown ethers are ligands in which the oxygen atoms are replaced by nitrogen atoms in the crown ether ring systems. This type of ligand possesses specific complexation with metal ions, such as those of transition-metals, rare earths, alkali metals and alkaline earths, which form metal complexes whose structures are similar to those of some biological enzymes. In recent decades, research on aza-crown ethers and their metal complexes as mimics of nucleases in hydrolysing nucleic acids has attracted increasing attention. These studies illuminate the mechanism of nucleic acid hydrolytic cleavage as catalysed by natural nucleases. In order to assist the design and synthesis of highly active, selective and stable mimic nucleases, this paper reviews recent progress in the investigation of aza-crown ether metal complexes as mimic nucleases, including: the relationship between the structures and activities of synthetic metallonucleases; multicentre synergistic catalysis of metal ions in multinuclear complexes; bifunctional cooperative catalysis of the branches and ions in the complexes; and especially, the structural characteristic and catalytic mechanism of aza-crown ether metal complexes as mimic nucleases.

Supramolecular catalysis. Part 2: artificial enzyme mimics

The design of artificial catalysts able to compete with the catalytic proficiency of enzymes is an intense subject of research. Non-covalent interactions are thought to be involved in several properties of enzymatic catalysis, notably (i) the confinement of the substrates and the active site within a catalytic pocket, (ii) the creation of a hydrophobic pocket in water, (iii) self-replication properties and (iv) allosteric properties. The origins of the enhanced rates and high catalytic selectivities associated with these properties are still a matter of debate. Stabilisation of the transition state and favourable conformations of the active site and the product(s) are probably part of the answer. We present here artificial catalysts and biomacromolecule hybrid catalysts which constitute good models towards the development of truly competitive artificial enzymes.

Metal ion induced allosteric transition in the catalytic activity of an artificial phosphodiesterase

An artificial phosphodiesterase () bearing two types of metal binding sites, a catalytic site and a regulatory bipyridine site showed a unique allosteric transition in the catalytic activity against the metal concentration. The rate constants for the hydrolysis reaction of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) and RNA dimer (ApA) with and without an effector metal ion were evaluated; the k(obs) value of HPNP hydrolysis for .(Zn(2+))(3) (2.0 x 10(-4) s(-1)) is 3.3 times larger than that for .(Zn(2+))(2). In the case of and Cu(2+), a 19.4 times larger k(obs) value was obtained for .(Cu(2+))(3) (1.2 x 10(-3) s(-1)) against .(Cu(2+))(2). The increase in the catalytic activity is ascribed to the allosteric conformational transition of induced by the coordination of effector metal ion to the Bpy moiety. A detailed investigation revealed that a conformational change of induced by the third M(2+) complexation enhances the rate of hydrolysis rather than a change in the substrate affinity.

Signal Amplification and Detection via a Supramolecular Allosteric Catalyst

The design of a supramolecular allosteric catalyst system for catalytic signal amplification and detection is presented. The catalyst was switched "on" by the introduction of an analyte that also behaves as an allosteric activator. Concentrations of Cl- ions as low as 800 nM were catalytically amplified and detected. The signal was transduced via a pH-sensitive fluorescent probe and observed visually using a laboratory, handheld UV lamp and by spectrophotometry. Furthermore, the allosteric effect was quantified using gas chromatography for a range of Cl- concentrations. This three-part detection scheme involving analyte binding, allosteric catalyst activation, and signal transduction represents a new approach to small-molecule detection.

On/off regulation of catalysis by allosteric control of metal complex nuclearity

The nature of the allosteric metal ion M (Pd2+ or Pt2+) in complexes ML of a polytopic ligand controls uptake of additional Cu2+ ions; while [Cu2Pd(L-4H)]2+ is a highly active catalyst for phosphodiester cleavage, [CuPt(L-4H)] is inactive.