Dissipative self-assembly is exploited by nature to control important biological functions, such as cell division, motility and signal transduction. The ability to construct synthetic supramolecular assemblies that require the continuous consumption of energy to remain in the functional state is an essential premise for the design of synthetic systems with lifelike properties. Here, we show a new strategy for the dissipative self-assembly of functional supramolecular structures with high structural complexity. It relies on the transient stabilization of vesicles through noncovalent interactions between the surfactants and adenosine triphosphate (ATP), which acts as the chemical fuel. It is shown that the lifetime of the vesicles can be regulated by controlling the hydrolysis rate of ATP. The vesicles sustain a chemical reaction but only as long as chemical fuel is present to keep the system in the out-of-equilibrium state. The lifetime of the vesicles determines the amount of reaction product produced by the system.

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The development of synthetic agents able to hydrolytically cleave DNA with high efficiency and selectivity is a fascinating challenge that will show the way to obtaining artificial nucleases able to compete with the natural enzymes. This Feature Article highlights the progress reported toward the realization of synthetic nucleases with particular attention to the strategies that can be pursued to improve efficiency and sequence selectivity.

We describe here a simple assay that allows the visual detection of a protease. The method takes advantage of the high molar absorptivity of the plasmon band of gold colloids and is based on the color change of their solution when treated with dithiols. We used C-and N-terminal cysteinyl derivatives of a peptide substrate exploiting its selective recognition and cleavage by a specific protease. Contrary to the native ones, cleaved peptides are unable to induce nanoparticles aggregation; hence, the color of the solution does not change. The detection of two proteases is reported: thrombin (involved in blood coagulation and thrombosis) and lethal factor (an enzyme component of the toxin produced by Bacillus anthracis). The sensitivity of this nanoparticle-based assay is in the low nanomolar range.lethal factor ͉ plasmon surface band ͉ thrombin E nzymes analytical detection is a key tool in enzymology, extremely important for the screening of noxious toxins and pathologies associated with their presence, and for the development of effective and selective therapeutics. Among enzymes, proteases (1, 2) are particularly relevant because proteolytic processing is the final step in the expression of the activity of a great variety of proteins (3). Standard assays for proteases include those based on radioisotopes or on fluorogenic substrates. A protease assay system that uses functionalized, supermagnetic nanoparticles as magnetic relaxation switches and bi-biotinylated peptide substrates for particles clustering has been reported (4). All of these techniques require specific instrumentation and hence an equipped laboratory. We report here an assay based on nanometer-size gold colloids. Citrate stabilized gold colloids of Ն4 nm diameter present an absorption band at Ϸ520 nm due to plasmon resonance (5, 6) with a very high molar absorptivity. This band is shifted to longer wavelengths upon clustering of the colloids, thus leading to color changes of the solution, from pink-red to violet-blue (7). Clustering may be induced by physical methods (like the increase of the ionic strength of the solution) (8) or chemically by addition of molecules able to connect one nanoparticle to another (9). By taking advantage of this phenomenon, very sensitive detection procedures have been introduced for analytes ranging from DNA to proteins and metal ions (10). Because thiols interact strongly with gold nanoparticles, a molecule featuring a head and tail thiol causes such a process (11). Indeed, when we treat a gold colloid solution with a peptide of the general formula Cys-(AA) n -Cys (where AA is any amino acid but cysteine), the color of the solution turns from pink-red to violet-blue. No change of color, however, is observed with a peptide lacking one of the terminal cysteines. Accordingly, we reasoned that the cleavage of a Cys-(AA) n -Cys peptide in two fragments, each containing a single cysteine, would result in a system unable to induce aggregation of the gold nanoparticles and, hence, failing to induce the color change of the s...

We report here the first example of peptide-functionalized gold nanoparticles hydrolytically active against carboxylate esters. The active units are constituted by His-Phe-OH terminating thiols. The confinement of the catalytic units in the monolayer covering the nanoparticles triggers a cooperative hydrolytic mechanism operative at pH < 7 in which a carboxylate and an imidazolium ion act as general base and general acid, respectively. Such a mechanism is absent with an analogous monomeric dipeptide, and this results in a more than 300-fold rate acceleration of the hydrolytic process at low pH in the presence of the functional nanoparticles.

Besonders effektiv: Durch Selbstorganisation von Triazacyclonan‐funktionalisierten Thiolen auf der Oberfläche von nanometergroßen Goldpartikeln sind funktionalisierte Goldnanopartikel einfach zugänglich. Durch Komplexierung mit ZnII werden sie zu leistungsfähigen Katalysatoren für die Spaltung von Phosphatestern (siehe Schema). Wegen ihres RNase‐artigen Verhaltens werden sie Nanozyme genannt.

Catalytically active peptide-nanoparticle complexes were obtained by assembling small peptide sequences on the surface of cationic self-assembled monolayers on gold nanoparticles. When bound to the surface, the peptides accelerate the transesterification of the p-nitrophenyl ester of N-carboxybenzylphenylalanine by more than 2 orders of magnitude. The gold nanoparticle serves as a multivalent scaffold for bringing the catalyst and substrate into close proximity but also creates a local microenvironment that further enhances the catalysis. The supramolecular nature of the ensemble permits the catalytic activity of the system to be modulated in situ.

The development of synthetic agents able to hydrolytically cleave DNA with high efficiency and selectivity is still a fascinating challenge. Over the years, many examples have been reported reproducing part of the behaviour of the corresponding natural enzymes. Eventually, even the possibility to apply such systems to the manipulation of DNA of higher organisms has been demonstrated. However, efficiency of enzymes is still unrivalled. This feature article discusses the progress reported toward the realization of synthetic nucleases with particular attention to the comprehension of the reaction mechanisms and to the strategies that need to be addressed to obtain more efficient systems.