Transient signal generation in a self-assembled nanosystem fueled by ATP

A fundamental difference exists in the way signal generation is dealt with in natural and synthetic systems. While nature uses the transient activation of signalling pathways to regulate all cellular functions, chemists rely on sensory devices that convert the presence of an analyte into a steady output signal. The development of chemical systems that bear a closer analogy to living ones (that is, require energy for functioning, are transient in nature and operate out-of-equilibrium) requires a paradigm shift in the design of such systems. Here we report a straightforward strategy that enables transient signal generation in a self-assembled system and show that it can be used to mimic key features of natural signalling pathways, which are control over the output signal intensity and decay rate, the concentration-dependent activation of different signalling pathways and the transient downregulation of catalytic activity. Overall, the reported methodology provides temporal control over supramolecular processe

Photoswitchable catalysis by a nanozyme mediated by a lightsensitive cofactor

The activity of a gold nanoparticle-based catalyst can be reversibly up- and down-regulated by light. Light is used to switch a small molecule between cis- and trans-isomers, which inhibits the catalytic activity of the nanoparticles to different extent. The system is functional in aqueous buffer, which paves the way for integrating the system in biological networks

Controlling DNA nanodevices with light-switchable buffers

Control over synthetic DNA-based nanodevices can be achieved with a variety of physical and chemical stimuli. Actuation with light, however, is as advantageous as difficult to implement without modifying DNA strands with photo-switchable groups. Herein, we show that DNA nanodevices can be controlled using visible light in photo-switchable aqueous buffer solutions in a reversible and highly programmable fashion. The strategy presented here is non-invasive and allows the remote control with visible light of complex operations of DNA-based nanodevices such as the reversible release/loading of cargo molecules

label free fluorescence detection of kinase activity using a gold nanoparticle based indicator displacement assay

A straightforward fluorescence indicator-displacement assay (IDA) has been developed for the quantitative analysis of ATP→ADP conversion

Depression is associated with increased disease activity and higher disability in a large Italian cohort of patients with rheumatoid arthritis

Depression is a quite common comorbidity in patients with rheumatoid arthritis (RA) and is thought to influence its severity. This study aims to estimate, in a large cohort of Italian patients with RA, the prevalence of depression and to investigate the clinical correlates of depression in terms of disease activity and disability

An electric molecular motor

The computational investigations at California Institute of Technology were supported by National Science Foundation grant no. CBET-2005250 (W.-G.L. and W.A.G.).Macroscopic electric motors continue to have a large impact on almost every aspect of modern society. Consequently, the effort towards developing molecular motors that can be driven by electricity could not be more timely. Here we describe an electric molecular motor based on a [3]catenane , in which two cyclobis(paraquat-p-phenylene) (CBPQT4+) rings are powered by electricity in solution to circumrotate unidirectionally around a 50-membered loop. The constitution of the loop ensures that both rings undergo highly (85%) unidirectional movement under the guidance of a flashing energy ratchet , whereas the interactions between the two rings give rise to a two-dimensional potential energy surface (PES) similar to that shown by F0F1ATP synthase . The unidirectionality is powered by an oscillating voltage or external modulation of the redox potential . Initially, we focused our attention on the homologous [2]catenane, only to find that the kinetic asymmetry was insufficient to support unidirectional movement of the sole ring. Accordingly, we incorporated a second CBPQT4+ ring to provide further symmetry breaking by interactions between the two mobile rings. This demonstration of electrically driven continual circumrotatory motion of two rings around a loop in a [3]catenane is free from the production of waste products and represents an important step towards surface-bound electric molecular motors.Publisher PDFPeer reviewe

Organization and signal regulation in complex chemical systems

Supramolecular chemistry is the chemistry of the non-covalent bond, i.e. all those chemical processes relying on non-covalent interactions between molecules. In the last decades, chemists have learned to exploit non-covalent interactions for the construction of sensors, catalysts and materials. In particular self-assembly, defined as the spontaneous organization of small molecules into a well-defined structure has emerged as the most attractive way to prepare highly complex molecular architectures of nanosized dimensions. In this Thesis, the self-assembly of small molecules on the surface of monolayer protected gold nanoparticles (Au NPs) is introduced as an approach toward the realization of complex chemical systems with minimal synthetic efforts. An essential role is played by Au NPs as they provide a robust multivalent surface for the binding of external molecules. The unique features of Au NPs such as stability, biocompatibility, ease of preparation and optoelectronic properties have led to their wide-spread use in a variety of functional supramolecular systems. The Au NPs used in this Thesis have a monolayer composed of thiols terminating with a 1,4,7-triazacyclononane (TACN)•Zn2+ complex. The resulting multivalent cationic surface provides a scaffold for the binding of small anionic molecules (e.g. peptides and nucleotides). In the first part, the attention is focused on understanding the interactions that drive the self-assembly of small oliogoanions on the monolayer surface. This process was studied by means of fluorescence spectroscopy, taking advantage of the well-known ability of gold clusters to quench the fluorescence of bound fluorophores. It emerged that the high affinity is determined by i) the number of negative charges of the oligoanion, ii) the chemical nature of the anionic groups and iii) the presence of hydrophobic moieties able to penetrate into the apolar part of the monolayer. These studies also showed that the metal ions in the monolayer acts as regulatory elements of the self-assembly process. It was shown that the valency of the self-assembled system, i.e. the number of bound molecules , can be precisely controlled in a reversible manner by the addition and removal of Zn2+ from the monolayer. The ability to control the self-assembly process was demonstrated by showing that a mixture of two different oligoanions, with the same number of negative charges but with different anionic groups (phosphate vs carboxylate), spontaneously self-sorted on two different monolayer surfaces, thus creating two discrete topological domains in a homogeneous system. In the second part of the thesis, the obtained knowledge was used for the development of supramolecular sensors for the detection of small molecules and enzymes. The self-assembly of multiple fluorescence indicators on the monolayer surface resulted in a dynamic responsive surface able to generate finger-print patterns upon the addition of eight different di- and tri-nucleotides. The ability of the system to discriminate between ATP and ADP was then used for the development of a protein kinase assay relying on the monitoring of ATP→ADP conversion. With the aim to improve the sensitivity of this assay, an alternative system was subsequently developed in which ATP→ADP conversion led to activation of the catalytic activity of Au NPs. Also in this case a crucial role was played by the Zn2+ metal ions in the monolayer, by the formation of catalytic pockets able to catalyze a chromogenic reaction generating the output signal. In the final chapter all concepts were used to set up a dissipative system able to generate a transient signal, whose duration is determined by the amount of ATP added to the system. This last methodology provides for a straightforward way to gain temporal control over supramolecular processes, showing important analogies with the behaviours of natural systems.La chimica supramolecolare è definita come la chimica del legame non covalente, ovvero la chimica di tutti quei processi chimici che dipendono da interazioni non-covalenti tra molecole. Negli ultimi decenni, i chimici hanno imparato a sfruttare le interazioni non covalenti nello sviluppo di sensori, catalizzatori e materiali. In particolare, l'autoassemblaggio, definito come l'organizzazione spontanea di piccole molecole in una struttura ben definita, si è dimostrato essere il modo più conveniente per preparare architetture molecolari molto complesse e di dimensioni nanometriche. In questa Tesi, l'auto-assemblaggio di piccole molecole sulla superficie di nanoparticelle d'oro funzionalizzate (Au NPs) è usato come approccio per la realizzazione di sistemi chimici complessi, senza l'ausilio di complicate vie di sintesi. Le Au NPs svolgono un ruolo fondamentale, in quanto forniscono una robusta superficie polivalente per il legame con molecole esterne. Le caratteristiche uniche delle Au NPs, quali la stabilità, la biocompatibilità, la facilità di preparazione e le proprietà optoelettroniche, hanno portato ad una loro larga diffusione. Le Au NPs utilizzate in questa Tesi sono ricoperte da un monostrato organico composto da tioli la cui unità periferica è un legante (1,4,7-triazaciclononano) in grado di complessare ioni metallici come lo Zn2+. La superficie cationica multivalente che ne deriva fornisce un'ottima piattaforma per il legame di piccole molecole anioniche (per esempio peptidi e nucleotidi). Nella prima parte di questa Tesi, l'attenzione è stata focalizzata sulla comprensione delle interazioni che guidano l'auto-assemblaggio di piccoli oliogoanioni sulla superficie del monostrato. Questo processo è stato studiato mediante spettroscopia di fluorescenza, sfruttando le note capacità dei cluster d'oro di spegnere la fluorescenza di fluorofori ad essi legati. Da questi studi è emerso che l'alta affinità è determinata i) dal numero di cariche negative dell'oligoanione, ii) dalla natura chimica dei gruppi anionici e iii) dalla presenza di porzioni idrofobiche in grado di penetrare nella parte apolare del monostrato. Questi studi hanno inoltre dimostrato che gli ioni metallici nel monostrato sono in grado di regolare il processo di auto-assemblaggio. È stato dimostrato che la valenza del sistema auto-assemblato, ovvero il numero di molecole legate, può essere controllata con precisione in modo reversibile attraverso l'aggiunta e la rimozione di Zn2+. La capacità di controllare il processo di auto-assemblaggio è stato confermato dimostrando come due oligoanioni differenti, aventi lo stesso numero di cariche negative ma diversi gruppi anionici (fosfato vs carbossilato), siano capaci di auto-organizzarsi spontaneamente sulla superficie di due monostrati differenti, creando due domini topologici in un sistema omogeneo. Nella seconda parte della Tesi, la conoscenza acquisita è stata utilizzata per lo sviluppo di sensori supramolecolari atti alla rivelazione di piccole molecole ed enzimi. Attraverso l'auto-assemblaggio di più indicatori di fluorescenza sulla superficie di un unico monostrato è stato possibile realizzare una superficie in grado di generare segnali specifici in risposta all'aggiunta di otto diversi nucleotidi. La capacità del sistema di discriminare tra ATP e ADP è stata poi fruttata per lo sviluppo di un saggio per protein-chinasi, basato sul monitoraggio della conversione ATP→ADP. Al fine di migliorare la sensibilità di questo saggio, è stato successivamente sviluppato un sistema alternativo, in cui la conversione ATP→ADP porta all'attivazione dell'attività catalitica delle Au NPs. Anche in questo caso, gli ioni Zn2+ presenti nel monostrato giocano un ruolo cruciale, formando dei siti catalitici in grado di catalizzare una reazione cromogena e quindi di generare un segnale rilevabile. Nel capitolo finale, questi concetti sono stati usati per sviluppare un sistema dissipativo in grado di generare un segnale transiente, la cui durata dipende dalla quantità di ATP aggiunto al sistema. Quest'ultima metodologia fornisce un modo semplice per controllare processi supramolecolari a livello temporale, mostrando importanti analogie proprie dei sistemi naturali

Controlling supramolecular complex formation on the surface of a monolayer-protected gold nanoparticle in water

A combination of hydrophobic and electrostatic interactions drives the self-assembly of a large number of small molecules on the surface of a monolayer-protected gold nanoparticle. The hydrophobic interactions originate from the insertion of an aromatic unit in the hydrophobic part of the monolayer.This is evidenced by a shift in the emission wavelength of the fluorogenic probe upon binding. Up to around 35 small molecules can be simultaneously bound to the monolayer surface at micromolar concentrations in water. It is shown that an understanding of the supramolecular interactions that drive complex formation on the monolayer surface provides unprecedented control over the supramolecular chemistry occurring on the surface. By taking advantage of the different kinds of noncovalent interactions present in different probes, it is possibile to displace one type of surface-bound molecule from a heteromeric surface selectively. Finally, it is also possible to catch and release one type of surface-bound molecule selectively

Zn2+-Regulated Self-Sorting and Mixing of Phosphates and Carboxylates on the Surface of Functionalized Gold Nanoparticles

Herein, we describe the self-sorting of phosphateand carboxylate-containing molecules on the surface of monolayer-protected gold nanoparticles. Self-sorting is driven by selective interactions between the phosphate probe and Zn2+ complexes in one monolayer; these interactions force the carboxylate probe to move to a second type of nanoparticle. This process effectively separates the probes and causes their localization in well-defined spaces surrounding the nanoparticles. The removal/addition of Zn2+ metal ions from the system is used to convert the system from an ordered to a disordered state and vice versa. The possibility to control the location and transport of populations of molecules in a complex mixture creates new perspectives for the development of innovative complex catalytic systems that mimic nature

Light-induced assembly and disassembly of polymers with PdnL2n-type network junctions

Polymers containing PdnL2n complexes as network junctions were obtained by reaction of poly(ethylene glycol)-linked N-donor ligands with Pd2+. The addition of a metastable state photoacid renders the networks light sensitive, and gel–sol transitions can be achieved by irradiation with light. The inverse process, a light-induced sol–gel transition, was realized by using a molecularly defined Pd complex as an acid-sensitive reservoir for Pd2+. Upon irradiation, Pd2+ ions are released, allowing the formation of an acid-resistant polymer network. Both the gel–sol and the sol–gel transitions are reversed in the dark