Paolo Tecilla

Exploiting the Self-Assembly Strategy for the Design of Selective CuII Ion Chemosensors

Simply by mixing in water, a liphophilic dipeptide (L), a surfactant (S), and a fluorophore (F) self-assemble to give a sensor able to detect Cu(II) ions (see scheme). Despite the ease of construction, the sensor displays high selectivity and a low detection limit for the target ion. This new modular approach to sensing devices allows easy variations of the components, making optimization of the system very simple and fast.

Zinc(II) complexes as hydrolytic catalysts of phosphate diester cleavage: from model substrates to nucleic acids

The development of synthetic agents able to hydrolytically cleave phosphate diester bonds with high efficiency is a fascinating challenge, which will ultimately open the way to artificial nucleases able to compete with the natural enzymes. This Perspective highlights the progress reported in the realization of hydrolytic catalysts based on the Zn2+ ion, a metal ion which, due to its peculiar properties, is a very promising candidate. The review critically examines the reactivity of such catalysts toward model substrates and nucleic acids, paying particular attention to the strategies that can be pursued to improve efficiency and sequence selectivity.

Aluminium fluorescence detection with a FRET amplified chemosensorElectronic supplementary information (ESI) available: experimental details and spectra. See http://www.rsc.org/suppdata/cc/b3/b303195k/

A selective Al3+ fluorescence chemosensor able to detect concentrations of metal ion in the nanomolar range has been realized. The remarkable sensitivity is the result of the FRET amplification of the fluorescence emission of the ligand subunit.

Surface modification of silica nanoparticles: a new strategy for the realization of self-organized fluorescence chemosensors

The self-organization of the proper subunits of a fluorescence chemosensor on the surface of silica nanoparticles allows the easy design and realization of new effective sensing systems. Commercially available silica particles (20 nm diameter) were functionalized with triethoxysilane derivatives of selective Cu(II) ligands and fluorescent dyes. Grafting of the sensor components to the particle surface ensures the spatial proximity between the sensor components and, as a consequence, binding of Cu(II) ions by the ligand subunits leads to quenching of the fluorescent units emission. In 9 : 1 DMSO–water solution, the coated silica nanoparticles (CSNs) selectively detect copper ions down to nanomolar concentrations. The operative range of the sensors can be tuned either by switching the ligand units or by modification of the components ratio. Sensors with the desired photophysical properties can be easily prepared by using different fluorescent dyes. Moreover, the organization of the network of sensor components gives rise to cooperative and collective effects: on one hand, the ligand subunits bound to the particle surfaces cooperate to form multivalent binding sites with an increased affinity for the Cu(II) ions; on the other hand, binding of a single metal ion leads to the quenching of several fluorescent groups producing a remarkable signal amplification.

A fluorescence nanosensor for Cu2+ on silica particlesElectronic supplementary information (ESI) available: experimental procedure; TEM images; NMR, UV-vis and fluorescence spectra; fluoresence titration. See http://www.rsc.org/suppdata/cc/b3/b310582b/

A fluorescence nanosensor for Cu2+ ions has been obtained by surface functionalization of silica particles with trialkoxysilane derivatized ligand and fluorescent dye.

Fluorescence sensing of ionic analytes in water: from transition metal ions to vitamin B13.

The fluorescence chemosensor ATMCA has been realised by appending an anthrylmethyl group to an amino nitrogen of TMCA (2,4,6-triamino-1,3,5-trimethoxycyclohexane), a tripodal ligand selective for divalent first-row transition metal ions in water. The ATMCA ligand can act as a versatile sensor for ZnII and CuII ions. Its sensing ability can be switched by simply tuning the operating conditions. At pH 5, ATMCA detects copper(II) ions in aqueous solutions by the complexation-induced quenching of the anthracene emission. Metal ion concentrations < 1 microM can be readily detected and very little interference is exerted by other metal ions. At pH 7, ATMCA signals the presence of ZnII ions at concentrations < 1 microM by a complexation-induced enhancement of the fluorescence. Again the sensor is selective for ZnII over several divalent metal ions, with the exception of CuII, CoII and HgII. Most interestingly, the [ZnII(atmca)]2+ complex can act as a fluorescence sensor for specific organic species, notably selected dicarboxylic acids and nucleotides, by the formation of ternary ligand/zinc/substrate complexes. The oxalate anion is detected in concentrations <0.1 mM; however, no effects on the systems fluorescence is observed in the presence of monocarboxylic acids and long-chain dicarboxylic acids. Among the nucleotides, those containing an imide or amide function are readily detected and an unprecedented high sensitivity for guanine derivatives allows the determination of this nucleotide for 0.05-0.5 mM solutions. Moreover, [ZnII(atmca)]2+ is a very effective and selective sensor in the case of vitamin B13 (orotic acid) in sub-micromolar concentrations. The operative features of the systems investigated are also clearly suitable for intracellular analyses. The factors at the source of organic substrate recognition, here briefly discussed, are of paramount importance for further developments in the applicability of these sensing systems.

A new selective fluorescence chemosensor for Cu(II) in water

A new chemosensor for the Cu(II) ion has been realized by connecting via an amido bond an anthracenyl residue to the all cis 2,4,6-triamino-1,3,5-trihydroxycyclohexane ligand (TACI). This sensor is able to detect micromolar concentrations of Cu(II) ions in water at pH 7 without interference with many other divalent transition metal ions.

Ion transport through lipid bilayers by synthetic ionophores: modulation of activity and selectivity.

The ion-coupled processes that occur in the plasma membrane regulate the cell machineries in all the living organisms. The details of the chemical events that allow ion transport in biological systems remain elusive. However, investigations of the structure and function of natural and artificial transporters has led to increasing insights about the conductance mechanisms. Since the publication of the first successful artificial system by Tabushi and co-workers in 1982, synthetic chemists have designed and constructed a variety of chemically diverse and effective low molecular weight ionophores. Despite their relative structural simplicity, ionophores must satisfy several requirements. They must partition in the membrane, interact specifically with ions, shield them from the hydrocarbon core of the phospholipid bilayer, and transport ions from one side of the membrane to the other. All these attributes require amphipathic molecules in which the polar donor set used for ion recognition (usually oxygens for cations and hydrogen bond donors for anions) is arranged on a lipophilic organic scaffold. Playing with these two structural motifs, donor atoms and scaffolds, researchers have constructed a variety of different ionophores, and we describe a subset of interesting examples in this Account. Despite the ample structural diversity, structure/activity relationships studies reveal common features. Even when they include different hydrophilic moieties (oxyethylene chains, free hydroxyl, etc.) and scaffolds (steroid derivatives, neutral or polar macrocycles, etc.), amphipathic molecules, that cannot span the entire phospholipid bilayer, generate defects in the contact zone between the ionophore and the lipids and increase the permeability in the bulk membrane. Therefore, topologically complex structures that span the entire membrane are needed to elicit channel-like and ion selective behaviors. In particular the alternate-calix[4]arene macrocycle proved to be a versatile platform to obtain 3D-structures that can form unimolecular channels in membranes. In these systems, the selection of proper donor groups allows us to control the ion selectivity of the process. We can switch from cation to anion transport by substituting protonated amines for the oxygen donors. Large and stable tubular structures with nanometric sized transmembrane nanopores that provide ample internal space represent a different approach for the preparation of synthetic ion channels. We used the metal-mediated self-assembly of porphyrin ligands with Re(I) corners as a new method for producing to robust channel-like structures. Such structures can survive in the complex membrane environment and show interesting ionophoric behavior. In addition to the development of new design principles, the selective modification of the biological membrane permeability could lead to important developments in medicine and technology.

Nucleophilic catalysis of hydrolyses of phosphate and carboxylate esters by metallomicelles: Facts and misconceptions

Metallomicelles of Zn(II) and Cu(II) provide impressive accelerations of hydrolyses of triarylphosphates and p-nitrophenyl acetate, which are often ascribed to some special feature due to incorporation in an association colloid. If the rate data are analyzed in terms of local reactant concentrations in the micellar pseudo-phase, the second-order rate constants are very similar to those of reactions of monomeric complexes in water, i.e. the rate increases are due largely to concentration of reactants in the small volume at the micelle–water interface. Therefore the special micellar effects which are postulated to provide impressive accelerations of reactions are chimera which disappear when transfer equilibria between the aqueous and micellar pseudo-phases are taken into account.

Size-dependent cation transport by cyclic α-peptoid ion carriers

N-Benzyloxyethyl macrocyclic peptoids 3 and 4 were synthesized and subjected to alkali metal binding studies; these compounds, plus the known 1 and 2, when subjected to ion transport studies, demonstrated size-dependent selectivity for the first group alkali metals cation transport.