Umberto Tonellato

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.

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.

Phosphate Diester and DNA Hydrolysis by a Multivalent, Nanoparticle-Based Catalyst

2-nm gold nanoclusters coated with Zn(II) complexes bearing auxiliary hydrogen bond donors act as multivalent catalysts capable of promoting the hydrolysis of model phosphate diesters with exceptional activity and inducing DNA double strand cleavage.

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.

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.

Very strong binding and mode of complexation of water-soluble porphyrins with a permethylated β-cyclodextrin

Abstract Heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin in a pH=7.0 aqueous solution binds meso -tetrakis(4-carboxyphenyl) porphyrin and its zinc complex to yield 2:1 complexes with exceptionally high binding constants. The mode of binding, involving the inclusion of two opposite aryl groups in the cyclodextrin cavity, is clearly defined by a detailed NMR analysis.

Insights on Nuclease Mechanism: The Role of Proximal Ammonium Group on Phosphate Esters Cleavage

The role of remotely located ammonium groups in the active site of many phosphate-cleaving enzymes is investigated by using model systems thus providing mechanistic hints to a still unsolved problem.