Nelsi Zaccheroni

Systematic approach in Mg2+ ions analysis with a combination of tailored fluorophore design

A systematic study of a series of diaza-18-crown-6 8-hydroxyquinoline (DCHQ) chemosensors, devoted to Mg(II) ion detection, was performed. Functionalization of DCHQ by peripheral substituents allowed the development of novel all-solid-state optodes via inclusion inside PVC-based polymeric films. The influence on the DCHQ-based optode response of the lipophilic sites functionalization and of the nature of the plasticizer, was investigated. Fluorimetric studies on optodes sensitivity towards a number of different metal cations (Ca2+, Na+, K+, Li+, Co2+, Cd2+, Pb2+, Cu2+, Hg2+, Zn2+) and NH4+ were carried out. The results demonstrated the suitability of the DCHQ optodes to perform fast monitoring (<10s) of magnesium (II) ions. Emission light signal was sufficiently brilliant to be captured by a low-cost computer webcam. The phenyl-substituted DCHQ-Ph derivative showed the best performance with a wide range for Mg(II) ion determination between 2.7xa0×xa010-7 and 2.2xa0×xa010-2xa0mol/L. It was possible, therefore, to determine the concentrations of Mg(II) in commercial fertilizer samples by DCHQ-Ph-based optodes with acceptable results: recoveries of 96.2-104.9% and relative standard deviation (RSD, nxa0=xa06) less than 5%. Moreover, in comparison to single sensors, the use of an array composed of five optodes (the ones showing the best performances in the preliminary tests) has allowed to reduce the RSD of magnesium determination in real samples (down to 3.7% with respect to 5.5% for single optodes) and to achieve a detection limit (estimated by s/nxa0=xa03 method) as low as 4.6xa0×xa010-7xa0mol/L.

Naturally Inspired Molecules as Multifunctional Agents for Alzheimer’s Disease Treatment

Alzheimer’s disease (AD) has been defined as a multi-factorial disorder resulting from a complex array of networked cellular and molecular mechanisms. In particular, elevated levels of Aβ protein and its aggregation products in the presence of metal ions proved to be highly neurotoxic and therapeutic strategies aimed at preventing Aβ generation and oxidative stress may represent an effective approach for AD treatment. A recent paradigm for the treatment of complex diseases such as AD suggests the employment of multifunctional compounds, single chemical entities capable of simultaneously modulating different targets involved in the pathology. In this paper, the “pharmacophores combination” strategy was applied, connecting the main scaffold of the BACE-1 ligand 1 to that of the chalcone 2, as metal chelating pharmacophore, to obtain a small library of compounds. Conjugate 5 emerged as the most interesting derivative, proving to inhibit BACE-1 with low-micromolar potency, and showing neuroprotective effects. In particular, 5 proved to be able to protect from metal-associated oxidative stress by hampering intracellular Cu2+-induced ROS formation without any direct neurotoxic effect.

Visible and Near-IR Emissions from k2N- and k3N-Terpyridine Rhenium(I) Assemblies Obtained by an [n*1] Head-to-Tail Bonding Strategy

An [n×1] head-to-tail bonding strategy has been used for the synthesis of ReI metallacycles. From a k3 N-dicarbonyl precursor, a single discrete [4×1] square assembly was isolated and characterized, whereas a k2 N-tricarbonyl precursor led to two major species, a square and a [3×1] triangular assembly. Solid-state X-ray diffraction study has confirmed the high angular distortion (71° to 96°) of the k2 N precursors. The electrochemical reversibility of the triangular (5) and square (6, 7) assemblies is increased with respect to that of their precursors. Photophysical investigation has confirmed pronounced red-shifts in the emissions of the k3 N-dicarbonyl species 4 (935u2005nm) and 7 (980u2005nm), as confirmed by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.

Luminescent Silica Nanoparticles Featuring Collective Processes for Optical Imaging

The field of nanoparticles has successfully merged with imaging to optimize contrast agents for many detection techniques. This combination has yielded highly positive results, especially in optical and magnetic imaging, leading to diagnostic methods that are now close to clinical use. Biological sciences have been taking advantage of luminescent labels for many years and the development of luminescent nanoprobes has helped definitively in making the crucial step forward in in vivo applications. To this end, suitable probes should present excitation and emission within the NIR region where tissues have minimal absorbance. Among several nanomaterials engineered with this aim, including noble metal, lanthanide, and carbon nanoparticles and quantum dots, we have focused our attention here on luminescent silica nanoparticles. Many interesting results have already been obtained with nanoparticles containing only one kind of photophysically active moiety. However, the presence of different emitting species in a single nanoparticle can lead to diverse properties including cooperative behaviours. We present here the state of the art in the field of silica luminescent nanoparticles exploiting collective processes to obtain ultra-bright units suitable as contrast agents in optical imaging and optical sensing and for other high sensitivity applications.

Zn2+/Cd2+ optical discrimination by fluorescent acridine-based bis-macrocylic receptors

Abstract A new acridine-based fluorescent chemosensor, L2, featuring two sulfurated macrocyclic units has been synthesised. Proton and metal binding properties of L2 have been studied in H2O/CH3CN (1:1 v/v) by potentiometric and spectrophotometric measurements and compared with those of the analogous and previously published bis-macrocyclic receptor featuring two [9]aneN3 units (L1). Despite a thermodynamic selectivity observed for Zn2+ with both L1 and L2, L2 shows a marked sensing selectivity towards Cd2+ via a chelation enhancement of fluorescence (CHEF) effect both in H2O/CH3CN (1:1 v/v) and in H2O using silica core-PEG shell nanoparticles as vehiculant. On the other hand, L1 shows a selective optical sensing towards Zn2+ in agreement with the thermodynamic selectivity observed for the same metal ion.

Luminescent Chemosensors: From Molecules to Nanostructures

Chemical analysis has been improved by the advent of sensory devices based on chemosensors that are able to transform chemical information (composition, concentration, etc.) into an analytically useful signal. These devices, in fact, find applications in many different areas of great social and economic impact. Among all the possible chemosensors, we focus here our attention on luminescent ones as they present many advantages such as sensitiveness, low cost, ease of use and versatility. After a discussion on their pros and cons and of the most important features in the design of new species with customized properties, we present selected examples of different chemosensors that take advantage from various transduction mechanisms always following a supramolecular approach. A step forward in the research and application has been done implementing these structures in nanosized materials to obtain powerful and versatile platforms for addressing crucial issues in sensing, imaging, and molecular testing. In this context we have chosen to restrict the discussion on luminescent multichromophoric silica-based nanoprobes as a virtuous example of how a high design versatility allows the preparation of nanostructures where modulation and multifunctionality offer the possibility to induce collective energy- and electron-transfer processes, that are at the base of signal amplification effects.