Self-assembled fluorescent chemosensors

Self-assembling and self-organizing methodologies are powerful tools for the "bottom-up" approach for the realization of complex structure with functional properties. Recently, this concept has been extended to the design of fluorescent chemosensors providing new exciting potentialities for the development of innovative sensing systems. This Concept Article deals mainly with this new approach and discusses its evolution, applications, and limitations.     

On the intercalation of the iodine-iodide couple on layered double hydroxides with different particle sizes

Molecular iodine was intercalated from nonaqueous solution into microsized ZnAl-layered double hydroxide (LDH) in the iodide form, generating the I(3)(-)/I(-) redox couple into the interlayer region. Chloroform, ethanol, acetonitrile, or diethyl ether were used as solvents to dissolve the molecular iodine. The intercalation compounds were characterized by thermogravimetric analysis, X-ray powder diffraction, UV-vis spectroscopy, and scanning and transmission electron microscopy. The stability of iodine-solvent adducts and the iodine concentration affected the LDH iodine loading, and samples with I(2)/I(-) molar ratio ranging from 0.14 to 0.82 were prepared. Nanosized, well dispersible LDH, synthesized by the urea method in water-ethylene glycol media, were also prepared and successfully functionalized with the I(3)(-)/I(-) redox couple applying the conditions optimized for the micrometric systems.     

Fluid-like behavior of a one-dimensional granular gas

We study the properties of a one-dimensional (1D) granular gas consisting of N hard rods on a line of length L (with periodic boundary conditions). The particles collide inelastically and are fluidized by a heat bath at temperature Tb and viscosity gamma. The analysis is supported by molecular dynamics simulations. The average properties of the system are first discussed, focusing on the relations between granular temperature Tg=mv2, kinetic pressure, and density rho=N/L. Thereafter, we consider the fluctuations around the average behavior obtaining a slightly non-Gaussian behavior of the velocity distributions and a spatially correlated velocity field; the density field displays clustering: this is reflected in the structure factor which has a peak in the k approximately 0 region suggesting an analogy between inelastic hard core interactions and an effective attractive potential. Finally, we study the transport properties, showing the typical subdiffusive behavior of 1D stochastically driven systems, i.e., approximately Dt(1/2), where D for the inelastic fluid is larger than the elastic case. This is directly related to the peak of the structure factor at small wave vectors.     

Preparation,characterization, and structure of zirconium fluoride alkylamino-N,N-bis methylphosphonates: a new design for layered zirconium diphosphonates with a poorly hindered interlayer region

This paper reports the preparation and characterization of the homologous series of layered zirconium fluoride n-alkylamino-N,N-bis methylphosphonates, of general formula ZrF(O(3)PCH(2))(2)NHC(n)H(2n+1) (n = 1, 2, 3, 4, 5, 6, 8, 9, 10), in which the two phosphonic groups of each diphosphonate building block participate in the assembly of a single lamella, because they are joined to zirconium atoms belonging to the same layer. The crystal structure of one of the series of these zirconium diphosphonates, ZrF(O(3)PCH(2))(2)NHC(5)H(11), has been solved "ab initio" by X-ray powder diffraction data. The structure is monoclinic, space group P2(1)/c. The zwitterionic character of the diphosphonate moiety is a distinctive feature which acts as a structure-orienting factor, generating a layer framework which is different from the other structures known for zirconium phosphates and phosphonates. This compound undergoes a phase transition at 117 degrees C which involves a rearrangement of the interlayer alkyl chains. The structure of the high-temperature phase has been refined by the Rietveld method. Because only one organic residue is associated with two phosphonate tetrahedra, a poorly hindered interlayer region is formed, and alkyl chains bonded to adjacent layers are interdigitated. Preliminary experiments have shown that these compounds are able to intercalate organic molecules, such as n-alkanols, from very dilute water solutions.     

Heterodinuclear Ln[bond]Na complexes with an asymmetrical macrocyclic compartmental Schiff base

Heterodinuclear lanthanide(III)-sodium(I) complexes [LnNa(L)(Cl)(2)(CH(3)OH)] (Ln=La[bond]Nd, Sm[bond]Lu), where H(2)L is a [1+1] asymmetric compartmental macrocyclic ligand containing a N(3)O(2) Schiff base and a O(3)O(2) crown-ether-like coordination site, have been prepared and characterized by IR, (1)H, (13)C, and (23)Na NMR spectroscopy, mass spectrometry, and electron microscopy. In the solid state, the lanthanide(III) ions coordinate the Schiff-base N(3)O(2) site, and the sodium ion occupies the O(3)O(2) crownlike cavity, as shown by the X-ray crystal structures of the Nd, Eu, Gd, and Yb derivatives. In these complexes, the lanthanide(III) ion is coordinated by two chlorine atoms in the trans position and by three nitrogen and two negatively charged phenol oxygen atoms of the Schiff base, and the ion is heptacoordinated with a pentagonal bipyramidal geometry. The sodium ion is coordinated by three etheric oxygen atoms and the two phenolic oxygens that act as a bridge. A methanol molecule is also coordinated in the apical position of the resulting pentagonal pyramidal polyhedron. A detailed (1)H and (13)C NMR study was carried out in CD(3)OD for both diamagnetic and paramagnetic heterodinuclear complexes [LnNa(L)(Cl)(2)(CH(3)OH)]. The complexes are also isostructural in solution, and their structures parallel those found in the solid state. Moreover, some significative distances determined in the solid state and in solution are comparable. Finally, the potential use of these complexes as molecular probes for the selective recognition of specific metal ions has been tested. In particular, their ability to act as shift reagents and the selectivity of the O(3)O(2) site towards Li(+), Ca(2+), and K(+) were investigated by (23)Na NMR spectroscopy.     

Interaction of NO with nanosized Ru-, Pd-, and Pt-Doped SnO2: electron paramagnetic resonance, Mössbauer, and electrical investigation

The mechanism of NO interaction with nanosized Ru(Pd,Pt)-doped SnO(2) was studied by electron paramagnetic resonance, M?ssbauer, and electric resistance measurements. Three steps were proposed for the reaction between the semiconductor oxide and the gaseous component: (i) the formation of bielectronic oxygen vacancies (V(o)) in SnO(2); (ii) their single-ionization (V(o)(*)) with injection of electrons into the SnO(2) conduction band; (iii) the subsequent transfer of electrons from V(o)(*) to [Ru(Pd,Pt)](4+). The last process induces the formation of further oxygen vacancies which reduce the transition metal centers to lower oxidation states; the redox processes is enhanced and the electrical resistance in transition metal-doped SnO(2) is stronger modified with respect to the undoped material.     

Oxazinins from toxic mussels: isolation of a novel oxazinin and reassignment of the C-2 configuration of oxazinin-1 and -2 on the basis of synthetic models

The analysis of a batch of toxic mussels (Mytilus galloprovincialis) from the Northern Adriatic Sea led to the isolation of a novel oxazinin, oxazinin-4. Its structure including the relative stereochemistry has been elucidated through extensive NMR analysis. A synthetic route to oxazinins has been crucial in establishing the absolute stereochemistry of oxazinin-4 and for reassigning the absolute C-2 configuration of oxazinin-1 and -2 previously isolated from toxic shellfish and stereostructurally characterized.