Francesco Foti

Using micelles for a new approach to fluorescent sensors for metal cations

A new approach based on self-assembly inside micelles has been individuated to prepare a system behaving as a water-operating selective fluorescent sensor for Cu2+ and Ni2+.

Light-emitting molecular machines: pH-induced intramolecular motions in a fluorescent nickel(II) scorpionate complex.

A cyclam-like macrocycle has been synthesized with a pendant arm containing a dansylamide group. In the corresponding nickel(II) complex, binding of the pendant arm to the metal is pH controlled. In particular, at pH 4.3, the sulfonamide group deprotonates and coordinates the NiII center, giving rise to a complex of trigonal bipyramidal stereochemistry, as shown by X-ray diffraction studies performed on the crystalline complex salt. At pH 7.5, an OH- ion binds the metal and a six-coordinate species forms. The binding-detachment of the pendant arm to/from the NiII center is signaled by changes in the emission properties of the dansyl subunit in the side chain; the fluorescence of this side chain is high when the pendant arm is not coordinated and low when the sulfonamide group is bound to the metal. The system investigated represents the prototype of a light-emitting molecular machine, driven by a pH change.

Further insights on the high–low spin interconversion in nickel(II) tetramine complexes. Solvent and temperature effects

The spin interconversion equilibrium involving the [Ni(II)(cyclam)]2+ complex has been investigated in a variety of polar solvents, at varying temperatures. The greater the donor tendencies of the solvent, the higher the endothermicity of the high-to-low-spin conversion. In particular, a positive linear relationship exists between DeltaHdegrees and Gutmanns Donor Number (DN). In the same way, higher donor tendencies of the solvent favour the occurrence of the Ni(II)-to-Ni(III) oxidation process and negative linear relationship has been found between the E1/2(Ni(III)/Ni(II)) and DN. General behaviour is related to the intensity of the metal-solvent axial bonds in the octahedrally elongated cyclam complexes (of both Ni(II) and Ni(III)).

Molecular Devices Based on Metallocyclam Subunits

Publisher Summary This chapter explains that metal complexes of cyclam derivatives, including scorpionands, can perform some elementary functions at the molecular level (signalling, sensing, controlling of molecular motions). These, and other, functions result from the combination of the unique properties displayed by cyclam and related synthetic macrocycles. Cyclam (1,4,8,11-tetra-aza-cyclotetradecane, 3) is the prototype of synthetic aza-macrocycles. It tends to encircle transition metal ions to give complexes of trans-octahedral geometry, which display some peculiar properties: (i) high thermodynamic stability (the thermodynamic macrocyclic effect); (ii) extreme inertness to demetallation (the so-called kinetic macrocyclic effect); (iii) rich redox activity of the metal centre and stabilization of unusually high oxidation states: Ni III , Cu III , Ag II and Ag III and, as a transient, Hg III . The chapter discusses various properties that make cyclam and its metal complexes convenient and versatile subunits for building multicomponent systems displaying a variety of functions. The 2-substituted positional isomer is expected to favor the coordination of the nitro–nitronate group to transition metal centre, encircled by the cyclam ring.

5-Benzoylamino-3-bromo-4-(4-methoxyphenyl)-4,5-dihydroisoxazole-5-carboxylic acid.

The title compound, C18H15BrN2O5, a promising N-protected alpha-amino acid, was synthesized directly from an unusual bromo dipole and a 4-(arylmethylene)oxazolone. The crystal packing of the title compound is a racemic mixture. Peculiar graph-set motifs driven by the most important hydrogen bonds are described.

Four bromo-substituted pyrazoline and isoxazolinone spiro derivatives

Conformational analyses and a structural comparison of the four spiro compounds 3-bromo-1,9-diphenyl-4-p-tolyl-7-oxa-1,2,8-triazaspiro[4.4]nona-2,8-dien-6-one, (I), C(24)H(18)BrN(3)O(2), 3-bromo-4-(4-methoxyphenyl)-1,9-diphenyl-7-oxa-1,2,8-triazaspiro[4.4]nona-2,8-dien-6-one, (II), C(24)H(18)BrN(3)O(3), 3-bromo-4-(4-chlorophenyl)-1,7,9-triphenyl-1,2,7,8-tetraazaspiro[4.4]nona-2,8-dien-6-one, (III), C(29)H(20)BrClN(4)O, and 3-bromo-1,7,9-triphenyl-4-p-tolyl-1,2,7,8-tetraazaspiro[4.4]nona-2,8-dien-6-one, (IV), C(30)H(22.89)Br(1.11)N(4)O, are presented. The molecular structures are rather similar, which is as expected since the compounds are all products of concerted 1,3-dipolar attack on (Z)-4-arylidene oxazolone and pyrazolone derivatives. The observed conformations tend to favour extended pi conjugation of the benzene rings and other pi systems, as shown by a comparison of selected geometric parameters of the four structures.

Regio and diastereoselective lactonisation of enolisable 1,3-dicarbonyls by reaction with mesoionic 1,3-oxazolium-5-olatesElectronic supplementary information (ESI) available: 3-D rotatable structure of 3a. See http://www.rsc.org/suppdata/cc/b3/b304560a/

The one-pot reaction of enolisable 1,3-dicarbonyls and N-methyl-1,3-oxazolium-5-olate derivatives provided enol lactones directly in good yield and with excellent regio- and diastereocontrol.