Luca Giorgi

A Macrocyclic Ligand as Receptor and ZnII‐Complex Receptor for Anions in Water: Binding Properties and Crystal Structures

Binding properties of 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo[19.5.5.0(5,8).0(14,17)]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Δ(5,8),Δ(14,17)-diene ligand L towards Zn(II) and anions, such as the halide series and inorganic oxoanions (phosphate (Pi), sulfate, pyrophosphate (PPi), and others), were investigated in aqueous solution; in addition, the Zn(II)/L system was tested as a metal-ion-based receptor for the halide series. Ligand L is a cryptand receptor incorporating two squaramide functions in an over-structured chain that connects two opposite nitrogen atoms of the Me(2)[12]aneN(4) polyaza macrocyclic base. It binds Zn(II) to form mononuclear species in which the metal ion, coordinated by the Me(2)[12]aneN(4) moiety, lodges inside the three-dimensional cavity. Zn(II)-containing species are able to bind chloride and fluoride at the physiologically important pH value of 7.4; the anion is coordinated to the metal center but the squaramide units play the key role in stabilizing the anion through a hydrogen-bonding network; two crystal structures reported here clearly show this aspect. Free L is able to bind fluoride, chloride, bromide, sulfate, Pi, and PPi in aqueous solution. The halides are bound at acidic pH, whereas the oxoanions are bound in a wide range of pH values ranging from acidic to basic. The cryptand cavity, abundant in hydrogen-bonding sites at all pH values, allows excellent selectivity towards Pi to be achieved mainly at physiological pH 7.4. By joining amine and squaramide moieties and using this preorganized topology, it was possible, with preservation of the solubility of the receptor, to achieve a very wide pH range in which oxoanions can be bound. The good selectivity towards Pi allows its discrimination in a manner not easily obtainable with nonmetallic systems in aqueous environment.

Efficient fluorescent sensors based on 2,5-diphenyl[1,3,4]oxadiazole: a case of specific response to Zn(II) at physiological pH.

The coordination properties and photochemical responses of three fluorescent polyamine macrocycles, 9,12,15,24,25-pentaaza-26-oxatetracyclo[21.2.1.0(2,7).0(17,22)]hexaicosa-2,4,6,17,19,21,23,25(1)-octaene (L1), 9,12,15,18,27,28-hexaaza-29-oxatetracyclo[24.2.1.0(2,7).0(20,25)]enneicosa-2,4,6,20,22,24,26,28(1)-octaene (L2), and 9,12,15,18,21,30,31-heptaaza-32-oxatetracyclo[27.2.1.0(2,7).0(23,28)]diatriconta-2,4,6,23,25,27,29,31(1)-octaene (L3), toward Cu(II), Zn(II), Cd(II), and Pb(II) are reported. Each ligand contains the 2,5-diphenyl[1,3,4]oxadiazole (PPD) moiety inserted in a polyamine macrocycle skeleton. The stability constants were determined by means of potentiometric measurements in aqueous solution. L1 forms mononuclear complexes only with Cu(II). L2 and L3 form stable mononuclear species with all of the metals, while L3 is able to form dinuclear Cu(II) species. The fluorescence of all ligands was totally quenched by the presence of Cu(II). L2 behaves as an OFF-ON sensor for Zn(II) under physiological conditions, even in the presence of interfering species such as Cd(II) and Pb(II). This ligand combines selective binding of Zn(II) with a highly specific fluorescent response to Zn(II) due to the chelating enhancement of fluorescence (CHEF) effect. The interaction of Zn(II), Cd(II), and Pb(II) with L3 does not produce an appreciable enhancement of fluorescence at the same pH. The different behavior is attributed to the cavity size of the macrocycle and to the number of amine functions. L2 possesses the best arrangement of these two characteristics, allowing a full participation of all of the amine functions in metal coordination, as shown by the crystal structures of [CuL2(ClO(4))](ClO(4))·H(2)O and [ZnL2Br]Br·H(2)O species; this prevents the PET effect and supplies the higher CHEF effect. The interaction between L2 and Zn(II) can also be observed with the naked eye as an intense sky blue emission.

A new versatile solvatochromic amino-macrocycle. From metal ions to cell sensing in solution and in the solid state

A new fluorescent NBD-polyaza-macrocycle sensor (L) was synthesized. The coordination of Cu(ii) and Zn(ii) in acetonitrile switches on the fluorescence with different emission wavelengths. Cu(ii) complexes showed solid-state fluorescence. Both L and Cu-complex interact with human cell line (U937) highlighting the cell membrane by fluorescence microscopy.

Oxidized Ultrashort Nanotubes as Carbon Scaffolds for the Construction of Cell-Penetrating NF-κB Decoy Molecules

Oligonucleotide (ODN) decoys are synthetic ODNs containing the DNA binding sequence of a transcription factor. When delivered to cells, these molecules can compete with endogenous sequences for binding the transcription factor, thus inhibiting its ability to activate the expression of target genes. Modulation of gene expression by decoy ODNs against nuclear factor-kappaB (NF-kappaB), a transcription factor regulating many genes involved in immunity, has been achieved in a variety of immune/inflammatory disorders. However, the successful use of transcription factor decoys depends on an efficient means to bring the synthetic DNA to target cells. It is known that single-walled carbon nanotubes (SWCNTs), under certain conditions, are able to cross the cell membrane. Thus, we have evaluated the possibility to functionalize SWCNTs with decoy ODNs against NF-kappaB in order to improve their intracellular delivery. To couple ODNs to CNTs, we have exploited the carbodiimide chemistry which allows covalent binding of amino-modified ODNs to carboxyl groups introduced onto SWCNTs through oxidation. The effective binding of ODNs to nanotubes has been demonstrated by a combination of microscopic, spectroscopic, and electrophoretic techniques. The uptake and subcellular distribution of ODN decoys bound to SWCNTs was analyzed by fluorescence microscopy. ODNs were internalized into macrophages and accumulated in the cytosol. Moreover, no cytotoxicity associated with SWCNT administration was observed. Finally, NF-kappaB-dependent gene expression was significantly reduced in cells receiving nanomolar concentrations of SWCNT-NF-kappaB decoys compared to cells receiving SWCNTs or SWCNTs functionalized with a nonspecific ODN sequence, demonstrating both efficacy and specificity of the approach.

Multi-use NBD-based tetra-amino macrocycle: fluorescent probe for metals and anions and live cell marker.

Ligand L (4-(7-nitrobenzo[1,2,5]oxadiazole-4-yl)-1,7-dimethyl-1,4,7,10-tetra-azacyclododecane) is a versatile fluorescent sensor useful for Cu(II), Zn(II) and Cd(II) metal detection, as a building block of fluorescent metallo-receptor for halide detection, and as an organelle marker inside live cells. Ligand L undergoes a chelation-enhanced fluorescence (CHEF) effect upon metal coordination in acetonitrile solution. In all three complexes investigated the metal cation is coordinatively unsaturated; thus, it can bind secondary ligands as anionic species. The crystal structure of [ZnLCl](ClO(4)) is discussed. Cu(II) and Zn(II) complexes are quenched upon halide interaction, whereas the [CdL](2+) species behaves as an OFF-ON sensor for halide anions in acetonitrile solution. The mechanism of the fluorescence response in the presence of the anion depends on the nature of the metal ion employed and has been studied by spectroscopic methods, such as NMR spectroscopy, UV/Vis and fluorescence techniques and by computational methods. Subcellular localization experiments performed on HeLa cells show that L mainly localizes in spot-like structures in a polarized portion of the cytosol that is occupied by the Golgi apparatus to give a green fluorescence signal.

Direct Preparation of Unsymmetrical Difunctionalized Cyclen Derivatives by an Ugi Multicomponent Reaction

A new and efficient synthetic protocol for the preparation of unsymmetrical difunctionalized cyclen and its close derivatives using a modified Ugi reaction (N-split Ugi) is described. The scope of this methodology is further extended by the successful use of various isocyanides, highly functionalized carboxylic acids, and aldehydes.

Polynuclear Complexes: Two Amino−Phenol Macrocycles Spaced by Several Linear Polyamines; Synthesis, Binding Properties, and Crystal Structure

The synthesis and characterization of the new polytopic ligands 1,14-bis(3,6,9-triaza-15-hydroxybicyclo[9.3.1]pentadeca-11,13,1(15)-trien-6-yl)-3,6,9,12-tetraazatetradecane L1, 1,15-bis(3,6,9-triaza-15-hydroxybicyclo[9.3.1]pentadeca-11,13,1(15)-trien-6-yl)-3,6,10,13-tetraazapentadecane L2, and 1,16-bis(3,6,9-triaza-15-hydroxybicyclo[9.3.1]pentadeca-11,13,1(15)-trien-6-yl)-3,7,10,14-tetraazahexadecane L3, containing two equal amino-phenol macrocycles spaced by several linear tetraamines, are reported. The basicity and coordination behavior toward the Cu(II) ion were potentiometrically determined in aqueous solution at 298.1 K. All the ligands show similar acid-base properties behaving as octaprotic bases in the examined pH range (pH = 2-12). The acid protons of L1-L3 cannot be removed under the experimental conditions used; thus, the main deprotonated species obtainable in aqueous solution are the neutral ligands, having amphionic character as demonstrated by UV-vis experiments. These species are able to form mono-, di-, and trinuclear Cu(II) complexes having stoichiometry [CuL](2+), [Cu(2)L](4+), and [Cu(3)L](6+), respectively, that can lose one or two protons giving rise to [CuH(-1)L](+), [Cu(2)H(-2)L](2+), and [Cu(3)H(-2)L](4+). Depending on the used ligand to metal molar ratio, the mono-, di-, or trinuclear species prevail over the others in solution. Both di- and trinuclear complexes are able to add secondary ligands (such as OH(-)), and in some cases two Cu(II) can cooperate to stabilize them by coordinating the guest in a bridged conformation. The structure of the [Cu(2)L3](4+) cation was resolved by X-ray analysis of the {[Cu(2)L3](ClO(4))(4) x 3 H(2)O}(2) x H(2)O crystalline complex. It shows that each Cu(II) is penta-coordinated by one phenolate oxygen, two amine functions, belonging to one macrocyclic unit, and two amine functions of the spacer; in this species the distance between the two Cu(II) is about 5.3 A.

Modulating the Sensor Response to Halide Using NBD-Based Azamacrocycles

Ligand L (2,6-bis{[7-(7-nitrobenzo[1,2,5]oxadiazole-4-yl)-3,10-dimethyl-1,4,7,10-tetraazacyclododeca-1-yl]methyl}phenol) is a fluorescent sensor that is useful for detecting Cu(II), Zn(II), and Cd(II). Some of the complexes formed are able to sense the presence of halides in solution. L passes through the cellular membrane, becoming fluorescent inside cells. The H(-1)L- species is able to form dinuclear complexes with [M(2)H(-1)L]3+ stoichiometry with Cu(II), Zn(II), and Cd(II) ions, experiencing a CHEF effect upon metal coordination in an acetonitrile/water 95:5 (v/v) solution. In all three of the complexes investigated, the metal cations are coordinatively unsaturated and can therefore bind secondary ligands as anionic species. The crystal structure of [Cd(2)(H(-1)L)Cl(2)](ClO(4))·4H(2)O is discussed. The Zn(II) complex behaves as an OFF-ON sensor for fluoride and chloride anions.

New family of polyamine macrocycles containing 2,5-diphenyl[1,3,4]oxadiazole as a signaling unit. Synthesis, acid-base and spectrophotometric properties.

Synthesis and acid-base properties for three fluorescent polyamine macrocycles 9,12,15,24,25-pentaaza-26-oxatetracyclo[21.2.1.0(2,7).0(17,22)]hexaicosa-2,4,6,17,19,21,23,25(1)-octaene (L1), 9,12,15,18,27,28-hexaaza-29-oxatetracyclo[24.2.1.0(2,7).0(20,25)]enneicosa-2,4,6,20,22,24,26,28(1)-octaene (L2) and 9,12,15,18,21,30,31-heptaaza-32-oxatetracyclo[27.2.1.0(2,7).0(23,28)]diatriconta-2,4,6,23,25,27,29,31(1)-octaene (L3) are reported. Each ligand contains the 2,5-diphenyl[1,3,4]oxadiazole (PPD) unit incorporated in the polyamine macrocycle. The protonation constants of L1-L3 were determined by means of potentiometric measurements in 0.15 mol dm(-3) NaCl aqueous solution at 298.1 K. All the ligands are highly fluorescent in aqueous solution under acidic conditions (pH < 2) and their emission drastically decreases when the pH is increased. At pH > 8, a total quenching of fluorescence is observable in all the ligands. The fluorescence is given by the PPD unit, while the behavior as a function of pH can be rationalized on the basis of photoinduced intramolecular electron transfer (PET) from the HOMO of the donor macrocycle nitrogen atoms to the excited fluorophore unit. The insertion of PPD in a polyamine skeleton strongly improves the fluorescence quantum yield of this class of ligands with respect to those already known.

Two polyaminophenolic fluorescent chemosensors for H+ and Zn(II). Spectroscopic behaviour of free ligands and of their dinuclear Zn(II) complexes

The UV-Vis and fluorescence optical properties of the two polyamino-phenolic ligands 3,3′-bis[N,N-bis(2-aminoethyl)aminomethyl]-2,2′-dihydroxybiphenyl (L1) and 2,6-bis{[bis(2-aminoethyl)amino]methyl}phenol (L2) were investigated in aqueous solution at different pH values as well as in the presence of Zn(II) metal ion. Both ligands show two diethylenetriamine units separated by the 1,1′-bis(2-phenol) (BPH) or the phenol (PH) for L1 and L2, respectively. Both ligands are fluorescence-emitting systems in all fields of pH examined, with L1 showing a higher fluorescence emission than L2. In particular, the emission of fluorescence mainly depends on the protonation state of the phenolic functions and thus on pH. The highest emitting species is H3L3+ for both systems, where the BPH is monodeprotonated (in L1) and the PH is in the phenolate form (in L2). On the contrary, when BPH and PH are in their neutral form both ligands show the lowest fluorescence, since H-bonds occurring between the phenol and the closest tertiary amine functions decrease fluorescence. The Zn(II)-dinuclear species are also fluorescent in the pH range where they exist; the highest emitting species being [Zn2(H−2L1)]2+ and [Zn2(H−1L2)]3+ which are present in a wide range of pH including the physiological one. Fluorescence experiments carried out at physiological pH highlighted that, in the case of L1, the presence of Zn(II) ion in solution produces a simultaneous change in λem with a drop in fluorescence due to the formation of the [Zn2(H−2L1)]2+ species, while, in the case of L2, it gives rise to a strong CHEF effect (a twenty-fold enhancement was observed) due to the formation of the [Zn2(H−1L2)]3+ species. These results, supported by potentiometric, 1H and 13C NMR experiments, are of value for the design of new efficient fluorescent chemosensors for both H+ and Zn(II) ions.