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Piero Paoletti

Publications and source records attributed to Piero Paoletti.

8 recordsLinked to original sources
PubMed2004

Coordination features of ditopic oxa-azamacrocycles toward Ni(II) and Co(II). Dioxygen uptake by their dinuclear Co(II) complexes.

The coordination properties of the ditopic oxa-aza macrocycles L1-L3 toward Ni(II) and Co(II) have been investigated by means of potentiometric and UV-vis spectrophotometric measurements. L1-L3 contain two triamine and/or tetraamine chains separated by two dioxa chains and form both mono- and dinuclear complexes in aqueous solution. In the [ML]2+ complexes, the metal ion is coordinated by one of the two polyamine moieties, while the other does not participate in the coordination. In the dinuclear complexes each metal ion is coordinated, almost independently, to a single polyamine moiety. Under aerobic conditions the binuclear Co(II) complexes of the ligands L1-L3 are able to bind molecular oxygen, with a bridging coordination of O2 between the two metals.

Aza Compounds↗
PubMed2002

Synthesis of new tren-based tris-macrocycles. Anion cluster assembling inside the cavity generated by a bowl-shaped receptor.

The synthesis of three new tris-macrocycles, containing three [12]aneN(4) (L1), [12]aneN(3)O (L2), or [14]aneN(4) (L3) moieties appended to a tren unit, is reported. The crystal structure of the [(Na(ClO(4))(6)) subset L1(2)H(13)]Na(6)Cl(2)(ClO(4))(12) compound shows the anionic cluster [Na(ClO(4))(6)](5)(-) assembled inside the cavity defined by two bowl-shaped polyammonium receptors, held by multiple charge-charge and hydrogen bond interactions.

Journal Article↗
PubMed1999

Design of Ligands That Stabilize Cu(I) and Shift the Reduction Potential of the Cu(II/I) Couple Cathodically in Aqueous Solutions.

The ligands R(2)NCH(2)CH(2)N(R)CH(2)CH(2)N(R)CH(2)CH=CH(2), where R = H, CH(3), were synthesized. The stability constants of their complexes with Cu(II) and Cu(I) in aqueous solutions were determined. Both ligands stabilize Cu(I) in aqueous solutions, though the reduction potentials of both (CuL(i)())(2+/+) couples are shifted cathodically in comparison to the Cu(2+/+)(aq) couple. These properties indicate that these complexes should be good catalysts for a variety of processes that are catalyzed by Cu(I).

Journal Article↗
PubMed1999

Palladium(II) Complexation by p-Cyclophane Receptors. A Solution and Solid State Study.

The coordination properties of the macrocyclic ligands 1,4,7,16,19,22-hexamethyl-1,4,7,16,19,22-hexaaza[9.9]-p-cyclophane (L1) and 1,4,7-trimethyl-19,22,28,31-tetraoxa-1,4,7,14,23-pentaaza[9.25]-p-cyclophane (L2) have been studied by means of potentiometric and (1)H and (13)C measurements in aqueous solution. L1 is composed of two equal triamine binding units connected by p-phenylene spacers. L2 presents a similar molecular architecture, a triamine moiety of L1 being replaced by a cyclic N(2)O(4) binding unit. L1 can form both mono- and dinuclear complexes in aqueous solution, while L2 gives only mononuclear species. The potentiometric data indicate that in the L1 dinuclear complex each metal is coordinated by a triamine moiety. In the L2 mononuclear complex the Pd(II) ion is coordinated by the N(3) unit. The N(2)O(4) moiety does not show any binding ability toward Pd(II), but exhibits a high tendency to protonate. These solution data are confirmed by the crystal structures of [Pd(2)Cl(2)L1](ClO(4))(2).H(2)O (a) and [PdClL2H(2)(H(2)O)](ClO(4))(3) (b). In complex a, each Pd(II) ion is four coordinated by the three amine groups of the triaza moiety and a chloride anion, in a square planar geometry. In the mononuclear complex b, the metal is coordinated by the N(3) moiety, with a coordination environment almost equal to that found in complex a. The N(2)O(4) moiety is diprotonated and encapsulates in its cavity a water molecule, held by a hydrogen-bond network. The solution structures of the L1 and L2 complexes have been studied by means of (1)H and (13)C NMR measurements. The analysis of the NMR data reveals that the dinuclear L1 complex and the L2 mononuclear one show structural features in solution almost equal to those found in the solid state. Solution and solid state data indicate that the Pd(II) complexation gives a marked stiffening of the macrocyclic structures.

Journal Article↗
PubMed1997

Carboxy and Phosphate Esters Cleavage with Mono- and Dinuclear Zinc(II) Macrocyclic Complexes in Aqueous Solution. Crystal Structure of [Zn(2)L1(&mgr;-PP)(2)(MeOH)(2)](ClO(4))(2) (L1 = [30]aneN(6)O(4), PP(-) = Diphenyl Phosphate).

The ligand [30]aneN(6)O(4) (L1) binds two Zn(II) in aqueous solution. The stability constants of the L1 complexes have been determined at 308.1 K by means of potentiometric measurements. Dinuclear monohydroxo [Zn(2)L1OH](3+) and dihydroxo [Zn(2)L1(OH)(2)](2+) complexes are formed in aqueous solution from neutral to alkaline pH. The kinetics of promoted hydrolysis of p-nitrophenyl acetate (NA) was studied. Both hydroxo species promote p-nitrophenyl acetate (NA) hydrolysis at 298.1 K with second-order kinetics. The activity of these species in NA hydrolysis is similar to that found for the mononuclear L2-Zn-OH(+) complex (L2 = [15]aneN(3)O(2)), indicating that the hydrolytic process takes place via a simple bimolecular mechanism. The hydrolysis rate of bis(p-nitrophenyl) phosphate (BNP) was measured in aqueous solution at 308.1 K in the presence of the L1and L2 zinc complexes. The hydrolysis rate of BNP is increased almost 10-fold by the dinuclear [Zn(2)L1(OH)(2)](2+) complex with respect to the mononuclear L2-Zn-OH(+) one. This result indicates a cooperative role of the two metals in the hydrolytic mechanism. A bridging coordination of the phosphate ester to the two Zn(II) ions can be suggested. The crystal structure of [Zn(2)L1(&mgr;-PP)(2)(MeOH)(2)](ClO(4))(2) (PP(-) = diphenyl phosphate) (space group P&onemacr;, a = 10.681(5) Å, b = 12.042(1) Å, c = 13.191(3) Å, alpha = 74.63(2) degrees, beta = 71.74(3) degrees, gamma = 68.41(2) degrees, V = 1476.4(8) Å(3), Z = 1, R = 0.0472, R(w)(2) = 0.1166) strongly supports this hypothesis, since in the [Zn(2)L1(&mgr;-PP)(2)(MeOH)(2)](2+) cation the diphosphate anions bridge the two metals. The dinuclear Zn(II) complexes of L1 provide a simple model system for hydrolytic dizinc enzymes.

Journal Article↗
PubMed1996

CO(2) Fixation by Novel Copper(II) and Zinc(II) Macrocyclic Complexes. A Solution and Solid State Study.

Solutions containing Zn(II) and Cu(II) complexes with [15]aneN(3)O(2) rapidly adsorb atmospheric CO(2) to give {[ZnL](3)(&mgr;(3)-CO(3))}.(ClO(4))(4) (2) and {[CuL](3)(&mgr;(3)-CO(3))}.(ClO(4))(4) (4) complexes. The crystal structures of both complexes have been solved (for 2, space group R3c, a, b = 22.300(5) Å, c = 17.980(8) Å, V = 7743(4) Å(3), Z = 6, R = 0.0666, R(w)(2) = 0.1719; for 4, space group R3c, a, b = 22.292(7) Å, c = 10.096(8) Å, V = 7788(5) Å(3), Z = 6, R = 0.0598, R(w)(2) = 0.1611), and the spectromagnetic behavior of 4 has been studied. In both compounds a carbonate anion triply bridges three metal cations. Each metal is coordinated by one oxygen of the carbonate, three nitrogens, and an oxygen of the macrocycle; the latter donor weakly interacts with the metals. Although the two compounds are isomorphous, they are not isostructural, because the coordination geometries of Zn(II) in 2 and Cu(II) in 4 are different. The mixed complex {[CuZn(2)L(3)](&mgr;(3)-CO(3))}.(ClO(4))(4) has been synthesized. X-ray analysis (space group R3c, a, b = 22.323(7) Å, c = 17.989(9) Å, V = 7763(5) Å(3), Z = 6, R = 0.0477, R(w)(2) = 0.1371) and EPR measurements are in accord with a &mgr;(3)-carbonate bridging one Cu(II) and two Zn(II) ions in {[CuZn(2)L(3)](&mgr;(3)-CO(3))}(4+). Both the Zn(II) and Cu(II) cations exhibit the same coordination sphere, almost equal to that found in the trinuclear Zn(II) complex 2. The systems Zn(II)/L and Cu(II)/Lhave been studied by means of potentiometric measurements in 0.15 mol dm(-)(1) NaCl and in 0.1 mol dm(-)(3) NaClO(4) aqueous solutions; the species present in solution and their stability constants have been determined. In both systems [ML](2+) species and hydroxo complexes [M(II)LOH](+) (M = Zn, Cu) are present in solution. In the case of Cu(II), a [CuL(OH)(2)] complex is also found. The process of CO(2) fixation is due to the presence of such hydroxo-species, which can act as nucleophiles toward CO(2). In order to test the nucleophilic ability of the Zn(II) complexes, the kinetics of the promoted hydrolysis of p-nitrophenyl acetate has been studied. The [ZnLOH](+) complex promotes such a reaction, where the Zn(II)-bound OH(-) acts as a nucleophile to the carbonyl carbon. The equilibrium constants for the addition of HCO(3)(-) and CO(3)(2)(-) to the [ZnL](2+) complex have been potentiometrically determined. Only [ML(HCO(3))](+) and [ML(CO(3))] species are found in aqueous solution. A mechanism for the formation of {[ML](3)(&mgr;(3)-CO(3))}.(ClO(4))(4) is suggested.

Journal Article↗
PubMed1996

Effect of Nitrogen Methylation on Cation and Anion Coordination by Hexa- and Heptaazamacrocycles. Catalytic Properties of These Ligands in ATP Dephosphorylation.

The stability constants of the complexes formed by 1,10-dimethyl-1,4,7,10,13,16-hexaazacyclooctadecane (L) and 1,4,7-trimethyl-1,4,7,10,13,16,19-heptaazacyclohenicosane (L1) with Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Pb(2+), as well as that for the formation of PbL2(2+) (L2 = 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane), were determined by means of potentiometric (pH-metric) titrations in 0.15 mol dm(-)(3) NaClO(4) at 298.1 +/- 0.1 K. The enthalpy changes for the formation of Cu(2+) complexes with L and L1 were measured by means of microcalorimetry. These thermodynamic data were compared with those previously reported for L2, 1,4,7,10,13,16-hexaazacyclooctadecane (L3), and 1,4,7,10,13,16,19-heptaazacyclohenicosane (L4) evidencing that nitrogen methylation can produce lower or higher complex stability depending on the metal ion and the number of methylated nitrogens. The equilibria of complexation of ATP(4)(-), ADP(3)(-), AMP(2)(-), P(2)O(7)(4)(-), and [Co(CN)(6)](3)(-) by Land L1 were studied by means of pH-metric titrations in 0.15 mol dm(-)(3) NaClO(4) at 298.1 +/- 0.1 K. The catalytic reactions of ATP dephosphorylation induced by these ligands in solution were followed by (31)P NMR spectroscopy at different temperature and pH values. L is the most appropriate receptor, among L-L4, in the recognition of the nucleotide. The catalytic efficiency of hexa- and heptaazaligands increases in the order L < L3 < L2 and L1 < L4, respectively, L4 being the most efficient. Namely, di- and tetramethylation of L3 produces opposite effects on its catalytic properties.

Journal Article↗