Antonino Giannetto

Molecular logics: a mixed bodipy–bipyridine dye behaving as a concealable molecular switch

A species based on a bodipy chromophore and containing bipyridine chelating sites behaves as a concealable molecular switch, featuring part of the properties of D-latch circuits by integrating two logic gates, a NOR and an INHIBIT gate, with both gates sharing the same inputs.

Luminescence of a Pt(II) complex in the presence of DNA. Dependence of luminescence changes on the interaction binding mode

Luminescence intensity changes of a Pt(II) complex which is known to bind externally to DNA at low [DNA]/[complex] ratio and to intercalate at high [DNA]/[complex] ratio are studied in the presence of calf thymus DNA. External binding is demonstrated to induce luminescence enhancement whereas intercalation leads to luminescence quenching. The reasons for this behaviour are discussed.

Relationship between binding affinity for calf-thymus DNA of [Pt(2,2′-bpy)(n-Rpy)2]2+(n= 2,4) and basicity of coordinated pyridine

The binding affinity for DNA of the complexes [Pt(2,2′-bpy)(n-Rpy)2]2+(n= 2,4) systematically increases on increasing pKa of the coordinated pyridine, with the exception of the 2-methyl-substituted derivative.

KINETICS OF LIGAND REPLACEMENT, IN N-SUBSTITUTED ETHYLENEDIAMINE PALLADIUM(II) COMPLEXES

Abstract The rate of substitution by ethylenediamine, of Cl−, in the substrates [Pd(R2N(CH2)2NR2)Cl2] and of 2,2′-bipyridine (bpy), in the complexes [Pd(bpy)(R2N(CH2)2NR2)] (R = H, methyl, ethyl or phenyl) have been studied, at 25°C, respectively in dimethylformamide and in water. In both processes the rate of reaction depends on the nature of the substituent R at nitrogen. While the kinetic data for neutral complexes can be accounted for simply in terms of electronic and steric properties of the ligands, the trend of the kinetic constants seem to be related to the capacity of the various complexes to form hydrogen bonding with water.

Kinetics of the reaction between substituted thioureas and the palladium (II) aquocomplex of 1, 1, 7, 7-tetraethyldiethylenetriamine in water and in aqueous micellar solutions

The kinetics of water replacement in the complex [Pd(Et4dien)(H2O)](NO3)2, where Et4 dien = Et2N[CH2]2NH[CH2]2 NEt2, by thiourea and its methyl, ethyl, n-butyl, N, N′-dimethyl, N, N′-diethyl, N, N′-di-n-butyl and p-tolyl derivatives have been studied at 25 °C and ionic strength 0.03 mol dm–3 in water and in the presence of cationic (CTAN) and anionic (SDS) micelle-forming surfactants. All the reactions studied are first order with respect to both reactant species. The reaction rates in water depend on both the steric hindrance and the inductive effects of the alkyl groups present in the parent thiourea molecule. The substitution reactions are inhibited by the CTAN micelles and take place in the bulk water, the nucleophiles being partitioned between the aqueous and micellar pseudo-phases. Anionic SDS micelles accelerate the overall reactions, which occur in the micellar phase with the same mechanism as in water. The estimated binding constants of the nucleophiles are larger with CTAN micelles than with SDS micelles and depend on the hydrophobic nature and number of the alkyl groups present in the unsubstituted thiourea. In the case of the CTAN surfactant the standard transfer free energies of the thioureas from water in the micelle suggest that binding of the solubilizates occurs in the palizade layer of the micelle.

Thermodynamics of complex formation of Ag(I). Part 10. Investigations on complex equilibria between Ag(I) and thioureas in ethanol

Abstract The complex equilibria between Ag(I) and thiourea or N -alkyl-substituted thioureas have been investigated in ethanol by potentiometry at different temperatures in the range 0–45°C. The free energy, enthalpy and entropy changes at 25°C and ionic strength μ = 0 for the formation of mono-, bi- and tri-coordinate compounds are given. The investigated alcohols favour the complex formation, but specific factors operate on the transfer of each reaction from water to methanol to ethanol. Interaction between tetramethylthiourea and Ag(I) involves a different mechanism compared with the other thioureas owing to the different electronic structure of the ligand. The ranked affinity sequences of the ligands follow different orders according to the coordination level of the substratum.

Thermodynamics of complex formation of Ag(I). Part 9. Investigations on Ag(I)—thiourea—thioacetamide—halide systems in aqueous solution

Abstract Complex formation in the three-ligand systems Ag(I)-SCN 2 H 4 -SCN − −X (X = Cl − , Br − ,I − ) has been investigated by potentiometry in aqueous solution at ionic strength μ = 1 using KNO 3 and different temperatures. Enthalpy and entropy changes have been evaluated from the free energy change dependence on temperature. Predominance diagrams for the two-ligand systems Ag(I)-SCN − -X (X = Cl − , Br − , I − ) and the three-ligand systems Ag(I)-SCN 2 H 4 -X (X = Cl − , Br − , I − ) at 25°C and μ = 1 for KNO 3 are shown. The free energy changes for the coordination reactions of thiourea or thiocyanate indicate higher affinities for the dicoordinated substrata than for the monocoordinated ones. The ionic charges of both the substrata and the entering group are not the main factors in determining the affinity sequences. The parameters of the Gibbs equation are interrelated, though in different ways, in both the overall and stepwise complex formation.

Thermodynamic relationships of complex formation: Part 5. Isoequilibrium relationships in soft-soft interactions in hard solvents

Abstract The inspection of the Δ H -Δ S patterns for reactions between Ag(I) complex substrata and various entering ligands discloses linear interplay between the two parameters. The actual Δ H (Δ S ) values demonstrate that soft-hard interactions can produce favourable enthalpy changes coupled to unfavourable entropy changes, and confirm that soft-soft interactions can yield unfavourable enthalpy changes coupled to favourable entropy changes. These results, together with the already published enthalpy-entropy interplays, which show negative values of both Δ H and Δ S for hard-hard interactions in aqueous solution, demonstrate that in this solvent soft-soft (hard-hard) interactions do not necessarily produce Δ H H > 0) coupled to Δ S S > 0) because their values also descend from the role of the solvent molecules in the specific reaction. The coordinated solvent produces a sort of ‘shielding’ or ‘levelling’ of the acceptor and donor abilities.

Luminescent Ir(III) Complex Exclusively Made of Polypyridine Ligands Capable of Intercalating into Calf-Thymus DNA

Efficient intercalation of a luminescent Ir(III) complex exclusively made of polypyridine ligands in natural and synthetic biopolymers is reported for the first time. The emission of the complex is largely enhanced in the presence of [poly(dA-dT)(2)] and strongly quenched in the presence of [poly(dG-dC)(2)]. By comparing the emission decays in DNA and in synthetic polynucleotides, it is proposed that the emission quenching of the title compound by guanine residues in DNA is no longer effective over a distance of four dA-dT base pairs.

Thermodynamic relationships on complex formation. Part VII. ΔHΔS interplay in the equilibria for the formation of amine complexes in aqueous solution

Abstract ΔHΔS values for the protonation and complexing reaction series of amines in aqueous solution have been inspected for the occurrence of functional relationships or regular patterns. Both non-linear and anti-compensative relationships have been evidenced.