Giuseppe Saba

Divalent metal–acetate complexes in concentrated aqueous solutions. An x‐ray diffraction and NMR spectroscopy study

Divalent metal–acetate solutions have been investigated by the x‐ray scattering technique and 13C NMR spectroscopy. The aim of this work was to study the complex formation between the divalent metals and a typical organic complexing ligand in concentrated aqueous solutions. The correlation functions and the analysis of the structure functions agree with the literature information that the species present in solution are Me(H2O)2+6 , Me(H2O)6−z(CH3COO)2+−zz , and Me(H2O)6−2z(CH3COO)2+−zz . Good agreement with experimental data is achieved through a model in which the acetate ions are bonded as a monodentate ligand to the Mg, Co, Mn, and Zn cations and as a bidentate to the Cd cation. The cations also possess a second coordination shell of water molecules. Some indications have been obtained supporting the presence of hydration water around the acetate anions.

Study of dimethyl-substituted benzene derivatives by 13C nuclear magnetic resonance spectroscopy and INDO MO calculations

A 13C n.m.r. investigation of some substituted dimethyl benzenes is reported. The spectral analysis were carried out by the iterative Laocoon III and a spin-simulation program furnished carbon–proton coupling constants that have been rationalized with the aid of the FPT–INDO MO calculations. The angular dependences of the calculated 3JC,CHO and 1JCHO coupling constants have been analysed and the preferred conformations are discussed.

NMR Investigation of Imidazolium-Based Ionic Liquids and Their Aqueous Mixtures

(1)H and (13)C NMR spectroscopy is employed to investigate the interaction of water with two imidazolium-based ionic liquids (ILs), 1-hexyl-3-methylimidazolium bromide ([C(6)mim]Br) and 1-octyl-3-methylimidazolium bromide ([C(8)mim]Br), at IL concentrations well above the critical aggregation concentration (CAC). The results are compared with those of the neat samples. To this aim, a detailed analysis of the changes in the (1)H chemical shifts, (13)C relaxation parameters, and 2D ROESY data due to the presence of water is performed. The results for both neat ILs are consistent with a packed structure where head-to-head, head-to-tail, and tail-to-tail contacts occur and where the site of maximal mobility restriction is at the polar head. At the lowest investigated water content, the presence of water influences mainly the environment around the IL polar head, slowing down the motional dynamics of the aromatic ring with respect to the alkyl chain. At higher water contents this difference diminishes, the motional freedom of the whole molecule increasing. The presence of ROESY cross-peaks between protons in the polar and apolar IL regions, as well as between protons in non-neighboring alkyl groups, at all investigated water contents suggests that the alkyl tails are not fully segregated in hydrophobic domains, as expected for micelle-like structures.

Binding of Ru(II) polyazaaromatic complexes to DNA: A 23Na NMR spin-lattice relaxation study

The possibility of using sodium-23 spin-lattice relaxation rate measurements to probe the interaction modes of Ru11 polyazaaaromatic complexes with DNA is investigated. The following complexes are considered: Ru(phen)3(2+) (phen = 1.10-phenanthroline), Ru(phen)2HAT2+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene), and Ru(diMeTAP)3(2+) (diMeTAP = 2,7-dimethyl-1,4,5,8-tetraazaphenanthrene). The addition of Ru(diMeTAP)3(2+) to a solution of NaDNA leads to a decrease in the sodium-23 spin-lattice relaxation rate (R1) similar to the effect observed upon addition of Mg2+. This indicates that Ru(diMeTAP)3(2+) interacts like Mg2+ with DNA and consequently that the electrostatic interaction dominates the association with DNA, Ru(phen)3(2+) and Ru(phen)2HAT2+ diminish R1 more efficiently than Mg2+, in a manner similar to ethidium bromide, which is known for its intercalation properties. Thus interactions other than electrostatic occur between these two complexes and DNA. These results are in agreement with data obtained from other techniques, according to which Ru(phen)3(2+) and Ru(phen)2HAT2+ are located partially inside the DNA double helix, in contrast to Ru(diMeTAP)3(2+) which remains in the ionic atmosphere around the phosphate backbone.

Recognition and quantitation of cis-vaccenic and eicosenoic fatty acids in olive oils by 13C nuclear magnetic resonance spectroscopy.

The presence of 11-cis monoenoic fatty acids was detected in olive oil samples by means of 13C nuclear magnetic resonance spectroscopy, and the positional isomery on the glycerol backbone was derived. The 11-cis vaccenic and eicosenoic fatty acid resonances were recognized and the amounts of the fatty acids quantified. For comparison purposes, a quantitative analysis was also made by gas chromatography.

NMR, EPR, and INDO Studies on the complexes of dopamine with Cu2+, Mn2+, and Fe3+ in aqueous solution

Abstract The spin-lattice relaxation rates of dopamine in the presence of Cu2+, Mn2+, and Fe3+ have been investigated by FT NMR spectroscopy in aqueous solution. The Solomon-Bloembergen equation is found to hold in the case of Mn2+ complex while a failure of its applicability was observed in Cu2+ and Fe2+ complexes. Rationalization of the relaxation rates with the aid of EPR spectroscopy allowed the estimation of the pertinent molecular correlation time. Furthermore INDO MO calculations furnished detailed information on the mechanism of spin density onto the ligand.

C-13 magnetic relaxation rates and H-1 and C-13 paramagnetic shifts of Ni(II) complex of dopamine

Abstract The 1 H and 13 C isotropic contact shifts and the 13 C relaxation times of dopamine in aqueous solution have been measured in the presence of the Ni(II) ion. The pD dependence of the 1 H and 13 C paramagnetic shifts was also investigated. From the analysis of the shifts at pD = 6.5 and from the INDO MO calculations on selected models of dopamine radicals, a dominant σ delocalization mechanism of the spin density is proposed. From the spin distribution on the ligand carbon atoms, the metal centered as well as the ligand centered dipolar contributions of the modified Solomon—Bloembergen equation were calculated and an estimate of the correlation time τ c was given.

Recognition and characterization of binding modes of Δ- and Λ-[Ru(phen)3]2+ and Δ- and Λ-[Ru(phen)2DPPZ]2+ by the 23Na NMR Relaxation and Binding Free Energy Parameters

Na-23 NMR relaxation rates were measured in Na-DNA aqueous solutions in the presence of Delta- or Lambda-enantiomer of [Ru(phen)(3)](2+) and [Ru(phen)(2)DPPZ](2+). From the analysis of the spin-lattice and spin-spin relaxation rates evidence is given that a decrease of the quadrupolar coupling constant for the slow motions occurs, due to the structural and dynamical modifications of DNA induced by the binding of the ruthenium complexes. Furthermore a linear dependence between the changes of the broad component, R-2bB, and the relative polyelectrolyte contributions to the binding free energy, Delta G(pe)/Delta G, was found. In particular for the intercalators Delta- and Lambda-[Ru(phen)(2)DPPZ](2+), a direct dependence on Delta G(pe)/Delta G was observed, as already found for ethidium, propidium and dq2pyp; while [Ru(phen)(3)](2+) complexes and the pure electrostatic Mg2+ showed an inverse dependence. These results have been discussed in terms of the polyelectrolyte interactions responsible for the R-2bB changes.

Equilibrium constants of the Fe(III)dopamine system in aqueous solution

Abstract The system Fe(III)Dopamine was investigated potentiometrically in aqueous solution and equilibrium constants were evaluated for the resulting complexes by means of a fitting procedure. The existence of hydroxy complexes is hypothesized which is consistent with the results of a previous EPR and NMR investgation.

A 23Na and 31P NMR investigation of the binding of Ni2+ to Na-DNA

Abstract A 23Na and 31P NMR study of the Na-DNA and Na-DNA-Ni systems in aqueous solution has been undertaken. Analysis of the relaxation rates provides evidence that Ni2+ displaces Na+ ions from the condensation layer of Na-DNA. Furthermore, it was found that Ni2+ binds specifically to the DNA phosphate to some extent and that multiple chemical equilibria are involved in the interactions.