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Paola Franchi

Publications and source records attributed to Paola Franchi.

7 recordsLinked to original sources
PubMed2006

Synthesis and characterization of a persistent paramagnetic rotaxane based on alpha-cyclodextrin.

The synthesis and spectroscopic properties of a novel paramagnetic [2]rotaxane is described. This rotaxane is made from molecules having an alkyl chain flanked by 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) groups. Complexation of sebacoyl chloride by alpha-cyclodextrin followed by reaction with a bulky aminonitroxide resulted in the trapping of the cyclodextrin, threaded by the alkyl chain, thus generating the rotaxane structure. The structure of the paramagnetic [2]rotaxane was fully characterized by ESI-MS, 1D and 2D NMR and ESR spectroscopy.

Journal Article↗
PubMed2005

Effect of core size on the partition of organic solutes in the monolayer of water-soluble nanoparticles: an ESR investigation.

ESR spectroscopy has been used to study the interaction of para-pentylbenzyl hydroxyalkyl nitroxide with the monolayer of water-soluble protected gold clusters having a core diameter ranging from 1.6 to 5.3 nm. The solubilization of the nitroxide probe in the more hydrophobic environment of the monolayer strongly depends on the size of the gold core. In particular, the partition equilibrium constant increases as the nanoparticle diameter decreases. These results have been attributed to the different packing of the chains in the monolayer resulting from the different radius of curvature of the investigated nanoparticles. This represents, to the best of our knowledge, the first report demonstrating that the core size of metallic nanoparticles affects the solvating properties of the protective organic monolayer.

Journal Article↗
PubMed2004

EPR study of dialkyl nitroxides as probes to investigate the exchange of solutes between the ligand shell of monolayers of protected gold nanoparticles and aqueous solutions.

EPR spectroscopy has been used to study the interaction of para-substituted benzyl hydroxyalkyl nitroxides with the monolayer of water-soluble protected gold cluster made by a short alkyl chain and a triethylene glycol monomethyl ether unit. The inclusion of nitroxide probes in the more hydrophobic environment of the monolayer gave rise to a reduction of the value of both nitrogen and beta-proton hyperfine splittings. The spectra also showed selective line broadening attributed to modulation of the spectroscopic parameters as the result of exchange between free and complexed nitroxide. The rate constants were obtained by analyzing the EPR line shape variations as functions of nanoparticle concentration and temperature. This represents, to the best of our knowledge, the first determination of rate constants for the solubilization of organic substrates in a monolayer-protected cluster.

Electron Spin Resonance Spectroscopy↗
PubMed2004

Combining magnetic resonance spectroscopies, mass spectrometry, and molecular dynamics: investigation of chiral recognition by 2,6-di-O-methyl-beta-cyclodextrin.

EPR spectroscopy has been employed to investigate the formation of complexes between heptakis-(2,6-O-dimethyl)-beta-cyclodextrin (DM-beta-CD) and different enantiomeric pairs of chiral nitroxides of general structure PhCH2NO.CH(R)R'. Accurate equilibrium measurements of the concentrations of free and included radicals afforded the binding constant values for these nitroxides. The relationship between the stereochemistry of the DM-beta-CD complexes and the thermodynamics of complexation was elucidated by correlating EPR data with 1H-1H NOE measurements carried out on the complexes between DM-beta-CD and the structurally related amine precursors of nitroxides. NOE data suggested that inclusion of the stereogenic center in the DM-beta-CD cavity occurs only when the R substituent linked to the chiral carbon contains an aromatic ring. For these types of complexes, molecular dynamics simulation indicated that the depth of penetration of the stereogenic center into the cyclodextrin cavity is determined by the nature of the second substituent (R') at the asymmetric carbon and is responsible for the observed chiral selectivity. Analysis of mass spectra showed that, for the presently investigated amines, electrostatic external adducts of CDs with protonated amines are detected by ESI-MS.

Journal Article↗
PubMed2002

Nitroxide radicals as hydrogen bonding acceptors. An infrared and EPR study.

The equilibrium constants for the formation of hydrogen-bonded complexes with phenol, benzyl alcohol and diphenyl amine of a persistent nitroxide radical (TEMPO) have been measured for the first time by IR spectroscopy in solution. By making use of the data obtained with IR measurements it was possible to quantitatively determine the effect of hydrogen bonding on the nitrogen hyperfine-splitting constant. On this basis it is shown that EPR spectroscopy can be used as an alternative to IR spectroscopy for the determination of the thermodynamic parameters of hydrogen bond formation with nitroxides by following the dependence of the experimental EPR nitrogen hyperfine splitting of these radicals upon changing the nature of the solvent. The experimental data obtained from both IR and EPR spectroscopy indicate that nitroxides are versatile hydrogen bond acceptors giving hydrogen bonds of strength similar to that of ethers or esters. The corresponding Abraham's beta 2H values have been determined as 0.46.

Alcohols↗