Antonella Cartoni

Double CH activation of ethane by metal-free SO2.+ radical cations

The room-temperature C-H activation of ethane by metal-free SO(2)(*+) radical cations has been investigated under different pressure regimes by mass spectrometric techniques. The major reaction channel is the conversion of ethane to ethylene accompanied by the formation of H(2)SO(2)(*+), the radical cation of sulfoxylic acid. The mechanism of the double C-H activation, in the absence of the single activation product HSO(2)(+), is elucidated by kinetic studies and quantum chemical calculations. Under near single-collision conditions the reaction occurs with rate constant k=1.0 x 10(-9) (+/-30%) cm(3) s(-1) molecule(-1), efficiency=90%, kinetic isotope effect k(H)/k(D)=1.1, and partial H/D scrambling. The theoretical analysis shows that the interaction of SO(2)(*+) with ethane through an oxygen atom directly leads to the C-H activation intermediate. The interaction through sulfur leads to an encounter complex that rapidly converts to the same intermediate. The double C-H activation occurs by a reaction path that lies below the reactants and involves intermediates separated by very low energy barriers, which include a complex of the ethyl cation suitable to undergo H/D scrambling. Key issues in the observed reactivity are electron-transfer processes, in which a crucial role is played by geometrical constraints. The work shows how mechanistic details disclosed by the reactions of metal-free electrophiles may contribute to the current understanding of the C-H activation of ethane.

Oxidative Degradation of Cardiotoxic Anticancer Anthracyclines to Phthalic Acids NOVEL FUNCTION FOR FERRYLMYOGLOBIN

We show that the pseudoperoxidase activity of ferrylmyoglobin (MbIV) promotes oxidative degradation of doxorubicin (DOX), an anticancer anthracycline known to induce severe cardiotoxicity. MbIV, formed in vitro by reacting horse heart MbIII with H2O2, caused disappearance of the spectrum of DOX at 477 nm and appearance of UV-absorbing chromophores that indicated opening and degradation of its tetracyclic ring. Electron spray ionization mass spectrometry analyses of DOX/MbIV ultrafiltrates showed that DOX degradation resulted in formation of 3-methoxyphthalic acid, the product of oxidative modifications of its methoxy-substituted ring D. Other methoxy-substituted anthracyclines similarly released 3-methoxyphthalic acid after oxidation by MbIV, whereas demethoxy analogs released simple phthalic acid. Kinetic and stoichiometric analyses of reactions between DOX and MbIII/H2O2 or hemin/H2O2 showed that the porphyrin radical of MbIV-compound I and the iron-oxo moiety of MbIV-compound II were sequentially involved in oxidizing DOX; however, oxidation by compound I formed more 3-methoxyphthalic acid than oxidation by compound II. Sizeable amounts of 3-methoxyphthalic acid were formed in the heart of mice treated with DOX, in human myocardial biopsies exposed to DOX in vitro, and in human cardiac cytosol that oxidized DOX after activation of its endogenous myoglobin by H2O2. Importantly, H9c2 cardiomyocytes were damaged by low concentrations of DOX but could tolerate concentrations of 3-methoxyphthalic acid higher than those measured in murine or human myocardium. These results unravel a novel function for MbIV in the oxidative degradation of anthracyclines to phthalic acids and suggest that this may serve a salvage pathway against cardiotoxicity.

Water activation by SO2˙+ ions: an effective source of OH˙ radicals

A novel O-H bond activation reaction is reported: thermal SO(2)(*+) radical cations activate water in the gas phase forming OH* radicals with 100% efficiency.

A mass spectrometric and computational study of gaseous peroxynitric acid and (HOONO2)H+ protomers

Abstract The positive ion chemistry of peroxynitric acid ( 1 ) was investigated in the gas phase by mass-analyzed ion kinetic, collisionally activated dissociation, and Fourier transform-ion cyclotron resonance mass spectrometric techniques and theoretical methods up to the B3LYP/6-311++g(3 df ,2 pd ) and G2, i.e. QCISD(T)/6-311+g(3 df ,2 pd ), levels. The ion–neutral complex HOOH–NO 2 + ( 1a ) is the only detectable protomer in CI experiments involving the protonation of 1 by H 3 O + , and can also be obtained from the reaction of NO 2 + with H 2 O 2 . 1a behaves as a protonating and nitrating agent toward gaseous nucleophiles. The experimental proton affinity of 1 is estimated to be 176 ± 3 kcal mol −1 , in excellent agreement with the 175 ± 2 kcal mol −1 G2 PA. The theoretical results show that 1a is more stable than the HOONO 2 H + ( 1b ) and the H 2 OONO 2 + ( 1c ) protomers by 13 and 16 kcal mol −1 , respectively, at the B3LYP level of theory, and account for the exclusive formation of 1a in the CI experiments. The experimental and B3LYP theoretical binding energy of NO 2 + to H 2 O 2 amounts to 18 ± 2 kcal mol −1 .

The HSSS radical and the HSSS- anion.

The HS3 radical and the HS3(-) anion, the sulfur analogues of HO3 and HO3(-), have been detected for the first time by mass spectrometric experiments performed in the gas phase. The structural and energetic features of HS3 and HS3(-) have been investigated by ab initio calculations. Both HS3 and HS3(-) are characterized by HSSS open-chain structures, stable toward the dissociation into S2 and HS(0/-). HS3 adds to HS and HS2 as the known HS n species, and HS3(-) is the conjugate base of a strong Brønsted acid, the trisulfane HSSSH.

Photofragmentation spectra of halogenated methanes in the VUV photon energy range

In this paper an investigation of the photofragmentation of dihalomethanes CH2X2 (X = F, Cl, Br, I) and chlorinated methanes (CH(n)Cl(4-n) with n = 0-3) with VUV helium, neon, and argon discharge lamps is reported and the role played by the different halogen atoms is discussed. Halogenated methanes are a class of molecules used in several fields of chemistry and the study of their physical and chemical proprieties is of fundamental interest. In particular their photodissociation and photoionization are of great importance since the decomposition of these compounds in the atmosphere strongly affects the environment. The results of the present work show that the halogen-loss is the predominant fragmentation channel for these molecules in the VUV photon energy range and confirm their role as reservoir of chlorine, bromine, and iodine atoms in the atmosphere. Moreover, the results highlight the peculiar feature of CH2F2 as a source of both fluorine and hydrogen atoms and the characteristic formation of I2(+) and CH2(+) ions from the photofragmentation of the CH2I2 molecule.

Gas-phase fluorination of acetylene by XeF+: Formation, structure and reactivity of C2H2F+ isomeric ions

Abstract The gas-phase reactivity of XeF+ towards acetylene was investigated by triple quadrupole mass spectrometry. XeF+ promotes both F+ and Xe+ transfer to acetylene, yielding C2H2F+ and C2H2Xe+, respectively. The C2H2F+ ions formed were probed by low-energy collisionally activated dissociation mass spectrometry and characterized as CH2CF+, namely the isomer identified as the most stable by previous theoretical studies. The 1-fluorovinyl cation reacts in the gas-phase with typical nucleophiles (CH3COCH3,CH3CN,CH3OH,C2H4), as a Bronsted acid and/or as a fluorinating agent, depending on the thermochemistry of the processes involved.

Feasibility of beta-particle radioguided surgery for a variety of “nuclear medicine” radionuclides

PURPOSE Beta-particle radioguided tumor resection may potentially overcome the limitations of conventional gamma-ray guided surgery by eliminating, or at least minimizing, the confounding effect of counts contributed by activity in adjacent normal tissues. The current study evaluates the clinical feasibility of this approach for a variety of radionuclides. Nowadays, the only β- radioisotope suited to radioguided surgery is 90Y. Here, we study the β- probe prototype capability to different radionuclides chosen among those used in nuclear medicine. METHODS The counting efficiency of our probe prototype was evaluated for sources of electrons and photons of different energies. Such measurements were used to benchmark the Monte Carlo (MC) simulation of the probe behavior, especially the parameters related to the simulation of the optical photon propagation in the scintillation crystal. Then, the MC simulation was used to derive the signal and the background we would measure from a small tumor embedded in the patient body if one of the selected radionuclides is used. RESULTS Based on the criterion of detectability of a 0.1 ml tumor for a counting interval of 1 s and an administered activity of 3 MBq/kg, the current probe yields a detectable signal over a wide range of Standard Uptake Values (SUVs) and tumor-to-non-tumor activity-concentration ratios (TNRs) for 31Si, 32P, 97Zr, and 188Re. Although efficient counting of 83Br, 133I, and 153Sm proved somewhat more problematic, the foregoing criterion can be satisfied for these isotopes as well for sufficiently high SUVs and TNRs.

A joint theoretical and experimental study on diiodomethane: Ions and neutrals in the gas phase

The chemical physics of halomethanes is an important and challenging topic in several areas of chemistry in particular in the chemistry of the atmosphere. Among the class of halomethanes, the diiodomethane molecule has attracted some interest in the last years, but despite this, the information on its radical cation [CH2I2](⋅+) is still limited. In this work, we measured and calculated the appearance energy (AE) of the ionic fragments I2(⋅+) and CH2(⋅+) and correlated the different fragmentation channels to the electronic states of the cation via photoelectron-photoion coincidence (PEPICO) experiments. In the case of the CH2/I2(⋅+) channel, the experimentally determined AE is in excellent agreement with the adiabatic theoretical value while a discrepancy is observed for the CH2(⋅+)/I2 channel. This discrepancy can be understood accounting for a fragmentation involving the formation of two I atoms (CH2(⋅+)/2I channel), which, as explained by time dependent density functional theory (TD-DFT) calculations, occurs when [CH2I2](⋅+) excited states are involved.

Gold nanoparticles functionalized by rhodamine B isothiocyanate: a new tool to control plasmonic effects

Gold nanoparticles with an average diameter of 10 nm, functionalized by the dye molecule rhodamine B isothiocyanate, have been synthesized. The resulting material has been extensively characterized both chemically, to investigate the bonding between the dye molecules and the nanoparticles, and physically, to understand the details of the aggregation induced by interaction between dye molecules on different nanoparticles. The plasmonic response of the system has been further characterized by measurement and theoretical simulation of the static UV-Vis extinction spectra of the aggregates produced following different synthesis procedures. The model parameters used in the simulation gave further useful information on the aggregation and its relationship to the plasmonic response. Finally, we investigated the time dependence of the plasmonic effects of the nanoparticles and fluorescence of the dye molecule using an ultrafast pump-probe optical method. By modulating the quantity of dye molecules on the surface of the nanoparticles it was possible to exert fine control over the plasmonic response of nanoparticles.