High-resolution kinetic energy release distributions and dissociation energies for fullerene ions C(n)(+), 42 \u3c= n \u3c= 90

We have measured the kinetic energy released in the unimolecular dissociation of fullerene ions, C(n)(+)--\u3eC(n-2)(+)+C(2), for sizes 42less than or equal tonless than or equal to90. A three-sector-field mass spectrometer equipped with two electric sectors has been used in order to ensure that contributions from isotopomers of different masses do not distort the experimental kinetic energy release distributions. We apply the concept of microcanonical temperature to derive from these data the dissociation energies of fullerene cations. They are converted to dissociation energies of neutral fullerenes with help of published adiabatic ionization energies. The results are compared with literature values. (C) 2004 American Institute of Physics

Near-infrared photoabsorption by C(60) dianions in a storage ring

We present a detailed study of the electronic structure and the stability of C(60) dianions in the gas phase. Monoanions were extracted from a plasma source and converted to dianions by electron transfer in a Na vapor cell. The dianions were then stored in an electrostatic ring, and their near-infrared absorption spectrum was measured by observation of laser induced electron detachment. From the time dependence of the detachment after photon absorption, we conclude that the reaction has contributions from both direct electron tunneling to the continuum and vibrationally assisted tunneling after internal conversion. This implies that the height of the Coulomb barrier confining the attached electrons is at least similar to 1.5 eV. For C(60)(2-) ions in solution electron spin resonance measurements have indicated a singlet ground state, and from the similarity of the absorption spectra we conclude that also the ground state of isolated C(60)(2-) ions is singlet. The observed spectrum corresponds to an electronic transition from a t(1u) lowest unoccupied molecular orbital (LUMO) of C(60) to the t(1g) LUMO+1 level. The electronic levels of the dianion are split due to Jahn-Teller coupling to quadrupole deformations of the molecule, and a main absorption band at 10723 cm(-1) corresponds to a transition between the Jahn-Teller ground states. Also transitions from pseudorotational states with 200 cm(-1) and (probably) 420 cm(-1) excitation are observed. We argue that a very broad absorption band from about 11 500 cm(-1) to 13 500 cm(-1) consists of transitions to so-called cone states, which are Jahn-Teller states on a higher potential-energy surface, stabilized by a pseudorotational angular momentum barrier. A previously observed, high-lying absorption band for C(60)(-) may also be a transition to a cone state

Lifetimes of C-60(2-) and C-70(2-) dianions in a storage ring

C-60(2-) and C-70(2-) dianions have been produced by electrospray of the monoanions and subsequent electron pickup in a Na vapor cell. The dianions were stored in an electrostatic ring and their decay by electron emission was measured up to 1 s after injection. While C-70(2-) ions are stable on this time scale, except for a small fraction of the ions which have been excited by gas collisions, most of the C-60(2-) ions decay on a millisecond time scale, with a lifetime depending strongly on their internal temperature. The results can be modeled as decay by electron tunneling through a Coulomb barrier, mainly from thermally populated triplet states about 120 meV above a singlet ground state. At times longer than about 100 ms, the absorption of blackbody radiation plays an important role for the decay of initially cold ions. The tunneling rates obtained from the modeling, combined with WKB estimates of the barrier penetration, give a ground-state energy 200 +/- 30 meV above the energy of the monoanion plus a free electron and a ground-state lifetime of the order of 20 s. (c) 2006 American Institute of Physics

Numerical simulation of the thermal fragmentation process in fullerene C60

The processes of defect formation and annealing in fullerene C60 at T=(4000-6000)K are studied by the molecular dynamics technique with a tight-binding potential. The cluster lifetime until fragmentation due to the loss of a C2 dimer has been calculated as a function of temperature. The activation energy and the frequency factor in the Arrhenius equation for the fragmentation rate have been found to be Ea = (9.2 +- 0.4) eV and A = (8 +- 1)10^{19} 1/s. It is shown that fragmentation can occur after the C60 cluster loses its spherical shape. This fact must be taken into account in theoretical calculations of Ea.Comment: 12 pages, 3 figure

Estrogen-Eluting Stents

Coronary stenting is routinely utilized to treat symptomatic obstructive coronary artery disease. However, the efficacy of bare metal coronary stents has been historically limited by restenosis, which is primarily due to excessive neointima formation. Drug-eluting stents (DES) are composed of a stainless steel backbone encompassed by a polymer in which a variety of drugs that inhibit smooth muscle cell proliferation and excessive neointima formation are incorporated. DES have significantly reduced the incidence of restenosis but are also associated with a small (~0.5% per year) but significant risk of late stent thrombosis. In that regard, estrogen-eluting stents have also undergone clinical evaluation in reducing restenosis with the additional potential benefit of enhancing reendothelialization of the stent surface to reduce stent thrombosis. Estrogen directly promotes vasodilatation, enhances endothelial healing, and prevents smooth muscle cell migration and proliferation. Due to these mechanisms, estrogen has been postulated to reduce neointimal hyperplasia without delaying endothelial healing. In animal studies, estrogen treatment was effective in decreasing neointimal hyperplasia after both balloon angioplasty and stenting regardless of the method of drug delivery. The first uncontrolled human study using estrogen-coated stents demonstrated acceptable efficacy in reducing late lumen loss. However, subsequent randomized clinical trials did not show superiority of estrogen-eluting stents over bare metal stents or DES. Further studies are required to determine optimal dose and method of estrogen delivery with coronary stenting and whether this approach will be a viable alternative to the current DES armamentarium

Doubly charged clusters - neutral atom charge transfer: the role of the Coulombic repulsion

We have studied experimentally the collisional charge transfer between a neutral atom and a multicharged metal-atom cluster. The charge transfer cross section measured for Na$_{31}^{++} +$ Cs is in the range of 400 Å2. The time-of-flight mass analysis of the singly charged collision products demonstrates that an energy of about 0.5 eV is deposited in the cluster fragment during the charge transfer collision. This effect can be interpreted as a charge transfer to an excited state of the metal cluster. The measured cross section for Na$_{31}^{++} +$ Cs is larger than the one for Na$_{31}^{+} +$ Cs collisions. This difference between these two systems is due to the existence, for the first one, of a Coulombic repulsion term in the collision output channel

Acrilamide e furani negli alimenti: un problema per la ristorazione collettiva?

Negli ultimi anni i compilatori dei database nutrizionali sono stati chiamati a considerare la composizione degli alimenti in un\u2019ottica pi\uf9 complessa (www.eurofir.net/eurofir_aisbl), che tenga conto sia delle trasformazioni e manipolazioni subite dagli alimenti sia del continuo aumento dei consumi fuori-casa (ISTAT, 2008). La valutazione dell\u2019esposizione a sostanze tossiche di processo (idrocarburi policiclici aromatici, ammine biogene, acrilamide, furani, ecc) \ue8 ulteriormente complicata dal fatto che non esistono dati di composizione degli alimenti completi e rappresentativi, che i meccanismi di formazione di tali sostanze, se pur noti, sono di difficile previsione, e che l\u2019uso di biomarcatori \ue8 oneroso. Inoltre, le modalit\ue0 di cottura degli alimenti e le caratteristiche compositive della materia prima, aspetti importanti nei meccanismi di formazione di queste sostanze, necessitano ancora di approfondimento per i trattamenti non di tipo industriale. Acrilamide e Furani sono molecole tossiche che si formano in seguito alla reazione di Maillard in prodotti sottoposti a trattamenti termici intensi ma compatibili con le tecniche di cottura dell\u2019industria alimentare e della ristorazione (casalinga o collettiva). Esse sono state riconosciute come mutagene e potenzialmente cancerogene per l\u2019uomo (IARC, 1994; 1995) e l\u2019Autorit\ue0 Europea per la Sicurezza Alimentare (EFSA) ha suggerito di ridurne i livelli negli alimenti (EFSA, 2003). Per quanto riguarda l\u2019Acrilamide, la Commissione Europea solo recentemente ha emanato un documento nel quale vengono suggeriti i valori massimi di concentrazione di acrilamide per alcune categorie di alimenti (European Commission Raccomandation of 10.01.2011). Inoltre, a beneficio dell\u2019industria di trasformazione la Confederation of Food and Drink Industry (CIAA, 2009) ha stilato un libro bianco, nel quale sono descritti gli interventi tecnologici pi\uf9 idonei a minimizzare la formazione di acrilamide negli alimenti trattati termicamente. Per quanto riguarda i Furani, al momento non sono stati stabiliti limiti di contenuto negli alimenti e neppure strategie per la loro riduzione, e l\u2019EFSA si limita a suggerirne la riduzione (EFSA, 2010). Va osservato, che sono del tutto assenti indicazioni sulle modalit\ue0 di riduzione della formazione di concentrazione di acrilamide e furani in alimenti destinati alla ristorazione collettiva, che tuttavia svolge un ruolo primario nella trasformazione e somministrazione di alimenti anche a categorie sensibili (bambini, anziani, malati). Ad esempio patate e derivati, particolarmente ricchi in acrilammide, sono alimenti molto consumati in tutte le fasce di et\ue0 ed in particolar modo dai bambini (Leclercq et al., 2009). In questo lavoro verranno presentate le principali problematiche relative al contenuto di Acrilamide e Furani negli alimenti in un\u2019ottica di previsione e riduzione del loro contenuto attraverso l\u2019adozione di corrette pratiche nella ristorazione collettiva