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Roberto Bini

Publications and source records attributed to Roberto Bini.

12 recordsLinked to original sources
PubMed2006

Triggering dynamics of the high-pressure benzene amorphization.

Success in designing and tailoring solid-state reactions depends on the knowledge of the mechanisms regulating the reactivity at the microscopic level. In spite of several attempts to rationalize the reactivity of crystals, the question of the existence of a critical distance for a reaction to occur remains unsolved. In this framework, the role of lattice phonons, which continuously tune the relative distance and orientation of the molecules, is still not fully understood. Here, we show that at the onset of the transformation of crystalline benzene to an amorphous hydrogenated carbon the intermolecular C-C distance is always the same (about 2.6 A) once collective motions are taken into account, and it is independent of the pressure and temperature conditions. This conclusion is supported by first-principles molecular-dynamics simulations. This is a clear demonstration of the role of lattice phonons in driving the reactivity in the crystalline phase by fine-tuning of the nearest-neighbour distances. The knowledge of the critical C-C distance can be crucial in planning solid-state reactions at moderate pressure.

Journal Article↗
PubMed2006

Amorphous silica-like carbon dioxide.

Among the group IV elements, only carbon forms stable double bonds with oxygen at ambient conditions. At variance with silica and germania, the non-molecular single-bonded crystalline form of carbon dioxide, phase V, only exists at high pressure. The amorphous forms of silica (a-SiO2) and germania (a-GeO2) are well known at ambient conditions; however, the amorphous, non-molecular form of CO2 has so far been described only as a result of first-principles simulations. Here we report the synthesis of an amorphous, silica-like form of carbon dioxide, a-CO2, which we call 'a-carbonia'. The compression of the molecular phase III of CO2 between 40 and 48 GPa at room temperature initiated the transformation to the non-molecular amorphous phase. Infrared spectra measured at temperatures up to 680 K show the progressive formation of C-O single bonds and the simultaneous disappearance of all molecular signatures. Furthermore, state-of-the-art Raman and synchrotron X-ray diffraction measurements on temperature-quenched samples confirm the amorphous character of the material. Comparison with vibrational and diffraction data for a-SiO2 and a-GeO2, as well as with the structure factor calculated for the a-CO2 sample obtained by first-principles molecular dynamics, shows that a-CO2 is structurally homologous to the other group IV dioxide glasses. We therefore conclude that the class of archetypal network-forming disordered systems, including a-SiO2, a-GeO2 and water, must be extended to include a-CO2.

Journal Article↗
PubMed2005

Pressure-induced polymerization in solid ethylene.

Ethylene is the simplest organic molecule containing a double bond and is the starting monomeric unit in the synthesis of polyethylene, one of the most largely produced polymers. Here we report a high pressure infrared study of ethylene at room temperature. A polymerization reaction is observed when the crystalline phase I is compressed above 3.0 GPa. The reaction kinetics was investigated at two different pressures, 3.6 and 5.4 GPa. The recovered product was identified in both cases as polyethylene, but while a conformationally disordered and branched low-density polymer is obtained at the highest pressure, a high-density crystalline polymer is obtained at 3.6 GPa. A reaction mechanism was proposed on the basis of the kinetic data and the structural information.

Journal Article↗
PubMed2005

High-pressure reactivity of propene.

The phase diagram of propene has been investigated at high pressure by using the diamond anvil cell technique and Fourier transform infrared spectroscopy. The pressure conditions necessary to induce a spontaneous reaction of the sample have been found at different temperatures, allowing the stability boundary of propene to be drawn. The reaction is diffusion controlled and seems to occur only in the fluid phase, implying a slope inversion of the stability boundary at about 250 K. The product of the reaction is a mixture of linear oligomers independently of the P-T conditions. The activation volume and energy of the process have been obtained from the kinetic data. Also the activation of the reaction by laser absorption has been carefully studied. A high proton mobility has been identified as the likely reason that limits the lengthening of the chain up to six to eight monomeric units preventing the polymer formation.

Journal Article↗
PubMed2004

Linear carbon dioxide in the high-pressure high-temperature crystalline phase IV.

High-temperature IR absorption spectra of solid CO2 in phases II and IV were measured in a resistive heated diamond anvil cell up to 30 GPa. The spectral structures of the bending mode, observed in high quality thin crystalline samples, and of the IR lattice phonons, measured for the first time between 80 and 640 K, are discussed using group theory arguments. According to this analysis the claimed bent molecular geometry of CO2 in phase IV can be unambiguously ruled out. Furthermore, the structures of both phases II and IV have been identified, among those so far proposed, as orthorhombic.

Journal Article↗
PubMed2004

High-pressure synthesis of crystalline polyethylene using optical catalysis.

Polymerization processes are probably the most relevant example of a chemical reaction activated by catalysts or radical initiators. Among polymers, polyethylene is by far the most common and largely produced. Here we present a high-pressure synthesis of high-density crystalline polyethylene by using only physical tools such as pressure and light. Low-density polyethylene is obtained by compressing ethylene at room temperature above 3 GPa in the ordered crystal phase, and a highly crystalline polymer is produced in the fluid phase at pressures lower than 1 GPa by using continuous-wave laser lines (lambda < or = 460 nm) as an optical catalyst. The photo-activation is based on a two-photon absorption process to pi* antibonding states, where the change in molecular geometry favours the polymeric chain formation. The high yield and crystallinity of the polymer recovered by the photoinduced reaction and the simplicity of the synthesis make this process appealing for large-scale applications.

Journal Article↗
PubMed2004

Laser-assisted high-pressure chemical reactions.

The growing need for production methods with a reduced environmental impact drives the search for new synthetic approaches in chemistry. Here we report the state of the art of a recently developed branch of ultra-high-pressure chemistry, employing high pressure to create the necessary reaction conditions to transform simple hydrocarbons and monochromatic light to trigger and direct, according to selective paths, the chemical reaction. For the available systems studied up to now, we will provide an overview of the different effects that can be obtained by the combined use of pressure and laser light.

Journal Article↗
PubMed2004

"Torsade de pointes" in a patient with variant angina.

Ventricular tachyarrhythmias have been well documented in patients with variant angina. Episodes of torsade de pointes have been described infrequently. We report a case of a 60-year-old male with a previous history of one vessel artery disease and a successful coronary angioplasty with stenting of the left anterior descending artery, who experienced an episode of angina at rest and electrocardiographic evidence of self-terminating torsade de pointes. After a negative coronary angiography and a positive hyperventilation test, the diagnosis of variant angina was considered and beta-blockers discontinued and calcium channel antagonists prescribed. No other episodes of angina were documented during the following 6 months of follow-up.

Angina Pectoris, Variant↗
PubMed2002

Laser-induced selectivity for dimerization versus polymerization of butadiene under pressure.

The pressure-induced chemical reaction of liquid butadiene was studied by Fourier transform infrared spectroscopy in a diamond anvil cell. Dimerization was found to occur above 0.7 gigapascal, giving vinylcyclohexene according to a cyclo-addiction reaction and only a trace amount of polybutadiene forms. By irradiating the high-pressure sample with a few milliwatts of the 488-nanometer argon+ laser line, the dimerization was completely inhibited, and the rapid formation of pure trans-polybutadiene was observed. The use of different excitation wavelength allows us to emphasize the selectivity of the process and to identify the active role of the 2(1)Ag state in this pressure- and laser-induced chemical reaction.

Journal Article↗
PubMed2002

High pressure photoinduced ring opening of benzene.

The chemical transformation of crystalline benzene into an amorphous solid (a-C:H) was induced at high pressure by employing laser light of suitable wavelengths. The reaction was forced to occur at 16 GPa, well below the pressure value (23 GPa) where the reaction normally occurs. Different laser sources were used to tune the pumping wavelength into the red wing of the first excited singlet state S(1)((1)B(2u)) absorption edge. Here the benzene ring is distorted, presenting a greater flexibility which makes the molecule unstable at high pressure. The selective pumping of the S(1) level, in addition to structural considerations, was of paramount importance to clarify the mechanism of the reaction.

Journal Article↗
PubMedDate not supplied

[Nonoperative management of traumatic liver injuries].

BACKGROUND: Nonoperative management (TNO) of traumatic liver injury is the choice in hemodinamically stable patients without other abdominal injuries requiring celiotomy, apart from liver injury grading and amount of free peritoneal blood. CT-scan and angiographic embolization availability increase TNO feasibility. AIMS: To investigate feasibility of TNO in 16-months period consecutive liver injuries. MATERIALS AND METHODS: All data of severe trauma patients admitted to our facility during the study period were recorded. Clinical decision scheme of our facility indicates TNO in hemodynamically stable patients with liver injury and no need for celiotomy. CT-scan is performed and injury grading evaluated. Angiographic embolization is done if contrast medium extravasation is present at CT-scan. Laparoscopy is suggested if ongoing bleeding with negative CT-scan for blushing. RESULTS: Liver injury was detected in 34 of 452 severe trauma patients. Fifty percents of patients underwent TNO. In this group, bleeding control was achieved by angiographic embolization in 8 cases and by laparoscopy in 1. None of these patients needed celiotomy. None of TNO patients died. CONCLUSIONS: In a trauma referral center TNO of liver injury is possible in about 50%. TNO in severe trauma is improved if a correct CT-scan evaluation at the admission is performed and angiography correctly applied. Laparoscopy is an useful adjunctive tool in control of bleeding.

Adult↗