Biomedical subjects

Mario Santoro

Publications and source records attributed to Mario Santoro.

8 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.

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PubMed2006

Specific mutations in HIV-1 gp41 are associated with immunological success in HIV-1-infected patients receiving enfuvirtide treatment.

OBJECTIVES: To investigate gp41 variability and correlation with viro-immunological parameters in 54 HIV-1-infected patients receiving enfuvirtide added as single active drug to a failing regimen. METHODS: One hundred and two HIV-1 gp41 sequences and clinical follow-up from 54 enfuvirtide-treated patients were analysed from baseline to week 36 of treatment. The association of mutations with viraemia/CD4 count was assessed by Mann-Whitney test. RESULTS: The addition of enfuvirtide to the failing regimen induced at week 4 a viraemia decrease from 5.1 to 4.3 log(10)/mL (P = 0.0002) and a CD4 increase from 48 to 106 cells/mm(3) (P = 0.008). While viraemia rebounded to 4.8 and 4.6 log(10)/mL at week 12 and 36, respectively, CD4 continued to increase to 136 cells/mm(3) at week 36. Enfuvirtide resistance mutations, rarely found at baseline, occurred in 45/54 (83.3%) enfuvirtide-treated patients. V38A/E were the most represented mutations at all time-points. The presence of V38A/E was significantly associated with a 4.5-fold CD4 increase from baseline to week 24 and with a 6-fold increase at week 36 (P = 0.004 and 0.02 compared without V38A/E, respectively), without significant correlation with viraemia. In contrast, Q40H + L45M (present in six enfuvirtide-treated patients at week 36) correlated with CD4 loss from baseline to week 36 (P = 0.02), without significant correlation with viraemia. Mutation N126K (observed in six enfuvirtide-treated patients, never found at baseline) abrogates the fourth gp41 glycosylation site and correlates with a 2.1-fold CD4 increase at week 24. CONCLUSIONS: Specific enfuvirtide resistance mutations (V38A/E) are associated with a sustained CD4 increase, without remarkable effects upon viraemia. This CD4 recovery, due to virus- and immune-mediated mechanisms most probably not applicable to protease/reverse transcriptase inhibitors, is important for innovative therapeutic strategies.

Adult↗

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.

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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.

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PubMed2004

New phase diagram of oxygen at high pressures and temperatures.

In situ high P-T Raman measurements and optical observations of solid and fluid oxygen up to 1250 K between 8 and 25 GPa reveal the existence of a new molecular phase eta and strikingly unusual behavior of the melting curve. Three triple points were also identified in the P-T domain of the new phase. The data give a direct measure of the melting curve that greatly extends previous optical investigations. We find the melting temperature is significantly higher than that indicated by the existing phase diagram (e.g., 400 K higher at 25 GPa). Raman measurements in low and high frequency regions reveal the extent of orientational order disorder and persistence of strong intermolecular interactions in the high P-T phases.

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PubMed2004

In situ high P-T Raman spectroscopy and laser heating of carbon dioxide.

In situ high P-T Raman spectra of solid CO(2) up to 67 GPa and 1,660 K have been measured, using a micro-optical spectroscopy system coupled with a Nd:YLF laser heating system in diamond anvil cells. A metallic foil was employed to efficiently absorb the incoming Nd:YLF laser and heat the sample. The average sample temperature was accurately determined by detailed balance from the anti-Stokes/Stokes ratio, and was compared to the temperature of the absorber determined by fitting the thermal radiation spectrum to the Planck radiation law. The transformation temperature threshold and the transformation dynamics from the molecular phases III and II to the polymeric phase V, previously investigated only by means of temperature quench experiments, was determined at different pressures. The P-T range of the transformation, between 640 and 1,100 K in the 33-65 GPa pressure interval, was assessed to be a kinetic barrier rather than a phase boundary. These findings lead to a new interpretation of the high P-T phase diagram of carbon dioxide. Furthermore, our approach opens a new way to perform quantitative in situ Raman measurements under extremely high pressures and temperatures, providing unique information about phase relations and structural and thermodynamic properties of materials under these conditions.

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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.

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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.

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