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Firenze, Italy

Molin L.,CNR Institute of Neuroscience | Seraglia R.,CNR Institute of Neuroscience | Dani F.R.,CISM | Moneti G.,CISM | Traldi P.,CNR Institute of Neuroscience
Rapid Communications in Mass Spectrometry | Year: 2011

1,5-Diaminonaphthalene (DAN) has been described as an interesting and effective matrix for matrix-assisted laser desorption/ionization (MALDI) experiments in positive ion mode, being able to activate in-source decomposition phenomena and, when employed for the analysis of proteins containing disulphide bridge(s), being able to activate reduction processes, resulting in disulphide bridge cleavage. The mechanisms of the DAN reactivity have been studied in detail, and the results indicate that the reduction properties of the matrix are of a radical nature. In the present study the structure of the reactive species produced by DAN, responsible for its reductive properties, has been investigated by accurate mass measurements and tandem mass spectrometry (MS/MS) experiments. Contrary to what is usually observed by laser irradiation of other MALDI matrices (with the sole formation of the MH + ion of the matrix), DAN leads to the formation of odd-electron molecular ions M +̇. This can be rationalized by the occurrence of two photon pooling processes, due to the low ionization energy of DAN. Thus the M +̇ ion of DAN can be considered responsible for both analyte protonation and disulphide bond reduction and some mechanisms are proposed for this behaviour. © 2011 John Wiley & Sons, Ltd. Source


Marchioli C.,CISM | Soldati A.,CISM
Acta Mechanica | Year: 2013

In this paper, the rotation of rigid fibers is investigated for the reference case of turbulent channel flow. The aim of the study is to examine the effect of local shear and turbulence anisotropy on the rotational dynamics of fibers with different elongation and inertia. To this aim, statistics of the fiber angular velocity, Ω, are extracted from direct numerical simulation of turbulence at shear Reynolds number Re τ = 150 coupled with Lagrangian tracking of prolate ellipsoidal fibers with Stokes number, St, ranging from 3 to 100 and aspect ratio, λ, ranging from 1 to 50. Accordingly, the fiber-to-fluid density ratio ranges from $${S \simeq 7}$$ S ≠7 (for St = 1, λ = 50) to $${S \simeq 3, 470}$$ S ≠3, 470 (for St = 100, λ = 1). Statistics are compared one to one with those obtained for spherical particles to highlight effects due to elongation. Results for mean and fluctuating angular velocities show that elongation is important for fibers with small inertia (St ≤ 5 in the present flow-fiber combination). For fibers with larger inertia, elongation has an impact on fiber rotation only in the streamwise and wall-normal directions, where mean values of Ω are zero. It is also shown that, in the center of the channel, the Lagrangian autocorrelation coefficients of Ω and corresponding rotational turbulent diffusivities match the exponential behavior predicted by the theory of homogeneous dispersion. In this region of the channel, the probability density function of fiber angular velocities is generally close to Gaussian, indicating that particle rotation away from solid walls can be modeled as a diffusion process of the Ornstein-Uhlenbeck type at stationary state. In the strong shear region (comprised within a distance of 50 viscous units from the wall in the present simulations), fiber anisotropy adds to flow anisotropy to induce strong deviations on fiber rotational dynamics with respect to spherical particles. The database produced in this study is available to all interested users at https://www.fp1005.cism.it. © 2013 Springer-Verlag Wien. Source

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