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Bryk T.,University of Rome La Sapienza | Bryk T.,NASU Institute of Physics | De Panfilis S.,University of Rome La Sapienza | De Panfilis S.,Italian Institute of Technology | And 8 more authors.
Physical Review Letters | Year: 2013

Density-driven phase transformations are a known phenomenon in liquids. Pressure-driven transitions from an open low-density to a higher-density close-packed structure were observed for a number of systems. Here, we show a less intuitive, inverse behavior. We investigated the electronic, atomic, and dynamic structures of liquid Rb along an isothermal line at 573 K, at 1.2-27.4 GPa, by means of ab initio molecular dynamics simulations and inelastic x-ray scattering experiments. The excellent agreement of the simulations with experimental data performed up to 6.6 GPa validates the overall approach. Above 12.5 GPa, the breakdown of the nearly-free-electron model drives a transition of the pure liquid metal towards a less metallic, denser liquid, whose first coordination shell is less compact. Our study unveils the interplay between electronic, structural, and dynamic degrees of freedom along this liquid-liquid phase transition. In view of its electronic nature, we believe that this behavior is general for the first group elements, thus shedding new light into the high-pressure properties of alkali metals. © 2013 American Physical Society.

Calamai M.,CNR Institute of Neuroscience | Calamai M.,European Laboratory for Non linear Spectroscopy | Pavone F.S.,European Laboratory for Non linear Spectroscopy | Pavone F.S.,University of Florence | Pavone F.S.,National Research Council Italy
FEBS Letters | Year: 2013

Growing evidence shows that GM1 ganglioside is involved in amyloid deposition and toxicity. By means of real-time single particle tracking, we show that amyloid oligomers and aggregates formed by Aβ1-42 and amylin, two peptides associated, respectively, with the development of Alzheimer's disease and type II diabetes, interact with GM1 and decrease dramatically its lateral diffusion on the plasma membrane of living neuroblastoma cells. The confinement of GM1, a constituent of membrane rafts involved in neuroprotection, at the level of both types of amyloid aggregates can interfere with cell signaling pathways and contribute to the loss of neuroprotection. © 2013 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Elangovan R.,University of Florence | Capitanio M.,European Laboratory for Non linear Spectroscopy | Melli L.,University of Florence | Pavone F.S.,European Laboratory for Non linear Spectroscopy | And 2 more authors.
Journal of Physiology | Year: 2012

A new efficient protocol for extraction and conservation of myosin II from frog skeletal muscle made it possible to preserve the myosin functionality for a week and apply single molecule techniques to the molecular motor that has been best characterized for its mechanical, structural and energetic parameters in situ. With the in vitro motility assay, we estimated the sliding velocity of actin on frog myosin II (V F) and its modulation by pH, myosin density, temperature (range 4-30°C) and substrate concentration. V F was 8.88 ± 0.26 μm s -1 at 30.6°C and decreased to 1.60 ± 0.09 μm s -1 at 4.5°C. The in vitro mechanical and kinetic parameters were integrated with the in situ parameters of frog muscle myosin working in arrays in each half-sarcomere. By comparing V F with the shortening velocities determined in intact frog muscle fibres under different loads and their dependence on temperature, we found that V F is 40-50% less than the fibre unloaded shortening velocity (V 0) at the same temperature and we determined the load that explains the reduced value of V F. With this integrated approach we could define fundamental kinetic steps of the acto-myosin ATPase cycle in situ and their relation with mechanical steps. In particular we found that at 5°C the rate of ADP release calculated using the step size estimated from in situ experiments accounts for the rate of detachment of motors during steady shortening under low loads. © 2012 The Authors. The Journal of Physiology © 2012 The Physiological Society.

Capitanio M.,European Laboratory for Non linear Spectroscopy | Capitanio M.,University of Florence | Pavone F.S.,European Laboratory for Non linear Spectroscopy | Pavone F.S.,University of Florence | Pavone F.S.,National Research Council Italy
Biophysical Journal | Year: 2013

Single molecule force spectroscopy methods, such as optical and magnetic tweezers and atomic force microscopy, have opened up the possibility to study biological processes regulated by force, dynamics of structural conformations of proteins and nucleic acids, and load-dependent kinetics of molecular interactions. Among the various tools available today, optical tweezers have recently seen great progress in terms of spatial resolution, which now allows the measurement of atomic-scale conformational changes, and temporal resolution, which has reached the limit of the microsecond-scale relaxation times of biological molecules bound to a force probe. Here, we review different strategies and experimental configurations recently developed to apply and measure force using optical tweezers. We present the latest progress that has pushed optical tweezers' spatial and temporal resolution down to today's values, discussing the experimental variables and constraints that are influencing measurement resolution and how these can be optimized depending on the biological molecule under study. © 2013 Biophysical Society.

Asllani M.,University of Insubria | Asllani M.,University of Florence | Challenger J.D.,University of Florence | Pavone F.S.,University of Florence | And 5 more authors.
Nature Communications | Year: 2014

Dynamical processes on networks have generated widespread interest in recent years. The theory of pattern formation in reaction-diffusion systems defined on symmetric networks has often been investigated, due to its applications in a wide range of disciplines. Here we extend the theory to the case of directed networks, which are found in a number of different fields, such as neuroscience, computer networks and traffic systems. Owing to the structure of the network Laplacian, the dispersion relation has both real and imaginary parts, at variance with the case for a symmetric, undirected network. The homogeneous fixed point can become unstable due to the topology of the network, resulting in a new class of instabilities, which cannot be induced on undirected graphs. Results from a linear stability analysis allow the instability region to be analytically traced. Numerical simulations show travelling waves, or quasi-stationary patterns, depending on the characteristics of the underlying graph. © 2014 Macmillan Publishers Limited. All rights reserved.

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