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Good quality extended x-ray absorption fine structure (EXAFS) spectra near the Ga K edge have been collected in wide pressure and temperature ranges (namely 0--16 GPa, 298--498 K) using the dispersive setup installed at the LURE synchrotron radiation facility and diamond anvil cell as pressure device. Energy dispersive x-ray diffraction data have been also measured in similar thermodynamical conditions. EXAFS spectra are shown to be sensitive to phase transitions occurring at high pressures and temperatures. Occurrence of stable and metastable phases and location of the coexistence lines are discussed in light of the results obtained using both experimental techniques. The phase diagram of pure gallium has been extended considering present experimental results. EXAFS data-analysis is performed using advanced ab initio methods (GNXAS). Accurate information about local structure in solid and liquid gallium at extreme conditions is obtained. The short-range two-body distribution functions are reconstructed by EXAFS for liquid and solid gallium as a function of pressure and temperature.

Inelastic x-ray measurements of polybutadiene are reported, performed over a wide temperature range covering both the glass and the liquid phase. At each temperature, the frequency position $\ensuremath{\Omega}$ and the width $\ensuremath{\Gamma}$ of the inelastic peaks of the spectra have been obtained for different values of the scattering vector $Q$. A linear behavior of $\ensuremath{\Omega}(Q)$ for $Ql4{\mathrm{nm}}^{\ensuremath{-}1}$ has been revealed, allowing the determination of the unrelaxed sound velocity ${v}_{\ensuremath{\infty}}.$ Consistently with the results obtained in different glass-forming systems, the Q dependence of $\ensuremath{\Gamma}$ is well represented by a ${Q}^{2}$ law. For $Qg5{\mathrm{nm}}^{\ensuremath{-}1}$ the values of $\ensuremath{\Gamma}$ overtake those of $\ensuremath{\Omega}$ and the acousticlike excitations progressively loose their propagative nature. In the glass, ${v}_{\ensuremath{\infty}}(T)$ compares well with previous Brillouin Light Scattering (BLS) determinations, while in the liquid the BLS sound velocity shows a steeper temperature dependence related to the structural relaxation. The temperature behavior of the nonergodicity factor has been derived both from ${v}_{o}$ and ${v}_{\ensuremath{\infty}}$ (in the liquid phase) and from the ratio between elastic and inelastic intensities of inelastic x-ray scattering spectra (in the whole investigated temperature range). Both temperature and Q behavior of this quantity might be consistently interpreted in the framework of the mode coupling theory.

Evidence of transverse acoustic waves in glycerol is given by Brillouin light scattering over a temperature interval ranging from a few kelvins below the glass transition temperature T g = 187 K to some 30 K above T g. The analysis of Brillouin doublets shows a linear temperature dependence of the unrelaxed shear modulus G ∞ above T g, which is close to that extrapolated from ultrasonic data. This behaviour seems to be rather unusual when compared with the linear dependence of previously documented in a number of glass-forming systems. By decreasing the temperature, G ∞(T) shows a bend at the glass transition and, for lower temperatures, a weaker temperature dependence. In this region, a value of about 0.5 has been found for the ratio of the characteristic frequencies of transverse acoustic to longitudinal acoustic excitations, consistent with the value recently found for the ratio of the energies of the collective modes revealed by inelastic X-ray scattering in the terahertz region.

The dynamics of the fragile glass-forming liquid diglycidyl ether of bisphenol-A was studied by depolarized Rayleigh-Brillouin light-scattering and photon correlation spectroscopy above the glass transition, in the temperature range from 261 to 473 K and in the frequency range from 1 Hz to 300 GHz. The structural (alpha-) relaxation process was revealed and no signature of the secondary relaxation previously evidenced by dielectric spectroscopy at about 0.1 GHz was observed. The characteristic time of the alpha process differs from that determined by dielectric spectroscopy of an amount, which increases with increasing temperature. The relaxation times were compared with viscosity data to test the predictions of the classic Stokes-Einstein-Debye model. The tau proportional, variant eta behavior was verified for dielectric data, while a fractional power law of viscosity tau proportional, variant eta(0.89) was obtained for light-scattering relaxation times, extending over more than seven decades in viscosity and time. This deviation of light scattering from viscosity data could be interpreted in terms of cooperative motion in the supercooled liquid with a characteristic length xi(a) proportional, variant(T-T0)(-v) where T(0)=229 K is the Vogel temperature and v is close to 2 / 3 which is consistent with the prediction of the fluctuation theory of glass transition.

The elastic and viscoelastic properties of the epoxy system Epon 828 have been studied by means of the Brillouin light scattering (BLS) technique. The specimen, consisting of a transparent epoxy film supported by an opaque substrate, has been analyzed by means of a high contrast Fabry-Perot tandem interferometer. The characteristic frequency and lifetime of longitudinal and transverse acoustic modes have been measured in a wide temperature range, above and below the glass transition temperature T/sub g/=257 K. From these data, the temperature behavior of both the teal and imaginary pair of the elastic moduli was obtained at the frequency of the Brillouin peak (/spl ap/10 GHz). Evidence is given of a very broad dispersion associated to both a structural and secondary relaxation. A full spectrum analysis has been also performed in order to determine the frequency dependence of the longitudinal elastic modulus.

The main protease (Mpro or 3CLpro) is an enzyme that is evolutionarily conserved among different genera of coronaviruses. As it is essential for processing and maturing viral polyproteins, Mpro has been identified as a promising target for the development of broad-spectrum drugs against coronaviruses. Like SARS-CoV and MERS-CoV, the mature and active form of SARS-CoV-2 Mpro is a dimer composed of identical subunits, each with a single active site. Individual monomers, however, have very low or no catalytic activity. As such, inhibition of Mpro can be achieved by molecules that target the substrate binding pocket to block catalytic activity or target the dimerization process. In this study, we investigated GC376, a transition-state analog inhibitor of the main protease of feline infectious peritonitis coronavirus, and Nirmatrelvir (NMV), an oral, bioavailable SARS-CoV-2 Mpro inhibitor with pan-human coronavirus antiviral activity. Our results show that both GC376 and NMV are capable of strongly binding to SARS-CoV-2 Mpro and altering the monomer-dimer equilibrium by stabilizing the dimeric state. This behavior is proposed to be related to a structured hydrogen-bond network established at the Mpro active site, where hydrogen bonds between Ser1’ and Glu166/Phe140 are formed in addition to those achieved by the latter residues with GC376 or NMV.