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Kinetic energy and radial momentum distribution of hydrogen and oxygen atoms of water confined in silica hydrogel in the temperature interval 170–325 K
No full textWater is an ubiquitous liquid and it is necessary for life;. Studies on water are therefore of obvious scientific and ....
technological relevance. In view of its peculiar physicalproperties (the so-called water anomalies, particularly relevant
at low temperatures [1]), studies on water structureand dynamics in ample temperature intervals, covering also
the supercooling region, have attracted much interest in recent years. In particular, studies focused on the supercooled
phase are important in order to test theories and hypotheses[2,3], including the liquid-liquid phase transition hypothesis
[4-6] and the related fragile-to-strong crossover observed inwater confined in silica matrices and in the hydration water
of proteins [7,8]. In this context, water confined withinnanometer-sized porous hydrophilic/hydrophobic matrices
has been investigated both to extend the supercooling temperaturerange accessible to experiment and to mimic the
crowding/confined conditions experienced by water moleculesin biological systems relevant to biophysics, bio-preservation,and pharmaceutics. In view of the abovearguments, studies on the short-time dynamics of hydrogen
and oxygen atoms of supercooled water (bulk or confined) are of great relevance
Low-temperature optical spectroscopy of cobalt in Cu,Co superoxide dismutase: A structural dynamics study of the solvent-unaccessible metal site RID F-2353-2010 RID F-2664-2011 RID A-4573-2009
No full textThe temperature dependence (300 to 10 K) of the electronic absorption spectra of the cobalt chromophore in bovine superoxide dismutase (SOD) having the native Zn(II) ion selectively replaced by Co(II) has been investigated in four different derivatives: Cu(II),Co(II) SOD, N-3(-)-Cu(II),Co(II) SOD, Cu(I),Co(II) SOD, and E,Co(II) SOD in which the copper ion has been selectively removed. In the Cu(II),Co(lI) SOD, the cobalt spectrum is characterized at room temperature by three bands centered at 18,472, 17,670, and 16,793 cm(-1); the low-frequency band is split, at low temperatures, into two components, indicating a lower symmetry contribution to a predominantly tetrahedral crystal field. Addition of N-3(-) to the Cu(II),Co(II) SOD introduces slight changes in all the Co(II) visible bands, indicating the occurrence of minor perturbations of the structural cobalt site upon anion binding to the catalytic copper site. Analysis of the spectra in the Cu(I),Co(II) and E,Co(II) enzymes indicates that the His61 imidazolate bridge is released from the copper upon reduction. This is also confirmed by the analysis of the zeroth, first, and second moments of the various bands in the different derivatives. The cobalt site is characterized by a harmonic dynamics, at variance with what observed in the solvent accessible copper site [Cupane, A., Leone, M., Militello, V., Stroppolo, M. E., Polticelli, F., & Desideri, A. (1994) Biochemistry 33, 15103-15109]. The degree of local microheterogeneity at the cobalt site is smaller than that observed for the copper site and increases in the order N-3(-)-Cu(II),Co(II)approximate to Cu(I),Co(II) < Cu(I),Co(II) < E,Co(II) indicating a different local packing and the presence of different constraints on the cobalt site in the four derivatives. The different dynamic behavior with respect to the catalytic, solvent-accessible, copper site is discussed
Reply to “Comment to ‘Dynamics of supercooled confined water measured by deep inelastic neutron scattering’ by Y. Finkelstein and R. Moreh”
No full textWe reply to the comment [Front. Phys. 14(5), 53605 (2019)] by Y. Finkelstein and R. Moreh on our articleFront. Phys. 13(1), 138205(2018).Weagreewithsomeoftheircriticismsaboutourcalculation of the temperature effect on the kinetic energy of hydrogen atoms of supercooled confined water; we also agree with their statement that, in view of the current sensitivity of the technique, possible effects oftheliquid–liquidwatertransitionarehardlydetectedwithdeepinelasticneutronscattering(DINS). However, we disagree with their use of the translational mass ratio of a single water molecule and, in general, with their underestimation of collective effects
Dynamics of supercooled confined water measured by deep inelastic neutron scattering
No full textIn this paper, we present the results of deep inelastic neutron scattering (DINS) measurements on supercooled water confined within the pores (average pore diameter similar to 20 angstrom) of a disordered hydrophilic silica matrix obtained through hydrolysis and polycondensation of the alkoxide precursor Tetra-Methyl-Ortho-Silicate via the sol-gel method. Experiments were performed at two temperatures (250 K and 210 K, i.e., before and after the putative liquid-liquid transition of supercooled confined water) on a "wet" sample with hydration h similar to 4 0 %w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually "dry" sample at h similar to 7 % was also investigated to measure the contribution of the silica matrix to the neutron scattering signal. As is well known, DINS measurements allow the determination of the mean kinetic energy and the momentum distribution of the hydrogen atoms in the system and therefore, allow researchers to probe the local structure of supercooled confined water. The main result obtained is that at 210 K the hydrogen mean kinetic energy is equal or even slightly higher than at 250 K. This is at odds with the predictions of a semi-empirical harmonic model recently proposed to describe the temperature dependence of the kinetic energy of hydrogen in water. This is a new and very interesting result, which suggests that at 210 K, the water hydrogens experience a stiffer intermolecular potential than at 250 K. This is in agreement with the liquid-liquid transition hypothesis
Protein dynamics: conformational disorder, vibrational coupling and anharmonicity in deoxy-hemoglobin and myoglobin
No full textIn this work we study the temperature dependence of the Soret band lineshape of deoxymyoglobin and deoxyhemoglobin, in the range 300-20 K. To fit the measured spectra we use an approach originally proposed by Champion and coworkers (Srajer et al. 1986; Srajer and Champion 1991). The band profile is modelled as a Voigt function that accounts for the coupling with low frequency vibrational modes, whereas the coupling with high frequency modes is responsible for the vibronic structure of the spectra. Moreover, owing to the position of the iron atom out of the mean heme plane, inhomogeneous broadening brings about a non-Gaussian distribution of 0-0 electronic transition frequencies. The reported analysis enables us to isolate the various contributions to the overall bandwidth, and their temperature dependence points out the relevance of low frequency vibrations and of large scale anharmonic motions starting at temperatures higher than 170 K. Information on the mean iron-heme plane distance and on its temperature dependence, as well as on the heme pocket conformational disorder, is also obtained. © 1993 Springer-Verlag
Incoherent elastic and quasi-elastic neutron scattering investigation of hemoglobin dynamics
No full textIn this work we investigate the dynamic properties of hemoglobin in glycerolD(8)/D(2)O solution using incoherent elastic (ENS) and quasi-elastic (QENS) neutron scattering. Taking advantage of complementary energy resolutions of backscattering spectrometers at ILL (Grenoble), we explore motions in a large space-time window, up to 1 ns and 14 A; moreover, in order to cover the harmonic and anharmonic protein dynamics regimes, the elastic experiments have been performed over the wide temperature interval of 20-300 K. To study the dependence of the measured dynamics upon the protein quaternary structure, both deoxyhemoglobin (in T quaternary conformation) and carbonmonoxyhemoglobin (in R quaternary conformation) have been investigated. From the ENS data the mean square displacements of the non-exchangeable hydrogen atoms of the protein and their temperature dependence are obtained. In agreement with previous results on hydrated powders, a dynamical transition at about 220 K is detected. The results show interesting differences between the two hemoglobin quaternary conformations, the T-state protein appearing more rigid and performing faster motions than the R-state one; however, these differences involve motions occurring in the nanosecond time scale and are not detected when only faster atomic motions in the time scale up to 100 ps are investigated. The QENS results put in evidence a relevant Lorentzian quasi-elastic contribution. Analysis of the dependence of the Elastic Incoherent Structure Factor (EISF) and of the Lorentzian halfwidth upon the momentum transfer suggests that the above quasi-elastic contribution arises from the diffusion inside a confined space, values of confinement radius and local diffusion coefficient being compatible with motions of hydrogen atoms of the amino acid side chains. When averaged over the whole range of momentum transfer the QENS data put in evidence differences between deoxy and carbonmonoxy hemoglobin and confirm the quaternary structure dependence of the protein dynamics in the nanosecond time scale
Investigating protein structure and dynamics through wide-angle X-ray solution scattering
Full text linkWide-angle X-ray scattering (WAXS) is a powerful tool that can be used to gain information on the structure and dynamics of proteins and other biomolecules in solution. Improved methods for the calculation of WAXS patterns from available or putative protein models allow to better exploit the structural information contained in the experimental data. These methods, together with recent applications of static and time-resolved WAXS, are briefly reviewed
Hysteresis in the temperature dependence of the IR bending vibration of deeply cooled confined water
No full textUsing Fourier Transform Infrared (FTIR) spectroscopy, we investigate the temperature dependence of the bending vibrations of water confined in the pores of a silica hydrogel in the temperature interval of 270-180 K. We also investigate the presence of thermal hysteresis by cooling and reheating temperature scans. The results clearly show the presence, at about 230 K, of a crossover in the temperature dependence of the IR spectra; moreover, the presence of hysteresis is clearly demonstrated. By comparing FTIR data with neutron diffraction data and previous calorimetric data on the same samples, we conclude that the crossover and the hysteretical behavior do not involve a water glass transition or crystallization but are related to a first-order-like liquid-liquid transition
Heme symmetry, vibronic structure, and dynamics in heme proteins: ferrous nicotinate horse myoglobin and soybean leghemoglobin.
No full textDynamic properties of solvent confined in silica gels studied by broadband dielectric spectroscopy
No full textWe report the results of a broadband (10−2–107 Hz) dielectric spectroscopy study on a solvent system (glycerol–water solution) confined in a porous silica matrix. The dielectric relaxation of the system is studied as a function of both temperature (120–280 K) and solvent composition (0–36 glycerol molar percentage), at constant matrix composition. Our data show that glycerol–water systems confined inside silica gel are characterized by a very complex dynamics quite different from that observed in solution, thus indicating that confinement may deeply modify solvent dynamics. Indeed in addition to the relaxation processes similar to those occurring in bulk samples, new dielectric relaxations are detected: two non-collective relaxations, attributed to water molecules strongly interacting with pore surfaces and to the glycerol trapped within the matrix structure, respectively; a relaxation in the glycerol free sample (and in samples at very low glycerol content) almost coincident with that observed in other different confinement conditions and governed by geometrical confinement per se. Moreover, at high glycerol content we observe two non-Arrhenius processes at least 4 order of magnitude slower than solution-like main relaxation; at low glycerol content the two above relaxations merge and show a fragile to strong transition at about 200 K
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