Molecular-dynamics simulation evidences of a boson peak in protein hydration water

Paciaroni, Alessandro; Bizzarri, Anna Rita; Cannistraro, Salvatore

doi:10.1103/physreve.57.r6277

Cited by 35 publications

(48 citation statements)

References 25 publications

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“…In particular, the cosine transform (power spectrum) of the velocity autocorrelation function VAF( t ) ≡ <v( t )v( 0 )>/<v( 0 ) 2 > determines the vibrational density of states g( ω ). 129 Glass-forming liquids have as one of their distinctive hallmarks an excess density of states relative to crystals at low frequencies and the vibrational density of states g( ω ), normalized by the Debye g D ( ω ) for a crystal, exhibits a peak in glass-forming liquids. This universal feature of glass-forming liquids is termed the “Boson peak’ 22, 113, 130, 131 because its intensity scales according to Bose-Einstein statistics 132 , an appellation that certainly suggests some type of collective excitation phenomena is involved.…”

Section: Boson Peak Of Ni Nanoparticlesmentioning

confidence: 99%

Glassy interfacial dynamics of Ni nanoparticles: Part II Discrete breathers as an explanation of two-level energy fluctuations

Zhang

Douglas

2013

Soft Matter

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Recent studies of the dynamics of diverse condensed amorphous materials have indicated significant heterogeneity in the local mobility and a progressive increase in collective particle motion upon cooling that takes the form of string-like particle rearrangements. In a previous paper (Part I), we examined the possibility that fluctuations in potential energy E and particle mobility μ associated with this ‘dynamic heterogeneity’ might offer information about the scale of collective motion in glassy materials based on molecular dynamics simulations of the glassy interfacial region of Ni nanoparticles (NPs) at elevated temperatures. We found that the noise exponent associated with fluctuations in the Debye-Waller factor, a mobility related quantity, was directly proportional to the scale of collective motion L under a broad range of conditions, but the noise exponent associated with E(t) fluctuations was seemingly unrelated to L. In the present work, we focus on this unanticipated difference between potential energy and mobility fluctuations by examining these quantities at an atomic scale. We find that the string atoms exhibit a jump-like motion between two well-separated bands of energy states and the rate at which these jumps occur seems to be consistent with the phenomenology of the ‘slow-beta’ relaxation process of glass-forming liquids. Concurrently with these local E(t) jumps, we also find ‘quake-like’ particle displacements having a power-law distribution in magnitude so that particle displacement fluctuations within the strings are strikingly different from local E(t) fluctuations. An analysis of these E(t) fluctuations suggests that we are dealing with ‘discrete breather’ excitations in which large energy fluctuations develop in arrays of non-linear oscillators by virtue of large anharmonicity in the interparticle interactions and discreteness effects associated with particle packing. We quantify string collective motions on a fast caging times scale (picoseconds) and explore the significance of these collective motions for understanding the Boson peak of glass-forming materials.

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Section: Boson Peak Of Ni Nanoparticlesmentioning

confidence: 99%

Glassy interfacial dynamics of Ni nanoparticles: Part II Discrete breathers as an explanation of two-level energy fluctuations

Zhang

Douglas

2013

Soft Matter

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“…The structuring of liquids on these length scales is thought to be important in the liquid-to-glass transition [9,10]. A modification of the vibrational mode structure induced by nanometer-scale confinement has also been suggested by molecular dynamics simulations [11,12], and observed in microemulsion systems using neutron and light scattering techniques [13,14]. Another experimental probe of these vibrational modes is dielectric spectroscopy.…”

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Direct Observation of Terahertz Surface Modes in Nanometer-Sized Liquid Water Pools

et al. 2001

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The far-infrared absorption spectrum of nanometer-sized water pools at the core of AOT micelles exhibits a pronounced resonance which is absent in bulk water. The amplitude and spectral position of this resonance are sensitive to the size of the confined water core. This resonance results from size-dependent modifications in the vibrational density of states, and thus has far-reaching implications for chemical processes which involve water sequestered within small cavities. These data represent the first study of the terahertz dielectric properties of confined liquids.

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“…MD calculations found a reduced self diffusion coefficient of water in contact with solid hydrophilic surfaces, when compared to bulk water [11]. Moreover, a recent simulation study of water close to the surface of a protein evidenced a typical spectral glassy anomaly, the so called boson peak [12], which the authors related to protein-solvent coupling. These and other studies suggest the possibility of a common underlying molecular mechanism for the slowing down of the single particle dynamics of interfacial water.…”

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confidence: 99%

Non-exponential kinetic behaviour of confined water

et al. 2000

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Abstract. -We present the results of molecular dynamics simulations of SPC/E water confined in a realistic model of a silica pore. The single-particle dynamics have been studied at ambient temperature for different hydration levels. The confinement near the hydrophilic surface makes the dynamic behaviour of the liquid strongly dependent on the hydration level. Upon decrease of the number of water molecules in the pore we observe the onset of a slow dynamics due to the "cage effect". The conventional picture of a stochastic single-particle diffusion process thus looses its validity.The normal limit of supercooling and the possibility of vitrification of water is the subject of a longstanding scientific debate [1,2]. At T H ∼ 236 K homogeneous nucleation, due to the presence of impurities, drives bulk supercooled water into its solid, crystalline phase. Experiments sustain the hypothesis that the amorphous phase can be connected to the normal liquid phase through a reversible thermodynamic path [3]. Recent molecular dynamics (MD) simulations of bulk supercooled SPC/E [4] water also showed a kinetic glass transition as predicted by mode coupling theory (MCT) [5] at a critical temperature T C ∼ T S [6], where T S is the singular temperature of water [7], which is T S = 228K or 49 degrees below the temperature of maximum density.A comparison of the behaviour of the bulk liquid with the same liquid in a confined environment is highly interesting for the development of both biological and industrial applications. Understanding how the dynamics of liquid water is perturbed by the interaction with hydrophilic or hydrophobic substrates at various levels of hydration lays the physical basis for the prediction of stability and enzymatic activity of biologically important macromolecules [8]. Many experimental studies have been performed on confined and interfacial water. They all showed evidence of a substantial degree of slowing down of water when confined in the proximity of a polar surface [9]. Particularly significant in this context are the indications of Typeset using EURO-T E X

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Molecular-dynamics simulation evidences of a boson peak in protein hydration water

Cited by 35 publications

References 25 publications

Glassy interfacial dynamics of Ni nanoparticles: Part II Discrete breathers as an explanation of two-level energy fluctuations

Glassy interfacial dynamics of Ni nanoparticles: Part II Discrete breathers as an explanation of two-level energy fluctuations

Direct Observation of Terahertz Surface Modes in Nanometer-Sized Liquid Water Pools

Non-exponential kinetic behaviour of confined water

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