The aim of this paper is to discuss the relationship between the dynamics and thermodynamics of water in the supercooled region. Reviewed case studies comprehend bulk water simulated with the SPC/E, TIP4P and TIP4P/2005 potentials, water at protein interfaces, and water in solution with electrolytes. Upon supercooling, the fragile to strong crossover in the-relaxation of water is found to occur when the Widom line emanating from the liquid-liquid critical point is crossed. This appears to be a general characteristic of supercooled water, not depending on the applied interaction potential and/or different local environments.
With the aim of studying the effect of water dynamics on the properties of biological systems, in this paper, we present a quasi-elastic neutron scattering study on three different types of living cells, differing both in their morphological and tumor properties. The measured scattering signal, which essentially originates from hydrogen atoms present in the investigated systems, has been analyzed using a global fitting strategy using an optimized theoretical model that considers various classes of hydrogen atoms and allows disentangling diffusive and rotational motions. The approach has been carefully validated by checking the reliability of the calculation of parameters and their 99% confidence intervals. We demonstrate that quasi-elastic neutron scattering is a suitable experimental technique to characterize the dynamics of intracellular water in the angstrom/picosecond space/time scale and to investigate the effect of water dynamics on cellular biodiversity.
The hydrogen mean force from experimental neutron Compton profiles is derived using deep inelastic neutron scattering on amorphous and polycrystalline ice. The formalism of mean force is extended to probe its sensitivity to anharmonicity in the hydrogen-nucleus effective potential. The shape of the mean force for amorphous and polycrystalline ice is primarily determined by the anisotropy of the underlying quasi-harmonic effective potential. The data from amorphous ice show an additional curvature reflecting the more pronounced anharmonicity of the effective potential with respect to that of ice Ih.
The pressure versus temperature phase diagram of a system of particles interacting through a multiscale shoulder-like potential is exactly computed in one dimension. The N-shoulder potential exhibits N density anomaly regions in the phase diagram if the length scales can be connected by a convex curve. The result is analyzed in terms of the convexity of the Gibbs free energy.
Based on ab initio molecular dynamics simulations and density functional theory, we performed a systematic theoretical study to elucidate the correlation between the H-bonded environment and Xray emission spectra of liquid water. The spectra generated from excited water molecules embedded in an intact H-bonded environment yield broader spectral peaks and a larger spectral range than the spectra generated from water molecules in a broken H-bonded environment. Such differences are caused by the local electronic structures on the excited water molecules within the core-hole lifetime that evolve differently through the rearrangement of neighboring water molecules in different H-bonded environments.
Biological membranes are essential for cell life and hydration. Water provides the driving force for the assembly and stability of many cell components. Here, we study the structural properties of water in a phospholipid membrane. We characterize the local structures, inspecting the intermediate range order (IRO) and adopting a sensitive local order metric recently proposed by Martelli et al. that measures and grades the degree of overlap of the local environment with the structures of perfect ice. Close to the membrane, water acquires a high IRO and changes its dynamical properties; i.e., its translational and rotational degrees of freedom slow in a region that extends over ≃ 1 nm from the membrane interface. Surprisingly, we show that at distances as far as ≃ 2:5 nm from the interface, although the bulk-like dynamics are recovered, the IRO of water is still slightly higher than that in the bulk under the same thermodynamic conditions. Therefore, the water-membrane interface has a structural effect at ambient conditions that propagates further than the often-invoked 1-nm length scale. Consequently, this should be considered when analyzing experimental data of water confined by membranes and could help us to understand the role of water in biological systems.
A PEGylated-PLGA random nanofibrous membrane loaded with gold and iron oxide nanoparticles and with silibinin was prepared by electrospinning deposition. The nanofibrous membrane can be remotely controlled and activated by a laser light or magnetic field to release biological agents on demand. The nanosystems were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and thermogravimetric analyses. The drug loading efficiency and drug content percentages were determined by UV-vis optical absorption spectroscopy. The nanofibrous membrane irradiated by a relatively low-intensity laser or stimulated by a magnetic field showed sustained silibinin release for at least 60 h, without the burst effect. The proposed low-cost electrospinning procedure is capable of assembling, via a one-step procedure, a stimuli-responsive drug-loaded nanosystem with metallic nanoparticles to be externally activated for controlled drug delivery.
Herein we study the different microscopic interactions occurring in water/methanol solutions at different methanol molar fractions, using NMR spctroscopy. Temperature was found to determine which interaction dominates. It was found that the mixing between water and methanol is non-ideal because of the presence of interactions like hydrophobicity and hydrophilicity. These results indicate that the competition between hydrophilic and hydrophobic interactions is different in different thermal regions, and that the physical properties of the solution are determined by the character of the solution itself, which in turn depends on the mole fraction of methanol and on the temperature.
The degradation process of cellulose-made materials was investigated by means of nuclear magnetic resonance (NMR) spectroscopy, with particular emphasis on the role of water and on the hydration mechanism of cellulose fibrils. To accomplish this, the structure and dynamics of water within ancient and modern samples with different aging histories were investigated. The results mainly indicated that hydrolytic and oxidative reactions provoked the formation of acidic by-products. Furthermore, degradation processes were enhanced by higher amounts of water giving a progressive consumption of the amorphous regions of the cellulose. We propose NMR experiments as a benchmark for characterization of the degradation state of paper, as well as for investigating the effectiveness of restoration treatments.
Classical molecular dynamics simulations were performed to study the high-temperature (above 300 K) dynamic behavior of bulk water, specifically the behavior of the diffusion coefficient, hydrogen bond, and nearest-neighbor lifetimes. Two water potentials were compared: the recently proposed “globally optimal” point charge (OPC) model and the well-known TIP4P-Ew model. By considering the Arrhenius plots of the computed inverse diffusion coefficient and rotational relaxation constants, a crossover from Vogel–Fulcher–Tammann behavior to a linear trend with increasing temperature was detected atT*≈309 and T*≈285 K for the OPC and TIP4P-Ew models, respectively. Experimentally, the crossover point was previously observed atT*≈315±5 K. We also verified that for the coefficient of thermal expansion αP (T, P), the isobaric αP(T) curves cross at about the same T* as in the experiment. The lifetimes of water hydrogen bonds and of the nearest neighbors were evaluated and were found to cross nearT*, where the lifetimes are about 1 ps. For T<T*, hydrogen bonds persist longer than nearest neighbors, suggesting that the hydrogen bonding network dominates the water structure at T<T*, whereas for T>T*, water behaves more like a simple liquid. The fact that T* falls within the biologically relevant temperature range is a strong motivation for further analysis of the phenomenon and its possible consequences for biomolecular systems.
In this paper, we present the results of deep inelastic neutron scattering (DINS) measurements on supercooled water confined within the pores (average pore diameter ~20 Å) 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 hydrationh~40% w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually “dry” sample ath ~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 semiempirical 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.