Dynamical structure of water

Sucrose changes the dynamic structure of water molecules, which, in turn, affects the manner of aggregation of the DPPE. Citric acid changes the degree of dissociation of the head group of the DPPE molecules. It becomes, therefore, apparent that each chemical species affects the viscoelastic behavior of the lipid thin film in a characteristic manner. 

Water is one of the most familiar material in our life and is indispensable to all living things. In contrast to its apparently simple molecular structure, water shows many anomalous properties from both macroscopic and microscopic points of view. However, the basic physical property of water, for example the dynamical structure of water, has not yet been fully clioified. To un rstand the dynamical aspect of water structure and its significant role in life, it is essential to clarify not only the dynamics of water molecules themselves but also the dynamics of water in the aqueous solutions. 

The characteristic fiequencies of two damped oscillators in D-glucose aqueous solution are almost independent of concentration. This means that the molecular structure of glucose is just fitted with the dynamical structure of water cluster. 

As for the ascorbic acid solutions the effect on the dynamical structure of water is different between the isomerism. The effect of L-xylo ascorbic acid (Vitamin C) on the dyiiamical structure of water is less than that of D-arabo ascorbic acid which has little biological activity. It is interesting if this different effect on the dynamical structure of water may relate with a biological activity. 

A nonconventional view of membrane microstructure, which neither conforms with the solution nor with the porous rock picture, was recently suggested in Ref. 84. Classical MDs simulations on microstructure and molecular mobility in swollen Nation membranes revealed a picture of a rather dynamic structure of water clusters with temporary formation and break-up of water bridges between them. The frequency of intercluster bridge formation was found to be consistent with the experimental transport coefficients through the membrane. 

An investigation of FT Raman spectra of selectively substituted nitrates of carbohydrates has appeared in a symposium report. The depolarized low-frequency Raman spectra of aqueous solutions of L-xy/o-ascorbic acid and of its epimer D-arabinoascorbic acid have been studied as a function of concentration (at 30 °C). This provides evidence that the effect on the dynamical structure of water is greater for the former carbohydrate. ... 

M. L. Berkowitz, I.-C. Yeh, E. Spohr. Structure of water at the water/metal interface. Molecular dynamics computer simulations. In A. Wieckowski, ed. Interfacial Electrochemistry. New York Marcel Dekker, 1999, (in press). 

Repeat this example using 2060 water cells and 40 solute cells in the Example 4.2 Parameter Setup. This is approximately a 2% solution. Repeat the dynamics again with a higher concentration such as 2020 water cells and 80 solute cells, using Example 4.2 Parameter Setup. Compare the structures of water as characterized by their fx profiles and average cluster sizes. Some measures of the structure change in water as a fimction of the concentration are shown in Table 4.2. 

A. Structural and Dynamic Properties of Water-Containing Reversed Micelles... 

Clementi, E. Structure of water and counterions for nucleic acids in solution , in Structure and Dynamics Nucleic Acids and Proteins, Clementi, E., Sarma, R. H. (eds.), New York, Adeline Press 1983... 

Luck, W.A.P. 1981. Structures of water in aqueous systems. In Water Activity Influences on Food Quality (L.B. Rockland and G.F. Stewart, eds), pp. 407 134. Academic Press, New York. Ludescher, R.D., Shah, N.K., McCaul, C.P., and Simon, K.V. 2001. Beyond Tg Optical luminescence measurements of molecular mobility in amorphous solid foods. Food Hydro colloids 15, 331-339. Ludwig, R. 2001. Water From cluster to the bulk. Angewandte Chem. Int. Ed. 40, 1808-1827. Maclnnes, W.M. 1993. Dynamic mechanical thermal analysis of sucrose solutions. In The Glassy State in Foods (J.M.V. Blanshard and PJ. Lillford, eds), pp. 223-248. Nottingham Univ. Press, Loughborough, Leicestershire. 

Monte Carlo and Molecular Dynamics simulations of water near hydrophobic surfaces have yielded a wealth of information about the structure, thermodynamics and transport properties of interfacial water. In particular, they have demonstrated the presence of molecular layering and density oscillations which extend many Angstroms away from the surfaces. These oscillations have recently been verified experimentally. Ordered dipolar orientations and reduced dipole relaxation times are observed in most of the simulations, indicating that interfacial water is not a uniform dielectric continuum. Reduced dipole relaxation times near the surfaces indicate that interfacial water experiences hindered rotation. The majority of simulation results indicate that water near hydrophobic surfaces exhibits fewer hydrogen bonds than water near the midplane. 

In general, this central force approach appears to offer valuable insights into the structure of water, including dynamical effects. It should be improved and studied further. 

The microscopic structure of water at the solution/metal interface has been the focus of a large body of literature, and excellent reviews have been published summarizing the extensive knowledge gained from experiments, statistical mechanical theories of varied sophistication, and Monte Carlo and molecular dynamics computer simulations. To keep this chapter to a reasonable size, we limit ourselves to a brief summary of the main results and to a sample of the type of information that can be gained from computer simulations. 

The earliest fully atomistic molecular dynamic (MD) studies of a simplified Nation model using polyelectrolyte analogs showed the formation of a percolating structure of water-filled channels, which is consistent with the basic ideas of the cluster-network model of Hsu and Gierke. The first MD... 

Likhtenstein, G. 1. The Water-Protein Interactions and Dynamic Structure of Protein, in 14)... 

In Section VII we have applied a phenomenological approach in point of the forms of the potential wells characteristic for water. Now we shall consider a principally another way of modelling of intermolecular interactions pertinent to vibration of the H-bonded molecules. Recently [10, 12, 12a], a preliminary studies of the molecular dynamics was undertaken based on some picture (although very crude) of the molecular structure of water. We shall here briefly represent these results, namely ... 

To calculate L(Z) in terms of the structural-dynamical model of water, we introduce the longitudinal and transverse dimensionless projections, q = py /p and = p /p, of a dipole-moment vector p. These projections are directed, respectively, along and across to the local symmetry axis. In our case (see Fig. 56b), the latter coincides with an equilibrium direction of the H-bond. Next, we introduce the longitudinal and transverse spectral functions as... 

Various dynamic processes have been investigated using computer simulations of phospholipids. These include the dynamics of the alkyl chain movement of the phospholipid, the structure of water at the interface, diffusion of small molecules, interactions of phospholipids with water, dmgs, peptides, and proteins, and the effect of unsaturation or the presence of cholesterol on the phospholipid conformation. 

Polarizability and Water Density Constraint on the Structure of Water Near Charged Surfaces Molecular Dynamics Simulations. 

We have also studied the behavior of gas-phase radicals, such as the hy-droperoxyl radical (HO2) [62], in water clusters which is important in atmospheric science (Figure 16.4). The hydroperoxyl radical is a major species in the HOx chemical family [2] that affects the budgeting of many chemical systems in the atmosphere. The HOx system plays a central role (along with the OH radical) in oxidative chemistry in the troposphere and ultimately controls the production rate of tropospheric ozone [7,16]. It is hence considered significant in atmospheric [2,5] and combustion chemistry [184]. Recent theoretical studies [16,17] have indicated the HO2 radical to possess stable interactions with water clusters. Such stability provides an important sink for HOx compounds [16,17,61,185] in the troposphere. As a result, the structural and dynamical features of water clusters play a vital role on HO2 related chemistry. 

In the 1970s and 1980s, calculational approaches (in addition to the X-ray studies) were added to the tools for the attack on the structure of water. In the molecular dynamics approach, classical mechanics is used to calculate the successive movements of molecules in the structure. Such an approach is dependent on the correctness of the equation that represents the energies of interaction between the particles. The basic equation for these interactions is the Lennard-Jones 6-12 potential. 

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