Water at interface

K. Heinzinger. Molecular dynamics of water at interfaces. In J. Lipkowski, P. N. Ross, eds. Structure of Electrified Interfaces, Erontiers of Electrochemistry. New York VCH 1993, Chap 7, p. 239. 

Temp. Gas Water at Interface Out. °F Tube Ciun. Film Condensed, No. Gas Area Tube, Length of... 

A controversy exists over the interpretation of such a correlation. According to the simple two-state model for water at interfaces, the higher the preferential orientation of one of the states, the higher the value of BEa=Q/BT. If the preferentially oriented state is that with the negative end of the dipole down to the surface, the temperature coefficient of Ev is positive (and vice versa). Thus, in a simple picture, the more positive BEa=0/BTt the higher the orientation of water, i.e., the higher the hydro-philicity of the surface. On this basis, Silva et al.446 have proposed the... 

A case in point is water at interfaces. Any reasonable model for a water molecule and its interactions has the following features ... 

Lyklema, J. J. Coll, and Interface Sci. 58 (1977) 242. Water at interfaces A colloid chemical approach. 

Most of the new molecular-level results concern the structure and dynamics of water at interfaces. We begin this review with a brief summary of this area. Several recent review articles and books can be consulted for additional information. " We then examine in some detail the new insight gained from molecular dynamic simulations of the structure of the electric double layer and the general behavior of ions at the water/metal interface. We conclude by examining recent developments in the modeling of electron transfer reactions. 

The structure of water at interfaces in general, and at the metal surface in particular, is determined by a number of factors ... 

Much more detailed information about the microscopic structure of water at interfaces is provided by the pair correlation function which gives the joint probability of finding an atom of type/r at a position ri, and an atom of type v at a position T2, relative to the probability one would expect from a uniform (ideal gas) distribution. In a bulk homogeneous liquid, gfn, is a function of the radial distance ri2 = Iri - T2I only, but at the interface one must also specify the location zi, zj of the two atoms relative to the surface. We expect the water pair correlation function to give us information about the water structure near the metal, as influenced both by the interaction potential and the surface corrugation, and to reduce to the bulk correlation Inunction when both zi and Z2 are far enough from the surface. 

D.E. Woessner, NMR Studies of Preferentially Oriented Water at Interface. In R. Haque and F.J. Biros (eds.) Mass Spectrometry and NMR Spectroscopy in Pesticide Chemistry, Plenum Press, New York, 1974, pp. 279-304. 

Adhesion of water at interfaces generally creates negative hydrostatic pressures in the rest of the fluid (Eq. 2.25 describes this P near the air-water interface, where the gravitational term can be ignored). Such negative hydrostatic pressures arising from interfacial interactions have sometimes been treated in plant physiology as positive matric pressures, a convention that we mentioned earlier (Section 2.2G). 

Verdaguer A, Sacha GM, Bluhm M, Salmeron M. Molecular structure of water at interfaces wetting at the nanometer scale. Chem. Rev. 2006 106 1478-1510. 

The constitution of ordered layers of water at interfaces with carbonaceous adsorbents in aqueous suspensions is governed by three major factors, namely, hydrophilic properties of the surface, porosity of the material, and the feasibility of polarization of the surface at the expense of the formation of regions carrying electric charges of opposite signs. In the general case, the thickness of an adsorbed water layer on the surface is detennined by the action radius of surface forces in whose field the orientation of electric dipoles of water molecules occurs and the formation of its surface clusters takes place. 

Most often the parameter r is not known a priori on the basis of molecular size. Information about molecular orientation is also required for the adsorbate. In the case of aqueous solutions, water molecules may act in clusters because of hydrogen bonding, so that the effective size of water at interfaces may be larger than that estimated on the basis of one water molecule. 

All cellular processes take place in aqueous solution, and it is essential to understand the properties of water in order to understand biological processes. This statement comes from one of the most recent textbooks on molecular cell biology. Sadly, but common to such texts, what follows is but a brief description of the ordinary liquid. Its physical properties and peculiarities are described, but the reader is given no information about the nature and role of water at interfaces such as in the environment of the cell. In short, from such descriptions one must infer that water in cells is just the same as water in a beaker or a cup of tea—that water is water. 

K. Heinzinger, in Structure of Electrified Interfaces, Frontiers of Electrochemistry, edited by J. Lipkowski and P. N. Ross (VCH, New York, 1993), Chap. 7. Molecular Dynamics of Water at Interfaces, p. 239. 

What are some of the most important findings from these XAFS studies of metal ion sorption processes One is the discovery that metal ion complexes at mineral/water interfaces are often different from those in bulk aqueous solutions. These differences include higher degrees of hydrolysis and different first-shell coordination environments (e.g., ( ) surface complexes Bargar et al. 1997a), and a higher proportion of multinuclear complexes (e.g., ( ) and ( ) surface complexes on alumina Chisholm-Brause et al. 1990a Fitts et al. 2000) for surface complexes vs. solution complexes. These differences are likely related to differences in the properties of water at interfaces vs. in bulk solutions (see earlier... 

A key requirement for in-situ spectroscopic methods in these systems is surface specificity. At Uquid/Uquid junctions, separating interfacial signals from the overwhelmingly large bulk responses in linear spectroscopy is not a trivial issue. On the other hand, non-Unear spectroscopy is a powerful tool for investigating the properties of adsorbed species, but the success of this approach is closely linked to the choice of appropriate probe molecules (besides the remarkably sensitivity of sum frequency generation on vibrational modes of water at interfaces). This chapter presents an overview of linear and non-linear optical methods recently employed in the study of electrified liquid/liquid interfaces. Most of the discussion will be concentrated on the junctions between two bulk liquids under potentio-static control, although many of these approaches are commonly employed to study liquid/air, phospholipid bilayers, and molecular soft interfaces. 

Trasatti S (1987) Interfacial behaviour of non-aqueous solvents. Electrochim Acta 32 843-850 Trasatti S (1995) Surface science and electrochemistry concepts and problems. Surf Sci 335 1-9 Verdaguer A, Sacha GM, Bluhm H, Salmeron M (2006) Molecular structure of water at interfaces wetting at the nanometer scale. Chem Rev 106 1478-1510 Vogler EA (1999) Water and the acute biological response to surfaces. J Biomater Sci Polymer Edn 10 1015-1045... 

CoUins KD, Washabaugh MW (1985) The Hofmeister effect and the behaviour of water at interfaces. Quart Rev Biophys 18 323-401... 

The water molecules inside pores can form clusters, in which the average number of hydrogen bonds per molecule varies between 0.5 (for dimers adsorbed on nonpolar functionalities due to dispersion interaction) and approximately 3 (tiny droplets in pores). Mobility of water molecules, particularly their rotational characteristics in liquid water at interfaces, is influenced by the number of hydrogen bonds. The proton exchange between these clusters can be represented by the following scheme ... 

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