Interfaces, molecular structure

Sheals, J. et al.. Coadsorption of Cu(II) and glyphosate at the water-goethite (a-FeOOH) interface Molecular structures from FUR and EXAFS measurements, J. Colloid Inteif. Sci., 262, 38, 2003. 

An excellent review with compilation of spectroscopic methods with theoretical insights were previously done for the smectite-water system, where they concentrated their study on the structure of the water in the clay-water system (151). Due to the recent development of computational simulations, the same topic of interlayer surface structure was revisited, and this time the computer simulation part was embedded to support the conceptual understanding of the molecular aspect of clay-water interface molecular structure (1). 

The molecular structure and dynamics of the ice/water interface are of interest, for example, in understanding phenomena like frost heaving, freezing (and the inhibition of freezing) in biological systems, and the growth mechanisms of ice crystals. In a series of simulations, Haymet and coworkers (see Refs. 193-196) studied the density variation, the orientational order and the layer-dependence of the mobilitity of water molecules. The ice/water basal interface is found to be a relatively broad interface of about... 

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). 

Phosphorus-containing surfactants are amphiphilic molecules, exhibiting the same surface-active properties as other surfactants. That means that they reduce the surface tension of water and aqueous solutions, are adsorbed at interfaces, form foam, and are able to build micelles in the bulk phase. On account of the many possibilities for alteration of molecular structure, the surface-active properties of phosphorus-containing surfactants cover a wide field of effects. Of main interest are those properties which can only be realized with difficulty or in some cases not at all by other surfactants. Often even quantitative differences are highly useful. 

In the case of ionic adsorbates, the variation in WS50is normally unable to provide a clue to the molecular structure of the solvent since free charge contributions outweigh dipolar effects. In this case UHV experiments are able to give a much better resolved molecular picture of the situation. The interface is synthesized by adsorbing ions first and solvent molecules afterward. The variation of work function thus provides evidence for the effect of the two components separately and it is possible to see the different orientation of water molecules around an adsorbed ion.58,86,87 Examples are provided in Fig. 6. 

It has been pointed out321-324 that the two groups of solvents differ by some definite structural features. In particular, ED, 1,2-BD, and 1,3-BD possess vicinal OH groups that can form intramolecular hydrogen bonds. For these solvents, the ability of the organic molecule to interact with neighboring molecules is reduced. This results in the possibility of a different orientation at the interface because of different interactions of the OH groups with the Hg surface.323 The different molecular structure leads to different dipolar cooperative effects. As a result, the dependence of C on the bulk permittivity follows two different linear dependencies. 

Surfactants have a unique long-chain molecular structure composed of a hydrophilic head and hydrophobic tail. Based on the nature of the hydrophilic part surfactants are generally categorized as anionic, non-ionic, cationic, and zwitter-ionic. They all have a natural tendency to adsorb at surfaces and interfaces when added in low concentration in water. Surfactant absorption/desorption at the vapor-liquid interface alters the surface tension, which decreases continually with increasing concentrations until the critical micelle concentration (CMC), at which micelles (colloid-sized clusters or aggregates of monomers) start to form is reached (Manglik et al. 2001 Hetsroni et al. 2003c). 

It should be clear by now that inorganic solids (which consist of atoms bound together by both covalent and ionic forces) do not react by either changing the bonding within a molecular structure or by reacting one-on-one in a mobile phase such as a liquid, as do orgeuiic compounds. Solids can only react at the interfiace of another solid, or in the case of a liquid-solid reaction, react with the liquid molecule at the solid interface. 

Real Time Monitoring of Molecular Structure at Solid/Liquid Interfaces by Non-Linear Spectroscopy... 

Hydropolymer gel has been considered as a possible candidate for an artificial articular cartilage in artificial joints because it exhibits very low friction when it is in contact with a solid. The origin of such low friction is considered to be associated with the water absorbed in the gel [83-86], some of which is squeezed out from the gel under the load and serves as a lubricant layer between the gel and solid surface, resulting in hydrodynamic lubrication [87, 88]. Although the structural information about the interfacial water is important to understand the role of water for the low frictional properties of hydrogel in contact with a solid and the molecular structure of lubricants other than water at solid/solid interfaces have been investigated theoretically [89-91] and experimentally [92-98], no experimental investigations on water structure at gel/solid interfaces have been carried out due to the lack of an effective experimental technique. 

Nihonyanagi, S., Ye, S. and Uosaki, K. (2001) Sum frequency generation study on the molecular structures at the interfaces between quartz modified with amino-terminated self-assemhled monolayer and electrolyte solutions of various pH and ionic strength. Electrochim. Acta, 46, 3057—3061. 

Noguchi, H Okada, T. and Uosaki, K. (2008) Molecular structure at electrode/ electrolyte solution interfaces related to electrocatalysis. Faraday Discussion, 140, 125-137. 

However, analyses of the interface surrounded by some medium are not easy. When an interface of interest is exposed to a vacuum, electron-based or ion-based methods are available to determine the chemical composition and molecular structure of the top layers. The charged particles with limited penetration range result in a good vertical resolution. Buried interfaces are beyond the range of penetration. Photons, an alternative class of probe particles, have better ability for penetration. When the linear response to the incident electric field is analyzed, the vertical resolution is limited to the order of the wavelength, which is greater than the thickness of the top layers. 

Raghavan K, Poster K, Motakabbir K, Berkowitz ML. 1991. Structure and dynamics of water at the Pt(lll) interface molecular dynamics study. J Chem Phys 94 2110-2117. 

The present review intends to cover the work reported on nonlinear optics at liquid-liquid interface since the first report of S. G. Grubb et al. [18]. The theoretical aspects of nonlinear optics are first introduced in Section II. The experimental results covering the molecular structure of liquid interfaces are presented in Section III, followed by a section devoted to the dynamics and the reactivity at these interfaces. Section V focuses on new aspects where spherical interfaces with radii of curvature of the order of the wavelength of light are investigated. Section VI presents the field of SFG. 

One of the most attractive roles of liquid liquid interfaces that we found in solvent extraction kinetics of metal ions is a catalytic effect. Shaking or stirring of the solvent extraction system generates a wide interfacial area or a large specific interfacial area defined as the interfacial area divided by a bulk phase volume. Metal extractants have a molecular structure which has both hydrophilic and hydrophobic groups. Therefore, they have a property of interfacial adsorptivity much like surfactant molecules. Adsorption of extractant at the liquid liquid interface can dramatically facilitate the interfacial com-plexation which has been exploited from our research. 

General anesthetics are usually small solutes with relatively simple molecular structure. As overviewed before, Meyer and Overton have proposed that the potency of general anesthetics correlates with their solubility in organic solvents (the Meyer-Overton theory) almost a century ago. On the other hand, local anesthetics widely used are positively charged amphiphiles in solution and reversibly block the nerve conduction. We expect that the partition of both general and local anesthetics into lipid bilayer membranes plays a key role in controlling the anesthetic potency. Bilayer interfaces are crucial for the delivery of the anesthetics. 

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