Hydrophilic interface

T. Ohsaka, F. Matsumoto, and K. Tokuda, An electrochemical approach to dismutation of superoxide ion using a biological model system with a hydrophobic/hydrophilic interface, in Frontiers of Reactive Oxygen Species in Biological and Medicine (K. Asaka and T. Yoshikawa, eds), pp. 91—93. Elsevier Science B.V. Oxford (1994). 

Figure 13. A few microstructural parameters for Nafion and sulfonated poly(arylene ether ketone)s,i as a function of the solvent (water and/or methanol) volume fraction Xy. (a) the internal hydrophobic/hydrophilic interface, and (b) the average hydrophobic/hydrophilic separation and the diameter of the solvated hydrophilic channels (pores).

Fig. 6. Anisotropic repartitioning of the hydrophobic and hydrophilic interfaces observed m the crystal packing arrangement of tricolorin A (106)...

One aspect of the research will examine equilibrium aspects of solvation at hydro-phobic and hydrophilic interfaces. In these experiments, solvent dependent shifts in chromophore absorption spectra will be used to infer interfacial polarity. Preliminary results from these studies are presented. The polarity of solid-liquid interfaces arises from a complicated balance of anisotropic, intermolecular forces. It is hoped that results from these studies can aid in developing a general, predictive understanding of dielectric properties in inhomogeneous environments. 

Surface-mediated Solvation at Hydrophobic and Hydrophilic Interfaces (from Walker, 2001)... 

The interactions obviously differed between the lipid bilayers and the natural membranes. Furthermore, cholesterol slightly hinders the drug partitioning into the liquid-crystalline bilayers, in agreement with several previous reports, and the drug molecules interact electrostatically with membrane proteins at the hydrophilic interface adjacent to the polar headgroups of the phospholipid molecules (7). 

Krisdhasima, V., Vinaraphong, R, and McGuire, J. 1993. Adsorption kinetics and elutability of a-lactalbumin, p-casein, p-lactoglobulin and bovine serum albumin at hydrophobic and hydrophilic interfaces. J. Colloid Interface Sci. 161 325-334. 

As discussed in an earlier section, the chemistry exists to convert hydrophobic polyphosphazenes to materials with hydrophilic surfaces. Hydrogels of MEEP (3.79) have been radiation grafted to the surfaces of hydrophobic polymers to generate highly hydrophilic interfaces, and these systems have the advantage that the interior of the polymer retains its hydrophobicity and other properties, and only the surface layers are changed.187,188... 

Here v is the hydrophobic volume of the amphiphile, a is the interfacial energy and / is the chain length. The parameters describing the hydrophobic-hydrophilic interface are the mean curvature Hand the Gaussian curvature H(Figure 7.27). 

The presence of a hydrophobic-hydrophilic interface can dramatically change the reaction conditions. The hydrophobic core will selectively absorb hydrophobic species from the solution (Fig. 12), and this will result in a redistribution of monomer concentrations between the core and bulk solution. Because the probability of attachment for each comonomer is determined by its concentration in a relatively small reaction volume near an active chain end, the active center inside the hydrophobic core will mainly attach more hydrophobic species on the other hand, when the active center is located on the globule surface, it will mainly attach polar (soluble) monomers. In this way, the two-layer globule will grow, retaining its core-shell structure with a predominantly hydrophobic core and a hydrophilic outer envelope (see Fig. 12). 

Three, four, and five coordinated water molecules are a feature of the hydrates of the small biological molecules described in Part IV, Chap. 22. At present, there seems to be little support for the view that the structure of water at a hydropho-bic/hydrophilic interface is significantly different from that at the surface of pure water. 

Figure 33.7 depicts the influence of plasma pretreatment of CRS surface as well as the hydrophilicity of the plasma polymers on corrosion test results. The left half of the bar graph represents hydrophilic interface and some of top surface are also hydrophilic. The right half of the bar graph represents the water-insensitive interface and nonhydrophilic top surfaces except the plasma polymer of CH4, which was intentionally kept in air for 10 min before application of E-coat. The figure indicates two important factors, i.e., the removal of oxides from CRS/plasma polymer interface, and nonhydrophilic top surface of plasma coatings, for corrosion protection of CRS by plasma interface engineering, which involves application of cathodic E-coat. While the air exposure of plasma polymer of CH4 severely deteriorated the corrosion protection of E-coated sample, the same exposure of TMS surface showed no effect. This difference seems to reflect the reactivity of double bonds described in Chapter 7. 

Stratum corneum, the nonliving layer of skin, is refractory as a substrate for chemical reactions, hut it has a strong physical affinity for water. The chemical stability of stratum corneum is evident in its mechanical barriers which include insoluble cell membranes, matrix-embedded fibers, specialized junctions between cells, and intercellular cement. The hygroscopic properties of stratum corneum appear to reside in an 80 A-thick mixture of surface-active proteins and lipids that forms concentric hydrophilic interfaces about each fiber. This combination of structural features and surface-active properties can explain how stratum corneum retains body fluids and prevents disruption of living cells by environmental water or chemicals. 

If Swanbeck s 80-A layer is assumed to represent most of the hygroscopic substance, its water-binding capacity may be attributed to concentric hydrophilic interfaces (Figures 14B and 15). A myelin-like packing with the substitution of bimodal ER protein for the phospholipids of... 

The values obtained for /) ocai low and demonstrate the influence of the hydrophilic groups when one reaches a monolayer coverage of water molecules. Moreover, they are close to the values of the diffusion coefficient of water molecules at the immediate hydrophilic interface as determined in a recent MD simulation by Lee and Rossky ]33]. 

The area per surfactant molecule at the hydrophobic-hydrophilic interface -the head-group area - is prescribed by the temperature, water content, steric effects and ionic concentration for ionic surfactants. Assume for now that the area per each surfactant "block" making up the assembly is set a priori. This assumption implies that the surface to volume ratio of the mixture (assumed to be homogeneous) is set by the concentration of the surfactant. So the interfacial topology is predetermined by this global constraint, the surface to volume ratio. 

In Langmuir-Blodgett deposition (Fig. 10.24e), a film of molecules (with amphiphilic properties) is forced in a densely packed layer at a liquid-air interface or at a liquid-liquid (lipophilic/hydrophilic) interface. The substrate (submerged into the liquid beforehand) is pulled from the liquid to air to adsorb a monolayer. With this technique, the monolayer is forced into an organization by narrowing the organization area with movable sidewalls. The technique has been particular successful on molecules with liquid crystal properties [133, 87],... 

Many dye chromphores or reactive groups of electron donors and electron acceptors are hydrophilic and are therefore located at the hydrophilic interfaces of the mixed monolayers. According to the normal structure they are at the same interface or separated by at least two hydrocarbon chains yielding a distance of the order of 50 8 between the interfaces. This is an appropriate spacing between an excited energy donor layer... 

Figure 1. Amphiphilic molecules and schematic representation of aracltidic acid and N.N -dioctadecyloxacarhocyanine. Layer system assembled according to the usual technique with monolayer contacts at the hydrophilic interfaces and hydro-phobic interfaces (left) and with the unusual contact of one hydrophilic interface with a hydrophobic interface (right). Key O. hydrophilic groups and , hydrocarbon chain.

Weakly adsorbing surfaces can be prepared that either preferentially adsorb (hydrophilic interface) or repel (hydrophobic) water. Hydroxylated silica surfaces and... 

A characteristic feature of most but not all lipases is their activation by hydrophobic-hydrophilic interfaces, whereas the activity of esterases does not depend on the presence of a lipid-water interface. However, this classification of lipid-hydrolyzing enzymes is not generally applicable. Meanwhile, lipases have been found that hydrolyse long-chain lipids but do not show interfacial activation. Thus, lipases and esterases can be better defined as enzymes hydrolizing long-chain and short-chain lipids, respectively (3)... 

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