Interfaces hydrophilic/hydrophobic

A novel approach for ion sensing is based on the use of potential-sensitive or polarity-sensitive dyes (PSDs) and was presented first106 in 1987. PSDs are charge dyes and typically located at the interface between a lipophilic sensor phase and a hydrophilic sample phase. The transport of an ion into the lipophilic sensor layer causes the PSD to be displaced from the hydrophilic/hydrophobic interface into the interior of the respective phase (or vice versa), thereby undergoing a significant change in its fluorescence properties107 110. 

These micellar cubic mesophases require large surface curvature and low charge density. Their formation is thus favored by the use of surfactant molecules with large polar head group, and acidic conditions under which the charge density at the silicate/surfactant is always limited. The fact that this phase can be prepared with CTAB when PTES is present, suggests the existence of specific interactions between the phenyl groups and the polar head of the surfactant molecules. It was indeed reported that benzene molecules are preferably located at the hydrophilic-hydrophobic interface [29]. 

The interfacial adsorption theory proposes that the orientation of odorant molecules is dependenl upon their behavior at the hydrophilic-hydrophobic interface, taking into account interaction with the mucus and adjacent olfactory membrane. 

In the field of biology, the effects of hydration on equilibrium protein structure and dynamics are fundamental to the relationship between structure and biological function [21-27]. In particular, the assessment of perturbation of liquid water structure and dynamics by hydrophilic and hydrophobic molecular surfaces is fundamental to the quantitative understanding of the stability and enzymatic activity of globular proteins and functions of membranes. Examples of structures that impose spatial restriction on water molecules include polymer gels, micelles, vesicles, and microemulsions. In the last three cases since the hydrophobic effect is the primary cause for the self-organization of these structures, obviously the configuration of water molecules near the hydrophilic-hydrophobic interfaces is of considerable relevance. 

Figme 4.5 Local view of the hydrophilic-hydrophobic interfaces (parallel surfaces) and surfactant pacidng for a bilayer interface. If bodt monolayers are identically constituted, the mid-surface of the bilayer (at the free chain-ends) is a minimal surface. (For an interface consisting of a reversed bilayer the surfactant molecules are inverted so that the head groups lie closest to the mid-surface, and the volume between the minimal surface and the two parallel surfaces contains the polar matter, i.e. water and surfactant head-groups.)... 

Cellulose and hemicellulose containing a large amount of hydroxyl groups can be considered as hydrophilic substances,1 whereas lignins, constituted of phenyl propane subunits are rather hydrophobic and these polymers are closely associated within plant cell walls, forming hydrophilic/hydrophobic interfaces. 

Chain models capture the basic elements of the amphiphilic behaviour by retaining details of the molecular architecture. Ben-Shaul etal [ ] and others [61] explored the organization of the hydrophobic portion in lipid micelles and bilayers by retaining the conformational statistics of the hydrocarbon tail within the RIS (rotational isomeric state) model [4, 5] while representing the hydrophilic/hydrophobic interface merely by an... 

R. G. Ashcroft, H. G. L. Coster, and J. R. Smith, The Molecular Organization of Bimolecular Lipid Membranes. The Dielectric Structure of the Hydrophilic/Hydrophobic Interface, Biochim. Biophys. Acta 643, 191-204 (1981). 

FI GU RE 1.26 FTIR spectra over (a, b) different wavenumber ranges for nanosilica A-300 at different amounts of adsorbed water (excess water from 1.2 g/g to 30 mg/g) desorbed in air for approximately 40 min. (Adapted from A(iv. Colloid Interface Sci., 118, Gun ko, V.M., Turov, V.V., Bogatyrev, V.M. et al.. Unusual properties of water at hydrophilic/hydrophobic interfaces, 125-172,2005d. Copyright 2005, with permission from Elsevier.)... 

Water bound at the hydrophilic/hydrophobic interfaces can be assigned to several structural types as WAWs and SAWs, which can be also weakly or strongly bound to the solid surface or macromolecules. These types of water can be analyzed in the terms of HDW andLDW or CS and ES waters (Gun ko et al. 2005d). The molecular mobility of weakly associated interfacial water (unusual water because atypical value 5e= 1.1-1.7 ppm) depends weaker on temperature, and it is higher than that of SAW because of smaller number of the hydrogen bonds per molecule. Additionally, this water... 

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