Microheterogeneous environment

Microheterogeneous environments that control photosensitized ET processes by means of electrostatic interactions include micelles [49-52], polyelectrolytes [53, 54], colloids [55-57], and clays [58, 59], Hydrophilic-hydrophobic organized microenvironments include micelles [49, 50], water-in-oil and oil-in-water micro-... 

Other closely related microheterogeneous environments such as micelles [70] or tailored electron relays capable of micellization upon reduction [71], operate by related hydrophilic-hydrophobic interactions in controlling photosensitized ET processes. Similarly, separation of photoproducts at the molecular level, by means of hydrophobic interactions, has been accomplished by utilizing cyclodextrin receptors [66, 72]. This host component selectively associates one of the photoproducts into the hydrophobic receptor cavity and consequently back ET is retarded. 

In contrast to the periphery of the cyclodextrins, the internal cavities, with diameters of 5 to 8 A (Ihble 18.1), have hydrophobic character because they are lined by the methylene C-H groups and by the ether-like 0(4) and 0(5) oxygen atoms. The distribution of hydrophilic and hydrophobic surfaces, together with the annular shapes of the cyclodextrins, gives rise to the microheterogeneous environment [555] which is the reason for some of their most interesting properties (Box 18.1). 

Fig. 7. A schematic view of Nafion membrane showing the microheterogeneous environment. A hydrophobic fluorocarbon phase B hydrophilic sulfonate ionic clusters C interfacial region formed between A and B and Ru adsorbed ruthenium complex water oxidation catalyst...

The Ru-red or Ru-brown complex adsorbed in the Nafion membrane is probably present in a microheterogeneous environment imposed by hydro-phobic cluster made of fluorocarbon moiety and by hydrophilic cluster made of sulfonate ions, and the Ru-red or Ru-brown is electrostatically held by the sulfonate ions. In a polymer membrane, the metal complex molecules would be isolated and the microheterogeneous environment would alter the complex-solvent interaction. Such effects are well characterized for macromolecular metal complexes . Since Ru-red and Ru-brown water oxidation catalysts are strong oxidants in their higher oxidation states, they would attack organic ligands of the... 

Other complex molecules in a homogeneous solution and the decomposition products would be solvated and stabilL by water molecules. This kind of degradative oxidation is probably prevented by the microheterogeneous environment imposed by the polymer membrane on the isolated metal complex entities. This work not only demonstrates realization of an efficient four-electron water oxidation system utilizing a polymer membrane, but also shows remarkable stabilization of the water oxidation catalyst against decomposition in a membrane. 

The synthesis of particle takes place in a microheterogeneous environment in the presence of oil and surfactant. The dispersed nanodrop formed acts as a stable phase in a microreactor and then dispersed in a second phase known as continuous phase which is used for the preparation of nanomaterials with phase selection. 

To determine the role of stationary phase structure in the retention process, it is of primary importance to understand its structure in various solvent environments. Studies of the interphase region using deuterium NMR have shown that it is the mobile phase composition that determines the structure of the stationary phase (d). Results have shown that water does not associate strongly wdth the alkyl chains. However, acetonitrile can associate strongly, even at low mole fractions because of the microheterogeneous environments that exist for the binary mixture. Previous in situ studies of the alkyl stationary phases using surface enhanced Raman spectroscopy have also concluded that little conformational change occurs with the addition of a polar solvent to the interface (7). 

Microheterogeneous environments, such as those found in reverse micelles (RMs) and microemulsions, have tremendous promise because of the nonstandard environments they present. Often, chemistries that occur in these solutions do not occur in homogeneous liquid solutions [1-4]. Essentially, RMs are spatially ordered macromolecular assemblies of surfactants formed in nonpolar solvents, in which the polar head groups of the surfactants point inward toward a polar core and the hydrocarbon chains point outward toward the nonpolar medium [5, 6] (see schematic representation in Fig. 14.1). 

Microemulsions are thermodynamically stable, isotropic transparent mixtnres of two immiscible liqnids (polar and nonpolar) and an amphiphilic component (nsuaUy surfactants and cosnrfactants). The microheterogeneous environments present in reverse micelles (RMs) and microemnlsions hold potential promise for apphcations in different fields owing to the nonstandard environments they produce. Often, these systems exhibit entirely different chemistry than that observed in homogeneous liquid solutions [17,18]. Microemnlsions are capable of solubilizing both polar and nonpolar substances and have wide apphcations [19, 20] in various fields such as chemical reactions [21], preparation of nanomaterials [22], and drug delivery [23]. 

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