Self-organization, aqueous

Most studies of ORR catalysis by metalloporphyrins have been carried out using water-insoluble catalysts absorbed on a graphite electrode in contact with aqueous solution. In a limited number of cases, four other approaches have been used catalysts imbedded in an inert film (i.e., Nafion or lipid) on the electrode surface self-assembled monolayers of catalysts catalysts in aqueous or mixed organic/aqueous solutions in contact with an electrode and catalysis in mixed aqueous/organic medium using... 

The self-organization of polysilanols in the presence of other hydrogen bond acceptors has been studied by several groups.512-516 Several other publications have dealt with the stepwise synthesis of siloxane and siloxanol chains.450,517-522 Recent work on fully condensed siloxane rings and silsesquioxane cages involves the non-aqueous hydrolysis of chlorosilanes - as well as mechanistic and structural studies. 

What happens upon equilibration with liquid water instead of water vapor According to Equation (6.13), the capillary radius would go to infinity for PVP —> 1. Thus, in terms of external conditions, swelling would be thermodynamically unlimited, corresponding to the formation of an infinitely dilute aqueous solution of ionomer. However, the self-organized polymer is an effectively cross-linked elastic medium. Under liquid-equilibrated conditions, swelling is not controlled by external vapor... 

The organized structures give to the aqueous phases new macroscopic properties like iridescent colors, viscoelasticity, gel character, a yield stress, and, between crossed polarizers, beautifully colored patterns that make the order in the samples visible. The self-organization of the surfactant molecules is simply a result of the hydrophobic and electrostatic interaction between the individual molecules and the micellar structures. The size of the micellar structures, as in the case of small imUamellar vesicles, can be extremely monodisperse, even though one vesicle consists of hrmdreds of surfactant molecules. 

Reduced Surface Tension. Just as surfactants self-organize in the bulk solution as a result of their hydrophilic and hydrophobic segments, they also preferentially adsorb and organize at the solution—vapor interface. In the case of aqueous surfactant solutions, the hydrophobic tails protrude into the vapor and leave only (he hydrophilic head groups in contact with the solution. The favorable energetics of the arrangement can be seen by the reduction in Ihe interracial free energy per unit area, nr surface tension, it. 

Bisphenol-A is present as the disodium salt in the aqueous phase of the two-phase mixture. Phosgene enters the system and dissolves in the organic phase. It is believed that the reaction between phosgene and bisphenol-A occurs at the organic-aqueous interface to form the monochloroformate—Reaction 1—or bischloroformate—Reaction 2— ester of bisphenol-A. The chloroformate esters that form grow to oligomers by reaction with additional bisphenol-A or by self-condensation —Reactions 3 and 4, respectively. 

The design of artificial self-organizing systems is based on the ability of some molecules which contain simultaneously hydrophobic and hydrophilic groups to form molecular assemblies of definite structure in solution. Examples of the assemblies that can be used to suppress undesirable recombination processes are polyelectrolytes, micelles, microemulsions, planar lipid membranes covering an orifice in a film separating two aqueous solutions, unilamellar vesicles, multilamel-lar vesicles and colloids of various inorganic substances (see reviews [8-18] and references therein). 

The ability of the above mentioned substances to self-organize into bilayer membranes is caused by their amphiphility. During the formation of the vesicles the amphiphilic molecules orient themselves in such a way that their polar heads contact aqueous phases outside and inside the vesicle, while their nonpolar tails are directed towards the interior of the bilayer as shown in Fig. 2c. Vesicles can be classified in multilamellar, small unilamellar (d = 200-500 A) and large unilamellar (d = 1000-5000 A) ones. Since these are small unilamellar vesicles that are typically used for studying PET, in further discussion the term vesicle will always refer to the vesicles of this type, unless otherwise specified. 

Reverse micelles are self-organized aggregates of amphiphilic molecules that provide a hydrophilic nano-scale droplet in apolar solvents. This polar core accommodates some hydrophilic biomolecules stabilized by a surfactant shell layer. Furthermore, reverse micellar solutions can extract proteins from aqueous bulk solutions through a water-oil interface. Such a liquid-liquid extraction technique is easy to scale up without a loss in resolution capability, complex equipment design, economic limitations and the impossibility of a continuous mode of operation. Therefore, reverse micellar protein extraction has great potential in facilitating large-scale protein recovery processes from fermentation broths for effective protein production. 

R. Nagarajan, Solubilization of Hydrophobic Substances by Block Copolymer Micelles in Aqueous Solution, in Solvents and Self-Organization of Polymers (eds. S. E. Webber, P. Munk and Z. Tuzar), Kluwer Publishers, Amsterdam, 1988. 

Che et al. 215) extended the assembly into aqueous environments, describing the preparation of supramolecular polyelectrolytes by self-organization of cationic organoplatinmn (II) complexes in water through extended Pt- Pt and hydrophobic interactions (Fig. 13). Aligned films and discrete uniaxial microfibers with cofacial molecular orientations were readily produced with these phosphorescent viscoelastic mesophases. 

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