Ester inverse micelles

Photolyses of 31-34 in homogeneous solution results in the formation of diphylethanes 39 (5-15%), phenols 38 (5-15%), ortho-hydroxyphenone 36 (40-60%), and para-hydroxyphenones 37 (20-25%). Small amounts of phenyl benzyl ether 35 (3-8%) were also detected. However, photolyses of all of the four esters on NaY zeolite and Nafion only produce ortho rearrangement products 36. Molecular models suggest that esters 31-34 can enter into NaY zeolite internal surface and the inverse micelle of Nafion. We believe that the preference for formation of ort/zo-hydroxyphenones 36 in the products is a consequence of the restriction on diffusional and rotational motion of the geminate radical pair. 

It should be emphasized that these structural changes within a one-phase region may change the kinetics of a chemical reaction in a pronounced manner. As an example may be mentioned the catalytic effect of Inverse micelles on ester hydrolysis. Fig. 5 is from the first publication — on this subject. It clearly shows the lack of catalytic effect by the premicellar aggregates and the sudden increase of hydrolysis rate in the concentration range where the Inverse micelles begin being formed. 

This discovery has led to a vast array of small container-type molecules, which have been extensively reviewed [131]. Quite remarkably, this was approximately the same time that ester terminated PAMAM dendrimers were noted to dissolve and incarcerate copper salts to produce blue chloroform solutions due to their unimolecular, inverse micelle properties. This observation was publicly reported in 1984-1985 [72], during the same year that Smalley and Kroto et al. described the first synthesis of buckminsterfullerene [132]. Of course, it is well-known that bucky baUs will host a variety of metals. Thus, it is apparent that the emergence of container molecules" has followed the systematic enhancement of the organic host structure dimensions as illustrated in Figure 16. 

The first examples and observed dendritic inverse micelle properties were noted in the initial paper on poly(amidoamine) dendrimers published in 1984-1985 [35,50,72-76]. At that time, it was observed that methylene chloride or chloroform solutions of the methyl/alkyl ester modified dendrimers readily extracted copper ion (Cu+ ) from water into the organic phase. Beautiful blue chloroform solutions were obtained that were completely transparent and did not scatter light. It was assumed that the copper ions had been chelated into the interior and were being compatibilized by the more hydrophobic sheathing of the dendrimer surface groups. Variations of this work were both patented [156] and ultimately published [157] wherein, PAMAM dendrimers werehydrophobically modified with alkyl epoxides and used to extract metal ions into toluene, styrene monomer, or a variety of other hydrophobic solvents. 

For example, fragrance molecules were incorporated into a star polymer with nonpolar PCL arms that were polymerized via ROP of CL onto an hb poly(ester amide) as the core molecule." These star polymers formed inverse unimolecular micelles and were able to transport polar dyes from an aqueous phase to the organic phase. A similar approach was presented by Haag and co-workers employing hbPEI as the core and PEG as the arms these carriers were investigated for encapsulation and transport of dyes and therapeutics or diagnostic agents. A controlled release was possible by introduction of an acid-labile junction." " " ... 

Tetrahedron, 1993, 49, 6605 (d) Selke, R., Ohff, M. and Riepe, A., Asymmetric hydrogenation - influence of the structure of carbohydrate derived catalysts on the relative enantioselectivity Qn/Me regarding acid and ester substrates and its inversion. Selectivity increase in water by amphiphiles. Tetrahedron, 1996, 52, 15079 (e) Selke, R., Holz, J., Riepe, A. and Bdmer, A., Impressive enhancement of theenantioselectivity for a hydroxy containing rhodium (I) bisphosphine catalyst in aqueous solution by micelle forming amphiphiles, Chem. Ear. 1998,4, 769. 

In a former investigation, an inversion of the helix sense with dopant concentration has been observed which is unusual. The phenomenon was explained again by a change of the cisitrans ratio of the surfactant (the chloride of the decyl ester of L-proline). NMR gave at least qualitative evidence for the existence of the two rotamers [28]. An inversion of the twist sense has been found with a-hydroxy carbon acids and some corresponding potassium salts [23]. For all of the investigated couples the respective opposite handedness was proven by a twist compensation seen in contact preparations. The result is unexpected because the molecular chirality of the acid and the salt are nearly identical. It was supposed that the presumably different locations with respect to the micelles due to the ionic character of the salt and/or a dimerization of the acid could be the reason for the observed behavior. 

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