Head groups functional derivatives

The ligand group can be introduced either on the meso or on the /5-pyrrole position of the porphyrin ring, but the synthesis of the meso-functionalized derivatives is easier and has been more widely exploited. Balch (50-53) reported that the insertion of trivalent ions such as Fe(III) (32) and Mn(III) (33) into octaethyl porphyrins functionalized at one meso position with a hydroxy group (oxophlorins) leads to the formation of a dimeric head-to-tail complex in solution (Fig. 11a) (50,51). An X-ray crystal structure was obtained for the analogous In(III) complex (34), and this confirmed the head-to-tail geometry that the authors inferred for the other dimers in solution (53) (Fig. lib). The dimers are stable in chloroform but open on addition of protic acids or pyridine (52). The Fe(III) octaethyloxophlorin dimer (52) is easily oxidized by silver salts. The one-electron oxidation is more favorable than for the corresponding monomer or p-oxo dimer, presumably because of the close interaction of the 7r-systems in the self-assembled dimer. 

According to this method, Fyles analyzed the transport rate of alkali metal cations for a series of 21 synthetic transporters (Figure 14). The whole molecules were designed to elucidate the structure-function relationship. They are composed of three parts core, wall, and head units. The core units were derived from tartaric acids so that the wall units may be fixed to provide structural control by incorporating both the polar and nonpolar functionality (Y and Z in Figure 14). The head groups (X) are attached to provide an overall amphiphilic nature. 

Fig. 4.7 Location of amlo-dipine within the membrane bilayer derived from its cen-ter-of-mass location and crystal structure. Its location near the hydrocarbon corewater interface can facilitate both a hydrophobic interaction with the phospholipid acyl chain and an ionic interaction between the protonat-ed amino function of the drug and the charged anionic oxygen of the phosphate head group. Nimodipine structure and location are consistent with only hydrophobic interactions with the phospholipid acyl chains. No electrostatic interaction with the head groups of PI was noted. (Reprinted from Fig. 2 of ref. 95 with permission from the American Chemical Society.)...

It is evident that for bimolecular reactions in non-functional micelles in water the key factor in rate enhancement is the increased concentration of the two reactants in the micellar pseudophase (Table 3 and 4) and the same effect should be at work for reactions in functional micelles. The problem is simply that of estimating the concentration of functional groups in the micellar pseudophase. For the simplest case, that of a functional micelle, not involving deprotonation equilibria, with a nucleophilic head group denoted as N, there will be one reactive group per micellar head group, and if the substrate is fully micellar bound we can apply Eqn. 12, derived for reaction in non-functional surfactants, where ... 

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