Cationic heads

SCHEME 18. Synthesis of glucosylated porphyrins bearing cationic head-groups.153... 

Fig. 5 Schematic representation of locations of a weakly acidic indicator, , adjacent to the cationic head groups, , and of a functional hydroxyl group in the water-rich region...

The effects of cationic head groups on the alkaline hydrolysis of the quinoxaline (192) to give (193) have been looked at using the surfactants (194 R = Me, Et, n-Pr, n-Bu X = Cl, OH).164 The reactivity increases with increasing head-group size and is related to the disruption of the hydration of the HO ion. An earlier paper from the same group describes the synthesis of (192) and some micellar effects on its basic hydrolysis.165 A novel site-selection functionalization reaction is facilitated by histidine side-chains in helical structures which can catalyse the acylation by mono-p-nitrophenyl... 

Obata Y, Saito S, Takeda N et al (2009) Plasmid DNA-encapsulating liposomes effect of a spacer between the cationic head group and hydrophobic moieties of the lipids on gene expression efficiency. Biochim Biophys Acta-Biomembranes 1788 1148-1158... 

In addition, it was known that the phenolic hydroxyls are not essential for a activity and that the cationic head should not be too bulky. 

Sherrington and coworkers161 have examined the chlorination of phenol by J-butyl hypochlorite in the presence of cross-linked polystyrenes substituted by pendant polymethylene chains terminated with anionic or cationic head groups, as well as some hydrophilic acrylic polymers, in four solvents water, methanol, 1,2-dichloroethane and xylene. The polymers exerted a significant influence on the chlorination, particularly in polar solvents. However, no changes in the regioselectivity of the chlorination, in comparison to homogeneous systems, was observed. 

These data are consistent with a mechanism whereby the formation of CuX 2 species facilitate the metalatlon reaction. This could be effected in two ways. First, CuX is formed, attracted to the cation head groups (but not "bound"), Figure 4b. This would then Increase the concentration of Cu(II) in the interphase enhancing the probability of an encounter with a TPPH2 molecule. An alternate pathway requires that CuXo be the dominant... 

Metallosurfactants, where the cationic head group is a polyaza macrocycle or cavitand containing a strongly coordinated metal ion and the hydrophobic tail is a pendant arm attached to a nitrogen atom of the... 

It is important to determine whether or not each substituent parameter is an independent variable. If a considerable correlation exists between two parameters in a set of compounds, it is often difficult to evaluate the quality of structure—activity correlations. The data in Table II are for the muscarine-like activity of acetylcholine analogs measured by the blood pressure descent of cats (55). The effect of cationic head structure has been analyzed using physicochemical parameters of the N substituents (II). 

The myoneural-blocking pharmacophore in d-tubocurarine (118) was speculated to include the two cationic heads (the quaternary ammonium group and the protonated tertiary amine) the cationic heads are separated by 10 atoms (nine carbons and one oxygen). 

Figure 4.27 Long-chain bolaamphiphiles with an electroneutral and a cationic head group form membranes around anionic polymers (here DMA) and colloids. Synkinesis of organic-inorganic composite materials in bulk aqueous media can thus be achieved. ...

Figure 6.14 The repulsive interaction between cationic head groups enforces large gaps between sulfur-bound monolayers on gold. Anions can pass such a membrane cations cannof. ...

All of the cationic surfactants are quaternary ammonium compounds (Table 8-3). As such, they are always ionized in water and exhibit surface-active propcrtie.s. The compounds, with a polar head group and nonpolar hydrocarbon chain, form micelles by concentrating at the interface of immiscible solvents. The surface activity of lhe.se compound.s. exempli-fled by lauryl iricihylammonium sulfate, results from twu. structural moieties (a) a cationic head group, which has a high affinity for water, and (b) a long hydrocarbon tail, which has an affinity for lipids and nonpolar. solvents. 

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