Cationic head groups

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... 

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... 

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. 

As seen in Fig. 10, in aromatic hydrocarbons the Jt-electron-rich regions can interact with cations through so-called cation-7t interactions [40], In mixtures with ionic liquids, the aromatic molecules may be solvated in the nonpolar domains but they may have sufficient affinity for the cationic head-groups to be found among the polar domain as well. When looking at the structure of such mixtures, it is useful to study the local environments of the ions and of the aromatic compound. 

With cationic head groups, homology achieves simultaneously a progressive increase in bnlkiness and in lipophilic-ity. Figure 14.8 illustrates the influence of increasing buUciness aronnd the dopamine nitrogen in the antagonism of reserpine-indnced catalepsy in mice. 

A gemini surfactant is a dimeric molecule consisting of two hydrophobic tails and two head groups, linked together with a short spacer [14]. This is illustrated below for a molecule containing two cationic head groups (separated by two methylene groups) with two alkyl chains ... 

Thus the analogue N-propyl-apomorphine is a more powerful dopaminergic agonist than the apomorphine itself. The creation of bulkiness is obviously not limited to cationic head groups and lipophilic groups can be attached to any other part of the molecule (Fig. 12.18). ... 

If the surfactant has an anionic or cationic head group, then ionic interactions occur at the micellar surface. The improved approximate analytical solution of the Poisson-Boltzmann equation was used by Nagarajan for the calculations... 

A hydrophobic lipid anchor that aids in the formation of cationic liposomes that are critical components of the complex with DNA. A linker group that is located between the cationic head group of the molecule and the lipid tail. 

The cationic head group that is responsible for the complexation of the liposome with the negatively charged DNA. The cationic group is a singly or multiply charged primary, secondary, tertiary, or quaternary amine. The common counterions found with the cationic lipids are the bromide, chloride, or trifluoroacetate anion. 

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