Amphiphilic character

The microgels could be conveniently isolated by precipitation as white powders, readily redispersable in many different organic solvents such as dialkylamides, nitriles, dichloromethane, acetone and THF. Further to this, the DMAA-based microgels exhibited a rather amphiphilic character and were also soluble in water and in alcohols such as methanol or ethanol in contrast, their counterparts based on MMA turned out to be more lipophilic and therefore insoluble in water and alcohols but soluble in organic solvents of low polarity such as toluene. 

One question addressed in the literature is the relationship between the angle of orientation of the adsorbed species within the monolayer and their amphiphilic character. The case of surfactants like fatty acids or phospholipids is deferred until Section VI, since the technique of choice is SFG in order to perform a surface vibrational study. Phenol deri-... 

In keeping with the anisotropic electrostatic potential model for the halogen atoms, halogens show an amphiphilic character and can work both as the electrophilic sites and the nucleophilic sites when involved in short contacts (Fig. 3). 

Liposomes are formed due to the amphiphilic character of lipids which assemble into bilayers by the force of hydrophobic interaction. Similar assemblies of lipids form microspheres when neutral lipids, such as triglycerides, are dispersed with phospholipids. Liposomes are conventionally classified into three groups by their morphology, i.e., multilamellar vesicle (MLV), small unilamellar vesicle (SUV), and large unilamellar vesicle (LUV). This classification of liposomes is useful when liposomes are used as models for biomembranes. However, when liposomes are used as capsules for drugs, size and homogeneity of the liposomes are more important than the number of lamellars in a liposome. Therefore, "sized" liposomes are preferred. These are prepared by extrusion through a polycarbonate... 

There are two approaches to synthesizing hydrophilic carotenoids (1) appending a hydrophilic group to the carotenoid scaffold (Foss et al. 2006a) or (2) joining a carotenoid to a hydrophilic compound, Scheme 3.3 (Foss et al. 2003). Whereas the Scheme 3.3 intuitively explains the difference, these techniques cannot be clearly separated in praxis the distinction may appear more emotional than conceptual. Both methods are habitually hampered by low yields, find their limits in the availability of functionalized carotenoids, and cause problems in the work-up procedure due to the amphiphilic character of the products. 

A careful characterization of copolymers is quite time consuming and a combination of methods as discussed in Section 6.1 might be considered. In practice the situation is often complicated by an amphiphilic character of the copolymers, which leads additionally to micelle formation. 

Ligand (136), an analog of PPh3 with amphiphilic character, was used for making [Rh(CO) (136)(acac)]. The rhodium-based hydroformylation of 1-hexene using catalysts formed in situ... 

The number and position of the sulfonic acid substituents in zinc(II) phthalocyanine have an appreciable effect on bioactivity. Partial sulfonation gives the greatest activity, and the S2a derivatives (two sulfonic acid substituents on adjacent benzene rings) appear to be the most active.254,255 While this can be readily understood in general terms of developing amphiphilic character (Section 9.22.3), the detailed mechanism responsible for this result is not yet clear. The aggregation of zinc(II) sulphonic acid derivatives in solution and in tissue has been studied in relation to PDT.256... 

These AChE forms differ in solubility and mode of membrane attachment rather than in catalytic activity. One class of molecular forms exists as homomeric assemblies of catalytic subunits that appear as monomers, dimers or tetramers (Fig. 11-7). These forms also differ in hydrophobicity, and their amphiphilic character arises from either exposure of an amphipathic helix or post-translational addition of a glycophospholipid on the carboxyl-terminal amino acid. The glycophospholipid allows the enzyme to be tethered on the external surface of the cell membrane. 

Multihydroxyl containing monomeric or oligomeric p-cyclodextrins (PCD) such as those attained by grafting with glycidyl ethers of protected polyols (glycerol and pentitols) appeared rather promising components for their amphiphilic character, connected to the presence of an hydrophobic pocket and an external hydrophilic shell with an amplified number of hydroxyl groups. 

Drug molecules with amphiphilic character may form lyotropic mesophases, and amphiphilic excipients in drug formulations also form lyotropic liquid crystals. Especially surfactants, which are commonly used as emulsifiers in dermal formulations, associate to micelles after dissolution in a solvent. With increasing concentration of these micelles the probability of interaction between these micelles increases and thus the formation of liquid crystals. 

By covalent linkage of different types of molecules it is possible to obtain materials with novel properties that are different from those of the parent compounds. Examples of such materials are block-copolymers, soaps, or lipids which can self-assemble into periodic geometries with long-range order. Due to their amphiphilic character, these molecules tend to micellize and to phase-separate on the nanometer scale. By this self-assembly process the fabrication of new na-noscopic devices is possible, such as the micellization of diblock-co-polymers for the organization of nanometer-sized particles of metals or semiconductors [72 - 74]. The micelle formation is a dynamic process, which depends on a number of factors like solvent, temperature, and concentration. Synthesis of micelles which are independent of all of these factors via appropriately functionalized dendrimers which form unimolecular micelles is a straightforward strategy. In... 

The amide type local anesthetic lidocaine is broken down primarily in the liver by oxidative N-dealkylation. This step can occur only to a restricted extent in prilocaine and articaine because both carry a substituent on the C-atom adjacent to the nitrogen group. Articaine possesses a carboxymethyl group on its thiophen ring. At this position, ester cleavage can occur, resulting in the formation of a polar -COO group, loss of the amphiphilic character, and conversion to an inactive metabolite. 

A benzo[18]crown-6 adduct (72) of Cgg (not shown) has been synthesized by the addition of the corresponding o-quinodimethane 71 in toluene [58]. The solubility of 72 in pro tic solvents such as MeOH strongly increases after the complexation of ions, as shown by extraction experiments. The combination of the crown ether and the fullerene moiety in 72 provides a highly amphiphilic character. This behavior allowed the preparation of Langmuir-Blodgett films of monolayers on mica of 72 and its complex. 

The presence of a fluoroalkyl chain renders the molecule more hydrophobic and enhances its amphiphilic character by lowering the superficial pressure and the critical micellar concentration (CMC) (Figure 6.49). On the other hand, these chains do not cause any specific toxicity, and the hemostatic activity is often lowered. 

Figure 6.49 Effect of a fluoroalkyl chain on the amphiphilic character.

Figure 9.20 The amphiphilic character of vesicle-forming surfactant molecules the combination of oleic acid and oleate forms vesicles in the slightly alkaline pH range.

Figure 14. A general view of the designed transporter, which is composed of three units. The "core" unit lying near the bilayer mid-p a ie with "wall" units radiating from it. The core unit provides a rigid framework to direct the wall units to the face of the bilayer. The wall units are stiff to provide structural control, and incorporate both the polar and nonpolar functionality (Y, Z) required for a channel. The structure is completed with hydrophilic "head" groups (X) to provide overall amphiphilic character and to assist in the transmembrane orientation of the molecule.

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