Micelles types

Polymer micelles are nanometer sized (usually several tens of nanometers) self-assembled particles having a hydrophobic core and hydrophilic outer shell composed of amphiphilic AB- or ABA-type block copolymers, and are utilized as drug delivery vehicles. The first polymer micelle-type drug delivery vehicle was made of PEG-b-poly(aspartic acid) (PEG-b-PAsp), immobilizing the hydro-phobic anticancer drugDXR [188-191]. After this achievement by Kataoka et al., a great amount of research on polymer micelles has been carried out, and there are several reviews available on the subject [192-194]. 

Figure 13.2 Unimolecular micelle type dendrimer (1) reported by Newkome and probes...

Meijer et al [6] reported on inverted unimolecular micelle type dendrimers (Figure 13.4) which have a hydrophilic interior and a hydrophobic shell, synthesized by modifying the end groups of hydrophilic polypropylene imine) dendrimer with alkyl chains. It was shown that these dendrimers could host... 

Figure 13.4 Inverted unimolecular micelle type dendrimer (3) reported by Meijer and the probe...

KP and v can, in contrast to kp, not be determined via the concentration gradient for binary and ternary mixed micelles, because for the calculation of the Nemstian distribution a constant CMC and an almost constant partial molar volume must be assumed. The calculation of aggregation constants of simple bile salt systems based on Eq. (4) yields similar results (Fig. 8b). Assuming the formation of several concurrent complexes, a brutto stability constant can be calculated. For each application of any tenside, suitable markers have to be found. The completeness of dissolution in the micellar phase is, among other parameters, dependent on the pH value and the ionic strength of the counterions. Therefore, the displacement method should be used, which is not dependent on the chemical solubilization properties of markers. For electrophoretic MACE studies, it is advantageous for the micellar constitution (structure of micelle, type of phase micellar or lamellar) to be known for the relevant range of concentrations (surfactant, lipids). 

In addition to the micelle-type assemblies described above, there has been significant interest in developing conditions for forming vesicle-type assemblies from amphiphilic polymers. Polymeric vesicles are formed by bolamphiphilic block... 

Figure 11.9 (Top) A typical structure of Tha)oimanavan s amphiphilic dendrimers. (Bottom) Schematic representation of micelle-type and inverse miceUe-type structural organization.

It is also interesting that structures of the reverse micelle type have been observed in vivo (de Kruijff et al., 1980) where they seem to absolve specific, even if not dramatically important, functions - see Figure 9.15. 

Synthesis of oil soluble micellar calcium thiophosphate was performed in a one-step process involving the reaction of calcium oxide, tetraphosphorus decasulfide and water in the presence of an alkylaryl sulfonic acid. This product could be defined as a calcium thiophosphate hard-core surrounded by a calcium alkylarylsulphonate shell in accordance with a reverse micelle type association in oil. Three micellar products with the same chemical nature core were prepared, each with different core/shell ratio of 0.44, 0.92 and 1.54. Better performances are expected with products of higher core/shell ratios. The antiwear performance of micellar calcium carbonates is directly linked to the size of the mineral CaC03 colloidal particles. At a concentration of 2 % micellar cores, no antiwear effect is observed whatever the micellar size. At an intermediate concentration of 4 % of micellar cores, the wear scar diameter is clearly dependent on the micellar size, slipping from 1.70 mm to 1.10 mm, then to 0.79 mm when the core diameter moves from 4.37 nm to 6.07 nm, then to 6.78 nm. Size dependence is increased at a concentration of 5 % in colloidal cores. This clearly confirms the size dependence of the micellar cores on their antiwear performance (Delfort et al.,... 

Frey and Van Koten et al. [40-42] reported on the noncovalent encapsulation of sulfonated pincer-platinum(II) complexes in readily available amphiphilic nanocapsules based on hyperbranched polyglycerol, possessing a reverse micelle-type architecture. The incorporated platinum(II) complexes showed catalytic activity in a double Michael addition, albeit with decreased activities compared to the free pincer complex. Due to the size of... 

In this context, the chiral hyperbranched polyglycerols (-)-PG [Mn = 3000, with bis(2,3-dihydroxypropyl)undecenylamine as the initiator] and (+)-PG [Mn = 5500, with trimethylolpropane (TMP) as the initiator] were used. Esterification of the hydroxyl groups of these hyperbranched polyglycerols with hydrophobic alkyl chains as palmitoyl chloride, yielded amphiphilic molecular nanocapsules with reverse micelle-type architecture, in which approximately 50% of the hydroxyl groups were functionalized with palmitoyl chains [96-98]. These materials exhibit low polydispersity (Mw/Mn < 2), and the amphiphilic molecular nanocapsules are soluble in nonpolar solvents and irreversibly encapsulate various polar, water-soluble dye molecules in their hydrophilic interior by liquid-liquid extraction [96,98]. 

Negatively charged amphiphilic block copolymers, (I), prepared by Seo [2] were effective as cationic drug carriers and provided the advantages of increased blood concentration and improved drug stability. Stable polymeric micelle-type drug compositions were prepared by Seo [3]. 

Cosolvents Particle surface (porous, smooth) Micelles (type, charge)... 

In a 50/50 PP/hydrogenated poly(styrene-co-butadiene) (hSBR) blend, crystal lamellae were extremely fragmented to form the fringed-micelle type crystallites, as schematically shown in Figure... 

Figure 8.15 Eringed micelle-type PP crystallites in a 50/50 blend of PP with hydrogenated poly(styrene-co-butadiene) [Otsuka et al., 1998].

In contrast, Perdue and Wolfe (1982) observed that DOM retarded the basic hydrolysis of the octyl ester of 2,4-D. They found that the base-catalyzed rate constant was reduced in proportion to the fraction of the hydrophobic ester that was associated with the DOM. Perdue (1983) has proposed a micelle-type model to rationalize these results and those presented for atrazine. Perdue compares the physical characteristics of DOM, which is negatively charged at environmental pHs, to those of anionic surfactants. Anionic surfactants have been demonstrated to increase hydrolysis rates for acid-catalyzed processes and decrease rates for base-catalyzed processes (Fendler and Fendler, 1975). Rate enhancements for acid-catalyzed hydrolysis reactions are attributed to stabilization of the positive charge that is developed in the transition state, whereas base-catalyzed hydrolysis reactions are impeded due to destabilization of the negatively charged transition state. Although this is an attractive model, it remains largely untested. 

Cubic lattice with about 10 molecules per unit cell.< " The detailed molecular arrangement is not known, but is generally assumed to be of the micelle type. Thus this phase should probably be labelled as D rather than Smectic D. At present only four compounds are known to exhibit this phase, 4 -n-hexadecyloxy- and 4 -n-octadecyloxy-3 -nitrobiphenyl-4-carboxylic add and two similar acids with CN replacing NO. Interestingly, D occurs between S, and S, or between S and the isotropic phase. The manner in which such a structural rearrangement takes place is yet to be resolved. Three-dimensional crystal, orthorhombic with interlayer herringbone arrangement of the molecules. ... 

Structure of hydrolyzed membranes is generally believed to be of a (2-6) reverse micelle type, 30-50 A in size, containing the aqueous ions, acid, and/ or salt groups embedded in a continuous fluorocarbon phase. 

At low degrees of crystallinity in the bulk state, a fringed micelle type of model (admitting the possibility of chain folding) may be appropriate, whereas at higher degrees of crystallinity, a paracrystalline type of model such as is depicted in Figure 1.7 may better reflect reality. 

MICELLE TYPE AND SIZE VARY WITH CONCENTRATION... 

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