Hydrophilic substructures

In summary, incorporation of [60]flillerene into artificial bilayer membranes, despite being successful in principle, nevertheless, disclosed a number of unexpected complications. The most dominant parameter, in this view, is the strong aggregation forces among the fullerene cores. The lack of appropriately structured domains within the vesicular hosts, which could assist in keeping the fullerene units apart, is believed to be the reason for the instaneous cluster formation. The incorporation of a number of suitably functionalized derivatives, which on their own bear hydrophobic and hydrophilic substructures, will be discussed further below. 

In conclusion, by varying the number and kind of the attached substructures for exohedrally functionalized fullerenes the solubility in water can be fine-tuned. From a pharmacological point of view, a well-balanced arrangement of both hydrophilic and lipophilic behaviour is required in order to achieve favourable biodistribution. Amphiphilic monoadducts containing long lipophilic alkyl chains like 8 are promising candidates for potential medical applications. 

Figure 4 A fundamental structure proposed for the hydrophilic part of GL4. The sequence of each substructure (oligo-mannan) is interchangeable.

Type C repeats are very common in proteins. They are quantal in length, but the repeats themselves do not contain residues that are conserved absolutely in any position. However, several positions within the repeats are strongly conserved in character. A classic example of a Type C repeat is that given by the heptad substructure in a-fibrous proteins. This has the form (a—b-c—d—e—f—g)n with the a and d positions generally occupied by apolar residues, and the e and g positions by charged or hydrophilic residues. The heptad is characteristic of an Q-helical conformation (Cohen and Parry, 1986, 1990 Lupas, 1996), but comparison of any two sequences with a heptad substructure generally reveals only about 15—20% identity. The motif also implies that several Q-helices will aggregate to form a multistranded left-handed coiled-coil rope to shield the apolar stripes on the surface of the Q-helices from the aqueous environment. 

The biotransformations are implemented as rules based on the presence and absence of substructures. The rules act on the original query molecule to produce a first generation of metabolites and the process is repeated on the generated metabolites to produce a second generation and so on. No further metabolites are generated from a Phase II metabolite because this is regarded as hydrophilic and excretable. The overall process can be terminated when a set number of metabolites have been produced. No indication of the relative importance of the metabolites appears to be given. 

A key feature of the solid-phase ELISA is that antigens or antibodies can be attached to smfaces easily by passive adsorption. This proeess is commonly called coating. Most proteins adsorb to plastic smfaces, probably as a result of hydrophobie interactions between nonpolar protein substructures and the plastie matrix. The interactions are independent of the net charge of the protein, and thus each protein has a different binding constant. The hydrophobieity of the plastic/protein interaction can be e qjloited to increase binding since most of proteins hydrophilic residues are at the outside and most of the hydrophobic residues orientated towards the inside (1). 

The term simple amphiphile describes the principle of molecular constitution of compounds which will be discussed in this section. The simplest molecular architecture of an amphiphile consists of a hydrophilic group connected to a lipophilic substructure as shown in Fig. 4. 

Organophilic membranes have the same structure as hydrophihc ones. The dense separating layer is formed by crosslinked silicones, mostly polydimethyl siloxane (PDMS) or polymethyl octyl siloxane (POMS). The methods to apply the dense layer on the porous substructure are similar to those used for hydrophilic membranes. 

The chemical structures of synthetic dyes show considerable variety. They generally contain more than one aromatic group, condensed aromatic substructures or heterocyclic rings (pyrazolone, thiazole, acridine, thiazine, oxazine) which are mainly hydrophobic, and, frequently, a polar basic or cationic group which is strongly hydrophilic. Due to these structural characteristics, they readily bind both to polar adsorptive and apolar reversed-phase (RP) chromatographic supports, making their successful separation difficult. As the synthetic dyes are not volatile... 

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