Water-solubilising groups

Lignin is water-insoluble and it contains only a few hydrophilic functionalities (primarily the phenolic groups). In order to increase its solubility, aqueous pulping processes therefore seek either to introduce water solubilising groups, or to reduce the degree of polymerisation or both. 

The chemical answer to this is to identify the sites on the porph)rrin molecule where reactivity occurs and to bl(x k them. These sites are the mcso-carbons and the metal centre. Nature, of course, solved this problem eons ago by embedding the sensitive chlorophyll molecule in the protein-lipid matrix of the chloroplast membrane. Synthetically, this problem is solved by substituting water-solubilising groups in the wicso-positions so that a molecular chain covers that position and the metal centre like an umbrella. 

Surfactants in E/ectroc/eaners. Surfactants typically consist of a long-chain hydrocarbon molecule having a solubilising or water-loving group which can be anionic, cationic, or nonionic when solubilized. Thousands of surfactant products are marketed, usually under trade names (32). In commercially formulated electrocleaners, surfactants are usually anionic, and often mixtures of anionics and nonionics. 

The same group reported the simultaneous radiolabeling (with DOTA-anchored 4Cu) and fluorescence studies, coupled with biodistribution in vivo and in vitro (92). It is believed that appropriately functionalized SWNTs can efficiently reach tumor tissues in mice with no apparent toxicity (159). Furthermore, water-solubilised carbon nanotubes are nontoxic when taken up by cells even in high concentration (92). These studies have been complemented by the recent PET imaging of water-soluble 86Y labelled carbon nanotubes in vivo (mice) (160,161), to explore the potential usefulness of carbon nanocarriers as scaffolds for drug delivery. The tissue biodistribution and pharmacokinetics of model DOTA functionalized nanotubes have been explored in vivo (mouse model). MicroPET images indicated accumulation of activity mainly in the kidney, liver, spleen, and to a much less... 

Anionic Azo Dyes this group of azo dyes are characterised by the presence of one or more water-solubilising ionisable substituents, most often the readily available sulphonic acid group. Normally, the presence of such anionic group can increase the solubility of the dyes. 

Solubilization can also be illustrated by considering the phase diagrams of nonionic surfactants containing poly(ethylene oxide) (PEO) head groups. Such surfactants do not generally need a cosurfactant for microemulsion formation. Oil and water solubilisation by nonionic surfactants is represented in Figure 10.6. 

Positive photoresists, by contrast, are based on water-soluble novolak resins with naphthalene diazoquinone sulfonate (NDS) as the photosensi-tiser. On photolysis the NDS causes a rearrangement in the polymer to yield nitrogen gas plus an indene carboxylic acid. This latter functional group considerably increases the solubility of the polymer, hence solubilising those areas of the polymer that had been exposed to light. 

Many acrylic acid copolymers are water-soluble but unlike poly(vinyl alcohol) they are not degraded by alkali. In fact they need alkali for effective desizing as they are more soluble at alkaline pH than in neutral solutions. They are sensitive to acidic media, which should not be used. Solubilisation occurs by the formation of sodium carboxylate groups from the anionic polyacid. The polyelectrolyte formed in this way is readily soluble and shows a rapid rate of dissolution. However, the presence of electrolytes such as magnesium or calcium salts from hard water can inhibit removal [191]. 

Measurements of the surface tension of aqueous solutions of various sulphonated and unsulphonated phenylazonaphthol dyes showed that the degree of surface activity (that is, the lowering of surface tension) tended to increase progressively with the degree of alkyl substitution in the series of dyes [7]. The surface-active behaviour of such alkylated dye ions ensures that they become more concentrated at the interface between the dyebath and the fibre surface, just as they do at the air-water interface of the dye solution. Foaming of dyebaths can be a serious practical problem with relatively hydrophobic dye structures solubilised by means of a single ionised group. 

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