Induced Solubilization

Both chemically and electrochemically synthesized PPy s are typically insoluble in water and organic solvents, and are infusible because of strong intermolecular and intramolecular interactions of their polymer chains. There has been intense research over the past decade to overcome this serious hindrance to their proces-sibility and subsequent utilization. Several approaches have now been developed to improve the solubility of PPy s, namely (1) counterion-induced solubilization, (2) colloid formation, and (3) side-chain-induced solubilization. Each of these will be discussed in turn. 

An important breakthrough in PPy chemistry was the discovery by Lee and coworkers95 in 1995 of a chemical polymerization route to an unsubstituted PPy that was soluble in organic solvents. They exploited the surfactant-like qualities of added dodecylbenzenesulfonate (DBSA 9) as a dopant anion to solubilize PPy formed during oxidation of pyrrole by aqueous (Nn4)2S208. The PPy/DBSA product, isolated as a black powder in 42% yield after 40 h reaction at 0°C, was very soluble in m-cresol, and could be dissolved in weakly polar solvents such as chloroform and dichloro-methane by the addition of an equimolar amount of dodecylbenzenesulfonic acid. A film cast from chloroform solution exhibited an electrical conductivity of 5 S cm-1, and its UV-visible spectrum was similar to that of electrochemically deposited PPy. 

In a recent development, the first alcohol-soluble PPy s have been synthesized by the oxidation of pyrrole with aqueous (NII4)2S208 using di(2-ethylhexyl) sulfosuc-cinate sodium salt (NaDEHS 12) as the dopant anion.101 This dopant contains both nonpolar alkyl chains and polar oxygen centers, the latter of which are believed to form H-bonds with alcohol solvents, thereby facilitating dissolution. 

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G. J. D. Kirk and M. A. Saleque, Root-induced solubilization of phosphate in the rhizosphcre of lowland rice. New Phytol. 729 325 (1995). 

ECB deacylase is produced naturally by Actinoplanes utahensis. However, very little (—0.2%) deacylase activity was detected in the culture filtrate of Actinoplanes utahensis. Less than 5% of the cell-associated deacylase activity was released by incubation of the cells at 0.01 M KH2P04, pH 6, for 1 day. A simple salt treatment with 0.8 M KC1 resulted in 60-80% recovery of soluble deacylase at a high specific activity [25], This salt-induced solubilization suggests that the deacylase is loosely bound to the membrane of A. utahensis and can be released by disruption of ionic interactions [26]. The solubilized enzyme was stable and purified to apparent homogeneity by a four-step conventional procedure [25]. 

Figure 2 shows the solubility of indomethacin as a function of the CyS-A concentration and the system is compared with one containing p-CyD. The slopes of both isotherms are practically identical, and hence the stability of the CyS-A complex seems almost identical with that of the 3-CyD complex, but CyS-A-induced solubilization is greater since CyS-A has a much higher solubility than 3-CyD. Interaction between CyS-A and some drugs occurred very slowly. Vitamin D3, which practically insoluble in water, had detectable solubility in water containing CyS-A after 72 h. 

Soluble fiber has certain health benefits, including binding of bile acids in the small intestine, leading to reduced serum cholesterol levels. However, extrusion-induced solubilization may not offer the same health benefits. This new soluble fiber is chemically distinct from naturally soluble fiber compounds such as pectin and gums. Extrusion nearly doubled soluble fiber in potato peels, and significantly more cholic acid and deoxycholic acid were bound by peels extruded at the lower temperature studied (Camire et al., 1994). 

Alkyl chain substituted aromatic acids are known for their surfactant properties (e.g. dodecyl benzene sulphonic acid). Therefore, they may help to induce solubilization of polyaniline by micellar action. 

Electronic and vibrational energy levels of molecules are affected by their environment. The interaction is determined by the electronic charge distributions in the ground and excited electronic states of the absorbing entity, polymer dopant interaction (long-range dielectric and other field properties of the medium (dopant-induced solubilization). All these effects are reflected in the shapes and intensities of absorption bands. 

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