Matrix hydrophobicity

A more sophisticated class of optical sensors with high selectivity towards ions are the ion-selective optodes (ISOs) [21], where the matrix (hydrophobic polymer such as PVC) contains a selective lipophilic ionophore (optically silent), a chromoionophore, a plasticizer and an anionic additive. The measurement principle is based on a thermodynamic equilibrium that controls the ion exchange (for sensing cations) or ion coextraction (for sensing anions) with the sample. The source of optode selectivity is a preferential interaction between the target ion and an ionophore. For a dye to act as a chromoionophore, it must... 

Figure 7.S Reversed phase chromatography matrix. Hydrophobic molecules in solution (coloured) tend to associate with the non-polar hydrocarbon chains attached to the stationary phase...

Dopant molecules uniformly distributed throughout matrix particles diffuse through the huge microparticle inner porosity. Also in this case, the release velocity can be varied from mg/hours to mg/month by changing parameters such as the water-to-alkoxide ratio, pH, alkoxide concentration, and matrix hydrophobicity. 

Here, we will consider changes in the accessibility of electrodes to electroactive substances by switchable polymer films, which are not directly redox-sensitive. A gating of hexacyanoferrates could be modulated by the presence of cholesterol, which complexes the collapsed poly(vinyl pyridine) matrix (hydrophobic at the pH used) [425]. The preparation of this membrane leads to pores that are filled upon complexation with cholesterol. At the same time, the accessibility of the electrode... 

Phadke, A., Zhang, C., Hwang, Y.,Vecchio,K., and Varghese, S. 201 Oh. Templatedminerahzation of synthetic hydrogels for bone-Uke composite materials Role of matrix hydrophobicity. Biomacromolecules, 11, 2060-2068. 

Locally and densely sulfonated homopolymers, in which the concentrated sulfonic acid nnits in a membrane allow for the creation of hydrophilic domains (making the matrix hydrophobic), have been investigated as another approach to efficient PEMs. 

Internal surfactant antistats ate physically mixed with the plastic resin prior to processing. When the resin is melted, the antistat distributes evenly in the polymer matrix. The antistat usually has some degree of solubiUty in the molten polymer. However, when the polymer is processed (extmded, molded, etc) into its final form and allowed to cool, the antistat migrates to the surface of the finished article due to its limited solubiUty in the solidified resin. The molecule of a surface-active agent is composed of a polar hydrophilic portion and a nonpolar hydrophobic portion. The hydrophilic portion of the surfactant at the surface attracts moisture from the atmosphere it is the moisture that has the static dissipative effect. 

Although current matrix diffusional systems are most suitable for small-molecule compounds, it has been demonstrated (84) that soHd hydrophobic polymers allow dispersed powdered macromolecules of nearly any size, for example, ethylene—vinyl acetate copolymers containing dispersed polypeptides, to be released for periods exceeding 100 days. 

Phosphoric Acid Fuel Cell This type of fuel cell was developed in response to the industiy s desire to expand the natural-gas market. The electrolyte is 93 to 98 percent phosphoric acid contained in a matrix of silicon carbide. The electrodes consist of finely divided platinum or platinum alloys supported on carbon black and bonded with PTFE latex. The latter provides enough hydrophobicity to the electrodes to prevent flooding of the structure by the electrolyte. The carbon support of the air elec trode is specially formulated for oxidation resistance at 473 K (392°F) in air and positive potentials. 

Owing to the weak hydrophobicity of the PEO stationary phases and reversibility of the protein adsorption, some advantages of these columns could be expected for the isolation of labile and high-molecular weight biopolymers. Miller et al. [61] found that labile mitochondrial matrix enzymes — ornitine trans-carbomoylase and carbomoyl phosphate synthetase (M = 165 kDa) could be efficiently isolated by means of hydrophobic interaction chromatography from the crude extract. 

Figure 7. Mechanism of the proton-translocating ubiquinol cytochrome c reductase (complex III) Q cycle. There is a potential difference of up to 150 mV across the hydrophobic core of this complex (potential barrier represented by the vertical broken line). Cytochromes hour and b N are heme groups on the same peptide subunits of complex III which can transfer electrons across the hydrophobic core. The movement of two electrons provides the driving force to transfer two protons from the matrix to the cytosol. Diffusion of UQ and UQHj, which are uncharged, in the hydrophobic core, and lipid bilayer of the inner membrane is not influenced by the membrane potential (see Nicholls and Ferguson, 1992).

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