PH-response

More recendy, two different types of nonglass pH electrodes have been described which have shown excellent pH-response behavior. In the neutral-carrier, ion-selective electrode type of potentiometric sensor, synthetic organic ionophores, selective for hydrogen ions, are immobilized in polymeric membranes (see Membrane technology) (9). These membranes are then used in more-or-less classical glass pH electrode configurations. 

Immersion electrodes are the most common glass electrodes. These are roughly cylindrical and consist of a barrel or stem of inert glass that is sealed at the lower end to a tip, which is often hemispherical, of special pH-responsive glass. The tip is completely immersed in the solution during measurements. Miniature and microelectrodes are also used widely, particularly in physiological studies. Capillary electrodes permit the use of small samples and provide protection from exposure to air during the measurements, eg, for the determination of blood pH. This type of electrode may be provided with a water jacket for temperature control. 

The construction of these electrodes is exactly similar to that already described for the pH responsive glass electrode. They must of course be used in conjunction with a reference electrode and for this purpose a silver-silver chloride electrode is usually preferred. A double junction reference electrode is often used. The electrode response to the activity of the appropriate cation is given by the usual Nernst equation ... 

FIGURE 6-20 Configuration of a penicillin sensor based on an microarray electrode coated with a pH-responsive polypyrrole. Vq = gate voltage VD = drain voltage ID = drain current PS = potentiostat CE and RE = counter and reference electrodes, respectively. (Reproduced with permission from reference 76.)... 

A simple example of gel formation is provided by chitosan tripolyphosphate and chitosan polyphosphate gel beads the pH-responsive swelling abihty, drug-release characteristics, and morphology of the gel bead depend on polyelectrolyte complexation mechanism and the molecular weight. The chitosan beads gelled in pentasodium tripolyphosphate or polyphosphoric acid solution by ionotropic cross-hnking or interpolymer complexation, respectively. 

Poly[(4-carboxylatophenoxy)(methoxyethoxyethoxy)phosphazene] copolymers of variable compositions were synthesized by Allcock [645] in 1996. These polymers were found to be soluble in alkaline solutions. When crosslinked (by y-rays or by addition of CaCl2 to the polymer solution) the resulting hydrogels were found able to contract or expand as a function of the pH of the solution and their utilization as pH-responsive materials for drug delivery systems could be envisaged. 

Rajagopal K, Lamm MS, Haines-Butterick LA et al (2009) Tuning the ph responsiveness of beta-hairpin peptide folding, self-assembly, and hydrogel material formation. Biomacromolecules 10 2619-2625... 

Fig. 1. Schematic diagram of the first reported pH responsive CHEMFET...

Since the initial report of the pH responsive CHEMFET in 1970, CHEMFET s for other species such as Ca , Na", and penicillin have been descril d. In addition, some of these devices have been tested for in vivo or on-line continuous whole blood monitoring. While problems associated with mass production of the more complex CHEMFET s such as those employing enzymes (for example, with the penicillin CHEMFET) have not yet been fully solved, the technology for mass production of the relatively simple pH CHEMFET is api rently now available and problems noted with early devices attributable to irreversible SiO changes and... 

Avdeef and Bucher [24] investigated the use of universal buffers in potentiomet-ric titrations. Recently, such a buffer system, formulated with several of the Good components, has been designed specifically for robotic applications, where automated pH control in 96-well microtiter plates is required, with minimal interference to the UV measurement [48]. This universal buffer has a nearly perfectly linear pH response to additions of standard titrant in the pH 3-10 region [8, 48]. 

F. Robinson. Polymers useful as pH responsive thickeners and monomers therefor. Patent WO 9610602,1996. 

Preparation and Characterisation of Novel pH Responsive Microgel Particles. Matt Hearn, Department of Chemistry, University of Bristol, http //www.chm.bris.ac.uk/vincent/matt.html... 

Figure 13 shows pH response of bromothymol blue (BTB) as coimmobilized non fluorescent pH indicator detect by fluorescence. 

A different pH-triggered deshielding concept with hydrophilic polymers is based on reversing noncovalent electrostatic bonds [78, 195, 197]. For example, a pH-responsive sulfonamide/PEl system was developed for tumor-specific pDNA delivery [195]. At pH 7.4, the pH-sensitive diblock copolymer, poly(methacryloyl sulfadimethoxine) (PSD)-hZocA -PEG (PSD-b-PEG), binds to DNA/PEI polyplexes and shields against cell interaction. At pH 6.6 (such as in a hypoxic extracellular tumor environment or in endosomes), PSD-b-PEG becomes uncharged due to sulfonamide protonation and detaches from the nanoparticles, permitting PEI to interact with cells. In this fashion PSD-b-PEG is able to discern the small difference in pH between normal and tumor tissues. 

Bulmus V, Woodward M, Lin L, Murthy N, Stayton P, Hoffman A (2003) A new pH-responsive and glutathione-reactive, endosomal membrane-disruptive polymeric carrier for intracellular delivery of biomolecular drugs. J Control Release 93 105-120... 

Murthy N, Campbell J, Fausto N, Hoffman AS, Stayton PS (2003) Design and synthesis of pH-responsive polymeric carriers that target uptake and enhance the intracellular delivery of oligonucleotides. J Control Release 89 365-374... 

Sethuraman VA, Na K, Bae YH (2006) pH-responsive sulfonamide/PEI system for tumor specific gene delivery an in vitro study. Biomacromol 7 64-70... 

Meyer M, Wagner E (2006) pH-responsive shielding of non-viral gene vectors. Expert Opin Drug Deliv 3 563-571... 

Meyer M, Philipp A, Oskuee R, Schmidt C, Wagner E (2008) Breathing life into polycations functionalization with pH-responsive endosomolytic peptides and polyethylene glycol enables siRNA delivery. J Am Chem Soc 130 3272-3273... 

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