Responses to pH

The principles on which carbonylmetal-based IR read-out of changes in pH are based [26] have already been introduced in Section 7.4. The hexadienoate complex 1 (Fig. 7.5) provides a typical example. Both the symmetric and antisymmetric modes respond to changes in pH, but the v CO) band provides the simplest case, because Vj,5y j(CO) in this case comprises an overlapping pair of antisymmetric modes. The position of Vgy (CO), however, can simply be measured from the peak top. In Fig. 7.8a, the data represented by filled drdes (read against the scale on the left hand vertical axis) shows the position of the Vsj, ,(CO) band of 1/2 in a pH range between 3 and 8.6 [26]. 

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Polymer gels In response to pH changes in their enviromnent, materials derived from poly(acrylonitrile) will swell or shrink in a slow analogy to muscle action, thought to have robotic applications. 

Monoprotic Surface Groups. It has been stated that for some oxides the surface potential response to pH is close to the Nernstian value, and that relatively large values of in the model were necessary to be consistent with this observation. For -= 1,... 

T.W. Hamann, F. Gstrein, B.S. Brunschwig, N.S. Lewis, Measurement of the driving force dependence of interfacial charge transfer rate constants in response to pH changes at n-ZnO/ H20 interfacies, Chem. Phys. 326 (2006) 15-23. 

Mayer LD, Tai LCL, Bally MB, et al. Characterization of liposomal systems containing doxorubicin entrapped in response to pH gradients. Biochim Biophys Acta 1990 1025 143. 

Liposomes prepared from diacetylene hydrazide 7 undergo chromatic transitions in response to pH changes (Jonas et al. 1999). Liposomes of 7, which form only in... 

Two similar approaches were adopted by Ishihara et al. [364-368]. Membranes based on hydroxyethyl acrylate, dimethylaminoethyl methacrylate and trimethyl silyl styrene were solvent cast, and capsules containing insulin and glucose oxidase were prepared by interfacial precipitations. The authors reported dramatic changes in permeability in response to pH changes between 6.1 and 6.2. Moreover, addition of glucose induced an increase in the permeation rate of insulin, and upon removal of the glucose the permeability rates returned to their original levels. However, the conclusions were criticized [361] due to... 

This time-dependent response to pH of the swelling medium was modelled with a Boltzmann superposition type model shown in Eq, (46) ... 

Alcohol oxidase. We have chosen to use alcohol oxidase from Hansenula polv-morpha (2) in our research. The enzyme has eight sub-units, all of which must be associated for the enzyme to exhibit activity. It is a large enzyme Mn 600,000 and has poor stability upon freeze drying. This factor combined with an almost flat activity response to pH between 6 and 10 and a maximum temperature activity at 40-50°C made the enzyme an ideal candidate for the study of enzyme stabilization in the dry state, especially as we wished to prepare diagnostic kits for ethanol and solid phase enzyme based sensors. 

We have demonstrated that these types of polymers swell and increase their permeability to insulin in response to pH changes at physiologic ionic strength and pH (6-10). For example, a polymer with... 

The two sites also differ in their pH stability towards iron release. Experiments on serum transferrin showed that one site loses iron at a pH near 6.0, and the other at a pH nearer 5.0 (203, 204), giving a distinctly biphasic pH-induced release profile (Fig. 28). The acid-stable A site was later shown to be the C-terminal site (202). It is this differential response to pH, together with kinetic effects (below), that enables N-terminal and C-terminal monoferric transferrins to be prepared (200). Although the N-terminal site is more labile, both kinetically and to acid, the reasons are not necessarily the same the acid stability may depend on the protonation of specific residues (Section V.B) and is likely to differ somewhat from one transferrin to another in response to sequence changes. The biphasic acid-induced release of iron seen for transferrin is not shared by lactoferrin. Although biphasic release from lactoferrin, in the presence at EDTA, has been reported (205), under most conditions both sites release iron essentially together at a pH(2.5-4.0) several units lower than that for transferrin (Fig. 28). 

Pressey and Avants (80) separated, by DEAE Sephadex A-50 chromatography, four forms of tomato pectinesterase, with molecular weights 35,500, 27,000, 23,700, and 24,300. The number and relative amounts of these components varied considerably with ripeness and variety of tomato, and no single extract contained all four. The four forms diflFered in heat stability and response to pH and cation concentration. The fourth form, the major species in most tomato extracts, had properties similar to those of the enzyme described by Lee and Macmillan (75), whose molecular weight, however, was estimated on Sephadex G-75 as 27,500 (81),... 

Characteristics of the Enzyme. S-alkyl-L-cysteine sulfoxide lyases prepared from garlic 17, 19) and onion 24, 25, 39) are similar. They differ primarily in their response to pH—the garlic enzyme has a broad pH optimum from 5 to 8 and may be precipitated at pH 4.0 and redissolved without loss of activity (17) while the onion enzyme is sensitive to acid and is most active at pH 8.8 in pyrophosphate buffer 24, 39). The purified garlic enzyme showed a sharper pH optimum at pH 6.5 40). The Brassica enzyme is most active at pH 8.5 in borate buffer (27) and remains soluble and active when other proteins are precipitated at pH 4.0. 

The strong affinity of iron oxides for Se(IV) has been well documented (Dzombak and Morel, 1990) and calculations based on the Dzombak and Morel (1990) diffuse double-layer model and default HFO database show the principal response to pH and redox speciation changes (Figure 11). The selenate species is less strongly adsorbed by iron oxides at near-neutral pH than the selenite species (Figure 11). Clay minerals (Bar-Yosef and Meek, 1987) also adsorb Se(IV). 

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