At various pH values

FIGURE 2.14 The titration curve for phosphoric acid. The chemical formulas show the prevailing ionic species present at various pH values. Phosphoric acid (H3PO4) has three titratable hydrogens and therefore three midpoints are seen at pH 2.15 (p. i), pH 7.20 (p. 2). and pH 19.4 (p. 3). 

In the search for new fluorometric reagents for trace metal determinations, ferroin-type compounds, namely 2-(2-pyridyl)-2//- and 2-(3-isoquinolyl)-3//-imidazo[4,5-/i]quinolines, and their silver, lead, and zinc chelates were tested for luminiscence in aqueous ethanol solutions at various pH values (80TAL1021). 

Capacities at Various pH Values pKa Values for Phosphoric Acid Resin ... 

Henderson-Hasselbaich equation (Sections 20.3, 24.5, 26.2) An equation for determining the extent of deprotonation of a weak acid at various pH values. 

The hydrolytic behavior of sulfosuccinates as such and in formulations is depicted in the following pictures (Figs. 4-7). Two substances-DLAS and DLSS—were chosen to illustrate these properties. The tests were performed at room temperature and 40°C at various pH values (pH = 5, 6, 8) and—in the case of DLSS—without adjusting pH in a long-term run (24 weeks). Changes were evaluated by determination of pH and active matter. 

FIGURE 2 pH dependance of the erosion rate of PCPP versus time. Discs of PCPP were formulated into 1.4-cm-diameter discs 1 mm thick by compression molding, and placed into 0.1 M phosphate buffers at various pH values at 37°C. The cumulative percentage of the polymer which degraded was measured by absorbance at 250 nm. 

FIGURE 23 Release of cyclobenzaprine hydrochloride (CBP) from discs prepared from 3,9-bis(ethylidene-2,4,8,10-tetraoxaspiro[5,5]-undecane) and a 20 80 mole ratio of trans -cyclohexane dimethanol and 1,6-hexanediol at various pH values and 37°C. Polymer contained 3 wt% phthalic anhydride and 7.5 wt% CBP. 

Fig. 22.—Circular Dichroism of Methyl a-D-Mannopyranosiduronic Acid at Various pH Values. (Redrawn from Ref. 47.)...

Ketoprofen, a weak-acid drug, with a pKa 4.12 (25°C, 0.01 M ionic strength), was selected to illustrate Eqs. (7.20) and (7.21) in a series of simulation calculations, as shown in Fig. 7.16. The membrane-buffer apparent partition coefficients /(piii were calculated at various pH values, using the measured constants from... 

FIGURE 6.1 Relationship between H2S03 and HS03 at various pH values. (Taken from Krofta, M. and Wang, L.K., Design of Innovative Flotation-Filtration Wastewater Treatment Systems for a Nickel-Chromium Plating Plant, U.S. Department of Commerce, National Technical Information Service, Springfield, VA, Technical Report PB-88-200522/AS, January 1984.)... 

Privalov et al. (1989) also reported the temperature dependence of the ellipticity at 222 nm for the proteins studied at various pH values (Fig. 28). At the highest temperature studied (80°C), the 222 nm ellipticity value for the thermally unfolded, acid-unfolded, and Gdm-HCl-unfolded proteins appear to be converging, but show a range of 2000 deg cm2/dmol out of a total of 5000 deg cm2/dmol. (ApoMb is an exception in that, as noted before, the thermally denatured protein is apparently an associated /1-sheet. However, the acid- and Gdm HC1-unfolded forms of apoMb have similar [0] 222 values at 80°C.)... 

Table 10.25 Effect of alkali used with peracetic acid at various pH values on the degree of polymerisation of cotton cellulose [256]...

Figure 3.6 compares iso-pH permeabilities of ketoprofen at various pH values in a 2% DOPC-dodecane model (open circles) and the 20% soy lecithin with SLS in the acceptor compartment (filled circles, data in Table 3.5). In the presence of the latter negatively charged lipids (with the make-up similar to that of BBM in Table 3.1), ketoprofen is intrinsically more permeable, by a factor of 17. The UWL limit, indicated by the solid curves in low-pH solutions, and consistent with the permeability Pu 19.8 x 10-6 cm s 1 (log Pu —4.7), masks the true intrinsic permeability of the membranes, P0. However, it is possible to deduce the membrane permeability if the pKa is known. In Fig. 3.6, the bending in the dashed (calculated) curves at pH 4 corresponds to the pKa of the molecule. Due to the UWL, the point of bending is shifted to higher pH values in the solid (measured) curves. The difference between the apparent pKa (pK 5.3 for DOPC and 6.3 for soy) and the true pKa (4.12) is the same as the difference between log P0 and log Pu [23],... 

The enzymatic activities of intercalated GOx-AM P layered nanocomposites at various pH values and temperatures were compared with the native enzyme in aqueous solution. In both cases, characteristic linear plots consistent with Michalis-Menton kinetics were obtained. The Lineweaver-Burk plots indicated that the reaction rates (Vmax) for free and intercalated GOx (3.3 and 4.0 pM min 1 respectively), were comparable, suggesting that the turnover rate at substrate saturation was only marginally influenced by entrapment between the re-assembled organoclay sheets. However, the dissociation constant (Km) associated with the activity of the enzyme was higher for intercalated GOx (6.63 mM) compared to native GOx (2.94 mM), suggesting... 

Electrochemical Parameters of SODs at MPA-modified electrode at various pH values... 

The rate constant of electron transfer (ks) and anodic and cathodic electron transfer coefficients (aa and ac) of the SODs at various pH values were estimated with Laviron s equation and summarized in Table 6.5. Interestingly, the fastest electron transfer of the SODs was essentially achieved in a neutral solution, probably in agreement with the biological conditions for the inherent catalytic mechanisms of the SODs for 02" dismutation, although the electrode processes of the SODs follow a different mechanism. 

FIGURE 6.12 Plots of amperometric responses of Cu, Zn-SOD/MPA-modified (A), Mn-SOD/MPA-modified (O), and Fe-SOD/MPA-modified ( ) Au electrodes toward 13 nM min 1 O2 in 25 mM phosphate buffer at various pH values from pH 5.8 to 9.5. The solution was stirred with a magnetic stirrer at 200rpm. (Reprinted from [138], with permission from die American Chemical Society.)... 

Additional mechanistic insight into the reductive nitrosylation of ferri-heme proteins was obtained from kinetic studies carried out on aqueous solutions of Cytm, metMb, and metHb at various pH values (67). For example, Cytm undergoes reduction by NO to Cyt11 in aqueous solutions at pH values > 6.5. A hypothetical reaction mechanism is shown in Scheme 2 which would predict the rate law presented in Eq. (31) (67). 

The influence of metal ions on the aggregation of Cl Reactive Red 2 (3.14) in aqueous solution at various pH values has been examined in detail recently [18]. Sodium ions have a profound effect on these disulphonated dye anions, so that the enhancement of substantivity during the dyeing process is accompanied by aggregation attributable to hydrophobic interaction between the phenyl and s-triazine ring systems. Aggregation is much greater,... 

The presence of residual unbound transition-metal ions on a dyed substrate is a potential health hazard. Various eco standards quote maximum permissible residual metal levels. These values are a measure of the amount of free metal ions extracted by a perspiration solution [53]. Histidine (5.67) is an essential amino acid that is naturally present as a component of perspiration. It is recognised to play a part in the desorption of metal-complex dyes in perspiration fastness problems and in the fading of such chromogens by the combined effects of perspiration and sunlight. The absorption of histidine by cellophane film from aqueous solution was measured as a function of time of immersion at various pH values. On addition of histidine to an aqueous solution of a copper-complex azo reactive dye, copper-histidine coordination bonds were formed and the stability constants of the species present were determined [54]. Variations of absorption spectra with pH that accompanied coordination of histidine with copper-complex azo dyes in solution were attributable to replacement of the dihydroxyazo dye molecule by the histidine ligand [55]. 

Part A Determination of the Color at Various pH Values Procedure... 

Figure 5.3 displays a comparison of one-dimensional spectra of a neuropeptide in the presence of either DPC or SDS micelles at various pH values. Note that the signal at approx. 8.6 ppm due to HE1 of His vanishes in SDS at a much higher pH compared to DPC. In general, spectra in SDS still yield reasonable quality at neutral pH in contrast to those recorded in DPC. 

Table 5-6 shows for semiconductor metal oxides the flat band potential in aqueous solutions at various pH values and the conduction band edge potential E c at the iso-electric point pH,. ... 

At Coventry University [20] we have obtained similar results to Tu under conventional (silent) conditions. Our initial thoughts were that if the effect of the tail off was either a consequence of mass transfer to the electrode, or a consequence of some problem with the diffusion layer, then ultrasound might be expected to have an effect and thus improve the plating rate. Investigations in the presence of ultrasound and at various pH values did not significantly affect the plating characteristics i. e. the plateau effect still remained. However, the overall efficiency in the presence of ultrasound was affected (Fig. 6.10). 

Figure 4. Equilibrium adsorption densities of polyacrylic acid on hematite at various pH values. Reproduced with permission from Ref. 22. Copyright 1983, Colloids and Surfaces.

Adsorption and electrokinetic effects of amino acids, solid-aqueous interface, 311-26 Adsorption density, equilibrium PAA at various pH values, 299f PAA on hematite, 304f SDS with and without polymer, 298f,303f... 

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