Basicity and pH

Thus at acidic pH the formation of ions increases the conductivity, while at basic pH the higher specific conductivity anion OH- is replaced by the less-conducting (CH3)2S02-anion. The yield of the sulfinic anion can be measured from the decrease in conductivity at basic pH and the increase at acidic pH (equation 26-27). 

Acetochlor and its metabolites are extracted from plant and animal materials with aqueous acetonitrile. After filtration and evaporation of the solvent, the extracted residue is hydrolyzed with base, and the hydrolysis products, EMA and HEMA (Figure 1), are steam distilled into dilute acid. The distillate is adjusted to a basic pH, and EMA and HEMA are extracted with dichloromethane. EMA and HEMA are partitioned into aqueous-methanolic HCl solution. Following separation from dichloromethane, additional methanol is added, and HEMA is converted to methylated HEMA (MEMA) over 12 h. The pH of the sample solution is adjusted to the range of the HPLC mobile phase, and EMA and MEMA are separated by reversed phase HPLC and quantitated using electrochemical detection. 

Table 1. Selected absorption indicators for measurements of acidic or basic pHs, and respective pKa values at room temperatures1.

Disulfide exchange reactions occur over a broad range of conditions—from acid to basic pH—and in a wide variety of buffer constituents. Most crosslinking reactions involving disulfide exchange are done under physiological conditions or those most appropriate to maintain stability of the protein or other molecule being modified. 

The main drawback of the DHAP-dependent aldolases is their strict specificity for the donor substrate. Apart from the scope limitation that this fact represents, DHAP is expensive to be used stoichiometrically in high-scale synthesis, and labile at neutral and basic pH, and therefore its effective concentration decreases over time in enzymatic reaction media, hindering the overall yield of the aldol reaction. In addition, due to the presence of a phosphate group in both DHAP and the... 

A solution of LAH in anhydrous THF under N2 (15 mL of a 1.0 M sol ution) was cooled to 0 °C and vigorously stirred. There was added, dropwise, 0.40 mL 100% H2S04, followed by about 3 g of the crude 3-ethoxy-4-ethylthio-5-methoxy-phenylacctonitrile diluted with a little anhydrous THF. The reaction mixture was stirred until it came to room temperature, and then held at reflux on the steam bath for 2 h. After cooling to room temperature, there was added IPA to destroy the excess hydride (there was quite a bit of it) and then 15% NaOH to bring the reaction to a basic pH and convert the aluminum oxide to a loose, white, filterable consistency. This was removed by filtration, and washed first with THF followed... 

As already pointed out in our previous papers [48-50], the high stability is probably the result of the newly developed chemical modification procedure which may lead to a stronger adsorption of the PB particles on the electrode surface. In contrast to the PB layer obtained with the more commonly used electrochemical procedures, these modified electrodes are in fact more stable at basic pH and their continuous use is possible with a minimal loss of activity after several hours. Moreover, with respect to the electrochemical procedure, our chemical deposition is much more suitable for mass production since no electrochemical steps are required and a highly automated process could be adopted (see Procedure 17 in CD accompanying this book). 

The pH-dependent properties of the hydrophilic positively charged colloidal particles favor the adsorption of negatively charged nucleic acids at acidic pH and at low salt concentration. However, the desorption is favored at basic pH and at high ionic strength. The concentration process of adsorbed nucleic acid materials was performed via centrifugation [9], filtration, or magnetic separation [10] of the used colloidal particles. 

A second group of endo pectin lyases is characterized by optimum activity at slightly basic pH and by the ability to degrade polygalac-turonic acid (even though pectin is still favored). Sherwood 129) isolated this type of pectin lyase from Rhizoctonia solani. The enzyme had an optimal activity at pH 7.2 and degraded pectin faster than pectic acid. Bateman 128) found two pectin lyases from this microorganism which, when purified, were stimulated by cations and inhibited by EDTA. Optimal activity was between pH 8.0 and 9.0. 

Figures I2.12A and 12.12B show the spectra of a Li/Al hydrotalcite phase synthesised at a basic pH and the spectrum of this phase detected on the support after impregnation.

A different problem occurs with 7-methylguanosine. The purine base of this nucleoside is hydrolyzed at basic pH, and very significant degradation occurs in an hour at pH 9.5 at room temperature. The mixture of oxidized nucleoside and protein, therefore, is kept at pH 9.1 and at 0-4°, at which only very limited hydrolysis of the base occurs in 1 hr. A different reducing agent, tert-butylamine borane (Aldrich Chemical Co.), is used the reduction is done for only 30-60 min at 4°, and the product is separated from free nucleoside on a Sephadex G-25 column at 4°. The nucleotide of the 7-methylguanosine is more stable than the nucleoside, and it also has been used to induce antibody to the 7-methylguanine structure. ... 

This results in more basic pH and thus more negative mobility. Usually the pH is measured before but not during or after the electrokinetic measurements. The electrolysis products can be in situ neutralized using buffer solutions rather than strong 1-1 electrolytes. However, such solutions often contain strongly adsorbing ions that shift the lEP. 

The different hydration and ionization states were correlated with the dielectric property of melanins (299). The dielectric constants and specific conductivities of melanin suspensions followed the sequence acidic > neutral > basic pH and showed dependence on the time of hydration. 

In a similar investigation, Besson et al. [45] found that addition of bismuth to platinum had a similar effect. As in the previous investigation, however, the reaction was conducted at basic pH, and the yield of 2-keto-D-gluconate was limited by the formation of degradation products. 

In addition to pore structure, tlie surface chemistry of the adsorbent may have a strong influence on the adsorption of aromatic compounds. Fig. 7 (from [48]) shows that the Langmuir adsorption capacity of phenol is dependent tai the concentration of acidic surface oxides, as defined by Boehm [49]. Furthermore, for acidic and basic species, the effect of the adsorbent s surface charge combined with that of the pH of the solution is extremely important because it determines the nature of the forces (attractive/repulsive) between the adsorbate and the adsorbent surface. For cationic dyes, adsorption is promoted when the surface charge is negative adsorption capacities are 1.7 to 2.3 times higher at basic pH and adsorption rates are doubled [50]. 

Sukumar, N., Biswal, B.K., Vijayan, M. Structures of orthorhombic lysozyme grown at basic pH and its low-humidity variant. Acta CrystaUogr. D Biol. CrystaUogr. 1999, 55(Pt 4), 934-7. 

The antigen is covalently coupled to a matrix (e.g., proteins or peptides in Affigel 10) via a primary amino, carboxyl, or sulfhydryl group. Coupling methods are described in Section 53. The experimenter pumps the diluted serum or the hybridoma supernatant over the column, washes out the unbound protein, and successively eludes with acidic pH, basic pH, and 3 M MgClj. 

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