3-Nitrophenol: titration curve

The titration of a mixture ofp-nitrophenol (pfQ = 7.0) and m-nitrophenol pK = 8.3) can be followed spectrophotometrically. Neither acid absorbs at a wavelength of 545 nm, but their respective conjugate bases do absorb at this wavelength. The m-nitrophenolate ion has a greater absorbance than an equimolar solution of the p-nitrophenolate ion. Sketch the spectrophotometric titration curve for a 50.00-mL mixture consisting of 0.0500 M p-nitrophenol and 0.0500 M m-nitrophenol with 0.100 M NaOH, and compare the curve with the expected potentiometric titration curves. 

The pH titration curve of 3-nitrophenol with a pH range near the pK. ... 

Figure 11.33 Ionization of p-nitrophenol in the presence of sodium dodecyl sulphate. The fractional ionization, a, was calculated from the absorbance of the p-nitrophenolate ion at 400 nm. The total p-nitrophenol concentration was 1 x 10 moll The solvent was 0.004 m sodium phosphate buffer, or 0.004 m glycylglycine buffer for the higher pH values, adjusted to the pH indicated and to a constant ionic strength of 0.1 m with NaCl. The solid lines are standard titration curves for the dissociation of a monobasic acid. The NaLS concentrations in g ml" were a, 0 b, 0.0144 c, 0.0288 d, 0.0576. From Herries et al [218].

A binuclear zinc complex of the 2,6-bis [(2-pyridylmethyl)(2-hydroxyethyl) amino]methyl -4-methylphenol ligand (L33, Fig. 63) catalyzes the hydrolysis of bis(4-nitrophenyl) phosphate in aqueous buffer solution to yield 4-nitrophenol and 4-nitrophenyl phosphate.246 Analysis of the pH-rate profile revealed a sigmoidalshaped curve with a pKa = 7.13. This value is similar to a deprotonation event characterized by potentiometric titration and has been assigned to deprotonation of... 

MNPHP is a well-known irreversible inhibitor of lipases that is highly specific for reaction with active-site serine residues. Thus, MNPHP was selected as the inhibitor to determine, by titration, the fraction of catalytic sites that are accessible and active. Since we are concerned with CALB activity in organic media, inhibition was studied in heptane. LC-MS was used to determine the release of p-nitrophenol (pNP) which corresponds with accessible active sites. To ensure that adsorption of pNP by resins was taken into consideration, pNP concentration was corrected as follows. A fixed quantity of enzyme-free resin was incubated overnight in acetonitrile with different concentrations of j NP. Standard curves of pNP adsorption by each resin as a function of pNP concentration were constructed from LC-MS measurements. MNPHP-inhibited immobilized enzymes were used for e-caprolactone ring-opening polymerizations in toluene (70 C). No conversion of monomer was observed in 30 minutes. Hence, MNPHP titration resulted in complete inhibition of CALB activity. 

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