P-Nitrophenol concentrations

Roan CC, Morgan DP, Cook N, et al. 1969. Blood cholinesterases, serum parathion concentrations and urine p-nitrophenol concentrations in exposed individuals. Bull Environ Contam Toxicol 4 362-369. 

Place 0.05 to 0.50 ml of 0.5 mM p-nitrophenol standard solution into ten individual 15- to 20-ml test tubes and dilute each to 5 ml with 0.1 M Tris-Cl buffer, pH 8.2. This yields a standard curve of 0.005 to 0.05 fimol p-nitrophenol/ml. 2. Measure A410 using 0.1 M Tris Cl buffer, pH 8.2, as a blank, and make a standard curve by plotting A410 versus the p-nitrophenol concentration in each tube. 3. For each lipase activity assay, place 2.5 ml of 0.1 M Tris-Cl buffer, pH 8.2, and 2.5 ml of 420 pM p-nitrophenyl laurate substrate solution into a 15- to 20-ml test tube. Prepare one extra tube for a reagent blank. 4. Add 1 ml water to the reagent blank. Lypolytic Enzymes... 

Urinary p-nitrophenol concentrations were obtained by the Elliott (3) method and a thin layer chromatography method. To compare these two methods, duplicate analyses were run on 45 urine samples with levels of PNP (measured by Elliott) ranging from 0.10 to 11.3 p.p.m. In both methods the urine was hydrolyzed with concentrated hydrochloric acid and heated. The benzene-ethyl ether extracts were made and either tested as described by Elliott (3) or evaporated, resuspended in ether, and applied to silica gel plates for chromatographic separation. Kidney concentrations were obtained from a weighed, hydrolyzed, benzene-ethyl ether extract of homogenized kidney (5 to 10 grams) and treated by the Elliott procedure (3) for urinary assay. 

Product inhibition by p-nitrophenol has been reported in transglycosylation reactions [17, 18]. This was minimised by diluting p-nitrophenol concentration by using larger volumes of solvent in reactions. 

To confirm the turnover of a catalyst, substrate must be added in large excess to the catalyst. Variation of p-nitrophenol concentration with time in the hydrolysis of p-nitrophenyl acetate under this condition ([substrate] >> [catalyst]) is shown in Figure 1. It shows that after reaction for 5 hours 3-CD hydrolyzed p-nitrophenyl acetate only 1/4 molar quantity of the catalyst, but 3-CD-histamine acted more than 4 times. After the reaction for 24 hours, 3-CD-histamine was separated from the substrate and products by HPLC, and this recovered catalyst reacted at the same rate as the original catalyst. This result reveals that the catalyst is not modified by p-nitrophenol or p-nitrophenyl acetate. Under this condition [S] >> [E], the deacylation of acetyl-catalyst is the rate-determing step for hydrolysis of p-nitrophenyl acetate (scheme 1). In the case of 3-CD, the rate constant of deacylation (k )... 

Figure 1. Variation of p-nitrophenol concentration with time in the hydrolysis of p-nitrophenyl acetate. [E] = 1.0 x 10 5 M, [S] = 1.0 x 10-3 M.

Blood Cholinesterase, Serum Para-thion Concentrations, and Urine p-Nitrophenol Concentrations in Exposed Individuals Bull. Environ. Contam. Toxicol. 4(6) 362-369 (1969) CA 72 77892m... 

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].

The operation of the nitronium ion in these media was later proved conclusively. "- The rates of nitration of 2-phenylethanesulphonate anion ([Aromatic] < c. 0-5 mol l i), toluene-(U-sulphonate anion, p-nitrophenol, A(-methyl-2,4-dinitroaniline and A(-methyl-iV,2,4-trinitro-aniline in aqueous solutions of nitric acid depend on the first power of the concentration of the aromatic. The dependence on acidity of the rate of 0-exchange between nitric acid and water was measured, " and formal first-order rate constants for oxygen exchange were defined by dividing the rates of exchange by the concentration of water. Comparison of these constants with the corresponding results for the reactions of the aromatic compounds yielded the scale of relative reactivities sho-wn in table 2.1. 

Chloroanisole and p-nitrophenol, the nitrations of which are susceptible to positive catalysis by nitrous acid, but from which the products are not prone to the oxidation which leads to autocatalysis, were the subjects of a more detailed investigation. With high concentrations of nitric acid and low concentrations of nitrous acid in acetic acid, jp-chloroanisole underwent nitration according to a zeroth-order rate law. The rate was repressed by the addition of a small concentration of nitrous acid according to the usual law rate = AQ(n-a[HN02]atoioh) -The nitration of p-nitrophenol under comparable conditions did not accord to a simple kinetic law, but nitrous acid was shown to anticatalyse the reaction. 

The procedure of simultaneous extracting-spectrophotometric determination of nitrophenols in wastewater is proposed on the example of the analysis of mixtures of mono-, di-, and trinitrophenols. The procedure consists of extraction concentrating in an acid medium, and sequential back-extractions under various pH. Such procedures give possibility for isolation o-, m-, p-nitrophenols, a-, P-, y-dinitrophenols and trinitrophenol in separate groups. Simultaneous determination is carried out by summary light-absorption of nitrophenol-ions. The error of determination concentrations on maximum contaminant level in natural waters doesn t exceed 10%. The peculiarities of application of the sequential extractions under fixed pH were studied on the example of mixture of simplest phenols (phenol, o-, m-, />-cresols). The procedure of their determination is based on the extraction to carbon tetrachloride, subsequent back-extraction and spectrophotometric measurement of interaction products with diazo-p-nitroaniline. 

Fig. 5a and b. a Plots of kobrf m. concentration of CTAB for the release of p-nitrophenol from 1. b Plots of kobs[Pg.158]

Fig. 12. Plots of pseudo-first-order rate constants for the release of p-nitrophenol from L-52 and D-52 as a function of zinc ion concentration. See Table 9 for other conditions...

The antibody solution (1.6x10 M) and substrate solutions with various concentration from 10 M to 10 M were mixed on a BSA-coated plate. The mixed solution of antibodies and substrates was allowed to stand for 1 day at room temperature, and then transported to the ELISA plates pre-coated with BSA-hapten and BSA blocking buffer. Absorbance at 405 nm for the resulting enzymatic hydrolysis product (p-nitrophenolate) by alkalinephosphatase of the second antibody was recorded on an Immuno-Mini NJ-2300 to determine the amount of antibody bound to BSA-hapten. 

Rubin HE, M Alexander (1983) Effect of nutrients on the rates of mineralization of trace concentrations of phenol and p-nitrophenol. Environ Sci Technol 17 104-107. 

Hemoglobin is another heme-containing protein, which has been shown to be active towards PAH, oxidation in presence of peroxide [420], This protein was also modified via PEG and methyl esterification to obtain a more hydrophobic protein with altered activity and substrate specificity. The modified protein had four times the catalytic efficiency than that of the unmodified protein for pyrene oxidation. Several PAHs were also oxidized including acenaphthene, anthracene, azulene, benzo(a)pyrene, fluoranthene, fluorene, and phenanthrene however, no reaction was observed with chrysene and biphenyl. Modification of hemoglobin with p-nitrophenol and p-aminophenol has also been reported [425], The modification was reported to enhance the substrate affinity up to 30 times. Additionally, the solvent concentration at which the enzyme showed maximum activity was also higher. Both the effects were attributed to the increase in hydrophobicity of the active site. 

The / -glucosidase activity was determined by measuring the release of p-nitrophenol from p-nitrophenyl-/i-D-glucopyranoside one unit of / -glucosidase activity (U) is defined as the amount of enzyme that releases 1 [mu] mol p-nitrophenol per minute. AU samples were assayed in potassium phosphate buffer (50 mM, pH 7.0) at 50 °C under conditions that activity was proportional to enzyme concentration. 

N-Carbobenzoxy-L-alanine-/>-nitrophenyl ester is a specific substrate for elastase in which the rate-limiting step is deacylation, that is, hydrolysis of the acyl-enzyme intermediate. In 70% methanol over a reasonable temperature range the energy of activation of the turnover reaction, that is, deacylation, is 15.4 kcal mol. In the pH 6-7 region in this cryoprotective solvent, the turnover reacdon can be made negligibly slow at temperatures of -50 C or below. Under such conditions/i-nitro-phenol is released concurrent to acyl enzyme formation in a 1 1 stoichiometry with active enzyme in the presence of excess substrate. In other words, even at low temperatures, the acylation rate is much faster than deacylation and the acyl enzyme will accumulate on the enzyme. The rate of acyl-enzyme formation can be monitored by following the rate of p-nitrophenol release, and thus the concentration of trapped acyl enzyme may be determined. This calculadon has been carried out and... 

Calculate the concentration of p-nitrophenolate ion produced using molar absorbtivity of 1.78 x lOVM/cm. 

Hydrolysis of parathion in a loessial semiarid soil was investigated by Nelson et al. (1982). They found that Arthrohacter sp. hydrolyzed parathion rapidly in sterilized, parathion-treated soil under aerobic conditions (20% w/w water content). This bacterium was isolated from a silty loam, sierozem soil of loessial semiarid origin (Gilat). It uses parathion or its hydrolysis product, p-nitrophenol, as the sole carbon source. However, when parathion hydrolysis causes the amount of p-nitrophenol to reach a concentration greater than 1 mM or if the concentration is greater than 1 mM in the case of a single application of p-nitrophenol, the hydrolysis product becomes noxious to the bacteria and their growth is inhibited. 

Figure 1. Pseudo-first-order kinetic plot of - n(A -Ao)/ A -Ag) versus time for production of p-nitrophenolate from reaction of sodium perborate at various concentrations with EPMP at 27.5 oc, pH = 8.

In determining enzyme activities, it is usually assumed that at a fixed set of so-called saturating substrate concentrations a sufficiently accurate value of F, ax is obtained. Bisubstrate kinetic analyses of UDP-glucu-ronyltransferase [assayed with bilirubin (P5) and p-nitrophenol (V6), respectively] indicate that a true measure of the amount of enzyme can be obtained only by suitable extrapolation procedures. This restriction applies in particular to bilirubin (A2, HIO, T8) and other aglycons (M15, V6) because of substrate inhibition. UDP-glucuronic acid was inhibitory at concentrations only about 10-fold higher than the apparent Km value (HIO) this was most pronounced at relatively short incubation times. Mg was noninhibitory at concentrations equal to 20 times the apparent Km values (F3, HIO). 

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