P-nitrophenyl caproate

Fig. 6. Hydrolysis of p-nitrophenyl caproate at pH 7.2, 25°C (O) lauroyl, histidyl ghosts ( ) lauroyl ghosts ( ) imidazole ( ) background.

Cleavage of p-nitrophenyl caproate [(3)] was followed by the appearance of p-nitrophenolate ion, as detected by increased absorbance at... 

Fig. 6. Rates of esterolysis of p-nitrophenyl caproate at pH7.3 and 25°C in presence of a derivative of polyethylenimine (PEI-600) containing 10% of its residues alkylated with dodecyl groups and 15% alkylated with methyleneimidazole substituents. The numbers shown adjacent to each curve are the residue molar concentrations of imidazole groups in solution. Initial concentration of substrate was 1 x 10-4M.

Several additional features of the model are noteworthy. First, it is possible to build it without straining chemical bonds or causing unfavorable steric interactions. The polyamine chain is sufficiently long to reach around a cluster, but it is not so long or so bulky as to cause excessive crowding near the surface of the cluster. The spaces at this surface between the polyamine chains (Fig. 11) are likely binding sites for small apolar molecules, since such molecules can be bound at the interface or partially penetrate into the domain of the hydrocarbon sphere in response to favorable apolar interactions. In the model shown in Fig. 11, three bound p-nitrophenyl caproate molecules have also been included to illustrate possible modes of binding. An arrow points to one of these small molecules. 

Amine p-Nitrophenyl acetate p-Nitrophenyl caproate p-Nitrophenyl laurate... 

Figure 3.3 Rate (second order)-pH profile for hydrolysis of p-nitrophenyl caproate in aqueous solution at 25 °C by...

Table 6-1. Reaction of p-nitrophenyl caproate with polyethyleneimine derivatives ...

The polymer was 10 times as effective as a small-molecule analog, dimethy-benzylamine 10 in the case of p-nitrophenyl caproate 6. The rate enhancement is larply attributed to favorable binding. No difference in catalytic activity was found between linear and branched polyethyleneimine derivatives. It is curious that desorption of the product is rate-limiting according to the kinetic analysis. 

PEI derivatives.(21-24) A series of substituted aminopyridines, covalently attached to laurylated PEI, hydrolyzed p-nitrophenyl-caproate (Sg) 50-2000 times faster than the isolated aminopyridines. The aminopyridines are better nucleophiles than imidazole due to their higher pKa values. (25) Klotz intends to produce stereoselective PEI catalysts by coupling optically active amino acids to the aminopyridine nucleophile.(26 27)... 

The rate of p-nitrophenyl caproate hydrolysis by modified PEI, containing imidazole groups in the presence of metal ions, increased in the sequence Mn, Ni, Zn, Co , Cu [92], Among the selected metals, a copper complex was shown to be most effective, the maximum rate being achieved at a [imidazole]/[copper] ratio of 2.75. 

Esterase activity was measured as an increase in absorbance at 420 nm caused by the cleavage of ester bonds in p-nitrophenyl caproate (PNP), releasing p-nitrophenol The reaction mixture contained 0 5 ml of enzyme, 1 75 ml cholate buffer (as above) and 0 25 ml 5 niM PNP (in cholate buffer) Absorbance was recorded very 30 seconds for 5 min and... 

Rates of hydrolysis of p-nitrophenyl esters of alkanecarboxylic acids in the pH range 12-92 increased with chain length up to 27 times faster for the dodecanoic ester with soluble polymeric catalyst (56) than with 4-(l-pyrrolidinyl)pyridine as catalyst.Enhanced activity is attributed to the lower pX (7.8) of the conjugate acid of the polymer than of the soluble analogue pK 10.5), and to attraction of the lipophilic substrate to the polymer in an aqueous solution. Catalyst (57) bound to poly(ethyleneimine) was 2000 times more active than its monomeric analogue for hydrolysis of p-nitrophenyl caproate at pH 7.3. ... 

Hydrolysis of p-Nitrophenyl Caproate by Laurylated Polyethyleneimine with Imidazole Groups in the Presence of Cu(ll) Ion... 

If an amine P-NH2 is used in the aqueous solution, one obtains RCONHP instead of RCOOH. Rates of cleavage of three acyl nitrophenyl esters were followed by the appearance of p-nitrophenolate ion as reflected by increased absorbances at 400 nm. The reaction was carried out at pH 9.0, in 0.02 M tris(hydroxymethyl)aminomethane buffer, at 25°C. Rate constants were determined from measurements under pseudo-first-order conditions, with the residue molarity of primary amine present in approximately tenfold excess. First-order rate graphs were linear for at least 80% of the reaction. With nitrophenyl acetate and nitrophenyl caproate, the initial ester concentration was 6.66xlO 5M. With nitrophenyl laur-ate at this concentration, aminolysis by polymer was too fast to follow and, therefore, both substrate and amine were diluted tenfold for rate measurements. 

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