Metal ion catalyzed hydrolysis of ethyl p-nitrophenyl phosphate
15N isotope effects in the nitro group and 18O isotope effects in the phenolic oxygen have been measured for the hydrolysis of ethyl p-nitrophenyl phosphate catalyzed by several metal ions. Co(III)–cyclen at pH 7, 50 °C, gave an 15N isotope effect of 0.12% and an 18O one of 2.23%, showing that P–O c...
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Veröffentlicht in: | Journal of inorganic biochemistry 2003, Vol.93 (1), p.61-65 |
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Sprache: | eng |
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Zusammenfassung: | 15N isotope effects in the nitro group and
18O isotope effects in the phenolic oxygen have been measured for the hydrolysis of ethyl
p-nitrophenyl phosphate catalyzed by several metal ions. Co(III)–cyclen at pH 7, 50
°C, gave an
15N isotope effect of 0.12% and an
18O one of 2.23%, showing that P–O cleavage is rate limiting and the bond is ∼50% broken in the transition state. The active catalyst is a dimer and the substrate is presumably coordinated to the open site of one Co(III), and is attacked by hydroxide coordinated to the other Co(III). Co(III)–tacn under the same conditions shows a similar
15N isotope effect (0.13%), but a smaller
18O one (0.8%). Zn(II)–cyclen at pH 8.5, 80
°C, gave an
15N isotope effect of 0.05% and an
18O one of 0.95%, suggesting an earlier transition state. The catalyst in this case is monomeric, and thus the substrate is coordinated to one position and attacked by a
cis-coordinated hydroxide. Eu(III) at pH 6.5, 50
°C, shows a very large
15N isotope effect of 0.34% and a 1.6%
18O isotope effect. The large
15N isotope effect argues for a late transition state or Eu(III) interaction with the nitro group, and was also seen in Eu(III)-catalyzed hydrolysis of
p-nitrophenyl phosphate [Bioorg. Chem. 28 (2000) 283]. |
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ISSN: | 0162-0134 1873-3344 |
DOI: | 10.1016/S0162-0134(02)00435-X |