Kober reaction kinetics and their influence on the design of assays for oestrogens in urine during pregnancy.
Rates of reaction of different oestrogens in Kober reagent vary greatly. Rate constants were measured between 100 degrees C and 150 degrees C. Oestradiol, oestrone, 16-oxo-oestradiol, 16 alpha hydroxyoestrone, 16-epioestriol and urine pool show two sequential first order reactions at 100 degrees C; oestriol and its conjugates give a single reaction (slower than the other oestrogens except for the very slow oestretrol). Above 120 degrees C differences decrease, all oestrogens having one rate for Kober product formation: the decay reaction, which is also first order, becomes significant. Oestriol and its conjugates have relatively high apparent activation energies in the Kober reaction (120-138 kJmol-1) compared to other oestrogens studied (105-124 kJmol-1). The apparent activation energy for the decay reaction is the same within experimental error (115 +/- 3 kJmol-1). This is consistent with a common product formed from oestrogen reacting with Kober reagent. Analytical methods must respond similarly to major urinary oestrogens. Appropriate conditions include 100 degrees C for at least 20 min or 135 degrees C for 3 to 4 minutes.
D001322:Autoanalysis / Q000379:methods; D004958:Estradiol / Q000031:analogs & derivatives / Q000652:urine; D004964:Estriol / Q000652:urine; D004967:Estrogens / Q000652:urine*; D004970:Estrone / Q000652:urine; D005260:Female; D006358:Hot Temperature; D006801:Humans; D006894:Hydroxyestrones / Q000652:urine; D007202:Indicators and Reagents; D007700:Kinetics; D011247:Pregnancy; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D013816:Thermodynamics
D004967:Estrogens; D006894:Hydroxyestrones; D007202:Indicators and Reagents; D004970:Estrone; D004958:Estradiol; C003599:16-ketoestradiol; D004964:Estriol