title: Kober reaction kinetics and their influence on the design of assays for oestrogens in urine during pregnancy.
abstract: 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.
mesh_terms: 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
chemical_list: D004967:Estrogens; D006894:Hydroxyestrones; D007202:Indicators and Reagents; D004970:Estrone; D004958:Estradiol; C003599:16-ketoestradiol; D004964:Estriol