Biodegradability of Urea-Aldehyde Condensation Products

Condensation products of urea and different aldehydes (formaldehyde, isobutyraldehyde, crotonaldehyde) are used in large amounts (more than 300,000 tons per year) as resins, binders, and insulating materials for industrial applications, as well as in controlled-release nitrogen fertilizer for greens, lawns, or bioremediation processes. The biodegradability of these condensates and the enzymic mechanism of their degradation was studied in mircoorganisms isolated from soil, which were able to use these compounds as the sole source of nitrogen for growth. Different pure cultures of both gram-positive and gram-negative bacteria completely degraded methylenediurea, dimethylenetriurea, isobutylidenediurea, and crotonylidenediurea to urea, ammonia, and the corresponding aldehydes and carbon dioxide. Enzymes initiating this degradation were purified and characterized and turned out to be different with regard to their regulation of expression, their physicobiochemical properties, and their reaction mechanism.     

Ecotoxicology of narcosis: stereoselectivity and potential target sites

The stereoselectivity of certain anesthetics is currently thought to be inconsistent with lipid theories of narcosis. The EC50-values of etomidate enantiomers for tadpole narcosis are now examined as a function of octanol/water partition coefficients, and enhancement factors for predicted over experimental EC50 values are determined from a calibration curve for non-selective narcosis. The unfavored S-(-)-enantiomers of etomidate and two analogues surprisingly still fulfill the Meyer-Overton rule. The R+-enantiomers of etomidate and four structural analogues are up to 34-fold more active than expected. The non-chiral anesthetic, propofol, is 8-fold more active than expected. It is concluded that there may be two pathways to tadpole narcosis: enhanced narcosis involving specific receptor binding sites and non-selective narcosis corresponding to the Meyer-Overton rule and operating on the lipid/protein interface.