Structure—activity relationships for chloro- and nitrophenol toxicity in the pollen tube growth test

✍ Scribed by Gerrit Schüürmann; Rayasamuda K. Somashekar; Udo Kristen

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 88 KB
• Volume: 15
• Category: Article
• ISSN: 0730-7268
• DOI: 10.1002/etc.5620151008

✦ Synopsis

Acute toxicity of 10 chlorophenols and 10 nitrophenols with identical substitution patterns is analyzed with the pollen tube growth (PTG) test. Concentration values of 50% growth inhibition (IC50) between 0.1 and 300 mg/L indicate that the absolute sensitivity of this alternative biotest is comparable to conventional aquatic test systems. Analysis of quantitative structure-activity relationships using lipophilicity (log K ow ), acidity (pK a ), and quantum chemical parameters to model intrinsic acidity, solvation interactions, and nucleophilicity reveals substantial differences between the intraseries trends of log IC50. With chlorophenols, a narcotictype relationship is derived, which, however, shows marked differences in slope and intercept when compared to reference regression equations for polar narcosis. Regression analysis of nitrophenol toxicity suggests interpretation in terms of two modes of action: oxidative uncoupling activity is associated with a pK a window from 3.8 to 8.5, and more acidic congeners with diortho-substitution show a transition from uncoupling to a narcotic mode of action with decreasing pK a and log K ow . Model calculations for phenol nucleophilicity suggest that differences in the phenol readiness for glucuronic acid conjugation as a major phase-II detoxication pathway have no direct influence on acute PTG toxicity of the compounds.