Quantitative Structure Activity Relationship (QSAR)

We can understand a lot about how a molecule is going to behave from its structure. For example, small molecules containing from one to four carbon atoms are gases at room temperature (methane CH4, ethane C2H6, propane C3H8, butane C4H10). As more carbons are added, the substance becomes a liquid (hexane, a liquid, has six carbon atoms, C6H14) and finally a solid (octadecane, a solid, C18H38).

If we add one oxygen atom to methane (CH4), the molecule formed is a liquid we know as methanol (CH3OH). As we add chlorine atoms, nitrogen atoms or any other atom, we can predict the effect these additions will have on the molecule's behaviour. This behaviour is not limited to predicting whether the molecule is a solid, liquid or gas, but includes predicting how toxic or biodegradable the compound will be.

This field of science combines mathematics and chemistry and is called computational chemistry. It deals with finding relationships called Quantitative Structure Property Relationships (QSPRs) or Quantitative Structure Activity Relationships (QSARs).

The tools and approaches used to generate a QSPR and a QSAR are similar. Which one the scientist uses just depends on whether they are predicting a chemical property like solubility in water or a chemical activity like toxicity to algae or even humans. Scientists use this information to predict where a chemical goes in the environment (see Fate pages) or the toxicity of a chemical. Since QSARs and QSPRs are equations that help to predict fate or effect values from chemical structure, they are quick and inexpensive to use.

Fate and effects work at P&G uses a step-wise or tiered approach, beginning with screening level tools for an initial assessment. More sophisticated tools are used as needed. These different tiers allow P&G to eliminate compounds that will never make it to market for environmental or human health reasons, and to quickly identify less toxic, more rapidly degradable compounds. Ideally, we would like to eliminate problem compounds before much time and money are spent on research and development. QSARs and QSPRs are tier 1 tools and allow us to understand basic properties, such as toxicity, fate and biodegradability, before any data are generated in the laboratory. From the toxicity, fate and biodegradation  information, we are able to estimate exposure and risk to humans and the environment.

• Cronin, M., Jaworska, J., Walker, J., Comber, M., and Watts. C. Use Of QSARs in International Decision-Making Frameworks to Predict Ecological Effects and Environmental Fate of Chemical Substances. Environmental Health Perspectives, in Press.
• Dyer, S.D., Lauth, J.R., Morrall, S.W., Herzog, R.R., and Cherry, D.S., 1997. Development of a Chronic Toxicity Structure-Activity Relationship for Alkyl Sulfates. Environmental Toxicology and Water Quality, 12, pp. 295-303.
• Dyer, S.D., Stanton, D.T., Lauth, J.R., and Cherry, D.S., 2000. Acute and Chronic Structure Activity Relationships for Alcohol Ethersulfates. Environmental Toxicology and Chemistry, 19, pp. 608-616.
• Jaworska, J., Dimitrov, S., Nikolova, N., and Mekenyan, O., 2002. Chemical Biodegradability. Probabilistic Prediction Based on a Metabolic Pathway. SAR and QSAR in Environmental. Research, 13, pp. 307-323.
• Jaworska, J., Dimitrov, S., Nikolova, N., and Mekenyan, O., 2002. Chemical Biodegradability. Probabilistic Prediction Based on a Metabolic Pathway. SAR and QSAR in Environmental. Research, 13, pp. 307-323.
• Jaworska, J., Howard, P., and Boethling, R.S., 2003. Quantitative Structure Biodegradadation Relationships - A Review. Environmental Toxicology and Chemistry, in Press.
• Morrall, D.D., Belanger, S.E., and Dunphy, J.C. Acute and Chronic Aquatic Toxicity Structure-Activity Relationships for Alcohol Ethoxylates. Ecotoxicology and Environmental Safety, in Press.
• Morrall, S.M., Rosen, M.J., Zhu, Y., Versteeg, D.J., and Dyer, S.D., 1997. Physicochemical Descriptors for Development of Aquatic Toxicity QSARs for Surfactants. In Chen, F. and Schuurmann, G. (Eds.), QSAR '96, 7th International Workshop on QSARs in Environmental Sciences. SETAC Press, Pensacola, FL, pp. 299-313.
• Rosen, M.J., Li, F., Morrall, S.M., and Versteeg, D.J., 2001. The Relationship between the Interfacial Properties of Surfactants and Their Toxicity to Aquatic Organisms. Environmental Science and Technology, 35, pp. 954-959.
• Versteeg, D.J., Stanton, D.T., Pence, M.A., and Cowan, C.E., 1997. Effects of Surfactants on the Rotifer, Brachionus Calyciflorus, in a Chronic Toxicity Test and the Development of QSARs. Environmental Toxicology and Chemistry, 16, pp. 1051-1058.