Copyright©2008 Antony Williams
The Environmental Protection Agency has provided permission for ChemSpider to utilize their EPI SuiteTM software to predict a number of physical properties for the chemicals on the ChemSpider database. The properties include:
• KOWWIN™: Estimates the log octanol-water partition coefficient, log KOW, of chemicals using an atom/fragment contribution method.
• AOPWIN™: Estimates the gas-phase reaction rate for the reaction between the most prevalent atmospheric oxidant, hydroxyl radicals, and a chemical. Gas-phase ozone radical reaction rates are also estimated for olefins and acetylenes. In addition, AOPWIN™ informs the user if nitrate radical reaction will be important. Atmospheric half-lives for each chemical are automatically calculated using assumed average hydroxyl radical and ozone concentrations.
• HENRYWIN™: Calculates the Henry’s Law constant (air/water partition coefficient) using both the group contribution and the bond contribution methods.
• MPBPWIN™: Melting point, boiling point, and vapor pressure of organic chemicals are estimated using a combination of techniques. Included is the subcooled liquid vapor presssure, which is the vapor pressure a solid would have if it were liquid at room temperature. It is important in fate modeling.
• BIOWIN™: Estimates aerobic and anaerobic biodegradability of organic chemicals using 7 different models; two of these are the original Biodegradation Probability Program (BPP™). The seventh and newest model estimates anaerobic biodegradation potential.
• BioHCWIN: Estimates biodegradation half-life for compounds containing only carbon and hydrogen (i.e. hydrocarbons).
• PCKOCWIN™: The ability of a chemical to sorb to soil and sediment, its soil adsorption coefficient (Koc), is estimated by this program. EPI’s Koc estimations are based on the Sabljic molecular connectivity method with improved correction factors.
• WSKOWWIN™: Estimates an octanol-water partition coefficient using the algorithms in the KOWWIN™ program and estimates a chemical’s water solubility from this value. This method uses correction factors to modify the water solubility estimate based on regression against log Kow.
• WATERNT™: Estimates water solubility directly using a “fragment constant” method similar to that used in the KOWWIN™ model.
• HYDROWIN™: Acid- and base-catalyzed hydrolysis constants for specific organic classes are estimated by HYDROWIN™. A chemical’s hydrolytic half-life under typical environmental conditions is also determined. Neutral hydrolysis rates are currently not estimated.
• BCFWIN™: This program calculates the BioConcentration Factor and its logarithm from the log Kow. The methodology is analogous to that for WSKOWWIN™. Both are based on log Kow and correction factors.
• KOAWIN: KOA is the octanol/air partition coefficient and has multiple uses in chemical assessment. The model estimates KOA using the ratio of the octanol/water partition coefficient (KOW) from KOWWIN™, and the dimensionless Henry’s Law constant (KAW) from HENRYWIN™. • AEROWIN™: Estimates the fraction of airborne substance sorbed to airborne particulates, i.e. the parameter phi (φ), using three different methods. AEROWIN™ results are also displayed with AOPWIN™ output as an aid in interpretation of the latter.
• WVOLWIN™: Estimates the rate of volatilization of a chemical from rivers and lakes; calculates the half-life for these two processes from their rates. The model makes certain default assumptions-water body depth; wind velocity; etc.
• STPWIN™: Using several outputs from EPI Suite™, this program predicts the removal of a chemical in a Sewage Treatment Plant; values are given for the total removal and three contributing processes (biodegradation, sorption to sludge, and stripping to air.) for a standard system and set of operating conditions.
• LEV3EPI™: This level III fugacity model predicts partitioning of chemicals between air, soil, sediment, and water under steady state conditions for a default model “environment”; various defaults can be changed by the user.
The values for individual structures are available in the Record View under the EPI Summary.
For example, the information for Xanax is below.
Log Octanol-Water Partition Coef (SRC): Log Kow (KOWWIN v1.67 estimate) = 3.87 Log Kow (Exper. database match) = 2.12 Exper. Ref: BioByte (1995) Boiling Pt, Melting Pt, Vapor Pressure Estimations (MPBPWIN v1.42): Boiling Pt (deg C): 441.81 (Adapted Stein & Brown method) Melting Pt (deg C): 185.42 (Mean or Weighted MP) VP(mm Hg,25 deg C): 1.65E-008 (Modified Grain method) Subcooled liquid VP: 7.84E-007 mm Hg (25 deg C, Mod-Grain method) Water Solubility Estimate from Log Kow (WSKOW v1.41): Water Solubility at 25 deg C (mg/L): 13.1 log Kow used: 2.12 (expkow database) no-melting pt equation used Water Sol Estimate from Fragments: Wat Sol (v1.01 est) = 0.15855 mg/L ECOSAR Class Program (ECOSAR v0.99h): Class(es) found: Aliphatic Amines Henrys Law Constant (25 deg C) [HENRYWIN v3.10]: Bond Method : 9.77E-012 atm-m3/mole Group Method: Incomplete Henrys LC [VP/WSol estimate using EPI values]: 5.117E-010 atm-m3/mole Log Octanol-Air Partition Coefficient (25 deg C) [KOAWIN v1.10]: Log Kow used: 2.12 (exp database) Log Kaw used: -9.399 (HenryWin est) Log Koa (KOAWIN v1.10 estimate): 11.519 Log Koa (experimental database): None Probability of Rapid Biodegradation (BIOWIN v4.10): Biowin1 (Linear Model) : 0.6009 Biowin2 (Non-Linear Model) : 0.2660 Expert Survey Biodegradation Results: Biowin3 (Ultimate Survey Model): 2.2574 (weeks-months) Biowin4 (Primary Survey Model) : 3.1733 (weeks ) MITI Biodegradation Probability: Biowin5 (MITI Linear Model) : -0.1488 Biowin6 (MITI Non-Linear Model): 0.0042 Anaerobic Biodegradation Probability: Biowin7 (Anaerobic Linear Model): -0.4906 Ready Biodegradability Prediction: NO Hydrocarbon Biodegradation (BioHCwin v1.01): Structure incompatible with current estimation method! Sorption to aerosols (25 Dec C)[AEROWIN v1.00]: Vapor pressure (liquid/subcooled): 0.000105 Pa (7.84E-007 mm Hg) Log Koa (Koawin est ): 11.519 Kp (particle/gas partition coef. (m3/ug)): Mackay model : 0.0287 Octanol/air (Koa) model: 0.0811 Fraction sorbed to airborne particulates (phi): Junge-Pankow model : 0.509 Mackay model : 0.697 Octanol/air (Koa) model: 0.866 Atmospheric Oxidation (25 deg C) [AopWin v1.92]: Hydroxyl Radicals Reaction: OVERALL OH Rate Constant = 7.6246 E-12 cm3/molecule-sec Half-Life = 1.403 Days (12-hr day; 1.5E6 OH/cm3) Half-Life = 16.834 Hrs Ozone Reaction: No Ozone Reaction Estimation Fraction sorbed to airborne particulates (phi): 0.603 (Junge,Mackay) Note: the sorbed fraction may be resistant to atmospheric oxidation Soil Adsorption Coefficient (PCKOCWIN v1.66): Koc : 2.151E+006 Log Koc: 6.333 Aqueous Base/Acid-Catalyzed Hydrolysis (25 deg C) [HYDROWIN v1.67]: Rate constants can NOT be estimated for this structure! Bioaccumulation Estimates from Log Kow (BCFWIN v2.17): Log BCF from regression-based method = 0.932 (BCF = 8.559) log Kow used: 2.12 (expkow database) Volatilization from Water: Henry LC: 9.77E-012 atm-m3/mole (estimated by Bond SAR Method) Half-Life from Model River: 1.053E+008 hours (4.388E+006 days) Half-Life from Model Lake : 1.149E+009 hours (4.786E+007 days) Removal In Wastewater Treatment: Total removal: 2.37 percent Total biodegradation: 0.10 percent Total sludge adsorption: 2.27 percent Total to Air: 0.00 percent (using 10000 hr Bio P,A,S) Level III Fugacity Model: Mass Amount Half-Life Emissions (percent) (hr) (kg/hr) Air 0.000217 33.7 1000 Water 21 900 1000 Soil 78.9 1.8e+003 1000 Sediment 0.094 8.1e+003 0 Persistence Time: 1.48e+003 hr
We started the calculations a number of weeks ago and are updating our progress on the ChemSpider Forum here. We now have values predicted for 3 million compounds.
It is NOT possible at present to search on these properties in the same way that other properties can be searched on the Search Predicted Properties page as shown below.
After all EPI Suite properties are predicted we will selectively make some of these available for searching. The interest so far appears to be in Henry’s Law values, Water Solubility and Melting Point (something that is very difficult to predict with accuracy!). We welcome your comments.
We will be able to extract experimental values for some properties and display directly. For example, logP shows an “experimental database match” for Xanax.
Log Octanol-Water Partition Coef (SRC):
Log Kow (KOWWIN v1.67 estimate) = 3.87
Log Kow (Exper. database match) = 2.12
Exper. Ref: BioByte (1995)
It is going to take a number of weeks to generate EPI Suite values for 21.5 million molecules but we are moving in that direction. Our sincere thanks to the EPA for allowing us to use their EPI Suite software on ChemSpider for the benefit of the communityStumble it!