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Physical & Chemical properties

Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
May 2018
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a (Q)SAR model, with limited documentation / justification, but validity of model and reliability of prediction considered adequate based on a generally acknowledged source
Justification for type of information:
Results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification
Qualifier:
no guideline followed
Principles of method if other than guideline:
The US EPA EPI Suite v4.00 KOWWIN v1.68 model uses a "fragment constant" methodology to predict logarithm octanol-water partition coefficient (log Kow) property data.  In a "fragment constant" method, a structure is divided into fragments (atom or larger functional groups) and coefficient values of each fragment or group are summed together to yield the log Kow estimate.   KOWWIN’s methodology is known as an Atom/Fragment Contribution (AFC) method.  Coefficients for individual fragments and groups were derived by multiple regression of 2447 reliably measured log Kow values.  KOWWIN’s "reductionist" fragment constant methodology (i.e. derivation via multiple regression) differs from the "constructionist" fragment constant methodology of Hansch and Leo (1979) that is available in the CLOGP Program (Daylight, 1995).  See the Meylan and Howard (1995) journal article for a more complete description of KOWWIN’s methodology.

To estimate log Kow, the KOWWIN v1.68 model initially separates a molecule into distinct atom/fragments.  In general, each non-hydrogen atom (e.g. carbon, nitrogen, oxygen, sulfur, etc.) in a structure is a "core" for a fragment; the exact fragment is determined by what is connected to the atom.  Several functional groups are treated as core "atoms"; these include carbonyl (C=O), thiocarbonyl (C=S), nitro (-NO2), nitrate (ONO2), cyano (-C/N), and isothiocyanate (-N=C=S).  Connections to each core "atom" are either general or specific; specific connections take precedence over general connections.
GLP compliance:
no
Type of method:
other: calculation
Partition coefficient type:
octanol-water
Type:
log Pow
Partition coefficient:
7.73
Temp.:
20 °C
pH:
7
Conclusions:
Calcium Docusate Log Kow = 7.73
Executive summary:

According to EU method A.8 (2008), shake flask (OECD 107) and HPLC (OECD 117) experimen methods are "not applicable to surface active materials (for which a calculated value or an estimate based on the individual n-octanol and water solubilities should be provided)". Experimental data concerning the solubility of docusate calcium in water and n-octanol are not yet available so in the absence of this a log Kow value has been predicted using the US EPA EPI Suite v4.00 KOWWIN v1.68 software package.

CAS number 128-49-4 was used as input to the model to derive the predicted log Kow value

The predicted log Kow for docusate calcium was found to be 7.73

Description of key information

The predicted log Kow for docusate calcium was found to be 7.73.

However, given that the log Kow value for the structurally analagous monovalent docusate sodium salt was found to be 1.99 based on the ratio of it's solubility in n-octanol and water, the QSAR predicted value of 7.73 for the divalent docusate calcium salt appears to be rather high. Therefore, this value will be revised once experimental data is made available.

Key value for chemical safety assessment

Log Kow (Log Pow):
8.9
at the temperature of:
20 °C

Additional information

According to EU method A.8 (2008), shake flask (OECD 107) and HPLC (OECD 117) experimen methods are "not applicable to surface active materials (for which a calculated value or an estimate based on the individual n-octanol and water solubilities should be provided)". Experimental data concerning the solubility of docusate calcium in water and n-octanol are not yet available so in the absence of this a log Kow value has been predicted using the US EPA EPI Suite v4.00 KOWWIN v1.68 software package.

CAS number 128-49-4 was used as input to the model to derive the predicted log Kow value.

The predicted log Kow for docusate calcium was found to be 7.73

Given that the log Kow value for the structurally analagous monovalent docusate sodium salt was found to be 1.99 based on the ratio of it's solubility in n-octanol and water, the QSAR predicted value of 7.73 for the divalent docusate calcium salt appears to be rather high. Therefore, this value will be revised once experimental data is made available.