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Partition coefficient

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Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification
Remarks:
Prediction method using model KOWWIN v.1.67a (September 2008) validated with other measured values for related biphenyl structures.
Justification for type of information:
1. SOFTWARE
KOWWIN

2. MODEL (incl. version number)
KOWWIN v1.68 (EPISUITE 4.1 version developed by EPA’s Office of Pollution Prevention Toxics and Syracuse Research Corporation)

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
Oc(ccc(c(ccc(O)c1)c1)c2)c2

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: yes, 1.6. Octanol-water partition coefficient (Kow)
- Unambiguous algorithm: yes; ‘KOWWIN’ estimates the partition coefficient using a fragment contribution method. The structure is divided into fragments. Then the coefficient values of each fragment or group are summed together in order to estimate the partition coefficient.
- Defined domain of applicability: yes, see 'Accuracy & Domain' section in KOWWIN Help user guide
- Appropriate measures of goodness-of-fit and robustness and predictivity: yes, see 'Accuracy & Domain' section in KOWWIN Help user guide
- Mechanistic interpretation: The descriptors used are small functional group. The partition coefficient is in function of the hydrophilic and lipophilic affinity of atoms and bounding between atoms. Depending on the nature of the functional group (nature of the atoms and the type of bounding), its log Kow is estimated. Then log Kow of the substance is obtained by the sum of the Log KOW of each functional group and correction factor is needed.

5. APPLICABILITY DOMAIN
- Descriptor domain: KOWWIN allows the calculation of partition coefficient for a large type of organic substances
- Structural and mechanistic domains: no
- Similarity with analogues in the training set: yes

6. ADEQUACY OF THE RESULT
KOWWIN calculate the log of partition coefficient. This physico-chemical parameter is used to estimate the potential for bioaccumulation and for biomagnification in the tissues of organisms of successive levels of aquatic and terrestrial food chains. 
Principles of method if other than guideline:
The prediction of log Kow for biphenyl-4,4‘-diol was performed using the model KOWWIN v.1.67a (September 2008), which was developed by the Syracuse Research Corporation and is available from the US EPA as part of a collection of estimation programs collectively called EPI (Estimation Programme Interface) SuiteTM (Ref. 1). The intended application domain of EPI Suite is organic chemicals. The KOWWIN program estimates the log octanol/water partition coefficient of organic chemicals using an atom/fragment contribution method described by Meylan and Howard (1995).
GLP compliance:
no
Type of method:
calculation method (fragments)
Remarks:
Prediction performed using the model KOWWIN v.1.67a (September 2008).
Partition coefficient type:
octanol-water
Key result
Type:
log Pow
Partition coefficient:
2.8
Temp.:
25 °C
Remarks on result:
other: pH value not specified

The predicted log Kowvalue for biphenyl-4,4‘-diol is presented in the table below. 

Input chemical name

Predicted log Kow

Biphenyl-4,4‘-diol
(1,1‘-biphenyl -4,4‘-diol);
SMILES notation: Oc(ccc(c(ccc(O)c1)c1)c2)c2

2.80

 

No measured log Kowvalue for biphenyl-4,4‘-diol was available from the database used in the construction of the model. 

However, log Kowvalues measured for various other, related phenol and biphenyl structures are included in the KOWWIN database and can be used to validate the model prediction for biphenyl‑4,4‑diol. The KOWWIN predictions and the corresponding measured log Kowheld in the model database for these substances are presented in the table below. 

Chemical name,
input SMILES notation

Log Kow

KOWWIN-predicted

Measured

Benzene (CAS # 71-43-2)
c1ccccc1

1.99

2.13a

Phenol (CAS # 108-95-2)
c1(O)ccccc1

1.51

1.46a

Catechol (CAS # 120-80-9)
c1(O)c(O)cccc1

1.03

0.88a

Resorcinol (CAS # 108-46-3)
c1(O)cc(O)ccc1

1.03

0.80a

Hydroquinone (CAS # 123-31-9)
c1(O)ccc(O)cc1

1.03

0.59a

1,3,5-Trihydroxybenzene (CAS # 108-73-6)
c1(O)cc(O)cc(O)cc(O)c1

0.55

0.16a

Biphenyl (92-52-4)
c1ccc(c2ccccc2)cc1

3.76

3.98b

p‑Phenylphenol (CAS # 92-69-3)
c1ccc(c2ccc(O)cc2)cc1

3.28

3.20a

2‑Phenylphenol (CAS # 90-43-7)
c1ccc(c2c(O)cccc2)cc1

3.28

3.09a

3‑Phenylphenol (CAS # 580-51-8)
c1ccc(c2cc(O)ccc2)cc1

3.28

3.23a

a              Attributed to Hanschet al. (1995). [Citation: Hansch, C., Leo, A. and Hoekman, D. (1995). Exploring QSAR. Hydrophobic, Electronic andSteric constants. ACS Professsional Reference Book. Washington DC: American Chemical Society]. 

b              Attributed to Sangster (1993). [Citation: Sangster, J. (1993). LOGKOW Databank. A databank of evaluated octanol-water partition coefficients (Log P) on microcomputer diskette. Montreal, Quebec, Canada: Sangster Research Laboratories]. 

 

The measured values above indicate a consistent pattern whereby the log Kowof the basic phenyl structure (i.e. benzene, biphenyl) is lowered by the attachment of –OH substituents. The higher the number of –OH substituents, the larger the reduction in log Kow, indicating that the attachment of –OH groups confers enhanced water solubility relative to solubility in n‑octanol. 

Considering biphenyl and the mono-substituted biphenyls - which are most closely related in structure to biphenyl‑4,4‘‑diol - the following comparisons can be made between the measured and predicted log Kowvalues:

  • predicted and measured values are in good agreement and differ by only between 0.05 and 0.22 log units;
  • the predicted log Kowvalues for –OH substituted benzene and biphenyl are consistently higher than the corresponding measured values;
  • the measured log Kowvalues range from 3.98 for biphenyl to 3.09 for 2‑phenylphenol;
  • there are small differences between the measured log Kowvalues for the three mono-substituted biphenyls, however KOWWIN makes no allowance for the position of the –OH substitution. 

No measured log Kowvalues were found in the KOWWIN database for any bi-substituted biphenyls. However, based on the trends noted above, the presence of a single –OH substituent on both phenyl rings of the biphenyl‑4,4’‑diol structure would be expected to reduce its log Kowbelow the experimentally-determined values recorded for biphenyl and all of the three mono-phenol derivatives of biphenyl. 

The KOWWIN-predicted log Kowof 2.80 for biphenyl‑4,4’‑diol is consistent with this expectation.

Conclusions:
KOWWIN predicts a log Kow value of 2.80 for biphenyl-4,4‘-diol.
Executive summary:

KOWWIN predicts a log Kowvalue of 2.80 for biphenyl-4,4‘-diol. 

The log Kowvalue predicted for biphenyl-4,4‘-diol is consistent with measured values for other, related structures that were included in the database used to construct the KOWWIN model. The KOWWIN-predicted log Kowof 2.80 for biphenyl‑4,4’‑diol is likely to error on the side of over- rather than under-estimation. 

The log Kowvalue predicted for biphenyl‑4,4‘‑diol lies below the threshold of 3.00 which triggers the requirement to determine bioconcentration in fish experimentally, and indicates a negligible potential for bioaccumulation and for biomagnification in the tissues of organisms of successive levels of aquatic and terrestrial food chains. 

Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
Estimated value of log P quoted in a published paper.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Estimated value using literature data for related compounds.
GLP compliance:
no
Type of method:
other: estimated using literature data for related compounds
Partition coefficient type:
octanol-water
Specific details on test material used for the study:
Biphenyl-4,4’-diol / CAS 92-88-6
Analytical method:
not specified
Key result
Type:
log Pow
Partition coefficient:
2.7
Remarks on result:
other: estimated value
Details on results:
The partition coefficient was estimated to be 2.7 using literature data for related compounds and group contribution methods.

No further information on results is reported.

Conclusions:
The log octanol-water partition coefficient was estimated to be 2.7
Executive summary:

The log octanol-water partition coefficient was estimated to be 2.7 using literature data for related compounds and group contribution methods.

Endpoint:
partition coefficient
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
Calculated partition coefficient in peer reviewed handbook
Qualifier:
no guideline followed
GLP compliance:
no
Type of method:
other: calculated
Partition coefficient type:
octanol-water
Specific details on test material used for the study:
Biphenyl-4,4’-diol / CAS 92-88-6
Analytical method:
not specified
Key result
Type:
log Pow
Partition coefficient:
2.7
Remarks on result:
other: calculated
Details on results:
The log octanol-water partition coefficient was calculated to be 2.7.

No further results to report.

Conclusions:
The log octanol-water partition coefficient was calculated to be 2.7.
Executive summary:

The log octanol-water partition coefficient was calculated to be 2.7.

Description of key information

The log octanol-water partition coefficient was calculated to be 2.7.
The calculated estimate is consistent with the result of the Koc determination summarised at Point 5.4.1.

Measured Koc values in soil and sewage works sludge were in the range 79 to 200 L/kg. These low values imply a high mobility and low affinity for organic matter in soil and are consistent with a correspondingly low log Kow (< 3.0).

Key value for chemical safety assessment

Log Kow (Log Pow):
2.7
at the temperature of:
20 °C

Additional information