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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Study period:
June 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: estimation method (solubility ratio)
Qualifier:
no guideline followed
Guideline:
other: As the specified test methods (shake flask and HPLC) detailed in EC Method A8 failed, the log Pow has been determine based on the ratio of the n-octanol solubiliy / water solubility. Please see Principles of method if other than guideline section.
Principles of method if other than guideline:
Feasibility work performed during HPLC method development indicated that the test item was unretained on the column under standard conditions. This indicates that the HPLC method is not suitable for assessment of partition coefficient for the test item.
Feasibility work performed for the shake flask methodology indicated that it was not possible to prepare test item solutions in pre-saturated solvent at the required concentrations to perform the test. This indicates that the shake flask method is not suitable for assessment of partition coefficient for the specific test item hence the Log P was estimated based on the water and n-octanol solubility data.
GLP compliance:
yes
Type of method:
estimation method (solubility ratio)
Remarks:
Log P was estimated based on the water and n-octanol solubility ratio
Partition coefficient type:
octanol-water
Key result
Type:
log Pow
Partition coefficient:
1.46
Temp.:
25 °C
Remarks on result:
other: Mean log P
Details on results:
Log P was determined for each test condition as the log10 (mean n-octanol solubility / water solubility), where the water solubility was 167 mg/L.

The results show that solubility in n-octanol is slightly higher following sonication compared to 4 hour- stirring and overnight stirring, which were comparable. Differences between loading rates (1% and 2%) and between replicates were negligible.Therefore different Log P values were obtained from the different test conditions but the difference in values is not thought to be significant. With consideration of the observed behaviour of the test item in solution suggesting variation in solubility with time, the mean n-octanol solubility has been used to estimate the Log P value to be reported.

n-Octanol Solubility and Partition Coefficient Results

Test solution
(Replicate)

Absorbance

Lambda max

Test Item Concentration (mg/L)a

Solubility in n-Octanol

(mg/L in filtrate)b

Mean solubility in n-Octanol

(mg/L in filtrate)

Partition Coefficient
(log P)

 

n-Octanol Blank

No peaks detected

N/A

N/A

N/A

N/A

 

Overnight    stirring 1% (1)

0.885

340.0

18.09

4523

4541

1.43

 

Overnight   stirring 1% (2)

0.892

339.9

18.23

4558

 

Overnight   stirring 2% (1)

0.908

339.8

18.56

4640

4650

1.44

 

Overnight   stirring 2% (2)

0.912

339.9

18.64

4660

 

4hr stirring 1% (1)

0.876

340.6

17.90

4475

4473

1.43

 

4hr stirring 1% (2)

0.875

340.5

17.88

4470

 

4hr stirring 2% (1)

0.870

340.7

17.78

4445

4463

1.43

 

4hr stirring 2% (2)

0.877

340.7

17.92

4480

 

Sonication 1% (1)

1.062

340.0

21.71

5428

5369

1.51

 

Sonication 1% (2)

1.039

340.2

21.24

5310

 

Sonication 2% (1)

1.068

340.3

21.83

5458

5436

1.51

 

Sonication 2% (2)

1.059

340.1

21.65

5413

 

 

 

 

 

 

Mean Log P:

1.46

 

a: Determined from calibration curve (linearity)

b: calcutaed as mg/l of test item x 100 / 0.04 (dilution in DMSO)

Conclusions:
The partition coefficient (log10 Pow) of the test item is estimated based on the ratio of n-octanol solubility and water solubility to be 1.46 at 25.0 +/- 1°C.

Description of key information

Key value for chemical safety assessment

Log Kow (Log Pow):
1.46
at the temperature of:
25 °C

Additional information

Key Study:

In a study conducted according to GLP, the partition coefficient (log Pow) of 5,5'-Dithiodi-1,3,4-thiadiazole-2(3H)-thione estimated based on the ratio of n-octanol solubility and water solubility is 1.46 at 25 ± 1°C (Intertek Pharmaceutical Services Manchester, 2016).