Xanthylium, 3,6-bis(ethylamino)-9-[2-(methoxycarbonyl)phenyl]-2,7-dimethyl-, molybdatetungstatephosphate

Partition coefficient

Description of key information

No experimental determination was possible.

Additional information

No experimental determination was possible according to Method A8 Partition Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008, Method 107 of the OECD Guidelines for Testing of Chemicals, 27 July 1995 or Method 117 of the OECD Guidelines for Testing of Chemicals, 13 April 2004.

Performance of the Test:

Solubilities in pure solvents / Shake flask method:

The approximate saturation solubilities of the test item in n-octanol and water were initially assessed visually.

The water solubility of the test item was further determined by column elution (see water solubility). It was also attempted to analytically obtain a reduced limit value for the solubility of the test item in n-octanol, using a flask method approach. Approximately 0.1 g of test item was mixed with 100 mL of n-octanol, shaken at 200 rpm and 30°C for 18 hours and then equilibrated at 20°C for 4 hours.

HPLC method:

The feasibility of the HPLC estimation method was established through assessment of structural information.

Computer modeling:

The application of available computer modeling methodologies was evaluated based on structural information.

This estimation method is based on the theoretical fragmentation of the molecule into substructures for which reliable log P_ow increments are known. The log P_ow is obtained by summing the fragment values and the correction terms for intramolecular interactions.

Results:

Solubilities in pure solvents / Shake flask method:

Preliminary visual solubilities showed that the test item had a solubility of less than 10 mg/L in both n-octanol and water.

The water solubility of the test item was further determined analytically to be less than 1.00 x 10^-5 g/L by column elution (see water solubility).

It was not possible to completely remove the dispersed undissolved test item from the n-octanol sample prepared using the flask method. The analysis of this sample had to be aborted.

Therefore, no estimation of the partition coefficient could be calculated based on the solubilities of the test item in n-octanol and water. Also, the shake flask method was then assessed as not suitable, due to the insolubility of the test item in n-octanol and water.

HPLC method:

The structure of the test item indicated the unsuitability of the HPLC method, which is not applicable to metal complexes. The presence of charges in the structure could also allow secondary, non-partitioning interactions with the HPLC column stationary phase. In addition, guideline OECD 117 does not include reference substances structurally related to the test item, with which to generate the calibration curve of capacity factor versus known partition coefficient.

Computer modeling:

On assessment of the complexity of the test item structure, it was concluded that even available specialized predictive software would not provide a confident prediction of partitioning characteristics between n-octanol and water.

Discussion:

The partition coefficient was demonstrated not to be a valid data endpoint for the test item, based on its insolubility in both n-octanol and water.

Assessments of all experimental options for the determination of partition coefficient within the OECD Guidelines for Testing of Chemicals were shown to be either unsuitable or invalid. The low solubility of the test item in most commonly used solvents and its tendency to form colloidal dispersions, together with the complexity of its structure, including charges and electron delocalization, were the main problems encountered.

Alternative evaluation methods, discussed within the OECD guidelines, could not be employed either to produce an estimation of the partition coefficient, since the complexity of the test item composition was considered beyond the scope of available software.