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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Study period:
03 October 2003 - 27 October 2003
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Remarks:
Dissociation constants were estimated by calculation. Although this is not considered to be the most accurate method, it was used to determine the dissociation constants for the main component in the UVCB substance.
Reason / purpose for cross-reference:
reference to same study
Principles of method if other than guideline:
Estimation using an expert system for the calculation of dissociation constants. For complex mixtures (e.g. UVCBs) containing ionisable components the assessment of pKa is clearly complicated. Estimation of the individual components¿ pKa values is therefore considered as an alternative.
GLP compliance:
yes
Specific details on test material used for the study:
SMILES used: CH3-CH2-CH(NH2)-CH2-O-CH2-CH2-O-CH2-CH(NH2)-CH2-CH3
Dissociating properties:
yes
No.:
#1
pKa:
9.9
Remarks on result:
other: R-NH3+
No.:
#2
pKa:
9.3
Remarks on result:
other: R-NH3+
No.:
#3
pKa:
-4.7
Remarks on result:
other: R-O-R
No.:
#4
pKa:
-5.3
Remarks on result:
other: R-O-R
Conclusions:
The pKa values were calculated for the following structure with SMILES representation CH3-CH2-CH(NH2)-CH2-O-CH2-CH2-O-CH2-CH(NH2)-CH2-CH3 to be 9.9 and 9.3 (both R-NH3+) and -4.7 and -5.3 (both R-O-R). As the substance is an UVCB, the calculated values should be considered as indicative.

Description of key information

The dissociation constant of the substance was calculated from the structure of the main component following Perrin's calculation method. This GLP study revealed a pKa of 9.9 and 9.3 for both the R-NH3+ groups (Baltussen, 2004).

Key value for chemical safety assessment

Additional information

For complex mixtures (e.g. UVCBs) containing ionisable components the assessment of pKa is clearly complicated. Estimation of the pKa values of the main component is therefore considered as an alternative.

In addition to the pKa values for the R-NH3+ groups, pKa values were calculated for the R-O-R groups to be -4.7 and -5.3.