1 vote

Theoretical studies on the pK_a values of perfluoroalkyl carboxylic acids: Non-helical conformation acidity constants for n-perfluorooctanoic acid (n-PFOA)

Sierra Rayne¹ and Kaya Forest²

Correspondence: (Login to view email address)

1. Ecologica Research
2. Okanagan College

PDF (647.1 KB)

Document Type:

Manuscript

Date:

Received 08 October 2009 03:17 UTC; Posted 08 October 2009

Subjects:

Chemistry, Earth & Environment

Tags:

• n-perfluorooctanoic acid
• pKa
• acidity constant
• conformational search
• Environmental fate

Abstract:

A molecular mechanics force field method (MMFF94) systematic rotor conformational search was conducted on the well known environmental contaminant n-perfluorooctanoic acid (n-PFOA). The MMFF94 conformational search yielded 2915 separate low- through high-energy conformers of n-PFOA. Ranking of these structures gave the 94 lowest MMFF94 energy conformations that were subjected to subsequent density functional theory (DFT) computational investigations at the B3LYP/6-311++G(d,p) level of theory. Application of a thermodynamic cycle approach, coupled with aqueous and gas phase DFT calculations on the molecular and anionic forms for each of the 94 lowest energy n-PFOA conformers, gave estimated acidity constants (pK_a values) for a final converged set of twelve n-PFOA conformers, including the global minimum helical perfluoroalkyl chain geometry and eleven non-helical higher energy conformations. Collectively, the twelve lowest energy conformers appear to encompass 85% of the total conformational space for n-PFOA, indicating no higher energy conformations likely remain that could appreciably influence the observed composite aqueous pK_a of this compound. The estimated pK_a values of all eleven non-helical n-PFOA conformers were within 0.2 pK_a units of the helical conformer pK_a. The findings support previous predictions and recent experimental evidence for an aqueous phase n-PFOA monomeric pK_a of about zero.

Discussion

Votes:

1 vote

(Login to vote)

Comments:

0 comments

(Login to post a comment)

Share:

(Login to share with a colleague)

Additional information

License:

This document is licensed to the public under the Creative Commons Attribution 3.0 License

How to cite this document:

Rayne, Sierra and Forest, Kaya. Theoretical studies on the pK_a values of perfluoroalkyl carboxylic acids: Non-helical conformation acidity constants for n-perfluorooctanoic acid (n-PFOA). Available from Nature Precedings <http://hdl.handle.net/10101/npre.2009.3837.1> (2009)

Version info:

Other versions of this document in Nature Precedings

None.

Other versions of this document elsewhere on the web

None known.

Submit a new version link