textbook 6.21 Thymine (& EDTA) [ENDORSED]

[Tiao Tan 3C]

Hi.
The solution for 6.21 says that protons can only bind to the lone pairs on nitrogen.
And Dr. Lavelle's reply in another post explains that:
"Oxygen, as the more electronegative element, holds more tightly to its lone pair than the nitrogen. The nitrogen lone pair, therefore, is more available to form a new bond to a proton. This makes the nitrogen lone pair more basic." viewtopic.php?f=58&t=70413

This question kinda reminds me of EDTA and how it has a coordination number of 6 (cations can bind to the lone pairs on O and N).
I'm not entirely sure if they are related...but why can EDTA's lone pairs on oxygen atoms accept cations while Thymine's lone pairs on oxygen can't accept protons?

[Chem_Mod]

Because the oxygen atoms that bind in EDTA are negatively charged.

One needs to compare relative stabilities.

I should use some of these Q&A in future tests. :-)