A major challenge of organ transplantation is overcoming the body’s immunological response to foreign tissue, which leads to high rejection rates. Recent research into solving this problem involved the preparation of a segment of trachea for transplantation by performing a process called decellularization, which effectively removes the compounds responsible for triggering the body’s immune system, while preserving the 3D structure of the organ. (Mater. Sci. Eng. C 2019, 105, 110–142.) The procedure involves treating the trachea with ultrasound and guanidine, a naturally occurring base found in urine. Which is the most basic nitrogen atom in guanidine? Consider the availability of the nitrogen atom lone pairs, as well as the stability of the possible conjugate acids—both approaches lead to the same conclusion.

Nitrogen atom A ⟹ ..
NH
||
.. / \ ..
Nitrogen atom B ⟹ H₂N NH₂
Guanidine

Mark all of the statements that are true.
O B is the more basic nitrogen atom, because it has a conjugate base with a delocalized positive charge.
O A is the more basic nitrogen atom, because it has a localized lone pair.
O A is the more basic nitrogen atom, because it has a conjugate base with a delocalized positive charge.
O B is the more basic nitrogen atom, because it has a delocalized lone pair.
O B is the more basic nitrogen atom, because it has a localized lone pair.
O A is the more basic nitrogen atom, because it has a delocalized lone pair. e Textbook and Media Automate of 1 used