passages.id: split_4_validation_1224_passage
passages.type: progene_text
passages.text: Thus , the results ( B3LYP ; epsilon = 2 calculations ) support a mechanism for both folate and DHF reduction in which the OD2 carboxyl oxygen is first protonated , followed by a direct protonation at N8 ( folate ) and N5 ( DHF ) to obtain the active cation complexes , i.e. , doubly protonated .