Using density furictional, theory, we studied denitrification reaction mechanisms of topper adducts of tris(pyrazolyl)methane and hydrotris(pyrazol)borate-models of a Copper nitrite reductase (Cu-NiR), and herein propose several possible reaction pathways, including some parts that have never been examined previously: Because electron and protein transfer, reactions participate in the enzymatic cycles of - the Gibbs energy of a proton in solution, G(H+), and the redox potential, E-redox, of the model Cu-NiR are also evaluated. Although the pathway where a nitrite is provided as HNO2 is energetically preferable, a well-known reaction pathway passing through the testing state with an active site occupied by a water molecule where nitrite is provided as NO2- is the main recognized pathway under normal conditions. These features do,riot change whether the electron transfer occurs before production of NO or not. However, our results suggest that the pathway involving HNO2 might become dominant under low pH conditions in conjunction with experimental results.