I'm trying to generalize a theorem on $\operatorname{SL}_n(\mathbb Z)$ to the Chevalley groups over $\mathbb Z$.
In the theorem, there is a heavy use in the element $e_{1,n}(1)$ where 
$$e_{1,n}(m)=
    \begin{pmatrix}
    1 & 0 & \cdots & m\\
     & 1 &  & \vdots\\
     &  & 1 & 0\\
     &  &  & 1\\
    \end{pmatrix},
$$  
together with a general element from the Bruhat big cell.

I was wondering if there is a way to characterize $e_{1,n}(1)$ in the general Chevalley groups over $\mathbb Z$?