Published online by Cambridge University Press: 20 November 2018
Let $R$ be an
$n!$-torsion free semiprime ring with involution
$*$ and with extended centroid
$C$, where
$n\,>\,1$ is a positive integer. We characterize
$a\,\in \,K$, the Lie algebra of skew elements in
$R$, satisfying
${{(\text{a}{{\text{d}}_{a}})}^{n}}\,=\,0$ on
$K$. This generalizes both Martindale and Miers’ theorem and the theorem of Brox et al. In order to prove it we first prove that if
$a,\,b\,\in \,R$ satisfy
${{(\text{a}{{\text{d}}_{a}})}^{n}}\,=\,\text{a}{{\text{d}}_{b}}$ on
$R$, where either
$n$ is even or
$b\,=\,0$, then
${{(a\,-\,\lambda )}^{[(n+1)/2]}}\,=\,0$ for some
$\lambda \,\in \,C$.