Brackets in representation algebras of Hopf algebras

For any graded bialgebras $A$ and $B$, we define a commutative graded algebra $A_B$ representing the functor of so-called $B$-representations of $A$. When $A$ is a cocommutative graded Hopf algebra and $B$ is a commutative ungraded Hopf algebra, we introduce a method deriving a Gerstenhaber bracket in $A_B$ from a Fox pairing in $A$ and a balanced biderivation in $B$. Our construction is inspired by Van den Bergh's non-commutative Poisson geometry, and may be viewed as an algebraic generalization of the Atiyah-Bott-Goldman Poisson structures on moduli spaces of representations of surface groups.